1 00:00:05,960 --> 00:00:03,949 and tonight we have a lithograph this is 2 00:00:10,910 --> 00:00:05,970 a brand-new one of the Lagoon Nebula 3 00:00:13,640 --> 00:00:10,920 Messier 8 and thanks to a a person on 4 00:00:16,160 --> 00:00:13,650 who wrote me and said hey can you share 5 00:00:18,470 --> 00:00:16,170 that with the online audience well I 6 00:00:20,840 --> 00:00:18,480 found it very hard to send paper through 7 00:00:22,340 --> 00:00:20,850 the internet unless you're wreckit-ralph 8 00:00:24,800 --> 00:00:22,350 you can't be traveling through the 9 00:00:28,910 --> 00:00:24,810 internet and bringing things around but 10 00:00:31,009 --> 00:00:28,920 I can share with you the URL of where 11 00:00:34,160 --> 00:00:31,019 these lithographs are posted on our 12 00:00:37,510 --> 00:00:34,170 amazing space so our G website so that 13 00:00:40,490 --> 00:00:37,520 URL amazing space to our G resource page 14 00:00:43,700 --> 00:00:40,500 548 will get you to the Lagoon Nebula 15 00:00:45,889 --> 00:00:43,710 and there is a PDF file of it and those 16 00:00:48,410 --> 00:00:45,899 of you on the webcast can look at it and 17 00:00:50,479 --> 00:00:48,420 you too can say oh and AH over the 18 00:00:52,729 --> 00:00:50,489 pretty picture and then turn over and 19 00:00:57,799 --> 00:00:52,739 read about what that pretty picture is 20 00:01:00,860 --> 00:00:57,809 really about okay tonight we have black 21 00:01:02,660 --> 00:01:00,870 holes and other dark matters which is 22 00:01:04,670 --> 00:01:02,670 the reason why I think this place is 23 00:01:06,800 --> 00:01:04,680 packed because once you put the term 24 00:01:08,420 --> 00:01:06,810 black holes in your talk everyone says 25 00:01:12,890 --> 00:01:08,430 oh we got to find out about this okay 26 00:01:16,670 --> 00:01:12,900 all right upcoming we have January 15 27 00:01:20,120 --> 00:01:16,680 now first Tuesday in January is New 28 00:01:21,679 --> 00:01:20,130 Year's Day second Tuesday in January is 29 00:01:24,320 --> 00:01:21,689 the American Astronomical Society 30 00:01:26,300 --> 00:01:24,330 meeting out in Seattle and I'll be out 31 00:01:30,740 --> 00:01:26,310 there and so a lot of other astronomers 32 00:01:34,819 --> 00:01:30,750 so we have postponed it yet again to the 33 00:01:37,940 --> 00:01:34,829 third Tuesday January 15th and it's 34 00:01:40,190 --> 00:01:37,950 really good because what this is what 35 00:01:41,810 --> 00:01:40,200 Scott will be talking about some new 36 00:01:44,899 --> 00:01:41,820 stuff will be announced at the double-a 37 00:01:46,550 --> 00:01:44,909 s meeting so you'll get some some really 38 00:01:49,190 --> 00:01:46,560 cool new stuff I'll be talking about 39 00:01:50,719 --> 00:01:49,200 initial exoplanet discoveries with Tess 40 00:01:53,270 --> 00:01:50,729 the transiting exoplanet survey 41 00:01:54,410 --> 00:01:53,280 satellite you're going to want to hear 42 00:01:57,770 --> 00:01:54,420 that because that's that's cool stuff 43 00:01:58,969 --> 00:01:57,780 about exoplanets February 5th back to 44 00:02:01,280 --> 00:01:58,979 the first Tuesday of the month 45 00:02:04,910 --> 00:02:01,290 am i immoral Martin will be talking 46 00:02:07,910 --> 00:02:04,920 about your place in the Stars and in 47 00:02:10,820 --> 00:02:07,920 March we have our familiar TBA showing 48 00:02:13,830 --> 00:02:10,830 up again which means I need to schedule 49 00:02:17,580 --> 00:02:13,840 somebody I might fill in this one myself 50 00:02:20,070 --> 00:02:17,590 with our visualization talk when that is 51 00:02:22,770 --> 00:02:20,080 decided it will be announced up here on 52 00:02:24,330 --> 00:02:22,780 our website if you go to your favorite 53 00:02:26,729 --> 00:02:24,340 search engine and search for Space 54 00:02:28,350 --> 00:02:26,739 Telescope public Hubble public talks 55 00:02:30,900 --> 00:02:28,360 you'll fly in this and we have our list 56 00:02:34,080 --> 00:02:30,910 of our upcoming links to our live and 57 00:02:38,339 --> 00:02:34,090 our archives as well as our email list 58 00:02:39,930 --> 00:02:38,349 server sign up that email will send you 59 00:02:42,449 --> 00:02:39,940 out announcements we send up by about 60 00:02:46,500 --> 00:02:42,459 two every month two or three a month so 61 00:02:49,140 --> 00:02:46,510 not not a huge crush on your inbox and 62 00:02:50,699 --> 00:02:49,150 we promise no spam if you have comments 63 00:02:56,460 --> 00:02:50,709 or questions you can send them to this 64 00:02:59,190 --> 00:02:56,470 email public lecture at STScI edu social 65 00:03:01,530 --> 00:02:59,200 media for the Hubble Space Telescope for 66 00:03:03,300 --> 00:03:01,540 the James Webb Space Telescope and for 67 00:03:06,059 --> 00:03:03,310 the Space Telescope Science Institute on 68 00:03:08,640 --> 00:03:06,069 Facebook Twitter YouTube and Instagram 69 00:03:11,970 --> 00:03:08,650 I myself dabble a little bit in Facebook 70 00:03:15,750 --> 00:03:11,980 Google+ and Twitter but not that much 71 00:03:17,729 --> 00:03:15,760 and tonight yes we have the observatory 72 00:03:20,400 --> 00:03:17,739 it's clear enough tonight that we will 73 00:03:22,319 --> 00:03:20,410 be doing observing it's nice and cool so 74 00:03:24,870 --> 00:03:22,329 hopefully the air is nice and still and 75 00:03:25,800 --> 00:03:24,880 you have some beautiful seeing it's one 76 00:03:28,590 --> 00:03:25,810 of the unfortunate things about 77 00:03:34,170 --> 00:03:28,600 astronomy that the best nights for 78 00:03:34,740 --> 00:03:34,180 seeing freezing cold okay so bring some 79 00:03:38,330 --> 00:03:34,750 hot chocolate 80 00:03:41,670 --> 00:03:38,340 so ireenie will be here at the end and 81 00:03:43,860 --> 00:03:41,680 take people across the street will 82 00:03:46,319 --> 00:03:43,870 probably gathered over here on this side 83 00:03:49,050 --> 00:03:46,329 of the room at the end if I forget to 84 00:03:52,949 --> 00:03:49,060 announce it remind me or I'm sure arena 85 00:03:55,970 --> 00:03:52,959 will remind me and now our news from the 86 00:04:00,330 --> 00:03:55,980 universe for December 2018 87 00:04:03,360 --> 00:04:00,340 our first story a stellar hazmat warning 88 00:04:05,009 --> 00:04:03,370 and I told you guys within the while we 89 00:04:08,129 --> 00:04:05,019 were vamping that osiris-rex was a 90 00:04:09,750 --> 00:04:08,139 tortured acronym hazmat is a slightly 91 00:04:12,240 --> 00:04:09,760 tortured acronym too and I'll get to 92 00:04:15,000 --> 00:04:12,250 that in a minute but let's start with 93 00:04:16,920 --> 00:04:15,010 the hertzsprung-russell diagram how do 94 00:04:19,800 --> 00:04:16,930 you take an astronomy 101 and know the 95 00:04:21,330 --> 00:04:19,810 hertzsprung-russell diagram how many are 96 00:04:25,210 --> 00:04:21,340 going oh my gosh is he gonna give a 97 00:04:27,910 --> 00:04:25,220 lecture now here alright okay class 98 00:04:28,600 --> 00:04:27,920 the hearts no I don't need you to 99 00:04:31,120 --> 00:04:28,610 understand the hertzsprung-russell 100 00:04:33,880 --> 00:04:31,130 diagram except to recognize that this is 101 00:04:35,740 --> 00:04:33,890 how astronomers organize all the various 102 00:04:37,720 --> 00:04:35,750 stars in the universe okay 103 00:04:40,810 --> 00:04:37,730 it's got temperature on one axis and 104 00:04:43,060 --> 00:04:40,820 luminosity on the y-axis and the 105 00:04:45,370 --> 00:04:43,070 important thing here is that the 106 00:04:47,290 --> 00:04:45,380 brightest stars the most luminous stars 107 00:04:49,270 --> 00:04:47,300 are up on the left and there's this 108 00:04:51,190 --> 00:04:49,280 diagonal track leading down to the lower 109 00:04:56,020 --> 00:04:51,200 right which we call the main sequence 110 00:04:58,810 --> 00:04:56,030 and the most luminous stars are few and 111 00:05:01,000 --> 00:04:58,820 far between whereas the least luminous 112 00:05:04,390 --> 00:05:01,010 stars the red dwarfs in the lower right 113 00:05:06,280 --> 00:05:04,400 are all over the place okay the meek 114 00:05:09,040 --> 00:05:06,290 have already inherited the cosmos 115 00:05:12,310 --> 00:05:09,050 because there are so many more red 116 00:05:16,030 --> 00:05:12,320 dwarfs than there are blue giant stars 117 00:05:18,490 --> 00:05:16,040 okay and so the red dwarf stars the ones 118 00:05:20,650 --> 00:05:18,500 in the lower right the the red ones the 119 00:05:23,050 --> 00:05:20,660 the low luminosity ones the low 120 00:05:25,990 --> 00:05:23,060 temperature ones they are actually 121 00:05:29,650 --> 00:05:26,000 extremely important because they are the 122 00:05:31,300 --> 00:05:29,660 most numerous stars in the universe so 123 00:05:33,900 --> 00:05:31,310 if you're going to be looking for 124 00:05:37,930 --> 00:05:33,910 planets and life in the universe 125 00:05:40,030 --> 00:05:37,940 they matter an awful lot okay another 126 00:05:44,469 --> 00:05:40,040 thing that matters about stars is that 127 00:05:47,140 --> 00:05:44,479 stars have energetic activity on them 128 00:05:49,510 --> 00:05:47,150 this is an ultraviolet light image of a 129 00:05:51,340 --> 00:05:49,520 solar prominence all right now many 130 00:05:53,920 --> 00:05:51,350 people mistake this and call this a 131 00:05:55,570 --> 00:05:53,930 solar flare it's not a solar flare it's 132 00:05:58,420 --> 00:05:55,580 a solar prominence and there's magnetic 133 00:06:00,370 --> 00:05:58,430 fields that are spewing all sorts of 134 00:06:02,710 --> 00:06:00,380 energy around on the surface of the Sun 135 00:06:05,710 --> 00:06:02,720 and there are things called solar flares 136 00:06:08,350 --> 00:06:05,720 they don't look like this they look like 137 00:06:11,920 --> 00:06:08,360 this and these are magnetic reconnection 138 00:06:14,830 --> 00:06:11,930 events that send out tremendous amounts 139 00:06:16,450 --> 00:06:14,840 of energy across our solar system we 140 00:06:18,219 --> 00:06:16,460 also have things called coronal mass 141 00:06:20,650 --> 00:06:18,229 ejections that send particles of high 142 00:06:23,860 --> 00:06:20,660 energies and we have what we call in our 143 00:06:25,600 --> 00:06:23,870 solar system space weather and a lot of 144 00:06:28,390 --> 00:06:25,610 some of our satellites are out there to 145 00:06:30,730 --> 00:06:28,400 monitor the space weather and you may 146 00:06:32,140 --> 00:06:30,740 have heard that sometimes when one of 147 00:06:34,450 --> 00:06:32,150 these coronal mass ejections or 148 00:06:36,640 --> 00:06:34,460 something is sent in the direction of 149 00:06:37,920 --> 00:06:36,650 Earth it hits our magnetic field and 150 00:06:39,779 --> 00:06:37,930 sometimes 151 00:06:43,590 --> 00:06:39,789 disrupt our communication satellites 152 00:06:47,249 --> 00:06:43,600 okay or if the astronauts are up in the 153 00:06:49,529 --> 00:06:47,259 and the space station they need to get 154 00:06:51,350 --> 00:06:49,539 inside and protect themselves okay when 155 00:06:55,800 --> 00:06:51,360 one of these solar storms commits 156 00:06:58,560 --> 00:06:55,810 however that's just for a Sun sized star 157 00:07:02,129 --> 00:06:58,570 and the Sun is a medium-sized star these 158 00:07:06,080 --> 00:07:02,139 small stars these red dwarf stars can 159 00:07:10,260 --> 00:07:06,090 have much more energetic activity and 160 00:07:13,920 --> 00:07:10,270 that is when we get to hazmat so this is 161 00:07:16,589 --> 00:07:13,930 a study habitable zones and m-dwarf 162 00:07:20,249 --> 00:07:16,599 activity over time can you see how you 163 00:07:22,920 --> 00:07:20,259 get hazmat out of that yeah okay 164 00:07:26,100 --> 00:07:22,930 but the acronym is actually appropriate 165 00:07:28,740 --> 00:07:26,110 because they're studying how volatile 166 00:07:32,159 --> 00:07:28,750 these M Dwarfs the red dwarf stars are 167 00:07:34,469 --> 00:07:32,169 and could they affect the planets 168 00:07:36,749 --> 00:07:34,479 forming around them and perhaps life 169 00:07:38,790 --> 00:07:36,759 forming on those planets and what's 170 00:07:40,589 --> 00:07:38,800 important is to take a look at stars at 171 00:07:42,629 --> 00:07:40,599 different ages this is the activity over 172 00:07:44,909 --> 00:07:42,639 time part of it okay looking at you know 173 00:07:46,680 --> 00:07:44,919 billion year old red dwarfs versus you 174 00:07:48,629 --> 00:07:46,690 know a few hundred million years old 175 00:07:51,810 --> 00:07:48,639 versus tens of millions of year old red 176 00:07:53,820 --> 00:07:51,820 dwarfs okay and what they found in this 177 00:07:56,550 --> 00:07:53,830 study and they basically these solar 178 00:07:57,960 --> 00:07:56,560 flares occur are easiest to see in 179 00:08:00,719 --> 00:07:57,970 ultraviolet so well that's why you need 180 00:08:02,399 --> 00:08:00,729 Hubble to do this because Hubble being 181 00:08:04,860 --> 00:08:02,409 above our atmosphere can see the 182 00:08:08,249 --> 00:08:04,870 ultraviolet light and they looked at a 183 00:08:11,969 --> 00:08:08,259 population of 40 million year old stars 184 00:08:13,439 --> 00:08:11,979 and a 40 million years old is old' for 185 00:08:18,029 --> 00:08:13,449 you and me but it's young for a star 186 00:08:21,719 --> 00:08:18,039 these are just born stars and the energy 187 00:08:25,350 --> 00:08:21,729 in the solar flares was one hundred to a 188 00:08:27,659 --> 00:08:25,360 thousand times stronger than it was for 189 00:08:30,870 --> 00:08:27,669 the billion year old stars the old stars 190 00:08:34,459 --> 00:08:30,880 so there's a lot more energy happening 191 00:08:37,430 --> 00:08:34,469 and this has interesting implementation 192 00:08:42,230 --> 00:08:37,440 implications for planets formation 193 00:08:44,550 --> 00:08:42,240 because at 40 million years that's when 194 00:08:47,130 --> 00:08:44,560 earth sized planets will be forming 195 00:08:50,930 --> 00:08:47,140 terrestrial planets will be forming so 196 00:08:54,950 --> 00:08:50,940 these impor stars the most new 197 00:08:57,410 --> 00:08:54,960 stars the universe have a energetic she 198 00:09:00,170 --> 00:08:57,420 appeared to be very energetic just at 199 00:09:02,330 --> 00:09:00,180 the time that planets are forming so if 200 00:09:05,480 --> 00:09:02,340 you want to form life on them 201 00:09:08,320 --> 00:09:05,490 could these m-dwarf act does could this 202 00:09:11,750 --> 00:09:08,330 end dwarf activity be effectively hasmat 203 00:09:15,920 --> 00:09:11,760 could they interfere with the formation 204 00:09:19,040 --> 00:09:15,930 of life on these planets and this is not 205 00:09:21,350 --> 00:09:19,050 a conclusive study in terms of that 206 00:09:24,170 --> 00:09:21,360 actually does or does not but it shows 207 00:09:26,810 --> 00:09:24,180 that we have to not only think about how 208 00:09:29,360 --> 00:09:26,820 we form these planets around a star but 209 00:09:31,820 --> 00:09:29,370 we also have to think about the activity 210 00:09:34,100 --> 00:09:31,830 of the star itself while those planets 211 00:09:36,620 --> 00:09:34,110 are forming so this is a interesting 212 00:09:39,260 --> 00:09:36,630 study that will I'm sure we followed up 213 00:09:41,570 --> 00:09:39,270 much further in the future trying to 214 00:09:43,370 --> 00:09:41,580 look and understand you know this whole 215 00:09:47,560 --> 00:09:43,380 process of plant information that you 216 00:09:50,570 --> 00:09:47,570 know we are still still you know just 217 00:09:52,670 --> 00:09:50,580 really you know if this is so exciting 218 00:09:56,780 --> 00:09:52,680 how much we're learning about this 219 00:10:02,150 --> 00:09:56,790 process as we go on alright our second 220 00:10:03,950 --> 00:10:02,160 story is the ghost of Cassiopeia this is 221 00:10:06,590 --> 00:10:03,960 the constellation of Cassiopeia and this 222 00:10:08,930 --> 00:10:06,600 beautiful image from Akira Fuji II it's 223 00:10:12,200 --> 00:10:08,940 that W you see in the center there okay 224 00:10:14,030 --> 00:10:12,210 and a Cassiopeia is a wonderful 225 00:10:15,590 --> 00:10:14,040 constellation for those of us in the 226 00:10:18,320 --> 00:10:15,600 northern hemisphere because it's 227 00:10:20,540 --> 00:10:18,330 circumpolar it's always around the North 228 00:10:22,970 --> 00:10:20,550 Pole and goes just circles around the 229 00:10:24,800 --> 00:10:22,980 North Pole so most of the times most 230 00:10:28,040 --> 00:10:24,810 times the year you can find Cassiopeia 231 00:10:31,100 --> 00:10:28,050 on the night sky and find that W and 232 00:10:35,350 --> 00:10:31,110 that Center star in the W is known as 233 00:10:38,260 --> 00:10:35,360 gamma Cassiopeia and gamma Cassiopeia