I can not seem to grasp, why exactly does light travelling through space without the need of any medium was baffling for the scientists of 1800's.
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4$\begingroup$ Because most of other non-EM type waves needs medium to propagate, like mechanical waves, pressure waves, etc ? $\endgroup$– Agnius VasiliauskasCommented Feb 28 at 21:42
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4$\begingroup$ What is waving if there is no medium? $\endgroup$– Andrew SteaneCommented Feb 28 at 21:44
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$\begingroup$ what do you mean @AndrewSteane ? $\endgroup$– SumirCommented Feb 28 at 21:49
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1$\begingroup$ technically a vacuum is not “nothing” but is made of fields. No “physical” medium may be a more accurate way to ask. $\endgroup$– joseph hCommented Feb 28 at 21:51
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2$\begingroup$ I wonder if History of Science and Mathematics might be more appropriate for such a question, as the answer almost certainly would require a historical perspective. $\endgroup$– Kyle KanosCommented Feb 28 at 22:53
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3 Answers
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If you are used to waves traveling down a string, the wave is a traveling sideways deflection of the string. For sound waves, it is a traveling compression of the air.
In the 1800's, waves were mechanical. If something was a traveling deflection of the medium, there must be a medium to deflect.
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Consider the famous Cheshire cat from Alice in Wonderland. It periodically disappears so that only its grin is still visible. A wave without a medium is like such a grin without a face. Note that also quantum mechanical waves have no medium.
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A water wave, or a wave on a string served as a mental model to describe the behavior of light. The mental model was needed because the actual propagation could not be directly seen or physically perceived (as sound waves could).
Until the mathematical description of this mental model became sufficient, the physical sense of the model was all that one had to go by. The physical sense suggests that a wave moves by periodically disturbing a medium (water, string, air). Without such a medium, it isn't trivial to understand what is being disturbed and therefore how a wave can propagate.
