OH YARN I don’t have my glasses and I couldn’t work out how someone was knitting with a yam

No idea if I can reply to a deleted comment but I read the root comment totally wrong and just restated everything they said. My bad.

deleted by creator

If that was the case, we would already have a quantum theory of gravity. The fact that “gravitons” (here I mean the particles of a second quantisation of GR) can interact with themselves makes the theory almost completely useless.

It’s technically possible to write down such a theory, but the only way to get results out of it is to first perform an infinite number of experiments.

Almost none of this applies in the case of something like loop quantum gravity, which I understand very little of but I don’t believe it’s possible to discuss it using the language of QFT like I have above.

I briefly worked in this area of physics, it’s complicated and depends on your definition of a particle and which quantum gravity model you’re talking about.

To simplify things you can just ask the same thing about non-quantum gravity. Why does gravity escape the black hole? The painfully mundane answer is that the black hole is gravity, it’s not escaping itself. Gravitational waves can’t be emitted from inside the black hole but that’s because those are a form of radiation and not the structure of spacetime.

This is specifically important because even quantum gravity (the kind with gravitons) still has this distinction. Particles belong to a field and are excitations of it, the gravitational field itself is not made of those particles. The force associated with that field is mediated by gravitons, but what that really means is complicated and honestly possibly just the result of a cool mathematical trick. It also comes with a bunch of crazy behaviour where you have particles that can break the laws of physics by just kinda doing it so quickly that nature blinks and misses it.

The point is, the quantum gravitational field is enough for the black hole to do its job when objects come by, gravitons don’t actually need to escape, though they are involved in complicated ways.

Hard agree, unsubscribed from real engineering the moment I realised they made ads without ever declaring it. It’s literally just propaganda at this point

If you’re looking for books, then it depends on what field you want to study. Generally just I’d search for recommended textbooks for that field and then I’d definitely buy it and wouldn’t just download it from libgen.is

Now I’m wondering, surely someone has already made a language that’s designed to read like scripture?

The only thing that keeps me sane while working for capitalists is that I get paid to do a lot of nothing

Oh god the case for a photon is super hard to talk about in any meaningful way, photons “see” every point in their journey as happening at the same instant of time and at the same place, null geodesics are nuts.

But yeah, the underlying mathematics that causes this can (kinda) just be pinned on the normalisation of the four velocity, which I think is what you’re describing.

Only a few really dry textbooks I’m afraid, it’s a subject that’s extremely difficult to explain in lay terms as the mathematics is so complicated.

That said if you’re feeling masochistic, Schultz’s first course in GR is the most approachable that I know.

It’s just meant as a physical analogue to demonstrate some features (namely how the shape of the sheet/gravity affects things that travel on/through it) in a way that people can understand easily.

Variational principle goes brrrrr

Oh yes let’s talk about my favourite subject ever!

The coolest thing I know of comes from wondering why bent spacetime makes you move at all. The answer is that you always move through time and the bending of spacetime actually turns a bit of time into space and vice versa.

This leads to my favourite saying about black holes, once you enter them you can no more escape falling to the singularity than you can escape tomorrow.

Are you using web or an app? If it’s an app then I guess it just depends what you’re using?

Come on, you can’t just leave those dummy indices dangling, at least sum over them with a kronecker delta or the minkowski metric if this is some approximation of curved space.

(2) Appears to have a typo, but it could just be that the sqrt symbol won’t extend further, which isn’t good either lol

🙏

Holy shit this is some of the absolute worst data visualisation I’ve ever seen, thankyou for this

If only… 🥲