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← Can Matter Exist Without Space? - Ask the Experts #18

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Showing Revision 5 created 04/11/2014 by Chimene ELESSA.

  1. Hi, Spaceland,
  2. I'm Matt Kleban.
  3. I'm an associate professor of physics at New York University
  4. and I'm here to answer your questions.
  5. First question is:
  6. Is there a maximum size for a black hole?
  7. So, it's a very good question.
  8. Before I answer it, just quickly:
  9. What do we mean by the "size of a black hole"?
  10. The size of a black hole is the radius of the event horizon.
  11. Black holes are regions that not even light can escape from.
  12. There is a certain size to the region from which no light can get out.
  13. The edge of that region is called the "event horizon"
  14. and has a radius, it has a size.
  15. That's what we mean by the size of a black hole.
  16. Actually, the radius of the event horizon,
  17. so the size of the black hole, is just proportional
  18. to the amount of matter and energy that you throw into it.
  19. In fact, if you had access to an infinite amount of matter and energy,
  20. you could just keep feeding into the black hole,
  21. and it could just keep growing bigger and bigger.
  22. There's no limit in that sense.
  23. But, of course, in the universe we live in,
  24. we don't have access to an infinite amount
  25. of matter and energy.
  26. And even if we could somehow fly around
  27. all of the universe and collect all the matter and energy in it,
  28. even if we did that, we would still have a maximum size.
  29. Because there's a finite amount of matter and energy
  30. in the universe that we could collect.
  31. That size would be a fraction of the size of the universe today.
  32. So, it would be maybe billions of light year across,
  33. very very big, but still a finite size.
  34. The second question is:
  35. Can matter exist without space?
  36. That's a very good question and a very hard question.
  37. The honest answer is: We don't know for sure.
  38. But what we can say is that we have a theory that relates
  39. matter to space, and to time as well.
  40. Although we don't think that theory is an exact description
  41. of the world, it's the best one we've got.
  42. That theory is called "general relativity."
  43. It's the theory that Albert Einstein, in 1916 or so, first discovered.
  44. According to Einstein, there's an equation -actually a set
  45. of equations, called "Einstein's equations",
  46. which relate matter to space and time.
  47. It turns out it's possible to solve those equations
  48. when there's no matter.
  49. You can have zero matter and zero energy,
  50. but still have space and time.
  51. But it's not possible to solve those equations
  52. when you have matter but without space and time.
  53. In other words, you can have space and time without matter but,
  54. at least according to Einstein's equations,
  55. you can't have matter without space and time.
  56. We don't think that that's the end of the story.
  57. We don't think that the exact laws of physics.
  58. It could be that whatever is the exact laws of physics could
  59. somehow allow matter to exist without space.
  60. But, I think, at least for the moment,
  61. the state of the art is no.
  62. As far as we know it's not possible.
  63. The third question is:
  64. If we were able to overcome the problem
  65. of infinite energy for light travel
  66. and travel through space at C [at the speed of light],
  67. would time dilation mean that from our perspective
  68. traveling anywhere would be instantaneous?
  69. And would this then mean that we would actually
  70. exist at every point in our vector at the same time?
  71. That's another good question.
  72. The reason for the question is that when you move very fast,
  73. when you move very close to the speed of light,
  74. there's a phenomenon called "time dilation",
  75. which means that for you, if you're the one moving very
  76. close to the speed of light, not very much time
  77. is going to pass.
  78. For instance, if you travel from the Earth to Alpha Centauri
  79. on a spaceship that is moving
  80. very close to the speed of light,
  81. then very little time will pass for you.
  82. You won't age very much at all.
  83. Your clocks won't take off very much time.
  84. The people on Earth and the people on Alpha Centauri will
  85. watch you make this trip
  86. and they'll say it took you a couple of years
  87. at least to make that trip.
  88. But for you, it could be a very short amount of time.
  89. The interesting thing is this is a theory of relativity
  90. and everything should be relative to the observer
  91. so, you might ask:
  92. How could it be that you could make that trip in such
  93. a short period of time?
  94. And the answer is if you go to your "reference frame",
  95. if you're driving a car in the highway,
  96. you see buildings and trees, and stuff like that
  97. along the road, coming toward you at 60 m/h,
  98. you at rest, the trees and the buildings
  99. are coming towards you.
  100. That's your reference frame.
  101. In the spaceship, you are at rest,
  102. and Alpha Centauri is coming towards you.
  103. The speed is coming towards you is pretty close
  104. to the speed of light.
  105. It can never be greater.
  106. It can never go faster than the speed of light.
  107. But it will be coming toward you at nearly the speed of light.
  108. The reason that you make the trip in such a short period of time,
  109. is because there's another strange phenomenon
  110. in relativity which is called "Lorenz contraction":
  111. Distances get contracted.
  112. Distances look shorter when objects are moving fast.
  113. The distance that you would measure
  114. between you and Alpha Centauri,
  115. is much shorter than the distance that someone at rest
  116. on Earth would measure.
  117. That's how you are able to make the journey
  118. in such a small period of time.
  119. So, to answer the question about whether everything
  120. would be instantaneous in the limit that
  121. you're moving at the speed of light,
  122. the answer is yes.
  123. Because in the limit that you are moving
  124. at the speed of light,
  125. no time passes for you as you make this trip.
  126. And from your point of view,
  127. there's no distance actually between Earth and Alpha Centauri.
  128. That's how you can cross it in just an instant.
  129. So yes.
  130. You would be everywhere between Earth and Alpha Centauri
  131. at the same time in one instant.
  132. Thanks for the great questions.
  133. If you have more questions for the next expert,
  134. please leave them in the comments below.