科学家们发现: 万有引力根本就不是一种力

原作者：
来源New Theories Test Our Understanding of Nature’s Most Elemental Force | Popular Science
译者zenerna

No one has ever quite nailed down gravity. Newton saw that bodies appeared to attract each other even at a great distance, and from this observation was able to construct a mathematical formula that predicted the motion of the planets with astonishing accuracy. Einstein improved on that definition by stating that massive objects attract lesser ones by bending the space around them—like how a bowling ball deforms the surface of a trampoline so that a marble will roll toward it—and based on this insight was able to construct his theory of general relativity, which proved to be even more elegant and predictive.

      在牛顿（Newton）创造相对论之前，从没有人曾十分准确的定义过万有引力（gravity）。牛顿发现物体（body）彼此之间会产生相互吸引，甚至在距离十分遥远的天体间也存在着这种相互吸引。并且在他的观察结果之上能够构造出一个用来预测星球运动的数学方程式（mathematical formula），该方程预测的结果的准确度令人感到惊奇。爱因斯坦（Einstein）在那个方程的基础上又做了进一步的改进，他规定质量非常大的物体（massive object）通过将围绕它的空间进行一定程度的弯曲来吸引质量小的物体——就像在保龄球这个项目中将球道变形到一定的程度，以便大理石做的保龄球可以沿着它滚向球瓶——并且在这个见解上可以构造出他的著名的广义相对论（General relativity）理论，该理论后来被世人证明是非常的简洁且极具预测性的物理界重大理论基石。

But not perfect. Einstein’s theory posits that the universe is expanding such that each object is moving away from everything else, which Hubble Space Telescope observations have confirmed. Yet for this theory to hold, it requires a far more complicated conclusion: If everything is moving apart as it goes forward in time, then at some moment everything in the universe must have been gathered into a single point.

      但是，他的广义相对论并不是完美无缺的。爱因斯坦在其理论中假定宇宙是不断扩张的，以致于每个物体都会远离其他的物体。他的这个假定后来被哈勃太空望远镜（Hubble Space Telescope）的观察所证明。然而为了保证这个理论依然有效，它需要得出一个远比这复杂的结论：如果随着时间的推移，物体间不断的相互分离，那么在某一瞬间宇宙的所有物体必然曾经聚集成过一个点。

The problem, which has challenged theorists for nearly a century, is that Einstein constructed several specific mathematical formulas from his general theory, and they have proved accurate in describing nearly everything—except the proposed origins of the universe itself. When mathematicians reverse the theory to repackage the universe as it was before the big bang, the math produces something infinitely small and dense. This “singularity” is a common sign that something in the equation is amiss. “Physicists don’t like infinite numbers because they imply a solution that isn’t very physical,” says Nikodem Poplawski, a gravitational theorist at Indiana University. But this summer, two physicists may have figured out how to bring order to Einstein’s universe.

      但问题是爱因斯坦在他的广义相对论的基础上又构造出了几个具体的数序方程式，这些方程被证明在描述几乎所有物体时都是对的——除了被提及的宇宙的来源本身。这个问题萦绕在理论家们的心间已经近一个世纪了。当数学家们用“就像在大爆炸（Big Bang）之前宇宙被重新包裹（repackage）”将这个理论推翻后，这个数学方程式演算出了一个无限小且密度无限大的东西。这个“奇点”（singularity）就是证明广义相对论方程是错误的最普通的标志。“物理学家们都不喜欢‘无穷数’（infinite number）这个概念，因为他们暗示如果这样的话，那么这个解（solution）就不是物理意义上的解，”Nikodem Poplawski（印第安纳大学（Indiana University）万有引力理论家）表示。但是这个夏天，两位物理学家可能已经计算出如何将秩序（order）带到爱因斯坦所描述的宇宙世界中。

Astrophysicists Maximo Bañados and Pedro Ferreira of the University of Oxford replaced the Einstein-Hilbert action—the equation from which all of general relativity’s other equations are derived—with a modified Born-Infeld action, which describes electromagnetism. With Born-Infeld conditions in place, Ferreira and Bañados were able to replicate Einsteinian gravity in normal situations, and they were also consistent with the conditions scientists have observed about the origins of the universe.

