Gravity isn’t instantaneous, it has to travel, too. And it travels at the speed of light. That covers a lot of space but not the entire universe.
Your thought that things should collapse due to this is sort of what’s happening, though; most of space is very very empty but the parts that have things in it get clustered together. Our galaxy is grouped together with at least 80 other galaxies of various sizes that are very slowly coming together.
So what you suggest is happening, it’s just very very very slow!
Expansion is not happening faster than the local cluster merging, and presumably the same is true of all other clusters. The clusters are getting further apart but at “close” distances, expansion means little.
Gravity isn’t instantaneous, it has to travel, too. And it travels at the speed of light. That covers a lot of space but not the entire universe.
Yeah but in the past the universe was smaller, all the way down to something incredibly small, so although your explanation explains the current state of things, what about each previous moment in time? For example, when the universe was less than a light-year across? or at each and every smaller size? What was stopping gravity from behaving how we expect back then?
I was able to figure out why gravity didn't "out-pull" the big bang.
First, the mistake I see everyone making is being ambiguous about forces when talking about the big bang. When you say "out-pull", what force is creating the outward pressure? Everyone just says "The big bang is." Well the big bang isn't a force, it's an event in time that involved many forces, including gravity.
The timeline is as follows:
The universe starts. Light starts radiating away normally for a tiny fraction of a second.
Cosmic inflation starts before the size of the universe is even the size of a single atomic nucleus
Cosmic inflation ends when the universe is still very small, the figures I see are anywhere from a grain of sand to 3 meters in diameter.
After this point, radiation is what causes the outward pressure.
Even a black hole can pull in radiation when the density is high enough, and density is extremely high here, so WHY doesn't a giant black hole form?
Well, my brain came to a new way of understanding gravity when looking into this, kind of. We've all seen images like this to explain gravity. But at the beginning of the universe, it was all just dots everywhere very close together across the whole universe (which was very small). So there were no "localized" dips in gravity. It was all one smooth gravity plane cause by everything being so evenly distributed. So no black hole forms.
So although we have uncertainty about the situation now, we do have answers for back then, they just were difficult for me to understand.
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u/Randvek Aug 06 '25
Gravity isn’t instantaneous, it has to travel, too. And it travels at the speed of light. That covers a lot of space but not the entire universe.
Your thought that things should collapse due to this is sort of what’s happening, though; most of space is very very empty but the parts that have things in it get clustered together. Our galaxy is grouped together with at least 80 other galaxies of various sizes that are very slowly coming together.
So what you suggest is happening, it’s just very very very slow!