![](https://images.ecency.com/DQmPkGr1zzrTjYmsqqqjZb1K4DqA56qMjwSz5WzTp7aQ1oL/image.png) > 题图:Cheva 用AI创作 物理学的两大支柱之一——广义相对论,也是众多科普文章和视频乐衷于介绍的。但是和量子力学一样,广义相对论所展现出的时空观,与牛顿的时空观大相径庭,完全不符合人类的直觉。所以科普作品中,都会使用一些人们日常生活中,能够见到的事物进行类比和比喻。 因为爱因斯坦本人和其他一些科学牛都说过广义相对论告诉我们:质量可以让时空弯曲,而引力就是弯曲时空所造成的假象,比如著名的科学家惠勒,就曾简单的总结:“广义相对论就是——质量告诉时空如何弯曲,弯曲的时空告诉质量如何运动。”所以很多科普作品,都把时空比喻成有弹性的膜,而质量就是重物,比如大铅球,把一个大铅球放到弹性膜上,本来是一个二维平面的弹性膜,就会像三维空间凹陷,形成一个曲面,而原本在弹性膜上可以沿直线运动的很轻的小弹珠,这时就会沿曲线运动,这就是引力。虽然这个比喻把抽象的,由数学公式构成的广义相对论,表现得非常直观,普通人也可以理解。但本身却是并不准确的,广义相对论的很多其他性质,不能从这个类比中推导出来。而且最大的问题就是,它有点像循环论证,它本身是想要解释引力如何产生的,而有质量的铅球,本身就是在引力的作用下,让弹性膜凹陷的。 昨天在油管上看到一个很有趣的科普视频,它用了一种新的,在其他科普作品中未曾见过的类比来解释广义相对论和引力如何产生,让很多问题变得更加清晰了。这个模型就是河流模型。 其实看似复杂深奥的广义相对论,爱因斯坦推导它的逻辑起点,却是非常简单——就是等效原理。所谓等效原理就是引力和加速度其实是一回事。如果把你关在一个没有窗户的箱子里,然后把这个箱子放在地球上,或者放到太空中,但是给箱子装上火箭发动机,让箱子以9.8米/平方秒的加速度,加速飞行。你在箱子里面观察到的所有现象都将是一样的,苹果会落向地面,你蹦起来也会落回原地,你无法区分,你到底是在地球上还是在太空中,这就是等效原理。然后他进一步思考,如果一个人从很高的大楼上坠落,他会体验到什么呢?——虽然这是一个有点残酷的思想实验,但是他却启发了二十世纪最伟大的科学发现——当一个人从高楼上坠落的时候,他会体验到失重,这种感觉就像在太空中不受引力的束缚是一样的。这说明当一个自由下落的物体作为参照物建立参照系,和一个匀速直线运动的惯性参考系是一样的,也就是说,自由下落的时空和漂浮在没有星球的虚无时空是一样的,都会体验到失重。而从高楼上落下的人最后都会重重地摔到地上。与一般的直觉理解,是人加速撞向地面不同,以等效原理来思考这个场景,人在坠落过程中其实和在宇宙空间中漂浮是一回事,之所以会摔到地上,不是人在加速向下,而是地面在加速冲上天去,撞到了漂浮状态的人。 但是毕竟向地球这样大质量的物体并没有爆炸,所以更好的理解和比喻应该是,时空网格就像水流一样,向着有质量的区域流动,像地球这样巨大的星球,就像水槽中的排水口,四面八方的水流都向它流动,而引力就代表着水面上的船只,或漂浮物被水流所牵引而做出的运动。 这个模型可以很简单很直观地解释很多和重力有关的现象,比如,在比较火的国产科幻片《流浪地球》的两部系列电影中都出现了,“洛西极限”的概念,《洛西极限》——就是当一个质量较小的星球,接近一个质量较大的星球,到达一定的范围内,就会被潮汐力扯得粉碎。用水流模型就很容易解释这两种现象,想象地球就是水槽中的排水孔,越靠近排水孔水流速度就会越快,而离排水孔越远的地方水流速度就会慢下来。因此一个处在这样的水面上的船只,它面向排水孔的一面将受到更大的牵引力,而远离排水孔的一面,因为水流速度较小,受到的牵引力也较小,这样就会对船体产生一个拉扯的力量。 然后黑洞也很容易理解了,黑洞就像是一个瀑布——飞流直下三千尺,在瀑布的某个区域,水流速度快到了和光速一样,这个地方就是事件视界,就是光子也无法逃离出来。当然在这个越过事件视界之后,如果继续按照水流模型来推理的话,在事件视界的内部,也就是我们俗称的黑洞内部,时空的移动速度应该是超过光速的。因此我曾经产生过这样一个想法,如果一个人掉进了黑洞里面,那他是不是就可以追上光速。按照狭义相对论,那他就回到过去了呢?我去问过GPT-4这个问题,也许这个河流模型还是很新颖的,GPT4模型似乎并不知道,只是说不能将广义相对论中的引力场比喻成水流。不过看过这个油管视频之后,我认为想通了这个问题,答案也许并不是那么复杂。其实这就有点像双生子佯谬等相对论的现象。落入黑洞内部会超光速,只是相对于我们这些在黑洞外静止的观测者。对落入黑洞的人来说,他和他周围的一部分时空始终是处于惯性运动的状态,就像漂浮在虚空中一样,而狭义相对论已经给出了答案,相对任何惯性参考系,光速都是不变的。所以落入黑洞的人并不会追上光速,回到过去。其实相对论中很多这样的例子,选择的参考系不一样,得到的结论也会不同。而且事件视界实际上隔绝了黑洞的内部和外部,落入黑洞的人永远不可能再出来,所以尽管与黑洞外的观测者的观察相矛盾,这样的矛盾并不会给宇宙的的稳定带来什么问题。
author | cheva |
---|---|
permlink | d07a803bd8586 |
category | hive-105017 |
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created | 2023-06-08 10:20:54 |
last_update | 2023-06-08 11:23:45 |
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body_length | 2,166 |
