光線的結構

Visible light is electromagnetic wave in nature. Electromagnetic wave doesn't required a medium to propagate.

Electromagnetic wave travels by the mutual induction of electric and magnetic fields. Since electric anf magnetic fields can exist in vacuum, electromagnetic wave is thus able to travel in a vacuum.

In fact, the presence of a medium, like glass or water, would slow down the travelling of electromagnetic wave. It is because material in the medium weakens both electric and magnetic fields.

光帶有能量, 如果我們相信愛因斯坦的 E=mc2, 光代表有質量 (雖然 rest mass = 0), 也是物質, 為什麼一定要有媒介才可傳播?
不過, 場 (field) 又是怎樣傳播的呢?

真空沒有空氣，所以光在真空行走，肯定和閃電不同。

沒有medium，光卻可以行走，我也說不出原因。好奇怪。

這個問題，有如我不明白，磁力場是怎樣在真空運作。沒有medium，為甚麼可以令真空中的一塊鐵移動呢？

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