full transcript

## 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
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

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
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
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