1 00:00:01,160 --> 00:00:03,578 ln the beginning, there was darkness... 2 00:00:03,663 --> 00:00:05,747 and then, bang... 3 00:00:05,790 --> 00:00:08,959 giving birth to an endless expanding existence... 4 00:00:09,001 --> 00:00:11,544 of time, space, and matter. 5 00:00:11,587 --> 00:00:13,838 Now, see further than we've ever imagined... 6 00:00:13,881 --> 00:00:15,757 beyond the limits of our existence... 7 00:00:15,800 --> 00:00:18,635 in a place we call "The Universe." 8 00:00:21,347 --> 00:00:24,140 lt is both mighty and meek. 9 00:00:28,354 --> 00:00:33,608 Humanity's quest is to harness its power and escape its bonds. 10 00:00:35,236 --> 00:00:38,154 Holy cow! 11 00:00:38,197 --> 00:00:40,198 This is what an astronaut feels. 12 00:00:41,367 --> 00:00:46,663 lt creates and breaks the stars, the planets, the galaxies... 13 00:00:46,706 --> 00:00:49,624 and directs their cosmic roller coaster ride. 14 00:00:51,585 --> 00:00:53,086 Gravity is ourfriend and ourfoe. 15 00:00:53,129 --> 00:00:57,257 Without it, life as we know it would end. 16 00:00:57,299 --> 00:00:58,967 The Earth would literally explode. 17 00:01:00,970 --> 00:01:04,305 lt is the magnificent and mystifying force... 18 00:01:04,348 --> 00:01:07,559 that rules the universe: Gravity. 19 00:01:24,577 --> 00:01:28,038 Gravity is the most pervasive force in the universe. 20 00:01:29,415 --> 00:01:34,461 lt is at work on massive and minute scales... 21 00:01:34,503 --> 00:01:37,964 on the routine and the extreme. 22 00:01:39,592 --> 00:01:41,676 A surfer needs it to hang ten. 23 00:01:43,596 --> 00:01:46,056 When you ride a wave, you're going to slide down the front... 24 00:01:46,098 --> 00:01:48,266 and you're going to use that pull of gravity to get you going. 25 00:01:48,309 --> 00:01:50,143 lt's your acceleration force. 26 00:01:50,186 --> 00:01:52,520 lt's your accelerator. Gravity is your accelerator. 27 00:01:54,565 --> 00:01:57,358 A skier uses it to race downhill. 28 00:01:59,737 --> 00:02:02,739 A snowboarder must have it to get big air. 29 00:02:04,450 --> 00:02:08,912 lt acts on everything with mass, including us, 24/7... 30 00:02:08,954 --> 00:02:12,040 even when sleeping or standing. 31 00:02:13,876 --> 00:02:17,420 Gravity here on Earth, of course, is always accelerating us down... 32 00:02:17,463 --> 00:02:20,340 toward the center of the Earth at 32 feet per second squared. 33 00:02:25,763 --> 00:02:28,932 At a theme park, gravity is the galactic gas... 34 00:02:28,974 --> 00:02:33,603 that makes roller coasters roar and people scream. 35 00:02:33,646 --> 00:02:36,272 The gravity of the Earth pulls us down... 36 00:02:36,315 --> 00:02:38,566 and that's going to make us go really, really fast. 37 00:02:44,949 --> 00:02:47,617 All objects with mass or energy-- 38 00:02:47,660 --> 00:02:53,790 particles, people, planets, stars, and galaxies-- 39 00:02:53,833 --> 00:02:56,501 produce gravity. 40 00:02:56,544 --> 00:02:58,962 Omnipotent and omnipresent... 41 00:02:59,004 --> 00:03:04,384 gravity attracts, governs, warps, shapes, makes... 42 00:03:04,426 --> 00:03:09,848 and takes all matter and mass in the universe. 43 00:03:09,890 --> 00:03:10,890 So it's pervasive. 44 00:03:10,933 --> 00:03:14,978 lt acts on all things through extremely large distances... 45 00:03:15,020 --> 00:03:17,313 and nothing escapes its pull. 46 00:03:18,482 --> 00:03:22,318 lt is gravity that holds our solar system together. 47 00:03:22,361 --> 00:03:23,486 The force of gravity... 48 00:03:23,529 --> 00:03:26,322 is basically that thing that holds us on the planet... 49 00:03:26,365 --> 00:03:28,116 keeps us from flying off. 50 00:03:32,496 --> 00:03:36,833 lt is the cosmic glue that binds all matter in the universe together. 51 00:03:38,294 --> 00:03:41,087 lfyou were to imagine taking two dice... 52 00:03:41,130 --> 00:03:46,009 and putting them perfectly at rest out in the middle of space... 53 00:03:46,051 --> 00:03:48,344 and separating them by a centimeter... 54 00:03:48,387 --> 00:03:51,723 then what you'd see is that over a course of an hour or so... 55 00:03:51,765 --> 00:03:55,560 those two dice would slowly come together and touch. 56 00:03:59,190 --> 00:04:02,192 Gravity made ourworld. 57 00:04:02,234 --> 00:04:05,236 Our Sun formed from a vast cloud of gas... 58 00:04:05,279 --> 00:04:07,947 that gravitationally contracted. 59 00:04:07,990 --> 00:04:12,035 Similarly, our Earth formed through the gravitational attraction... 60 00:04:12,077 --> 00:04:14,537 of little particles, little bitty things... 61 00:04:14,580 --> 00:04:18,208 gradually growing into a bigger and bigger object. 62 00:04:19,710 --> 00:04:22,045 When it comes to gravity's pulling power... 63 00:04:22,087 --> 00:04:24,839 mass and distance matter. 64 00:04:24,882 --> 00:04:27,592 lt depends on the masses of each object... 65 00:04:27,635 --> 00:04:29,802 the amount of matter within each object. 66 00:04:29,845 --> 00:04:33,223 So it's proportional to the product of the two masses. 67 00:04:34,850 --> 00:04:36,851 ln otherwords, the bigger it is... 68 00:04:36,894 --> 00:04:39,187 the harder it pulls on other objects. 69 00:04:40,272 --> 00:04:41,606 But that's not all. 70 00:04:42,900 --> 00:04:44,234 And it's inversely proportional... 71 00:04:44,276 --> 00:04:47,487 to the square of the distance between them. 72 00:04:47,529 --> 00:04:51,241 This means ifyou double the distance between two objects... 73 00:04:51,283 --> 00:04:55,662 the attraction or pull is only a quarter of its original strength. 74 00:04:58,707 --> 00:05:02,460 The pulling power of gravity lets it direct the motion and movement... 75 00:05:02,503 --> 00:05:07,340 of all matter, however massive, in the universe. 76 00:05:07,383 --> 00:05:09,509 So you have whole galaxies, for example... 77 00:05:09,551 --> 00:05:11,010 in orbit around each other. 78 00:05:11,053 --> 00:05:17,058 Clusters of galaxies all orbit around their common center of mass. 79 00:05:25,067 --> 00:05:29,362 But it is the practical potential of harnessing this relentless force... 80 00:05:29,405 --> 00:05:32,949 that has obsessed scientists for centuries. 81 00:05:35,286 --> 00:05:40,373 lt would literally fall to Galileo Galilei, the 17th-century truth-seeker... 82 00:05:40,416 --> 00:05:44,627 to first recognize that gravity even existed. 83 00:05:44,670 --> 00:05:48,381 Galileo found that objects having a different weight... 84 00:05:48,424 --> 00:05:50,466 fall at the same rate. 85 00:05:50,509 --> 00:05:53,011 So here's a very heavy steel ball... 86 00:05:53,053 --> 00:05:56,806 and a light ping-pong ball of the same size. 87 00:05:56,849 --> 00:05:59,142 And if l drop them at the same time... 88 00:05:59,184 --> 00:06:01,936 they hit the ground at exactly the same time as well... 89 00:06:01,979 --> 00:06:04,272 because they fall at the same rate. 90 00:06:08,193 --> 00:06:12,655 To illustrate Galileo's most profound gravitational discovery... 91 00:06:12,698 --> 00:06:17,160 that all objects, regardless of mass, fall at the same rate... 92 00:06:18,787 --> 00:06:22,915 we take a ride on the mega-fast "Superman: The Escape"... 