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← Traveling to a far away star and getting back in time for dinner | Miguel Alcubierre | TEDxCuauhtémoc

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Showing Revision 43 created 04/07/2019 by Sebastian Betti.

  1. I want to ask you something:
  2. When was the last time
    you watched the stars?
  3. I know most people forget they exist
  4. specially in this polluted city
  5. which is sometimes foggy,
  6. we never see them.
  7. But since I was a kid,
    maybe not that young,
  8. maybe 12 or 13 years,
  9. I've been captivated by stars
    and would watch them whenever possible.
  10. My dad gave me a small telescope
  11. by the time I was 14 and I spent hours
  12. watching planets and stars
  13. and always wondering:
  14. What is out there?
  15. Is there someone watching me back
  16. with a telescope, wondering
    what is out here?
  17. This allure went on for years
  18. and at some point
    I decided to be an astronomer.
  19. In Mexico, in order to be an astronomer
    you need to be a physicist.
  20. So I studied physics.
  21. I never got to be an astronomer,
    now I'm something in between,
  22. half an astrophysicist, half a physicist
  23. but this idea of stars
  24. and the possibility of reaching them
  25. remained with me.
  26. When I started my major in physics
  27. I realized something many of you
  28. have heard of, even if you are not
    totally clear about it:
  29. that more than 100 years ago, in 1905,
  30. this guy named Albert Einstein,
  31. discovered that light speed
  32. is the fastest in the universe.
  33. That might not say you a lot
  34. because light speed is huge.
  35. Light moves up to 186,000 mi/s
  36. so high a speed that we can phone call
  37. someone in India or Japan
  38. with no problem at all.
  39. Even astronauts who went
    to the moon 40 years ago
  40. were interviewed and
    the President could talk to them
  41. with no evident delay
  42. even though the astronauts
    were in the moon,
  43. thing is that light speed is huge
  44. and the universe gigantic.
  45. We cannot travel faster than light speed
  46. and that is a severe problem
  47. to reach for the stars.
  48. Sun is 8 light-minutes away,
  49. that is, it takes 8 minutes for light
  50. to get here from the Sun,
    from the Sun to us.
  51. If the Sun exploded right now,
  52. nobody would notice
    up until eight minutes later.
  53. The closest star after the Sun
  54. is Alfa Centauri,
  55. it takes four years for light to travel
  56. and it's right besides the Sun.
  57. We live in a galaxy
  58. that is a star spiral called Milky Way.
  59. The center of our galaxy
    was 30,000 light years away,
  60. it takes 30,000 light years
    for light to travel
  61. from the center of the galaxy to us,
  62. and two million years
  63. in traveling from Andromeda galaxy
  64. that is one of our neighbor galaxies.
  65. The universe is huge, vast,
  66. if we ever want to reach the stars
  67. the light limit is very serious,
  68. a very serious problem, but why?
  69. Why we cannot travel faster than light?
  70. And it's not because Einstein said so,
  71. that is no how science works.
  72. In science
    there is no authority principle;
  73. it's not because some famous guy says so.
  74. There are reasons, theoretical reasons,
  75. observational reasons,
  76. experiments show it,
  77. it is a verified fact,
  78. but why?
  79. Basically, the answer is that
    theory of relativity prevents it,
  80. so I will tell you a bit,
  81. a very quick course:
  82. Relativity in a couple of minutes.
  83. Don't be afraid,
    I'll give a general overview,
  84. normally it takes six months to teach this
  85. to sixth and seventh graders
    of physics major.
  86. So right now I will explain it
  87. in two minutes and for non-physicists.
  88. So, don't worry.
  89. Relativity is an old concept
  90. though it wasn't called like that.
  91. The concept can be traced
    back from Galileo Galilei
  92. around 1620, in the 17th century.
  93. Galileo was the first one
    to realize something interesting,
  94. when it comes to movement, when I move,
  95. my movement is always relative
    to something else.
  96. Movement is said to be relative,
  97. here on the stage,
    my movement is relative to the floor.
  98. The measurement of your car speed
    is relative to the street,
  99. actually planes speed measurement
  100. is made relative to the air,
    not the floor.
  101. You might have noticed this
    while watching a movie.
  102. A plane speed measurement
    is relative to the air,
  103. and the Earth spins around the Sun, etc.
  104. If you were somewhere in space
  105. in the middle of nowhere
    it would be useless
  106. to ask if you are moving or not
  107. because there is no reference
    to compare your position,
  108. so movement is relative,
    speeds are relative,
  109. because they are always measured
    in relation to something else.
  110. This was discovered
    by Galileo 400 years ago.
  111. That was an interesting fact
  112. for all physic studies made after Galileo.
  113. Newton and all great advances
    of the 18th and 19th centuries
  114. agreed with Galileo.