is 234 00:10:42,770 --> 00:10:38,270 illuminating some of the gas around it 235 00:10:46,579 --> 00:10:42,780 that sort of the the faint red blotch on 236 00:10:48,620 --> 00:10:46,589 the left is called IC 59 and that bright 237 00:10:53,000 --> 00:10:48,630 one down bottom that looks sort of like 238 00:10:54,170 --> 00:10:53,010 a mountain that is IC 63 this is a 239 00:10:56,480 --> 00:10:54,180 wonderful image from the 240 00:10:58,790 --> 00:10:56,490 astrophotographer robert Gendler and you 241 00:11:02,600 --> 00:10:58,800 can see that the sort of the mountain in 242 00:11:03,740 --> 00:11:02,610 IC 63 is pointed toward gamma casts all 243 00:11:04,519 --> 00:11:03,750 right that shows that it's the 244 00:11:06,169 --> 00:11:04,529 ultraviolet 245 00:11:08,569 --> 00:11:06,179 the energy from gamma cos that's 246 00:11:11,749 --> 00:11:08,579 sculpting that gas that's blowing away 247 00:11:12,919 --> 00:11:11,759 the low-density gas and ionizing the gas 248 00:11:16,999 --> 00:11:12,929 to make it glow 249 00:11:20,059 --> 00:11:17,009 and Hubble does various pretty picture 250 00:11:22,339 --> 00:11:20,069 release images and when we did our 251 00:11:24,049 --> 00:11:22,349 pretty picture release image going 252 00:11:25,639 --> 00:11:24,059 through the various pretty pictures they 253 00:11:28,339 --> 00:11:25,649 thought that this looked like a ghost 254 00:11:35,679 --> 00:11:28,349 and so we released for Halloween a 255 00:11:38,269 --> 00:11:35,689 picture of the ghost of Cassiopeia I 256 00:11:39,889 --> 00:11:38,279 looks more like a hooded shroud or 257 00:11:41,479 --> 00:11:39,899 something like this but it it's really 258 00:11:43,849 --> 00:11:41,489 kind of cool so this is this is what 259 00:11:45,679 --> 00:11:43,859 they called the ghost of Cassiopeia not 260 00:11:47,629 --> 00:11:45,689 to be confused with the ghost nebula or 261 00:11:48,709 --> 00:11:47,639 the little ghost nebula or like three 262 00:11:50,869 --> 00:11:48,719 other things that are called ghost 263 00:11:52,369 --> 00:11:50,879 nebula type things but they nicknamed 264 00:11:55,129 --> 00:11:52,379 this the ghost of Cassiopeia 265 00:11:59,779 --> 00:11:55,139 we took this light invisible we also 266 00:12:02,329 --> 00:11:59,789 took a image in infrared light and to 267 00:12:04,639 --> 00:12:02,339 give it that really spooky feel we 268 00:12:08,659 --> 00:12:04,649 created an animated gif that goes back 269 00:12:10,819 --> 00:12:08,669 from visible to infrared and that was a 270 00:12:14,599 --> 00:12:10,829 sort of a Halloween pretty picture 271 00:12:20,210 --> 00:12:14,609 release the ghost of Cassiopeia and 272 00:12:22,069 --> 00:12:20,220 that's our news for this evening now we 273 00:12:32,239 --> 00:12:22,079 go to our main speaker of the night and 274 00:12:34,129 --> 00:12:32,249 our main speaker tonight is get there 275 00:12:36,799 --> 00:12:34,139 yes okay 276 00:12:40,460 --> 00:12:36,809 our speaker tonight is dr. Mark 277 00:12:42,289 --> 00:12:40,470 kamionkowski whom I had the extensive 278 00:12:45,829 --> 00:12:42,299 pleasure of working with up at Columbia 279 00:12:47,419 --> 00:12:45,839 University I was a postdoc working at 280 00:12:49,129 --> 00:12:47,429 Columbia half time at Columbia and half 281 00:12:53,029 --> 00:12:49,139 time at the American Natural History 282 00:12:57,589 --> 00:12:53,039 when Mark was up at Columbia he did his 283 00:13:00,259 --> 00:12:57,599 degree at Caltech and didn't Chicago 284 00:13:02,229 --> 00:13:00,269 right all right I thought I'd confirmed 285 00:13:08,959 --> 00:13:02,239 it was Caltech I'm wrong okay 286 00:13:11,719 --> 00:13:08,969 sorry at Chicago and then went to 287 00:13:13,519 --> 00:13:11,729 Columbia and after a few years he missed 288 00:13:15,470 --> 00:13:13,529 me so much he decided he'd come down to 289 00:13:17,420 --> 00:13:15,480 Johns Hopkins not quite 290 00:13:18,500 --> 00:13:17,430 who he came down he's in the department 291 00:13:21,550 --> 00:13:18,510 across the street at Johns Hopkins 292 00:13:26,480 --> 00:13:21,560 University he is one of the celebrated 293 00:13:28,670 --> 00:13:26,490 cosmologists and a real big expert on 294 00:13:30,020 --> 00:13:28,680 the Cosmic Microwave Background but he's 295 00:13:32,390 --> 00:13:30,030 not going to talk to you that about that 296 00:13:34,730 --> 00:13:32,400 tonight instead he's going to talk about 297 00:13:36,890 --> 00:13:34,740 cosmic ripples from black holes and the 298 00:13:56,590 --> 00:13:36,900 Big Bang ladies and gentlemen dr. Mark 299 00:14:03,380 --> 00:14:00,410 so today I'm going to talk to you about 300 00:14:05,630 --> 00:14:03,390 dark matter but the story is actually 301 00:14:07,640 --> 00:14:05,640 going to begin with them the discovery 302 00:14:12,170 --> 00:14:07,650 of gravitational waves from a binary 303 00:14:15,800 --> 00:14:12,180 black hole system two years ago and this 304 00:14:20,690 --> 00:14:15,810 is work that began in the cafeteria here 305 00:14:22,250 --> 00:14:20,700 in Asif Ron in January of 2016 the rumor 306 00:14:24,350 --> 00:14:22,260 started heating up in the astrophysics 307 00:14:25,370 --> 00:14:24,360 community that LIGO had detected 308 00:14:26,690 --> 00:14:25,380 something and there's gonna be an 309 00:14:28,970 --> 00:14:26,700 announcement it was going to be big and 310 00:14:31,790 --> 00:14:28,980 so I was sitting around the lunch table 311 00:14:32,900 --> 00:14:31,800 with some of my collaborators and we 312 00:14:34,700 --> 00:14:32,910 were thinking well we got to think of 313 00:14:37,010 --> 00:14:34,710 something interesting to say because 314 00:14:39,530 --> 00:14:37,020 this is gonna be big and we started 315 00:14:42,080 --> 00:14:39,540 brainstorming and we came up with that 316 00:14:44,930 --> 00:14:42,090 most ridiculous ideas you can possibly 317 00:14:49,280 --> 00:14:44,940 imagine and at some point we came up 318 00:14:52,220 --> 00:14:49,290 with an idea that was ridiculous but not 319 00:14:55,370 --> 00:14:52,230 completely ridiculous and so we decided 320 00:14:58,100 --> 00:14:55,380 to write a paper and in brief and what 321 00:15:01,400 --> 00:14:58,110 I'll tell you over the next 40 minutes 322 00:15:03,230 --> 00:15:01,410 is that we simply postulated that the 323 00:15:05,780 --> 00:15:03,240 black holes that they discovered might 324 00:15:08,480 --> 00:15:05,790 actually be the dark matter that we have 325 00:15:11,390 --> 00:15:08,490 for a long time known to exist in the 326 00:15:14,960 --> 00:15:11,400 universe but we have no idea what it is 327 00:15:17,660 --> 00:15:14,970 and it was a crazy idea but as I said 328 00:15:20,390 --> 00:15:17,670 not completely crazy there was an 329 00:15:23,150 --> 00:15:20,400 interesting coincidence that popped up 330 00:15:25,190 --> 00:15:23,160 when we considered this possibility and 331 00:15:26,720 --> 00:15:25,200 so we wrote this paper and a lot of 332 00:15:30,370 --> 00:15:26,730 people found it interesting it's got a 333 00:15:34,699 --> 00:15:32,900 do black holes like the ones that like 334 00:15:37,430 --> 00:15:34,709 oh detective make up the dark matter as 335 00:15:39,379 --> 00:15:37,440 I'll tell you we don't know two years 336 00:15:41,750 --> 00:15:39,389 ago I was fairly optimistic things have 337 00:15:46,250 --> 00:15:41,760 developed since then I'm a little less 338 00:15:48,560 --> 00:15:46,260 optimistic but the jury is still out so 339 00:15:50,900 --> 00:15:48,570 the title is cosmic ripples from the big 340 00:15:52,400 --> 00:15:50,910 from black holes in the Big Bang cosmic 341 00:15:54,379 --> 00:15:52,410 ripples refers to the gravitational 342 00:15:55,610 --> 00:15:54,389 waves I'll tell you about black holes 343 00:16:01,040 --> 00:15:55,620 were first two black holes in the Big 344 00:16:02,540 --> 00:16:01,050 Bang is the Big Bang please interrupt me 345 00:16:04,310 --> 00:16:02,550 if there are questions this is 346 00:16:06,110 --> 00:16:04,320 gravitational waves general relativity 347 00:16:08,150 --> 00:16:06,120 black holes dark matter it's not rocket 348 00:16:13,819 --> 00:16:08,160 science so everyone should be able to 349 00:16:19,370 --> 00:16:13,829 understand so the story begins February 350 00:16:21,620 --> 00:16:19,380 of 2016 there was a front-page article 351 00:16:22,819 --> 00:16:21,630 in The New York Times that pointed out 352 00:16:24,740 --> 00:16:22,829 the gravitational waves have been 353 00:16:27,290 --> 00:16:24,750 detected and it was a beautiful 354 00:16:28,790 --> 00:16:27,300 beautiful timing because I'm Albert 355 00:16:31,579 --> 00:16:28,800 Einstein realized that gravitational 356 00:16:33,829 --> 00:16:31,589 waves should exist almost a hundred 357 00:16:35,840 --> 00:16:33,839 years before we sort of put the 358 00:16:38,809 --> 00:16:35,850 finishing pieces of this theory of 359 00:16:41,269 --> 00:16:38,819 general relativity at the end of 2015 360 00:16:43,699 --> 00:16:41,279 and the gravitational wave signal was 361 00:16:50,059 --> 00:16:43,709 actually detected in September of 2015 362 00:16:52,819 --> 00:16:50,069 so very very nice coincidence this 363 00:16:56,059 --> 00:16:52,829 discovery was absolutely spectacular 364 00:16:57,680 --> 00:16:56,069 there's nobody in science who was so 365 00:16:59,900 --> 00:16:57,690 jaded as to say out and detected 366 00:17:03,130 --> 00:16:59,910 gravitational waves what's the big deal 367 00:17:06,140 --> 00:17:03,140 actually there is a story I have to say 368 00:17:09,470 --> 00:17:06,150 so this was a huge discovery and there 369 00:17:11,179 --> 00:17:09,480 was a press conference online that that 370 00:17:14,390 --> 00:17:11,189 NASA was brought I'm sorry that the NSF 371 00:17:16,909 --> 00:17:14,400 was broadcasting and some people in the 372 00:17:19,309 --> 00:17:16,919 physics department had set up a seminar 373 00:17:20,720 --> 00:17:19,319 room like this one so we could play it 374 00:17:22,549 --> 00:17:20,730 on video and everyone can come and watch 375 00:17:24,919 --> 00:17:22,559 and some people sort of got doughnuts 376 00:17:27,620 --> 00:17:24,929 and coffee and we're milling about 377 00:17:29,390 --> 00:17:27,630 before the thing started and there were 378 00:17:31,220 --> 00:17:29,400 two undergraduate students walking by 379 00:17:33,200 --> 00:17:31,230 and one of them was hard to say the 380 00:17:34,850 --> 00:17:33,210 other one what's going on here and the 381 00:17:35,990 --> 00:17:34,860 only goes I don't know that this covered 382 00:17:41,060 --> 00:17:36,000 gravitational waves or something like 383 00:17:47,340 --> 00:17:43,590 anyway it was one of the quickest Nobel 384 00:17:49,080 --> 00:17:47,350 Prizes ever awarded these people also 385 00:17:50,760 --> 00:17:49,090 received the Gruber prize that catalyzed 386 00:17:53,789 --> 00:17:50,770 the sharp rise in the breakthrough prize 387 00:17:55,770 --> 00:17:53,799 any possible scientific recognition or 388 00:17:58,320 --> 00:17:55,780 honor that is available immediately went 389 00:18:03,750 --> 00:17:58,330 to the team that discovered these 390 00:18:08,430 --> 00:18:03,760 gravitational waves and as I said this 391 00:18:09,870 --> 00:18:08,440 phenomenon was sort of predicted by 392 00:18:12,570 --> 00:18:09,880 Albert Einstein's theory of general 393 00:18:16,320 --> 00:18:12,580 relativity and this goes back 100 years 394 00:18:18,630 --> 00:18:16,330 to 1915 and the basic idea of general 395 00:18:21,480 --> 00:18:18,640 relativity is the following equation and 396 00:18:24,630 --> 00:18:21,490 I'm always told that I shouldn't show 397 00:18:26,010 --> 00:18:24,640 equations in popular talks but I like to 398 00:18:27,990 --> 00:18:26,020 show equations because I'm a theoretical 399 00:18:30,360 --> 00:18:28,000 physicist this is really all I have I'm 400 00:18:32,070 --> 00:18:30,370 not in the survey tional strong I don't 401 00:18:34,049 --> 00:18:32,080 have pretty pictures of nebula and 402 00:18:42,360 --> 00:18:34,059 things like that this is the best I can 403 00:18:44,010 --> 00:18:42,370 do we're really proud of it but the 404 00:18:47,580 --> 00:18:44,020 point of an equation is that there's an 405 00:18:48,990 --> 00:18:47,590 equal sign in the middle there's 406 00:18:51,330 --> 00:18:49,000 something on the left and there's 407 00:18:52,770 --> 00:18:51,340 something on the right and the thing on 408 00:18:54,840 --> 00:18:52,780 the left is supposed to be the same as a 409 00:18:56,399 --> 00:18:54,850 thing on the right so this is known as 410 00:18:58,680 --> 00:18:56,409 Einstein's equation nine Stein wrote 411 00:19:00,510 --> 00:18:58,690 this down and this encapsulate the 412 00:19:01,799 --> 00:19:00,520 theory of general relativity and simple 413 00:19:03,930 --> 00:19:01,809 and elegant because the thing on the 414 00:19:05,070 --> 00:19:03,940 left is a capital G with some Greek 415 00:19:07,020 --> 00:19:05,080 letters on there and the thing on the 416 00:19:08,789 --> 00:19:07,030 right is capital T and I remember I 417 00:19:11,100 --> 00:19:08,799 first learned this equation when I was a 418 00:19:14,370 --> 00:19:11,110 senior in college and I was taking a 419 00:19:16,529 --> 00:19:14,380 general relativity class and I passed by 420 00:19:20,070 --> 00:19:16,539 a professor I had for a quantum 421 00:19:21,149 --> 00:19:20,080 mechanics class and he said how's it 422 00:19:22,350 --> 00:19:21,159 going I was going great what are you 423 00:19:23,850 --> 00:19:22,360 taking I'm taking John Rolfe everies 424 00:19:25,710 --> 00:19:23,860 like what I think I said so simple and 425 00:19:27,659 --> 00:19:25,720 elegant you know G me nu equals team you 426 00:19:32,100 --> 00:19:27,669 know he goes yeah but what's G mu nu 427 00:19:33,690 --> 00:19:32,110 what's team you know yeah anyway this 428 00:19:36,690 --> 00:19:33,700 actually has a fairly simple 429 00:19:37,140 --> 00:19:36,700 interpretation G mu nu the thing on the 430 00:19:39,899 --> 00:19:37,150 left 431 00:19:42,200 --> 00:19:39,909 describes the curvature of space and 432 00:19:44,310 --> 00:19:42,210 space-time and the thing on the right 433 00:19:47,730 --> 00:19:44,320 describes the matter content of the 434 00:19:49,919 --> 00:19:47,740 universe and so this describes a picture 435 00:19:52,560 --> 00:19:49,929 that looks like this so according to 436 00:19:57,480 --> 00:19:52,570 general relativity space 437 00:19:59,549 --> 00:19:57,490 time can be bent and distorted and the 438 00:20:02,070 --> 00:19:59,559 distortion of space-time is given by the 439 00:20:04,919 --> 00:20:02,080 presence of massive objects so massive 440 00:20:06,960 --> 00:20:04,929 objects distort space-time and this 441 00:20:12,240 --> 00:20:06,970 equation tells you how that works 442 00:20:14,580 --> 00:20:12,250 the space-time curvature is related to 443 00:20:16,860 --> 00:20:14,590 the distribution of massive objects 444 00:20:19,590 --> 00:20:16,870 which is teeming of the matter content 445 00:20:21,779 --> 00:20:19,600 on the right hand side in words what 446 00:20:23,190 --> 00:20:21,789 this says is that space-time tells 447 00:20:25,470 --> 00:20:23,200 matter how to move and matter tells 448 00:20:27,960 --> 00:20:25,480 space-time how to move so the second 449 00:20:29,999 --> 00:20:27,970 thing I told you so matter tells the 450 00:20:32,100 --> 00:20:30,009 space-time how to curve and then the 451 00:20:33,930 --> 00:20:32,110 curvature of space-time tells you how 452 00:20:37,019 --> 00:20:33,940 objects move and I'll show you better 453 00:20:39,149 --> 00:20:37,029 pictures of this in a second but you 454 00:20:40,860 --> 00:20:39,159 know if someone was if a particle is 455 00:20:42,360 --> 00:20:40,870 gonna go along a straight line and this 456 00:20:44,249 --> 00:20:42,370 Crouch space-time it couldn't go along a 457 00:20:46,619 --> 00:20:44,259 straight line the trajectory is actually 458 00:20:49,919 --> 00:20:46,629 deflected if the space-time is curved if 459 00:20:52,470 --> 00:20:49,929 I take a very soft mattress and I put a 460 00:20:54,119 --> 00:20:52,480 very heavy bowling ball somewhere in the 461 00:20:55,799 --> 00:20:54,129 middle that sort of pushes that mattress 462 00:20:58,049 --> 00:20:55,809 down and then if I try to roll a 463 00:20:59,970 --> 00:20:58,059 ping-pong ball PLAs that bowling ball 464 00:21:03,210 --> 00:20:59,980 the trajectory of the ping-pong ball 465 00:21:05,369 --> 00:21:03,220 will be deflected by the curvature in 466 00:21:09,060 --> 00:21:05,379 the mattress so that's basically what 467 00:21:10,560 --> 00:21:09,070 