You said "文章說的是光速在真空中的速度，不是在不同介質的速度". That is not an essential difference. Vacuum is a just special medium. More importantly, the equations itself say nothing about μ and ε, whether they are constant or dependent on space. The derivation of the wave equation is the same independent of whether μ and ε are functions of space. Maxwell's equations say nothing about in what medium the electromagnetic disturbance is traveling in. As a matter of fact, there needs to be an exogenous assumption on in what medium the wave is propagating in. There was even a name for this medium the light is propagating in, ether. One important contribution Einstein made was the complete elimination of ether and postulate that the electromagnetism creates its own field and the light travels in this field.
More importantly, you have confused different notions of constancy of light. The revolutionary notion Einstein put forward is that the speed of light is invariant with respect to different inertial frames in vacuum, not that the speed is constant at different spatial point in vacuum in one frame. This is NOT expressed by the formula c=sqrt（1/μ0ε0), but by the Lorentzian transform group or the inertial frame invariance of space-time, which is the core of the special relativity.
溪畔竹吟 發表評論於
von Neunman 是學霸，Einstein 是天才，沒可比性。學霸沒天才的思考、眼界和原創性，更沒天才的氣場。
北佛風光 發表評論於
回複 '朱朱八八' 的評論 : “阿爾伯特·愛因斯坦（ Albert Einstein） 在過去的一百年來幾乎是天才的同義詞。但他們同時代的世界頂尖科學家都紛紛認為馮?諾伊曼比愛因斯坦更聰明，這些人包括我們已經很熟悉的諾貝爾獎得主尤金.維格納，恩裏克·費米，理查德·費曼……”
博主寫的科學家曆史故事很有趣， 支持繼續科普！
丁丁貓和熊貓貓 發表評論於
開掛的人生不需要解釋！
bashfulx 發表評論於
vacuum Is a just special case of medium.
permitivity or permeability of vacumm has to have a value or values. It is simple to assume a constant value than uncertain possibilities of values
"麥克斯韋方程可以推導出真空中電磁波速是常數c=sqrt（1/μ0ε0)." No. Like I said, c is a constant only when μ0ε0 is a constant. You can derive the the wave equation with speed c=sqrt（1/με). But the Maxwell's equations do not specify whether με is a constant. For example, for light traveling in an isotropic medium rather than a vacuum. μ and ε depend on the medium and can even be made to depend on the position in the medium by changing the density or structure of the medium. The Maxwell's equations themselves do not assume the constancy of μ and ε and therefore the constancy of c=sqrt（1/με).
I can understand relativity theory now.
But I cannot wrap my mind around quantum physics.
The particle wave duality, the uncertainty principle, the spooky interactions, the delayed choice, etc. etc
nightrider 發表評論於
Interesting article. Maxwell's equations do not imply the constancy of the speed of light. It is a simple function of the permitivity and permeability of vacuum, just as you write in your article, the constancy of which is not specified by the equations themselves but depends on exogenous assumptions. Einstein's special relativity postulates the speed of light is constant or that both the permitivity and permeability of vacuum are constant.
