On 1/7/2014 10:13 AM, Jesse Mazer wrote:



On Tue, Jan 7, 2014 at 12:16 PM, Jason Resch <jasonre...@gmail.com <mailto:jasonre...@gmail.com>> wrote:




    On Tue, Jan 7, 2014 at 11:00 AM, Jesse Mazer <laserma...@gmail.com
    <mailto:laserma...@gmail.com>> wrote:



        So, to explain the asymmetry between past and future--the "arrow of 
time"--the
        2nd law alone won't do it. You need to either assume low-entropy 
conditions at
        the Big Bang (which might themselves have some explanation in an 
"eternal
        inflation" theory, see for example Sean Carroll's theory which he 
summarizes in
        a blog post at
        http://preposterousuniverse.blogspot.com/2004/10/arrow-of-time.html and 
also in
        the paper linked to there, and further in his book "From Eternity to 
Here"), or
        some basic time-asymmetry in the fundamental laws of physics, although 
I get the
        sense that the second is not a very popular approach to explaining the 
arrow of
        time among physicists (and it's not really clear to me what the 
connection would
        be between time-asymmetry in some new theory like quantum gravity, and 
the
        failure of the 2nd law to apply in reverse).


    Jesse,

    That is interesting.  Is it the same idea that David Layzer uses here
    http://www.informationphilosopher.com/problems/arrow_of_time/ to use the 
expansion
    of the universe to explain the increasing room for explaining how the room 
for
    possible entropy grows faster than energy and matter equilibration?


They seem to have in common the idea that the maximum entropy can continually increase due to the expansion of space. But I don't think Layzer's account works as a full explanation for the arrow of time, since you imagine a universe that on a cosmological scale looks like the time-reverse of an expanding universe, but without needing to reverse the arrows of time due to local increases in entropy (for example, the psychological arrow of time for intelligent beings would be such that they measure the universe to be contracting rather than expanding).

Layzer of course didn't know about the holographic principle, which implies that the maximum possible entropy increases in proportion to the surface area of the Hubble sphere rather than the volume. Vic Stenger has noted that if you assume the degrees of freedom for the vacuum are proportional to this area (in Planck units) you get the right order of magnitude for the energy density of the cosmological constant.

Brent

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