Dark Matter: Can It Stop Universe Expansion?

In summary, if the universe has a flat topology and there is enough dark matter or dark energy, the expansion rate of the universe will eventually decrease and the size of the universe will asymptotically approach a finite value. However, if there is no dark energy, the size of the universe will continue to increase without bound.
  • #1
LSulayman
42
0
Is it true that, if there was enough dark matter in the universe it could stop the expansion of it?
If it is, can someone explain to me how?
 
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  • #2
Well, roughly, speaking, yes.

In general the universe can have one of three topologies. (see http://en.wikipedia.org/wiki/Shape_of_the_Universe). Either the universe is below the critical density and will expand forever (this is called an open universe), or the universe is at the critical density and will expand forever (this is called a flat universe), or the universe is above the critical density and will eventually stop collapsing and start contracting (this is called a closed universe). Observations indicate that the universe is very close to being flat.

So in principle, if there was more dark matter in the universe, so that the density was more than the critical density, it would eventually stop expanding. However, the same effect could be had by adding more dark energy, or more regular matter.
 
  • #3
nicksauce said:
or the universe is at the critical density and will expand forever (this is called a flat universe)

Would it be correct to say that in a flat universe the expansion rate decreases asymptotically and that the size of the universe increases asymptotically never exceeding a certain size?
 
  • #4
Dark energy dominates the energy density and put that kind of matter/energy content into Einstein's Equations and you get an accelerating universe.
Cosmologists estimate that the acceleration began roughly 5 billion years ago.
 
  • #5
PhilKravitz said:
Would it be correct to say that in a flat universe the expansion rate decreases asymptotically and that the size of the universe increases asymptotically never exceeding a certain size?

From the Friedmann equations, the expansion rate is

[tex]H^2 = H_0^2\left( \Omega_M(a^{-3}) + \Omega_{\Lambda}\right)[/tex]

So in a flat universe the expansion rate asymptotes to [tex]H_0\sqrt{\Omega_{\Lambda}}[/tex].

The proper size of the observable universe is given by

[tex] R = \frac{a}{H_0}\int\frac{da}{a^2\sqrt{\Omega_Ma^{-3}+\Omega_{\Lambda}}}[/tex]

So if there is dark energy, then this will asymptotes to a finite value, but if there is no dark energy, then it will be unbounded.
 

1. What is dark matter?

Dark matter is a type of matter that is believed to make up approximately 85% of the total matter in the universe. It does not emit or absorb light, making it invisible to telescopes and difficult to detect. Its existence is inferred by its gravitational effects on visible matter.

2. How does dark matter affect the expansion of the universe?

Dark matter is thought to play a crucial role in the expansion of the universe. It is believed to provide the necessary gravitational pull to counteract the expansion caused by dark energy, allowing for a stable and steady expansion of the universe.

3. Can dark matter stop the expansion of the universe?

While dark matter does have a significant influence on the expansion of the universe, it is not believed to be able to stop it completely. The expansion of the universe is a result of multiple factors, including dark energy, and it is unlikely that any single factor, including dark matter, can completely halt it.

4. How is dark matter being studied and detected?

Dark matter is being studied through various methods, including observations of its gravitational effects on visible matter, as well as experiments such as the Large Hadron Collider. Detecting dark matter directly is challenging, but scientists are using advanced technologies such as underground detectors and particle accelerators to try and identify it.

5. What are the potential implications of dark matter on the fate of the universe?

The presence and behavior of dark matter is crucial in determining the ultimate fate of the universe. If the amount and distribution of dark matter are not fully understood, it could greatly impact our understanding of the universe's future. Some theories suggest that dark matter may eventually lead to a collapse of the universe, while others propose a never-ending cycle of expansion and contraction.

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