Full disclosure: I’m high, but what exactly is expanding in the universe? Like I read something at some point that said that galaxies and cosmological bodies aren’t actually moving away from us faster than light, the space between them is just expanding. They made a distinction somehow but now, a long time after reading that, I’m sitting here wondering what it is that’s expanding… and wouldn’t whatever it is be expanding faster than light? I hope someone can help because I’m starting to spiral out.
In: Physics
Imagine you have an elastic band line and you put two points on it close by. As you stretch the band, it expands, however the two points close together barely move apart.
Another example is a crowd of people, if the space between all the people grows by a foot, then the whole crowd will grow quite a bit, but individuals haven’t moved much.
So in the universe, the space between everything is growing. Gravity, electromagnetism, and the strong and weak nuclear forces keep things together, however when you have very very long distances where gravity is tiny, such as between galaxies, this expansion is noticeable.
> wouldn’t whatever it is be expanding faster than light?
Yes. The *cumulative* effect of expansion over long distances makes galaxies drift apart faster than light. You can’t move through space faster than light, but the galaxies themselves aren’t moving…*space itself* is expanding.
Think about baking chocolate chip cookies. When you put the little balls of cookie dough into the oven, all the chocolate chips are fairly close together. As the cookies bake, the dough expands and the chocolate chips are spread further apart. The chips themselves didn’t move through the dough, the dough itself expanded.
The chocolate chips are galaxies and the dough is spacetime. Objects can’t move through spacetime faster than light, but spacetime itself can expand much faster.
And since you’re high I probably just made you want cookies. Sorry about that.
Best example I know is the balloon example
Draw a bunch of dots 1 inch apart on a balloon. Now blow up the balloon. As you fill the balloon, the dots get further apart The dots didn’t move, but the space between them is now larger
Instead of the two dimensional surface of the balloon stretching and growing, it’s all of space stretching and growing. It’s not that the stars are moving away from eachother; just like the edits on the balloon the space between us is simply growing
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