full transcript

From the Ted Talk by Andrew Pontzen and Tom Whyntie: The fundamentals of space-time Part 2

Unscramble the Blue Letters

Light: it's the fastest thing in the universe, but we can still measure its speed if we slow down the aoitamnin, we can analyze light's motion using a space-time diagram, which takes a flipbook of animation panels, and turns them on their side. In this lesson, we'll add the snigle erntiaeepxml fact that whenever anyone measures just how fast light moves, they get the same answer: 299,792,458 meters every second, which means that when we draw light on our space-time diagram, it's world line always has to appear at the same angle. But we saw previously that speed, or enivuqtllaey world line agelns, change when we look at things from other people's perspective. To explore this cirdaotcotnin, let's see what happens if I start moving while I stand still and shine the lsaer at Tom. First, we'll need to construct the space-time dagriam. Yes, that means taking all of the different pelnas showing the different moments in time and stacking them up. From the side, we see the world line of the laser light at its correct fxeid angle, just as before. So far, so good. But that space-time diagram represents Andrew's pvpeectsrie. What does it look like to me? In the last lesson, we showed how to get Tom's perspective mnovig all the panels along a bit until his world line is ctoelelmpy vertical. But look carefully at the light world line. The rearrangement of the panels means it's now tilted over too far. I'd measure light traveling festar than Andrew would. But every experiment we've ever done, and we've tried very hard, says that everyone mesauers light to have a fixed speed. So let's satrt again. In the 1900s, a clever chap named ablert Einstein wekrod out how to see things properly, from Tom's point of view, while still getting the speed of lgiht right. First, we need to glue together the separate panels into one solid block. This gives us our space-time, turning space and time into one smooth, continuous material. And now, here is the trick. What you do is stretch your block of space-time along the light world line, then squash it by the same amount, but at right angles to the light wrold line, and abracadabra! Tom's world line has gone vertical, so this does represent the world from his point of view, but most importantly, the light world line has never changed its angle, and so light will be measured by Tom going at the correct speed. This superb trick is known as a Lorentz transformation. Yeah, more than a trick. Slice up the space-time into new panels and you have the physically correct animation. I'm stationary in the car, everything else is coming past me and the speed of light works out to be that same fixed value that we know everyone measures. On the other hand, something sanrtge has happened. The fence posts aren't spaced a meter apart anymore, and my mom will be worried that I look a bit thin. But that's not fair. Why don't I get to look thin? I thought physics was supposed to be the same for everyone. Yes, no, it is, and you do. All that stretching and squashing of space-time has just muddled together what we used to think of separately as scape and time. This particular squashing efefct is known as lerntoz cincottoran. Okay, but I still don't look thin. No, yes, you do. Now that we know better about space-time, we should redraw what the scene looked like to me. To you, I appear Lorentz ctcoanretd. Oh but to you, I appear Lorentz contracted. Yes. Uh, well, at least it's fair. And speaking of fairness, just as space gets muddled with time, time also gets muddled with space, in an effect known as time dilation. No, at everyday speeds, such as Tom's car reaches, actually all the effects are much, much slamelr than we've illustrated them. Oh, yet, careful experiments, for instance watching the behavior of tiny particles whizzing around the lgare Hadron Collider cfominerd that the effects are real. And now that space-time is an experimentally confirmed part of reality, we can get a bit more ambitious. What if we were to start playing with the martieal of space-time itself? We'll find out all about that in the next animation.

