Ask Ethan: How fast do gravitational waves travel?
And if the Universe is expanding, does that mean these ripples can break the speed of light?
“Einstein’s gravitational theory, which is said to be the greatest single achievement of theoretical physics, resulted in beautiful relations connecting gravitational phenomena with the geometry of space; this was an exciting idea.” -Richard P. Feynman
One of the most surprising predictions of Einstein’s General Relativity is the existence of not just matter, radiation and other particle-based forms of energy, but the existence of gravitational radiation itself, or fundamental “ripples” in the very fabric of spacetime. This is one of the toughest things to understand, and Patreon supporter Robert J. Hansen wants to know more:
[Gravitational] waves are perturbations of spacetime which travel at c. However, spacetime is allowed to expand and contract faster than c. An expansion followed by a compression is pretty much the definition of a compression wave. This appears to produce a paradox: gravity waves travel at c, but there appears to be a way for them to be superluminal. What’s the resolution of this apparent paradox?
First off, let’s start with the concept of this radiation (and how it’s produced) itself.