93 00:06:22,958 --> 00:06:26,544 at Six Flags Magic Mountain in Southern California. 94 00:06:27,921 --> 00:06:30,340 The theme park ride is the stage... 95 00:06:30,382 --> 00:06:33,426 for a spectacular free-fall demonstration. 96 00:06:33,469 --> 00:06:36,512 lt will showwhat happens when a carfull of people... 97 00:06:36,555 --> 00:06:40,350 and a tennis ball fall from 415 feet in the air. 98 00:06:43,812 --> 00:06:45,855 Okay. Here we go. All right. 99 00:06:45,898 --> 00:06:48,191 Oh, my. Oh, my God. 100 00:06:54,198 --> 00:06:57,533 The riders are shot up the 41-story-tall tower... 101 00:06:57,576 --> 00:06:59,327 at a hundred miles an hour. 102 00:06:59,370 --> 00:07:03,915 With their eyes open, gravity will help them see a superhero. 103 00:07:08,045 --> 00:07:09,754 Oh, my God. Okay. 104 00:07:09,797 --> 00:07:11,255 l'm going to drop this ball now and-- 105 00:07:11,298 --> 00:07:13,007 Oh, my God, it's floating around! 106 00:07:13,050 --> 00:07:14,675 lt's floating! lt's floating! 107 00:07:18,931 --> 00:07:22,433 Oh, the wind blew the ball away that time. 108 00:07:22,476 --> 00:07:27,063 While we expect all objects to fall freely together, regardless of mass... 109 00:07:27,106 --> 00:07:31,234 on a windy day, results aren't always perfect. 110 00:07:35,781 --> 00:07:37,657 All right. Oh, my God. 111 00:07:37,699 --> 00:07:41,536 At the very top of the ride, when upward motion has stopped... 112 00:07:41,578 --> 00:07:45,790 gravity takes over and the downward free fall begins. 113 00:07:47,501 --> 00:07:48,626 l'm going to drop this ball... 114 00:07:48,669 --> 00:07:50,378 and it's going to float. lt's going to float. 115 00:07:50,421 --> 00:07:52,088 Oh, it's floating. lt's floating. 116 00:07:57,219 --> 00:07:59,137 l'm going to release this ball now. 117 00:07:59,179 --> 00:08:01,472 And then, for a few blissful seconds... 118 00:08:01,515 --> 00:08:04,058 theme park thrill-seekers feel weightless... 119 00:08:04,101 --> 00:08:09,480 as ifthey are free of gravity, or in what scientists call zero-G. 120 00:08:13,402 --> 00:08:16,654 Oh, that one floated well. That one floated well. 121 00:08:26,874 --> 00:08:29,292 Oh, l'm going to try dropping the ball. 122 00:08:29,334 --> 00:08:31,586 But zero-G isjust an illusion. 123 00:08:31,628 --> 00:08:33,963 ln reality, gravity is running this ride. 124 00:08:35,340 --> 00:08:39,218 lt's the force that yanks the car, the people, and the tennis ball... 125 00:08:39,261 --> 00:08:43,806 indifferent to their mass, back down to Earth at the same rate. 126 00:08:47,519 --> 00:08:49,020 Oh, that's a fantastic ride. 127 00:08:49,062 --> 00:08:52,398 l mean, feeling oneself drop is amazing. 128 00:08:52,441 --> 00:08:54,942 But what's really great is dropping the ball... 129 00:08:54,985 --> 00:08:57,612 and seeing it floating above my face. 130 00:08:57,654 --> 00:09:00,156 Now--l mean, it's falling. l know it's falling... 131 00:09:00,199 --> 00:09:02,366 but l'm falling at exactly the same rate. 132 00:09:02,409 --> 00:09:04,827 lt doesn't matter how massive something is. 133 00:09:04,870 --> 00:09:08,206 lt falls, under the force of gravity, at exactly the same rate. 134 00:09:12,211 --> 00:09:14,420 Thanks to experiments like this... 135 00:09:14,463 --> 00:09:18,132 we now know that objects all fall at the same rate. 136 00:09:18,884 --> 00:09:22,595 But what would it take to launch a cannonball into orbit? 137 00:09:29,811 --> 00:09:32,688 When the famous British physicist Sir lsaac Newton... 138 00:09:32,731 --> 00:09:36,692 saw the apple fall that, some say, hit him on the head... 139 00:09:36,735 --> 00:09:38,736 it changed the world. 140 00:09:39,696 --> 00:09:41,781 You got the apple falling from the tree... 141 00:09:41,823 --> 00:09:45,493 and he looks up and sees the Moon in orbit around the Earth... 142 00:09:45,536 --> 00:09:49,205 and judges that not only is the apple falling to Earth... 143 00:09:49,248 --> 00:09:50,915 so too is the Moon. 144 00:09:55,587 --> 00:09:58,130 But could the Moon really be falling? 145 00:10:00,133 --> 00:10:01,133 Load! 146 00:10:01,927 --> 00:10:06,389 By thinking of a cannon and the trajectory of the ball it shoots... 147 00:10:06,431 --> 00:10:10,142 Newton used math to unlock a cosmic mystery. 148 00:10:17,442 --> 00:10:23,823 lt came in his landmark publication, "Principia Mathematica," in 1687. 149 00:10:24,825 --> 00:10:26,659 lsaac Newton has a famous drawing... 150 00:10:26,702 --> 00:10:29,412 and in it, he draws a planet and a little mountain. 151 00:10:29,454 --> 00:10:31,539 There's a little projectile first kicked off the mountain... 152 00:10:31,582 --> 00:10:33,165 and it falls down a little bit. 153 00:10:33,208 --> 00:10:35,459 You give it more speed, it goes a little farther out. 154 00:10:36,295 --> 00:10:38,337 Now say you could just increase the force all you wanted. 155 00:10:38,380 --> 00:10:41,465 lt can go fifty miles, it can go a hundred miles before it fell. 156 00:10:44,511 --> 00:10:49,098 By adding more gunpowder and withjust the right angle offire... 157 00:10:49,141 --> 00:10:52,935 a cannonball can be made to go faster and farther. 158 00:10:55,022 --> 00:10:58,065 lnevitably, however, gravity wins... 159 00:10:58,108 --> 00:11:01,986 pulling the cannonball back down to Earth. 160 00:11:02,029 --> 00:11:05,781 The Earth is round and not flat, so Newton realized... 161 00:11:05,824 --> 00:11:10,244 that if the cannonball is fired at sufficient speed... 162 00:11:12,664 --> 00:11:14,999 the cannonball would actually go into orbit. 163 00:11:17,336 --> 00:11:19,587 For that to happen, Newton determined... 164 00:11:19,630 --> 00:11:22,089 the ball would need to be shot out of the cannon... 165 00:11:22,132 --> 00:11:25,551 at17,500 miles an hour. 166 00:11:26,637 --> 00:11:28,054 lt starts curving around the Earth... 167 00:11:28,096 --> 00:11:31,223 and he realized that there must be a speed... 168 00:11:31,266 --> 00:11:34,018 where it goes completely around the Earth... 169 00:11:34,061 --> 00:11:35,436 and hits you in the back of the head... 170 00:11:35,479 --> 00:11:38,981 never actually hitting Earth's surface. 171 00:11:39,024 --> 00:11:41,651 And ifyou duck, it'll just keep going... 172 00:11:41,693 --> 00:11:44,111 and lo and behold, you have an orbit. 173 00:11:46,365 --> 00:11:49,033 But why doesn't the Moon fall to Earth? 174 00:11:49,910 --> 00:11:53,079 The Moon also has some sideways motion... 175 00:11:53,121 --> 00:11:55,414 so for every little bit that it falls down... 176 00:11:55,457 --> 00:11:58,584 it also moves off in this direction... 177 00:11:58,627 --> 00:12:04,715 and the sum of all those motions is an orbit around the Earth. 178 00:12:06,843 --> 00:12:11,555 Newton also realized that the Earth is in a giant freefall around the Sun. 179 00:12:12,516 --> 00:12:15,893 With gravity forging the path, our planet rounds the Sun... 180 00:12:15,936 --> 00:12:19,063 like an endless cosmic roller coaster ride. 181 00:12:21,441 --> 00:12:23,609 Newton cracked the gravity code... 182 00:12:23,652 --> 00:12:28,698 and physicists are still using his ideas to solve all sorts of problems... 