How do the rays from a satellite propagate in space without medium?

Sound cannot propagate in space because there is no medium present. Don’t the signals from a satellite need medium?

Asker: Dennis, 37 years old


No. Electromagnetic waves also propagate in a vacuum.

Sound waves require a medium. After all, they are pressure waves: the disturbance propagates because the center is constantly compressed and can then relax again. Without medium there can be no pressure waves, and therefore there is no sound.

In electromagnetic waves, it is electrical and magnetic fields that propagate, and they can travel through empty space, just like particles. It also makes sense, by the way, to think of light and other electromagnetic rays (like signals from a spacecraft) as propagating particles; these particles are called photons.

Your question makes a lot of sense. By analogy with sound waves, it has long been thought that a medium was also needed to propagate electromagnetic waves. This hypothetical medium was called the ‘ether’. Ultimately, it is none other than Einstein who has done away with the need for an ether.

Answered by

Prof. dr. Christopher Waelkens


Catholic University of Leuven
Old Market 13 3000 Leuven


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