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Why The Speed of Light Matters
为什么光速是至关重要的？
Wynne Parry, LiveScience Senior Writer
怀恩·帕里（Wynne Parry）LiveScience的资深作家
Date: 26 September 2011 Time: 05:01 PM ET
2011年9月26日，美国东部时间：下午05:01
Einstein's theory of special relativity sets of the speed of light, 186,000 miles per second (300 million meters per second), as a cosmic speed limit. Some researchers think they may have broken this limit, and the implications are mind bending.
爱因斯坦的狭义相对论把光速定位在每秒186,000英里（每秒300,000米），并把它作为宇宙的速度限制。可是某些研究人员却认为，他们可能已经打破了这个限制，然而其含意却是离奇古怪令人费解的。
提供者：威廉·迪杰斯特拉（Willem Dijkstra），图片素材
CREDIT: Willem Dijkstra, Shutterstock
When physicists announced last week that they had detected subatomic particles, called neutrinos, that appeared to be traveling faster than the speed of light, it seemed to be an exception to a cosmic speed limit set by Albert Einstein's special theory of relativity.
物理学家于上星期宣布，他们发现了称为中微子的亚原子粒子，其行驶的速度超过了光速，这似乎是爱因斯坦狭义相对论所确定的宇宙速度限制的一个例外情况。
Einstein's theory, which he proposed in 1905, describes the relativity of motion, particularly the motion of anything moving at or close to the speed of light. At the time, people believed that light waves, just as sound waves, ocean waves or shock waves, had to travel through a medium. But rather than air, water or ground, they believed light waves traveled through a substance called ether, less tangible than air, that pervaded the universe.
爱因斯坦在1905年提出的理论，描述了运动的相对性，尤其是对任何接近光速物体的运动。当时，人们认为，光波就像声波、海浪波或冲击波一样，它们的运行必须穿过介质。可是对于光，与其说是通过空气、水还是大地，他们认为还不如说通过了一种比空气还要无形无踪而弥漫于宇宙之间称为“以太”的介质。
Scientists assumed that the laws of physics would be different for an object at rest with respect to the ether, and with the proper experiments it would be possible to figure out what was truly at rest, according to Peter Galison, a professor of physics and the history of science at Harvard University. [Twisted Physics: 7 Mind-Blowing Findings]
科学家们一直认为对于那些在“以太”中静止的对象，物理规律是不同的，可是如果采用合适的实验，有可能在“以太”中真正地找到静止，据哈佛大学科学史和物理学教授，彼得·盖利森（Peter Galison）所说。 【扭曲物理学：7个令人兴奋的发现】
"Einstein got rid of that," Galison said. "There are no physical properties that go with the statement 'I am truly at rest.' That's really what special relativity is about."
“可是爱因斯坦却摆脱了这种学说，” 盖利森说。“世界上没有与‘我是真正地处于静止’ 声明相匹配的物理性质。“那就是狭义相对论所要陈述的观点。”
In other words, the properties of physics are the same for me whether I am riding my bicycle or sitting on a park bench. Special relativity, however, does not apply to acceleration. Einstein would tackle this later in his general theory of relativity.
换句话说，物理性质对于我来说都是一样，不管我是骑在自行车上，还是坐在公园里的长椅上。然而，狭义相对论，它并不适用于有加速度的运动。爱因斯坦在他后来的广义相对论中去处理这个问题。
Special relativity is also based on a second assumption that gives the speed of light — 186,000 miles per second (300 million meters per second) — in a vacuum a special status. Einstein postulated that light always travels at the same speed for every observer, regardless of that observer's speed, Galison explained.
狭义相对论也奠基于它的第二个假设：他所设定的真空中光速为每秒186,000英里（每秒300,000米）有它的特殊地位。爱因斯坦假定，相对于每一个观察者，无论这个观察者以怎样的速度在运动，光总是以相同的速度在运动着，而与观察者的速度无关，盖利森解释道。
So, if you have a fast enough car, in theory, you could catch up to a bullet. But you could never catch up to, or even reduce the apparent speed of a pulse of light, regardless of whether you were driving toward it or away from it.
所以，如果你乘上一辆速度够快的车子，从理论上来讲，你可以赶上一颗已经射出的子弹，可是你永远无法赶上光，甚至不能减低光脉冲的视速度，而与你是面向着光脉冲驾驶或还是背离着光脉冲驾驶无关。
Ultimate speed limit
终极的速度限制
Under Einstein's theory, the speed of light becomes a sort of ultimate speed limit. In fact, objects with mass, be they cars or neutrinos, can't reach the speed of light because they would need infinite energy to do so, according to the theory.
根据爱因斯坦的理论，光的速度变成了一种终极的速度限制。事实上，对象具有质量，根据爱因斯坦的理论，不管是人们的汽车，还是中微子，都不可能达到光的速度，因为它们要这样做就需要无限大的能量。
Some experiments have appeared to play with the speed of light, but these effects are illusory, according to Galison. Light traveling through different mediums, such as chilled sodium gas, does slow substantially, but this is because the light is being bounced between the atoms within the medium. But between interactions with atoms, it is still traveling at 186,000 miles per second (300 million meters per second), he said.
一些实验已经出现了玩弄光速的游戏，可是他们所得到效果都是虚幻的。根据盖利森的意见，光可以通过不同的介质运行，如在通过冷冻的纳气时，光的速度实质上变慢了。然而这是因为光线在运行介质里的原子之间时，会反复地反弹。他说，但在与原子相互作用之间，光仍然以每秒186,000英里（每秒30,000米）的速度运动。
Claims that it's possible to push light beyond 186,000 miles per second (300 million meters per second), are equally illusory, Galison said.
