1. Why don't electromagnetic waves need a medium to propagate?

  2. How does light get such a magnificent velocity?

  • 3
    $\begingroup$ This question does not show any research effort. $\endgroup$ Sep 12, 2015 at 2:14
  • $\begingroup$ I need the answer.. $\endgroup$
    – Ishaque
    Sep 12, 2015 at 2:15
  • 1
    $\begingroup$ Being a beginner doesn't absolve you of anything. Electromagnetism doesn't require a medium, vacuum is just fine. Look up: 'Maxwell's equations of electromagnetism'. Maxwell derived the speed of light. $\endgroup$
    – Gert
    Sep 12, 2015 at 2:30
  • 1
    $\begingroup$ let me ask a counter question: why does light need a medium to propagate? $\endgroup$
    – Shing
    Sep 12, 2015 at 3:06
  • 1
    $\begingroup$ Make sure that Google is your best friend. Use it first. How do you use it? In your case, for your question, just search on the words "electromagnetic waves" (you can leave off the quotes). The top hits are usually good places to start. This should tell you some things that then result in the need for more googling. But, when you find a physics concept or specific question you can come back and try here. It is best to ask very specific questions and then fill in things that you read elsewhere. The experience of doing research on the Internet is one of the best skills to learn. $\endgroup$
    – K7PEH
    Sep 12, 2015 at 3:21

2 Answers 2


Why don't electromagnetic waves need a medium to propagate?

That's a "Why question". It's dangerous to ask "Why" in physics, because the answer is simply "they do". "How" is more interesting, and in this case it is very complicated. Just know that for a very long time, people really thought that electromagnetic waves needed a medium to propagate, Maxwell like others. And this medium was the "Ether". After lot of efforts to try to find this Ether with no result at all (look for the Michelson-Morley experiment), scientists were very disoriented. Lorentz and Poincaré mainly (but there were others) tried to understand the no result of Michelson-Morley and they came with the right mathematical solution, but the wrong explanation of the phenomena of propagation of EM. Einstein was the guy who found the good explanation who leaded to the same mathematical result of Lorentz and Poincaré with his Special Relativity. So why don't electromagnetic waves need a medium? Because they are not the same type of waves that waves in water or waves that makes sound.

How does light get such a magnificent velocity?

Light don't go that fast if you thing about the distance in universe. It's even very slow... But why this speed? Because the photon is massless. But why this particular speed? We don't really know actually. But it is a very important constant. But again, very complicated subject.

Good luck for your research and studies, it's all very interesting! ;)


That a rigid body can move without medium - in vacuum - is without any doubt. The same is possible for gas or single atoms or electrons ... Beside matter exist energy. Max Planck explored the black body radiation and found, that energy consists of energy packages.

Planck not believe, that the energy packages in his formula are real. Einstein stated, that the photoelectric effect is based of such packages and call them quanta, later this quanta were named photons. Photons are real, they observable for example on film emulsions, CCD chips or single photon experiments.

Photons are indivisible particles, that are emitted from electrons and other subatomic particles and live until they get absorbed by subatomic particles. So they are some kind of rigid body too? Physics say no because Maxwell long before the photons discovery find out that light has to be the same as radio waves. Radio waves one produce by accelerating periodically electrons in an antenna rod. The resulting emission is periodically too, it is a radio wave. This wave has one more important characteristic, it has a swelling magnetic component and a swelling electric component, both directed under 90° to each over and to the direction of propagation.

The characteristic of radio waves overshadowed the fact, that it contains photons. So if one think in the analogy to water waves it seems impossible that a radio wave moves without medium. Thinking in terms of photons of course it is possible in the same way as it is possible for rigid bodies. It was found out, theoretical by Maxwell and in a lot of experiments, that photons from infrared to gamma emission propagate in vacuum with the same velocity. That is a fact. It seems to be realistic, that the mechanism behind the emission of photons from subatomic particles is not discoverable. So it stays the fact only, that in vacuum and in the surrounding of our gravitational potential the speed of light is approx. 300,000 km/s.


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