1/271 0.09-0.81 jd 各位同学大家好，09-01 13:44:52-09-01 13:44:53Hello everyone,
2/271 0.93-1.77 jd 我是李勇的老师。09-01 13:44:53-09-01 13:44:55I am Li Yong's teacher.
3/271 2.19-4.29 jd 今天我们继续来聊相对论的话题。09-01 13:44:55-09-01 13:44:57Today, we continue to discuss the topic of relativity.
4/271 4.71-7.17 xss 在爱因斯坦提出侠义相对论之后啊，09-01 13:44:57-09-01 13:46:48After Einstein proposed the theory of relativity,
5/271 7.35-11.37 jd 许多科学家都对这种惊世骇俗的世界观产生过质疑。09-01 13:44:58-09-01 13:45:00Many scientists have questioned this shocking worldview.
6/271 11.79-12.63 hp 比如说马赫、09-01 13:44:59-09-01 13:45:01For example, Mach
7/271 12.87-13.29 n 庞加莱、09-01 13:44:59-09-01 13:45:00Poincaré,
8/271 13.47-14.13 de 洛伦兹等人，09-01 13:45:00-09-01 13:45:29Lorentz et al.
9/271 14.43-16.23 n 他们都是相对论的先驱，09-01 13:45:01-09-01 13:45:02They were all pioneers of relativity.
10/271 16.59-19.29 de 但是呢最初都怀疑相对论的正确性，09-01 13:45:01-09-01 13:45:47However, initially there were doubts about the correctness of relativity.
11/271 19.89-23.73 hp 不过他们都没有发现侠义相对论真正的问题所在。09-01 13:50:03-09-01 13:50:08However, they failed to realize the real problem of the theory of chivalrous relativity.
12/271 24.21-24.81 jd 这个问题呢，09-01 13:45:03-09-01 13:45:04This question is...
13/271 24.93-28.59 n 是在十年之后的一九一五年由爱因斯坦本人发现的。09-01 13:45:03-09-01 13:45:06It was discovered by Einstein himself in 1915, ten years later.
14/271 29.37-32.44 aaa 那么狭义相对论究竟有什么问题呢？09-01 13:45:04-09-01 13:45:05What are the problems with special relativity?
15/271 32.92-35.02 hp 狭义相对论中呢有两条基本原理、09-01 13:45:05-09-01 13:45:08In special relativity, there are two fundamental principles:
16/271 35.26-37.06 bg 相对性原理和光速不变原理。09-01 13:45:05-09-01 13:45:45Relativity principle and the constancy of light speed.
17/271 37.48-39.22 n 如果非要找一条更基本的，09-01 13:45:06-09-01 13:45:08If you absolutely have to find a more fundamental one,
18/271 39.46-41.02 jd 我想应该是相对性原理。09-01 13:45:07-09-01 13:45:08It should be the principle of relativity.
19/271 41.5-43.12 aaa 在所有惯性参考系中，09-01 13:45:07-09-01 13:45:09In all inertial reference frames,
20/271 43.36-44.62 n 物理规律都是相同的。09-01 13:45:08-09-01 13:45:10The laws of physics are the same.
21/271 45.1-47.5 n 那么什么是惯性参考系呢？09-01 13:45:09-09-01 13:45:10What is an inertial reference frame?
22/271 47.8-52.78 jd 我们通常说呀惯性参考系就是静止或者匀速直线运动的参考系。09-01 13:45:09-09-01 13:45:13We usually say that an inertial reference frame is a reference frame that is either at rest or moving with uniform velocity.
23/271 53.26-56.62 hp 比如说匀速运动的火车就是一个惯性系，09-01 13:45:10-09-01 13:45:15For example, a train moving at a constant speed is an inertial frame of reference.
24/271 57.04-60.53 aaa 在火车上做任何物理实验都和地面上没有区别，09-01 13:45:11-09-01 13:45:13Doing any physical experiment on a train is no different from doing it on the ground.
25/271 60.97-63.85 n 但是加速运动的火车就不是惯性系了。09-01 13:45:11-09-01 13:45:14However, the accelerating train is not an inertial frame.
26/271 64.22-67.76 n 如果火车加速在车厢里看地板上有一个小球，09-01 13:45:12-09-01 13:45:16If a train is accelerating, and you are looking at the floor inside the carriage,
27/271 68.12-69.74 jd 虽然没有受到水平方向的力，09-01 13:45:13-09-01 13:45:15Although not subjected to horizontal forces,
28/271 69.98-71.42 aaa 但是也会向后滚动。09-01 13:45:14-09-01 13:45:16However, it will also scroll backwards.
29/271 71.95-75.07 n 但是啊这种说法存在严重的理论缺陷，09-01 13:45:15-09-01 13:45:17However, this statement has serious theoretical flaws.
30/271 75.71-77.21 jd 静止和运动都是相对的。09-01 13:45:16-09-01 13:45:17Stillness and movement are relative.
31/271 77.449-79.13 hp 只有相对于惯性参考系，09-01 13:45:16-09-01 13:45:19Only relative to an inertial reference frame,
32/271 79.31-82.15 aaa 静止或匀速直间运动的参考系才是惯用参考器。09-01 13:45:17-09-01 13:45:21A reference frame in which an object is either at rest or moving with constant velocity is a non-inertial reference frame.
33/271 82.53-85.35 n 就比如说你要判断火车是不是惯性系，09-01 13:45:18-09-01 13:45:22For example, if you want to determine whether a train is in an inertial frame.
