"But where does that special state come from? Does it simply have to be postulated or can its origin be understood in a natural way? Most speculations proceed from the fact that we live in a relatively young Universe, that is, in temporal vicinity of a distinguished event called the Big Bang. The task, then, is to explain the low entropy of the Big Bang. Carroll follows a different route that he presents in the last part of his book ....
The idea is as follows: Carroll argues that empty de Sitter spacetime corresponds to a state with high entropy. In addition, he imagines the possibility of baby universes branching off. Those baby universes are supposed to start in a dense, low-entropy state, and thus exhibit local arrows of time as they expand. (The whole picture is time-symmetric.) Because in this scenario the overall entropy is unbounded, baby universes can always form as a means to increase the total entropy, and we just happen to live in one of them and experience its local arrow of time.
Although this may be a consistent scenario, the picture is still very much rooted in classical physics. In earlier chapters, the author has presented an excellent and detailed discussion of quantum theory and the Everett interpretation, so I wonder why he seems to have forgotten this in the last part of the book. If one looks for a quantum wave equation that gives Einstein's equations in the semiclassical limit, one immediately finds the Wheeler–DeWitt equation of quantum gravity, as briefly mentioned elsewhere in the book. This equation has astonishing features. It is timeless in the sense of being devoid of any external time parameter. It instead contains an intrinsic time-like variable that can be constructed from the size of the (spatial) Universe. And it is highly asymmetric with respect to this intrinsic time. In typical semiclassical situations, an approximate time parameter can be recovered, which is correlated with the size of the Universe. The equation thus offers by its very mathematical structure the means to explain the arrow of time. ...
Despite this being a speculative scenario, I feel it is more conservative than the multiverse and baby universe scenarios, and it is consistently quantum. At least it would have deserved to be mentioned. ..."
Nature Physics 6, 398 - 399 (2010)
doi:10.1038/nphys1695
Can we understand the arrow of time?
Claus Kiefer1
Claus Kiefer is at the Institut für Theoretische Physik, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany.
e-mail:
In my theory we are 3D hologram images projected backward in global time from our future observer-dependent dark energy 2D de Sitter horizon in a Novikov consistent loop in time via the Wheeler-Feynman mechanism. Tamara Davis's 2004 PhD University of South Wales Fig 5.1 below explains why the inflationary Alpha Point creation has only one BIT of entropy whilst our future entropy asymptotes to ~ 10^122 BITs.
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Since we are hologram images computed on our personal pixelated anyonic horizon computing screen, it's obvious why our total observable universe thermodynamic entropy now is the area of our future horizon at its intersection with our future light cone as shown in Tamara Davis's Fig 1.1 below.
