Flat vs Open Universe: CMBR & Type Ia Supernovae

In summary, the conversation discusses the concept of a flat universe and its implications on the expansion of the universe. It is noted that a flat universe with a nonzero cosmological constant/dark energy would result in an accelerating expansion, which is supported by observations of distant type Ia supernovae. This suggests that the universe is open, closed, or flat in spatial geometry.
  • #1
Willfrid Somogyi
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So CMBR points to a flat universe, and this seems to be the generally accepted model. But in a flat universe is expansion not supposed to slow exponentially, stopping after an infinite time? How does this fit with the observation that distant type Ia supernovae show the universe's expansion to be accelerating, which would point to an open universe.
 
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  • #3
Willfrid Somogyi said:
But in a flat universe is expansion not supposed to slow exponentially, stopping after an infinite time?

Only if there is no cosmological constant/dark energy.

Willfrid Somogyi said:
the universe's expansion to be accelerating, which would point to an open universe.

No, it points to there being a nonzero cosmological constant/dark energy. An open universe with zero cosmological constant would still have slowing expansion; but it would never slow to a complete stop, even after an infinite time. The only way to get accelerating expansion is to have a nonzero cosmological constant/dark energy; and such models are possible with closed, flat, or open spatial geometry.
 
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  • #4
PeterDonis said:
Only if there is no cosmological constant/dark energy.
No, it points to there being a nonzero cosmological constant/dark energy. An open universe with zero cosmological constant would still have slowing expansion; but it would never slow to a complete stop, even after an infinite time. The only way to get accelerating expansion is to have a nonzero cosmological constant/dark energy; and such models are possible with closed, flat, or open spatial geometry.

Thanks!
 

1. What is the main difference between a flat and open universe?

The main difference between a flat and open universe is the curvature of space. In a flat universe, space is completely flat and infinite, while in an open universe, space is curved and also infinite. This curvature is determined by the amount of matter and energy in the universe.

2. How does the Cosmic Microwave Background Radiation (CMBR) support the idea of a flat universe?

The CMBR is radiation that is left over from the early stages of the universe, and it is used as evidence for the flatness of the universe. This radiation is very uniform and evenly distributed, which suggests that the universe is flat. If the universe were curved, the CMBR would appear distorted.

3. What role do Type Ia Supernovae play in determining the shape of the universe?

Type Ia Supernovae are used as standard candles in cosmology, meaning that their brightness can be used to measure distances in the universe. By measuring the brightness and distance of these supernovae, scientists can determine the expansion rate of the universe and therefore its shape.

4. How do scientists measure the curvature of the universe?

Scientists use a variety of methods to measure the curvature of the universe, including observing the CMBR, studying the large-scale structure of the universe, and analyzing the patterns of light from distant galaxies. These methods all provide evidence for a flat universe.

5. What are the implications of a flat or open universe for the future of the universe?

If the universe is flat, it will continue to expand at a constant rate and eventually reach a state of infinite expansion. However, if the universe is open, it will continue to expand at an increasing rate and eventually reach a state of infinite expansion. The ultimate fate of the universe is still uncertain and will depend on the actual shape of the universe.

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