34/271 85.76-89.0 n 不光要看火车有没有在地面上静止或匀速，09-01 13:45:18-09-01 13:45:25It's not just about whether the train is stationary or moving at a constant speed, but also about its position relative to other objects.
35/271 89.38-92.74 jd 你还得判断地面本身是不是静止或匀素的。09-01 13:45:19-09-01 13:45:22You also need to determine whether the ground is stationary or moving at a constant speed.
36/271 93.21-95.61 hp 如果你用这种办法去寻找惯性系的话，09-01 13:45:20-09-01 13:45:23If you use this method to find inertial frames,
37/271 95.79-99.84 aaa 那就逼迫我们承认宇宙中存在一套特殊的参考系。09-01 13:45:21-09-01 13:45:24That forces us to admit the existence of a special reference frame in the universe.
38/271 100.19-101.99 n 他们彼此之间是等价的，09-01 13:45:23-09-01 13:45:24They are equivalent to each other.
39/271 102.23-103.01 jd 他们是惯性系，09-01 13:45:23-09-01 13:45:24They are in the inertial frame.
40/271 103.43-107.21 hp 而其他的参考器呢与它们是不等价的就不是惯性器。09-01 13:45:24-09-01 13:45:29And the other reference frames are not equivalent to inertial frame, if they aren't.
41/271 107.92-111.4 aaa 其实呢这种想法还是牛顿的绝对时空观，09-01 13:45:24-09-01 13:45:27Actually, this idea is still Newton's absolute time and space view.
42/271 111.83-115.07 n 只不过牛顿认为存在一个绝对的空间，09-01 13:45:25-09-01 13:45:27However, Newton believed that there was an absolute space.
43/271 115.4-118.52 jd 而这种观点认为存在一套绝对的空间，09-01 13:45:26-09-01 13:45:28And this view holds that there exists an absolute space.
44/271 118.88-120.98 n 二者呢其实并没有本质的区别。09-01 13:45:27-09-01 13:45:29In fact, there is no fundamental difference between the two.
45/271 121.41-123.63 aaa 还有一种说法是惯性参考系，09-01 13:45:28-09-01 13:45:29Another explanation is the inertial reference frame.
46/271 123.81-126.09 n 就是牛顿第一定律成立的参考系。09-01 13:45:28-09-01 13:45:30The reference frame in which Newton's first law holds.
47/271 126.55-129.67 jd 也就是啊如果你在一个参考器里不受力的物体，09-01 13:45:29-09-01 13:45:31So, if you have a weak object in a reference frame,
48/271 129.79-131.95 hp 能够保持静止或者匀速直线运动，09-01 13:45:30-09-01 13:45:34Able to remain stationary or move at a constant speed in a straight line,
49/271 132.36-134.64 n 那么这个参考系就是惯性参考系了，09-01 13:45:30-09-01 13:45:32Therefore, this reference frame is an inertial reference frame.
50/271 135.32-138.32 de 可是我们真的能够找到一个不受力的物体吗？09-01 13:45:31-09-01 13:46:02But can we really find an object that is not effective?
51/271 139.12-141.16 n 宏观的作用力主要有电磁力，09-01 13:45:32-09-01 13:45:34The main macroscopic forces are electromagnetic force,
52/271 141.4-142.24 jd 还有万有引力，09-01 13:45:33-09-01 13:45:34There is also gravity,
53/271 142.55-145.1 n 那么电磁力呢是可以用导体壳来屏蔽的。09-01 13:45:34-09-01 13:45:36Can electromagnetic force be shielded by a conductor shell?
54/271 145.55-147.409 aaa 不过万有引力不能屏蔽，09-01 13:45:34-09-01 13:45:36However, gravity cannot be shielded.
55/271 148.05-149.43 n 比如说飞船里有一个石头，09-01 13:45:35-09-01 13:45:37For example, there is a rock in the spaceship.
56/271 149.86-152.98 jd 它相对于飞船呢正在做匀速直线运动，09-01 13:45:36-09-01 13:45:38It is currently moving at a constant speed in a straight line.
57/271 153.44-155.48 hp 你也不能说飞船就是惯星系，09-01 13:45:36-09-01 13:45:41You can't say that a spaceship is just an ordinary star,
58/271 155.99-161.69 aaa 因为你不知道这块石头是不是受到了飞船或者来自其他星球的引力。09-01 13:45:37-09-01 13:45:40Because you don't know if this rock was affected by a spaceship or from another planet.
59/271 162.24-163.68 n 如果我们打开中学课本啊，09-01 13:45:38-09-01 13:45:40If we open the middle school textbooks,
60/271 163.8-165.06 n 你可能会看到这样的文字，09-01 13:45:38-09-01 13:45:40You might see such text,
61/271 165.66-167.46 jd 地球呢接近于一个惯性系，09-01 13:45:39-09-01 13:45:41The Earth is approaching an inertial frame.
62/271 167.94-170.04 n 太阳呢是比地球更好的惯性系。09-01 13:45:40-09-01 13:45:43The sun is a better inertial frame than the Earth.
63/271 170.56-173.44 n 银河系中心呢又是比太阳更好的惯性系。09-01 13:45:41-09-01 13:45:45The center of the Milky Way is also a better inertial frame than the Sun.
64/271 173.98-177.58 aaa 这种说法其实回避了究竟什么是惯性参考系的问题。09-01 13:45:42-09-01 13:45:44This statement actually avoids the question of what an inertial reference frame is.