183 00:12:32,869 --> 00:12:35,496 some ofthem stranger than others... 184 00:12:35,539 --> 00:12:39,625 like, what would happen if a person tried to travel through a tunnel... 185 00:12:39,668 --> 00:12:42,211 from one side of the planet to the other? 186 00:12:43,672 --> 00:12:45,131 ln this wild scheme... 187 00:12:45,173 --> 00:12:47,466 you would have to drive a straight-line tunnel... 188 00:12:47,509 --> 00:12:52,722 right through the Earth and use gravity alone to propel a traveler... 189 00:12:52,764 --> 00:12:55,599 down this so-called gravity express. 190 00:12:57,769 --> 00:12:59,311 So, suppose you've got one ofthese tunnels... 191 00:12:59,354 --> 00:13:01,230 and youjump in. 192 00:13:01,273 --> 00:13:03,524 lnitially, the Earth is pulling down. 193 00:13:03,567 --> 00:13:05,109 You're going toward the center of the Earth... 194 00:13:05,152 --> 00:13:07,528 and so you're accelerating toward it. 195 00:13:07,571 --> 00:13:09,905 But as you pass through the center ofthe Earth... 196 00:13:09,948 --> 00:13:13,159 and start going out toward the opposite side... 197 00:13:13,201 --> 00:13:15,995 the gravity ofthe Earth is trying to pull you back... 198 00:13:16,037 --> 00:13:17,997 so it's decelerating you. 199 00:13:20,292 --> 00:13:22,877 So gravity's actually having a braking effect. 200 00:13:23,587 --> 00:13:25,629 There's no fear of shooting out the hole... 201 00:13:25,672 --> 00:13:27,840 on the other side of the Earth at some tremendous velocity... 202 00:13:27,883 --> 00:13:29,675 and shooting yourself back into space... 203 00:13:29,718 --> 00:13:33,179 but, in fact, you reach the surface ofthe Earth exactly. 204 00:13:33,221 --> 00:13:35,181 You would coast to a perfect rest. 205 00:13:35,223 --> 00:13:37,224 ln forty-two minutes, you'd be there. 206 00:13:39,019 --> 00:13:42,104 Whichever two cities you connect with a straight-line tunnel... 207 00:13:42,147 --> 00:13:45,733 it takes gravity exactly forty-two minutes to get you there. 208 00:13:45,776 --> 00:13:49,820 Thejourney from Los Angeles to Paris, forty-two minutes. 209 00:13:51,198 --> 00:13:53,449 Suppose you wanted to go from Los Angeles to Tokyo... 210 00:13:53,492 --> 00:13:56,327 forty-two minutes. 211 00:13:56,369 --> 00:13:58,537 lt doesn't matterwhich path you take through the Earth. 212 00:13:58,580 --> 00:14:01,749 Thejourney is always forty-two minutes long. 213 00:14:02,876 --> 00:14:07,213 lt takes Newton's math to figure out why this works. 214 00:14:07,255 --> 00:14:09,298 lfwe connect Los Angeles to NewYork... 215 00:14:09,341 --> 00:14:11,300 digging a tunnel, obviously... 216 00:14:11,343 --> 00:14:12,468 a tunnel would not go straight down... 217 00:14:12,511 --> 00:14:15,554 but it has to go down at an angle. 218 00:14:15,597 --> 00:14:19,308 The angle slows the speed of descent. 219 00:14:19,351 --> 00:14:20,768 But the distance is also less. 220 00:14:20,811 --> 00:14:22,728 And ifyou work out the equations... 221 00:14:22,771 --> 00:14:25,439 lo and behold, the two effects cancel... 222 00:14:25,482 --> 00:14:27,608 and you still get there in forty-two minutes. 223 00:14:28,527 --> 00:14:31,487 lt takes forty-two minutes regardless of the path you take. 224 00:14:31,530 --> 00:14:32,696 That's really cool. 225 00:14:36,076 --> 00:14:39,411 Newton figured out what gravity does... 226 00:14:39,454 --> 00:14:42,414 but it took the brilliance of physicistAlbert Einstein... 227 00:14:42,457 --> 00:14:44,917 to work out why it was doing it. 228 00:14:48,588 --> 00:14:53,175 Einstein realized that gravity is really caused by huge objects... 229 00:14:53,218 --> 00:14:57,721 like stars and planets, literally bending space itself. 230 00:14:57,764 --> 00:14:59,932 Like a massive rubber sheet... 231 00:14:59,975 --> 00:15:04,019 space is curved where massive objects sit in it. 232 00:15:04,062 --> 00:15:08,732 ln fact, Einstein proposed that the path planets take around their stars... 233 00:15:08,775 --> 00:15:13,904 their orbits, are all a direct result of this curvature of space. 234 00:15:15,448 --> 00:15:16,532 He said that what an orbit is... 235 00:15:16,575 --> 00:15:18,367 is really something traveling in a straight line. 236 00:15:18,410 --> 00:15:20,703 When something is free-falling towards another object... 237 00:15:20,745 --> 00:15:23,497 it really isjust traveling in a straight line through space-time. 238 00:15:23,540 --> 00:15:28,711 However, the curvature of space-time bends its path into a closed orbit... 239 00:15:28,753 --> 00:15:32,047 but space itself curves it back in on itself. 240 00:15:33,133 --> 00:15:38,596 This revolutionary discovery came when Einstein, in the early1910s... 241 00:15:38,638 --> 00:15:43,058 realized that orbits of stars and planets in the observable cosmos... 242 00:15:43,101 --> 00:15:45,978 behavejust as Newton's math predicted... 243 00:15:46,021 --> 00:15:48,564 except one: Mercury. 244 00:15:50,567 --> 00:15:53,903 lts orbit essentially wobbles. 245 00:15:53,945 --> 00:15:58,365 Einstein described gravity as a curvature in space and time... 246 00:15:58,408 --> 00:16:02,620 and the orbit of Mercury works perfectly when you take that into account. 247 00:16:02,662 --> 00:16:06,582 Mercury isn't moving in flat space, but curved space around the Sun. 248 00:16:06,625 --> 00:16:08,000 Then the orbit's perfect. 249 00:16:10,295 --> 00:16:14,924 This curvature of space is at play in our own solar system. 250 00:16:14,966 --> 00:16:19,428 Earth is simply following what it thinks is a straight-line path... 251 00:16:19,471 --> 00:16:21,347 the shortest distance between two points... 252 00:16:21,389 --> 00:16:24,558 in this intrinsically curved space. 253 00:16:26,478 --> 00:16:30,439 Einstein not only determined that mass warps space... 254 00:16:30,482 --> 00:16:32,149 it warps time, too. 255 00:16:32,984 --> 00:16:35,402 So, henceforth, Einstein proclaimed... 256 00:16:35,445 --> 00:16:38,948 physicists should not speak of space and time separately... 257 00:16:38,990 --> 00:16:42,409 but of space-time as one unified object. 258 00:16:44,037 --> 00:16:46,455 While it's uncomfortable to many the first time you hear it... 259 00:16:46,498 --> 00:16:49,792 ifyou stop and think about it, it's actually quite obvious. 260 00:16:49,834 --> 00:16:51,293 lf l'm going to make an appointment with somebody... 261 00:16:51,336 --> 00:16:54,046 l don't say, "l'll meet you at 3:00." 262 00:16:54,089 --> 00:16:55,339 That's not enough information. 263 00:16:55,382 --> 00:16:57,257 There's got to be a question that follows that. 264 00:16:57,300 --> 00:16:58,384 What is that question? 265 00:16:58,426 --> 00:16:59,468 Where? 266 00:17:01,179 --> 00:17:04,765 lf l say, "Meet you in room 203." 267 00:17:06,643 --> 00:17:07,935 When? 268 00:17:07,978 --> 00:17:12,022 Any time you intersect with someone's else's life... 269 00:17:12,065 --> 00:17:15,234 you do so at a time and at a place. 