Open Cloze

Light: it's the fastest thing in the universe, but we can still measure its speed if we slow down the _________, we can analyze light's motion using a space-time diagram, which takes a flipbook of animation panels, and turns them on their side. In this lesson, we'll add the ______ ____________ fact that whenever anyone measures just how fast light moves, they get the same answer: 299,792,458 meters every second, which means that when we draw light on our space-time diagram, it's world line always has to appear at the same angle. But we saw previously that speed, or ____________ world line ______, change when we look at things from other people's perspective. To explore this _____________, let's see what happens if I start moving while I stand still and shine the _____ at Tom. First, we'll need to construct the space-time _______. Yes, that means taking all of the different ______ showing the different moments in time and stacking them up. From the side, we see the world line of the laser light at its correct _____ angle, just as before. So far, so good. But that space-time diagram represents Andrew's ___________. What does it look like to me? In the last lesson, we showed how to get Tom's perspective ______ all the panels along a bit until his world line is __________ vertical. But look carefully at the light world line. The rearrangement of the panels means it's now tilted over too far. I'd measure light traveling ______ than Andrew would. But every experiment we've ever done, and we've tried very hard, says that everyone ________ light to have a fixed speed. So let's _____ again. In the 1900s, a clever chap named ______ Einstein ______ out how to see things properly, from Tom's point of view, while still getting the speed of _____ right. First, we need to glue together the separate panels into one solid block. This gives us our space-time, turning space and time into one smooth, continuous material. And now, here is the trick. What you do is stretch your block of space-time along the light world line, then squash it by the same amount, but at right angles to the light _____ line, and abracadabra! Tom's world line has gone vertical, so this does represent the world from his point of view, but most importantly, the light world line has never changed its angle, and so light will be measured by Tom going at the correct speed. This superb trick is known as a Lorentz transformation. Yeah, more than a trick. Slice up the space-time into new panels and you have the physically correct animation. I'm stationary in the car, everything else is coming past me and the speed of light works out to be that same fixed value that we know everyone measures. On the other hand, something _______ has happened. The fence posts aren't spaced a meter apart anymore, and my mom will be worried that I look a bit thin. But that's not fair. Why don't I get to look thin? I thought physics was supposed to be the same for everyone. Yes, no, it is, and you do. All that stretching and squashing of space-time has just muddled together what we used to think of separately as _____ and time. This particular squashing ______ is known as _______ ___________. Okay, but I still don't look thin. No, yes, you do. Now that we know better about space-time, we should redraw what the scene looked like to me. To you, I appear Lorentz __________. Oh but to you, I appear Lorentz contracted. Yes. Uh, well, at least it's fair. And speaking of fairness, just as space gets muddled with time, time also gets muddled with space, in an effect known as time dilation. No, at everyday speeds, such as Tom's car reaches, actually all the effects are much, much _______ than we've illustrated them. Oh, yet, careful experiments, for instance watching the behavior of tiny particles whizzing around the _____ Hadron Collider _________ that the effects are real. And now that space-time is an experimentally confirmed part of reality, we can get a bit more ambitious. What if we were to start playing with the ________ of space-time itself? We'll find out all about that in the next animation.

Solution

  1. laser
  2. start
  3. large
  4. albert
  5. measures
  6. animation
  7. contradiction
  8. space
  9. diagram
  10. lorentz
  11. confirmed
  12. smaller
  13. equivalently
  14. panels
  15. single
  16. moving
  17. contracted
  18. angles
  19. contraction
  20. worked
  21. perspective
  22. faster
  23. strange
  24. world
  25. fixed
  26. experimental
  27. light
  28. effect
  29. material
  30. completely