65/271 178.63-180.91 jd 爱因斯坦在提出狭义相对论之后，09-01 13:45:42-09-01 13:45:44After Einstein proposed special relativity,
66/271 181.15-183.49 hp 反复思索惯性参考系到底是什么？09-01 13:45:43-09-01 13:45:46Repeatedly pondering what an inertial reference frame is.
67/271 183.8-187.7 n 他实在找不出惯性参考系和其他非惯性参考系的区别，09-01 13:45:44-09-01 13:45:49He really couldn't find the difference between an inertial reference frame and other non-inertial reference frames.
68/271 187.94-192.08 aaa 那么凭什么物理规律就只能在惯性参考系中成立呢？09-01 13:45:45-09-01 13:45:47Why can't the laws of physics apply in non-inertial reference frames?
69/271 192.64-196.9 jd 建立在惯性参考系上的相对性原理很有可能是有问题的，09-01 13:45:45-09-01 13:45:48The principle of relativity, which is based on the inertial reference frame, is likely to be problematic.
70/271 197.37-199.89 n 整个狭义相对论没有坚实的根基。09-01 13:45:46-09-01 13:45:49The entire special theory of relativity lacks a solid foundation.
71/271 200.4-203.28 bg 爱因斯坦回想自己创立狭义相对论的过程，09-01 13:45:47-09-01 13:46:38Einstein reflected on the process of formulating his theory of special relativity,
72/271 203.4-205.74 hp 就是大胆的把一些无法测量的假设，09-01 13:45:47-09-01 13:45:51Boldly put some unmeasurable assumptions,
73/271 206.13-207.63 de 比如说绝对空间去掉，09-01 13:45:48-09-01 13:46:09For example, if the absolute space is removed.
74/271 208.08-210.48 aaa 取而代之的是一种更加合理的假设。09-01 13:45:49-09-01 13:45:51Instead, a more reasonable assumption is made.
75/271 210.72-211.68 jd 比如说光速不变，09-01 13:45:49-09-01 13:45:51For example, the speed of light is constant.
76/271 212.23-216.25 n 那么现在既然没有办法来确定哪个参考系是惯用参考系，09-01 13:45:50-09-01 13:45:54So now that there's no way to determine which reference frame is the inertial one,
77/271 216.43-217.45 n 为什么不大胆一点，09-01 13:45:51-09-01 13:45:52Why not be bolder,
78/271 217.77-219.27 hp 认为在所有参考系下，09-01 13:45:51-09-01 13:45:55In all reference frames, it is believed that...
79/271 219.57-221.31 aaa 物理规律都是一样的呢？09-01 13:45:52-09-01 13:45:54The laws of physics are the same, right?
80/271 221.7-224.46 jd 于是啊爱因斯坦就把狭义的相对性原理，09-01 13:45:53-09-01 13:45:55So Einstein then put forward the principle of special relativity,
81/271 224.83-227.29 n 所有惯性参考器下物体规律相同，09-01 13:45:53-09-01 13:45:56All objects follow the same laws of motion in all inertial reference frames.
82/271 227.66-229.52 aaa 修改成广义的相对性原理，09-01 13:45:54-09-01 13:45:56Modified the principle of general relativity,
83/271 229.93-232.09 n 所有参考系下物的规律相同了。09-01 13:45:55-09-01 13:45:57The laws governing all objects are the same.
84/271 232.88-234.32 hp 你可能会感觉到奇怪啊，09-01 13:45:56-09-01 13:45:58You might feel strange,
85/271 234.44-238.29 jd 那匀速运动的火车上一个小球会竖直下落，09-01 13:45:56-09-01 13:45:59A small ball moving at a constant speed on a moving train will fall vertically.
86/271 238.69-240.52 aaa 而加速运动的火车上呢，09-01 13:45:57-09-01 13:45:59And what about the train moving at high speed?
87/271 240.699-243.22 n 一个小球松手之后会斜着往下落，09-01 13:45:58-09-01 13:46:01A small ball, when dropped, will fall at an angle.
88/271 243.64-246.58 n 这两个参考系怎么会有相同的物理规律呢？09-01 13:45:58-09-01 13:46:01How can these two reference frames have the same physical laws?
89/271 246.93-248.34 hp 这就涉及到第二个问题了，09-01 13:45:59-09-01 13:46:02This brings us to the second question.
90/271 248.82-250.92 aaa 引力和加速度的等效性。09-01 13:46:00-09-01 13:46:01Equivalence of gravity and acceleration.
91/271 251.78-255.32 jd 传说呀伽利略在比萨斜塔上扔下了两个铁球，09-01 13:46:00-09-01 13:46:03Legend has it that Galileo dropped two iron balls from the top of the Leaning Tower of Pisa.
92/271 255.81-258.57 n 结果发现无论铁球质量大小如何呢，09-01 13:46:01-09-01 13:46:04The results show that regardless of the size of the iron ball,
93/271 258.75-259.95 aaa 他们都是同时落地的。09-01 13:46:02-09-01 13:46:03They all landed at the same time.
94/271 260.43-262.71 n 虽然这个实验不一定真实的发生过，09-01 13:46:03-09-01 13:46:05Although this experiment may not have actually happened,
95/271 262.95-266.36 hp 但是人们对这个现象的重复从来就没有停止过。09-01 13:46:03-09-01 13:46:07However, the phenomenon has been repeated over and over again.
96/271 266.91-268.05 de 在上中学的时候啊，09-01 13:46:04-09-01 13:46:24When I was in middle school,
97/271 268.23-270.39 jd 老师会把一个管子中间抽成真空，09-01 13:46:05-09-01 13:46:07The teacher will create a vacuum in the middle of a tube.
