Something comes from nothing (take that, Rogers and Hammerstein)

An article at PhysOrg describes a way of making a heap of particles out of nothing. Takes a fair bit of energy though, so I don’t think we’ll be building a second earth this way anytime soon.

In other “where did this all come from?” news, I meant to note last week that Roger Penrose and a collaborator had published a paper showing nice circles in the universe’s cosmic background radiation, with the following implication :

The discovery doesn't suggest that there wasn't a Big Bang - rather, it supports the idea that there could have been many of them. The scientists explain that the CMB circles support the possibility that we live in a cyclic universe, in which the end of one “aeon” or universe triggers another Big Bang that starts another aeon, and the process repeats indefinitely.

However, according to physicist (and irritating anti-religion polemicist in the culture wars) Sean Carroll, there are two papers out already saying that the circles mean no such thing. Most interestingly, he writes how he’s got his hands on Penrose’s (recent, I think) book, and just can’t see how Penrose’s idea of a cyclic universe is supposed to happen. (Unlike the old view that the universe would contract to a Big Crunch, and maybe bounce back from that, it would seem everyone is now accepting that the universe dies in an ever expanding wimper.):

The basic point is this. The very early universe is smooth. The universe right now is lumpy, with stars and galaxies and black holes all over the place. But the future universe will be smooth again — black holes will evaporate and the cosmological constant will disperse all the matter, leaving us nothing but empty space. (Just wait about 10¹⁰⁰ years.) So, Penrose says, we can map the late universe onto a future phase that looks just like our early universe, simply by a conformal transformation (a change of scale). Do this an infinite number of times, and you have a cyclic cosmology — the universe goes through a series of “aeons” that start with a smooth Big Bang, get lumpy as structure forms, smooth out again, and then gets matched onto another smooth Big-Bang-like phase, etc.

If you’re sketchy on that last bit, join the club. Sure, mathematically we can map the smooth late universe onto the smooth early universe. But what physical process would actually cause that to happen? Despite having the book in my hands, I’m still unclear on this. (I absolutely confess that the answer might be in there, but I simply haven’t read it carefully enough.) While the early and late universes are both smooth, they are very different in other obvious ways, such as the energy density. What causes the low-density late universe to come alive into something like the high-density early universe? Something like that happens in the Steinhardt-Turok cyclic universe, but in order to make it happen you need to specify some particular matter fields with very specific dynamics. This isn’t a trivial task; there are things you can try, but they generally are plagued by instabilities and singularities. I don’t see where Penrose has done that, so I’m not even sure what there is to be criticized.

Penrose is getting old, but he remains a well respected figure. But it would be good to know how he thinks his cycles may happen.