On 12/19/2012 11:58 AM, Richard Ruquist wrote:
On Wed, Dec 19, 2012 at 2:30 PM, meekerdb<meeke...@verizon.net>  wrote:

On 12/19/2012 8:34 AM, Roger Clough wrote:

Hi meekerdb and Stephen,

If information is stored in quantum form,
I can't see why the number of particles
in the universe can be a limiting fsactor.


Information has to be instantiated in matter (unless you're a Platonist like
Bruno).  No particles, no excited field modes ->  no information.

Also there are ways of storing information
holographically, so size gets a bit ambiguous.


The holographic principle says that the information that can be instantiated
in spherical must be less than the area of the bounding surface in Planck
units.  So there's a definite bound.  If we looks at the average information
density in the universe (which is dominated by low energy photons from the
CMB) and ask at what radius does the spherical volume times the density
equal the holographic limit for that volume based on the surface area we
find it is on the order of the Hubble radius, i.e. the radius at which
things are receding at light speed.  This suggests the expansion rate of the
universe and and gravity are entropic phenomena.

Brent
Brent, Perhaps you or somebody can help me out.

I always believed that the Hubble radius was much larger than the age
of the universe times the speed of light. To my surprise the
Wiki-Hubble Volume says that the age is 13,7 Byrs as expected , but
that the Hubble radius divided by the speed of light is 13.9 Byrs,
which is rather close.

They would be the same except that the expansion rate has not been constant (it has been slightly increasing).


Does that mean that in 200 Myrs (minus 380,000 years) the Cosmic
Microwave Background will disappear outside the Hubble bubble and that
400 Myrs later the now detected light from the first stars will also
disappear, even though the universe right now is many times larger
than 13.7 billion light-years?

I don't understand the significance of 200Myrs? The CMB isn't going to disappear, ever. It's just going to be more and more redshifted by the expansion of the universe. There's an excellent tutorial on these questions by Ned Wright at UCLA

http://www.astro.ucla.edu/~wright/cosmo_03.htm


And if information can be instantaneous as has been suggested here,
shouldn't we use the present size of the universe holographically. I
think that's where the Penrose limit of 10^124 comes from whereas the
Lloyd limit of 10^120 is based on the age of the universe.

I don't know where 10^124 comes from, but 10^120 is what I get for the 
holographic limit.

Brent

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