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well this is more of a technical talk

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but partly inspired by the fact that UFO

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reports frequently discuss impressive

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maneuverability at with usually no

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indication of conventionally known

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drives and to cut to the chase just in

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case I should run out of time a

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sufficiently advanced technology can use

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antimatter annihilation to power a

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reaction drive whose only exhaust is an

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intense beam of neutrinos this would not

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be visible it would be very hard to

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detect by any means but it is

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potentially a testable hypothesis from

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retrospective evidence that already

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exists just as a note by a sufficiently

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advanced technology I mean something

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that can accomplish anything that can be

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known that is known to be physically

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possible but that does not require any

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new physics simply on the grounds that I

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felt that a hypothesis is more credible

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if it sticks to things that we know are

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possible in principle now there's been a

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fair amount of discussion about

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theoretical space propulsion at the

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moment the only physics we know of

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relevant to space propulsion involves a

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law of equal action and reaction the

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only way you can move in one direction

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is to throw something else reaction mass

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as I call it in the other direction

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there are some variations that basically

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involve getting your reaction mass from

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outside the vehicle but they still

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adhere to Newton's third law and the

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most powerful known reaction drive is an

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i-i-i was told after i submitted my

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abstract that it would be good to

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provide a brief primer on on what

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antimatter is to begin with so every

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type of particle making up normal matter

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has a corresponding anti particle the

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relation between antimatter and normal

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matter is that every measurable property

46
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is either identical or exactly the

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opposite between the two mass is one of

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the identical properties antimatter

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particles have the same mass as matter

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particles electrical charge is one of

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the reversed properties the anti

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electron is also called the positron

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because it has a positive charge the

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antiproton has a negative charge when

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matter and antimatter meet they

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annihilate releasing energy and just

57
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historically the first antiparticle

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discovered was the anti electron or

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okay now electron positron annihilation

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is nice and simple

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they simply meet each other and convert

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into a pair of gamma rays carrying all

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of the energy ah now in accelerators

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we've been studying anti protons for

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decades now their annihilation is more

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complicated partly because a proton is a

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composite object made of three quarks an

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antiproton of course is made of three

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anti quarks and partly because the

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energy release is so much bigger that

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completely new particles or rather

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particle-antiparticle pairs can be

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created out of the energy this is a

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reversible process but there is no

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material particle lighter than the

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electron so there's no alternative but

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photons here the primary annihilation

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gives you a mess of unstable reaction

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products that ultimately are all going

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to decay or mutually annihilate into

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photons and neutrinos the now if a

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single antiproton annihilates inside a

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large nucleus most of the intermediate

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products are strongly

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interacting maisons which are very

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efficient at transferring energy to the

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rest of the nucleus so most aside from

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photons most of the energy appears as

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thermal excitation in a nucleus that's

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literally been blown apart by the excess

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energy however if an antiproton

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annihilates an isolated proton the

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ultimate products all break down into

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photons and neutrinos and the neutrinos

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end up with the lion's share of the

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energy for technical reasons that I can

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get into later on if anybody is really

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interested now for a reaction Drive the

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faster you throw away your reaction mass

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the more efficient your drive is the

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more thrust you get per unit of fuel

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you're using up the ultimate reaction

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Drive would have an exhaust velocity

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equal to the speed of light

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now since which essentially amounts to

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turning your fuel mass into radiation

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and beaming it out the back you might

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think that you can do that with

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antimatter since it annihilates matter

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completely into energy except that the

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aforementioned neutrino problem the

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neutrinos fly off in all directions

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equally you can't direct them you can't

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manipulate them so much of the energy is

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lost in terms of neutrinos that a rich

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Mitch makes antimatter rocket would

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actually be terribly inefficient but

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that assumes you're just burning the

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matter antimatter makes in a reaction

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chamber ah the trick is to pre

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accelerate the particles you're going to

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annihilate as in a particle accelerator

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on earth you accelerate both the proton

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and the antiproton to high speed but in

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the same direction not ramming them into

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each other the way we do for experiments

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they annihilate in at high speed the

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reaction products inherit that center of

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mass motion and then you put in a

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retrieval stage the stuff that you can

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interact with you capture reprocess the

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energy use it to power the acceleration

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for the next particle pair meanwhile the

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neutrinos escape all of the momentum

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that has been put into them by the pre

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acceleration is just carried out of the

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chamber and you get a net thrust I'm

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going to skip quickly over the math here

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it we can refer to it in question two

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and answer if people really want but

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this graphic illustrates the drive

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attributes and a perhaps somewhat more

