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Ian
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What is the magnitude of the Hubble length and what does it signify?
Also, does anyone have any idea what the estimated mass of the universe is.
Also, does anyone have any idea what the estimated mass of the universe is.
Ian said:What is the magnitude of the Hubble length and what does it signify?
Also, does anyone have any idea what the estimated mass of the universe is.
Ian said:Thanks Marcus, any idea on the estimated mass of the universe?
Ian.
Ian said:That sounds odd Marcus, how can you estimate the density without knowing the mass or volume.
How many kg's of mass are there thought to be in the universe, (excluding dark matter)?
marcus said:something to notice is that H(t) used to be hundreds of times larger and it has been decreasing as time goes along. H(t) decreasing makes c/H(t) increase. So the Hubble length has been growing---very fast in the early universe, really shooting out.
H(t) is still decreasing, but more slowly. H0 is destined to decline some more. So the Hubble length still has a ways to increase.
IIRC according to one common version of the standard model it will increase some 30 percent to an assymptotic value. but that doesn't matter so much. the main thing is the Hubble length is growing only very slowly now.
moving finger said:Has anyone noticed that (assuming the current lambda-CDM model) if you plot c/H(t)/R against R (where R is the scale size or "radius" of the universe), you get an interesting "peak" in the curve which corresponds to R approx equal to 10^10 light years?
For both low values of R (< 10^9 light years) and high values of R (>10^11 light years) this ratio c/H(t)/R is small; in the present epoch it goes through a maximum.
Does anyone have an explanation for this?
Thanks
MF
yogi said:For a critical density Hubble sphere, its about 10^53 kgm. For those models of the universe where all observers view the same Hubble sphere, but from different vantage points, this may be all there is.
Himarcus said:hi MF, no I hadnt noticed this, and the notation c/H(t)/R is at least superficially ambiguous.
but I understand that you mean (c/H(t))/R(t) which would be a dimensionless number.
so you are plotting
[tex]\frac{\frac{c}{H(t)}}{R(t)}= \frac{\text{Hubble length at time t}}{\text{scale factor at time t}}[/tex]
I do not remeber ever seeing a plot of that. I wish you would post a dozen or so sample values in the form of a list, or a table, so then i could see what you are talking about
moving finger said:Has anyone noticed that (assuming the current lambda-CDM model) if you plot c/H(t)/R against R (where R is the scale size or "radius" of the universe), you get an interesting "peak" in the curve which corresponds to R approx equal to 10^10 light years?
Thank you Space Tiger!SpaceTiger said:It looks like you're just plotting:
[tex]\frac{c}{\dot{R}}[/tex] vs [tex]R[/tex]
The critical point for this curve will just be the point at which [tex]\ddot{R}=0[/tex], which is the point at which the acceleration starts and lambda takes over (so to speak).
It maybe that Omega always has and always will be 1, but the cosmological dynamics right now depend on how this is split between Omega(mass) and Omega(vacuum energy) (assuming Omega(radiation) is negligible).Chronos said:I don't believe it's a coincidence. I think omega has, and will always be exactly 1. I haven't figured out the why part. But I refuse to believe we live at just the right time to see it pass from not 1 through 1 and continue on in whatever direction it had in mind.
moving finger said:I guess this is the source of the "coincidence" problem, that Omega(mass) is of the same order of Omega(vacuum energy) at the present epoch (ie the vacuum energy density is JUST about the right value that exponential expansion starts to take over just about now).
What does everyone think - is this purely a coincidence, or is there something deeper?
Advances are made by answering questions. Discoveries are made by questioning answers. (Bernard Haisch, Astrophysicist and past Editor of the Journal of Scientific Exploration)SpaceTiger said:You always seem to ask the best questions. .
Doesn't look so impressive on a linear plot though, does it?SpaceTiger said:Yeah, I dunno, but I suspect that it's nothing particularly deep. We were talking about this in the lounge a few weeks ago and I was drawing a logarithmic plot, marking the major events in cosmic history (decoupling, M-R equality, nucleosynthesis, etc.). I basically asked the question, if I pick a random point on this plot (i.e. a random proper time), what are the chances that I'll land near (in logarithmic interval) some major "event" in the universe's evolution?
It's obviously an extremely ambiguous question, as it depends on what one defines to be a "major" event, but I think it was worth the qualitative look, at least. My general conclusion was that it wasn't obviously strange that we landed this near the lambda transition, but is still worth looking into. Perhaps it's in some way related to the anthropic principle and that the growth of structure in the universe somehow naturally led to us existing near the transition. It's probably not worth thinking too hard about it until we have a better idea of what the dark energy is.
actually I reckon the total mass contained within the present Hubble radius (1.3 x 10^26m), assuming a mean mass-density of 2.55 x 10^-27 kg/m^3, is about 2.4 x 10^52 kg.Ian said:Thanks everyone for the info, I made an estimate of the mass of the universe of ~10^50 kg. Comparing the gravitational length (GM/c^2) of this mass to the Hubble length tells me something is out order with expansionist big bang ideas.
Interesting, but I was actually querying (in my last post) why Ian seemed to think there was a problem with the numbers?Garth said:In the Freely Coasting model R(t) = ct
[tex]\frac{\frac{c}{H(t)}}{R(t)}= \frac{\text{Hubble length at time t}}{\text{scale factor at time t}} = 1[/tex] and [tex]\ddot{R}=0[/tex] at all times..
May this be the explanation you are looking for moving finger?
Garth
The Hubble Length is a theoretical distance in the Universe that marks the boundary between where objects are moving away from each other due to the expansion of the Universe and where objects are gravitationally bound. It is named after American astronomer Edwin Hubble who first observed the expansion of the Universe. The current estimated value of the Hubble Length is about 14 billion light-years.
The Hubble Length is calculated by using Hubble's law, which states that the further away a galaxy is from us, the faster it appears to be moving away from us. By measuring the redshift of light from distant galaxies, we can determine how fast they are moving away from us. The Hubble Length is then derived from the Hubble constant, which is a measure of the rate of expansion of the Universe.
The Hubble Length is significant because it helps us understand the scale and size of the Universe. It serves as a boundary between where objects are affected by gravity and where they are not. It also gives us an idea of the age of the Universe, as objects beyond the Hubble Length cannot be seen due to the expansion of the Universe.
The Hubble Length is closely related to the mass of the Universe. It is thought that the total mass of the observable Universe is contained within a sphere with a radius of the Hubble Length. This is known as the Hubble Volume and is estimated to have a mass of about 10^53 kilograms.
No, the Hubble Length is not a fixed value. It is constantly changing as the Universe continues to expand. The Hubble Length also depends on the value of the Hubble constant, which is still being refined by scientists. As our understanding of the Universe evolves, the estimated value of the Hubble Length may also change.