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

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SUMMARY

The Hubble parameter will decrease to 0.85 of its current value due to the dynamics of energy density in the universe, as described by the Friedmann equations. The equation indicates that the total energy density is proportional to the matter density, which approaches zero, while dark energy density remains constant at approximately 73%. Consequently, as the universe expands, the Hubble parameter will reflect this shift, resulting in H² equating to 0.73 of its current value, leading to H equating to 0.85 of today's Hubble parameter in the long run.

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keepit
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Why will the Hubble parameter only decrease to .85 of today's Hubble parameter?
 
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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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