# Getting a feel for how much the Universe expands

1. Feb 7, 2016

### wolram

I am trying to get my head around how much the volume of the universe increases per some time scale, say 1000yrs, how would one calculate this?

2. Feb 7, 2016

### Orodruin

Staff Emeritus
You would take the Hubble parameter and multiply by the time.

3. Feb 8, 2016

### Jorrie

The volume of the universe is unknown, so you cannot calculate what you asked. To get a feeling, it is best to just realize that all large scale distances are presently increasing by about 68 km per second per Mpc, which translates to about 1/144 % per million years. So, pick any large volume that you fancy, increase the radius by 1/144 % and calculate the volume increase.

4. Feb 9, 2016

### Alltimegreat1

I get it that the universe is (presumably) infinite. But what about the distribution of matter? Is it likely that there are stars and galaxies trillions or quadrillions of lights years away from here?

5. Feb 9, 2016

### Orodruin

Staff Emeritus
According to the cosmological principle, which has proven quite good at describing the Universe at large scales, the universe is homogeneous. This would mean that the Universe at any other location would look very similar to our part of the Universe.

6. Feb 9, 2016

### Alltimegreat1

Interesting. So not only is space infinite, but there is also an infinite amount of matter in the universe.

7. Feb 9, 2016

### Orodruin

Staff Emeritus
We do not know if the universe is infinite or not.

8. Feb 9, 2016

### Alltimegreat1

But if it is, then there would also be an infinite amount of matter, right? I used to envision the universe as having a sphere of matter that is expanding outward, but beyond the edge of the furthest matter lie endless expanses of empty space.

9. Feb 9, 2016

### Orodruin

Staff Emeritus
This inherently assumes you can define a universal "now" at which you sum up the matter. While this is the case in the models describing the Universe on large scales, it gets problematic if these models are not accurate, eg, if you also want to describe smaller scales.

Your vision of a sphere expanding outwards is not correct. This is not what is meant by universal expansion.

10. Feb 9, 2016

### rootone

The Universe IS space.
There is nothing 'outside' which it expands 'into'.
https://en.wikipedia.org/wiki/Metric_expansion_of_space

11. Feb 10, 2016

### Alltimegreat1

According to that link, space only increases between galaxies that are sufficiently distant to each other. Apparently the Milky Way and Andromeda galaxies are too close to each other for that. Assuming spacetime continues to expand eternally, eventually after quadrillions of years we would be able to observe nothing else outside of our own galaxy?

12. Feb 10, 2016

### rootone

Yes that is one conclusion which a lot of people agree with, but it's somewhat debatable since it depends on how the rate of expansion might have changed over time.