In one of the most monumental discoveries of the 20th century, we learned that the Universe is not simply a static, unchanging background, but rather that space itself expands as time marches on. It’s as though the very fabric of the Universe itself is stretching so that distant objects get farther and farther apart. We see this phenomenon in all directions and in all locations in space when we look beyond the Local Group. And yet, nearly 100 years after it was all worked out, it’s still a puzzling, counterintuitive phenomenon, even for experts in astronomy and astrophysics.
It’s only natural to wonder, if the Universe is expanding, how fast is the expansion of space? That’s what Darren Bobley wants to know, asking:
“Hi! Would you kindly help me to understand how fast space is expanding compared to light – in lay terms? (That mega-parsec idea is too heady for me.) Is it roughly 2x the speed of light? 100x times? Etc.”
It’s common, when we think about something expanding, to think in terms of speed. And we can do that if we so choose, but the answer is going to be different for every single object we look at. Here’s why.
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