Hubble Science: Hubble Constant: Expanding Universe
We know that the universe is expanding we've known that for almost 100 years
the rate at which the universe expands is a number we refer to as the Hubble constant.
When Hubble was launched one of its main objectives was to measure the Hubble constant.
The expansion rate of the universe by resolving individual stars in distant galaxies Hubble was
really the first telescope that allowed us to easily resolve the individual components, the
stars, in a distant Galaxy to gauge its distance and that's part of the ingredients you need to
measure the expansion rate of the universe. Over time Hubble also was improved by a series of
servicing missions that increased the sensitivity, resolution, and also ultimately allowed us to make
observations in the near infrared which reduces the effects of dust, dust is scattered throughout
the Universe and if you're looking at a distant light and trying to tell how far away it is
dust can dim the light and fool you into the gates further away than it is. Hubble has sort
of all of these tools on its utility belt that allow us to measure the expansion rate as well
as it's been measured to date. Hubble found that the expansion rate of the universe is speeding
up it's accelerating due to a new component of the universe that we call dark energy.
Dark Energy actually reverses the sign of gravity it actually gives rise to a repulsive
gravity which is sounds very strange and it's not something that Isaac Newton would have understood
but it is a feature in Einstein's theory of general relativity Einstein's theory of gravity
that replaced Newton's theory of gravity and in that theory you can have such a material if you have a
constant energy and empty space that's unavoidable then it will give rise to this repulsive gravity.
Because gravity is weakest in the empty regions of space between galaxies dark energy has its most
pronounced effect in deep space it's driving now pushing the universe to expand faster and faster.
The James Webb Space Telescope has certain capabilities that are even greater than
Hubble's it will have greater resolution, it can extend observations further to the
infrared to even further diminish the impact of dust, so it will both simultaneously give
us a sharper view of these distant stars that are used to calibrate the expansion of
the universe and it will also allow us to see through the last little wisps of dust
in front of those our goal is to measure the Hubble constant to one percent precision and
so we are using the Hubble Space Telescope and James Webb Space Telescope to refine
those measurements and to learn about the equation of state of dark energy.
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