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Hubble Science:
Hubble Constant:
Expanding Universe

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We know that the universe is expanding 
we've known that for almost 100 years  

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the rate at which the universe expands is 
a number we refer to as the Hubble constant.  

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When Hubble was launched one of its main 
objectives was to measure the Hubble constant.  

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The expansion rate of the universe by resolving 
individual stars in distant galaxies Hubble was  

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really the first telescope that allowed us to 
easily resolve the individual components, the  

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stars, in a distant Galaxy to gauge its distance 
and that's part of the ingredients you need to  

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measure the expansion rate of the universe. Over 
time Hubble also was improved by a series of  

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servicing missions that increased the sensitivity, 
resolution, and also ultimately allowed us to make  

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observations in the near infrared which reduces 
the effects of dust, dust is scattered throughout  

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the Universe and if you're looking at a distant 
light and trying to tell how far away it is  

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dust can dim the light and fool you into the 
gates further away than it is. Hubble has sort  

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of all of these tools on its utility belt that 
allow us to measure the expansion rate as well  

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as it's been measured to date. Hubble found that 
the expansion rate of the universe is speeding  

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up it's accelerating due to a new component of 
the universe that we call dark energy.

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Dark Energy actually reverses the sign of 
gravity it actually gives rise to a repulsive  

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gravity which is sounds very strange and it's not 
something that Isaac Newton would have understood  

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but it is a feature in Einstein's theory of 
general relativity Einstein's theory of gravity  

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that replaced Newton's theory of gravity and in that 
theory you can have such a material if you have a  

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constant energy and empty space that's unavoidable 
then it will give rise to this repulsive gravity.  

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Because gravity is weakest in the empty regions 
of space between galaxies dark energy has its most  

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pronounced effect in deep space it's driving now 
pushing the universe to expand faster and faster.

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The James Webb Space Telescope has certain 
capabilities that are even greater than  

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Hubble's it will have greater resolution, it 
can extend observations further to the  

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infrared to even further diminish the impact 
of dust, so it will both simultaneously give  

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us a sharper view of these distant stars 
that are used to calibrate the expansion of  

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the universe and it will also allow us to 
see through the last little wisps of dust  

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in front of those our goal is to measure the 
Hubble constant to one percent precision and  

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so we are using the Hubble Space Telescope 
and James Webb Space Telescope to refine  

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those measurements and to learn about 
the equation of state of dark energy.

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