声称可能把光速增加到超过每秒186,000英里（每秒300,000米），同样也是虚幻的，盖利森说。
Galison uses a hypothetical to explain why. If you shine a laser pointer on the surface of the moon and flick your wrist to sweep across the surface, wouldn't that mean that the bright dot is crossing the surface of the moon faster than the speed of light? No, because nothing is actually crossing the surface of the moon — the dot isn't an actual object, it is just a series of photons in the laser beam hitting the surface.
盖利森采用了一个假设来解释这个问题。如果你把一个激光指示器照射到月球表面，然后摇动你的手腕去横扫它的表面，那是不是就意味着亮点横跨月球表面的速度要比光速还要快？其实不是这样，这是因为此时并没有什么实际的东西真正地横跨了月球的表面 - 亮点不是一个实体，它仅仅是击中月球表面激光束里一系列的光子。
"For 100 years, people have used these and more sophisticated paradoxes to try to say, 'Well isn't there this way to exceed the speed of light?'" Galison said. "They usually turn out to involve accelerating motion, something that is not really an object" — like the bright spot of the laser pointer — "or infinite energy." In other words, cheats.
“100多年来，人们已经使用过那些或者更加复杂的悖论，试图来说，‘好吧，这样的方法是不是可以说明了已经超过了光速？” 盖利森说。 “他们通常的试验结果都涉及了加速度运动，有些事情并不是真正的对象” – 就像那激光指示器指针所产生的亮点 – “或者需要无限大的能量。” 换句话说，这些都是欺骗。
In the lab, researchers can create the impression of sending light faster than the speed limit by tweaking the speed at which the wave crests of light propagate through space. This, however, does not increase the speed at which the actual electromagnetic information travels — this is conveyed by the overall shape of the wave's amplitude.
在实验室中，研究人员可以在光线传播通过空间时，对光的波峰稍作调整来造成发送光线的速度比极限的速度限制更快的印象。然而，这实际上这样并不能增加电磁信息的传播速度 - 电磁信息是靠波幅整体的形状来传递的。
Iron clad theory?
铁板一块的理论？
Since Einstein introduced special relativity, the theory and the special status it gives to the speed of light have appeared iron-clad.
自从爱因斯坦提出狭义相对论以来，这个理论和其把特殊地位赋给了光速，已经铁证如山。
Until now, that is. Scientists working on the OPERA experiment at the CERN laboratory in Switzerland beamed neutrinos 454 miles (730 kilometers) underground to Italy, and calculated how fast they made the trip. Shockingly, the neutrinos appeared to beat light speed by 60 billionths of a second. The finding appears to fly in the face of the last 106 years of physics.
到现在为止，在瑞士的欧洲原子核研究委员会的实验室里从事OPERA实验【1】工作的科学家在意大利的地下室里发射了长度为454英里（730公里）的中微子流，并计算出它们完成行程的速度。令人震惊的是，中微子出现了以1秒钟里的10亿分之60击败了光速的试验结果。这一发现似乎完全违反了106年来的物理学。
"Our understanding hasn't evolved at all, we've been doing extremely precise tests of special relativity since the very first days," said Ben Monreal, an assistant professor of physics at University of California, Santa Barbara. "Special relativity has been passing tests with flying colors for over 100 years now. That is why this result is so surprising and unexpected."
“我们的理解竟必还没有逐步形成到这个地步，我们一直在做有关狭义相对论的极为精确的测试，” 在圣巴巴拉的加州大学物理学助理教授本·蒙雷阿尔（Ben Monreal）说。 “到现在为止，狭义相对论已经出色地通过了100多年的测试，这就是为什么OPERA的实验结果会如此地令人吃惊和使人感到意外。”
If the finding of the OPERA experiment does pan out, the implications are much more mind-bending. Under special relativity, if something travels faster than the speed of light, it goes backwards in time. Such a proposition could interfere with the basic rule that cause precedes effect, called causality.
如果OPERA实验中发现取得了成功，其影响更让人刮目相看。根据狭义相对论，如果有什么东西比光速旅行得更快，它就会把时间向后推移。这个命题可能会与“原因领先于结果”的基本规则，即因果关系相抵触。
"The reason a lot of physicists are very unmoved by these claims is that it could make causality itself very problematic," Galison said. In other words, it raises the prospect of time travel.
“很多物理学家都非常不为这些断言所动的原因在于它可以使因果关系本身很成问题，” 盖利森说。换句话说，它提出了时间旅行的前景。
There is another issue too. Einstein introduced the speed of light as a mathematical constant, c. If neutrinos can indeed exceed the speed of light, then c loses its special status, giving rise to a host of other problems elsewhere in physics, where c has been used in calculations, such as the famous formula E=mc^2. [Warped Physics: 10 Effects of Faster-Than-Light Discovery]
还有一个另外的问题。爱因斯坦引进光速c作为一个数学常数，如果中微子确实可以超过光速的话，那么c就会失去它的特殊地位，从而引发了在物理学的其他领域里一直在进行计算时所存在的问题，如著名的公式E = mc^2。【[扭曲物理学：发现比光速更快的10个效应】
"For all of these reasons, people are going to need extra evidence to conclude that it is going to hold up," Galison said.“由于所有这些原因，人们还需要额外的证据，才能论定OPERA的实验结果是否站得住脚跟，” 盖利森说。