  

Pedro Ferreira proposes modifying Einstein’s theory of relativity by limiting gravity’s pull.  Oxford University

Pedro Ferreira建议通过限制万有引力的吸引力对爱因斯坦的广义相对论进行修改。

      两位来自牛津大学（University of Oxford）的天体物理学家Maximo Bañado和Pedro Ferreira用“伯恩-英菲尔德作用量”（Born-Infeld action，用来描述电磁）代替“爱因斯坦-希尔伯特作用量”（Einstein-Hilbert action，其他所有的广义相对论方程都是从这个方程中演变而来），如果伯恩-英菲尔德的条件得到满足，那么二人就能在正常条件下重现爱因斯坦的万有引力模型，并且他们也能将其与科学家们已经观察到的关于宇宙来源的情况保持一致。

According to Ferreira and Bañados, gravity is not strong enough to crumple the universe’s mass into an infinitely dense point, but with the limit they placed on gravity, it could have compressed the universe into an extremely small ball.

      据Ferreira和Bañados表示，万有引力的力度还不能能将宇宙的质量压缩成一个密度无穷大的点，但是如果加上他们给万有引力的设定的限定条件，它就能将宇宙压缩成一个非常小的球体。

Rather than emerging from a point, that ball may have been the densest part of an ongoing process, in which a previous universe had collapsed in on itself, “bounced” against the limits of density, and then expanded again to become our current universe. Or, after its initial growth, the universe may have paused before expanding as it does today. Future analysis of gravitational waves left over from the early universe could validate the work, Ferreira says. “Einstein’s theory is simpler,” he admits. “But sometimes the simplest idea isn’t the best one.”

      与其说宇宙来源自一个点，倒不如说是来源于那个球在不断发展的过程中可能是密度最大的时候，在那一刻以前的宇宙本身已经收缩完成，在达到密度的极限时被“弹回”（bounced），接着宇宙再一次扩张成我们现在生活的宇宙。或者，在宇宙开始扩张后的某一时刻，也就是说该时刻在宇宙扩张成今天这个样子之前，宇宙已经停顿下来。Ferreira表述，进一步对早期宇宙留下来的万有引力波（gravitational waves）进行分析证明它是对的。他承认“爱因斯坦的理论是简单，但有时最简单的想法不是最好的想法。”

“It’s a good step toward improving our understanding of gravity,” Poplawski says. But as it stands, the theory is less developed than other alternatives to Einstein’s gravity. There’s gravity in higher dimensions, gravity with extra curvature terms, and gravity coupled to a ‘chameleon field’ that makes the strength of gravity different near matter than in a vacuum. The recent appearance of so many theories may be a sign of a field on the verge of a breakthrough. Indeed, Erik Verlinde of the University of Amsterdam argues that gravity is not a force at all but rather an “emerging condition.” As he told the New York Times in July, “For me, gravity doesn’t exist.”

 

Erik Verlinde表示万有引力根本就不是一种力。

     Poplawski表示“这对改进我们对万有引力的理解是相当有用的一步”。但是就这个理论本身的所表述的观点来说，和其它的从爱因斯坦的万有引力发展而来的理论的发展来比，这个理论的发展较小。我们经常提到的是一个更广意义上的万有引力，一个与附加曲率项（extra curvature terms）有关的和与“chameleon field”（它能使物体间的万有引力在真空中和一般条件下的力度大小不同）相结合的万有引力。实际上，阿姆斯特丹大学（University of Amsterdam）的Erik Verlinde一直认为万有引力根本就不是一种力，恰相反的是它是一个“发生的条件”（emerging condition）。正像他对纽约时报（New York Times）所说的一样“对于我来说，万有引力根本不存在”。最近出现了许多关于万有引力的新理论，这或许是在某个领域将有重大突破的一个信号。