Could a Collapsing Universe Result in a Cosmological Blueshift?

In summary, the conversation discussed the concept of cosmological blueshift and the relevance of the scale factor in a contracting universe. It was concluded that the formula for the scale factor would change to 1/1(z-1) and that some galaxies may have a negative z value. The conversation also briefly touched on Einstein's popularity among teenagers and his iconic hairstyle.
  • #1
2203312
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If the Universe stopped expansion 10 million years ago and started to collapse
Whould it their be such a thing as cosmological blueshift?


Would the scalefactor-redshift be R=1/(z - 1) or R=1/(1+z)?

I think since universe is collapsing then spectra will be blueshifted!

The scale factor is still relevant but the formula is changed to 1/1(z-1)!
 
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  • #2
2203312 said:
If the Universe stopped expansion 10 million years ago and started to collapse
Whould it their be such a thing as cosmological blueshift?Would the scalefactor-redshift be R=1/(z - 1) or R=1/(1+z)?

I think since universe is collapsing then spectra will be blueshifted!

The scale factor is still relevant but the formula is changed to 1/1(z-1)!

If the universe had stopped expanding only fairly recently, like say a billion years ago, and had started to contract, then some galaxies would have a NEGATIVE z.

It would continue to be true that 1+z equals the ratio by which distances have changed while the light is in transit.

Some light would have z = 0 for example if the light was emitted 2 billion years ago and for the first billion year that it was in transit there was expansion and then for the next billion years there was contraction---then there would be no net change in the wavelength.
=======================

You don't need any new formula. You can always assume that 1+z is the ratio of distances, and also the ratio of wavelengths.
If the universe had been contracting for several billion years, so there was enough time for some distances to contract by a factor of 10, then there would be some galaxies with z = -0.9
That means the ratio of wavelengths is 1+z = 0.1
The wavelengths are ten times shorter----in other words bluer, more UV

The way that z is defined it cannot take on the value -1 or any value more negative than -1. The ratio of wavelengths is always a positive number 1+z>0 and that means that z>-1.
 
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  • #3
Many thanks,
Now the big question

How did Einstein get so popular with teenage kids and that hair style?
 

1. What is a closed universe?

A closed universe is a theoretical concept in cosmology that refers to a universe that is finite in size and has a specific shape, such as a sphere or torus. It is believed that the universe may be closed if it has enough matter to eventually stop its expansion and begin to contract.

2. How does a closed universe differ from an open universe?

A closed universe is fundamentally different from an open universe in terms of its shape and ultimate fate. An open universe is infinite in size and has a flat or negatively curved shape, while a closed universe is finite and has a positively curved shape. Additionally, an open universe is predicted to continue expanding forever, while a closed universe may eventually collapse in on itself.

3. How do scientists determine if the universe is closed?

There are several methods that scientists use to determine the shape and potential closure of the universe. One method is to study the cosmic microwave background radiation, which is leftover radiation from the early universe. Another method is to study the distribution of matter and galaxies in the universe. By analyzing these factors, scientists can make predictions about the overall shape and potential closure of the universe.

4. What are the implications of a closed universe?

If the universe is closed, it would have significant implications for our understanding of the universe and its ultimate fate. For example, a closed universe would mean that the universe is finite and that there may be a boundary or edge to the universe. It could also mean that the universe will eventually collapse in on itself, leading to a "Big Crunch" scenario.

5. What are some current theories about the shape and closure of the universe?

There are several theories about the shape and closure of the universe, with some scientists proposing that the universe is closed, while others argue that it is open. Some theories also suggest that the universe may have a "flat" shape, which would mean that it is neither open nor closed, but rather has a balance between expansion and collapse. However, the true nature of the universe's shape and closure is still a topic of ongoing research and debate among scientists.

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