ldunn

7 ms·

1.
by ldunn 1y ago
The diagram on the Wikipedia page for Kruskal-Szekeres coordinates[1] does the job. There you see the trajectory of some infalling observer along with some future light cones[2] of points along that trajectory and the event horizon marked a
2.
by ldunn 1y ago
It doesn't have to move in such a direction! Look at a spacetime diagram and think about the trajectory of your head and feet! Read a book on GR! Do literally anything except have strong opinions about GR when you don't know any G
3.
by ldunn 1y ago
I agree that if you are freely falling and then you are suddenly not freely falling because you hit the surface of a planet and experienced a huge acceleration, you will notice. That doesn't have anything to do with anything I said, bu
4.
by ldunn 1y ago
It is absolutely untrue that GR predicts that you would be knocked unconscious crossing the horizon. In fact one of the most fundamental aspects of GR (equivalence) predicts the exact opposite - there is no local experiment you can do as a
5.
by ldunn 1y ago
Why wouldn't you be able to see your feet? Your head is also falling through the horizon (hopefully - otherwise you are going to be very unhappy), so the light from your feet doesn't need to escape the horizon for you to see it.
6.
by ldunn 1y ago
Er, again, fine, but this has nothing to do with the question of "how can something so hard to detect be so abundant". The question isn't "should the non-detection of dark matter decrease my credence in it". It&#x27
7.
by ldunn 1y ago
This tells you that the chance of detecting dark matter is higher than it would be if it were only, say, 0.1% of the energy content of the Universe. Which is true, but so what? Maybe you mean that this is a sense in which how hard it is to
8.
by ldunn 1y ago
Why do you think that how hard it is to detect should have anything to do with how much of it there is?
9.
by ldunn 1y ago
It bears mentioning that the situation is even more constraining than this, because you're not just looking at galactic dynamics - you're looking at galaxy _cluster_ dynamics, and gravitational lensing measurements, and the CMB, a
10.
by ldunn 2y ago
Strain drops off as 1/r, not 1/r^2
11.
by ldunn 13y ago
I've done some very preliminary (and bumbling) work with that at https://github.com/ldunn/kern/ It's rudimentary, but it does compile and it does run, and I'm not aware of any particular obstacles t