98/271 270.85-272.65 aaa 让羽毛和硬币同时下落。09-01 13:46:05-09-01 13:46:07Let the feather and coin fall simultaneously.
99/271 273.14-273.8 n 你会发现呢，09-01 13:46:06-09-01 13:46:07You will find that,
100/271 273.98-276.02 n 他们同时落到管子的另外一端，09-01 13:46:07-09-01 13:46:09They both landed at the other end of the pipe.
101/271 276.43-277.78 jd 这叫做毛浅管实验。09-01 13:46:07-09-01 13:46:09This is called a simple tube experiment.
102/271 278.27-279.23 aaa 在一九七一年呢，09-01 13:46:08-09-01 13:46:09In 1971,
103/271 279.35-286.45 n 阿波罗十五号的宇航员大卫斯科特在没有空气的月球表面上同时扔下了一把锤子和一根羽毛。09-01 13:46:09-09-01 13:46:15In the Apollo 15 mission, astronaut David Scott simultaneously dropped a hammer and a feather on the moon's surface without air.
104/271 286.94-289.22 hp 在地球上亿万电视观众的面前，09-01 13:46:10-09-01 13:46:13In front of millions of television viewers on Earth,
105/271 289.58-291.68 n 锤子和羽毛同时落在月球。09-01 13:46:10-09-01 13:46:14A hammer and a feather fall at the same time on the moon.
106/271 291.8-294.29 jd 表面上爱因斯坦呢也在思考这个问题。09-01 13:46:11-09-01 13:46:12Einstein was also thinking about this.
107/271 294.589-294.83 de 他说，09-01 13:46:12-09-01 13:46:25He said,
108/271 295.31-299.45 aaa 小球下落是因为受到地球的引力而引力的产生，09-01 13:46:12-09-01 13:46:15The ball falls because of gravity, which is caused by the Earth's gravitational force.
109/271 299.63-301.91 jd 是因为地球周围有引力场，09-01 13:51:14-09-01 13:51:16Because there is a gravitational field around the Earth,
110/271 302.35-303.43 jd 小球又具有质量，09-01 13:46:14-09-01 13:46:15The small ball also has mass.
111/271 303.73-306.73 hp 小球受到的引力正比于小球的质量，09-01 13:46:14-09-01 13:46:19The gravitational force on the small ball is proportional to the mass of the small ball.
112/271 306.99-309.93 n 那么这种质量应该叫做眼力质量，09-01 13:46:15-09-01 13:46:18So, this kind of quality should be called visual quality.
113/271 310.32-313.5 n 也就是力等于引力场乘以引力质量。09-01 13:46:16-09-01 13:46:19That is, force equals the gravitational field multiplied by the mass.
114/271 313.99-315.61 jd 而根据牛顿第二定律呢，09-01 13:46:16-09-01 13:46:18According to Newton's second law,
115/271 315.849-317.95 aaa 物体受到外力之后会产生加速度，09-01 13:46:17-09-01 13:46:19Objects experience acceleration when acted upon by an external force.
116/271 318.31-320.11 jd 这个加速度与外力成正比，09-01 13:46:18-09-01 13:46:20This acceleration is proportional to the force.
117/271 320.23-321.13 n 与质量成反比。09-01 13:46:19-09-01 13:46:21Inversely proportional to quality.
118/271 321.53-323.509 n 这个质量叫做惯性质量，09-01 13:46:20-09-01 13:46:22This quantity is called inertia mass.
119/271 323.78-325.55 aaa 他是牛顿第二定据中的一项，09-01 13:46:20-09-01 13:46:22He is a part of Newton's second law.
120/271 326.05-329.4 hp 也就是力等于惯性质量乘以加速度。09-01 13:46:21-09-01 13:46:24That is, force equals mass times acceleration.
121/271 330.16-333.04 jd 现在呀如果一个物体只受到引力，09-01 13:46:22-09-01 13:46:24Now, if an object is only subjected to gravity,
122/271 333.28-338.63 n 那么它的加速度就应该等于引力质量除以惯性质量在乘以演内场。09-01 13:46:22-09-01 13:46:28Then its acceleration should be equal to the gravitational mass divided by the inertial mass multiplied by the dielectric constant.
123/271 339.05-341.09 n 对伽利略自由落体实验而言，09-01 13:46:23-09-01 13:46:25For Galileo's free fall experiment,
124/271 341.39-344.04 aaa 引力场是地球提供的是固定的，09-01 13:46:24-09-01 13:46:25The gravitational field is constant, provided by the Earth.
125/271 344.44-345.58 jd 无论大球还是小球，09-01 13:46:24-09-01 13:46:26Whether it's a big ball or a small ball,
126/271 345.88-347.14 de 下落的加速度都一样。09-01 13:46:25-09-01 13:46:53The acceleration due to gravity is the same.
127/271 347.57-351.77 n 这就说明啊两个球的引力质量和惯性质量的比是相同的。09-01 13:46:26-09-01 13:46:31This shows that the ratio of the gravitational mass and inertial mass of two balls is the same.
128/271 352.33-355.27 aaa 如果物体的引力质量和惯性质量的比是相同的，09-01 13:46:27-09-01 13:46:29If the ratio of an object's gravitational mass and inertial mass is equal,
129/271 355.45-356.71 jd 那么通过调整单位，09-01 13:46:28-09-01 13:46:29Then by adjusting the units,
130/271 356.89-360.43 de 我们就可以认为引力质量完全等于惯性质量，09-01 13:46:28-09-01 13:47:10We can therefore assume that the gravitational mass is exactly equal to the inertial mass.
