PeterDonis's latest activity

Not in the 1970 theorem, no. Not in the 1970 theorem, no. Not in the 1970 theorem, no. Yes--the technical assumption is that the...

Moderator's note: A question about the assumptions of the 1970 Hawking-Penrose singularity theorem has been spun off into its own thread...

Because the inner product of an inertial world line's four velocity and any of the Killing fields is constant.

For your first assumption, that's true. For your second assumption, that the topology allows for a global inertial chart, why do you...

Pish posh. LotR is formative reading - required reading at least thrice. (And I'm not even a fantasy reader). It is the benchmark: All...

Oh boy I finally got to watch season 2. What a fabulous... mess. I can say that: I liked most of the fabricated new plots related to...

I think the summary in Sabine Hossenfelder's new video is excellent. Many important points made, I have bolded two at the end that...

Moderator's note: Thread reopened.

Note that while the article does focus on semiconductors, the first example it gives of a band gap, in the figure at the top of the...

"Compressible" is a poor term. The key thing that a system of bosons can do that a system of fermions can't is to form a Bose-Einstein...

Not a vacuum spacetime, of course. But you might be able to by patching together regions with appropriate stress-energy tensors. I think...

Yes, it does! That was my point in post #15. Maximally extended Schwarzschild spacetime, which is a solution that meets the requirements...

That's correct. There are. One of them is...Schwarzschild spacetime! As I already pointed out in post #15. You are misunderstanding...

Yes, that's true, you can--for example, maximally extended Schwarzschild spacetime, with black hole and white hole singularities. Nor...

I think it is proven by Birkhoff’s theorem. Birkhoff’s theorem shows that the spherical vacuum metric is unique. If the metric you...