Original Text

Light: it's the fastest thing in the universe, but we can still measure its speed if we slow down the animation, we can analyze light's motion using a space-time diagram, which takes a flipbook of animation panels, and turns them on their side. In this lesson, we'll add the single experimental fact that whenever anyone measures just how fast light moves, they get the same answer: 299,792,458 meters every second, which means that when we draw light on our space-time diagram, it's world line always has to appear at the same angle. But we saw previously that speed, or equivalently world line angles, change when we look at things from other people's perspective. To explore this contradiction, let's see what happens if I start moving while I stand still and shine the laser at Tom. First, we'll need to construct the space-time diagram. Yes, that means taking all of the different panels showing the different moments in time and stacking them up. From the side, we see the world line of the laser light at its correct fixed angle, just as before. So far, so good. But that space-time diagram represents Andrew's perspective. What does it look like to me? In the last lesson, we showed how to get Tom's perspective moving all the panels along a bit until his world line is completely vertical. But look carefully at the light world line. The rearrangement of the panels means it's now tilted over too far. I'd measure light traveling faster than Andrew would. But every experiment we've ever done, and we've tried very hard, says that everyone measures light to have a fixed speed. So let's start again. In the 1900s, a clever chap named Albert Einstein worked out how to see things properly, from Tom's point of view, while still getting the speed of light right. First, we need to glue together the separate panels into one solid block. This gives us our space-time, turning space and time into one smooth, continuous material. And now, here is the trick. What you do is stretch your block of space-time along the light world line, then squash it by the same amount, but at right angles to the light world line, and abracadabra! Tom's world line has gone vertical, so this does represent the world from his point of view, but most importantly, the light world line has never changed its angle, and so light will be measured by Tom going at the correct speed. This superb trick is known as a Lorentz transformation. Yeah, more than a trick. Slice up the space-time into new panels and you have the physically correct animation. I'm stationary in the car, everything else is coming past me and the speed of light works out to be that same fixed value that we know everyone measures. On the other hand, something strange has happened. The fence posts aren't spaced a meter apart anymore, and my mom will be worried that I look a bit thin. But that's not fair. Why don't I get to look thin? I thought physics was supposed to be the same for everyone. Yes, no, it is, and you do. All that stretching and squashing of space-time has just muddled together what we used to think of separately as space and time. This particular squashing effect is known as Lorentz contraction. Okay, but I still don't look thin. No, yes, you do. Now that we know better about space-time, we should redraw what the scene looked like to me. To you, I appear Lorentz contracted. Oh but to you, I appear Lorentz contracted. Yes. Uh, well, at least it's fair. And speaking of fairness, just as space gets muddled with time, time also gets muddled with space, in an effect known as time dilation. No, at everyday speeds, such as Tom's car reaches, actually all the effects are much, much smaller than we've illustrated them. Oh, yet, careful experiments, for instance watching the behavior of tiny particles whizzing around the Large Hadron Collider confirmed that the effects are real. And now that space-time is an experimentally confirmed part of reality, we can get a bit more ambitious. What if we were to start playing with the material of space-time itself? We'll find out all about that in the next animation.

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
world line 7
light world 4
lorentz contracted 2

ngrams of length 3

collocation frequency
light world line 2

Important Words

  1. add
  2. albert
  3. ambitious
  4. amount
  5. analyze
  6. andrew
  7. angle
  8. angles
  9. animation
  10. anymore
  11. behavior
  12. bit
  13. block
  14. car
  15. careful
  16. carefully
  17. change
  18. changed
  19. chap
  20. clever
  21. collider
  22. coming
  23. completely
  24. confirmed
  25. construct
  26. continuous
  27. contracted
  28. contraction
  29. contradiction
  30. correct
  31. diagram
  32. dilation
  33. draw
  34. effect
  35. effects
  36. einstein
  37. equivalently
  38. everyday
  39. experiment
  40. experimental
  41. experimentally
  42. experiments
  43. explore
  44. fact
  45. fair
  46. fairness
  47. fast
  48. faster
  49. fastest
  50. fence
  51. find
  52. fixed
  53. flipbook
  54. glue
  55. good
  56. hadron
  57. hand
  58. happened
  59. hard
  60. illustrated
  61. importantly
  62. instance
  63. large
  64. laser
  65. lesson
  66. light
  67. line
  68. looked
  69. lorentz
  70. material
  71. means
  72. measure
  73. measured
  74. measures
  75. meter
  76. meters
  77. mom
  78. moments
  79. motion
  80. moves
  81. moving
  82. muddled
  83. named
  84. panels
  85. part
  86. particles
  87. perspective
  88. physically
  89. physics
  90. playing
  91. point
  92. posts
  93. previously
  94. properly
  95. reaches
  96. real
  97. reality
  98. rearrangement
  99. redraw
  100. represent
  101. represents
  102. scene
  103. separate
  104. separately
  105. shine
  106. showed
  107. showing
  108. side
  109. single
  110. slice
  111. slow
  112. smaller
  113. smooth
  114. solid
  115. space
  116. spaced
  117. speaking
  118. speed
  119. speeds
  120. squash
  121. squashing
  122. stacking
  123. stand
  124. start
  125. stationary
  126. strange
  127. stretch
  128. stretching
  129. superb
  130. supposed
  131. takes
  132. thin
  133. thought
  134. tilted
  135. time
  136. tiny
  137. tom
  138. transformation
  139. traveling
  140. trick
  141. turning
  142. turns
  143. uh
  144. universe
  145. vertical
  146. view
  147. watching
  148. whizzing
  149. worked
  150. works
  151. world
  152. worried
  153. yeah