# Is universe expanding or contracting?

## Main Question or Discussion Point

gravity pulls two galaxies. Andromeda and Milky Way are going to collide in few billion years. this seems to show that everything in the universe is moving close to each other i.e. contracting. but, since the universe was formed, it has been expanding due to dark energy. how do you explain this? secondly, are they (force by dark energy and gravity) in equlibrium? if not which one is dominating?

nicksauce
Homework Helper
The universe is definitely expanding. However, the expansion is only dominant on large scales. At small scales, gravity wins out, and that is why Andromeda and the Milky Way are getting closer together. Think about it this way... if I drop a ball, it falls to the group due to the earth's gravity. Does that mean the universe isn't expanding?

but, since the universe was formed, it has been expanding due to dark energy.
This is a false statement. First, dark energy was essentially negligible in the early stages of the universe. Second, even if there was no dark energy, the universe would still be expanding. The effect of dark energy is to cause the universe to expand at an accelerating rate.

secondly, are they (force by dark energy and gravity) in equlibrium? if not which one is dominating?
Well the universe continues to expand at an accelerating rate, so you could say that dark energy is dominating.

Thank you nicksauce. it was a very well written answer. i also discovered a new fact in the process. (the one that was false).

gravity pulls two galaxies. Andromeda and Milky Way are going to collide in few billion years. this seems to show that everything in the universe is moving close to each other i.e. contracting. but, since the universe was formed, it has been expanding due to dark energy. how do you explain this? secondly, are they (force by dark energy and gravity) in equlibrium? if not which one is dominating?
That depends on your POV. From inside it looks expanding, from outside it looks contracting.

George Jones
Staff Emeritus
Gold Member
That depends on your POV. From inside it looks expanding, from outside it looks contracting.
What does this mean?

What does this mean?
Don't bother.

Actually I was waiting for some clever response like "there is no outside to the universe".

russ_watters
Mentor
Don't bother.

Actually I was waiting for some clever response like "there is no outside to the universe".
Ok....so what is the point then?

Ok....so what is the point then?
There was no point.