270 00:17:16,695 --> 00:17:20,114 Einstein's realization that space is curved... 271 00:17:20,156 --> 00:17:23,409 and that time and space are, in fact, intertwined... 272 00:17:23,451 --> 00:17:26,203 is now the very definition of gravity. 273 00:17:27,580 --> 00:17:29,999 Liftoff of the Space Shuttle "Discovery." 274 00:17:30,041 --> 00:17:32,167 Unlocking the secrets of gravity... 275 00:17:32,210 --> 00:17:36,046 has enabled humanity to escape our earthly shackles... 276 00:17:36,089 --> 00:17:38,966 and opened the universe for exploration. 277 00:17:40,719 --> 00:17:43,971 But how can future astronauts on the long way to Mars... 278 00:17:44,014 --> 00:17:47,891 survive the disabling effects caused by zero-G? 279 00:17:58,903 --> 00:18:00,612 Gravity is ourfriend... 280 00:18:02,365 --> 00:18:03,907 and ourfoe. 281 00:18:06,161 --> 00:18:09,496 lt is the fearsome force that propels a skier... 282 00:18:09,539 --> 00:18:12,416 and the snowboarder down the mountain... 283 00:18:12,459 --> 00:18:14,460 and shoots them into the air. 284 00:18:15,754 --> 00:18:18,589 With enough momentum, an airborne snowboarder... 285 00:18:18,631 --> 00:18:21,175 can feel forfleeting moments... 286 00:18:21,217 --> 00:18:25,054 as if they are free of Earth's gravitational pull. 287 00:18:25,096 --> 00:18:28,557 You're actually weightless when you go offthejump. 288 00:18:28,600 --> 00:18:31,393 The period ofweightlessness is determined... 289 00:18:31,436 --> 00:18:36,190 by the duration ofyour trajectory as a function ofyour velocity... 290 00:18:36,232 --> 00:18:39,359 so that the snowboarder who gets really good big air... 291 00:18:39,402 --> 00:18:44,531 may achieve a second, two seconds, even three seconds ofweightlessness. 292 00:18:47,619 --> 00:18:50,037 But in the end, gravity wins... 293 00:18:50,080 --> 00:18:52,915 and the high-flying, free-falling boarder... 294 00:18:52,957 --> 00:18:55,542 just like the ball fired from the cannon... 295 00:18:55,585 --> 00:18:58,796 is eventually yanked back down to Earth. 296 00:18:58,838 --> 00:19:00,964 This free fall for the snowboarder... 297 00:19:01,007 --> 00:19:03,050 as he or she goes over thejump... 298 00:19:03,093 --> 00:19:06,303 and creates this trajectory isjust as much free fall... 299 00:19:06,346 --> 00:19:08,138 as a cannonball going through the air... 300 00:19:08,181 --> 00:19:10,432 and the trajectory is determined... 301 00:19:10,475 --> 00:19:13,560 only by the velocity and the force of gravity. 302 00:19:13,603 --> 00:19:16,563 Then, of course, what happens on the landing is another story. 303 00:19:20,652 --> 00:19:22,486 But what if a snowboarder... 304 00:19:22,529 --> 00:19:24,863 aspired to reach even greater heights? 305 00:19:25,698 --> 00:19:27,950 What if he wanted to overcome gravity... 306 00:19:27,992 --> 00:19:30,953 and launch himself right off the planet? 307 00:19:30,995 --> 00:19:33,122 You want to leave Earth entirely and forever? 308 00:19:33,164 --> 00:19:36,125 Earth has what we call the escape velocity... 309 00:19:36,167 --> 00:19:38,627 this magic speed where ifyou pass that speed... 310 00:19:38,670 --> 00:19:43,173 you will escape Earth forever, never to return. 311 00:19:45,051 --> 00:19:49,263 Escape velocity, the minimum speed any object needs to reach... 312 00:19:49,305 --> 00:19:51,431 in order to escape from the Earth... 313 00:19:51,474 --> 00:19:53,809 is about seven miles a second. 314 00:19:53,852 --> 00:19:56,895 That's 25,000 miles an hour. 315 00:19:59,357 --> 00:20:01,775 ln theory, even a snowboarder... 316 00:20:01,818 --> 00:20:05,362 with enough momentum and aimed in the right direction... 317 00:20:05,405 --> 00:20:07,698 can take offjust like a rocket. 318 00:20:12,203 --> 00:20:16,790 Escaping Earth's gravity may not be realistic for a snowboarder... 319 00:20:16,833 --> 00:20:22,337 but it has proven possible to launch people and projectiles into orbit. 320 00:20:22,380 --> 00:20:23,755 You can leave systems. 321 00:20:23,798 --> 00:20:26,049 Youjust need enough energy to do so. 322 00:20:26,092 --> 00:20:29,678 And we've garnered enough energy and technological know-how... 323 00:20:29,721 --> 00:20:32,431 to dojust that in ourvoyages to the Moon. 324 00:20:32,473 --> 00:20:35,559 And our hope is that that will continue on to Mars and beyond. 325 00:20:37,312 --> 00:20:39,438 To get to Mars and beyond... 326 00:20:39,480 --> 00:20:42,316 mankind will have to harness gravity's energy... 327 00:20:44,527 --> 00:20:48,530 just like we always do when we're seeking thrills to the extreme. 328 00:20:51,034 --> 00:20:53,368 Gravity gives us two types of energy... 329 00:20:55,580 --> 00:20:56,955 potential... 330 00:20:59,083 --> 00:21:00,250 and kinetic. 331 00:21:04,464 --> 00:21:06,548 Potential isjust that. 332 00:21:06,591 --> 00:21:09,176 lt is energy that's being stored... 333 00:21:09,219 --> 00:21:13,722 while kinetic is the result of all that pent-up potential energy. 334 00:21:16,601 --> 00:21:20,437 This fantastic phenomenon works on a roller coaster. 335 00:21:20,480 --> 00:21:23,774 As you're winched up on a hill, your potential energy is increasing. 336 00:21:23,816 --> 00:21:25,901 You literally have more energy... 337 00:21:25,944 --> 00:21:27,444 at the top of the roller coaster than at the bottom. 338 00:21:27,487 --> 00:21:29,947 lt's notjust a weird, abstract thing. 339 00:21:29,989 --> 00:21:32,532 You actually possess higher energy at the top... 340 00:21:32,575 --> 00:21:35,452 and that's turned into speed, into kinetic energy... 341 00:21:35,495 --> 00:21:37,913 as you go down that hill on the roller coaster. 342 00:21:39,207 --> 00:21:44,419 Pretty soon, l'll be converting my potential energy to kinetic energy. 343 00:21:48,841 --> 00:21:52,135 When a surfer hits that sweet spot on a wave... 344 00:21:52,178 --> 00:21:54,846 they're using energy's double act. 345 00:21:58,059 --> 00:22:01,019 NASA also uses this energy exchange principle... 346 00:22:01,062 --> 00:22:03,272 to add some speed to their missions. 347 00:22:04,565 --> 00:22:07,609 As a spacecraft nears the orbit of a planet... 348 00:22:07,652 --> 00:22:13,365 it, too, gathers kinetic energy at the expense of potential energy. 349 00:22:13,408 --> 00:22:17,286 Then as it rounds the planet on its cosmic coaster ride... 350 00:22:17,328 --> 00:22:19,246 the craft gets a slingshot effect... 351 00:22:19,289 --> 00:22:23,125 that punches it onward with more kinetic energy. 352 00:22:24,335 --> 00:22:30,215 When the Voyager spacecraft visited Jupiter in 1979, 1980... 353 00:22:30,258 --> 00:22:34,219 it flew past Jupiter, and Jupiter tugged on it... 354 00:22:34,262 --> 00:22:38,807 giving it extra motion, sort of a slingshot effect... 355 00:22:38,850 --> 00:22:40,976 not only changing its direction of motion... 356 00:22:41,019 --> 00:22:43,645 so that it was aimed towards Saturn... 357 00:22:43,688 --> 00:22:45,314 but also speeding it up. 358 00:22:47,233 --> 00:22:49,776 Knowing how to use the power of gravity... 