使自由空间中光速变慢的研究进展

1905年Einstein发表了著名的狭义相对论( SR)文章,其中说光在真空中总以不变的速度传播。然而这个光速不变性原理一直缺乏可靠的实验证明,近年来的一些研究成果倒像是证伪了这一原理。例如,美国Maryland大学的物理学家James Franson于2014年6月发表论文引起物理界的广泛关注,文章宣称已可证明光速比过去所认为的值要慢。他的论据来源于对1987年超新星SN1987A的观测,当时在地球上检测到由爆发而来的光子和中微子,而光子比中微子晚到4.7h,过去对此现象人们只作了模糊的解释。 Franson认为这可能是由光子的真空极化造成的———光子分开为一个正电子和一个电子,在很短时间内又重组为光子。在引力势作用下,重组时粒子能量有微小改变,使速度变慢。粒子在飞经168000光年的过程中(从SN1987A到地球),这种不断发生的分合将造成光子晚到4.7h。另一个例子是,2015年1月英国Glasgow大学的Padgett研究组做到了使光的运行比真空中光速( c)要慢。他们使光子经过一个专用的散射结构物,波形被改变,从而速度变慢。令人惊奇的是,光子出来后(即回到自由空间)仍以减慢了的速度行进。Franson理论和Padgett小组实验损坏了真空中光速的恒值性,使c成为“不恒定的常数”,或“不常的常数”。这种情况妨害了SR理论及现行米定义的理论基础。另外,本文比较了1993年的SKC实验和2015年的空间结构化光子实验,前者以量子隧穿和消失波为基础,后者则改变光束的横向空间结构。二者都使用相关光子对,结果都显示光子群速的变化。如今或许可以终结关于光速不变原理的讨论。……在现代物理学中波粒二象性仍是难题,但新近研究对此有新的理解,与互补原理不同；故更宜于用波理论解释粒子实验。在Padgett小组实验中,无论Bessel波束或Gauss波束光子群速均减小,表现为在1m的实验距离上迟到若干微米。……最后,本文指出近年来的光速研究为波科学带来丰富体验,为理论思维造成新机会。

Recent Advances in Study that Scientists Slow the Light Speed of Free Space

In 1905,Einstein published his famous paper of Special Relativity(SR),that the speed of light will be locally the same for all condition. But this principle be short of verification of experiment. In recent years,some results falsifying the principle of the light-speed constancy. For example,in June 2014,phys-icist James Franson of the University of Maryland,has captured the attention of the physics community by posting an article, in which he claims to have found evidence that suggests the speed of light as de-scribed by the theory of General Relativity( GR) ,is actually slower than has been thought. Franson’ s arguments are based on observations made of the supernova SN 1987A,it exploded in Feb 1987. Meas-urements here on Earth picked up the arrival of both photons and neutrinos from the blast but there was a problem—the arrival of the photons was later than expected,by 4. 7 hours. Scientists at the time attribu-ted it to a likelihood that the photons were actually from another source. But what if that wasn’ t what it was,Franson wonders,what if light slows down as it travels due to a property of photons known as vacuum polarization—where a photon splits into a positron and an electron,for a very short time before recombi-ning back into a photon. That should create a gravitational potential,between the pair of particles,which, he theorizes,would have a tiny energy impact when they recombine—enough to cause a slight bit of a sl-owdown during travel. If such splitting and rejoining occurred many times with many photons on a journey of 168000 light years,the distance between us and SN 1987A,it could easily add up to the 4. 7 hour de-lay. For another example,in Jan 2015,a team of scientists in Glasgow University has made light travel slower than speed of light in vacuum ( c) . The photons through a special mask,it changed the wave shape of photon,and slowed it to less than light speed c. But it had not just been slowed by the mask,but had continued to travel at less than light speed ( c) even after it has returned to free space. The theory of Franson and the experiment of Padgett’ s team wrecked the constancy of light-speed c in vacuum. Then,c is an “inconstant constant”,or an “not-so-constant constant”. This situation im-pair the theoretical basis of SR and the definity on meter by CGPM in 1983 . In other words,we compare the two experiments—the first article pulished in 1993,it named the“SKC experiment”;the second article pubished in Jan 2015 , it named “spatially structured photons ex-periment”. The first experiment was based on quantum tunneling effect and evanescent waves, and the second experiment was based on changing the beam’ s transverse spatial structure. Both them are using time-correlated photon pairs,and the results shows a variation of the group velocity of photons. Anyway, we may say perhaps that these experiments was the summation of discussions about the constancy of light speed c in free space. …… Now, the particle - wave duality still the magic ghost in modern phys-ics. Recent advances in study shows,the quantum objects can behave beyond the wave-particle duality and the complementarity principle would stimulate new conceptual examination and exploration of quan-tum theory at a deeper level. Then we are very reasonable if we expect to understand the photon’ s experi-ment that explaned by the wave’ s theory. In the article of Padgett’ s team,it shows a reduction of the group velocity of photons in both a Bessel beam and photons in a Gaussian beam. In both cases,the delay is several micrometers over a propagation distance of 1m. …… Finally,the study on light velocity in re-cent years has a great deal of experience on wave sciences,and bring the new chance on theoretical think-ing.