  115. Speed is relative, that's fine,
  116. speeds aren't absolute.
  117. But by the end of 19th century
    something strange happened,
  118. many physicists studying light
  119. discovered that light is quite weird,
  120. light speed is indeed absolute
  121. and though Galileo stated
    that speeds were relative,
  122. that's not the case of light,
    it's always the same number
  123. no matter who measures it,
  124. or how fast is going whoever is measuring,
  125. no matter how fast the lightbulb
    sending out the light is moving.
  126. The measurement always
    yields the same number
  127. and this was a problem.
  128. This might not seem interesting to you
  129. but physicists of the 19th
    century were going crazy.
  130. Problem was: either Galileo was wrong
  131. and speeds were indeed absolute,
  132. which was apparently nonsense;
  133. or those who were measuring light speed
  134. were wrong and didn't know how to measure.
  135. But nobody was wrong
  136. which was even worst.
  137. Decades went by,
  138. until in 1905 this guy appeared,
  139. a man called Albert Einstein,
  140. who devoted his life to bringing together
  141. Galileo's idea that speeds were relative
  142. and the apparently real fact
  143. shown by the experiments,
    that there was an absolute speed,
  144. light speed.
  145. Long story short,
  146. because math is complicated,
  147. part of Einstein genius
  148. was realizing there was a solution.
  149. There was a logical solution
    to the problem
  150. and that logical solution
    derived in what we now know
  151. as Einstein's theory of relativity.
  152. It's a very interesting theory
    that changes
  153. what we understand by space and time,
  154. for instance, nobody tells us
    that space is relative
  155. distances, object lengths
  156. depend on their movement;
    if an object moves fast, they shrink.
  157. Time is also relative,
  158. any watch ticking relative
    to my movement, would delay
  159. this we have measured many times,
  160. even worst: simultaneity is relative;
  161. when I say two things
    happen exactly at once,
  162. someone moving in relation to me
    would disagree.
  163. One of us sees something first
    and worst:
  164. we might be moving on opposed directions
  165. and watch things backwards:
  166. first this one, then that one.
  167. So the conclusion is that sometimes,
  168. the order in time of different things
  169. is not absolute, the order
    of time can change,
  170. one thing before, other thing after
  171. but this brings up another huge problem,
  172. if time order is not well defined,
    what about causality?
  173. If something causes something else
  174. that something should had happened first,
  175. but if we disagree on what happened first,
  176. where does that leaves causality?
  177. Another crisis.
  178. Part of what Einstein did
  179. was realizing that there was solution,
  180. a solution to protect causality
  181. was thinking that light speed
    is not absolute,
  182. but the maximum speed of universe.
  183. If nothing can travel faster than light
    we protect causality.
  184. If something could travel
    faster than light
  185. then we could travel to the past,
  186. we would be able to see
    the effect before the cause,
  187. which is not the proper way.
  188. So light speed is the maximum speed
  189. and that is to protect causality.
  190. So far as of the beginning
    of the 20th century,
  191. light speed was the fastest
  192. and if that was all left to say,
    my talk would be done
  193. and off we go.
  194. But, fortunately that's not the case.
  195. In 1916, Einstein developed
    a second theory,
  196. also called relativity and that's
    why people get confused
  197. this one is called general relativity,
  198. and it's a theory about gravity.
  199. Einstein tried to understand gravity,
  200. which we already understood
    a bit since Newton;
  201. but he noticed some problems,
  202. gravity was thought of
    by Newton as instantaneous,
  203. if someone moved the Sun,
    Earth would immediately react,
  204. this would go against the fact that
    nothing can travel faster than light,
  205. so Einstein began to develop
    a new gravity theory,
  206. it took him 10 years,
  207. an amazing achievement
    for someone as smart of Einstein,
  208. was based on a beautiful thing:
  209. the Equivalence Principle,
    also discovered by Galileo:
  210. all objects fall at the same speed
  211. if two things were dropped at once,
    they would fall at the same time,
  212. a bowling ball or a ping pong ball
    would fall just the same,
  213. the heavier one does not fall faster,
    in case you were wondering.
  214. That means, from another point of view,
  215. that the trajectory of an object
    when there is gravity,
  216. does not depend on the object.
  217. All objects follow the same trajectory
  218. curved trajectories, you've seen that,
  219. I throw objects and they move
    in parables and ellipses
  220. but if those trajectories are curve
    and nondependent of the object
  221. then trajectory is a property of space,
    but they are curve,
  222. then space must be curve.
  223. Einstein concluded
  224. that gravity is a space deformation.
  225. An interesting and beautiful thing,
  226. and what is beautiful about it
    is that I can cheat,
  227. I can use space deformation
  228. to cheat on Einstein himself,
  229. so I use Einstein to cheat on Einstein.