359 00:22:49,819 --> 00:22:54,573 will enable humanity to travel further and faster across the universe. 360 00:22:57,493 --> 00:23:00,829 Having the physics formulated and the technology available... 361 00:23:00,872 --> 00:23:05,334 isjust one part of the preparation for extraterrestrial travel. 362 00:23:05,376 --> 00:23:10,047 Readying people for the rigors of space is the other. 363 00:23:12,050 --> 00:23:15,010 Far away from Earth's gravitational pull... 364 00:23:15,053 --> 00:23:18,430 in a spaceship on the long journey to Mars, for example... 365 00:23:18,473 --> 00:23:23,185 future astronauts will have to learn to live, work, and play... 366 00:23:23,227 --> 00:23:27,105 in an environment free of Earth's sizeable gravity... 367 00:23:27,148 --> 00:23:30,150 one where they effectively feel weightless... 368 00:23:30,193 --> 00:23:33,528 and all objects move equally and freely. 369 00:23:36,699 --> 00:23:38,533 One fun way to experience... 370 00:23:38,576 --> 00:23:41,912 the astronautical thrills and spills of space travel... 371 00:23:41,954 --> 00:23:44,956 is to simulate it on a zero-G flight. 372 00:23:44,999 --> 00:23:46,541 l'm really looking forward to this. 373 00:23:46,584 --> 00:23:48,585 This is going to be an incredible experience. 374 00:23:49,170 --> 00:23:51,671 By riding the ultimate roller coaster... 375 00:23:51,714 --> 00:23:56,218 a specially modified zero-G Boeing 727 aircraft... 376 00:23:56,260 --> 00:24:02,933 astrophysicist Alex Filippenko is about to go on the ride of his life. 377 00:24:02,975 --> 00:24:05,227 This is going to be like a ball thrown up in the air... 378 00:24:05,269 --> 00:24:08,897 weightless because it will be in free fall... 379 00:24:08,940 --> 00:24:14,194 so l'll be floating around as though there's no ground holding me up. 380 00:24:16,406 --> 00:24:21,576 The zero-G flight flies between 24,000 and 32,000 feet. 381 00:24:21,619 --> 00:24:25,914 This is about the same altitude as a regular commercial jet... 382 00:24:25,957 --> 00:24:28,750 but that is where the similarity ends. 383 00:24:28,793 --> 00:24:30,168 The water's the next one? 384 00:24:30,211 --> 00:24:34,756 The path it follows is a series of coaster-like rolling hills... 385 00:24:34,799 --> 00:24:36,299 in the stratosphere. 386 00:24:36,342 --> 00:24:39,094 Just like "Superman: The Ride"... 387 00:24:39,137 --> 00:24:42,722 the super zero-G plane gathers potential energy... 388 00:24:42,765 --> 00:24:45,350 as it climbs up at forty-five degrees. 389 00:24:46,352 --> 00:24:48,854 Passengers feel this as an increase in weight. 390 00:24:48,896 --> 00:24:49,896 Oh, yeah. 391 00:24:49,939 --> 00:24:53,733 Gravity is measured in terms of g-forces. 392 00:24:53,776 --> 00:24:56,236 One G is the amount of gravitywe feel... 393 00:24:56,279 --> 00:24:58,029 standing on the surface ofthe Earth. 394 00:24:58,072 --> 00:25:01,575 l'm going to get back down like this and get ready. 395 00:25:01,617 --> 00:25:05,078 As the plane steeply climbs, accelerating upward... 396 00:25:05,121 --> 00:25:08,498 the gravity G count rises and people feel heavier. 397 00:25:08,541 --> 00:25:09,541 All right. 398 00:25:11,294 --> 00:25:13,753 The plane is accelerating us upwards... 399 00:25:13,796 --> 00:25:17,883 at about1.8 G at its maximum. 400 00:25:19,427 --> 00:25:23,305 As the flight approaches, then eases around the apex of the arc... 401 00:25:23,347 --> 00:25:26,183 the plane, as well as all the people inside it... 402 00:25:26,225 --> 00:25:28,518 are, in effect, in free fall. 403 00:25:31,564 --> 00:25:33,148 Zero-G comin' up. 404 00:25:33,191 --> 00:25:38,695 Oh, man, what an indescribable feeling. 405 00:25:38,738 --> 00:25:40,155 Holy cow! 406 00:25:42,492 --> 00:25:45,952 Oh, l'm out in free space. 407 00:25:47,705 --> 00:25:49,039 Floating, just floating. 408 00:25:49,081 --> 00:25:50,707 This is what an astronaut feels. 409 00:25:51,834 --> 00:25:56,379 The plane's trajectory induces weightlessness again and again... 410 00:25:56,422 --> 00:25:59,341 by flying a series of these parabolic arcs. 411 00:25:59,884 --> 00:26:02,761 Even though they are within the cabin of a plane... 412 00:26:02,803 --> 00:26:08,975 the zero-G passengers are freely falling towards the Earth just like skydivers. 413 00:26:09,018 --> 00:26:11,937 But what creates the sensation ofweightlessness? 414 00:26:18,194 --> 00:26:20,111 lt goes back to Galileo... 415 00:26:20,154 --> 00:26:23,490 who showed that all objects fall at the same rate. 416 00:26:25,409 --> 00:26:29,996 So, as the plane and the people inside fall freely toward Earth... 417 00:26:30,039 --> 00:26:33,375 they maintain the same position relative to each other... 418 00:26:33,417 --> 00:26:36,253 and that is why they feel weightless. 419 00:26:43,511 --> 00:26:46,304 The feeling lasted twenty-five full seconds... 420 00:26:46,347 --> 00:26:50,517 because, for twenty-five seconds, we were essentially in free fall. 421 00:26:50,560 --> 00:26:53,061 lt was like Superman just flying through the air. 422 00:26:53,104 --> 00:26:56,273 Oh, l cannot believe how it feels. 423 00:26:58,526 --> 00:27:02,070 When thejet's engines reengage and end the free fall... 424 00:27:02,113 --> 00:27:05,824 the passengers feel theirweight return. 425 00:27:05,866 --> 00:27:09,661 As Einstein would say, weightlessness is but an illusion. 426 00:27:13,291 --> 00:27:17,043 This is so awesome! So awesome! 427 00:27:17,086 --> 00:27:18,837 The zero-G plane takes advantage... 428 00:27:18,879 --> 00:27:22,090 of something Einstein worked out back in 1916... 429 00:27:22,133 --> 00:27:24,593 in his general theory of relativity... 430 00:27:24,635 --> 00:27:28,138 that acceleration is essentially the same as gravity. 431 00:27:36,272 --> 00:27:39,899 When you are thrust upward in a rocket or the zero-G plane... 432 00:27:39,942 --> 00:27:42,068 the G-forces you experience... 433 00:27:42,111 --> 00:27:44,696 are the same as you would feel being tugged downward... 434 00:27:44,739 --> 00:27:48,074 by the gravity of a massive object like a planet. 435 00:27:53,539 --> 00:27:57,792 So gravity and acceleration create the same sensation. 436 00:27:57,835 --> 00:28:00,295 That's how the passengers on a zero-G flight... 437 00:28:00,338 --> 00:28:02,130 can feel like an astronaut... 438 00:28:02,173 --> 00:28:05,383 and can experience thejoys ofweightlessness. 439 00:28:15,019 --> 00:28:17,479 The ball and l arejust freely falling... 440 00:28:17,521 --> 00:28:21,775 according to our natural path through curved space-time. 441 00:28:21,817 --> 00:28:24,152 This is what Einstein's theory says. 442 00:28:24,195 --> 00:28:28,657 lndependent ofthe mass, we all follow the same path. 443 00:28:28,699 --> 00:28:30,825 Oh, yeah, this is unbelievable. 444 00:28:32,244 --> 00:28:34,871 On the twenty-minute, fifteen-parabola flight... 445 00:28:34,914 --> 00:28:38,375 there's time in between the frights and delights... 446 00:28:38,417 --> 00:28:40,585 to further taunt the laws of gravity. 