- #1
spaghetti3451
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Is the Hubble constant decreasing over cosmological timescales?
Variation of Hubble constant in cosmological time
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- Thread starter spaghetti3451
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In summary, the Hubble constant, which measures the rate of expansion of the universe, has been found to vary over time in cosmological studies. This variation is believed to be caused by different factors, such as the amount of matter and dark energy present in the universe. Recent observations have shown that the Hubble constant is increasing, indicating that the expansion rate of the universe is accelerating. This discovery has raised questions about our current understanding of the fundamental laws of physics and the nature of the universe. Further research and observations are needed to fully understand the variation of the Hubble constant and its implications for our understanding of the cosmos.
- #2
Bandersnatch
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Yes:
- #3
spaghetti3451
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Why did the Hubble constant tend to infinity in the early universe?
- #4
Bandersnatch
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Mostly for the same reason that f(x)=1/x goes to infinity as x goes to 0. Remember that H is the proportionality factor between recessional velocities and distances: H=V/D. As the distances between receding objects decrease to 0, H goes to infinity.
An additional effect comes from V being larger in the past, but that's secondary.
An additional effect comes from V being larger in the past, but that's secondary.
- #5
spaghetti3451
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The relation
$$H = 1.67 \sqrt{g_{*}} \frac{T^{2}}{M_{P}}$$
is valid during the radiation-dominated epoch. Is it valid during the inflationary epoch?
$$H = 1.67 \sqrt{g_{*}} \frac{T^{2}}{M_{P}}$$
is valid during the radiation-dominated epoch. Is it valid during the inflationary epoch?
- #6
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No.spaghetti3451 said:
- #7
spaghetti3451
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What would be the correct relation for the Hubble parameter in the inflationary epoch?
- #8
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That would depend on the equation of state for whatever is driving inflation. If what drives inflation behaves as a cosmological constant, then the Hubble parameter would be constant during inflation.
- #9
spaghetti3451
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Would you share a review article which discusses this in more detail?
- #10
Bandersnatch
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Would this be of any help?
https://ned.ipac.caltech.edu/level5/Watson/Watson5_3.html
https://ned.ipac.caltech.edu/level5/Watson/Watson5_3.html