  230. I can imagine ways to distort space
  231. to work around the statement
    "nothing can go faster than light"
  232. and, technically, I could
    reach a faraway star
  233. and then come back in time for dinner.
  234. I will share with you two possibilities,
  235. that are allowed on Einstein theory,
  236. one is beautiful
  237. and its technical name
    is Einstein-Rosen bridge,
  238. sounds technical because Einstein
  239. and another scientist called Rosen
  240. had this idea in 1935.
  241. But in literature and on sci-fi movies
  242. it is called a Wormhole.
  243. If you like science fiction
    then you might have seen it recently,
  244. in the movie Interstellar.
  245. On the movie, they travel
    through a wormhole.
  246. A wormhole is like a tunnel,
  247. I enter here and I end up
    in Alpha Centauri,
  248. but traveling a shorter distance,
  249. like a shortcut in space.
  250. These structures --
  251. here is a beautiful diagram
    of a wormhole in two dimensions --
  252. are allowed by the Einstein's theory,
  253. because this theory allows these tunnels,
  254. one thing is that the theory allows it
  255. and another is having
    an idea of how to do that.
  256. Nobody knows how to make a wormhole,
  257. but at least theory allows it.
  258. Another idea,
    and I'll let you think about it,
  259. another idea is that it is not necessary
    to make holes in space,
  260. an idea that thought by some guy
    not so long ago,
  261. in 1994, this guy on the picture,
  262. and the idea is different;
    instead of making holes in space
  263. let's use another property of space.
  264. Space can bended, twisted and expanded,
  265. maybe you heard about
    how universe expands,
  266. galaxies move away from one another
  267. not because they are
    drifting away from a center
  268. where an explosion occurred, no.
  269. The way we understand it in physics
    is that galaxies are still,
  270. and what is growing bigger is space;
    space is expanding.
  271. So I can use this idea in a small scale.
  272. Imagine I'm standing here and somehow
  273. I can expand the space behind me.
  274. I would start to drift away
    from that wall,
  275. and if at the same time
    I shrink the space in front of me
  276. I would become closer
    to the wall in front of me.
  277. If I combine
    the expansion and contraction,
  278. I could move from here
    to that wall without moving,
  279. because the space made all the moving.
  280. This is called warp drive
    or drive through distortion
  281. and it's another way
    to travel faster than light,
  282. actually you could travel
    as fast as you wish.
  283. These are two ideas on how
    we could travel faster than light.
  284. But there is a price to pay.
  285. Such is life, whenever
    you find something cool
  286. it's too expensive.
  287. We have a similar case here:
  288. from those two ideas,
  289. both worm holes and warp propulsion
  290. require, whenever we do
    the math of something
  291. called negative energy, which might
    not be crystal clear for you,
  292. but remember what Einstein said:
  293. "mass and energy are equivalent",
    the same thing.
  294. Remember nuclear reactors
    and atomic bombs,
  295. mass and energy are the same.
  296. So negative energy equals negative mass,
  297. and I'd never went to buy
    minus 9 pounds of tortilla.
  298. There are no negative masses,
  299. without negative masses
    there are no negative energies
  300. and without negative energies
    none of this is possible,
  301. No holes in space-time,
  302. no warp propulsion,
  303. and that's a problem.
  304. Negative energy is not forbidden,
  305. physics laws don't forbid it,
  306. but we've never seen it.
  307. It's one of those things
    that simply do not exist.
  308. So, with this initial question:
  309. Can we travel faster than light?
  310. will we someday travel the stars
    and get back in time for dinner?
  311. In 1905 Einstein told us
    it was not possible,
  312. that light speed was a limit,
  313. but sometimes,
    using Einstein's other theory,
  314. general relativity, we can cheat
    and bend the space,
  315. expand it, compress it, make holes on it,
  316. and travel faster than light,
  317. however, the price of it
  318. is finding energies or negative masses,
  319. though they might not exist.
  320. So we are a bit stuck,
  321. but such is science
    and that's part of my message,
  322. science moves forward by making questions,
  323. and sometimes we find answers,
  324. sometimes we find answers we don't like,
  325. that aren't what we wanted,
    but universe is not how we want it.
  326. It is what it is and we
    sometimes find out
  327. that we don't have enough information,
  328. to answer the question,
  329. and that is our current situation.
  330. Currently, we do not have
    all the information.
  331. Luckily, in 20, 30 or 100 years
    someone will come
  332. and find the answer and tell us for once
  333. if we can reach the stars
    faster than light speed.
  334. Before I go I will ask you
    to do something,
  335. tonight, if clouds allow it, please go out
  336. and take a look of the stars
  337. and think, what is out there?
  338. Thank you so much.
  339. (Applause)