Flat and accelerating Universe

[oXDawidXo]

Hi!

I'm doing physics project and I'm stuck with a really awful paradox.

Universe appear to be flat (nearly), so it should expand forever (the critical universe). On the other hand we've got acceleration of the universe so open model. Which model is the right one?

 

[bapowell]

Hi!

I'm doing physics project and I'm stuck with a really awful paradox.

Universe appear to be flat (nearly), so it should expand forever (the critical universe). On the other hand we've got acceleration of the universe so open model. Which model is the right one?

An open universe is not accelerating. In the presence of ordinary matter and radiation, all three geometries-- open, flat, closed -- are decelerating. Closed universes eventually begin to contract again. Flat and open universes expand forever at a decelerating rates.

An accelerating spacetime is not inconsistent with flatness. In fact, accelerating spacetimes are driven towards flatness dynamically.

 

[Wallace]

Hi!

I'm doing physics project and I'm stuck with a really awful paradox.

Universe appear to be flat (nearly), so it should expand forever (the critical universe). On the other hand we've got acceleration of the universe so open model. Which model is the right one?

It sounds like you are reading some slightly older material. At one point we classified the Universe under the simple 'open/flat/closed' system because we thought the only thing that mattered was the density of matter. If there is not enough, we have an open universe, too much we collapse and just right leads to asymptotic decceleration.

It turns out though that there is more to the Universe. In fact we think most of the energy today is not in the form of matter but 'dark energy' which rather than acting to slow the expansion speeds it up.

Once you include dark energy, the geometry (open/flat/closed) and the fate of the universe (expand forever/collapse) become different questions, it depends on the properties of dark energy which are not yet fully understood.

Our present best guess is that the universe is flat, in that the sum of matter + dark energy density equals the critical density, but that the dark energy dominates and the expansion is accelerating. Out best guess says that this will continue in the future and the expansion will grow ever more rapid, but that question is far from settled.

 

[oXDawidXo]

I think I get it now
Thank you

 

[sardar]

Hello!

The concept of a flat and accelerating universe can be a bit confusing, but there are theories and evidence that can help explain this paradox. First, it's important to understand that the shape of the universe is not something that can be directly observed, but rather inferred from measurements of the universe's expansion and curvature.

The idea of a flat universe comes from the theory of general relativity, which suggests that the universe should have a flat geometry if it has a certain amount of matter and energy. This is often referred to as the critical density of the universe. However, this theory does not take into account the possibility of a mysterious force known as dark energy, which is thought to be responsible for the universe's acceleration.

Recent observations have shown that the expansion of the universe is indeed accelerating, which supports the idea of an open universe. However, this does not necessarily mean that the universe is not flat. In fact, some theories suggest that the universe can be both flat and accelerating, with the presence of dark energy causing the acceleration while still maintaining a flat geometry.

So, to answer your question, both models can be considered correct in their own ways. The key is to continue studying and gathering evidence to better understand the nature of our universe. Good luck with your project!