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As the universe approaches perfect exponential expansion the Hubble constant approaches a limiting value. What is the limiting value and how long from now will it be reached?
Ranku said:As the universe approaches perfect exponential expansion the Hubble constant approaches a limiting value. What is the limiting value and how long from now will it be reached?
marcus said:So when Uni has expanded ten-fold we will be pretty close to the asymptotic Hubble.
How long will it take for the universe to expand ten-fold ? How to calculate that?
I think you understand that it is the scalefactor a(t) that is increasing and acceleration means that a(t) increase is speeding up, the second time-derivative a"(t) is positive.
When the universe was decelerating was the scalefactor increasing at a decreasing rate?
For a constant H (a good approximation), you get the solution [itex] a \propto e^{Ht}[/itex]. That's an e-fold expansion in 1/H, and tenfold in 2.3/H ~ 31 Gy.How long will it take for the universe to expand ten-fold ? How to calculate that?
Yes.When the universe was decelerating was the scalefactor increasing at a decreasing rate?
The current accepted value for the Hubble constant is 70 km/s/Mpc. However, recent studies have suggested a slightly higher value of around 74 km/s/Mpc.
The Hubble constant is determined by measuring the rate at which galaxies are moving away from us, known as the redshift, and using the relationship between distance and redshift to calculate the expansion rate of the universe.
Yes, the limiting value of the Hubble constant has changed as our technology and methods for measuring it have improved. It was first estimated to be 500 km/s/Mpc by Edwin Hubble in the 1920s, and has since been refined to the current accepted value of 70 km/s/Mpc.
The limiting value of the Hubble constant is directly related to the age of the universe. A higher value would indicate a younger universe, while a lower value would suggest an older universe. However, there is currently no consensus on the exact value of the Hubble constant, so it is difficult to determine the precise age of the universe.
Dark energy, which is thought to be responsible for the accelerating expansion of the universe, can affect the limiting value of the Hubble constant. Some studies suggest that the Hubble constant could have a different value in different parts of the universe due to the presence of dark energy, leading to a more complex understanding of the expansion rate of the universe.