general relativity tells us space-time 468 00:21:13,049 --> 00:21:10,570 tells matter how to move and matter 469 00:21:15,919 --> 00:21:13,059 tells space-time how to curve that's the 470 00:21:19,560 --> 00:21:15,929 essence of Einstein's equation this was 471 00:21:22,440 --> 00:21:19,570 an incredible mathematical insight back 472 00:21:26,009 --> 00:21:22,450 in 1915 there was absolutely nothing in 473 00:21:29,070 --> 00:21:26,019 any that existed in physics before this 474 00:21:30,810 --> 00:21:29,080 to foreshadow this or to build up to it 475 00:21:31,230 --> 00:21:30,820 it sort of came out of absolutely 476 00:21:33,990 --> 00:21:31,240 nowhere 477 00:21:35,970 --> 00:21:34,000 but it turns out that the theory is 478 00:21:37,769 --> 00:21:35,980 correct then Albert Einstein actually 479 00:21:40,019 --> 00:21:37,779 realized that theory was correct almost 480 00:21:43,560 --> 00:21:40,029 immediately because there was one 481 00:21:45,450 --> 00:21:43,570 anomaly in planetary dynamics in 1915 482 00:21:47,759 --> 00:21:45,460 which was the perihelion advance of 483 00:21:49,830 --> 00:21:47,769 mercury so it turns out that Mercury's 484 00:21:51,720 --> 00:21:49,840 orbit around the Sun like that of most 485 00:21:54,450 --> 00:21:51,730 planets is not perfectly around it's 486 00:21:57,169 --> 00:21:54,460 actually elongated according to Newton's 487 00:22:00,240 --> 00:21:57,179 laws if according to inverse square law 488 00:22:02,909 --> 00:22:00,250 from note that Isaac Newton derived we 489 00:22:05,970 --> 00:22:02,919 wrote down you know back in the early 490 00:22:07,740 --> 00:22:05,980 1700s late 1600s 491 00:22:10,470 --> 00:22:07,750 these ellipses should close in on 492 00:22:12,360 --> 00:22:10,480 themselves but what was found is that 493 00:22:14,820 --> 00:22:12,370 Mercury's orbit does not close in on 494 00:22:16,799 --> 00:22:14,830 itself it sort of processes the it sort 495 00:22:18,840 --> 00:22:16,809 of the rotates around in this direction 496 00:22:20,520 --> 00:22:18,850 over here and it's a very tiny and 497 00:22:22,980 --> 00:22:20,530 subtle effect but hasn't been measured 498 00:22:25,380 --> 00:22:22,990 quite well to be two degrees per century 499 00:22:27,299 --> 00:22:25,390 and Albert Einstein realized that these 500 00:22:30,780 --> 00:22:27,309 equations that he wrote down could 501 00:22:33,090 --> 00:22:30,790 account for this perihelion advance and 502 00:22:34,200 --> 00:22:33,100 so there's a story that he couldn't 503 00:22:35,610 --> 00:22:34,210 sleep that night because he was so 504 00:22:37,140 --> 00:22:35,620 excited that he actually realized that 505 00:22:37,620 --> 00:22:37,150 this ridiculous equation that came out 506 00:22:40,650 --> 00:22:37,630 of nowhere 507 00:22:44,400 --> 00:22:40,660 was actually correct we also know it's 508 00:22:46,110 --> 00:22:44,410 like correct because of the existence of 509 00:22:48,900 --> 00:22:46,120 gravitational lensing or the bending of 510 00:22:53,720 --> 00:22:48,910 light and this was verified by a famous 511 00:22:56,940 --> 00:22:53,730 expedition by Sir Arthur Eddington 1919 512 00:22:58,830 --> 00:22:56,950 so it turns out that the gravitational 513 00:23:01,799 --> 00:22:58,840 field of a massive object like the Sun 514 00:23:04,500 --> 00:23:01,809 will actually bend the trajectory of 515 00:23:06,030 --> 00:23:04,510 light so at you know if you send a light 516 00:23:07,650 --> 00:23:06,040 ray out mil know where the light ray 517 00:23:09,180 --> 00:23:07,660 goes straight but if you send a near 518 00:23:11,010 --> 00:23:09,190 massive object the gravitational field 519 00:23:13,230 --> 00:23:11,020 of that massive object will actually 520 00:23:14,580 --> 00:23:13,240 blend the trajectory of light and this 521 00:23:16,799 --> 00:23:14,590 is something that's difficult to 522 00:23:18,419 --> 00:23:16,809 actually verify because the Sun is so 523 00:23:20,940 --> 00:23:18,429 bright that you can't see the stars 524 00:23:22,890 --> 00:23:20,950 behind it but if there's an eclipse 525 00:23:24,960 --> 00:23:22,900 if the moon passes in front of the Sun 526 00:23:26,460 --> 00:23:24,970 then for a brief period of time you can 527 00:23:29,880 --> 00:23:26,470 actually see the stars behind the Sun 528 00:23:32,610 --> 00:23:29,890 and so Eddington verified this that the 529 00:23:38,880 --> 00:23:32,620 this deflection of light during a solar 530 00:23:40,950 --> 00:23:38,890 eclipse in 1919 so I think I said 1916 531 00:23:42,750 --> 00:23:40,960 very shortly after the original theory 532 00:23:45,270 --> 00:23:42,760 was proposed Einstein realized that the 533 00:23:48,840 --> 00:23:45,280 theory predicts the existence of 534 00:23:51,390 --> 00:23:48,850 gravitational waves and here's a movie 535 00:23:53,520 --> 00:23:51,400 that I will show you and I'll show you 536 00:23:55,320 --> 00:23:53,530 another version later on and the basic 537 00:23:57,780 --> 00:23:55,330 idea is that there is a gravitational 538 00:24:00,120 --> 00:23:57,790 field due to a mass of objects so if I 539 00:24:02,039 --> 00:24:00,130 have one planted over here that gives me 540 00:24:03,870 --> 00:24:02,049 a gravitational field if there's a 541 00:24:05,789 --> 00:24:03,880 second planted over here that also has a 542 00:24:07,440 --> 00:24:05,799 gravitational field and the 543 00:24:09,240 --> 00:24:07,450 gravitational field due to the presence 544 00:24:11,940 --> 00:24:09,250 of two planets is going to be the sum of 545 00:24:14,490 --> 00:24:11,950 that from this one and the Sun the sum 546 00:24:19,260 --> 00:24:14,500 and the gravitational field from here 547 00:24:21,060 --> 00:24:19,270 now if I have a binary star system 5/2 548 00:24:23,820 --> 00:24:21,070 stars that are gravitationally bound and 549 00:24:26,640 --> 00:24:23,830 spinning around each other or for 550 00:24:28,440 --> 00:24:26,650 example if I have a planet star system 551 00:24:30,390 --> 00:24:28,450 like the earth or the planet Jupiter 552 00:24:32,270 --> 00:24:30,400 spinning around the Sun I will have 553 00:24:35,160 --> 00:24:32,280 something that looks sort of like this 554 00:24:37,050 --> 00:24:35,170 now as those planets move around each 555 00:24:38,400 --> 00:24:37,060 other those stars or black holes or 556 00:24:41,310 --> 00:24:38,410 whatever the massive objects you have 557 00:24:44,160 --> 00:24:41,320 move around each other the gravitational 558 00:24:49,440 --> 00:24:44,170 field is going to change and so that's 559 00:24:51,690 --> 00:24:49,450 what we see over here so if I'm sitting 560 00:24:55,260 --> 00:24:51,700 over here the gravitational field that I 561 00:24:57,090 --> 00:24:55,270 see due to those two stars changes if 562 00:24:58,800 --> 00:24:57,100 you're looking at a pair of stars over 563 00:25:00,060 --> 00:24:58,810 here you'll see one gravitational field 564 00:25:01,830 --> 00:25:00,070 if you see them over here to see a 565 00:25:03,570 --> 00:25:01,840 different gravitational field and as 566 00:25:06,300 --> 00:25:03,580 they spin around you will see a time 567 00:25:08,730 --> 00:25:06,310 varying gravitational field that time 568 00:25:10,860 --> 00:25:08,740 varying gravitational field propagates 569 00:25:16,350 --> 00:25:10,870 outward as a set of ripples in 570 00:25:19,500 --> 00:25:16,360 space-time so something like this maybe 571 00:25:22,620 --> 00:25:19,510 non-intuitive originally but it 572 00:25:26,100 --> 00:25:22,630 shouldn't be too non-intuitive the 573 00:25:31,080 --> 00:25:26,110 surface of a pond if it still is very 574 00:25:33,150 --> 00:25:31,090 flat and peaceful and calm but it can 575 00:25:35,970 --> 00:25:33,160 bob up and down and if I drop something 576 00:25:37,830 --> 00:25:35,980 in the middle of this pond that 577 00:25:41,130 --> 00:25:37,840 disturbance will propagate out as a 578 00:25:43,940 --> 00:25:41,140 series of waves and suppose I have a toy 579 00:25:47,670 --> 00:25:43,950 boat sitting at the edge of the pond 580 00:25:49,710 --> 00:25:47,680 these waves will propagate out and the 581 00:25:51,450 --> 00:25:49,720 toy boat will be sitting there still but 582 00:25:53,130 --> 00:25:51,460 at some point the waves will pass by and 583 00:25:57,570 --> 00:25:53,140 that toy boat will start to bounce up 584 00:26:01,860 --> 00:25:57,580 and down so if I move the fluid over 585 00:26:03,660 --> 00:26:01,870 here somehow those waves propagate out 586 00:26:07,140 --> 00:26:03,670 and they are detected because they then 587 00:26:12,030 --> 00:26:07,150 induce motion in some test object like 588 00:26:16,080 --> 00:26:12,040 this toy boat a large distance if I have 589 00:26:18,870 --> 00:26:16,090 a tight string and I shake it and they 590 00:26:20,760 --> 00:26:18,880 disturb it on one end that disturbance 591 00:26:23,340 --> 00:26:20,770 will propagate out in this direction as 592 00:26:26,760 --> 00:26:23,350 a wave and suppose I have some beads on 593 00:26:29,070 --> 00:26:26,770 the string at the other end those beads 594 00:26:32,600 --> 00:26:29,080 will start to move up and down as the 595 00:26:34,520 --> 00:26:32,610 wave encounters them so again a 596 00:26:37,280 --> 00:26:34,530 string is a medium that can carry 597 00:26:39,049 --> 00:26:37,290 wave-like motions or carry waves and the 598 00:26:40,669 --> 00:26:39,059 way I induce those waves is by shaking 599 00:26:42,440 --> 00:26:40,679 the string up and down and the way I 600 00:26:44,960 --> 00:26:42,450 detect those waves is through the 601 00:26:50,600 --> 00:26:44,970 motions that those wave induce in a set 602 00:26:53,780 --> 00:26:50,610 of test masses the same thing is true 603 00:26:57,530 --> 00:26:53,790 for radio waves does anybody actually 604 00:26:58,640 --> 00:26:57,540 listen to the radio anymore okay back in 605 00:27:00,289 --> 00:26:58,650 the old days there was something in your 606 00:27:04,039 --> 00:27:00,299 car called the radio you could turn it 607 00:27:06,289 --> 00:27:04,049 on and the way the radio works is that 608 00:27:08,659 --> 00:27:06,299 there is a transmitter you see them for 609 00:27:11,840 --> 00:27:08,669 example in TV tower and roughly speaking 610 00:27:14,750 --> 00:27:11,850 there are a bunch of electrons and each 611 00:27:16,370 --> 00:27:14,760 electron when it Wiggles sends out 612 00:27:18,409 --> 00:27:16,380 electromagnetic wave and the way I 613 00:27:21,140 --> 00:27:18,419 detect that is that if I have an antenna 614 00:27:24,289 --> 00:27:21,150 like in my car the wave is it hits the 615 00:27:28,010 --> 00:27:24,299 antenna sets free electrons into motion 616 00:27:33,409 --> 00:27:28,020 and then you know your receiver detects 617 00:27:37,250 --> 00:27:33,419 and amplifies those motions there's one 618 00:27:41,600 --> 00:27:37,260 more example usually we think of the 619 00:27:43,430 --> 00:27:41,610 ground as rigid and fixed you don't 620 00:27:48,140 --> 00:27:43,440 think of the ground is shaking and 621 00:27:49,880 --> 00:27:48,150 moving around on California you do but 622 00:27:51,620 --> 00:27:49,890 you know here you generally think well 623 00:27:52,970 --> 00:27:51,630 the ground is fixed I can walk across 624 00:27:55,070 --> 00:27:52,980 it's not going to shake it's not going 625 00:27:57,289 --> 00:27:55,080 to move but you've all set been sitting 626 00:28:00,020 --> 00:27:57,299 at home at some time when a very heavy 627 00:28:01,909 --> 00:28:00,030 truck rolls by and on a bumpy road that 628 00:28:04,130 --> 00:28:01,919 heavy truck bounces up and down and you 629 00:28:06,020 --> 00:28:04,140 can feel the shaking in your house so 630 00:28:08,419 --> 00:28:06,030 although the ground is seems to be very 631 00:28:10,190 --> 00:28:08,429 rigid in fact it's not perfectly rigid 632 00:28:12,190 --> 00:28:10,200 and if you have something that's 633 00:28:15,080 --> 00:28:12,200 officially massive that starts shaking 634 00:28:17,180 --> 00:28:15,090 the ground will transmit waves and you 635 00:28:19,430 --> 00:28:17,190 will then feel them since the ground is 636 00:28:21,110 --> 00:28:19,440 so rigid that thing has to be really 637 00:28:22,850 --> 00:28:21,120 heavy to actually shake the ground and 638 00:28:24,500 --> 00:28:22,860 when the ground does shake it doesn't 639 00:28:26,780 --> 00:28:24,510 shrink a whole lot you feel a slight 640 00:28:30,169 --> 00:28:26,790 tremor but it's not a huge thing it 641 00:28:32,960 --> 00:28:30,179 turns out as Albert Einstein predicted 642 00:28:34,640 --> 00:28:32,970 and as we now know due to all these 643 00:28:38,480 --> 00:28:34,650 experimental verifications of general 644 00:28:40,400 --> 00:28:38,490 relativity that space-time which we 645 00:28:44,120 --> 00:28:40,410 always think of intuitively is being 646 00:28:46,110 --> 00:28:44,130 perfectly rigid you know every position 647 00:28:48,990 --> 00:28:46,120 in this room can be specified 648 00:28:52,320 --> 00:28:49,000 by three numbers a cart you know the 649 00:28:54,029 --> 00:28:52,330 numbers on a Cartesian grid the position 650 00:28:55,289 --> 00:28:54,039 in that direction the position in that 651 00:28:57,529 --> 00:28:55,299 direction and the position in that 652 00:29:01,320 --> 00:28:57,539 direction and we always in physics 653 00:29:04,380 --> 00:29:01,330 imagine a lattice that represents you 654 00:29:09,120 --> 00:29:04,390 know points in this direction x equals 1 655 00:29:10,919 --> 00:29:09,130 2 3 4 y equals 1 2 3 4 z equals 1 2 3 4 656 00:29:12,360 --> 00:29:10,929 and the location of anything or anybody 657 00:29:15,320 --> 00:29:12,370 in this room can be represented in terms 658 00:29:17,519 --> 00:29:15,330 of those three numbers so space in 659 00:29:20,279 --> 00:29:17,529 space-time we would always think of as 660 00:29:22,799 --> 00:29:20,289 being very rigid but as it turns out 661 00:29:25,649 --> 00:29:22,809 that space-time is extremely rigid but 662 00:29:27,480 --> 00:29:25,659 it's not perfectly rigid and if there 663 00:29:29,039 --> 00:29:27,490 are massive objects they can curve the 664 00:29:31,080 --> 00:29:29,049 space-time and if you shake those 665 00:29:33,210 --> 00:29:31,090 massive objects those will shake the 666 00:29:36,240 --> 00:29:33,220 space-time and if the space-time shakes 667 00:29:41,630 --> 00:29:36,250 we'll feel it things will start to move 668 00:29:46,889 --> 00:29:41,640 around so this was all pretty much 669 00:29:51,180 --> 00:29:46,899 theoretical expectation until a few 670 00:29:59,000 --> 00:29:51,190 years ago so in 1916 these gravitational 671 00:30:01,620 --> 00:29:59,010 waves were predicted waves carry energy 672 00:30:03,840 --> 00:30:01,630 when the truck drives by and starts 673 00:30:05,610 --> 00:30:03,850 shaking if you're sitting there and your 674 00:30:08,430 --> 00:30:05,620 chairs start shaking there's energy in 675 00:30:11,100 --> 00:30:08,440 that motion so how to get there well the 676 00:30:14,279 --> 00:30:11,110 medium the grounds carried the energy 677 00:30:16,139 --> 00:30:14,289 from the truck over to you so likewise 678 00:30:20,039 --> 00:30:16,149 gravitational waves can also carry 679 00:30:27,029 --> 00:30:20,049 energy they propagate at the speed of 680 00:30:29,669 --> 00:30:27,039 light they were detected indirectly back 681 00:30:32,610 --> 00:30:29,679 in 9th in the early 70s and it was a 682 00:30:34,380 --> 00:30:32,620 Nobel Prize award in 1993 there was a 683 00:30:37,440 --> 00:30:34,390 system of two neutron stars neutron 684 00:30:40,710 --> 00:30:37,450 stars are very dense remnants of stars 685 00:30:42,870 --> 00:30:40,720 each one weighs 1.4 times the mass of 686 00:30:44,430 --> 00:30:42,880 the Sun and there are several binary 687 00:30:45,960 --> 00:30:44,440 pulsar systems that we know about which 688 00:30:49,169 --> 00:30:45,970 are two neutron star spinning around 689 00:30:50,760 --> 00:30:49,179 each other and it was seen that in one 690 00:30:52,919 --> 00:30:50,770 particular system the two neutron stars 691 00:30:56,430 --> 00:30:52,929 were spinning around each other but they 692 00:30:59,299 --> 00:30:56,440 were spinning up the orbital period was 693 00:31:01,820 --> 00:30:59,309 shortening they were speeding up as they 694 00:31:04,190 --> 00:31:01,830 there seem to be speeding up which was 695 00:31:09,680 --> 00:31:04,200 interpreted as speeding up due to the 696 00:31:11,960 --> 00:31:09,690 emission of gravitational waves so the 697 00:31:13,700 --> 00:31:11,970 signal from these neutron stars gave us 698 00:31:15,739 --> 00:31:13,710 good evidence that the gravitational 699 00:31:17,600 --> 00:31:15,749 waves exist that they were being emitted 700 00:31:19,519 --> 00:31:17,610 from the spine or a neutron star system 701 00:31:24,409 --> 00:31:19,529 but no one are actually seen or detected 702 00:31:26,419 --> 00:31:24,419 a gravitational wave so how do we detect 703 00:31:27,430 --> 00:31:26,429 gravitational waves directly I told you 704 00:31:32,149 --> 00:31:27,440 already 705 00:31:34,549 --> 00:31:32,159 waves are detected by the motions they 706 00:31:36,139 --> 00:31:34,559 induce in some type of test masses radio 707 00:31:39,649 --> 00:31:36,149 waves are detected by the motions they 708 00:31:41,299 --> 00:31:39,659 induce an electrons the round waves are 709 00:31:43,909 --> 00:31:41,309 detected by the motions they induced in 710 00:31:46,340 --> 00:31:43,919 the chair that we're sitting on the toy 711 00:31:49,940 --> 00:31:46,350 boat is used to detect waves and 712 00:31:52,850 --> 00:31:49,950 otherwise still pond gravity effects 713 00:31:54,919 --> 00:31:52,860 masses and so the way do we detect 714 00:31:56,899 --> 00:31:54,929 gravitational waves is through the 715 00:32:02,690 --> 00:31:56,909 characteristic motions they induce in a 716 00:32:09,190 --> 00:32:02,700 set of freely falling test masses so the 717 00:32:13,909 --> 00:32:11,779 this has scale in effect vastly 718 00:32:20,090 --> 00:32:13,919 exaggerated so I don't want to alarm 719 00:32:22,190 --> 00:32:20,100 anybody but they made a video of what it 720 00:32:23,869 --> 00:32:22,200 would look like if a very large 721 00:32:26,419 --> 00:32:23,879 amplitude gravitational wave were to 722 00:32:32,690 --> 00:32:26,429 pass through the earth and the video 723 00:32:34,820 --> 00:32:32,700 looks like this so this is a low 724 00:32:36,980 --> 00:32:34,830 amplitude gravitational wave and as 725 00:32:39,669 --> 00:32:36,990 we'll see the amplitude from a binary 726 00:32:44,450 --> 00:32:39,679 black hole mergers expected to increase 727 00:32:46,009 --> 00:32:44,460 and get faster so roughly speaking 728 00:32:48,379 --> 00:32:46,019 that's what's happening to the earth 729 00:32:51,259 --> 00:32:48,389 when a gravitational wave signal passes 730 00:32:52,759 --> 00:32:51,269 by the effect was greatly exaggerated 731 00:32:58,759 --> 00:32:52,769 they actually up to the effect is off 732 00:33:02,539 --> 00:32:58,769 one part in trillion trillion pretty 733 00:33:04,779 --> 00:33:02,549 small so in practice as I said the 734 00:33:09,019 --> 00:33:04,789 motions are getting extremely tiny and 735 00:33:12,680 --> 00:33:09,029 so what was done was something called 736 00:33:16,160 --> 00:33:12,690 laser interferometry and so 737 00:33:17,630 --> 00:33:16,170 what happens is the one of the 738 00:33:18,890 --> 00:33:17,640 characteristics of a gravitational wave 739 00:33:22,340 --> 00:33:18,900 is that if we have a gravitational wave 740 00:33:27,230 --> 00:33:22,350 propagating down but in a direction 741 00:33:29,180 --> 00:33:27,240 perpendicular to this plane the masses 742 00:33:31,310 --> 00:33:29,190 in this direction will get stretched out 743 00:33:34,550 --> 00:33:31,320 while the masses in this direction will 744 00:33:37,640 --> 00:33:34,560 get stretched inward and so what was 745 00:33:40,100 --> 00:33:37,650 people thought to do is to send a beam 746 00:33:42,200 --> 00:33:40,110 of light a laser signal through a 747 00:33:44,180 --> 00:33:42,210 half-silvered mirror that then splits 748 00:33:46,820 --> 00:33:44,190 the beam so that one beam goes towards 749 00:33:48,740 --> 00:33:46,830 this mirror over here and another beam 750 00:33:50,180 --> 00:33:48,750 goes toward this mirror over here the 751 00:33:52,280 --> 00:33:50,190 two beams then bounce back are 752 00:33:58,250 --> 00:33:52,290 recombined and then come back over here 753 00:34:01,040 --> 00:33:58,260 and since light is a wave when these two 754 00:34:04,460 --> 00:34:01,050 waves are recombined they can either add 755 00:34:07,370 --> 00:34:04,470 coherently or they can add destructively 756 00:34:09,320 --> 00:34:07,380 and if they add coherently the light 757 00:34:11,180 --> 00:34:09,330 signal that's received over here is 758 00:34:13,700 --> 00:34:11,190 stronger if they are destructively the 759 00:34:15,530 --> 00:34:13,710 light signal over here is weakened so 760 00:34:20,090 --> 00:34:15,540 again the LIGO people made a very nice 761 00:34:21,650 --> 00:34:20,100 movie of this which I can show you so 762 00:34:24,200 --> 00:34:21,660 there is the beam that gets split 763 00:34:28,880 --> 00:34:24,210 bounces back it comes back towards the 764 00:34:30,890 --> 00:34:28,890 detector and as these mirrors shake the 765 00:34:35,000 --> 00:34:30,900 light that's received in the detector is 766 00:34:37,100 --> 00:34:35,010 either brighter or weaker and the reason 767 00:34:41,720 --> 00:34:37,110 that happens is that each of these light 768 00:34:43,760 --> 00:34:41,730 rays is actually a wave and if the 769 00:34:45,490 --> 00:34:43,770 spacing between these two different arms 770 00:34:49,520 --> 00:34:45,500 is just right those two waves will add 771 00:34:51,440 --> 00:34:49,530 destructively and as the masses move 772 00:34:54,260 --> 00:34:51,450 around as the lengths in these two arms 773 00:34:56,420 --> 00:34:54,270 change what was otherwise the 774 00:34:58,910 --> 00:34:56,430 destructive interference might become a 775 00:35:02,030 --> 00:34:58,920 constructive interference and then the 776 00:35:03,710 --> 00:35:02,040 beam gets brighter so they have an 777 00:35:07,400 --> 00:35:03,720 interferometer that looks like this and 778 00:35:13,520 --> 00:35:07,410 what they look for is variable light 779 00:35:15,020 --> 00:35:13,530 brightness at that detector I am told 780 00:35:17,660 --> 00:35:15,030 that this is the most precise 781 00:35:20,050 --> 00:35:17,670 measurement ever made by a pretty wide 782 00:35:22,300 --> 00:35:20,060 stretch it was 40 years in the making 783 00:35:25,990 --> 00:35:22,310 from the time from the initial proposal 784 00:35:29,680 --> 00:35:26,000 so the detection was roughly 40 years 785 00:35:32,650 --> 00:35:29,690 technology development and science the 786 00:35:34,420 --> 00:35:32,660 detection was made by a collaboration an 787 00:35:36,730 --> 00:35:34,430 American collaboration LIGO they also 788 00:35:39,070 --> 00:35:36,740 used results from Burgo although they 789 00:35:41,500 --> 00:35:39,080 were not results which is a European 790 00:35:43,270 --> 00:35:41,510 collaboration there's a British German 791 00:35:45,760 --> 00:35:43,280 interferometer that's being built called 792 00:35:48,400 --> 00:35:45,770 Geo there's a Japanese interferometer 793 00:35:50,500 --> 00:35:48,410 being built Altima one in Australia and 794 00:35:52,900 --> 00:35:50,510 there's also one being built in India 795 00:35:54,700 --> 00:35:52,910 now but the original detection was by 796 00:35:56,380 --> 00:35:54,710 LIGO and in the future we're going to 797 00:35:59,680 --> 00:35:56,390 have networks of gravitational wave 798 00:36:02,290 --> 00:35:59,690 detectors all working together so LIGO 799 00:36:04,570 --> 00:36:02,300 stands for laser interferometer gravity 800 00:36:06,490 --> 00:36:04,580 wave observatory this is roughly 801 00:36:08,950 --> 00:36:06,500 speaking a billion dollars of taxpayer 802 00:36:12,970 --> 00:36:08,960 money very well spent it is the biggest 803 00:36:14,830 --> 00:36:12,980 NSF investment in single investment by a 804 00:36:16,510 --> 00:36:14,840 wide margin 805 00:36:18,760 --> 00:36:16,520 it's a us-led project it does have 806 00:36:22,270 --> 00:36:18,770 international collaboration they have 807 00:36:24,340 --> 00:36:22,280 two detectors one is in Washington State 808 00:36:26,260 --> 00:36:24,350 and the other one is in Louisiana and 809 00:36:28,210 --> 00:36:26,270 the reason they have two detectors is 810 00:36:30,700 --> 00:36:28,220 that if somebody told you they saw 811 00:36:33,070 --> 00:36:30,710 something go bump in the night you'd say 812 00:36:35,460 --> 00:36:33,080 what was that and see how if something 813 00:36:38,710 --> 00:36:35,470 went bump in the night Oh interesting 814 00:36:41,170 --> 00:36:38,720 but if somebody in Louisiana also says 815 00:36:43,420 --> 00:36:41,180 hey something went bump in the night and 816 00:36:44,950 --> 00:36:43,430 you say well what time did it help go 817 00:36:49,690 --> 00:36:44,960 bump in the night well it happened 818 00:36:52,390 --> 00:36:49,700 precisely at 12:03 a.m. plus sixteen 819 00:36:55,540 --> 00:36:52,400 point four eight seconds and then the 820 00:36:58,240 --> 00:36:55,550 people in Washington say oh wow we saw 821 00:37:00,820 --> 00:36:58,250 the exact same bump in the night so they 822 00:37:01,990 --> 00:37:00,830 used the simultaneity to reject spurious 823 00:37:04,680 --> 00:37:02,000 signals because things are always 824 00:37:07,090 --> 00:37:04,690 happening that shake those masses around 825 00:37:10,630 --> 00:37:07,100 the length of the arms are four 826 00:37:15,250 --> 00:37:10,640 kilometers and although there's four 827 00:37:16,750 --> 00:37:15,260 kilometers between these mirrors what 828 00:37:18,550 --> 00:37:16,760 they detect are motions that are a 829 00:37:21,430 --> 00:37:18,560 fraction of the size of an atomic 830 00:37:23,920 --> 00:37:21,440 nucleus so this is a picture of the 831 00:37:27,490 --> 00:37:23,930 Livingston Observatory from the sky four 832 00:37:32,290 --> 00:37:27,500 kilometers and four kilometers this is a 833 00:37:34,510 --> 00:37:32,300 another picture another picture and here 834 00:37:37,120 --> 00:37:34,520 is the Hanford Observatory there are 835 00:37:38,110 --> 00:37:37,130 more or less identical there are subtle 836 00:37:39,820 --> 00:37:38,120 differences but the more or less 837 00:37:43,870 --> 00:37:39,830 identical to four 838 00:37:48,520 --> 00:37:43,880 in her arms and the motion that they 839 00:37:49,840 --> 00:37:48,530 detect is illustrated by this movie in 840 00:37:53,190 --> 00:37:49,850 which the LIGO collaboration also 841 00:37:55,630 --> 00:37:53,200 provided so this is an atomic this is a 842 00:37:59,290 --> 00:37:55,640 that would let me start again what you 843 00:38:04,900 --> 00:37:59,300 started with was an electron spinning 844 00:38:08,590 --> 00:38:04,910 around let me go back because this is 845 00:38:10,510 --> 00:38:08,600 absolutely astounding this is a movie of 846 00:38:17,380 --> 00:38:10,520 an electron spinning around an atomic 847 00:38:21,970 --> 00:38:17,390 nucleus so that's pretty small so there 848 00:38:25,300 --> 00:38:21,980 is the atom and then we zoom in to the 849 00:38:31,630 --> 00:38:25,310 atomic nucleus which is composed of a 850 00:38:34,270 --> 00:38:31,640 couple of protons and neutrons and what 851 00:38:45,460 --> 00:38:34,280 they actually detect is a motion of that 852 00:38:47,940 --> 00:38:45,470 magnitude so that is incredible this is 853 00:38:54,670 --> 00:38:51,520 so when I so I was a professor at 854 00:38:56,470 --> 00:38:54,680 Caltech for a while and my office was 855 00:38:58,240 --> 00:38:56,480 down the hall from the people working on 856 00:38:59,650 --> 00:38:58,250 this project and they're always like 857 00:39:00,730 --> 00:38:59,660 walking past my hall looking really busy 858 00:39:02,770 --> 00:39:00,740 because they were gonna detect 859 00:39:03,700 --> 00:39:02,780 gravitational waves and every time I saw 860 00:39:05,170 --> 00:39:03,710 them walking around this is what I 861 00:39:09,730 --> 00:39:05,180 thought this is fit a scene from his 862 00:39:13,960 --> 00:39:09,740 fits corrado which is a movie by a 863 00:39:15,910 --> 00:39:13,970 Verner Herzog about a man in 19th 864 00:39:23,100 --> 00:39:15,920 century Brazil who decides he wants to 865 00:39:26,140 --> 00:39:23,110 carry a boat over a mountain anyway on 866 00:39:28,030 --> 00:39:26,150 September 14th 2015 they had upgraded 867 00:39:29,560 --> 00:39:28,040 their detectors and before they're 868 00:39:32,440 --> 00:39:29,570 actually gonna start doing science runs 869 00:39:33,850 --> 00:39:32,450 they were doing some test runs so they 870 00:39:35,230 --> 00:39:33,860 turned the machine on just to do some 871 00:39:39,430 --> 00:39:35,240 tests to see if everything was working 872 00:39:51,490 --> 00:39:39,440 and this is what happened and there's a 873 00:39:57,890 --> 00:39:55,220 so they're constantly measuring the 874 00:40:00,680 --> 00:39:57,900 separation of these mirrors with a very 875 00:40:02,240 --> 00:40:00,690 very small time resolution and the 876 00:40:04,460 --> 00:40:02,250 mirrors keep shaking around because when 877 00:40:07,070 --> 00:40:04,470 people drive by that shakes the ground 878 00:40:09,110 --> 00:40:07,080 and they when there's a lightning strike 879 00:40:11,390 --> 00:40:09,120 anywhere on the planet that shakes the 880 00:40:14,150 --> 00:40:11,400 things around so they're constantly see 881 00:40:16,280 --> 00:40:14,160 things in LIGO the custody see things in 882 00:40:18,260 --> 00:40:16,290 Livingston the number of things that 883 00:40:20,840 --> 00:40:18,270 affect the Hanford detector and the 884 00:40:22,730 --> 00:40:20,850 Livingston detector are pretty rare 885 00:40:27,200 --> 00:40:22,740 because they're several thousand miles 886 00:40:29,180 --> 00:40:27,210 away and what they saw though at the 887 00:40:31,210 --> 00:40:29,190 same time in both detectors is a very 888 00:40:35,990 --> 00:40:31,220 prominent signal that looked like that 889 00:40:39,500 --> 00:40:36,000 so here is another plot so this is the 890 00:40:43,670 --> 00:40:39,510 displacement of the mirrors as a 891 00:40:45,950 --> 00:40:43,680 function of time in the Hanford and you 892 00:40:46,970 --> 00:40:45,960 see that it goes up and down and up and 893 00:40:51,050 --> 00:40:46,980 down and up and down and up and down 894 00:40:53,450 --> 00:40:51,060 right faster faster and then stops and 895 00:40:57,050 --> 00:40:53,460 you see the exact same thing and the 896 00:41:04,600 --> 00:40:57,060 Livingston data goes up and down up and 897 00:41:09,800 --> 00:41:04,610 down up no it's big and then stops so 898 00:41:13,430 --> 00:41:09,810 this we are very very sure is the signal 899 00:41:14,450 --> 00:41:13,440 from a pair of black holes that are 900 00:41:16,100 --> 00:41:14,460 merging 901 00:41:19,070 --> 00:41:16,110 so another prediction of general 902 00:41:22,120 --> 00:41:19,080 relativity which was realized first by a 903 00:41:24,500 --> 00:41:22,130 guy named Karl Schwarzschild who was 904 00:41:27,800 --> 00:41:24,510 fighting in the trenches in World War 905 00:41:30,350 --> 00:41:27,810 one and figured this out while in the 906 00:41:34,610 --> 00:41:30,360 trenches and then passed away a few 907 00:41:37,580 --> 00:41:34,620 months later so Karl Schwarzschild 908 00:41:39,470 --> 00:41:37,590 figured out that the equations of 909 00:41:41,890 --> 00:41:39,480 general relativity allow for the 910 00:41:44,690 --> 00:41:41,900 existence of things called black holes 911 00:41:47,150 --> 00:41:44,700 these are the densest possible objects 912 00:41:49,130 --> 00:41:47,160 in nature and they are so strong that 913 00:41:50,480 --> 00:41:49,140 the grant they are so dense the 914 00:41:53,480 --> 00:41:50,490 gravitational field is so strong that 915 00:41:56,150 --> 00:41:53,490 not even light can escape so you know if 916 00:41:58,130 --> 00:41:56,160 I try to throw a ball in the air it goes 917 00:41:59,600 --> 00:41:58,140 up and it goes down but if I had a 918 00:42:03,670 --> 00:41:59,610 really good arm and I could throw the 919 00:42:05,349 --> 00:42:03,680 ball any velocity of 11 kilometers per 920 00:42:08,799 --> 00:42:05,359 second I shouldn't know what that is a 921 00:42:11,410 --> 00:42:08,809 miles per hour but I don't 11 kilometers 922 00:42:12,609 --> 00:42:11,420 per second the ball wouldn't return to 923 00:42:14,079 --> 00:42:12,619 Earth it would actually escape the 924 00:42:19,870 --> 00:42:14,089 gravitational pull of the earth and 925 00:42:21,400 --> 00:42:19,880 escape to infinity a black hole is an 926 00:42:22,930 --> 00:42:21,410 object that is so dense the 927 00:42:25,329 --> 00:42:22,940 gravitational field is so strong that 928 00:42:26,980 --> 00:42:25,339 the escape velocity from the surface is 929 00:42:28,089 --> 00:42:26,990 bigger than the speed of light and since 930 00:42:30,339 --> 00:42:28,099 nothing can travel faster than the speed 931 00:42:35,920 --> 00:42:30,349 of light nothing can escape from the 932 00:42:40,390 --> 