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accessible way down here at the bottom

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I've plotted the fraction of retrievable

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energy the amount of Annihilation energy

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that can be captured and used and that

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actually depends on how big your engine

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is and how much free path you have for

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intermediate reaction products to decay

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if something is still a Payan of some

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sort you can intercept it and use it it

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will decay naturally into neutrinos and

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photons and that that's that's where

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those neutrinos come from it's a process

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that takes time and requires a certain

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amount of free path to be completed now

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fortunately the math on the previous

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page indicates that the higher the mass

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retention that is the fewer neutrino

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decays you allow the higher your

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effective exhaust velocity the amount of

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thrust you get per unit of fuel that

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this is a good thing because that means

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that the smaller your engine the more

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powerful and efficient it can be just

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for comparison a allene mix antimatter

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rocket where you're doing simple a

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burning like effect and have perhaps 5%

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antimatter would have about this thrust

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to mass ratio an ideal fusion rocket

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would be down here an ideal fission

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rocket would be

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down here and the chemical rockets that

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were actually building nowadays would be

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so far down into the corner that there's

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no room for the font now what that means

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in terms of the performance of such a

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drive system if oh sorry I overshot this

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shaded area here shows the approximate

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regime for an engine of reasonable size

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a few meters across and you can see that

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our effective exhaust velocity is indeed

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very close to the ultimate possible

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limit a vehicle with a drive of this

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type if it made a constant 1g thrust

186
00:09:46,720 --> 00:09:42,590
trip from the moon to the earth it would

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use up 0.42 kilograms of fuel mass for

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each metric tonne a vehicle mass that's

189
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about 1 pound of fuel on eighth of a

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gallon to fly your car from the moon to

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the earth if a vehicle had a one to one

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00:10:06,970 --> 00:10:02,750
mass ratio meaning that the fuel tank

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00:10:10,980 --> 00:10:06,980
holds as much as the payload it could

194
00:10:13,720 --> 00:10:10,990
thrust at 1g continuously for 245 days

195
00:10:16,330 --> 00:10:13,730
this is the kind of figure people are

196
00:10:19,620 --> 00:10:16,340
talking about for interstellar travel by

197
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conventional means through normal space

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whatever we might think about

199
00:10:26,860 --> 00:10:23,810
interstellar travel this obviously gives

200
00:10:33,340 --> 00:10:26,870
us ample power for maneuvering and

201
00:10:39,290 --> 00:10:36,999
so in terms of empirical consequences

202
00:10:42,259 --> 00:10:39,300
detecting neutrinos is extremely

203
00:10:45,019 --> 00:10:42,269
difficult but there have been neutrino

204
00:10:46,309 --> 00:10:45,029
detectors in operation some of them are

205
00:10:48,379 --> 00:10:46,319
actually being called neutrino

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00:10:52,910 --> 00:10:48,389
telescopes these days because they

207
00:10:55,730 --> 00:10:52,920
detect astronomical events literally for

208
00:11:01,720 --> 00:10:55,740
decades they had already established a

209
00:11:04,460 --> 00:11:01,730
solar neutrino problem in the late 1970s

210
00:11:07,489 --> 00:11:04,470
now most of the output of a neutrino

211
00:11:10,639 --> 00:11:07,499
drive will be muon neutrinos because

212
00:11:13,850 --> 00:11:10,649
those are produced by the first step in

213
00:11:15,889 --> 00:11:13,860
the decay cascade and we recall that you

214
00:11:17,869 --> 00:11:15,899
want to keep the decay cascade short

215
00:11:22,100 --> 00:11:17,879
because that's what makes the drive more

216
00:11:23,900 --> 00:11:22,110
efficient however the solution to the

217
00:11:25,910 --> 00:11:23,910
solar neutrino problem that I mentioned

218
00:11:30,110 --> 00:11:25,920
a moment ago is that neutrinos oscillate

219
00:11:32,150 --> 00:11:30,120
they change identity muon neutrinos will

220
00:11:33,949 --> 00:11:32,160
over a sufficiently long flight path

221
00:11:37,040 --> 00:11:33,959
some fraction of them will transform

222
00:11:40,389 --> 00:11:37,050
into electron neutrinos which can be

223
00:11:43,100 --> 00:11:40,399
picked up by the detectors so this

224
00:11:47,210 --> 00:11:43,110
postulates the possibility of a very

225
00:11:50,929 --> 00:11:47,220
simple retrospective test for whether

226
00:11:53,030 --> 00:11:50,939
vehicles that we see do or that we think

227
00:11:56,090 --> 00:11:53,040
we see doing violent maneuvers in

228
00:11:59,210 --> 00:11:56,100
Earth's atmosphere are being powered by

229
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neutrino drives simply plot the