131/271 360.92-362.84 n 物体的质量可以引起引力，09-01 13:46:29-09-01 13:46:31Objects can generate gravity.
132/271 363.02-364.1 jd 又可以产生惯性，09-01 13:46:30-09-01 13:46:31Can also generate inertia.
133/271 364.43-365.87 hp 这两个性质并不一样。09-01 13:46:30-09-01 13:46:33These two properties are not the same.
134/271 366.24-368.58 aaa 所以呢这两个质量也没有理由一定相等。09-01 13:46:31-09-01 13:46:33So, these two qualities cannot be necessarily equal.
135/271 369.0-370.62 n 然而根据实验的结果呢，09-01 13:46:31-09-01 13:46:34However, according to the results of the experiment,
136/271 370.74-372.54 n 他们又好像确实是相等的。09-01 13:46:32-09-01 13:46:34They seem to be equal.
137/271 372.97-374.05 jd 后面我们会看到啊，09-01 13:46:33-09-01 13:46:34We will see later.
138/271 374.35-376.15 aaa 引力质量与惯性质量相等，09-01 13:46:33-09-01 13:46:35Gravity mass and inertia mass are equal,
139/271 376.52-379.28 hp 其实是广义相对性原理的一个结论。09-01 13:46:34-09-01 13:46:38In fact, it is a conclusion of the General Theory of Relativity.
140/271 379.86-380.16 jd 有一天，09-01 13:46:35-09-01 13:46:36One day,
141/271 380.34-381.54 n 爱因斯坦坐在办公室里，09-01 13:46:35-09-01 13:46:37Einstein was sitting in his office,
142/271 381.659-382.98 n 又在思索眼力的问题。09-01 13:46:36-09-01 13:46:38Still pondering the issue of eyesight.
143/271 383.16-386.34 aaa 他看在窗外猛然想到了一件非常可怕的事儿，09-01 13:46:37-09-01 13:46:39He suddenly thought of something very terrible while looking out the window.
144/271 386.75-388.91 jd 如果一个人不慎从楼上跌落，09-01 13:46:37-09-01 13:46:39If someone accidentally falls from a building,
145/271 389.15-390.23 n 他会有什么感觉呢？09-01 13:46:38-09-01 13:46:39What will he feel?
146/271 390.53-390.95 bg 显然呢，09-01 13:46:39-09-01 13:46:53Obviously,
147/271 391.36-393.58 n 相对于地面人正在自由落体。09-01 13:46:39-09-01 13:46:41The person is falling freely.
148/271 394.12-395.8 hp 但是相对于人本身而言，09-01 13:46:40-09-01 13:46:43However, compared to humans themselves,
149/271 395.979-397.42 aaa 他会感觉自己飘起来了，09-01 13:46:41-09-01 13:46:42He will feel like he is floating.
150/271 397.65-399.81 n 就好像完全不受地球引力一样，09-01 13:46:41-09-01 13:46:44It's like being completely unaffected by the Earth's gravity,
151/271 400.05-401.43 jd 用牛顿定律来解释，09-01 13:46:42-09-01 13:46:43Explain using Newton's laws.
152/271 401.61-403.23 n 这叫做完全失重。09-01 13:46:43-09-01 13:46:44This is called weightlessness.
153/271 403.68-405.33 aaa 可是如果这个人闭上眼睛，09-01 13:46:43-09-01 13:46:45But if this person closes their eyes,
154/271 405.57-407.25 hp 周围也没有空气阻力的话，09-01 13:46:44-09-01 13:46:47If there is no air resistance around,
155/271 407.49-411.69 jd 他似乎也没有办法区分自己到底是受到引力并且下落，09-01 13:46:45-09-01 13:46:47He seemed to have no way to distinguish whether he was being affected by gravity and falling,
156/271 412.05-414.15 n 还是漂浮在茫茫的宇宙中，09-01 13:46:45-09-01 13:46:48Still floating in the vast universe,
157/271 414.82-419.68 n 仿佛向下的引力和向下的加速度效果可以抵消一样。09-01 13:46:46-09-01 13:46:49It seems as if the downward force and downward acceleration have canceled each other out.
158/271 420.26-421.34 aaa 爱因斯坦又想啊，09-01 13:46:47-09-01 13:46:47Einstein thought again,
159/271 421.58-423.02 hp 如果有人在宇宙飞船中，09-01 13:46:48-09-01 13:46:50If someone is in a spaceship,
160/271 423.38-425.3 jd 飞船航行在茫茫宇宙里，09-01 13:46:48-09-01 13:46:50The spaceship sailed through the vast universe,
161/271 425.6-428.06 aaa 原本呢人在太空飞船里是失重的，09-01 13:46:49-09-01 13:46:51Originally, people were in a state of weightlessness on the spaceship.
162/271 428.37-432.63 n 可是突然有一天他感觉自己被一股力量拉向了飞船的地面，09-01 13:46:50-09-01 13:46:53Suddenly, he felt a force pulling him towards the floor of the spaceship.
163/271 432.93-434.37 xss 这是什么原因造成呢？09-01 13:46:50-09-01 13:48:23What is the reason for this?
164/271 434.96-437.96 n 第一种可能是啊飞船正停在某个星球上，09-01 13:46:51-09-01 13:46:54One possibility is that the spaceship is currently docked at a planet.
165/271 438.42-439.68 jd 星球对人有引力。09-01 13:46:52-09-01 13:46:53Planets have gravity.
