Is universe expanding or contracting?

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Discussion Overview

The discussion centers around the nature of the universe's expansion or contraction, exploring the roles of gravity and dark energy. Participants examine the implications of these forces on cosmic structures, particularly the Milky Way and Andromeda galaxies, and the conditions under which expansion or contraction may be observed.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants argue that while the universe is expanding due to dark energy, local gravitational effects, such as the attraction between the Milky Way and Andromeda, suggest a contracting behavior on smaller scales.
  • One participant asserts that dark energy was negligible in the early universe and that the universe would still expand even without it, emphasizing that dark energy causes the acceleration of this expansion.
  • There is a suggestion that the forces of dark energy and gravity may not be in equilibrium, with some indicating that dark energy is currently dominating the expansion of the universe.
  • Another perspective introduced is that the perception of the universe's expansion or contraction may depend on one's point of view, leading to confusion about the nature of these observations.

Areas of Agreement / Disagreement

Participants express differing views on the balance between gravitational attraction and the effects of dark energy, indicating that multiple competing perspectives remain without a clear consensus on the overall dynamics of the universe.

Contextual Notes

Some statements rely on assumptions about the nature of dark energy and gravity, and the discussion reflects varying interpretations of observational perspectives regarding cosmic expansion and contraction.

utkarsh009
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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?
 
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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).
 
utkarsh009 said:
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.
 
robheus said:
That depends on your POV. From inside it looks expanding, from outside it looks contracting.

:confused: What does this mean?
 
George Jones said:
:confused: What does this mean?

Don't bother.

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

There was no point.
 

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