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iidartzii
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To what extent is it decreasing? If it reaches zero, wouldn't all the galaxies light eventually reach us? If so, why do astrophysicists say that some galaxies light will never reach us?
iidartzii said:To what extent is it decreasing? If it reaches zero, wouldn't all the galaxies light eventually reach us? If so, why do astrophysicists say that some galaxies light will never reach us?
marcus said:The standard cosmology model depends on several key parameters that have to be estimated and what we expect the Hubble rate to do in the future depends on what values you plug into the model
A common cosmology calculator that people use a lot is Ned Wright's, here is the basic version:
http://www.astro.ucla.edu/~wright/CosmoCalc.html
It assumes the Hubble rate is 71, and the dark energy fraction is 0.73. It makes the standard assumptions about the character of dark energy (constant energy density etc.)
With those values, the Hubble rate will continue decreasing indefinitely and approach an asymptotic value of
71sqrt(.73). That equals 60.66, call it 61
In that scenario H keeps decreasing forever but as it nears 61 it decreases slower and slower so that it never reaches 61. It kind of declines but levels out at 61.
You can find explanations of what the numbers represent and what the units are, by looking around in Ned Wright's cosmology tutorial website, where the calculator is.
You can calculate the Hubble radius c/H yourself. At any given time it is the distance which is increasing at rate c. If a galaxy is at that distance, c/H, then its distance from us is increasing at the speed of light. Eventually this means that when H = 61, anything farther than c/H will not be able to get light to us.
If you want help calculating c/H, please ask.
If further more accurate measurements cause astronomers to change the parameters slightly, we might for example get a situation where the present value of H is estimated to be 72, and the dark energy fraction is estimated to be 0.74.
That might happen. The current numbers are supported by millions of datapoints, a huge body of data which the standard model fits remarkably well. But there is still some uncertainty.
If the estimates change like that, you can see that the asymptotic value of H, that it gradually declines to, will be
72 sqrt(.74), which is 61.94, call it 62.
So that number 61 I mentioned is subject to change a little, as more data is gathered, but roughly speaking it is probably pretty good already.
iidartzii said:Is it just a co-incidence that Hubble's radius is the almost the same as the age of the universe?
iidartzii said:Is it just a co-incidence that Hubble's radius is the almost the same as the age of the universe?
marcus said:And according to that model it was NOT true in the past that age approximately equaled 1/H,
Nor will it be true in the future.
sylas said:Current estimates tend to be around Ωm ~ 0.27, but 0.2624 falls within the confidence limits. This value decreases over time as the universe expands. So in the conventional model, the point of equality for 1/H and age was most likely very recently, in cosmological terms. Co-incidence? Yes, most likely; but this is not completely definite.
marcus said:If the estimates change like that, you can see that the asymptotic value of H, that it gradually declines to, will be 72 sqrt(.74), which is 61.94, call it 62.
Skolon said:I'm sorry but something is very wrong with my conception about expansion. The fact that expansion is accelerated doesn't mean that value of H is increasing with time? Why do you say that will gradually decline?
Skolon said:I'm sorry but something is very wrong with my conception about expansion. The fact that expansion is accelerated doesn't mean that value of H is increasing with time? Why do you say that will gradually decline?
Hubble's constant is a measure of the rate at which the universe is expanding. It was first calculated by astronomer Edwin Hubble in the 1920s and is denoted by the symbol H0.
There is ongoing debate and research in the scientific community about the exact value of Hubble's constant and whether it is changing over time. Some studies have suggested a decrease in Hubble's constant, while others have found no significant change.
One possible explanation for a decreasing Hubble's constant is the presence of dark energy, a mysterious force that is thought to be causing the expansion of the universe to accelerate.
A decreasing Hubble's constant would suggest that the universe is expanding at a slower rate than previously thought. This could have implications for our understanding of the age and size of the universe, as well as the nature of dark energy.
If Hubble's constant is indeed decreasing, it could challenge some of our current theories and models about the universe. It could also lead to new discoveries and a deeper understanding of the forces at work in the universe.