美科学家首次测量出卡西米尔斥力-超级军网

      真空中两块平行金属板之间存在某种吸引力，这种吸引力被称为卡西米尔力。通常情况下，这种力只会导致物体“相互吸引”，而非“相互排斥”。美国科学家最近在实验中成功将这种力转变为斥力，并对其进行了测量。

      这项研究由哈佛大学工程和应用科学学院教授费代里科·卡帕索领导。科学家发现，真空中两块平行金属板的表面距离小于100纳米时，产生的卡西米尔力十分明显。如果将其中一块金属板置换为硅板，并将它与另一块金属板浸入某些流体中，使它们距离非常接近，此时产生的卡西米尔力便是一种斥力。

      为了测量这种斥力，研究人员利用一个表面镀金的微型球和一块硅板模拟两个平行平板。在非常微小的距离内，二者的表面被认为是几乎平行的。研究人员将二者浸入无色油状液体溴苯中，使二者相互靠近，直至卡西米尔斥力开始发挥作用。此时，研究人员通过测量两者距离变动时微型球的偏转来测量卡西米尔斥力。

      卡西米尔力非常微弱，但却可以使纳米及毫米尺度的电子元件粘合在一起。例如，在计算机芯片工业，当硅片上的元件小到一定尺度，它们就会粘在一起。如果将卡西米尔引力转化为斥力，这种现象就不会发生。而且相关技术的应用前景将十分广阔，例如可以用于制造无摩擦轴承等理想设备。

      有关此项研究的论文1月8日将作为封面文章刊登在《自然》杂志上。

大多数人认为，真空是空荡荡的。但是，根据量子电动力学（一门在非常小的规模上描述宇宙行为的理论），没有比这种观点更加荒谬的了。实际上，真空中到处充满着称作“零点能”的电磁能，这正是麦克莱希望加以利用的能量。“零点能”中的“零”指的是，如果把宇宙温度降至绝对零度（宇宙可能的最低能态），部分能量就可能保留下来。实际上，这种能量是相当多的。物理学家对究竟有多少能量仍存在分歧，但麦克莱已经计算出，大小相当于一个质子的真空区所含的能量可能与整个宇宙中所有物质所含的能量一样多。　　平行板电容器在辐射场真空态中存在吸引力的现象称为卡西米尔效应。考虑一个辐射的电磁场，根据波粒二象性，辐射场可以看作是光子气，而光子气可看作是电磁辐射场的简谐振动。电磁场量子化后，可把辐射场哈密顿写成二次量子化的形式。　　可见对每个振动模式k，都有零点能（真空能）存在，这个结果是引入场量子化后的自然结果。由于真空能量的存在可以带来实验可观测的物理效应——卡什米尔效应。考虑一对距离为a的平行板电容器放在辐射场中，边界条件为：。可见随平行板距离的增大，所允许的振动模式越多，因此平行板电容器之间由于真空能量的存在而存在一种吸引力——卡什米尔力。反之如果认为不存在真空能，则没有这种力。在具体的计算过程中，由于U(a)的积分（求和）是发散的。为得到收敛的结果，数学上人为地引入一个切断因子。

In quantum field theory, the Casimir effect and the Casimir-Polder force are physical forces arising from a quantized field. The typical example is of two uncharged metallic plates in a vacuum, placed a few micrometers apart, without any external electromagnetic field. In a classical description, the lack of an external field also means that there is no field between the plates, and no force would be measured between them.[1] When this field is instead studied using quantum electrodynamics, it is seen that the plates do affect the virtual photons which constitute the field, and generate a net force[2]—either an attraction or a repulsion depending on the specific arrangement of the two plates. Although the Casimir effect can be expressed in terms of virtual particles interacting with the objects, it is best described and more easily calculated in terms of the zero-point energy of a quantized field in the intervening space between the objects. This force has been measured, and is a striking example of an effect purely due to second quantization.[3][4] However, the treatment of boundary conditions in these calculations has led to some controversy. In fact "Casimir's original goal was to compute the van der Waals force between polarizable molecules" of the metallic plates. Thus it can be interpreted without any reference to the zero-point energy (vacuum energy) or virtual particles of quantum fields.[5]

Dutch physicists Hendrik B. G. Casimir and Dirk Polder proposed the existence of the force and formulated an experiment to detect it in 1948 while participating in research at Philips Research Labs. The classic form of the experiment, described above, successfully demonstrated the force to within 15% of the value predicted by the theory.[6]

Because the strength of the force falls off rapidly with distance, it is only measurable when the distance between the objects is extremely small. On a submicrometre scale, this force becomes so strong that it becomes the dominant force between uncharged conductors. In fact, at separations of 10 nm—about 100 times the typical size of an atom—the Casimir effect produces the equivalent of 1 atmosphere of pressure (101.325 kPa), the precise value depending on surface geometry and other factors.[7]

In modern theoretical physics, the Casimir effect plays an important role in the chiral bag model of the nucleon; and in applied physics, it is significant in some aspects of emerging microtechnologies and nanotechnologies.[8]

基础研究啊……

lmjiao 发表于 2011-3-31 01:35
量子场论用大能标截断估算真空能的手段未必是有道理的，那样算出来的不会真的被当作是真空的能量。那是一个振荡的效应，但是应该不是真空衰变到下一个基态的时候可以提取的
衰变到下一个真空时能提取的真空能究竟多少，应该还是看今天的宇宙学常数，差了快一百个量级呢

怎么感觉像 Big Bang Theory ...... Sheldon ？

其实十月对以上现象有其他解释，不相信宇宙零点能

妈的这么搞下去迟早把宇宙搞到高潮崩溃了