ELi5: How does the whole light year thing work? How does something happen a long time ago that we know of yet we can still see it and have to wait for it to happen again (like those exploding star things on tt)
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When we say “speed of light” we are actually referring to the speed at which information about one part of the universe can get to another, so it’s actually the “speed of causality.” Other things like gravity and electromagnetism also propagate out at this speed. Even light is only going “light speed” in a vacuum. Things like air, water, or glass actually slows it down.
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