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You've heard the controversy. Particle physicists predict the world's new highest-energy atom smasher, the Large Hadron Collider (LHC) near Geneva, Switzerland, might create tiny black holes, which they say would be a fantastic discovery. Some doomsayers fear those black holes might gobble up Earth--physicist say that's impossible--and have petitioned the United Nations to stop the $5.5 billion LHC. Curiously, though, nobody had ever shown that the prevailing theory of gravity, Einstein's theory of general relativity, actually predicts that a black hole can be made this way. Now a computer model shows conclusively for the first time that a particle collision really can make a black hole. |
你可能听说过这场争论：粒子物理学家们预测，世界上最高能量的新型核粒子加速器——位于瑞士日内瓦附近的大型强子对撞机（LHC），可能会创造出微型黑洞，他们称这将是一个奇妙的发现；一些灾难预言者担心，这些黑洞可能会吞没地球，尽管物理学家们说这是不可能的，但他们还是请求联合国停止这个55亿美元的LHC项目。然而说来也怪，从来没有人证明过，流行的引力论——爱因斯坦的广义相对论，实际上预测了黑洞是可以通过对撞而产生的。现在，一次计算机模拟首次确切地证明，利用粒子对撞可以制造出黑洞。 |
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"I would have been surprised if it had come out the other way," says Joseph Lykken, a physicist at the Fermi National Accelerator Laboratory in Batavia, Illinois. "But it is important to have the people who know how black holes form look at this in detail." |
“如果模拟结果不是这样，我会感到吃惊的，”伊利诺斯州巴塔维亚市费米国家加速器实验室的物理学家约瑟夫·莱肯说，“但是，要让那些知道黑洞形成过程的人们仔细看看该模拟，这是很重要的。” |
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The key to forming a black hole is cramming enough mass or energy into a small enough volume, as happens when a massive star collapses. According to Einstein's theory of general relativity, mass and energy warp space and time, or spacetime, to create the effect we perceive as gravity. If a large enough mass or energy is crammed into a small enough space, that warping becomes so severe that nothing, not even light, can escape. The object thus becomes a black hole. And two particles can make a miniscule black hole in just this way if they collide with an energy above a fundamental limit called the Planck energy. |
形成黑洞的关键是在足够小的体积内塞进足够多的质量或能量，就象巨型恒星塌缩时所发生的情况。根据爱因斯坦的广义相对论，质量和能量可以使空间和时间（时空）发生扭曲，产生了我们所感觉到的引力效应。如果足够大的质量或足够高的能量塞进足够小的空间中，那么这种扭曲就会变得极为严重，以至于任何事物——甚至连光都无法逃脱。这样该物体就变成了黑洞。恰恰是利用这种办法，两个粒子可以形成一个微型黑洞，条件是以超出基本限度的能量进行对撞，这个能量限度被称为普朗克能量。 |
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Or so physicists have assumed. Researchers have based that prediction on the so-called hoop conjecture, a rule of thumb that indicates how much an object of a given mass has to be compressed to make a black hole, says Matthew Choptuik of the University of British Columbia in Vancouver, Canada. A calculation from the 1970s also suggested a particle collision could make a black hole, Choptuik notes, but it modeled the particles themselves as black holes and thus may have been skewed to produce the desired result. |
也许物理学家们这么猜测过。加拿大温哥华市英属哥伦比亚大学的马修·肖普提克说，研究人员根据所谓的“环绕猜测”得出了上述预言。环绕猜测是一个基本法则，它说明了一个特定质量的物体被压缩到何种程度才会形成黑洞。肖普提克指出，20世纪70年代的一次计算也表明，粒子碰撞可以形成黑洞，但是当时的模拟把粒子本身当作黑洞，因此可能会由于曲解而无法得到预期的结果。 |
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Now Choptuik and Frans Pretorius of Princeton University have simulated such collisions, including all the extremely complex mathematical details from general relativity. For simplicity and to make the simulations generic, they modeled the two particles as hypothetical objects known as boson stars, which are similar to models that describe stars as spheres of fluid. Using hundreds of computers, Choptuik and Pretorius calculated the gravitational interactions between the colliding particles and found that a black hole does form if the two particles collide with a total energy of about one-third of the Planck energy, slightly lower than the energy predicted by hoop conjecture, as they report in a paper in press at Physical Review Letters. |
现在，肖普提克和普林斯顿大学的弗朗斯·普雷托里斯模拟了这样的对撞，同时利用了广义相对论中全部特别复杂的数学资料。为了使模拟简便和具有普遍性，他们将两个粒子模拟成被称为玻色星体的假设物体，类似于把恒星做成流质球体的那种模型。肖普提克和普雷托里斯运用了几百台计算机，计算了两个对撞粒子之间的引力作用。他们发现，如果两个粒子对撞的总能量为普朗克能量的大约三分之一，确实可以形成一个黑洞，这个能量比环绕猜测中所预测的稍微低一点。他们在《物理评论快报》杂志纸质版的一篇论文中报道了该发现。 |
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Does that mean the LHC will make black holes? Not necessarily, Choptuik says. The Planck energy is a quintillion times higher than the LHC's maximum. So the only way the LHC might make black holes is if, instead of being three dimensional, space actually has more dimensions that are curled into little loops too small to be detected except in a high-energy particle collision. Predicted by certain theories, those extra dimensions might effectively lower the Planck energy by a huge factor. "I would be extremely surprised if there were a positive detection of black-hole formation at the accelerator," Choptuik says. Physicists say that such black hole would harmlessly decay into ordinary particles. |
这是否意味着LHC将会制造出黑洞呢？肖普提克说，不一定。普朗克能量比LHC可以达到的最高能量还要高出1×1018倍。因此，LHC可能制造出黑洞的唯一方法和条件是：空间不是三维的，它实际上拥有更多的维度，这些维度卷曲成极小的环状，只有在高能粒子对撞中才可以探测到。根据某些理论的预测，这些额外维空间可能会由于一个异常的因素而有效地降低普朗克能量。“如果确实在这个加速器中探测到了黑洞的形成，我会感到极为惊讶的，”肖普提克说。物理学家们说，这种黑洞会在没有任何危害的情况下衰变成普通粒子。 |
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"It's a real tribute to their skill that they were able to do this through a computer simulation," says Steve Giddings, a gravitational theorist at the University of California, Santa Barbara. Such simulations could be important to study particle collisions and black hole formation in greater detail, he says. Indeed, they may be the only way to study the phenomenon if space does not have extra dimensions and the Planck energy remains hopelessly out of reach. |
“能够通过计算机模拟做到这些，确实证明了他们的技术高超，”加州大学圣塔芭芭拉分校的引力理论家史蒂夫·吉丁斯说。他说，这样的模拟对于更加仔细地研究粒子碰撞和黑洞形成是很重要的。的确，如果太空中不存在额外维空间，如果普朗克能量仍然无望达到，模拟或许就是研究这种现象的唯一方法。 |