00:42:35,930 black hole so we can take the equations 933 00:42:42,069 --> 00:42:40,400 of general relativity and set them up so 934 00:42:44,620 --> 00:42:42,079 that there's not just one black hole but 935 00:42:48,099 --> 00:42:44,630 two black holes that are in orbit about 936 00:42:50,829 --> 00:42:48,109 each other and if you do that what you 937 00:42:53,680 --> 00:42:50,839 find is that gravitational waves will be 938 00:42:57,339 --> 00:42:53,690 emitted as the gravitational waves are 939 00:42:59,470 --> 00:42:57,349 emitted those gravitational waves carry 940 00:43:00,579 --> 00:42:59,480 energy away and if they carry energy 941 00:43:04,210 --> 00:43:00,589 away that means there has to be less 942 00:43:06,520 --> 00:43:04,220 energy for the remaining system a Barn's 943 00:43:09,099 --> 00:43:06,530 system of two objects actually has a 944 00:43:11,559 --> 00:43:09,109 negative energy it has a gravitational 945 00:43:13,059 --> 00:43:11,569 binding or potential energy and as they 946 00:43:15,549 --> 00:43:13,069 get closer that becomes increasingly 947 00:43:19,000 --> 00:43:15,559 negative so the energy that's carried 948 00:43:21,339 --> 00:43:19,010 away is gravitational waves causes the 949 00:43:24,220 --> 00:43:21,349 remaining binary to become closer and 950 00:43:25,930 --> 00:43:24,230 closer and as that binary as the two 951 00:43:27,280 --> 00:43:25,940 stars become closer and closer they spin 952 00:43:29,200 --> 00:43:27,290 around faster and faster 953 00:43:31,059 --> 00:43:29,210 you know mercury gets around the Sun a 954 00:43:32,109 --> 00:43:31,069 lot more quickly does the earth and the 955 00:43:36,700 --> 00:43:32,119 earth gets around the Sun a lot more 956 00:43:39,220 --> 00:43:36,710 quickly than Pluto so likewise when two 957 00:43:40,569 --> 00:43:39,230 black holes get closer and closer they 958 00:43:43,180 --> 00:43:40,579 start to spin around each other faster 959 00:43:45,339 --> 00:43:43,190 and faster and when they do that the 960 00:43:47,710 --> 00:43:45,349 gravitational wave frequency increases 961 00:43:50,920 --> 00:43:47,720 and the power and gravitational waves 962 00:43:54,210 --> 00:43:50,930 increases and so that is what is seen 963 00:43:56,859 --> 00:43:54,220 here and this is actually a scientific 964 00:43:59,620 --> 00:43:56,869 simulation this is actually full 965 00:44:03,039 --> 00:43:59,630 solution of the numerical solution of 966 00:44:05,319 --> 00:44:03,049 the equations of general relativity so 967 00:44:07,180 --> 00:44:05,329 that is what they look like they get 968 00:44:09,000 --> 00:44:07,190 closer and closer here you see the 969 00:44:12,370 --> 00:44:09,010 gravitational waves being emitted as 970 00:44:14,140 --> 00:44:12,380 they get closer and closer the orbit 971 00:44:15,490 --> 00:44:14,150 will orbital period will decrease 972 00:44:16,630 --> 00:44:15,500 they'll start to spin up and the 973 00:44:17,200 --> 00:44:16,640 gravitational wave soon will get 974 00:44:21,820 --> 00:44:17,210 stronger 975 00:44:23,620 --> 00:44:21,830 looks like when gravitational waves when 976 00:44:26,890 --> 00:44:23,630 two binary black to black holes merge 977 00:44:28,150 --> 00:44:26,900 and what's kind of interesting and I was 978 00:44:30,100 --> 00:44:28,160 surprised by when I first saw these 979 00:44:32,080 --> 00:44:30,110 numerical simulations is that when they 980 00:44:33,550 --> 00:44:32,090 finally merged it happens very quickly 981 00:44:37,470 --> 00:44:33,560 and there's a burst of gravitational 982 00:44:39,880 --> 00:44:37,480 waves emitted so it turns out that 983 00:44:43,720 --> 00:44:39,890 calculations such as the ones I just 984 00:44:45,640 --> 00:44:43,730 that I showed you here can allow you to 985 00:44:48,790 --> 00:44:45,650 predict a gravitational wave signal far 986 00:44:57,010 --> 00:44:48,800 away and that prediction turns out to be 987 00:44:59,770 --> 00:44:57,020 spot-on what was seen by LIGO not always 988 00:45:03,190 --> 00:44:59,780 it's spot-on but based on the properties 989 00:45:05,200 --> 00:45:03,200 of the signal you know the frequency how 990 00:45:07,330 --> 00:45:05,210 quickly the frequency increases the 991 00:45:09,670 --> 00:45:07,340 magnitude of the signal at the merger 992 00:45:13,780 --> 00:45:09,680 time and also the ring down and the 993 00:45:16,090 --> 00:45:13,790 final period from all that information 994 00:45:18,700 --> 00:45:16,100 we can actually infer that one of these 995 00:45:20,620 --> 00:45:18,710 black holes had a mass of about 36 times 996 00:45:23,140 --> 00:45:20,630 the mass of the Sun another was about 29 997 00:45:26,470 --> 00:45:23,150 times the mass of the Sun the final 998 00:45:29,950 --> 00:45:26,480 black hole had a mass of 62 and 62 minus 999 00:45:32,470 --> 00:45:29,960 36 months 29 is three so they're 1000 00:45:34,420 --> 00:45:32,480 actually you know from just from now you 1001 00:45:36,310 --> 00:45:34,430 know special relativity Albert Einstein 1002 00:45:38,620 --> 00:45:36,320 e equals mc-squared 1003 00:45:43,140 --> 00:45:38,630 energy is equivalent to mass there were 1004 00:45:45,670 --> 00:45:43,150 three solar masses of energy released as 1005 00:45:47,080 --> 00:45:45,680 gravitational waves and we can also 1006 00:45:49,750 --> 00:45:47,090 infer the distance which is about 1007 00:45:52,030 --> 00:45:49,760 billion light years which is good 1008 00:45:54,250 --> 00:45:52,040 because things are because it feels a 1009 00:45:57,490 --> 00:45:54,260 lot closer than that movie they showed 1010 00:46:03,460 --> 00:45:57,500 you of the earth bouncing around might 1011 00:46:04,960 --> 00:46:03,470 have been a little more realistic this 1012 00:46:06,220 --> 00:46:04,970 is kind of a cute movie this is actually 1013 00:46:11,530 --> 00:46:06,230 another movie that they made that 1014 00:46:14,980 --> 00:46:11,540 illustrates what the sky would look like 1015 00:46:19,240 --> 00:46:14,990 if you were looking through a pair of 1016 00:46:20,920 --> 00:46:19,250 binary a binary black hole system so the 1017 00:46:23,350 --> 00:46:20,930 black hole's I told you to flecked the 1018 00:46:24,460 --> 00:46:23,360 light and so the image of the stars that 1019 00:46:26,920 --> 00:46:24,470 are behind the black hole's get 1020 00:46:29,050 --> 00:46:26,930 distorted and again this is a scientific 1021 00:46:30,700 --> 00:46:29,060 simulation of what it would look like if 1022 00:46:38,320 --> 00:46:30,710 we were a lot closer to the spine 1023 00:46:40,450 --> 00:46:38,330 black hole system so as they move around 1024 00:46:42,520 --> 00:46:40,460 the lensing pattern would change and 1025 00:46:45,310 --> 00:46:42,530 that is what the sky would look like as 1026 00:46:48,970 --> 00:46:45,320 these things spiral around each other 1027 00:46:51,730 --> 00:46:48,980 and then merge and the merger is pretty 1028 00:46:54,220 --> 00:46:51,740 happens very quickly and suddenly and 1029 00:46:56,430 --> 00:46:54,230 then there's a very brief ring down any 1030 00:47:00,070 --> 00:46:56,440 second now 1031 00:47:09,550 --> 00:47:00,080 so they're they merge and then there's 1032 00:47:11,560 --> 00:47:09,560 this final ring down anyway there's a 1033 00:47:13,180 --> 00:47:11,570 big question which is the question we 1034 00:47:15,040 --> 00:47:13,190 were wondering in the Aza front and then 1035 00:47:20,770 --> 00:47:15,050 the Space Telescope cafeteria over here 1036 00:47:23,680 --> 00:47:20,780 in January of 2016 in February where do 1037 00:47:25,660 --> 00:47:23,690 these black holes come from we detected 1038 00:47:27,370 --> 00:47:25,670 them we're very very sure that that was 1039 00:47:29,339 --> 00:47:27,380 a binary black hole system that we saw 1040 00:47:31,599 --> 00:47:29,349 with these gravitational wave events and 1041 00:47:33,940 --> 00:47:31,609 subsequent developments have given us 1042 00:47:37,599 --> 00:47:33,950 even more confidence but where do they 1043 00:47:39,599 --> 00:47:37,609 come from I told you that they can exist 1044 00:47:41,829 --> 00:47:39,609 within the context of general relativity 1045 00:47:43,720 --> 00:47:41,839 but they're there they're not just 1046 00:47:45,730 --> 00:47:43,730 mathematical constructions and you know 1047 00:47:47,560 --> 00:47:45,740 figments of theoretical imagination this 1048 00:47:49,720 --> 00:47:47,570 measurement shows that these black holes 1049 00:47:53,980 --> 00:47:49,730 actually exist and they weigh you know 1050 00:47:56,470 --> 00:47:53,990 30 times the mass of the Sun so the most 1051 00:47:59,170 --> 00:47:56,480 reasonable explanation and the one that 1052 00:48:01,750 --> 00:47:59,180 you know with 99% confidence is going to 1053 00:48:04,540 --> 00:48:01,760 be correct to some extent is that they 1054 00:48:06,760 --> 00:48:04,550 probably come from massive stars so this 1055 00:48:10,359 --> 00:48:06,770 is a very busy plot and I want you to 1056 00:48:14,020 --> 00:48:10,369 look at everything but basically there 1057 00:48:15,550 --> 00:48:14,030 are a lot of stars in the universe like 1058 00:48:17,859 --> 00:48:15,560 the Sun some of them are more massive 1059 00:48:18,970 --> 00:48:17,869 than the stars then the Sun like those 1060 00:48:19,870 --> 00:48:18,980 of you who are paying attention to the 1061 00:48:22,359 --> 00:48:19,880 details of the hertzsprung-russell 1062 00:48:23,950 --> 00:48:22,369 diagram well remember that there were 1063 00:48:26,440 --> 00:48:23,960 blue giants which are extremely massive 1064 00:48:31,210 --> 00:48:26,450 and their red dwarfs which are very 1065 00:48:34,570 --> 00:48:31,220 low-mass so what we know is that stars 1066 00:48:37,870 --> 00:48:34,580 are powered by burning protons into 1067 00:48:40,570 --> 00:48:37,880 helium nuclei fission but there's only a 1068 00:48:44,559 --> 00:48:40,580 finite amount of fuel that a given star 1069 00:48:47,819 --> 00:48:44,569 has and when that fuel runs out the star 1070 00:48:50,680 --> 00:48:47,829 and it does not die an elegant death and 1071 00:48:52,720 --> 00:48:50,690 the way it dies and the remnant that it 1072 00:48:55,750 --> 00:48:52,730 leaves behind depends on its initial 1073 00:48:59,020 --> 00:48:55,760 mass so low mass stars like the Sun 1074 00:49:01,390 --> 00:48:59,030 we're pretty sure that when they use up 1075 00:49:02,890 --> 00:49:01,400 all their nuclear fuel they blow up into 1076 00:49:05,049 --> 00:49:02,900 a red giant for a brief period of time 1077 00:49:06,370 --> 00:49:05,059 they then blow off a lot of gas and they 1078 00:49:12,040 --> 00:49:06,380 leave behind something called a white 1079 00:49:14,940 --> 00:49:12,050 dwarf more massive stars though undergo 1080 00:49:18,069 --> 00:49:14,950 a similar evolution but when they 1081 00:49:19,780 --> 00:49:18,079 finally become a giant instead of just 1082 00:49:21,910 --> 00:49:19,790 blowing off a nebula leaving a white 1083 00:49:25,690 --> 00:49:21,920 dwarf they undergo this huge explosion 1084 00:49:27,849 --> 00:49:25,700 where their inner core's undergo 1085 00:49:31,390 --> 00:49:27,859 gravitational collapse and leave behind 1086 00:49:32,859 --> 00:49:31,400 either a neutron star or a black hole so 1087 00:49:38,020 --> 00:49:32,869 this is something that we're very very 1088 00:49:41,770 --> 00:49:38,030 sure about although the details we don't 1089 00:49:43,809 --> 00:49:41,780 have a lot of confidence in but we're 1090 00:49:47,650 --> 00:49:43,819 very very certain that neutron stars and 1091 00:49:54,609 --> 00:49:47,660 black holes are formed as the remnants 1092 00:49:58,450 --> 00:49:54,619 of massive stars now the issue that kind 1093 00:50:00,549 --> 00:49:58,460 of surprised us back in 2016 1094 00:50:02,770 --> 00:50:00,559 is that each of the black holes that 1095 00:50:05,049 --> 00:50:02,780 were detected in this original event had 1096 00:50:07,390 --> 00:50:05,059 a mass of 30 times the mass of the Sun 1097 00:50:09,700 --> 00:50:07,400 and the mass of the black hole that 1098 00:50:11,920 --> 00:50:09,710 remains is only a small fraction of the 1099 00:50:13,569 --> 00:50:11,930 mass of the original star because most 1100 00:50:16,660 --> 00:50:13,579 of the mass of the stars blown away in 1101 00:50:18,069 --> 00:50:16,670 this planetary nebula or supernova so 1102 00:50:20,049 --> 00:50:18,079 that means that a 30 solar mass black 1103 00:50:22,630 --> 00:50:20,059 hole would have had to come from a much 1104 00:50:24,579 --> 00:50:22,640 more massive star that's okay there are 1105 00:50:27,039 --> 00:50:24,589 many more much more massive stars in the 1106 00:50:28,329 --> 00:50:27,049 universe but if you're paying attention 1107 00:50:30,130 --> 00:50:28,339 when Frank was talking about the 1108 00:50:34,270 --> 00:50:30,140 hertzsprung-russell diagram he told you 1109 00:50:37,390 --> 00:50:34,280 that there are far more far far far more 1110 00:50:39,970 --> 00:50:37,400 low mass stars than there are high mass 1111 00:50:42,280 --> 00:50:39,980 stars and so it was kind of surprising 1112 00:50:46,210 --> 00:50:42,290 that the first black hole binary that 1113 00:50:49,630 --> 00:50:46,220 LIGO detected came from these very very 1114 00:50:51,760 --> 00:50:49,640 very rare supermassive stars we would 1115 00:50:53,829 --> 00:50:51,770 have thought we would see five or ten 1116 00:50:55,890 --> 00:50:53,839 solar mass black holes not 30 solar mass 1117 00:50:58,859 --> 00:50:55,900 black holes 1118 00:51:00,930 --> 00:50:58,869 and so that got us to thinking and I'm 1119 00:51:02,670 --> 00:51:00,940 not a gravitational wave astrophysicist 1120 00:51:04,019 --> 00:51:02,680 I'm not a stellar astrophysicist I'm not 1121 00:51:08,970 --> 00:51:04,029 a blackhole guy I'm not a neutron star 1122 00:51:11,160 --> 00:51:08,980 guy I'm a cosmologists and one of the 1123 00:51:13,009 --> 00:51:11,170 things that I get paid to do is think 1124 00:51:14,880 --> 00:51:13,019 about what the dark matter is 1125 00:51:18,239 --> 00:51:14,890 fortunately I don't get paid to actually 1126 00:51:20,910 --> 00:51:18,249 figure it out because that can only 1127 00:51:27,749 --> 00:51:20,920 happen once and once it happens we're 1128 00:51:29,849 --> 00:51:27,759 out of work so I think about what the 1129 00:51:31,739 --> 00:51:29,859 dark matter might be and so here are 1130 00:51:33,210 --> 00:51:31,749 black holes they're dark 1131 00:51:36,599 --> 00:51:33,220 they've been discovered they're out 1132 00:51:43,349 --> 00:51:36,609 there maybe there's the Dark Matter so 1133 00:51:47,370 --> 00:51:43,359 it's a silly idea so dark matter this is 1134 00:51:49,980 --> 00:51:47,380 a mystery that's been around for a good 1135 00:51:51,239 --> 00:51:49,990 fraction of a century and the reason we 1136 00:51:53,880 --> 00:51:51,249 believe in dark matter there are many 1137 00:51:55,019 --> 00:51:53,890 many lines of reasoning to tell us that 1138 00:51:57,329 --> 00:51:55,029 there's a lot of dark matter in the 1139 00:51:59,670 --> 00:51:57,339 universe but the simplest is perhaps 1140 00:52:03,359 --> 00:51:59,680 what we call galactic rotation curves so 1141 00:52:05,579 --> 00:52:03,369 there are a lot of galaxies like the 1142 00:52:07,499 --> 00:52:05,589 Milky Way which are a collection of a 1143 00:52:09,779 --> 00:52:07,509 gravitationally bound system of stars 1144 00:52:11,640 --> 00:52:09,789 and each star moves and the 1145 00:52:15,630 --> 00:52:11,650 gravitational potential due to every 1146 00:52:19,099 --> 00:52:15,640 other star and galaxies have some finite 1147 00:52:21,180 --> 00:52:19,109 extent they are ten what we call 1148 00:52:22,859 --> 00:52:21,190 kiloparsecs and the kiloparsec is 1149 00:52:24,839 --> 00:52:22,869 roughly 3,000 light years so here in 1150 00:52:26,430 --> 00:52:24,849 this diagram actually this is 10,000 1151 00:52:28,890 --> 00:52:26,440 light years this is a smallish galaxy 1152 00:52:31,229 --> 00:52:28,900 and then the star sort of peter out 1153 00:52:33,120 --> 00:52:31,239 there's not a whole lot out here but 1154 00:52:36,059 --> 00:52:33,130 occasionally you do find some star at 1155 00:52:37,680 --> 00:52:36,069 large distance or some gas cloud and you 1156 00:52:39,420 --> 00:52:37,690 can see these gas clouds spinning around 1157 00:52:41,430 --> 00:52:39,430 and you can measure the velocity which 1158 00:52:44,599 --> 00:52:41,440 they spin around and if you plot the 1159 00:52:48,420 --> 00:52:44,609 speed at which these gas clouds are 1160 00:52:50,999 --> 00:52:48,430 spinning around this galaxy it continues 1161 00:52:53,700 --> 00:52:51,009 to increase at