166/271 439.92-441.12 hp 那么在引力的作用下呢，09-01 13:46:52-09-01 13:46:56Then, under the influence of gravity?
167/271 441.3-442.98 aaa 人被拉向了飞船的地面。09-01 13:46:53-09-01 13:46:55People were pulled towards the ground of the spaceship.
168/271 443.62-447.3 jd 还有第二种可能飞船正航行在茫茫宇宙里，09-01 13:46:54-09-01 13:46:56There is another possibility that the spaceship is sailing through the vast universe.
169/271 447.48-448.74 de 周围并没有任何星球，09-01 13:46:54-09-01 13:47:16There are no planets around.
170/271 448.92-449.52 bg 对人有引力。09-01 13:46:55-09-01 13:47:25Attracts people.
171/271 449.92-453.04 n 但是呢飞船此刻正在有向上的加速度，09-01 13:46:56-09-01 13:46:58However, the spaceship is currently accelerating upwards.
172/271 453.48-456.36 n 于是相对于飞船人就会加速下落了。09-01 13:46:56-09-01 13:46:59Therefore, the spaceship will accelerate downwards.
173/271 456.71-459.41 aaa 也就是如果人感受到向下的力，09-01 13:46:57-09-01 13:46:58If a person feels an upward force,
174/271 459.83-463.07 hp 极有可能是因为受到了星球向下的引力，09-01 13:46:58-09-01 13:47:02It is likely that it was affected by the gravitational pull of a planet.
175/271 463.46-466.7 jd 也有可能是因为飞船具有向上的加速度。09-01 13:46:58-09-01 13:47:00It could also be because the spaceship has an upward acceleration.
176/271 467.29-469.39 aaa 如果这个人在飞船中不向外看，09-01 13:46:59-09-01 13:47:01If this person is in the spaceship and doesn't look outside,
177/271 469.69-472.99 n 他根本没有办法区分自己到底是哪种情况。09-01 13:47:00-09-01 13:47:03He couldn't tell what kind of situation he was in.
178/271 473.56-477.46 n 看起来啊静止在引力场中的飞船和没有引力场，09-01 13:47:00-09-01 13:47:05It seems that the spaceship is stationary in a gravitational field, while there is no gravitational field.
179/271 477.58-481.94 jd 但是有加速运动的飞船内部的物理规律呢是完全相同的。09-01 13:47:01-09-01 13:47:03However, the physical laws inside the accelerating spaceship are completely the same.
180/271 482.27-482.75 aaa 想到这里，09-01 13:47:02-09-01 13:47:03Thinking of this,
181/271 482.99-483.95 n 爱因斯坦顿悟了，09-01 13:52:03-09-01 13:52:04Einstein realized,
182/271 484.45-485.77 hp 物体处于引力场中，09-01 13:47:03-09-01 13:47:06Objects are in a gravitational field.
183/271 486.13-487.03 aaa 等效于物体，09-01 13:47:04-09-01 13:47:05Equivalent to an object,
184/271 487.15-488.53 jd 具有一个相反的加速度。09-01 13:47:04-09-01 13:47:06Has an opposite acceleration.
185/271 488.86-492.22 n 这就是爱因斯坦在一九零七年提出的等效原理，09-01 13:47:05-09-01 13:47:10This is Einstein's principle of equivalence, which he proposed in 1907.
186/271 492.96-495.12 n 引力大小正比于物体的引力质量，09-01 13:47:06-09-01 13:47:10The magnitude of the gravitational force is proportional to the mass of the object.
187/271 495.42-499.44 aaa 而加速度产生的等效引力呢正比于物体的惯性质量，09-01 13:47:06-09-01 13:47:09And the equivalent gravity produced by acceleration is proportional to the object's inertia mass.
188/271 499.79-502.01 jd 又因为引力质量等于惯性质量，09-01 13:47:07-09-01 13:47:09Because the gravitational mass is equal to the inertial mass,
189/271 502.24-506.89 hp 所以真实的引力才能和加速度产生的等效引力是一样大的。09-01 13:47:08-09-01 13:47:13Therefore, the real gravitational force must be equal to the equivalent gravitational force produced by acceleration.
190/271 507.32-508.1 jd 按照等效原理，09-01 13:47:10-09-01 13:47:11According to the principle of equivalence,
191/271 508.34-512.54 aaa 爱因斯坦想到了与牛顿定律不相同的关于惯性参考系的看法。09-01 13:47:10-09-01 13:47:13Einstein came up with a different view of inertial reference frames that differed from Newton's.
192/271 513.22-515.26 de 如果一个人站在地面上静止不动，09-01 13:47:11-09-01 13:47:51If a person is standing on the ground and not moving,
193/271 515.56-516.88 n 另外一个人呢自由落体，09-01 13:47:12-09-01 13:47:14Another person is falling freely.
194/271 517.26-518.16 n 他们谁是惯性呢？09-01 13:47:12-09-01 13:47:14Who are the ones who exhibit inertia?
195/271 518.4-520.62 jd 我们先来看站在地面上静止的人，09-01 13:47:13-09-01 13:47:15Let's first look at the person standing on the ground,
196/271 521.05-522.01 aaa 按照牛顿定律啊，09-01 13:47:14-09-01 13:47:16According to Newton's laws,
197/271 522.19-524.59 n 这个人受到向下的引力和向上的支持力，09-01 13:47:15-09-01 13:47:18This person is subject to both downward and upward forces.
198/271 525.09-525.87 n 合力呢是零，09-01 13:47:16-09-01 13:47:17The sum is zero.
199/271 526.17-527.25 jd 所以应该是惯性的。09-01 13:47:16-09-01 13:47:18So it should be inertia.
