Teoria relativităţii pe înţelesul tuturor - 2 — Transcript

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1. 0:02let's start our examination of
2. 0:04Relativity and light with a flashback
3. 0:08teaser imagine you and Sky King are
4. 0:11flying in the song bird and you have a
5. 0:13Red Rider BB gun with you you know that
6. 0:15you're flying at 150 mph and you also
7. 0:18know that when you fire your rifle at
8. 0:20the target range the bullet leaves the
9. 0:22muzzle at only 100 milph so the plane
10. 0:25flies faster than the
11. 0:27bullet now you point the rifle in the
12. 0:29same direction that you're flying and
13. 0:31pull the
14. 0:32trigger what happens does the bullet
15. 0:34ever leave the muzzle since you're
16. 0:36flying at 150 mph and the bullet only
17. 0:39travels at 100 a fun question but an
18. 0:43easy one sure it does the bullet speed
19. 0:47from the rifle gets added to the plane
20. 0:50speed and the bullet takes off at 250
21. 0:53mph reason it out this way the bullet is
22. 0:57moving at 150 m per hour just sitting in
23. 1:01the gun since it is moving along with
24. 1:03you and Sky King and the
25. 1:07Songbird then when you fire the gun the
26. 1:10bullet is blasted forward at an
27. 1:12additional 100 mph so it leaves the
28. 1:16muzzle at 250 mph relative to the ground
29. 1:21100 mph relative to you Sky King and the
30. 1:25Songbird this is classical relativity
31. 1:29simply add the
32. 1:31velocities okay but now suppose you're
33. 1:34with Snoopy in his sof with camel and
34. 1:37you know that on the ground light from
35. 1:38your flashlight travels at 186,000 M
36. 1:42perss now from the plane you point the
37. 1:44flashlight forward and turn on the beam
38. 1:48does the light travel forward at 186,000
39. 1:51Ms plus the speed of the plane I know
40. 1:55the answer but I don't understand
41. 1:58it if that's what you're going to talk
42. 2:00about today I can't wait preach away my
43. 2:06hero okay here we go
44. 2:11[Music]
45. 2:13Jes the example of adding velocities in
46. 2:17the bullettin plane example is classical
47. 2:19relativity at its
48. 2:22finest this classical version of
49. 2:24Relativity simply adding the velocities
50. 2:27worked perfectly well for centuries for
51. 2:30describing horse carts and
52. 2:33ships or baseballs and
53. 2:37[Music]
54. 2:41trucks even
55. 2:47airplanes and Rockets and
56. 2:52bullets but the relativity of classical
57. 2:55physics is merely a very close
58. 2:56approximation to
59. 2:58reality at at very very fast speeds
60. 3:01classical relativity breaks down but
61. 3:04this wouldn't be clear until scientists
62. 3:06began flying sop with camels and
63. 3:09examining the nature of the fastest
64. 3:11known thing
65. 3:15light in the middle of the 19th century
66. 3:18it had been known for quite some time
67. 3:20that electricity could be used to make a
68. 3:23magnet and that magnets could be used to
69. 3:26make electricity but the man who made
70. 3:28the first color photograph James Clerk
71. 3:30Maxwell unified everything known about
72. 3:33electricity and magnetism in four
73. 3:36magnificent
74. 3:38equations and these equations described
75. 3:40an electromagnetic wave that would
76. 3:42travel through the empty space at
77. 3:44exactly the measured speed of light and
78. 3:47in fact this wave was
79. 3:50[Music]
80. 3:53light according to Maxwell light was an
81. 3:55electromagnetic wave that moved through
82. 3:58empty space with a speed spe of
83. 4:01186,000 M
84. 4:04second but from the standpoint of
85. 4:07Relativity the question naturally arises
86. 4:10relative to
87. 4:12what the equation seemed to say that
88. 4:14light moved at
89. 4:16186,000
90. 4:18m/s relative to
91. 4:26everything this was a dilemma facing the
92. 4:28physicist at the turn of the 20th
93. 4:31century if Maxwell was right then light
94. 4:35moves with a velocity of C
95. 4:38186,000 m/s
96. 4:42always but if classical relativity was
97. 4:44right there is no absolute
98. 4:47velocities and the velocity of light
99. 4:50should depend on who is doing the
100. 4:51measuring and their motion relative to
101. 4:54the source of the
102. 4:55light how could both be right either our
103. 4:58understanding of motion or our
104. 5:00understanding of electromagnetism and
105. 5:02light were in Jeopardy the very
106. 5:05Foundation of physics was facing a
107. 5:07crisis a 26-year-old patent clerk named
108. 5:10Albert Einstein would provide the way
109. 5:13out of this
110. 5:14[Music]
111. 5:24crisis Einstein accepted both of these
112. 5:27seemingly contradictory Notions and
113. 5:30changed the course of
114. 5:31science he accepted the idea of relative
115. 5:34motion but restated it as
116. 5:37follows any person moving at a constant
117. 5:41velocity will observe the same laws of
118. 5:43physics that a stationary person
119. 5:47observes and since the speed of light is
120. 5:49part of the laws of physics Einstein
121. 5:52postulated that all observers will
122. 5:54measure the same speed of light
123. 5:57regardless of their state of motion
124. 5:59[Music]
125. 6:06but speed is just a measure of distance
126. 6:08moved in a given time and in order to
127. 6:11agree on the speed of light different
128. 6:14observers might have to disagree about
129. 6:17distance and
130. 6:18[Music]
131. 6:22time okay I think I'm getting it if we
132. 6:26have to agree on velocity
133. 6:29then we might have to disagree on the
134. 6:32components of
135. 6:34velocity absolutely true