### Going Big 2

This is what he says on his site (http://www.math.nus.edu.sg/~matmcinn/) which I have linked at the right in my links sidebar.

* And you thought the Big Crunch was bad.....how about a Big Smash?

Evidence for a positive cosmological constant keeps piling up. To be more precise, the evidence keeps piling up for some kind of "dark energy" with a *negative* pressure which is close in absolute value to its [positive] density. Of course, to say that the ratio of pressure to density is observationally close to -1 is to say that it might be slightly greater than -1.....or maybe slightly *less* than -1. In fact, there has been a lot of work on the former, which can be modelled by a "quintessence" field, but very little on the latter. Now in fact the "less than -1" cosmologies, called "Phantom Cosmologies" by R Caldwell http://www.dartmouth.edu/~caldwell/ [who was one of the quintessence pioneers] are very interesting indeed, for several reasons.

Caldwell's *particular* phantom cosmologies have the bizarre property that they come to an end eventually, like the familiar "Big Crunch" cosmologies----but in the phantom world, the end comes not because the Universe collapses to zero size, but rather because the distance between any two given galaxies becomes infinitely large in a finite proper time! [I like to call this the "Big Smash". Caldwell's "Big Rip" would really destroy the universe, but I think that it is more likely that the universe would shatter into disconnected pieces.

Which is why I prefer "smash" to "rip". Of course, I don't know what happens to the pieces---but, since the pieces are themselves infinitely large, I would expect them to shatter too, and that the process would continue forever.] More bizarre still is the fact that in these cosmologies, the density *increases* as the Universe expands, and in fact it diverges as the Universe expands "infinitely fast". That seems a little too extravagant for me, so I have constructed a family of [extremely simple] Phantom cosmologies with no beginning or end---they are in fact asymptotically deSitter in a certain sense. Like deSitter space, they have a disconnected conformal boundary, but *unlike* deSitter space, their Euclidean versions *still* have a disconnected boundary, so they are ideal for exploring the question as to whether the one-to-one bulk/boundary correspondence can really be maintained. In fact, I claim that this disconnectedness of the Euclidean boundary is a signal that, contrary to appearances, these spacetimes are "effectively disconnected". Using recent ideas of Andrew Strominger and Vijay Balasubramanian et al, I argue that, in these spacetimes, time flows away from *both* boundaries. But there is an alternative: maybe it is OK to have a disconnected boundary if there is a quantum-mechanical "entanglement" between the conformal field theories on the two connected components. This would be analogous to Maldacena's rather amazing analysis of the quantum mechanics of asymptotically anti-deSitter black holes. If this version is correct, then the evolution of our Universe is controlled by strictly quantum-mechanical effects in theories which are defined on our *infinite* future and *infinite* past! This ties in with the recent efforts of Turok and Steinhardt et al to abolish the Big Bang and replace it with a Big Bounce. My paper on this is number 48 above. A less technical and more literate version, complete with insults directed at the Null Energy Condition, may be found at http://arxiv.org/abs/astro-ph/0210321. This is a version of the talk I gave at the Institut d'Astrophysique de Paris, which is a nice place, in July 2002.

Papers

http://arxiv.org/abs/astro-ph/0210321

This is the more technical version

http://arxiv.org/abs/hep-th/0112066

Papers by others,

http://arxiv.org/abs/gr-qc/0307086

http://arxiv.org/abs/astro-ph/0407048

Finally I apologize as I have absolutely no idea what the heck the mathematics are about in the paper and cant give a layman interpretation of the big smash (like I somewhat did in the previous posts). Prolly I hope to read up something somehow and update this post.

Apologies

tiddwaylll