200/271 527.69-529.31 aaa 可是按照广义相对论呢，09-01 13:47:17-09-01 13:47:19However, according to the theory of general relativity,
201/271 529.8-530.76 n 向下的引力，09-01 13:47:18-09-01 13:47:19Gravity,
202/271 531.0-532.68 de 等效于向上的加速度，09-01 13:47:19-09-01 13:47:37Equivalent to upward acceleration,
203/271 533.04-536.4 hp 我们完全可以认为这个人只受到地面的支持力。09-01 13:47:19-09-01 13:47:24We can completely assume that this person is only supported by the ground.
204/271 536.76-538.38 jd 同时正在向上加速，09-01 13:47:20-09-01 13:47:21While simultaneously accelerating upwards,
205/271 538.74-540.18 n 所以他不是惯性的。09-01 13:47:21-09-01 13:47:23Therefore, he is not inertial.
206/271 540.41-541.76 n 我们再来看自由落体的人，09-01 13:47:21-09-01 13:47:24Let's take a look at the person falling freely.
207/271 542.28-543.42 aaa 按照牛顿定律呢，09-01 13:47:22-09-01 13:47:23According to Newton's laws,
208/271 543.66-546.42 jd 这个人受到引力具有向下的加速度，09-01 13:47:23-09-01 13:47:24This person is experiencing a gravitational acceleration that is directed downwards.
209/271 546.6-547.98 n 所以肯定是非惯性的。09-01 13:52:24-09-01 13:52:26Therefore, it must be inertial.
210/271 548.31-549.93 n 但是按照广义相对论呢，09-01 13:47:24-09-01 13:47:26However, according to the theory of general relativity,
211/271 550.29-553.23 aaa 向下的引力等效于向上的加速度，09-01 13:47:25-09-01 13:47:27The downward gravitational force is equivalent to an upward acceleration.
212/271 553.56-554.88 n 那么两个加速度抵消，09-01 13:47:25-09-01 13:47:27Then the two accelerations cancel each other out.
213/271 555.18-556.44 hp 这个人就没有加速度了。09-01 13:47:26-09-01 13:47:29This person has no acceleration.
214/271 556.94-557.9 jd 或者说反过来啊，09-01 13:47:27-09-01 13:47:28Or, conversely,
215/271 558.2-560.48 bg 向下的加速度等于向上的引力，09-01 13:47:27-09-01 13:48:08The downward acceleration is equal to the upward gravitational force.
216/271 560.78-561.74 n 两个引力抵消，09-01 13:47:28-09-01 13:47:29Two forces cancel each other out,
217/271 561.98-563.06 aaa 这个人也没有受力，09-01 13:47:29-09-01 13:47:30This person didn't get any support.
218/271 563.59-564.55 n 这个人既不受力，09-01 13:47:29-09-01 13:47:31This person is weak and unable to support themselves.
219/271 564.79-565.569 jd 也没有加速度，09-01 13:47:30-09-01 13:47:31No acceleration,
220/271 565.81-568.51 hp 所以自由落体的人才是惯性的。09-01 13:47:31-09-01 13:47:34Therefore, the person in free fall is experiencing inertia.
221/271 568.9-570.7 n 所以啊按照广义相对论，09-01 13:47:31-09-01 13:47:33So, according to the theory of general relativity,
222/271 570.879-573.7 aaa 我们反而需要给出完全不同的惯性系定义。09-01 13:47:32-09-01 13:47:34We need to give a completely different definition of inertia.
223/271 574.12-575.02 jd 除了引力之外，09-01 13:47:32-09-01 13:47:34In addition to gravity,
224/271 575.14-577.06 n 不再受到其他任何力的作用，09-01 13:47:33-09-01 13:47:35No longer affected by any other forces,
225/271 577.3-580.24 n 而且不旋转的物体处于惯性状态。09-01 13:47:34-09-01 13:47:36And objects at rest are in a state of inertia.
226/271 581.02-583.84 jd 现在我们可以回答最开始提出的问题了。09-01 13:47:35-09-01 13:47:36Now we can answer the question that was originally asked.
227/271 584.41-586.69 aaa 在一系列加速运动的火车中，09-01 13:47:35-09-01 13:47:37In a series of accelerating trains,
228/271 586.93-590.11 hp 物理规律为什么与匀速运动的火车是一样的呢？09-01 13:47:36-09-01 13:47:41Why are the laws of physics the same as those for a train moving at a constant speed?
229/271 590.46-591.36 n 我们可以这样理解，09-01 13:47:37-09-01 13:47:38We can understand it like this,
230/271 591.83-593.33 n 当火车加速的时候，09-01 13:47:37-09-01 13:47:39When the train accelerates,
231/271 593.57-595.01 jd 具有了向前的加速度，09-01 13:47:38-09-01 13:47:39has gained forward acceleration,
232/271 595.48-598.06 aaa 等效于车厢中存在向后的引力。09-01 13:47:39-09-01 13:47:41Equivalent to the presence of a backward force inside the compartment.
233/271 598.67-600.89 de 如果我们把这个引力考虑进去的话，09-01 13:47:39-09-01 13:48:08If we take this gravity into account,
234/271 601.07-605.57 n 那么车厢中的小球向后加速运动就是符合物理规律的。09-01 13:47:40-09-01 13:47:44Then the movement of small balls in the car towards backward is consistent with physical laws.
235/271 606.02-609.2 n 所以啊你把加速度等效成反向的引力，09-01 13:47:41-09-01 13:47:44So, you're treating acceleration as an inverse gravity.