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root_title | 更好理解广义相对论的类比——河流模型 |
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randomblock1 | 0 | 1,386,275,356 | 20% | ||
rivalhw | 0 | 2,110,806,055,440 | 100% | ||
theb0red1 | 0 | 64,376,687,894 | 20% | ||
mikehere | 0 | 4,399,337,296 | 20% | ||
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esteemapp | 0 | 36,316,936,928 | 17.47% | ||
bigtakosensei | 0 | 22,313,185,459 | 20% | ||
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sixexgames | 0 | 1,006,742,423 | 10% | ||
bloghound | 0 | 1,060,819,455 | 3.49% | ||
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sharkface | 0 | 21,292,015,557 | 20% | ||
sames | 0 | 7,267,949,179 | 20% | ||
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mrpointp | 0 | 39,981,660,959 | 10% | ||
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otage | 0 | 7,225,384,867 | 20% | ||
cn-reader | 0 | 16,833,242,136 | 50% | ||
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mrspointm | 0 | 54,353,019,054 | 10% | ||
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chimzycash | 0 | 5,417,569,144 | 20% | ||
davidke20 | 0 | 7,704,138,359 | 5% | ||
sorin.cristescu | 0 | 33,158,940,042 | 8.73% | ||
mawit07 | 0 | 11,013,401,734 | 5% | ||
jasonmunapasee | 0 | 7,216,840,807 | 20% | ||
esteem.app | 0 | 4,351,390,773 | 17.47% | ||
jaforce | 0 | 8,503,225,342 | 20% | ||
jychbetter | 0 | 62,981,616,246 | 10% | ||
winniex | 0 | 37,969,242,904 | 10% | ||
dbooster | 0 | 75,014,728,630 | 20% | ||
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myach | 0 | 3,650,700,137 | 20% | ||
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windowglass | 0 | 54,250,595,857 | 10% | ||
elderson | 0 | 15,023,850,876 | 20% | ||
auleo | 0 | 4,101,665,037 | 10% | ||
cheva | 0 | 66,325,617,466 | 20% | ||
slacktmusic | 0 | 3,612,365,461 | 20% | ||
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aliakbar2 | 0 | 69,748,788,937 | 20% | ||
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badmusgreene | 0 | 1,413,708,681 | 20% | ||
sanach | 0 | 9,358,565,697 | 20% | ||
cherryng | 0 | 5,155,005,018 | 10% | ||
nostalgic1212 | 0 | 57,787,970,652 | 10% | ||
moeenali | 0 | 139,312,901,833 | 20% | ||
funkymunky20000 | 0 | 2,657,265,310 | 20% | ||
damajicman3 | 0 | 556,450,208 | 20% | ||
robomode | 0 | 886,220,660 | 20% | ||
makingthebest09 | 0 | 1,283,612,383 | 20% | ||
randumb | 0 | 3,033,519,160 | 15% | ||