large distances from the 1162 00:52:55,319 --> 00:52:53,710 galaxies and that is unusual because if 1163 00:52:57,359 --> 00:52:55,329 this was all the manner that we saw then 1164 00:52:59,489 --> 00:52:57,369 according to Newton's laws the velocity 1165 00:53:02,009 --> 00:52:59,499 should decrease right in the solar 1166 00:53:05,279 --> 00:53:02,019 system the Sun is a very very massive 1167 00:53:06,690 --> 00:53:05,289 object right in the middle and mercury 1168 00:53:08,329 --> 00:53:06,700 which is right next to the Sun spins 1169 00:53:10,099 --> 00:53:08,339 around really really quickly 1170 00:53:12,529 --> 00:53:10,109 but as you go further out the solar 1171 00:53:14,469 --> 00:53:12,539 system Pluto takes forever to get around 1172 00:53:17,299 --> 00:53:14,479 the Sun because Pluto is so far away so 1173 00:53:20,059 --> 00:53:17,309 if this was all that we all the matter 1174 00:53:23,239 --> 00:53:20,069 in the galaxy we would expected to see 1175 00:53:25,249 --> 00:53:23,249 these speeds become much smaller at 1176 00:53:27,259 --> 00:53:25,259 large distances from the galaxy but 1177 00:53:30,859 --> 00:53:27,269 instead they're seen to increase and 1178 00:53:34,099 --> 00:53:30,869 this along with many other lines of 1179 00:53:37,130 --> 00:53:34,109 reasoning and many other forms of 1180 00:53:41,630 --> 00:53:37,140 evidence suggests that there is a lot of 1181 00:53:44,469 --> 00:53:41,640 dark matter non luminous matter that 1182 00:53:46,789 --> 00:53:44,479 surrounds the luminous stuff that we see 1183 00:53:48,469 --> 00:53:46,799 we don't know what it is though we're 1184 00:53:49,579 --> 00:53:48,479 very very sure that it's there when we 1185 00:53:52,190 --> 00:53:49,589 have no idea what it is 1186 00:53:54,170 --> 00:53:52,200 all we know is that it's dark it does 1187 00:53:58,789 --> 00:53:54,180 not emit light and it does not absorb 1188 00:54:00,709 --> 00:53:58,799 light we know now precisely how much 1189 00:54:02,299 --> 00:54:00,719 there is I can tell you it within a few 1190 00:54:04,089 --> 00:54:02,309 percent how much dark matter there is 1191 00:54:06,170 --> 00:54:04,099 even though I can't tell you what it is 1192 00:54:09,140 --> 00:54:06,180 and we know how its distributing 1193 00:54:11,390 --> 00:54:09,150 galaxies and elsewhere in the universe I 1194 00:54:13,519 --> 00:54:11,400 told you it does not emit nor absorb 1195 00:54:17,140 --> 00:54:13,529 light so it can't be the same stuff that 1196 00:54:19,700 --> 00:54:17,150 were made out of it can't be it atoms 1197 00:54:22,160 --> 00:54:19,710 for many years we've speculated that's 1198 00:54:23,420 --> 00:54:22,170 perhaps some new elementary particle and 1199 00:54:24,950 --> 00:54:23,430 we've been trying really hard to find 1200 00:54:28,999 --> 00:54:24,960 this elementary particle but we have not 1201 00:54:30,650 --> 00:54:29,009 yet succeeded and so it's not 1202 00:54:34,579 --> 00:54:30,660 unreasonable to entertain other 1203 00:54:37,910 --> 00:54:34,589 possibilities and Stephen Hawking back 1204 00:54:40,819 --> 00:54:37,920 in 1974 and others thought maybe there 1205 00:54:43,130 --> 00:54:40,829 are primordial black holes maybe the Big 1206 00:54:44,559 --> 00:54:43,140 Bang when it produced the universe and 1207 00:54:47,120 --> 00:54:44,569 produced all the stuff in the universe 1208 00:54:49,549 --> 00:54:47,130 maybe it also produced a whole bunch of 1209 00:54:53,479 --> 00:54:49,559 black holes which survived to become the 1210 00:54:55,339 --> 00:54:53,489 dark matter today so we tried to figure 1211 00:54:58,099 --> 00:54:55,349 out and these are some my collaborators 1212 00:54:59,839 --> 00:54:58,109 so my work is always done with students 1213 00:55:01,309 --> 00:54:59,849 and postdocs and in this particular case 1214 00:55:03,769 --> 00:55:01,319 I'm also with Adam riess who's a 1215 00:55:08,900 --> 00:55:03,779 colleague who has a Nobel Prize which 1216 00:55:11,029 --> 00:55:08,910 helps with the credibility so these are 1217 00:55:14,840 --> 00:55:11,039 all postdocs and one graduate student 1218 00:55:19,250 --> 00:55:17,660 so this was the paper we wrote I don't 1219 00:55:21,800 --> 00:55:19,260 remember the exact title but it was more 1220 00:55:23,420 --> 00:55:21,810 or less did LIGO detect arc matter so 1221 00:55:26,030 --> 00:55:23,430 it's a crazy idea it's a speculative 1222 00:55:27,920 --> 00:55:26,040 idea but not completely crazy and this 1223 00:55:29,570 --> 00:55:27,930 is the coincident I told you about so we 1224 00:55:32,870 --> 00:55:29,580 know how much dark matter there is in 1225 00:55:38,360 --> 00:55:32,880 the Galactic halo so we know how much 1226 00:55:40,460 --> 00:55:38,370 stuff there is out here if all of that 1227 00:55:43,730 --> 00:55:40,470 dark matter is composed of 30 solar mass 1228 00:55:45,830 --> 00:55:43,740 objects but then I can tell you how many 1229 00:55:48,560 --> 00:55:45,840 of them there should be and what the 1230 00:55:50,150 --> 00:55:48,570 typical spacing should be we also know 1231 00:55:52,970 --> 00:55:50,160 how fast these things are moving around 1232 00:55:54,980 --> 00:55:52,980 these dark matter objects whatever they 1233 00:55:56,660 --> 00:55:54,990 are in a galaxy like the Milky Way 1234 00:55:58,580 --> 00:55:56,670 galaxy are actually spinning around and 1235 00:56:03,710 --> 00:55:58,590 a speed of several hundred kilometers 1236 00:56:05,720 --> 00:56:03,720 per second and we also know that two 1237 00:56:08,600 --> 00:56:05,730 black holes if they pass by each other 1238 00:56:12,130 --> 00:56:08,610 can actually form very briefly a Brown 1239 00:56:14,270 --> 00:56:12,140 system that then spirals in and merges 1240 00:56:15,740 --> 00:56:14,280 so roughly speaking I've got you know 1241 00:56:17,900 --> 00:56:15,750 two ping-pong balls passing by each 1242 00:56:19,280 --> 00:56:17,910 other a large separation they're not 1243 00:56:22,190 --> 00:56:19,290 gonna hit each other but if the two 1244 00:56:24,830 --> 00:56:22,200 ping-pong balls pass by each other with 1245 00:56:26,390 --> 00:56:24,840 a separation that's smaller than their 1246 00:56:28,760 --> 00:56:26,400 size they're gonna run into each other 1247 00:56:33,440 --> 00:56:28,770 same thing is true of automobiles which 1248 00:56:35,180 --> 00:56:33,450 is why we have lanes so we know roughly 1249 00:56:38,060 --> 00:56:35,190 speaking how big a 30 solar mass black 1250 00:56:41,840 --> 00:56:38,070 hole is and so it is very very 1251 00:56:43,160 --> 00:56:41,850 straightforward to estimate how often 1252 00:56:45,980 --> 00:56:43,170 these things should run into each other 1253 00:56:49,730 --> 00:56:45,990 and so we did this estimate we did this 1254 00:56:52,940 --> 00:56:49,740 calculation and some of these people are 1255 00:56:54,290 --> 00:56:52,950 actually very well equipped in terms of 1256 00:56:57,320 --> 00:56:54,300 the theoretical background to do the 1257 00:57:00,140 --> 00:56:57,330 calculation properly and so we did it 1258 00:57:02,390 --> 00:57:00,150 and it turns out that the rate at which 1259 00:57:04,250 --> 00:57:02,400 such black holes would merge if they 1260 00:57:08,420 --> 00:57:04,260 made up the dark matter in galactic 1261 00:57:11,030 --> 00:57:08,430 halos agreed surprisingly well with the 1262 00:57:13,670 --> 00:57:11,040 rates at which black holes merge that we 1263 00:57:15,380 --> 00:57:13,680 infer from the fact that LIGO saw one of 1264 00:57:17,990 --> 00:57:15,390 these events after two weeks of 1265 00:57:20,180 --> 00:57:18,000 observation and it was that coincidence 1266 00:57:22,280 --> 00:57:20,190 that led us to write the paper and it's 1267 00:57:23,810 --> 00:57:22,290 that coincidence that has been very 1268 00:57:27,470 --> 00:57:23,820 intriguing for a number of our 1269 00:57:34,760 --> 00:57:30,020 so I think that this paper that we wrote 1270 00:57:39,080 --> 00:57:34,770 is the most highly cited post LIGO LIGO 1271 00:57:41,990 --> 00:57:39,090 related paper so this is a hypothesis 1272 00:57:43,550 --> 00:57:42,000 but it's not the answer I don't know 1273 00:57:47,240 --> 00:57:43,560 that this is the Dark Matter - pretty 1274 00:57:49,430 --> 00:57:47,250 out-there hypothesis but scientists are 1275 00:57:51,560 --> 00:57:49,440 supposed to not only propose hypotheses 1276 00:57:54,260 --> 00:57:51,570 but try to come up with ways to test the 1277 00:57:56,060 --> 00:57:54,270 hypotheses and that has been a very 1278 00:57:58,550 --> 00:57:56,070 active area of investigation for our 1279 00:58:00,560 --> 00:57:58,560 group and others I will not tell you all 1280 00:58:02,390 --> 00:58:00,570 the things that people have proposed but 1281 00:58:04,070 --> 00:58:02,400 I'll tell you about one thing that we 1282 00:58:10,550 --> 00:58:04,080 suggested and that we're hoping will be 1283 00:58:14,780 --> 00:58:10,560 done soon so it turns out that there are 1284 00:58:18,290 --> 00:58:14,790 these things called fast radio bursts so 1285 00:58:19,640 --> 00:58:18,300 you've all seen James Bond movies and 1286 00:58:21,800 --> 00:58:19,650 there's the one James Bond movie where 1287 00:58:24,760 --> 00:58:21,810 he goes to the Arecibo space there osebo 1288 00:58:26,540 --> 00:58:24,770 telescope which is this huge radio dish 1289 00:58:31,040 --> 00:58:26,550 you know what I'm talking about 1290 00:58:34,520 --> 00:58:31,050 okay so radio telescopes like Arecibo 1291 00:58:37,370 --> 00:58:34,530 and a few others detect radio frequency 1292 00:58:39,350 --> 00:58:37,380 radiation from the sky and for a number 1293 00:58:41,180 --> 00:58:39,360 of years I don't remember exactly a lot 1294 00:58:43,700 --> 00:58:41,190 but for about the past 10 years it's 1295 00:58:47,210 --> 00:58:43,710 been noticed that occasionally there is 1296 00:58:50,080 --> 00:58:47,220 a very brief flash of radio frequency 1297 00:58:52,790 --> 00:58:50,090 radiation coming from the sky 1298 00:58:55,490 --> 00:58:52,800 so these flashes lasts less than one 1299 00:58:56,780 --> 00:58:55,500 thousandth of a second and for a long 1300 00:58:58,990 --> 00:58:56,790 time people wonder whether there was 1301 00:59:01,280 --> 00:58:59,000 some type of problem with the telescope 1302 00:59:03,200 --> 00:59:01,290 but a number of different telescopes 1303 00:59:06,200 --> 00:59:03,210 started to see these things they did a 1304 00:59:07,700 --> 00:59:06,210 number of tests and it's now very 1305 00:59:09,920 --> 00:59:07,710 certain that these are actually coming 1306 00:59:11,780 --> 00:59:09,930 from the sky and for a variety of 1307 00:59:13,040 --> 00:59:11,790 reasons we believe these to be coming 1308 00:59:16,250 --> 00:59:13,050 from there are good reasons to believe 1309 00:59:18,320 --> 00:59:16,260 these are coming from large distances so 1310 00:59:20,150 --> 00:59:18,330 suppose one of these fast radio bursts 1311 00:59:22,970 --> 00:59:20,160 goes off and we have no idea I should 1312 00:59:24,170 --> 00:59:22,980 say where they come from or a pretty 1313 00:59:27,770 --> 00:59:24,180 sure they're coming from outside the 1314 00:59:29,660 --> 00:59:27,780 Milky Way but we have no idea what the 1315 00:59:31,400 --> 00:59:29,670 source is most people think that has 1316 00:59:33,140 --> 00:59:31,410 something to do with phenomena and the 1317 00:59:35,000 --> 00:59:33,150 surfaces of neutron stars but we can't 1318 00:59:37,460 --> 00:59:35,010 be absolutely sure but we don't even 1319 00:59:41,040 --> 00:59:37,470 care for our purposes so I should also 1320 00:59:42,420 --> 00:59:41,050 tell you that as of now they're about 50 1321 00:59:44,790 --> 00:59:42,430 fast radio bursts that have been 1322 00:59:47,160 --> 00:59:44,800 detected about a year ago there were 1323 00:59:49,080 --> 00:59:47,170 about 25 that have been detected but 1324 00:59:51,750 --> 00:59:49,090 there is a new telescope that the 1325 00:59:53,550 --> 00:59:51,760 Canadians have built called chyme which 1326 00:59:55,830 --> 00:59:53,560 stands for Canadian hydrogen intensity 1327 00:59:57,900 --> 00:59:55,840 mapping experiment and unlike the other 1328 00:59:59,820 --> 00:59:57,910 radio telescopes like Arecibo which 1329 01:00:01,890 --> 00:59:59,830 pointed a very small part of the sky on 1330 01:00:03,810 --> 01:00:01,900 this Canadian telescope points at a very 1331 01:00:05,730 --> 01:00:03,820 large fraction of the seas a very large 1332 01:00:08,730 --> 01:00:05,740 fraction in the sky and so they expect 1333 01:00:10,680 --> 01:00:08,740 to detect these fast radio bursts far 1334 01:00:12,270 --> 01:00:10,690 more frequently than the past and in 1335 01:00:14,160 --> 01:00:12,280 just a few months of observation they've 1336 01:00:16,170 --> 01:00:14,170 doubled the sample of fast radio bursts 1337 01:00:19,230 --> 01:00:16,180 already and they expect to see several 1338 01:00:20,970 --> 01:00:19,240 thousand more in the next few years so 1339 01:00:23,040 --> 01:00:20,980 suppose there's a fast radio bursts and 1340 01:00:25,370 --> 01:00:23,050 suppose the black hole's make up the 1341 01:00:29,540 --> 01:00:25,380 dark matter then there is some chance 1342 01:00:32,790 --> 01:00:29,550 that there will be such a black hole 1343 01:00:36,150 --> 01:00:32,800 along the line of sight to a given fast 1344 01:00:39,090 --> 01:00:36,160 radio bursts and if that's the case then 1345 01:00:41,790 --> 01:00:39,100 this massive object this black hole can 1346 01:00:43,320 --> 01:00:41,800 gravitationally lends the signal from 1347 01:00:44,940 --> 01:00:43,330 this fast radio bursts so the light from 1348 01:00:49,290 --> 01:00:44,950 this fast radio bursts these radio waves 1349 01:00:52,040 --> 01:00:49,300 can travel to us either along this 1350 01:00:54,480 --> 01:00:52,050 trajectory or along this trajectory and 1351 01:00:56,520 --> 01:00:54,490 it turns out that most generally these 1352 01:01:01,620 --> 01:00:56,530 two trajectories have slightly different 1353 01:01:05,910 --> 01:01:01,630 path lengths and the path lengths differ 1354 01:01:09,180 --> 01:01:05,920 by roughly a millisecond times the speed 1355 01:01:11,040 --> 01:01:09,190 of light or a few milliseconds time the 1356 01:01:15,980 --> 01:01:11,050 speed of light and so what we predict is 1357 01:01:18,420 --> 01:01:15,990 that instead of seeing one flash once 1358 01:01:20,550 --> 01:01:18,430 sub-millisecond flash which has been the 1359 01:01:21,360 --> 01:01:20,560 case for all the vast rate of earths 1360 01:01:23,730 --> 01:01:21,370 that have been seen 1361 01:01:26,400 --> 01:01:23,740 if these black holes are out there 1362 01:01:28,380 --> 01:01:26,410 roughly one in a hundred of them will be 1363 01:01:30,570 --> 01:01:28,390 gravitationally lensed and after seeing 1364 01:01:32,250 --> 01:01:30,580 the original flash you'll see the 1365 01:01:35,120 --> 01:01:32,260 flashes arriving through a second 1366 01:01:37,410 --> 01:01:35,130 trajectory and so you'll see and that go 1367 01:01:40,680 --> 01:01:37,420 so these measurements are now being made 1368 01:01:43,560 --> 01:01:40,690 as I said they've seen 50 in a few years 1369 01:01:46,110 --> 01:01:43,570 they'll have maybe 5,000 and if black 1370 01:01:48,480 --> 01:01:46,120 holes make up the dark matter then they 1371 01:01:50,970 --> 01:01:48,490 will see several hundred within a few 1372 01:01:52,770 --> 01:01:50,980 years that have an echo that looks like 1373 01:01:54,960 --> 01:01:52,780 this so 1374 01:01:56,130 --> 01:01:54,970 this is one way to test the scenario 1375 01:02:01,740 --> 01:01:56,140 there are other ways to test the 1376 01:02:05,430 --> 01:02:01,750 scenario I won't discuss them all but I 1377 01:02:06,990 --> 01:02:05,440 think I will close there so the era of 1378 01:02:08,670 --> 01:02:07,000 gravitational wave astronomy is here 1379 01:02:10,190 --> 01:02:08,680 we're learning all about black holes 1380 01:02:13,410 --> 01:02:10,200 about general relativity 1381 01:02:16,740 --> 01:02:13,420 spacetime Wiggles around maybe we'll 1382 01:02:18,870 --> 01:02:16,750 also learn something about dark matter I 1383 01:02:20,310 --> 01:02:18,880 should say the jury is still out as to 1384 01:02:25,170 --> 01:02:20,320 whether prime order black holes can make 1385 01:02:26,790 --> 01:02:25,180 up the dark matter there's still some 1386 01:02:28,290 --> 01:02:26,800 debate within the Astrophysical 1387 01:02:29,430 --> 01:02:28,300 community about whether they can make up 1388 01:02:32,400 --> 01:02:29,440 the dark matter or whether current 1389 01:02:33,690 --> 01:02:32,410 observations already