236/271 609.44-611.48 jd 那么无论在何种参考系中，09-01 13:47:42-09-01 13:47:43So, regardless of the reference frame,
237/271 611.72-613.7 aaa 物理规律都是完全相同的。09-01 13:47:42-09-01 13:47:44The physical laws are all the same.
238/271 613.94-617.78 hp 不过呢引力和加速度等效却又不完全是相同的东西。09-01 13:47:43-09-01 13:47:47However, gravity and acceleration are equivalent but not exactly the same thing.
239/271 618.27-620.01 jd 比如说一个星球的引力，09-01 13:47:44-09-01 13:47:45For example, the gravity of a planet,
240/271 620.189-622.65 aaa 往往是有心力引力场呢都是向心的。09-01 13:47:44-09-01 13:47:46Often, there is an attractive force between them.
241/271 623.07-625.35 n 但是啊如果有一个飞船匀加速运动，09-01 13:47:45-09-01 13:47:48But, if a spaceship is accelerating uniformly,
242/271 625.53-628.17 n 那么它产生的等效引力都是平行的。09-01 13:47:46-09-01 13:47:48Then the equivalent gravitational forces produced are parallel.
243/271 628.58-631.1 jd 所以啊我们只能在一个无穷小的点上，09-01 13:47:47-09-01 13:47:49So, we can only focus on an infinitely small point.
244/271 631.52-632.72 aaa 引力和加速度是等效，09-01 13:47:47-09-01 13:47:49Gravity and acceleration are equivalent.
245/271 632.9-633.8 hp 而且无法区分的。09-01 13:47:48-09-01 13:47:50And indistinguishable.
246/271 634.19-636.71 n 但如果我们考虑一个范围内的引力线，09-01 13:47:49-09-01 13:47:52However, if we consider a range of gravitational lines,
247/271 637.01-638.81 n 还是可以区分这种引力，09-01 13:47:50-09-01 13:47:52It is still possible to distinguish this gravity,
248/271 638.99-640.19 aaa 究竟是真实的引力，09-01 13:47:50-09-01 13:47:51Is it really gravity,
249/271 640.43-642.47 jd 还是加速度等效出的引力？09-01 13:47:51-09-01 13:47:52Is it equivalent to acceleration?
250/271 642.65-643.67 n 我们做一个比方吧，09-01 13:52:53-09-01 13:52:55Let's make an analogy,
251/271 643.97-644.81 hp 有人努力工作，09-01 13:47:53-09-01 13:47:55Some people work hard,
252/271 644.99-646.07 de 有人坑蒙拐骗，09-01 13:47:53-09-01 13:48:16Some people are cheating and deceiving.
253/271 646.25-647.03 aaa 他们都赚了钱。09-01 13:47:54-09-01 13:47:55They all made money.
254/271 647.52-649.83 n 那么在某一个时刻花起来是等效的，09-01 13:47:55-09-01 13:47:57So, at some point the cost is equivalent.
255/271 650.21-652.01 n 但是啊他们依然有所不同。09-01 13:47:55-09-01 13:47:57But they are still different.
256/271 652.31-653.15 jd 努力工作的人，09-01 13:47:56-09-01 13:47:57Hardworking people,
257/271 653.33-654.11 hp 钱是合法的，09-01 13:47:57-09-01 13:47:59Money is legal.
258/271 654.51-655.59 aaa 受到法律的保护，09-01 13:47:58-09-01 13:47:58Protected by law,
259/271 656.08-657.94 jd 坑蒙拐骗来的钱呢是违法的，09-01 13:47:58-09-01 13:48:00Money obtained through deception and fraud is illegal.
260/271 658.12-659.08 n 受到法律的制裁。09-01 13:47:59-09-01 13:48:00Subject to legal sanctions.
261/271 659.59-661.33 n 如果我们持续观察这两个人，09-01 13:48:00-09-01 13:48:02If we continue to observe these two people,
262/271 661.51-663.94 aaa 你就会发现其中有一个人越来越有钱。09-01 13:48:00-09-01 13:48:02You will find that one person is getting richer and richer.
263/271 664.12-665.62 hp 而另外一个人锒铛入狱，09-01 13:48:01-09-01 13:48:04And another person was imprisoned.
264/271 665.86-667.9 jd 我们还是可以区分出这两个人来。09-01 13:48:02-09-01 13:48:03We can still distinguish between the two people.
265/271 668.3-671.09 n 而且呀眼力会造成时空弯曲加速度，09-01 13:48:03-09-01 13:48:06And, the ability to see can cause spacetime curvature and acceleration.
266/271 671.21-672.47 n 并不会造成时空弯曲，09-01 13:48:03-09-01 13:48:05It will not cause spacetime curvature.
267/271 672.71-675.53 aaa 而是让平直时空的坐标系发生了弯曲。09-01 13:48:04-09-01 13:48:06Instead, the coordinate system of flat spacetime is warped.
268/271 676.06-677.8 jd 那么什么是时空弯曲呢？09-01 13:48:05-09-01 13:48:06So, what is spacetime curvature?
269/271 677.98-680.32 hp 这就是我们下一节课要讨论的内容了。09-01 13:48:05-09-01 13:48:09That's what we will be discussing in the next lesson.
270/271 680.74-681.04 n 关注我，09-01 13:48:06-09-01 13:48:07Follow me,
271/271 681.16-682.54 n 和我一起慢谈相对的。09-01 13:48:07-09-01 13:48:09Let's have a leisurely conversation about relativity.