altcoinbandit | 0 | 874,255,807 | 100% | ||
babarakas43 | 0 | 14,609,576,473 | 20% | ||
indiebandguru | 0 | 1,307,458,847 | 10% | ||
rativiv | 0 | 555,315,493 | 20% | ||
vonaurolacu | 0 | 6,537,005,901 | 10% | ||
greendeliverence | 0 | 10,279,036,460 | 20% | ||
truce | 0 | 642,165,080,005 | 20% | ||
hypersonic1 | 0 | 60,804,965,908 | 20% | ||
mimidee74 | 0 | 4,418,765,807 | 20% | ||
aellly | 0 | 26,632,135,501 | 10% | ||
thomasbrown | 0 | 27,558,461,813 | 20% | ||
yameen | 0 | 7,245,403,678 | 20% | ||
pasie15 | 0 | 865,744,205 | 20% | ||
elizabeth-22 | 0 | 518,950,022 | 10% | ||
headcrypto | 0 | 3,309,141,814 | 20% | ||
lordgod | 0 | 1,241,445,519 | 20% | ||
softmetal | 0 | 1,199,693,778 | 20% | ||
rightwing670 | 0 | 47,232,798,452 | 20% | ||
ragnar94 | 0 | 3,929,462,839 | 20% | ||
archisteem | 0 | 1,252,143,587 | 7.5% | ||
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byebyehamburgers | 0 | 17,133,803,920 | 20% | ||
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ireenchew | 0 | 12,142,076,424 | 20% | ||
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julian2013 | 0 | 6,092,854,339 | 10% | ||
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justinchicken | 0 | 2,310,849,740 | 20% | ||
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alokkumar121 | 0 | 175,669,877,315 | 20% | ||
marfonso | 0 | 22,722,818,109 | 20% | ||
tangela | 0 | 526,072,670 | 10% | ||
cherryzz | 0 | 9,618,660,732 | 10% | ||
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minhaz007 | 0 | 1,725,303,302 | 20% | ||
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nureza | 0 | 1,560,467,014 | 20% | ||
nworb | 0 | 12,623,513,884 | 20% | ||
solaiman | 0 | 7,560,333,544 | 20% | ||
unitqm | 0 | 1,235,799,127 | 10% | ||
brucutu | 0 | 15,467,215,800 | 20% | ||
ferrate | 0 | 18,634,107,670 | 20% | ||
bittrio | 0 | 7,299,124,279 | 20% | ||
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cryptovues | 0 | 11,122,061,895 | 20% | ||
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apokruphos | 0 | 9,279,653,352 | 3% | ||
snuff1 | 0 | 611,476,086 | 20% | ||
brada2550 | 0 | 1,161,170,305 | 20% | ||
paleotwist | 0 | 5,421,151,075 | 20% | ||
zellypearl | 0 | 20,314,493,209 | 20% | ||
hans001 | 0 | 1,998,589,164 | 20% | ||
foreversteem | 0 | 1,686,983,232 | 20% | ||
ano123 | 0 | 147,969,229,396 | 20% | ||
q-news | 0 | 1,555,518,686 | 20% | ||
coreyssteemit77 | 0 | 2,245,225,099 | 20% | ||
backscratcher | 0 | 9,327,061,087 | 20% | ||
