Why the Hubble Parameter Decreases to .85 of Today's Value

In summary, the Hubble parameter will eventually decrease to .85 of today's Hubble parameter because the matter density will decrease to zero and the dark energy density will remain constant, resulting in a total energy density that is 73% of what it is today. This is due to the Friedmann equation and in the long run, the Hubble parameter will be .73 of today's value. Taking the square root of both sides, this means that the Hubble parameter will be .85 of today's value.
  • #1
keepit
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Why will the Hubble parameter only decrease to .85 of today's Hubble parameter?
 
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  • #2
Think scalar field
 
  • #3
keepit said:
Why will the Hubble parameter only decrease to .85 of today's Hubble parameter?

Keepit, the basic equation of cosmology (due to Friedmann) says that in our kind of universe
H2 = energy density

that's where you convert all the matter to equivalent energy and include the 73% which is dark energy. It assumes approximately flat geometry (largescale on average) and evenly spread out matter.

I shouldn't say "equals" I should say "is proportional to".

The main thing is that matter density goes to zero and dark energy density is a constant so in the long run the total energy density will be 73% of what it is today. Essentially the matter energy will be all thinned out by expansion and virtually all the energy density will be due to dark. So total will be 73% what it is today.

So H2 will be 73% of what it is today. Because of the Friedmann equation.

that is to say H2 = .73 of today's H2 eventually in the long run.

Therefore H = .85 of today's H, eventually in the long run. Just take sqrt of both sides.
 
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1. Why does the Hubble parameter decrease over time?

The Hubble parameter, also known as the Hubble constant, is a measure of the rate at which the universe is expanding. As the universe expands, the distance between galaxies increases, leading to a decrease in the Hubble parameter over time.

2. What is the significance of the Hubble parameter decreasing to .85 of today's value?

This decrease in the Hubble parameter indicates that the expansion of the universe is slowing down, as the rate of expansion is not constant. This has important implications for the future of the universe and its eventual fate.

3. How is the Hubble parameter measured?

The Hubble parameter is typically measured using the Hubble Space Telescope, which observes the redshift of distant galaxies. The redshift is then used to calculate the distance and velocity of the galaxies, which can be used to determine the Hubble parameter.

4. What factors can affect the value of the Hubble parameter?

The value of the Hubble parameter can be affected by various factors, such as the amount and distribution of matter and energy in the universe, the presence of dark energy, and the curvature of space. These factors can influence the rate of expansion of the universe and therefore affect the value of the Hubble parameter.

5. Will the Hubble parameter continue to decrease in the future?

It is currently believed that the Hubble parameter will continue to decrease in the future, as the expansion of the universe is expected to slow down due to the effects of dark energy. However, the exact rate at which it will decrease is still uncertain and is an area of ongoing research in the field of cosmology.

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