Ask Ethan: Can the Universe ever expand faster than the speed of light?
How the Universe’s expansion rate continues to baffle us.
“In expanding the field of knowledge we but increase the horizon of ignorance.” -Henry Miller
It’s the most fundamental law of special relativity, and the realization that led Einstein to some of the greatest physics breakthroughs of all time: the idea that nothing can travel faster than light. That holds true even today, as all massless particles in a vacuum move exactly at the speed of light, while anything else — a massive particle anywhere or a massless one in a medium — are doomed to move slower than the speed of light. But when it comes to the expanding Universe, this seems like it might not still hold. Kevin Forward wants to know, as he asks:
In the first millionths of a second of the Big Bang did the universe not expand faster than the speed of light?
As a spoiler: no, it didn’t expand faster than light then, nor at any other time, nor will it ever do so. But there’s a good reason why one might think it once did.