230
00:12:03,949 --> 00:12:00,839
direction of the maneuvers in

231
00:12:07,009 --> 00:12:03,959
three-dimensional space no note what

232
00:12:09,769 --> 00:12:07,019
direction they're accelerating in plot

233
00:12:11,629 --> 00:12:09,779
the opposite direction ignoring trivial

234
00:12:14,150 --> 00:12:11,639
obstacles like a few thousand miles of

235
00:12:19,009 --> 00:12:14,160
rock and see if they intersect a

236
00:12:20,660 --> 00:12:19,019
neutrino telescope if they do consult

237
00:12:22,699 --> 00:12:20,670
their records and find out if they got a

238
00:12:26,059 --> 00:12:22,709
blip of neutrino events at the

239
00:12:28,579 --> 00:12:26,069
appropriate time I have no idea how such

240
00:12:33,259 --> 00:12:28,589
a test would come out but at least it's

241
00:12:38,749 --> 00:12:33,269
a test that's doable there are also some

242
00:12:41,389 --> 00:12:38,759
more practical consequences antimatter

243
00:12:44,059 --> 00:12:41,399
is a tremendously rich energy storage

244
00:12:46,420 --> 00:12:44,069
system there is a lot of storage that

245
00:12:49,930 --> 00:12:46,430
stored energy in such a drive equal

246
00:12:51,970 --> 00:12:49,940
mc-squared a vehicle that crashes or

247
00:12:56,860 --> 00:12:51,980
even just loses whatever its containment

248
00:13:01,510 --> 00:12:56,870
system is is going to explode with a

249
00:13:04,840 --> 00:13:01,520
great deal of power even a kilogram of

250
00:13:07,690 --> 00:13:04,850
so or or so of antimatter is going to be

251
00:13:09,550 --> 00:13:07,700
a multi Megaton blast among other things

252
00:13:11,889 --> 00:13:09,560
this means that shooting them down

253
00:13:16,990 --> 00:13:11,899
doesn't sound like a very good idea if

254
00:13:19,720 --> 00:13:17,000
they're using this drive off hand the

255
00:13:23,139 --> 00:13:19,730
only way I can think of to avoid a

256
00:13:25,900 --> 00:13:23,149
tremendous explosion on upon crash

257
00:13:28,750 --> 00:13:25,910
landing is if the vehicle has already

258
00:13:30,400 --> 00:13:28,760
run out of fuel which when you think

259
00:13:37,120 --> 00:13:30,410
about it is a pretty good reason for a

260
00:13:39,880 --> 00:13:37,130
crash landing to happen just as a note

261
00:13:42,160 --> 00:13:39,890
for possible implications there's still

262
00:13:46,630 --> 00:13:42,170
speculation about what the Tunguska

263
00:13:48,280 --> 00:13:46,640
explosion in 1908 was but the estimated

264
00:13:49,990 --> 00:13:48,290
power of the blast court would

265
00:13:52,690 --> 00:13:50,000
correspond to the amount of antimatter

266
00:13:59,620 --> 00:13:52,700
it would power a small vehicle for a few

267
00:14:01,360 --> 00:13:59,630
hours of haiji maneuvering so if a what

268
00:14:03,160 --> 00:14:01,370
one can only imagine what a large

269
00:14:05,829 --> 00:14:03,170
vehicle powered for more than a few

270
00:14:10,960 --> 00:14:05,839
hours of maneuvers would what would

271
00:14:15,730 --> 00:14:10,970
produce if something bad happened so

272
00:14:21,010 --> 00:14:15,740
that brings me to the end of my talk and

273
00:14:32,830 --> 00:14:30,820
a couple of questions so just a detail

274
00:14:36,010 --> 00:14:32,840
first you talked about efficiency

275
00:14:39,090 --> 00:14:36,020
improvement from the 30% to more by pre

276
00:14:41,890 --> 00:14:39,100
accelerating the matter/antimatter mix

277
00:14:44,590 --> 00:14:41,900
but from conservation of momentum it

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would seem that whatever you gained from

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the increase by pre accelerating you've

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lost by doing the pre accelerating let

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me let me just ask add something to this

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and then I'll get off the microphone a

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second thing related is that if we are

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to believe the UFO sightings these

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spaceships can make right angle turns

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and so on so any sort of immense

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acceleration from any sort of inertial

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accelerator would slam the poor