447 00:28:43,714 --> 00:28:46,174 Look at that. Look at that water. 448 00:28:46,217 --> 00:28:50,470 Oh, look at that water. l'm going to catch some. 449 00:28:52,223 --> 00:28:54,557 Okay, here we go. 450 00:28:54,600 --> 00:28:56,935 As well as entertaining weekend warriors... 451 00:28:56,977 --> 00:28:58,395 the parabolic flights... 452 00:28:58,437 --> 00:29:02,023 also inauspiciously called "The Vomit Comet"... 453 00:29:02,066 --> 00:29:03,900 have a practical purpose. 454 00:29:04,944 --> 00:29:07,862 They prepare NASA astronauts forworking and living... 455 00:29:07,905 --> 00:29:10,699 in the zero-G environment of space. 456 00:29:12,660 --> 00:29:15,453 With these sensational parabolic flights... 457 00:29:15,496 --> 00:29:18,790 humans have learned how to simulate the absence of gravity. 458 00:29:20,000 --> 00:29:24,421 But is it also possible to create artificial gravity in the lab? 459 00:29:24,463 --> 00:29:28,675 These experiments will lead to a successful exploration of Mars. 460 00:29:28,718 --> 00:29:30,385 lt is in ourfuture. 461 00:29:36,600 --> 00:29:41,730 At the dawn of the 21st century, overcoming the bonds of gravity... 462 00:29:41,772 --> 00:29:45,567 and escaping Earth's sizeable tug have been realized. 463 00:29:46,986 --> 00:29:50,572 The next step is to design and build the technology... 464 00:29:50,614 --> 00:29:55,160 that will allow humans to travel, work, and live... 465 00:29:55,202 --> 00:29:58,079 on exotic alien planets. 466 00:29:58,122 --> 00:29:59,914 And we've garnered enough engineering know-how... 467 00:29:59,957 --> 00:30:02,709 to dojust that in ourvoyages to the Moon. 468 00:30:05,212 --> 00:30:07,422 Thanks to state-of-the-art technology... 469 00:30:07,465 --> 00:30:13,720 humanity is on the brink of a new era in space exploration. 470 00:30:14,764 --> 00:30:20,268 The trip to Mars is beginning here at our laboratory at MlT. 471 00:30:20,311 --> 00:30:24,189 Artificial gravity may be one of the ways that we overcome... 472 00:30:24,231 --> 00:30:26,274 the debilitating effects ofweightlessness. 473 00:30:27,443 --> 00:30:29,402 Since the advent of the space age... 474 00:30:29,445 --> 00:30:32,614 scientists have been concerned with minimizing... 475 00:30:32,656 --> 00:30:35,784 the life-threatening risks and damaging effects... 476 00:30:35,826 --> 00:30:39,496 of being weightless at zero-G. 477 00:30:39,538 --> 00:30:43,416 The issues originally had to do with human survivability. 478 00:30:43,459 --> 00:30:47,003 We didn't even know back in the Apollo period... 479 00:30:47,046 --> 00:30:50,548 how people would react to stays in space... 480 00:30:50,591 --> 00:30:52,008 of more than a few hours. 481 00:30:53,344 --> 00:30:56,805 There was all kinds of concern about humans' ability... 482 00:30:56,847 --> 00:30:59,808 to control a vehicle after being exposed to weightlessness... 483 00:30:59,850 --> 00:31:01,851 for a long period of time. 484 00:31:03,521 --> 00:31:06,481 A mission to Mars would require astronauts... 485 00:31:06,524 --> 00:31:10,777 to be away from Earth's gravity for at least two, maybe three years. 486 00:31:12,363 --> 00:31:14,739 The human frame is simply not designed... 487 00:31:14,782 --> 00:31:18,910 for the absence of terrestrial one-G gravity. 488 00:31:18,953 --> 00:31:24,207 The architecture of our bodies is designed to withstand ourweight... 489 00:31:24,250 --> 00:31:25,708 under the forces of gravity. 490 00:31:25,751 --> 00:31:29,128 Gravity determines how our cardiovascular system reacts... 491 00:31:29,171 --> 00:31:30,672 so when you get out of bed... 492 00:31:30,714 --> 00:31:33,299 and you go from being supine to upright... 493 00:31:33,342 --> 00:31:36,386 there's a regulatory system that keeps the blood pressure... 494 00:31:36,428 --> 00:31:38,847 reacting against the forces of gravity. 495 00:31:39,765 --> 00:31:43,810 Experience has shown that being weightless for long periods... 496 00:31:43,853 --> 00:31:46,938 leads to bone loss, muscle deterioration... 497 00:31:46,981 --> 00:31:49,482 and life-threatening blood clots. 498 00:31:50,734 --> 00:31:53,945 Aeronautical engineers at NASA and MlT... 499 00:31:53,988 --> 00:31:56,948 are testing a personal centrifuge system... 500 00:31:56,991 --> 00:32:00,076 that may mitigate the very real dangers. 501 00:32:02,079 --> 00:32:04,372 They protect the heart, the bones, their muscles. 502 00:32:04,415 --> 00:32:08,626 And even in these early experiments, we have every reason to believe... 503 00:32:08,669 --> 00:32:10,879 that artificial gravity with short-radius centrifuges... 504 00:32:10,921 --> 00:32:15,174 may be the universal antidote that we're looking for... 505 00:32:15,217 --> 00:32:18,219 to protect people on the long trip to Mars. 506 00:32:20,097 --> 00:32:22,015 Just like a theme park ride... 507 00:32:22,057 --> 00:32:26,185 spinning a subject artificially creates g-forces. 508 00:32:27,771 --> 00:32:30,690 To prevent motion sickness in the MlT ride... 509 00:32:30,733 --> 00:32:33,401 astronauts are conditioned to keep their head still. 510 00:32:34,570 --> 00:32:37,906 By spinning a person at thirty revolutions a minute... 511 00:32:37,948 --> 00:32:40,408 the centrifuge imparts one G... 512 00:32:40,451 --> 00:32:44,454 the same force felt pulling down a person standing on Earth. 513 00:32:46,582 --> 00:32:50,877 Scientists hope that one day, a trip to Mars will be a reality. 514 00:32:51,712 --> 00:32:54,714 Onboard, they believe there should be a personal centrifuge. 515 00:32:55,883 --> 00:33:00,053 To get their Earthly gravity fill-up, 21st-century astronauts... 516 00:33:00,095 --> 00:33:04,182 could then just spend one hour a day on the machine. 517 00:33:04,224 --> 00:33:06,768 We get onto it for a brief period every day... 518 00:33:06,810 --> 00:33:08,811 and get spun up quite fast... 519 00:33:09,647 --> 00:33:12,023 spun up in what l'll call a spin in the gym. 520 00:33:12,066 --> 00:33:15,068 You go foryour exercise, you go foryourworkout... 521 00:33:15,110 --> 00:33:17,904 you get your G tonic, your gravity tonic. 522 00:33:19,698 --> 00:33:22,992 While a trip to Mars may still be decades away... 523 00:33:23,035 --> 00:33:26,788 astrophysicist and seasoned skier Larry Young... 524 00:33:26,830 --> 00:33:30,500 can dream of big air in the liberating gravity of Mars. 525 00:33:32,294 --> 00:33:35,922 On the surface, there is three-eighths the tug of Earth's gravity. 526 00:33:37,758 --> 00:33:39,801 Everyone likes to get some air. 527 00:33:39,843 --> 00:33:40,843 Everybody likes a little bit. 528 00:33:40,886 --> 00:33:43,930 Just think ifwe were on Mars. 529 00:33:46,850 --> 00:33:49,602 A person who weighs 100 pounds on Earth... 530 00:33:49,645 --> 00:33:52,897 would feel as if they weigh 38 pounds on Mars. 531 00:33:54,066 --> 00:33:56,901 Although a Martian skier would fly down Olympus Mons... 532 00:33:56,944 --> 00:33:59,445 at a third of the speed theywould on Earth... 