- #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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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
Related to Variation of Hubble constant in cosmological time
1. What is the Hubble constant?
The Hubble constant is a measure of how fast the universe is expanding. It represents the rate at which galaxies are moving away from each other due to the expansion of space.
2. How does the Hubble constant vary over time?
The Hubble constant is not a constant value, and it has been found to vary over time. This variation can be attributed to the changing density of matter in the universe and the effects of dark energy, which is causing the acceleration of the expansion of the universe.
3. Why is it important to study the variation of the Hubble constant?
Studying the variation of the Hubble constant is important because it can provide insights into the evolution of the universe and the role of different factors such as dark energy in shaping its expansion. It can also help us understand the nature of the universe and its future fate.
4. How do scientists measure the variation of the Hubble constant?
Scientists use various techniques to measure the variation of the Hubble constant, including studying the redshift of distant galaxies, the cosmic microwave background radiation, and the gravitational lensing effect. These methods provide different values for the Hubble constant, leading to ongoing research and debate in the scientific community.
5. What are the current theories explaining the variation of the Hubble constant in cosmological time?
There are various theories attempting to explain the variation of the Hubble constant in cosmological time. Some propose the existence of new physics, such as a varying dark energy or modified theories of gravity. Others suggest that the variation is simply due to uncertainties in our measurements and observational techniques. Further research and data analysis are needed to better understand this phenomenon.
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