WEBVTT FILE 1 00:00:00.000 --> 00:00:10.080 Hubble Science: Hubble Constant: Expanding Universe 2 00:00:10.080 --> 00:00:13.560 We know that the universe is expanding  we've known that for almost 100 years   3 00:00:13.560 --> 00:00:19.500 the rate at which the universe expands is  a number we refer to as the Hubble constant.   4 00:00:19.500 --> 00:00:23.640 When Hubble was launched one of its main  objectives was to measure the Hubble constant.   5 00:00:23.640 --> 00:00:30.120 The expansion rate of the universe by resolving  individual stars in distant galaxies Hubble was   6 00:00:30.120 --> 00:00:35.340 really the first telescope that allowed us to  easily resolve the individual components, the   7 00:00:35.340 --> 00:00:41.640 stars, in a distant Galaxy to gauge its distance  and that's part of the ingredients you need to   8 00:00:41.640 --> 00:00:46.680 measure the expansion rate of the universe. Over  time Hubble also was improved by a series of   9 00:00:46.680 --> 00:00:52.980 servicing missions that increased the sensitivity,  resolution, and also ultimately allowed us to make   10 00:00:52.980 --> 00:00:59.280 observations in the near infrared which reduces  the effects of dust, dust is scattered throughout   11 00:00:59.280 --> 00:01:02.880 the Universe and if you're looking at a distant  light and trying to tell how far away it is   12 00:01:02.880 --> 00:01:07.980 dust can dim the light and fool you into the  gates further away than it is. Hubble has sort   13 00:01:07.980 --> 00:01:13.740 of all of these tools on its utility belt that  allow us to measure the expansion rate as well   14 00:01:13.740 --> 00:01:19.380 as it's been measured to date. Hubble found that  the expansion rate of the universe is speeding   15 00:01:19.380 --> 00:01:26.280 up it's accelerating due to a new component of  the universe that we call dark energy. 16 00:01:26.280 --> 00:01:33.120 Dark Energy actually reverses the sign of  gravity it actually gives rise to a repulsive   17 00:01:33.120 --> 00:01:37.500 gravity which is sounds very strange and it's not  something that Isaac Newton would have understood   18 00:01:37.500 --> 00:01:43.020 but it is a feature in Einstein's theory of  general relativity Einstein's theory of gravity   19 00:01:43.020 --> 00:01:49.680 that replaced Newton's theory of gravity and in that  theory you can have such a material if you have a   20 00:01:49.680 --> 00:01:55.260 constant energy and empty space that's unavoidable  then it will give rise to this repulsive gravity.   21 00:01:55.260 --> 00:02:02.640 Because gravity is weakest in the empty regions  of space between galaxies dark energy has its most   22 00:02:02.640 --> 00:02:10.320 pronounced effect in deep space it's driving now  pushing the universe to expand faster and faster. 23 00:02:10.320 --> 00:02:15.960 The James Webb Space Telescope has certain  capabilities that are even greater than   24 00:02:15.960 --> 00:02:22.200 Hubble's it will have greater resolution, it  can extend observations further to the   25 00:02:22.200 --> 00:02:28.740 infrared to even further diminish the impact  of dust, so it will both simultaneously give   26 00:02:28.740 --> 00:02:34.080 us a sharper view of these distant stars  that are used to calibrate the expansion of   27 00:02:34.080 --> 00:02:38.700 the universe and it will also allow us to  see through the last little wisps of dust   28 00:02:38.700 --> 00:02:45.480 in front of those our goal is to measure the  Hubble constant to one percent precision and   29 00:02:45.480 --> 00:02:50.280 so we are using the Hubble Space Telescope  and James Webb Space Telescope to refine   30 00:02:50.280 --> 00:02:54.480 those measurements and to learn about  the equation of state of dark energy. 31 00:02:54.480 --> 00:02:58.811 Follow @NASAHubble on social media