1 00:00:00,020 --> 00:00:05,100 In 2017, NASA's Fermi Gamma-ray Space Telescope connected 2 00:00:05,100 --> 00:00:09,170 gamma rays, the highest-energy form of light, with new 3 00:00:09,170 --> 00:00:13,280 cosmic messengers--gravitational waves and high-energy neutrinos. 4 00:00:13,280 --> 00:00:17,470 For the first time, the discoveries linked these new signals to 5 00:00:17,470 --> 00:00:21,570 the one sky watchers have known for millennia -- light. 6 00:00:21,570 --> 00:00:25,710 First, gravitational waves and gamma rays were emitted from merging neutron 7 00:00:25,710 --> 00:00:29,850 stars. Fermi saw the first-ever light detected from 8 00:00:29,850 --> 00:00:33,970 a gravitational wave event. Then, just weeks later, Fermi 9 00:00:33,970 --> 00:00:38,020 connected a high-energy neutrino seen by the IceCube experiment at the 10 00:00:38,020 --> 00:00:42,080 South Pole to a black-hole-powered galaxy, which fires a jet of matter 11 00:00:42,080 --> 00:00:46,300 that emits both neutrinos and gamma rays. This is no 12 00:00:46,300 --> 00:00:50,360 overnight success story. The origins of both these breakthroughs 13 00:00:50,360 --> 00:00:54,420 span more than a century. As the 14 00:00:54,420 --> 00:00:58,480 19th century closed, scientists worked to understand many new phenomena 15 00:00:58,480 --> 00:01:02,580 including radioactivity, and new forms of light -- 16 00:01:02,580 --> 00:01:06,640 X-rays and gamma rays. Light was expected to need a medium, called 17 00:01:06,640 --> 00:01:10,730 the "aether," in order to move through space, which meant its speed should change when measured 18 00:01:10,730 --> 00:01:14,770 in different directions on the moving Earth. Yet no changes were seen. 19 00:01:14,770 --> 00:01:18,850 Solving this puzzle led to Einstein's special theory 20 00:01:18,850 --> 00:01:22,940 of relativity, which assumed light in a vacuum moves at a constant speed that 21 00:01:22,940 --> 00:01:27,030 nothing can exceed. His theory formed a theoretical basis for 22 00:01:27,030 --> 00:01:31,070 particle physics... ...which in 1912 incorporated an unexpected 23 00:01:31,070 --> 00:01:35,200 source -- a rain of particles from space called cosmic rays. 24 00:01:35,200 --> 00:01:39,290 Einstein's general theory of relativity, his theory 25 00:01:39,290 --> 00:01:43,390 of gravity, regarded space-time as the fabric of the cosmos. 26 00:01:43,390 --> 00:01:47,470 Space-time tells matter how to move, and matter tells space-time how to 27 00:01:47,470 --> 00:01:51,540 curve. As scientists probed the subatomic 28 00:01:51,540 --> 00:01:55,640 realm, one type of radioactive decay suggested the presence 29 00:01:55,640 --> 00:01:59,730 of a new lightweight particle, dubbed the "neutrino." 30 00:01:59,730 --> 00:02:03,930 Later, Einstein and Nathan Rosen showed 31 00:02:03,930 --> 00:02:08,010 that accelerating masses can create gravitational waves that ripple 32 00:02:08,010 --> 00:02:12,080 across space-time. 33 00:02:12,080 --> 00:02:16,160 Following World War II, technological advances permitted new kinds 34 00:02:16,160 --> 00:02:20,270 of observations. In the mid-Fifties, neutrinos were detected for the 35 00:02:20,270 --> 00:02:24,320 first time. Richard Feynman showed that gravitational waves must 36 00:02:24,320 --> 00:02:28,390 move matter, which means they're detectable. In a few years, the first 37 00:02:28,390 --> 00:02:32,490 efforts to do so began. The 1960s brought 38 00:02:32,490 --> 00:02:36,620 the first gamma rays seen in space, the first neutrinos 39 00:02:36,620 --> 00:02:40,670 detected from the Sun's interior, and something new -- later called 40 00:02:40,670 --> 00:02:44,740 gamma-ray bursts, or GRBs -- was caught by satellites looking for banned 41 00:02:44,740 --> 00:02:48,880 tests of nuclear weapons. In 1971, 42 00:02:48,880 --> 00:02:53,020 Rainer Weiss conceived of a way to detect gravitational waves 43 00:02:53,020 --> 00:02:57,120 using lasers, one of the roots of LIGO. 44 00:02:57,120 --> 00:03:01,190 1987 delivered the brightest supernova in nearly 400 45 00:03:01,190 --> 00:03:05,240 years. Three experiments caught neutrinos from the star's collapse. 46 00:03:05,240 --> 00:03:09,300 Instruments on balloons saw gamma rays from radioactive elements 47 00:03:09,300 --> 00:03:13,410 in the explosion's debris. The 1990s 48 00:03:13,410 --> 00:03:17,490 and 2000s brought: new satellites for exploring the 49 00:03:17,490 --> 00:03:21,570 gamma-ray universe; the construction and first operation of LIGO; 50 00:03:21,570 --> 00:03:25,680 and AMANDA, a neutrino detector built under the ice at the South Pole. 51 00:03:25,680 --> 00:03:29,810 In 2005, 52 00:03:29,810 --> 00:03:33,870 NASA's Swift satellite showed that short gamma-ray bursts likely come 53 00:03:33,870 --> 00:03:37,930 from merging neutron stars. Soon after, 54 00:03:37,930 --> 00:03:42,030 NASA launched Fermi, providing our best-ever view of the gamma-ray sky. 55 00:03:42,030 --> 00:03:46,140 AMANDA morphed into IceCube, which was completed in 2010. 56 00:03:46,140 --> 00:03:50,180 It monitors a cubic kilometer of ice under the South Pole 57 00:03:50,180 --> 00:03:54,250 for neutrinos. The same year, LIGO shut down 58 00:03:54,250 --> 00:03:58,330 for years of upgrades. IceCube reported more than 59 00:03:58,330 --> 00:04:02,420 two dozen high-energy neutrinos -- likely arrivals from 60 00:04:02,420 --> 00:04:06,550 beyond our galaxy. In 2015, the upgraded LIGO 61 00:04:06,550 --> 00:04:10,650 saw the first gravitational waves. The source: merging black holes 62 00:04:10,650 --> 00:04:14,730 over a billion light-years away. And in 2017, 63 00:04:14,730 --> 00:04:18,810 gamma-ray counterparts accompanied both a gravitational wave 64 00:04:18,810 --> 00:04:22,920 event and a cosmic neutrino source. 65 00:04:22,920 --> 00:04:27,080 66 00:04:27,080 --> 00:04:31,170 Multimessenger astronomy -- and its promise of greater insight into the most 67 00:04:31,170 --> 00:04:35,270 powerful processes in the universe -- has arrived. 68 00:04:35,270 --> 00:04:39,340 [Music] 69 00:04:39,340 --> 00:04:43,430 [Music] 70 00:04:43,430 --> 00:04:47,500 71 00:04:47,500 --> 00:04:51,690 [NASA Astrophysics] 72 00:04:51,690 --> 00:04:55,780 [Beeping] 73 00:04:55,780 --> 00:04:59,890 [Beeping] 74 00:04:59,890 --> 00:05:03,670 [Beeping]