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1、Theoretical physics: The origins of space and time理论物理学对时空起源的探索Many researchers believe that physics will not be complete until it can explain not just the behaviour of space and time, but where these entities come from. 许多研究人员认为，物理学不仅要能解释时空的表现，还要能解释时空本质的起源，否则物 理学的任务就不算完成。“Imagine waking up one day
2、and realizing that you actually live inside a computer game,” says Mark Van Raamsdonk, describing what sounds like a pitch for a science-fiction film. But for Van Raamsdonk, a physicist at the University of British Columbia in Vancouver, Canada, this scenario is a way to think about reality. If it i
3、s true, he says, “everything around us the whole three-dimensional physical world is an illusion born from information encoded elsewhere, on a two-dimensional chip”. That would make our Universe, with its three spatial dimensions, a kind of hologram, projected from a substrate that exists only in lo
4、wer dimensions.“想象一下，假如有一天你醒来，发现自己生活在计算机游戏里，”加拿大英属哥伦比亚大 学物理学家马克范拉姆斯东克(Mark Van Raamsdonk)说。这听起来像是科幻电影的情节， 但这正是他对现实的一种理解方式。如果这是真的，那“我们周围的一切整个三维的物 理世界就是一场幻觉，由来自某个地方的二维芯片上的编码信息所产生的幻觉”。这构 成了我们的三维空间宇宙，一种从低维底片上发出的全息投影。This holographic principle is strange even by the usual standards of theoretical physics
5、. But Van Raamsdonk is one of a small band of researchers who think that the usual ideas are not yet strange enough. If nothing else, they say, neither of the two great pillars of modern physics general relativity, which describes gravity as a curvature of space and time, and quantum mechanics, whic
6、h governs the atomic realm gives any account for the existence of space and time. Neither does string theory, which describes elementary threads of energy. 即使拿通常的理论物理学标准来衡量，这种“全息理论”也相当奇怪，但范拉莫斯东克是少 数前卫的研究人员之一，他们认为通常的理论尚不够奇怪。无论是现代物理学的两大支柱 广义相对论和量子力学(广义相对论把万有引力作为一种时空弯曲，而量子力学是原子领 域的统治法则)，还是描述基本一维能量线的弦理论
7、，都没有对时空本身的存在给出任何解 释。如果没有其它的，这种“全息理论”也不失为一种解释。Van Raamsdonk and his colleagues are convinced that physics will not be complete until it can explain how space and time emerge from something more fundamental a project that will require concepts at least as audacious as holography. They argue that such
8、a radical reconceptualization of reality is the only way to explain what happens when the infinitely dense singularity at the core of a black hole distorts the fabric of space-time beyond all recognition, or how researchers can unify atomic-level quantum theory and planet-level general relativity a
9、project that has resisted theorists efforts for generations.范拉姆斯东克和他的同事们认为，物理学如不能解释时空是如何以及从哪里产生的，它的任 务就不算完成。时空可能从某种更基本的东西产生，这种东西尚未命名，至少需要构造一个 像“全息”那样大胆的概念。他们认为，这种从根本上对现实的重新定义，是解释黑洞核心 那个无限致密的“奇点”怎样扭曲了时空构造的唯一方式，这超越了所有的认知。或者说， 研究人员怎样才能把原子尺度的量子理论和行星尺度的广义相对论统一起来，有一个东西长 期阻碍了理论学家的构建工作。“All our experiences
10、tell us we shouldnt have two dramatically different conceptions of reality there must be one huge overarching theory,” says Abhay Ashtekar, a physicist at Pennsylvania State University in University Park.“所有的经验都告诉我们，我们对现实不该有两种显著不同的构想，它必然是一个庞大的包 含所有的理论。”美国宾夕法尼亚大学物理学家阿贝阿什特卡(Abhay Ashtekar)说。Finding th
11、at one huge theory is a daunting challenge. Here, Nature explores some promising lines of attack as well as some of the emerging ideas about how to test these concepts (see The fabric of reality).找到一个庞大的理论是一项艰巨挑战。为此，自然杂志探索了现代几种较有前途的前进 路线一些新兴的观点以及对它们的检验。Gravity as thermodynamics万有引力热力学One of the most
12、 obvious questions to ask is whether this endeavour is a fools errand. Where is the evidence that there actually is anything more fundamental than space and time? 人们可能会问的一个最明显的问题是，这种努力是否徒劳？是否真的有某种东西比时空更基 本？证据何在？A provocative hint comes from a series of startling discoveries made in the early 1970s,
13、when it became clear that quantum mechanics and gravity were intimately intertwined with thermodynamics, the science of heat.一个令人兴奋的线索来自上个世纪70 年代早期取得的一系列不寻常的发现。当时，量子力 学和万有引力与热动力学开始紧密结合在一起，这一趋势日益明显。In 1974, most famously, Stephen Hawking of the University of Cambridge, UK, showed that quantum effects
14、 in the space around a black hole will cause it to spew out radiation as if it was hot. Other physicists quickly determined that this phenomenon was quite general. Even in completely empty space, they found, an astronaut undergoing acceleration would perceive that he or she was surrounded by a heat
15、bath. The effect would be too small to be perceptible for any acceleration achievable by rockets, but it seemed to be fundamental. If quantum theory and general relativity are correct and both have been abundantly corroborated by experiment then the existence of Hawking radiation seemed inescapable.
16、1974年，英国剑桥大学的斯蒂芬霍金证明，黑洞周围空间存在着量子效应，这使得黑洞 向外发出辐射，就好像它很热一样。其他物理学家也很快得出结论，这种现象在宇宙中其实 相当普遍。即使在真空里，正在加速的宇航员会感到他自己像是被包围在热水浴中。虽然对 目前火箭可达到的加速而言，这种效应太微弱了而无法被觉察到，但这或许是个基本原理。 如果量子理论和广义相对论是正确的这二者都已被众多实验所证实那霍金辐射的存在似乎是理所当然。A second key discovery was closely related. In standard thermodynamics, an object can radiate heat only by decreasing its entropy, a measure of the number of quantum states inside it. And so it is with bla
