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[Music]

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we know that the universe is expanding

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we've known that for almost 100 years

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the rate at which the universe expands

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is a number we refer to as the Hubble

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constant

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when Hubble was launched one of its main

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objectives was to measure the Hubble

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constant the expansion rate of the

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universe by resolving individual stars

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in distant galaxies Hubble was really

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the first telescope that allowed us to

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easily resolve the individual components

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the stars in a distant Galaxy to gauge

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its distance and that's part of the

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ingredients you need to measure the

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expansion rate of the universe over time

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Hubble also was improved by a series of

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servicing missions that increased the

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sensitivity resolution and also

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ultimately allowed us to make

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observations in the near infrared which

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reduces the effects of dust dust is

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scattered throughout the Universe and if

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you're looking at a distant light and

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trying to tell how far away it is dust

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can dim the light and fool you into the

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gates further away than it is Hubble has

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sort of all of these tools on its

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utility belt that allow us to measure

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the expansion rate as well as it's been

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measured to date

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Hubble found that the expansion rate of

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the universe is speeding up it's

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accelerating due to a new component of

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the universe that we call dark energy

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[Music]

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Dark Energy actually reverses the sign

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of gravity it actually gives rise to a

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repulsive gravity which is sounds very

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strange and it's not something that

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Isaac Newton would have understood but

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it is a feature in Einstein's theory of

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general relativity Einstein's theory of

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gravity that replacement theory of

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gravity and in that theory you can have

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such a material if you have a constant

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energy and empty space that's

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unavoidable then it will give rise to

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this repulsive gravity because gravity

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is weakest in the empty regions of space

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between galaxies dark energy has its

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most pronounced effect in deep space

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it's driving now pushing the inwards to

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the James Webb Space Telescope has

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certain capabilities that are even

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greater than Hubble's it will have

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greater resolution it can extend

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observations further to the room for red

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to even further diminish the impact of

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dust so it will both simultaneously give

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us a sharper view of these distant stars

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that are used to calibrate the expansion

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of the universe and it will also allow

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us to see through the last little wisps

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of dust in front of those our goal is to

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measure the Hubble constant to one

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percent precision and so we are using

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the Hubble Space Telescope and James

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Webb Space Telescope to refine those