533 00:33:59,488 --> 00:34:01,823 the lower gravity also means that theywould get... 534 00:34:01,865 --> 00:34:04,993 at least three times the big air. 535 00:34:05,035 --> 00:34:06,869 ln the case of gravity, it's mass that matters. 536 00:34:06,912 --> 00:34:09,872 The more mass you have, the stronger the pull of gravity. 537 00:34:09,915 --> 00:34:12,458 So when you think about what yourweight would be on the Earth... 538 00:34:12,501 --> 00:34:15,628 versus something more massive than the Earth, it's pretty direct. 539 00:34:15,671 --> 00:34:17,380 lf something were twice as massive as the Earth... 540 00:34:17,423 --> 00:34:19,257 you'd weigh about twice as much. 541 00:34:20,676 --> 00:34:24,012 The Big Kahuna in our solar system is Jupiter. 542 00:34:24,054 --> 00:34:26,514 On that planet, a 100-pound person... 543 00:34:26,557 --> 00:34:29,767 would weigh a whopping 254 pounds. 544 00:34:30,728 --> 00:34:33,187 Even if Jupiter had a solid surface... 545 00:34:33,230 --> 00:34:36,065 a skier there would have to fight for big air. 546 00:34:37,234 --> 00:34:40,111 What we already know about gravity, how it works... 547 00:34:40,154 --> 00:34:42,822 and how it can be used for practical purposes... 548 00:34:44,074 --> 00:34:47,076 could, in theory, even save the planet... 549 00:34:47,119 --> 00:34:49,746 from its ultimate cataclysmic fate. 550 00:34:50,914 --> 00:34:53,583 Here's how gravity can come to our rescue. 551 00:34:55,627 --> 00:34:58,546 Gradually, in about five billion years... 552 00:34:58,589 --> 00:35:02,675 our Sun will brilliantly flare, turn into a red giant... 553 00:35:02,718 --> 00:35:06,429 gloriously burn up and die. 554 00:35:06,472 --> 00:35:10,141 As this comes to pass, our inner solar system is engulfed... 555 00:35:11,643 --> 00:35:15,521 and Earth's gravity and atmosphere will be radically altered. 556 00:35:16,648 --> 00:35:20,610 At that point, life on the blue planet will end. 557 00:35:23,447 --> 00:35:26,407 But astrophysicist Greg Laughlin has a plan... 558 00:35:26,450 --> 00:35:29,577 to use gravity to save Earth. 559 00:35:29,620 --> 00:35:31,537 This environment that we have here now... 560 00:35:31,580 --> 00:35:33,581 would look very similar to the environment... 561 00:35:33,624 --> 00:35:36,042 that is holding sway on Venus right now. 562 00:35:36,085 --> 00:35:38,169 A crushing carbon dioxide atmosphere... 563 00:35:38,212 --> 00:35:40,213 temperatures hot enough to melt lead. 564 00:35:42,341 --> 00:35:46,052 But rest assured, if the worst hypothetical happens... 565 00:35:46,095 --> 00:35:49,889 gravitational science could save mother Earth. 566 00:35:49,932 --> 00:35:52,725 The one thing that we could do over the very long term... 567 00:35:52,768 --> 00:35:55,728 is to somehow move the Earth's orbit... 568 00:35:55,771 --> 00:35:59,398 out to a larger distance from the sun... 569 00:35:59,441 --> 00:36:01,651 where the temperature isn't so hot. 570 00:36:01,693 --> 00:36:06,489 And a way that you can do that, ifyou have enough time... 571 00:36:06,532 --> 00:36:09,575 ifyou have billions ofyears available to you... 572 00:36:09,618 --> 00:36:13,579 is to use a comet or an asteroid. 573 00:36:14,373 --> 00:36:17,875 This mega move would require astronauts and engineers... 574 00:36:17,918 --> 00:36:21,796 aboard a spacecraft to maneuver the comet or asteroid... 575 00:36:21,839 --> 00:36:24,298 just in front ofthe Earth. 576 00:36:24,341 --> 00:36:25,842 ln order to be most effective... 577 00:36:25,884 --> 00:36:28,136 the comet has to fly very close to the Earth... 578 00:36:28,178 --> 00:36:31,889 within orbital radius or so ofthe Earth. 579 00:36:33,433 --> 00:36:35,685 Then on the cosmic roller coaster... 580 00:36:35,727 --> 00:36:41,315 potential and kinetic energy are roused and gravity does the rest. 581 00:36:41,358 --> 00:36:45,653 lf that happens, then the comet pulls the Earth forward... 582 00:36:45,696 --> 00:36:47,488 the Earth pulls the comet backward... 583 00:36:47,531 --> 00:36:51,784 and the net result is that the Earth is given a boost. 584 00:36:51,827 --> 00:36:55,288 lt's given a boost to a slightly higher orbital radius... 585 00:36:55,330 --> 00:36:57,665 slightly larger distance from the Sun. 586 00:36:57,708 --> 00:37:00,626 And ifyou make one of these adjustments... 587 00:37:00,669 --> 00:37:03,880 one of these passages every10,000 years or so... 588 00:37:03,922 --> 00:37:06,924 then the Earth, over a period of a billion years... 589 00:37:06,967 --> 00:37:10,803 can move at a fast enough pace outward... 590 00:37:10,846 --> 00:37:14,056 to keep track with the steadily brightening sun. 591 00:37:15,684 --> 00:37:18,603 lf however, the experts get the math wrong... 592 00:37:18,645 --> 00:37:23,149 and the big gamble doesn't work, all bets are off. 593 00:37:23,192 --> 00:37:26,194 And ifyou screw that up, then you can have a collision... 594 00:37:26,236 --> 00:37:27,445 between the comet and the Earth. 595 00:37:27,487 --> 00:37:30,865 So a hundred-kilometer object crashing into the Earth... 596 00:37:30,908 --> 00:37:33,784 is absolutely an extraordinary disaster. 597 00:37:33,827 --> 00:37:38,539 lt's the kind of thing that causes huge extinctions... 598 00:37:38,582 --> 00:37:41,209 of gigantic numbers of species. 599 00:37:42,920 --> 00:37:46,797 Of course, this is only an extreme hypothetical scenario... 600 00:37:46,840 --> 00:37:48,549 but what is known for sure... 601 00:37:48,592 --> 00:37:51,844 is that our continued existence today here on Earth... 602 00:37:51,887 --> 00:37:55,806 is contingent on the presence of gravity. 603 00:37:55,849 --> 00:37:58,351 lt allows for the perfect conditions for life... 604 00:37:58,393 --> 00:38:01,520 and the pursuit of happiness. 605 00:38:01,563 --> 00:38:06,192 One G produces the surfer's dream: A perfect wave. 606 00:38:09,279 --> 00:38:11,697 But the wild waters enjoyed on Earth... 607 00:38:11,740 --> 00:38:15,243 are not the only kind of gravity-generated waves. 608 00:38:15,285 --> 00:38:21,040 There are cosmic waves so large they roll across the entire universe. 609 00:38:25,212 --> 00:38:31,008 Tidal torrents of gravity-boosted particles roll across the cosmos. 610 00:38:31,051 --> 00:38:32,426 According to Einstein... 611 00:38:32,469 --> 00:38:36,264 these gravitational waves wash through the universe. 612 00:38:37,808 --> 00:38:40,101 But what are they? 613 00:38:40,143 --> 00:38:41,936 Any change in the gravity... 614 00:38:41,979 --> 00:38:46,774 sends a ripple through that fabric of space... 615 00:38:46,817 --> 00:38:48,693 then moves at the speed of light. 616 00:38:49,278 --> 00:38:51,696 That would be a gravity wave. 617 00:38:51,738 --> 00:38:53,948 And why do they happen? 618 00:38:53,991 --> 00:38:57,118 lfyou have two objects, two compact stars... 619 00:38:57,160 --> 00:38:59,704 each ofwhich curves space around them... 620 00:38:59,746 --> 00:39:02,164 and they're orbiting one another... 621 00:39:02,207 --> 00:39:05,793 then the result is, is that these two curved regions... 622 00:39:05,836 --> 00:39:09,630 create a wave, a ripple in the structure... 