## October 28, 2004

### Roundup

Around the blogs:

- Matt continues his excellent review of Lattice Gauge Theory, with a post on the classic paper of Lepage and MacKenzie.
- Luboš blogs about the paper of Itzhaki and McGreevy that I discussed a while ago.
- Urs is musing abut the $n^3$ degrees of freedom in the low-energy theory on $n$ coincident M5-branes.
Sean writes about his new paper with Jennie Chen, on an attempt to explain why the initial state of the universe was one of low-entropy.

I haven’t read their paper yet, but the idea is that our universe originated as a thermal fluctuation in an ambient de Sitter space, which then inflated. Personally, I’m sceptical that quantum gravity in (eternal) de Sitter space makes sense. Tout court, while there are certainly metastable de-Sitter-like solutions, I don’t think *eternal* de Sitter space exists as a solution to String Theory. But an approach *like* that of Carroll and Chen certainly has the advantage that one is not immediately plunged into the tangled thicket of quantum cosmology. Those discussions never go anywhere because, sooner or later, someone mentions “the wave function of the universe,” the physics-equivalent of Godwin’s Law, and all rational discussion comes to an end.

Posted by distler at October 28, 2004 12:31 AM
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### Re: Roundup

Maybe this is the right place to annouce that the other day, reading in Lubos’ blog I made the mistake of clicking the “creat your own blog” button. So, here it is: atdotde.blogspot.com. There is not much there as, yet, but I promise I will do my best to make it interesting. I just don’t know how you people (esp. Lubos) manage to fit in blogging into a day of only 24 hours.

### Re: Roundup

[…] thicket of quantum cosmology. Those discussions never go anywhere because, sooner or later, someone mentions ‘the wave function of the universe,’ the physics-equivalent of Godwin’s Law, and all rational discussion comes to an end.

Not that I would want to discuss the ‘wave function of the universe’ but this concept, popular in the old days of quantum cosmology, while pretty intractable, has resurfaced in a slightly different guise in terms of the ‘landscape’, I’d think. Your comments on that are one example that rational discussion *need not* come to an end at this point.

### Re: Roundup

Jacques, thanks for the link. I’m not sure about eternal de Sitter either, but in fact it’s not required by our scenario. So long as the decay rate to a lower vacuum energy is less than the Hubble time (which it must be, phenomenologically), the phase transition never percolates, just as in old inflation. More and more space has decayed, but the physical volume in the de Sitter phase grows without bound, which is all we need.

Not that I would also place great odds that our scenario is “correct” in some strict sense. I’d be happy if something like it were on the right track.

## Re: Roundup

Maybe this is the right place to annouce that the other day, reading in Lubos’ blog I made the mistake of clicking the “creat your own blog” button. So, here it is: atdotde.blogspot.com. There is not much there as, yet, but I promise I will do my best to make it interesting. I just don’t know how you people (esp. Lubos) manage to fit in blogging into a day of only 24 hours.