The expansion of the universe

Factual Questions
1

Has anyone come up with an equation to explain (describe?) how the universe (space-time?) expanded and is still expanding? Need answer fast and faster.

2

The math describing the expansion of the universe comes out of the equations for General Relativity. Specifically the FLRW metric.

3

Note that you also need an equation of state to determine how the Universe expands; the equation of state tells you how the pressure and density of matter are related to each other. That plus the FLRW equations are enough to tell you the expansion rate of the Universe at any time.

4

Thanks! So the expanding universe can be mathematically described (way beyond my calculus miscomprehensions). Do they explain what is causing the expansion? Are these equations in any way related any of the four basic forces?

5

We can model what we observe about the universe fairly well mathematically, but as for why the universe is that way, nobody really knows.

General relativity is, of course, a mathematical model of gravity. So that’s pretty intimately related to a fundamental force.

6

“General relativity is, of course, a mathematical model of gravity. So that’s pretty intimately related to a fundamental force.”

Could gravity itself be a result of the expansion of space? Matter doesn’t expand, and neither does the space around it, causing a warp in space-time. (I’ve seen the videos of balls rotating towards the middle on stretched fabric).

This warp (unexpanded space) could maybe explain why matter is pulled or pushed towards other matter, no matter how far apart. (Gravity?)

May also explain why matter has mass.

Go ahead and start throwing the rocks, they just float around me in my multiverse.

7

“Why” questions never have an ultimate answer. Even if you can sometimes say “A is because of B”, that just opens up the question “Why B?”. At some point, you’re inevitably going to eventually get to “I don’t know”, or “It just is that way”, or some other such non-answer.

It’s hard to see how that could work. Gravity is observed on very small scales, such as objects on the surface of the Earth, and appears to follow the same laws on all scales. But the expansion of the Universe depends on scale, and is minuscule on scales as small as the Earth (about 10^-11 m/s).

8

Wait, you mean those emails I get about being 4" longer are true?