roll them out so 1390 01:02:35,310 --> 01:02:33,700 I'm not going to tell you I'm absolutely 1391 01:02:37,230 --> 01:02:35,320 certain that they can be the dark matter 1392 01:02:37,950 --> 01:02:37,240 but we are taking the idea very 1393 01:02:40,560 --> 01:02:37,960 seriously 1394 01:02:42,450 --> 01:02:40,570 either way it's a very exciting prospect 1395 01:02:45,120 --> 01:02:42,460 and many people are interested in in 1396 01:02:48,760 --> 01:02:45,130 trying to pursue further tests of this 1397 01:02:55,880 --> 01:02:48,770 scenario thank you very much 1398 01:02:55,890 --> 01:03:05,499 [Applause] 1399 01:03:24,249 --> 01:03:07,479 yes we are gonna have microphone here is 1400 01:03:27,370 --> 01:03:24,259 grant the bird at l2 that 2016 1401 01:03:37,079 --> 01:03:27,380 did you tell us more about bird there 1402 01:03:40,630 --> 01:03:37,089 was a bird was the Brit we had a Brit a 1403 01:03:47,510 --> 01:03:40,640 Frenchman and israeli-american 1404 01:03:54,180 --> 01:03:47,520 an Italian a Spaniard Greek and American 1405 01:03:59,400 --> 01:03:57,729 so this is a sermon bird is the big one 1406 01:04:05,410 --> 01:03:59,410 with a glasses 1407 01:04:17,949 --> 01:04:05,420 he's uh so he was just the lead authors 1408 01:04:19,359 --> 01:04:17,959 of Simon's Simeon Simeon I'm a kind of 1409 01:04:23,170 --> 01:04:19,369 veteran you've seen a lot of these 1410 01:04:25,930 --> 01:04:23,180 lectures and this black black dark 1411 01:04:34,279 --> 01:04:25,940 matter compared to nothing where does 1412 01:04:47,670 --> 01:04:43,829 that's a tricky question I would say 1413 01:04:49,859 --> 01:04:47,680 that we don't actually know very 1414 01:04:53,339 --> 01:04:49,869 precisely but we know that in the center 1415 01:04:57,299 --> 01:04:53,349 of a galaxy there is a high density of 1416 01:04:58,799 --> 01:04:57,309 dark matter and the density of dark 1417 01:05:01,020 --> 01:04:58,809 matter which is going to be very big 1418 01:05:04,500 --> 01:05:01,030 over here decreases as you go further 1419 01:05:06,359 --> 01:05:04,510 out but sooner or later there's going to 1420 01:05:08,789 --> 01:05:06,369 be another galaxy over here that has its 1421 01:05:10,170 --> 01:05:08,799 own Dark Matter halo and so it's not 1422 01:05:12,180 --> 01:05:10,180 clear that there's anywhere in the 1423 01:05:14,190 --> 01:05:12,190 universe where there is no dark matter 1424 01:05:16,049 --> 01:05:14,200 but the density of dark matter is 1425 01:05:20,309 --> 01:05:16,059 probably going to be smallest in the 1426 01:05:22,859 --> 01:05:20,319 places between the galaxies is there a 1427 01:05:27,120 --> 01:05:22,869 place where there is that better is just 1428 01:05:29,370 --> 01:05:27,130 nothing well you have points I don't 1429 01:05:31,170 --> 01:05:29,380 think so I would say that there are 1430 01:05:33,990 --> 01:05:31,180 places where we the dark matter density 1431 01:05:35,309 --> 01:05:34,000 is small but I don't think there's any 1432 01:05:36,779 --> 01:05:35,319 place in the universe that we can point 1433 01:05:49,470 --> 01:05:36,789 to where we're pretty sure that there is 1434 01:05:51,620 --> 01:05:49,480 no dark matter yeah I see a basis for a 1435 01:05:54,170 --> 01:05:51,630 new disaster movie in the making here 1436 01:05:56,279 --> 01:05:54,180 [Laughter] 1437 01:05:58,740 --> 01:05:56,289 just just like the opposite you had 1438 01:06:01,829 --> 01:05:58,750 mention are implied that that of a solar 1439 01:06:04,260 --> 01:06:01,839 system was fairly close to emerging 1440 01:06:06,000 --> 01:06:04,270 block merging black holes that the 1441 01:06:07,950 --> 01:06:06,010 distortion would be considerably greater 1442 01:06:13,170 --> 01:06:07,960 would they be enough to actually care 1443 01:06:14,640 --> 01:06:13,180 apart a solar system I don't think so it 1444 01:06:17,430 --> 01:06:14,650 would have to be I we went through this 1445 01:06:19,440 --> 01:06:17,440 calculation once but when we're sitting 1446 01:06:23,700 --> 01:06:19,450 in the cafeteria and tossing around 1447 01:06:26,490 --> 01:06:23,710 crazy ideas the the probability that 1448 01:06:29,849 --> 01:06:26,500 this would happen is extremely extremely 1449 01:06:31,829 --> 01:06:29,859 small so the rate at which such things 1450 01:06:35,519 --> 01:06:31,839 occur as we infer from the LIGO 1451 01:06:38,549 --> 01:06:35,529 measurements is so small that it's 1452 01:06:41,130 --> 01:06:38,559 unlikely that there was ever such an 1453 01:06:44,760 --> 01:06:41,140 event even in our own galaxy over the 1454 01:06:46,109 --> 01:06:44,770 entire history of the universe so these 1455 01:06:49,019 --> 01:06:46,119 these events are so 1456 01:06:52,650 --> 01:06:49,029 err that a typical galaxy will go the 1457 01:06:56,249 --> 01:06:52,660 entire link you know the entire universe 1458 01:06:57,809 --> 01:06:56,259 without ever seeing such an event thank 1459 01:06:59,400 --> 01:06:57,819 you have to be relieved you don't have 1460 01:07:00,680 --> 01:06:59,410 to be very very close I think closer 1461 01:07:23,730 --> 01:07:00,690 than the nearest stars 1462 01:07:27,559 --> 01:07:23,740 so if black holes were in some way dark 1463 01:07:30,150 --> 01:07:27,569 matter how how would that relate to the 1464 01:07:33,180 --> 01:07:30,160 accelerating expansion of the universe 1465 01:07:38,730 --> 01:07:33,190 is there any connection that's a good 1466 01:07:42,210 --> 01:07:38,740 question and I have no idea so I was 1467 01:07:43,710 --> 01:07:42,220 just giving a I was giving a talk about 1468 01:07:46,680 --> 01:07:43,720 something related this morning to a 1469 01:07:48,059 --> 01:07:46,690 philosophy class oh there's a philosophy 1470 01:07:49,920 --> 01:07:48,069 of science class and they just wanted 1471 01:07:53,489 --> 01:07:49,930 somebody to talk about things that we do 1472 01:07:55,559 --> 01:07:53,499 in physics so there's the dark matter 1473 01:07:58,979 --> 01:07:55,569 problem and then there's the dark energy 1474 01:08:03,749 --> 01:07:58,989 problem and in science we are always 1475 01:08:08,099 --> 01:08:03,759 told to look for economic solutions and 1476 01:08:10,259 --> 01:08:08,109 so ideally we would have one theory or 1477 01:08:13,380 --> 01:08:10,269 model that can explain both dark matter 1478 01:08:15,320 --> 01:08:13,390 and dark energy and some theorists have 1479 01:08:17,579 --> 01:08:15,330 tried to do that but it turns out to be 1480 01:08:18,240 --> 01:08:17,589 far more difficult than you would 1481 01:08:20,280 --> 01:08:18,250 imagine 1482 01:08:22,140 --> 01:08:20,290 and what it really wants all these 1483 01:08:24,479 --> 01:08:22,150 solutions where they try to merge the 1484 01:08:26,189 --> 01:08:24,489 two they really wind up looking like a 1485 01:08:27,689 --> 01:08:26,199 solution for dark matter and a 1486 01:08:30,709 --> 01:08:27,699 completely different solution for dark 1487 01:08:35,189 --> 01:08:30,719 energy that are then glued together I 1488 01:08:36,979 --> 01:08:35,199 don't know but I don't think that I'll 1489 01:08:39,349 --> 01:08:36,989 be surprised if I were to be like 1490 01:08:43,740 --> 01:08:39,359 resurrected a hundred years from now and 1491 01:08:45,689 --> 01:08:43,750 learn that they actually the solution 1492 01:08:49,289 --> 01:08:45,699 for dark energy was related to the 1493 01:08:50,240 --> 01:08:49,299 solution for dark matter I can imagine 1494 01:08:52,470 --> 01:08:50,250 that a hundred years from now 1495 01:08:55,890 --> 01:08:52,480 cosmologists we were looking at back at 1496 01:08:57,149 --> 01:08:55,900 us and thinking oh that was so quaint 1497 01:08:58,590 --> 01:08:57,159 and silly they thought that was dark 1498 01:09:00,310 --> 01:08:58,600 matter those dark energy they didn't 1499 01:09:03,320 --> 01:09:00,320 understand that was just 1500 01:09:05,180 --> 01:09:03,330 but I have no idea what that is yeah 1501 01:09:07,700 --> 01:09:05,190 our current understanding has the the 1502 01:09:09,800 --> 01:09:07,710 dark matter localized around galaxies 1503 01:09:13,040 --> 01:09:09,810 etcetera whereas the dark energy is sort 1504 01:09:15,050 --> 01:09:13,050 of round all of space and so that that 1505 01:09:16,790 --> 01:09:15,060 to me you know has always been the 1506 01:09:19,070 --> 01:09:16,800 fundamental problem trying to combine 1507 01:09:20,950 --> 01:09:19,080 the two is that the distribution 1508 01:09:23,990 --> 01:09:20,960 function is totally different right I 1509 01:09:28,130 --> 01:09:24,000 agree and that's how I view it that's 1510 01:09:31,550 --> 01:09:28,140 how 99% of people like us view the 1511 01:09:33,170 --> 01:09:31,560 problem but I kind of think that 1512 01:09:37,160 --> 01:09:33,180 sometime in the future there's gonna be 1513 01:09:38,750 --> 01:09:37,170 like a solution that's you know of which 1514 01:09:52,190 --> 01:09:38,760 these are two different aspects 1515 01:09:55,700 --> 01:09:52,200 that's a nice hopeful thought thank you 1516 01:09:59,870 --> 01:09:55,710 um how closely closely related to 1517 01:10:02,600 --> 01:09:59,880 project Einstein is this as far as the 1518 01:10:04,550 --> 01:10:02,610 detection of gravitational waves how 1519 01:10:07,700 --> 01:10:04,560 closely related this is this to project 1520 01:10:15,110 --> 01:10:07,710 Einstein yes I don't think I know what 1521 01:10:17,720 --> 01:10:15,120 project Einstein is well it is one part 1522 01:10:21,190 --> 01:10:17,730 of it is a distributed processing 1523 01:10:24,860 --> 01:10:21,200 research project using blink 1524 01:10:30,310 --> 01:10:24,870 uh-huh okay taking data from the Arecibo 1525 01:10:35,030 --> 01:10:30,320 telescope and from the legos in 1526 01:10:37,070 --> 01:10:35,040 Louisiana and in Washington Policy and 1527 01:10:41,680 --> 01:10:37,080 they're looking for that for the 1528 01:10:44,510 --> 01:10:41,690 apparently if I understand correctly 1529 01:10:48,550 --> 01:10:44,520 looking at the locations of pulsars 1530 01:10:50,930 --> 01:10:48,560 where you could do interferometry use oh 1531 01:10:54,620 --> 01:10:50,940 okay that yeah okay now I know I know 1532 01:11:01,870 --> 01:10:54,630 what you're talking about that that's a 1533 01:11:05,210 --> 01:11:01,880 very very interesting set of projects so 1534 01:11:07,760 --> 01:11:05,220 there are pulsars which are spending 1535 01:11:09,590 --> 01:11:07,770 neutron stars that are located you know 1536 01:11:11,000 --> 01:11:09,600 ten thousand light years away and 1537 01:11:12,980 --> 01:11:11,010 there's a bunch of them spread 1538 01:11:13,310 --> 01:11:12,990 throughout the sky and what I showed you 1539 01:11:15,020 --> 01:11:13,320 was the 1540 01:11:17,930 --> 01:11:15,030 gravitational wave detector that they'd 1541 01:11:21,109 --> 01:11:17,940 built in Washington in Louisiana that 1542 01:11:22,640 --> 01:11:21,119 had two arms so there was a set of test 1543 01:11:25,129 --> 01:11:22,650 masses over here that were oscillating 1544 01:11:28,700 --> 01:11:25,139 like this another set like this so it's 1545 01:11:30,620 --> 01:11:28,710 been proposed to use pulsars for the 1546 01:11:32,839 --> 01:11:30,630 gravitational wave as gravitational wave 1547 01:11:34,520 --> 01:11:32,849 detectors so if I have you know if we're 1548 01:11:37,790 --> 01:11:34,530 on earth right here and there's one 1549 01:11:39,680 --> 01:11:37,800 pulsar over here and another pulsar over 1550 01:11:43,370 --> 01:11:39,690 here and the gravitational wave passes 1551 01:11:45,109 --> 01:11:43,380 by the Pulsar over here will oscillate 1552 01:11:46,819 --> 01:11:45,119 in this direction the Pulsar over here 1553 01:11:49,339 --> 01:11:46,829 lastly in this direction those two 1554 01:11:53,720 --> 01:11:49,349 oscillations will be out of phase and we 1555 01:11:56,930 --> 01:11:53,730 can detect that in principle and people 1556 01:11:59,540 --> 01:11:56,940 are trying to do this and the principle 1557 01:12:01,339 --> 01:11:59,550 is exactly the same as LIGO the 1558 01:12:04,100 --> 01:12:01,349 difference is that the arm lengths are 1559 01:12:06,319 --> 01:12:04,110 10,000 light years as opposed to for at 1560 01:12:08,569 --> 01:12:06,329 supposed a couple of miles and so the 1561 01:12:11,300 --> 01:12:08,579 wavelengths of the gravitational waves 1562 01:12:18,700 --> 01:12:11,310 that you can detect are bigger by about 1563 01:12:22,609 --> 01:12:18,710 a factor of a billion it's a it's a very 1564 01:12:24,620 --> 01:12:22,619 10 years ago even three years ago three 1565 01:12:26,600 --> 01:12:24,630 years ago I would have told I would have 1566 01:12:28,520 --> 01:12:26,610 put my money that those Paul start 1567 01:12:33,410 --> 01:12:28,530 timing arrays would detect gravitational 1568 01:12:35,270 --> 01:12:33,420 waves before Alaia but they didn't but I 1569 01:12:37,780 --> 01:12:35,280 think they will I think we will see 1570 01:12:40,250 --> 01:12:37,790 something in the next few years 1571 01:12:41,359 --> 01:12:40,260 okay so mark there's a question from the 1572 01:12:43,220 --> 01:12:41,369 online audience that I'm sort of 1573 01:12:45,319 --> 01:12:43,230 summarizing from things is they want to 1574 01:12:46,700 --> 01:12:45,329 understand how many more gravitational 1575 01:12:49,430 --> 01:12:46,710 waves are out there you've got black 1576 01:12:50,780 --> 01:12:49,440 hole black hole mergers and obviously if 1577 01:12:52,339 --> 01:12:50,790 you had supermassive black hole 1578 01:12:53,959 --> 01:12:52,349 supermassive black hole murders you can 1579 01:12:55,580 --> 01:12:53,969 see along with that but you know the 1580 01:12:58,010 --> 01:12:55,590 neutron stars how many other different 1581 01:13:01,399 --> 01:12:58,020 types of events will these gravitational 1582 01:13:03,770 --> 01:13:01,409 wave detectors be able to see in the 1583 01:13:07,220 --> 01:13:03,780 near somewhat near future so their black 1584 01:13:08,899 --> 01:13:07,230 hole binary black hole mergers there was 1585 01:13:11,390 --> 01:13:08,909 a merger of it there's an event last 1586 01:13:13,490 --> 01:13:11,400 year there was either a binary neutron 1587 01:13:15,649 --> 01:13:13,500 star or a neutron star black hole we 1588 01:13:16,580 --> 01:13:15,659 don't know which but we do expect you 1589 01:13:18,410 --> 01:13:16,590 know over the next few years to see 1590 01:13:21,200 --> 01:13:18,420 neutron star neutron star mergers 1591 01:13:23,089 --> 01:13:21,210 neutron star or black hole murders we'll 1592 01:13:26,920 --> 01:13:23,099 see more black hole black hole mergers 1593 01:13:30,400 --> 01:13:26,930 there is a space-based gravitational 1594 01:13:32,530 --> 01:13:30,410 detector that we are considering the 1595 01:13:35,830 --> 01:13:32,540 European Space Agency's leading and NASA 1596 01:13:37,630 --> 01:13:35,840 is participating in if when that flies 1597 01:13:39,490 --> 01:13:37,640 that will detect or have sensitivity 1598 01:13:41,650 --> 01:13:39,500 detect mergers of supermassive black 1599 01:13:44,470 --> 01:13:41,660 holes black holes that each have a mass 1600 01:13:47,740 --> 01:13:44,480 of a billion times mass of a billion 1601 01:13:50,620 --> 01:13:47,750 times the mass of the Sun people have 1602 01:13:52,330 --> 01:13:50,630 also speculated that supernovae when a 1603 01:13:54,250 --> 01:13:52,340 star explodes and forms a neutron star 1604 01:13:57,220 --> 01:13:54,260 that there might be a gravitational wave 1605 01:13:59,740 --> 01:13:57,230 signal from that people have speculated 1606 01:14:02,770 --> 01:13:59,750 that some neutron stars might have 1607 01:14:05,170 --> 01:14:02,780 little mountains on them and those 1608 01:14:06,340 --> 01:14:05,180 mountains some the spending of a neutron 1609 01:14:08,830 --> 01:14:06,350 storm with the mountain might give you a 1610 01:14:10,570 --> 01:14:08,840 gravitational wave signal the 1611 01:14:12,490 --> 01:14:10,580 space-based observatories will also 1612 01:14:15,400 --> 01:14:12,500 detect gravitational waves from white 1613 01:14:18,460 --> 01:14:15,410 dwarf binaries so some of the you know 1614 01:14:20,110 --> 01:14:18,470 low mass stars at the end of their when 1615 01:14:22,420 --> 01:14:20,120 they sneeze up all the nuclear fuel turn 1616 01:14:24,100 --> 01:14:22,430 into white dwarfs so if I have a binary 1617 01:14:26,140 --> 01:14:24,110 star system that consists of two low 1618 01:14:28,510 --> 01:14:26,150 mass stars it will evolve to a white 1619 01:14:30,070 --> 01:14:28,520 dwarf binary and we actually know of a 1620 01:14:32,440 --> 01:14:30,080 number of white dwarf binary so there 