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inhabitants of the of the spaceship

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against the wall at with tremendous

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velocity therefore it seems like some

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sort of drive would have to turn off

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inertia rather than use it and then

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finally given what you've talked about

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with this very efficient drive how about

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looking for a new green technology okay

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to address those points one after

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another what happens with the pre

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acceleration is that because the

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neutrinos escape the portion of the

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imparted momentum that corresponds to

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their share of the total mass energy

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just leaves the system that's how you

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get thrust in terms of protection

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against high G maneuvers

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okay geometrically there's no such thing

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as a right angle turn it may require

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enormous acceleration but there is going

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writing about ways to protect against

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high accelerations is another issue but

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in principle we we think we can already

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imagine ways to shield human astronauts

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from accelerations up to 100 g or so

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we don't we are missing some of the

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chemical and biochemical technology for

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that but it's it seems to be a solvable

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problem and I did not want to try to

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branch into too many areas of technology

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in terms of a green technology

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antimatter has the drawback that it is a

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secondary fuel source

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it is a storage system rather than a

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power generation system okay Bernie and

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then we'll go to that side of the room

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I'm not surprised to hear you say that

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the most efficient form of caution is by

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having very high exhaust velocity but

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the ratio of the momentum to the energy

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go that's the inverse of the velocity

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which is the opposite of what you what

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you want

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ah the most efficient okay here I am

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turn casting efficiency in terms of how

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much Delta V can you get for a certain

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mass of fuel the higher the higher your

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exhaust velocity the less mass you use

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up but the more energy you expend and

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this is simply a fact of life about the

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way reaction drives work and the second

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question is back to what garrett alluded

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to that the reason you gave me the

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neutrinos to go out in one direction the

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direction that you want is because

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you're pre accelerating the the

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antimatter and so you've just

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transferred the acceleration process to

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the antimatter acceleration so there you

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have the same problem the same problem

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of not being able to get around Newton's

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third law uh the the whole point here is

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to work with Newton's third law if you

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had a fuel lump and you simply shook it

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back and forth accelerated it and then

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caught it and stopped it you would get

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nowhere because you can use this

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annihilation transformation to convert

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part of it into a form that simply

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escapes out the back the amount of

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thrust you produce in the acceleration

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phase is not completely neutralized by

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the catching process where you intercept

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the portion of the entry of the energy

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that still interacts with normal matter

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then you're using that energy to

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accelerate the next lump in the train in

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a realistic system this would be a

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continuous process but thinking of it as

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a sequence make makes the concepts a bit

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easier to follow okay if stoian zarg is

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in the room can you start coming up okay

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and do grant oh yes sir question I think

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this summer we'll learn a little bit

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more about what went on in Cusco when

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the Italian team digs down into that

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lake to find out whether or not it was

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from a comet that hit or not so I look

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forward to seeing that result I have a

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comment on the as a compulsion thing

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here neutrinos are really tough to

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detect and these detectors I'm aware of

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that are deep in mountains only catch a

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few hits a year so maybe there's going

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to be a change in the technology that

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might help increase that hit right now

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you might want to comment on that and

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the third comment I like to make is

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cosmologists do a lot of talk about

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eight years so 90% of the universe I

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think it's 96% of the universe being

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dark matter is any theoretical work done

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and how we might be able to capture dark

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matter okay I love these multi-part

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questions I am NOT trying to make a case

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that the Tunguska blast was an

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antimatter explosion I simply wished to

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point to it as an example of the type of

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event we're looking at in terms of

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neutrino detection that is constrained

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by particle interaction cross-sections

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which at the moment we have no idea how

401
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to manipulate and there may in fact be

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no way even in principle to manipulate

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them Oh dark matter we don't know what

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00:20:45,520 --> 00:20:43,760
dark matter is but whatever it is it

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presumably shares the properties of

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neutrinos and having very low

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interaction prosection z-- therefore

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being able to tap it for energy looks

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like an exceedingly remote prospect at

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this time I always bend the rules a

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little bit when younger people want to

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participate so we have one more

413
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question I was wondering how you would

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capture those particles to reuse them to

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get energy to use the other particles

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okay how do we have how do we actually

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do the capture and reprocessing that I

418
00:21:37,660 --> 00:21:34,280
refer to so glibly the the answer is

419
00:21:39,580 --> 00:21:37,670
that this is where I wave my hands with

420
00:21:42,700 --> 00:21:39,590
the phrase of sufficiently advanced

421
00:21:45,370 --> 00:21:42,710
technology we know that it's physically

422
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possible in principle we don't know how