虽然爱因斯坦是量子理论的创始人，可他从来不愿接受量子力学的怪诞结论。他说过一句很有名的话“上帝是不投骰子的”，旨在否定量子力学对物理世界概率性的描述。尽管爱因斯坦已经去世60年，但他给后人留下的争论一直是科学界的热门话题。然而，几天前由荷兰物理学家发布的实验结果终于表明，爱因斯坦错了。

从量子力学诞生开始，争论就没有停止过。尽管以丹麦物理学家波尔为代表的“哥本哈根学派”认为量子力学是完备且自圆其说的，爱因斯坦等物理学家却始终坚持量子力学不是最终理论。爱因斯坦认为，物理世界的主宰是传统的机械决定论，而非概率。 两派长期针锋相对，唇枪舌战，他们争论的焦点落在了“量子纠缠”（quantum entanglement）上，而量子纠缠直接挑战了经典物理学的定域性描述。比如，两个朝相反方向运动的光子，只要不受干扰，无论相距多远都可以在瞬间传递信息。打个比方，即使牛郎和织女分居在银河两头，彼此心映即刻完成，无需时间。

爱因斯坦难以接受这样的结论，因为按照他提出的相对论，信号传递的最快速度是光速，两个相距甚远的物体是不可能在瞬间交换信息的。也就是说，如果银河系有10万光年大，那么牛郎的呼唤需要10万年后才能被织女知道，绝不是发生于顷刻之间事情。 爱因斯坦为此还提出了著名的“隐变量理论”，将量子力学不能给出确定结果的概率问题，归咎于人们对某种尚未发现的“隐变量”的无知。他认为，那两个彼此背离而行的光子，一定是具有某种内在的机制，决定了它们之后的行为，只不过人们不知道罢了。也就是说，牛郎和织女在每年分手的时候都要约定好，在日后的某个时刻彼此互相思念，只是这样的约定还没有被王母娘娘发现而已。

简而言之，如果爱因斯坦是对的，那么人们依然可以按照传统的科学理念去理解世界。如果哥本哈根学派是对的，那么人们就不得不推翻许多根深蒂固的观念，重新去审视我们的世界。人们也不得不承认，真实的世界和我们通过感官所接触、所看到的世界在本质上是完全不同的。在当时，许多人都认为这样的争论不会有结果，因为这已然超越了科学范畴，上升为一个哲学问题。

可转机出现在上世纪60年代中叶，当时爱因斯坦已经去世10年。欧洲核子研究组织（CERN）的约翰·贝尔（John Bell）在赴美国访问期间，发表了著名的论文，将这一看似抽象的哲学问题简化为一个清晰的数学不等式，它被人们称为“贝尔不等式”。贝尔不等式其实是说，如果爱因斯坦提出的隐变量存在的话，那么在特定的实验条件下，实验结果（大量独立重复实验的统计概率）就会被限制在一个范围之内。一旦实验测量超出该范围，即贝尔不等式不成立的话，那么爱因斯坦就是错的，隐变量理论也就不正确。由于贝尔不等式可以直接付诸实验观测，爱因斯坦与哥本哈根学派之间的争论不再具有形而上的神秘色彩。取而代之的是，人们开始热衷于贝尔不等式的实验观测。

然而实验测量并不简单。在过去的50年里，人们提出了不计其数的实验方案，但每一个方案都有漏洞。所以，尽管许多实验得到了违反贝尔不等式的结果，但由于漏洞的存在也无法在逻辑上直接证明贝尔不等式不成立。令人振奋的是，最近由荷兰代尔夫特科技大学的Ronald Hanson领导的科研团队，终于实现了没有漏洞的实验观测，50年来第一次无懈可击地直接证明了贝尔不等式不成立。

Hanson团队的实验设计十分巧妙。他们在相距1.28千米的两个实验室里，分别用微波去激发处于极低温的钻石里的电子。当电子被激发出来时，它们同时也放出与自身相纠缠的光子。两边的光子通过光纤传送到位于两实验室之间的另一个探测地点，这里精确记录着光子到达的时间。如果两边发射过来的光子同时到达并以特定方式干涉，那么两个光子就会立即将自己所“代表”的电子纠缠起来，实现远程的量子纠缠。 这好比远隔10万光年的牛郎和织女各派一个天使在鹊桥相会，如果两个天使同时到达并正确表达了主人的意思，那么牛郎和织女就实现了远程的“约会”。

由于两边的实验室在同时测量电子的自旋，一旦两个电子实现了远程的量子纠缠，仪器就会记录它们自旋在不同方向出现的频率。大量观测数据的统计结果显示，贝尔不等式的确不成立。 该实验唯一不尽人意之处，在于两边的光子精确同时到达的成功率很低，大约1.5亿个光子对中才能有一对光子成功干涉并实现电子的远程纠缠。因此，该实验一共進行了22个多小时，却只得到245次有效数据。不过，该团队目前正在努力改進，以期提高效率。

他们的实验结果刚刚出炉，尚未来得及发表于正式期刊上，但已经得到物理学界的普遍关注。“这是量子物理学一项里程碑式的文章”，澳大利亚格里菲斯大学的Howard Wiseman评价道，尽管他本人没有参与这项实验。工作于悉尼大学的物理学家Christopher Ferrie认为该实验将有深远影响，他说“物理世界和人们日常直觉上看到的世界有着深刻的不同，人们将对此不再有任何的怀疑”。维也纳大学的Anton Zeilinger领导着一个与荷兰Hanson相竞争的科研团队，当他看到Hanson这项举世瞩目的成果时不禁说道“这是一个非常漂亮的实验，除了要祝贺他们的团队以外没有别的了。”