1621 01:14:37,300 --> 01:14:32,450 are signals from those binaries that we 1622 01:14:38,980 --> 01:14:37,310 expect to see I'm sure there are other 1623 01:14:41,230 --> 01:14:38,990 things but those are the ones that them 1624 01:14:43,210 --> 01:14:41,240 we generally hear most about and the 1625 01:14:45,100 --> 01:14:43,220 most promising so really gravitational 1626 01:14:46,900 --> 01:14:45,110 waves just are studying the interactions 1627 01:14:48,570 --> 01:14:46,910 of dead stars with the light dwarfs and 1628 01:14:50,680 --> 01:14:48,580 the neutron stars and black holes so 1629 01:14:52,480 --> 01:14:50,690 stars got to give up their lives in 1630 01:14:55,990 --> 01:14:52,490 order for a gravitational wave astronomy 1631 01:15:01,240 --> 01:14:56,000 to work right exactly all right do we 1632 01:15:03,730 --> 01:15:01,250 have more questions up here there was a 1633 01:15:07,120 --> 01:15:03,740 famous inflammatory experiment in the 1634 01:15:09,670 --> 01:15:07,130 late 1800s Michelson Morley when people 1635 01:15:11,560 --> 01:15:09,680 were looking for the ether yep what 1636 01:15:14,710 --> 01:15:11,570 would have happened if this 1637 01:15:17,860 --> 01:15:14,720 interferometer LIGO had existed back 1638 01:15:23,100 --> 01:15:17,870 then and had gotten this reading back 1639 01:15:26,350 --> 01:15:23,110 then so it is exactly the same type of 1640 01:15:27,700 --> 01:15:26,360 interferometer that they use but as you 1641 01:15:33,640 --> 01:15:27,710 know trillions of times better 1642 01:15:36,250 --> 01:15:33,650 sensitivity have they seen that probably 1643 01:15:37,630 --> 01:15:36,260 would have blown their mind I actually 1644 01:15:39,100 --> 01:15:37,640 don't know what they probably thought it 1645 01:15:40,229 --> 01:15:39,110 was just noise because they only had one 1646 01:15:43,800 --> 01:15:40,239 detector 1647 01:15:46,050 --> 01:15:43,810 in Cleveland and had we had just if 1648 01:15:47,250 --> 01:15:46,060 there was only one detector I don't know 1649 01:15:51,810 --> 01:15:47,260 the we would have been as confident 1650 01:15:54,660 --> 01:15:51,820 there was a real signal but with Rago if 1651 01:15:57,060 --> 01:15:54,670 we'd had if we'd had this result then if 1652 01:15:58,229 --> 01:15:57,070 we had this result then I don't know 1653 01:16:03,320 --> 01:15:58,239 what people would have made of it 1654 01:16:05,940 --> 01:16:03,330 because there was no concept of a 1655 01:16:10,890 --> 01:16:05,950 space-time curvature there was no 1656 01:16:12,930 --> 01:16:10,900 concept of gravitational waves I have no 1657 01:16:14,220 --> 01:16:12,940 idea what the what they would have made 1658 01:16:16,760 --> 01:16:14,230 of it they were they were looking for 1659 01:16:18,650 --> 01:16:16,770 exactly this they did have some sense of 1660 01:16:21,120 --> 01:16:18,660 curvature they just didn't have 1661 01:16:22,050 --> 01:16:21,130 space-time the modern concept well they 1662 01:16:23,970 --> 01:16:22,060 were looking for something a little 1663 01:16:25,770 --> 01:16:23,980 different they were looking to see 1664 01:16:28,080 --> 01:16:25,780 whether there was a difference between 1665 01:16:30,930 --> 01:16:28,090 what happens when the interferometer is 1666 01:16:33,240 --> 01:16:30,940 in like orient in this direction versus 1667 01:16:35,700 --> 01:16:33,250 oriented in this direction whereas the 1668 01:16:39,330 --> 01:16:35,710 signal that they saw all takes place 1669 01:16:41,660 --> 01:16:39,340 with one orientation and the the the 1670 01:16:43,740 --> 01:16:41,670 interferometer just started to vibrate 1671 01:16:46,740 --> 01:16:43,750 Michelson Morley we're looking to see 1672 01:16:50,280 --> 01:16:46,750 whether the the the the arm lengths 1673 01:16:54,030 --> 01:16:50,290 would change if as the orientation of 1674 01:16:55,709 --> 01:16:54,040 the detector was changed but I have no 1675 01:17:02,530 --> 01:16:55,719 idea what they would have made of it had 1676 01:17:05,170 --> 01:17:02,540 they seen something I guess so 1677 01:17:08,380 --> 01:17:05,180 there's an e equals mc-squared waiting 1678 01:17:12,550 --> 01:17:08,390 out there that will equate dark energy 1679 01:17:15,280 --> 01:17:12,560 and dark matter well there is a you know 1680 01:17:22,510 --> 01:17:15,290 there is some energy density in the dark 1681 01:17:24,310 --> 01:17:22,520 energy so there is some equivalence 1682 01:17:27,240 --> 01:17:24,320 between the mass of the dark energy and 1683 01:17:29,380 --> 01:17:27,250 its energy but I don't think there's any 1684 01:17:31,270 --> 01:17:29,390 correspondence there's no obvious 1685 01:17:38,820 --> 01:17:31,280 correspondence between the density of 1686 01:17:45,640 --> 01:17:43,690 I'm really struck by the the declaration 1687 01:17:49,750 --> 01:17:45,650 that there's the loss of three solar 1688 01:17:53,830 --> 01:17:49,760 masses in the combination of those two 1689 01:17:55,950 --> 01:17:53,840 black holes and I've got a couple 1690 01:17:58,480 --> 01:17:55,960 questions on that the first is with 1691 01:17:59,650 --> 01:17:58,490 given that that's that's based upon the 1692 01:18:01,240 --> 01:17:59,660 energy coming out of the gravitational 1693 01:18:03,610 --> 01:18:01,250 waves so it doesn't have to necessarily 1694 01:18:05,380 --> 01:18:03,620 be two black holes I mean if it was the 1695 01:18:07,720 --> 01:18:05,390 black hole and really anything else that 1696 01:18:10,300 --> 01:18:07,730 would just be on a smaller scale correct 1697 01:18:13,480 --> 01:18:10,310 yes and then my question when that would 1698 01:18:16,980 --> 01:18:13,490 be brings to mind Hawking radiation and 1699 01:18:20,260 --> 01:18:16,990 the idea of black hole evaporation but 1700 01:18:22,150 --> 01:18:20,270 if there's three solar masses that are 1701 01:18:23,320 --> 01:18:22,160 getting pulled out based on 1702 01:18:26,110 --> 01:18:23,330 gravitational waves 1703 01:18:27,760 --> 01:18:26,120 I feel like Hawking radiation really 1704 01:18:29,530 --> 01:18:27,770 pales in comparison to whatever might 1705 01:18:32,380 --> 01:18:29,540 come out of just the gravitational 1706 01:18:34,810 --> 01:18:32,390 effects well it depends on the mass of 1707 01:18:38,190 --> 01:18:34,820 the black hole if for some reason there 1708 01:18:43,030 --> 01:18:38,200 were black holes that had a mass of a 1709 01:18:45,850 --> 01:18:43,040 thousand trillion grams a trillion 1710 01:18:48,150 --> 01:18:45,860 kilograms so if there was a black hole 1711 01:18:52,390 --> 01:18:48,160 down at a mass of a trillion kilograms 1712 01:18:54,580 --> 01:18:52,400 it would Hawking evaporate in less than 1713 01:18:56,770 --> 01:18:54,590 the age of the universe and the vast 1714 01:18:58,960 --> 01:18:56,780 majority that energy would be released 1715 01:19:02,440 --> 01:18:58,970 in a very short period of time now the 1716 01:19:04,320 --> 01:19:02,450 total energy is very small compared with 1717 01:19:06,250 --> 01:19:04,330 the total energy that's released in the 1718 01:19:07,750 --> 01:19:06,260 black holes that they've seen but those 1719 01:19:10,480 --> 01:19:07,760 but that's because those black holes are 1720 01:19:11,040 --> 01:19:10,490 so much more massive when when a black 1721 01:19:13,750 --> 01:19:11,050 hole 1722 01:19:16,390 --> 01:19:13,760 you know explodes by a Hawking 1723 01:19:17,620 --> 01:19:16,400 evaporation the entire rest mass energy 1724 01:19:20,290 --> 01:19:17,630 black hole as far as we know would be 1725 01:19:24,820 --> 01:19:20,300 released in radiation here it was just a 1726 01:19:29,620 --> 01:19:24,830 measly five percent okay but I should 1727 01:19:32,830 --> 01:19:29,630 say the the energy radiated that three 1728 01:19:35,380 --> 01:19:32,840 solar masses of energy was rated in one 1729 01:19:40,840 --> 01:19:35,390 millisecond and during that millisecond 1730 01:19:43,300 --> 01:19:40,850 this one system was more luminous than 1731 01:19:44,260 --> 01:19:43,310 the rest of the universe combined then 1732 01:19:47,290 --> 01:19:44,270 all the other stars in the universe 1733 01:19:48,640 --> 01:19:47,300 combined yeah there's a couple more 1734 01:19:54,820 --> 01:19:48,650 questions we had to this gentleman in 1735 01:19:57,580 --> 01:19:54,830 green here or like there there we go you 1736 01:19:59,410 --> 01:19:57,590 haven't talked about the speed of 1737 01:20:00,220 --> 01:19:59,420 gravitational waves at all do you think 1738 01:20:03,150 --> 01:20:00,230 about that 1739 01:20:05,770 --> 01:20:03,160 ah so general relativity predicts that 1740 01:20:10,810 --> 01:20:05,780 gravitational waves propagate at the 1741 01:20:12,160 --> 01:20:10,820 speed of light and we now know that that 1742 01:20:18,120 --> 01:20:12,170 prediction that prediction has been 1743 01:20:22,990 --> 01:20:18,130 verified because there was an event in 1744 01:20:25,300 --> 01:20:23,000 late in August of 2017 where there's a 1745 01:20:27,220 --> 01:20:25,310 gravitational wave signal seen from the 1746 01:20:31,000 --> 01:20:27,230 merger of either two neutron stars or 1747 01:20:33,550 --> 01:20:31,010 neutron star in a black hole and the 1748 01:20:36,100 --> 01:20:33,560 neutron star or neutron star merger 1749 01:20:37,600 --> 01:20:36,110 neutron star black hole merger some of 1750 01:20:40,470 --> 01:20:37,610 the material from the neutron star was 1751 01:20:44,740 --> 01:20:40,480 ripped out and there was a very visible 1752 01:20:47,170 --> 01:20:44,750 a very bright invisible explosion and so 1753 01:20:49,480 --> 01:20:47,180 this event was detected by a huge array 1754 01:20:50,950 --> 01:20:49,490 of telescopes simultaneously with the 1755 01:20:54,250 --> 01:20:50,960 ground with a gravitational wave 1756 01:20:56,260 --> 01:20:54,260 detection so we saw this one event in 1757 01:20:58,480 --> 01:20:56,270 gravitational waves and simultaneously 1758 01:21:00,490 --> 01:20:58,490 in electromagnetic waves and so from 1759 01:21:03,430 --> 01:21:00,500 that we know that they do propagate at 1760 01:21:08,640 --> 01:21:03,440 the speed of light so this this event 1761 01:21:11,550 --> 01:21:08,650 was astounding so the gravitational wave 1762 01:21:13,930 --> 01:21:11,560 observatory x' alerted the entire 1763 01:21:15,940 --> 01:21:13,940 astronomical community anybody who had a 1764 01:21:18,040 --> 01:21:15,950 telescope found out about this and 1765 01:21:21,130 --> 01:21:18,050 anybody who could pointed the telescope 1766 01:21:25,240 --> 01:21:21,140 at it and as it turns out one of nasa's 1767 01:21:28,180 --> 01:21:25,250 other one of nasa satellites the the 1768 01:21:30,540 --> 01:21:28,190 Fermi satellite detected 1769 01:21:34,000 --> 01:21:30,550 a gravitational wave burst 1770 01:21:35,800 --> 01:21:34,010 simultaneously and independently and 1771 01:21:37,570 --> 01:21:35,810 another you know telescopes like the 1772 01:21:39,130 --> 01:21:37,580 Hubble Space Telescope was as quickly as 1773 01:21:40,900 --> 01:21:39,140 possible pointed at that region of the 1774 01:21:43,180 --> 01:21:40,910 sky I'm all these ground-based 1775 01:21:45,729 --> 01:21:43,190 observatories radio telescopes all 1776 01:21:47,740 --> 01:21:45,739 observed that part of the sky and the 1777 01:21:51,430 --> 01:21:47,750 papers that resulted from this one event 1778 01:21:54,310 --> 01:21:51,440 I think one out of three astronomers in 1779 01:21:56,530 --> 01:21:54,320 the world and had a name on one of those 1780 01:21:58,270 --> 01:21:56,540 papers and I got a call from some 1781 01:21:59,380 --> 01:21:58,280 reporters and asked him how can you not 1782 01:22:00,640 --> 01:21:59,390 calling me about this because I'm not 1783 01:22:01,990 --> 01:22:00,650 really an expert on this kind of thing 1784 01:22:03,189 --> 01:22:02,000 and they said well you're the only 1785 01:22:09,520 --> 01:22:03,199 person we could think of it wasn't a 1786 01:22:11,850 --> 01:22:09,530 co-author on one of the papers there's 1787 01:22:13,780 --> 01:22:11,860 another astronomer in the room they were 1788 01:22:19,810 --> 01:22:13,790 yeah half the people in this building 1789 01:22:22,030 --> 01:22:19,820 were co-authors on one of the papers um 1790 01:22:23,800 --> 01:22:22,040 things have been moving around in our 1791 01:22:26,170 --> 01:22:23,810 solar system and bumping into each other 1792 01:22:29,020 --> 01:22:26,180 since time immemorial I mean supposedly 1793 01:22:31,810 --> 01:22:29,030 we were pelted by a mars-sized planet in 1794 01:22:33,790 --> 01:22:31,820 the past with what we can conceivably 1795 01:22:38,520 --> 01:22:33,800 build in the near future 1796 01:22:44,979 --> 01:22:41,520 that's a good question 1797 01:22:48,040 --> 01:22:44,989 there are not nobody has really thought 1798 01:22:49,030 --> 01:22:48,050 of any other plausible Astrophysical 1799 01:22:52,780 --> 01:22:49,040 source that would produce a 1800 01:22:56,380 --> 01:22:52,790 gravitational wave signal involving an 1801 01:23:00,340 --> 01:22:56,390 object any less massive than a white 1802 01:23:01,689 --> 01:23:00,350 dwarf which the white dwarfs that exist 1803 01:23:04,959 --> 01:23:01,699 typically have a mass of about six 1804 01:23:08,050 --> 01:23:04,969 tenths the mass of the Sun the way that 1805 01:23:10,870 --> 01:23:08,060 the general relativity works the the 1806 01:23:13,360 --> 01:23:10,880 strength of the signal the gravitational 1807 01:23:15,729 --> 01:23:13,370 wave luminosity it greases very very 1808 01:23:17,140 --> 01:23:15,739 rapidly as you decrease the mass of the 1809 01:23:20,140 --> 01:23:17,150 system and also as you do as you 1810 01:23:22,840 --> 01:23:20,150 decrease the density so black holes are 1811 01:23:25,060 --> 01:23:22,850 the densest possible object and you know 1812 01:23:29,050 --> 01:23:25,070 those give us an observable signal if 1813 01:23:31,810 --> 01:23:29,060 there are very very massive but once you 1814 01:23:36,060 --> 01:23:31,820 go to something like a star an ordinary 1815 01:23:39,189 --> 01:23:36,070 star or a planet it's so diffuse that 1816 01:23:41,890 --> 01:23:39,199 the signals are conceivable signals are 1817 01:23:43,720 --> 01:23:41,900 way too weak to be detected 1818 01:23:45,700 --> 01:23:43,730 okay so I think we had one last question 1819 01:23:48,220 --> 01:23:45,710 over here and then we got to cut it off 1820 01:23:51,580 --> 01:23:48,230 a rainy is here to take people across 1821 01:23:55,450 --> 01:23:51,590 the street for the observing so catch 1822 01:23:57,960 --> 01:23:55,460 that does the expansion of space-time 1823 01:24:01,420 --> 01:23:57,970 affect the LIGO measurements and 1824 01:24:06,540 --> 01:24:01,430 interaction yes it does 1825 01:24:11,140 --> 01:24:09,670 so the expansion of space-time affects 1826 01:24:14,410 --> 01:24:11,150 the gravitational wave signal in that 1827 01:24:17,350 --> 01:24:14,420 the the binary black hole system is 1828 01:24:20,110 --> 01:24:17,360 moving away from us and so the 1829 01:24:22,750 --> 01:24:20,120 gravitational wave signal is Doppler 1830 01:24:26,590 --> 01:24:22,760 shifted or red shifted relative to what 1831 01:24:28,000 --> 01:24:26,600 it is when it is emitted and given the 1832 01:24:30,550 --> 01:24:28,010 equivalence principle and the way 1833 01:24:32,410 --> 01:24:30,560 general relativity works there's a 1834 01:24:34,660 --> 01:24:32,420 degeneracy between two black holes that 1835 01:24:37,330 --> 01:24:34,670 have say a mass of 30 solar masses that 1836 01:24:40,120 --> 01:24:37,340 are at some distance and two black holes 1837 01:24:43,690 --> 01:24:40,130 that have say a mass of 15 solar masses 1838 01:24:47,980 --> 01:24:43,700 that are at a closer distance but there 1839 01:24:51,340 --> 01:24:47,990 are ways to break that degeneracy okay 1840 01:24:54,700 --> 01:24:51,350 so I hope you have plenty to think about 1841 01:24:56,820 --> 01:24:54,710 from here this is the questions and the 1842 01:25:00,510 --> 01:24:56,830 comments online of to show that mark has 1843 01:25:03,280 --> 01:25:00,520 taken us new places here tonight ireenie 1844 01:25:04,540 --> 01:25:03,290 Lambrini says you want to be over here 1845 01:25:05,950 --> 01:25:04,550 to take people because you can go out 1846 01:25:08,110 --> 01:25:05,960 that door over there so if you would 1847 01:25:10,390 --> 01:25:08,120 like to go across the street to do the 1848 01:25:14,170 --> 01:25:10,400 observing or renew a joinery knee over 1849 01:25:17,260 --> 01:25:14,180 here our next talk is the third Thursday 1850 01:25:25,159 --> 01:25:17,270 January 15th and let's give mark one