Both photons and gravitational waves propagate at the speed of light through the vacuum of empty space itself. Despite the fact that it isn’t intuitive, there’s no evidence that there’s a physical medium, or aether, required for these entities to travel through. (NASA/SONOMA STATE UNIVERSITY/AURORE SIMONNET)

Ask Ethan: Does The Aether Exist?

Not everything needs a medium to travel through. If we can overcome that assumption, we don’t need the aether at all.

All throughout the Universe, different types of signals propagate. Some of them, like sound waves, require a medium to travel through. Others, like light or gravitational waves, are perfectly content to traverse the vacuum of space, seemingly defying the need for a medium altogether. Irrespective of how they do it, all of these signals can be detected from the effects they induce when they eventually arrive at their destination. But is it really possible for waves to travel through the vacuum of space itself, without any medium at all to propagate through? That’s what Wade Campbell wants to know, asking:

Back in the late 1800s, an “aether” was proposed as the medium that light travels through. We now don’t believe that is the case. What is the evidence and/or proof that no aether exists?

It’s an easy assumption to make, but a difficult assertion to disprove. Here’s the story.

Whether through a medium, like mechanical waves, or in vacuum, like electromagnetic and gravitational waves, every ripple that propagates has a propagation speed. In no cases is the propagation speed infinite, and in theory, the speed at which gravitational ripples propagate should be the same as the maximum speed in the Universe: the speed of light. (SERGIU BACIOIU/FLICKR)