当然也有些质疑，Kaiser 认为还有一个潜在的问题没有解决，那就是实验所得出的结果很微妙，也许是挑出来的可预测的部分，对此我们很难探测到。他期待有更强的实验结果出来。 

这大概会成为诺贝尔获奖级别的工作。虽然实验结果证实了量子纠缠可以超越光速，但这并不意味着能否认爱因斯坦相对论中的宏观运动学理论，不过毫无疑问如果爱因斯坦天上有灵会感到十分惊讶。可以想象如果此种现象得到进一步证实，这个世界的物理研究将会有一个质的飞跃。届时可能会因此解释包括引力的同时性等一系列未知问题。

刚刚发现Nature letter的文章。http://www.docin.com/p-1330022454.html

附英文报导：

In a landmark study, scientists at the Delft University of Technology in the Netherlands reported that they had conducted an experiment they say proved one of the most fundamental claims of quantum theory - that objects separated by great distance can instantaneously affect each other's behavior.

The finding is another blow to one of the bedrock principles of standard physics known as "locality," which states that an object is directly influenced only by its immediate surroundings.

The Delft study, published Wednesday in the journal Nature, lends further credence to an idea that Albert Einstein famously rejected. He said quantum theory necessitated "spooky action at a distance," and he refused to accept the notion that the universe could behave in such a strange and apparently random fashion.

In particular, Einstein derided the idea that separate particles could be "entangled" so completely that measuring one particle would instantaneously influence the other, regardless of the distance separating them.

Einstein was deeply unhappy with the uncertainty introduced by quantum theory and described its implications as akin to God playing dice.

But since the 1970s, a series of precise experiments by physicists are increasingly erasing doubt - alternative explanations that are referred to as loopholes - that two previously entangled particles, even if separated by the width of the universe, could instantly communicate.

The new experiment, conducted by a group led by Ronald Hanson, a physicist at the Dutch university's Kavli Institute of Nanoscience, and joined by scientists from Spain and England, is the strongest evidence yet to support the most fundamental claims of the theory of quantum mechanics about the existence of an odd world formed by a fabric of subatomic particles, where matter does not take form until it is observed and time runs backward as well as forward.

The researchers describe their experiment as a "loophole-free Bell test" in a reference to an experiment proposed in 1964 by the physicist John Stewart Bell as a way of proving that "spooky action at a distance" is real.

"These tests have been done since the late '70s but always in the way that additional assumptions were needed," Hanson said. "Now we have confirmed that there is spooky action at distance."

The scientists say they have now ruled out all possible so-called hidden variables that would offer explanations of long-distance entanglement based on the laws of classical physics.

The Delft researchers were able to entangle two electrons separated by a distance of 1.3 kilometers (eight-tenths of a mile) and then share information between them. Physicists use the term "entanglement" to refer to pairs of particles that are generated in such a way that they cannot be described independently. The scientists placed two diamonds on opposite sides of the Delft University campus, 1.3 km apart.

Each diamond contained a tiny trap for single electrons, which have a magnetic property called a "spin." Pulses of microwave and laser energy are then used to entangle and measure the "spin" of the electrons.

The distance - with detectors set on opposite sides of the campus - ensured that information could not be exchanged by conventional means within the time it takes to do the measurement.

"I think this is a beautiful and ingenuous experiment and it will help to push the entire field forward," said David Kaiser, a physicist at the Massachusetts Institute of Technology, who was not involved in the study. However, Kaiser, who is with another group of physicists who are preparing to perform an even more ambitious experiment next year that will soon measure light captured at the far edges of the universe, also said he did not think every scintilla of doubt had been erased by the Dutch experiment.

The tests take place in a mind-bending and peculiar world. According to quantum mechanics, particles do not take on formal properties until they are measured or observed in some way. Until then, they can exist simultaneously in two or more places. Once measured, however, they snap into a more classical reality, existing in only one place.

Beyond the immediate result, physicists noted that the experiment represented an advance in the understanding of a Lilliputian world that was once largely the province of theory. Quantum mechanics has already had a huge effect on modern technology and industry: It is the foundation for modern computers and lasers.

"What I do find interesting is that the experimenters are learning how to manipulate quantum systems, and do experiments that are far beyond what was possible when I was starting in physics," said Leonard Susskind, a theoretical physicist at Stanford. "Things which were at best 'thought experiments' become possible, then routine. That is incredibly impressive."

Indeed, the experiment is not merely a vindication for the exotic theory of quantum mechanics, it is a step toward a practical application known as a "quantum Internet." Currently the security of the Internet and the electronic commerce infrastructure is fraying in the face of powerful computers that pose a challenge to encryption technologies based on the ability to factor large numbers and other related strategies.

Researchers like Hanson envision a quantum communications network formed from a chain of entangled particles girdling the entire globe. Such a network would make it possible to securely share encryption keys, and know of eavesdropping attempts with absolute certainty.

For some physicists, even though the new experiment claims to be "loophole free," the matter is not yet completely closed.

"The experiment has closed two of the three major loopholes beautifully, but two out of three isn't three," Kaiser said. "I believe in my bones that quantum mechanics is the correct description of nature. But to make the strongest statement, frankly we're not there."

A potential weakness of the experiment, he suggested, is that an electronic system the researchers used to add randomness to their measurement may in fact be predetermined in some subtle way that is not easily detectable, meaning that the outcome might still be predetermined as Einstein believed.

To attempt to overcome this weakness and close what they believe is a final loophole, the National Science Foundation has financed a group of physicists led by Kaiser and Alan H. Guth, also at MIT, to attempt an experiment that will have a better chance of ensuring the complete independence of the measurement detectors by gathering light from distant objects on different sides of the galaxy next year, and then going a step further by capturing the light from objects known as quasars near the edge of the universe in 2017 and 2018.