荷兰物理学家Hendrik Casimir于1948年提出存在一种Casimir力——当计算两个互相平行的不带电导体板之间的能量时,电磁真空边界环境造成两板互相吸引.在经典物理中对两板的作用力不会发生,因此这纯粹是一种量子效应.Casimir效应为“量子真空是一种物理实在”提供了直接的显示和证明.按照量子力学(QM)中的零点能(ZPE)理论,两平行金属板中场的每个模式对每块板都产生一定的压强;这种已由实验证明其存在的力使两板靠近.基本原因在于:虽然零点能(ZPE)不能直接计算和测量,但置入两板前后的能量差值却可由计算和测量而确定,即得到Casimir能Ec.Casimir效应使真空能(或者说真空电磁场)的存在成为可观察的效应.在这里“真空”一词是指物理真空,而非工程技术的真空.可以认为真空中放置双板后改变了真空的结构,故有两种真空:板外的常态真空或自由真空,板间的负能真空,后者的折射率小于1(n＜1).对于与板垂直的电磁波传播而言,真空中的光速并不相同,变化量(Δc/c)约为1.6×10-600d-4,故当d =10-9m时Δc=10--24c.因此量子电动力学双环效应,会使电磁波的相速和群速大于真空中光速c.虽然超光速的量很小,但却提升了对原理的兴趣.从1948年至今,70年后Casimir力仍然令人惊奇.Casimir效应的普遍性使其获得了广泛应用,本文从理论和实验方面的论述提供了对现象的深刻理解.%The Casimir force was predicted in 1948 by Dutch physicist Hendrik Casimir,he realized that when calculating the energy between two parallel uncharged conducting plates,the attraction each other resulting from the modification of electromagnetic vacuum by the boundaries.But there is no force acting between neutral plates in classical physics,so it is a purely quantum effect.The Casimir effect being a direct manifestation of physical reality,i.e.the quantum vacuum.According to the theory of zero-point energy(ZPE) in Quantum Mechanics,when we consider two parrallel uncharged conducting plates,each mode of field contributes to a pressure on the plate and other,this experimentally confirmed small forces drawing the plates together.The principle based on that,although the vacuum energy(ZPE) can't be compute and test directly,but the energy difference of put-in and get-out the parallel plates are capable to compute and test,so we can obtain the Casimir energy Ec.The Casimir effect is one observable of the existence of the vacuum energy,i.e.the existence of vacuum electromagnetic field.The meaning of this word "vacuum" is physical-vacuum,not technology vacuum.Then,we say that the change in the vacuum structure enforced by the plates.There are two kinds of vacuum,one is usual vacua or free vacua (outside the plates).Another is the negative energy vacua (inside the plates),and the refraction index less than 1(n ＜1).That cause a change in the light speed for electromagnetic waves propagating perpendicular to the plates:A c/c≌ 1.6× 10-60d-4,and d is the plate distance.When d =10-9m(1nm),A c =10-24c.Then,a two-loop QED effect cause the phase and group velocities of an electromagnetic wave to slightly exceed c.Though the difference are very small,that raise interesting matters of principle.Since 1948,the Casimir forces still surprising after 70 years.The Casimir effect is very general and finds applications in various situation of physics.The theoretical and experimental results described here provide a deeper understanding of the phenomenon.
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