623 00:39:09,673 --> 00:39:12,967 in the shape of space that moves outwards... 624 00:39:13,010 --> 00:39:15,136 carrying energy with it. 625 00:39:15,178 --> 00:39:17,680 That's called a gravitational wave. 626 00:39:18,849 --> 00:39:21,434 l mean, literally, you can think about space and time... 627 00:39:21,476 --> 00:39:23,769 having a wave, just like an ocean wave in it... 628 00:39:23,812 --> 00:39:25,896 that travels through the universe. 629 00:39:25,939 --> 00:39:27,940 Gravitywaves arejust the same. 630 00:39:30,527 --> 00:39:34,155 Any type of mass in motion, big or small... 631 00:39:34,197 --> 00:39:36,991 generates a gravitational wave. 632 00:39:37,034 --> 00:39:39,493 And like the Earth's ocean tides... 633 00:39:39,536 --> 00:39:44,373 gravitational waves roll ceaselessly across the cosmos. 634 00:39:45,292 --> 00:39:49,670 ln theory, a surfer launched into space could experience... 635 00:39:49,713 --> 00:39:52,131 an out-of-this-world wipeout and warp. 636 00:39:53,383 --> 00:39:57,053 lf a gravitational wave was created in space or somewhere... 637 00:39:57,095 --> 00:39:59,680 and went through you, what would happen... 638 00:39:59,723 --> 00:40:03,184 is you'd get fat and then you'd get skinny... 639 00:40:03,226 --> 00:40:05,603 meaning that space was distorted. 640 00:40:05,645 --> 00:40:08,230 Space in one direction made you fatter. 641 00:40:08,273 --> 00:40:10,441 ln the other direction, it squashed you. 642 00:40:10,484 --> 00:40:11,734 And it goes back and forth. 643 00:40:15,113 --> 00:40:20,076 But for earthbound scientists to detect any faint G-wave signals... 644 00:40:20,118 --> 00:40:22,411 the disturbance needs to be propagated... 645 00:40:22,454 --> 00:40:24,580 by a massive cosmic object. 646 00:40:26,750 --> 00:40:29,752 Black holes and spinning neutron stars can do it. 647 00:40:30,587 --> 00:40:32,088 Another thing that can make a gravity wave... 648 00:40:32,130 --> 00:40:34,048 is an explosion, say, a supernova. 649 00:40:34,091 --> 00:40:36,092 A star explodes and it goes--whack-- 650 00:40:36,134 --> 00:40:38,803 and that actually pushes a gravity wave forward. 651 00:40:42,224 --> 00:40:47,603 The tool to catch the light-like signal from a wave is the LlGO... 652 00:40:47,646 --> 00:40:51,774 the Laser lnterferometer Gravitational Wave Observatory. 653 00:40:53,443 --> 00:40:56,695 There are two identical, ground-based LlGO labs. 654 00:40:56,738 --> 00:40:59,865 One is in Hanford, Washington... 655 00:40:59,908 --> 00:41:02,576 and the other is more than 2,000 miles away... 656 00:41:02,619 --> 00:41:04,787 near Baton Rouge, Louisiana. 657 00:41:08,792 --> 00:41:13,796 lf a wave comes by, each lab's results will be vital to confirm the event. 658 00:41:15,298 --> 00:41:16,715 Here's how it works. 659 00:41:16,758 --> 00:41:21,929 Super polished glass mirrors are at the fulcrum of the interferometer... 660 00:41:21,972 --> 00:41:23,431 which is a tool that basically... 661 00:41:23,473 --> 00:41:25,766 compares two light wave measurements... 662 00:41:25,809 --> 00:41:29,103 and identifies the differences between them. 663 00:41:29,146 --> 00:41:32,231 Precision laser light is fired back and forth... 664 00:41:32,274 --> 00:41:36,235 and split between two calibrated mirrors. 665 00:41:36,278 --> 00:41:39,780 ln normal circumstances, as the light bounces up and down... 666 00:41:39,823 --> 00:41:43,367 the 2 1/2-Mile long, L-shaped vacuum tubes... 667 00:41:43,410 --> 00:41:46,078 the two laser beams are basically in sync. 668 00:41:47,456 --> 00:41:50,875 This means the beams effectively cancel each other out... 669 00:41:50,917 --> 00:41:52,918 and no light escapes the tunnel. 670 00:41:54,004 --> 00:41:55,921 But when a gravity wave rolls through... 671 00:41:55,964 --> 00:41:59,967 space is ever so slightly stretched or squashed. 672 00:42:00,010 --> 00:42:03,220 As a result, the laser beams are thrown out of phase... 673 00:42:03,263 --> 00:42:07,141 and only then a small amount of light is emitted... 674 00:42:07,184 --> 00:42:10,936 a tiny signal, less than the diameter of a human hair... 675 00:42:10,979 --> 00:42:15,483 1/1000th the size of a proton will register. 676 00:42:15,525 --> 00:42:17,985 Converted into a sound and a light signal... 677 00:42:18,028 --> 00:42:20,613 it will be seen and heard. 678 00:42:22,073 --> 00:42:23,866 The scientists' greatest hope... 679 00:42:23,909 --> 00:42:28,162 is to catch the most massive event that ever occurred in the universe... 680 00:42:28,205 --> 00:42:30,331 the Big Bang. 681 00:42:30,373 --> 00:42:32,917 Gravitywaves may be our best chance to look... 682 00:42:32,959 --> 00:42:35,753 very, very close to the beginning of the universe. 683 00:42:35,795 --> 00:42:38,631 About 300,000 years after the Big Bang... 684 00:42:38,673 --> 00:42:41,717 the universe was so dense, it was actually opaque to light. 685 00:42:41,760 --> 00:42:44,845 Light could not travel through it. 686 00:42:44,888 --> 00:42:48,724 So if light can't travel through the universe, what can? 687 00:42:48,767 --> 00:42:49,808 A gravity wave. 688 00:42:52,395 --> 00:42:55,731 The problem is a miniscule signal from a gravitywave... 689 00:42:55,774 --> 00:42:58,025 has yet to be caught. 690 00:42:58,068 --> 00:42:59,527 lt's clearly hard. 691 00:42:59,569 --> 00:43:04,823 ln fact, when Einstein predicted them, he thought it was a nice idea... 692 00:43:04,866 --> 00:43:07,159 but no one would ever be able to detect them. 693 00:43:07,202 --> 00:43:10,871 lt's only the advances of technology that give us a chance. 694 00:43:11,957 --> 00:43:15,167 LlGO scientists, like astrosurfers... 695 00:43:15,210 --> 00:43:17,670 live for the day when they can hang ten... 696 00:43:17,712 --> 00:43:21,549 and ride theirvery own perfect wave of gravity. 697 00:43:21,591 --> 00:43:24,218 We've seen what we think are the effects of gravity waves... 698 00:43:24,261 --> 00:43:28,764 the loss of energy from a system by way of gravity waves... 699 00:43:28,807 --> 00:43:30,599 but we never directly detected one. 700 00:43:30,642 --> 00:43:32,643 That's one of the last frontiers. 701 00:43:33,812 --> 00:43:36,438 lf the LlGO scientists' quest is successful... 702 00:43:36,481 --> 00:43:40,859 and they catch a wave, it could change science. 703 00:43:40,902 --> 00:43:44,530 So, l think that long term, it's first to understand gravity... 704 00:43:44,573 --> 00:43:47,283 and then, even more interestingly, to understand the universe. 705 00:43:51,121 --> 00:43:55,082 The force of gravity has domain over our universe. 706 00:43:55,959 --> 00:44:00,504 lt created and can destroy the cosmos, the stars... 707 00:44:00,547 --> 00:44:03,924 the planets, and the people. 708 00:44:05,468 --> 00:44:11,974 lt controls our lives, our play, and our endeavors. 709 00:44:12,017 --> 00:44:14,059 And therein is this cosmic ballet. 710 00:44:15,270 --> 00:44:18,647 Our collective future depends on the grace and greatness... 711 00:44:18,690 --> 00:44:22,443 ofthe mighty ruler of the cosmos, gravity. 9999 00:00:0,500 --> 00:00:2,00 www.tvsubtitles.net