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.
Oh god, no fluid mechanics is way too difficult. I stuck to studying quantum effects of black holes, which is much easier.
(This isn't a joke, it's literally true)
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.
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.
::: spoiler Unnecessary tangent For a horrible but intuitive explanation of how this works, time is kinda just a direction and bending sorta rotates things so that time looks like it's one of the space directions. Just like turning to the left makes what was your left look like it's straight ahead. :::
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.
Having never done it as part of one such group, I don't know exactly what goes on, but essentially there's a large body of literature on leftist political concepts, covering the ideas of why anarchy rather than archy, how to practice it, how to organise etc. I'm definitely the wrong person to explain it, generally socialists (at least here) are the ones doing all the reading, I'm a lot more interested in praxis tbh.
Some classic anarchist writers include Kropotkin, Bakunin and Proudhon, but the communist and socialist literature often applies too.
The anarchist library has lots to browse and the anarchist faq is a great starting place despite its huge volume of content, I highly recommend casually browsing it.
We do! In my area there are quite a few of us and we operate a number of collectives providing things like:
Of course there's also a lot of direct action going on for various causes.
@Sasha
@lemmy.blahaj.zone