 Quote by marcus
Great talk.
I heard him give the same talk---same slides etc---in person at the Math Institute at UCB.
I'm glad you made a thread about it.
We have used that link to the 2005 online version before in some PF threads, but it has been some time ago and i don't remember which. No use delving back in time to find them.
For me, the whole crux of his talk---the linchpin or fulcrum that it all depends on---is the picture of phase space: the map with the small and large regions----with the system doing a kind of random walk squiggle as it goes along, getting into larger and larger regions.
that is his picture of the Second Law. and everything he says in the talk---the whole motivation for his speculative cosmology idea---depends on that picture.
The trouble is THAT PICTURE REQUIRES SPECIFYING AN OBSERVER.
to define entropy you need to say where the observer is whose map of phase space is being used-----in whose eyes are some regions large and some small---who defines what the macrostates are.
the second law basically says no one should expect to observe a decrease in entropy.
but if the universe collapses, and there's a bounce (as in quite a bit of recent quantum cosmology work) and a new expand phase, then where is the observer who sees a sudden decrease in entropy? Neither Mr Before nor Mr After sees. So Penrose can not rule out a simple bounce scenario (kind of thing that is much more off-the-shelf than what he eventually starts describing)
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His Phase Space chart is just a visualization of the 2nd law of thermodynamics. Its just showing that the universe goes from low entropy to high entropy and eventually end in thermal equilibrium.
His theory does not really center around the phase space chart . The diagram makes no new claims its just a visualization of 2nd law thermodynamics.
His theory centers around how the end of the universe in its infinity is the same as (or leads to) the infinity of the beginning. From what I can understand certain conditions remain at the end at are in common with the beginning. 1) only energy is left. 2) density variations are present as gravitational waves. 3) time-space is lost or redefined. Maybe its the same in the math.
I am still a little fussy as to why time-space is lost. Time is lost some how because with no mass there is nothing to keep track of time or nothing that is influenced by it. So if one second passes or an eternity passes it would not make a difference to the energy that is left in the universe. As for space, I'm not too sure. But somehow the infinite space would be the zero space that is the singularity of the big bang.
Any thoughts?