PeterDonis's latest activity

That's not just a "restriction" on ##\mathbf{V}~##. It means ##\mathbf{V}~## has to vanish. The SET vanishing means no stress-energy can...

There is an analogue of Birkhoff's Theorem that shows that the only spherically symmetric electrovacuum solution (i.e., the only...

Yes, the way I phrased it was odd. I should have said that the eternal inflation models that are ruled out meet condition (b) (because...

It rules out models that (a) are expanding everywhere, and (b) do not have a past spacetime boundary. As I noted earlier, de Sitter...

Correction to what? In the sense that, while every worldline has a finite extent into the past, there is no upper bound to those finite...

No. There are no such models; "extend infinitely into the past" and "contain singularities" are contradictory. They can't both be true...

Ah, thanks for the link. Note that in the further discussion in that thread, a model due to Linde was mentioned which he still describes...

Yes, that's true. But one of the assumptions is that there has to be an everywhere expanding congruence in the spacetime. de Sitter...

The terminology in the literature is unfortunately not consistent on this point. To me, it makes the most sense to use the term "Big...

In the Hawking no boundary proposal, as I noted before, the manifold describing the universe "before the Big Bang" is purely spacelike...

I briefly looked at some GR books for an explanation but didn't find anything. I had better luck with graduate-level E&M books; in...

It's a very new and speculative field. No. It's too early to tell. This is a question you'll need to answer by looking at the...

In Hawking's "no boundary" model, the portion of the model "before" the initial time (which is shaped, heuristically, like a hemisphere...