rocketpower | 0 | 2,637,000,447 | 100% | ||
photographercr | 0 | 8,173,259,284 | 3.49% | ||
curtley | 0 | 484,760,481 | 100% | ||
red-devils | 0 | 760,731,480 | 20% | ||
moro1992 | 0 | 1,570,189,945 | 20% | ||
xyzxyz | 0 | 9,573,814,055 | 20% | ||
evanstinger | 0 | 8,599,335,639 | 20% | ||
ying82 | 0 | 9,993,602,922 | 10% | ||
aekraj | 0 | 20,928,050,009 | 20% | ||
h-hamilton | 0 | 7,270,871,778 | 20% | ||
supremebape | 0 | 40,250,688,224 | 20% | ||
kryptoking1 | 0 | 11,393,828,158 | 20% | ||
atyh | 0 | 29,369,437,447 | 10% | ||
naej | 0 | 3,911,080,312 | 20% | ||
bo022 | 0 | 6,116,406,400 | 20% | ||
photosnap | 0 | 1,089,000,029 | 20% | ||
kgsupport | 0 | 943,334,770 | 20% | ||
sandyo | 0 | 621,705,204 | 20% | ||
lovequeen | 0 | 31,113,007,856 | 10% | ||
luckyali | 0 | 284,624,486,397 | 20% | ||
blackgeek | 0 | 924,347,122 | 20% | ||
ecency | 0 | 4,451,818,621,106 | 17.47% | ||
balvinder294 | 0 | 983,437,218 | 10% | ||
jsalvage | 0 | 446,537,414 | 10% | ||
cronicasdelcesar | 0 | 3,497,117,124 | 100% | ||
ecency.stats | 0 | 5,337,146,887 | 17.47% | ||
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evahe | 0 | 26,356,129,529 | 10% | ||
aceh-media | 0 | 747,920,584 | 20% | ||
hivevote | 0 | 3,438,276,060 | 10% | ||
jingjing1616 | 0 | 102,872,936,094 | 100% | ||
borniet | 0 | 3,938,059,324 | 10% | ||
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ericaliu | 0 | 4,269,918,555 | 10% | ||
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everlandd | 0 | 2,672,534,465 | 10% | ||
celeste413 | 0 | 6,486,674,630 | 7.5% | ||
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waivio.curator | 0 | 1,549,692,021 | 2.97% | ||
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sagarkothari88 | 0 | 64,030,399,889 | 5% | ||
waliphoto | 0 | 1,113,592,064 | 20% | ||
sam9999 | 0 | 1,717,832,612 | 10% | ||
joelibra | 0 | 8,313,116,087 | 20% | ||
alex2alex | 0 | 1,015,801,470 | 3.49% | ||
kathyto | 0 | 3,979,212,351 | 10% | ||
cryoverall | 0 | 818,842,680 | 50% | ||
mukadder | 0 | 1,621,070,516 | 8.73% | ||
huolian | 0 | 7,393,847,441 | 20% | ||
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beauty197 | 0 | 616,839,969 | 8.73% | ||
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lifang123 | 0 | 1,963,185,614 | 10% | ||
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richardlin | 0 | 1,724,531,129 | 10% | ||
faiz1971 | 0 | 71,771,245,343 | 20% | ||
did-mini | 0 | 2,207,279,156 | 100% |