So,
The implication from your post is that now matter how big a black hole you enter, no matter how you enter it, you pass through it (from your point of view) at the speed of light.
Or more correctly speaking I guess, the event horizon sweeps past you at the speed of light from your POV.
Here’s another way of thinking about it.
At exactly the event horizon, a particle would have to move at c to escape from the black hole. Another way of putting it would be that the particle would have to have infinite energy, which is of course impossible.
But just outside the event horizon there will be a zone where a particle could escape the black hole by traveling slower than c, the only problem is that it would take more energy than exists in the entire observable universe to accelerate it to that speed. So even though the particle is outside the event horizon, it is within the practical event horizon. And outside that band there are particles that could escape if they had the energy of a quasar to accelerate them, and particles that could escape if they had the energy of an entire star to accelerate them, and so on.
I’m not a physicist, but I would imagine that if you were close enough to the event horizon to stick a hand in, most of the rest of your body would be in a zone where it would take some ludicrous amount of energy for to escape. Maybe not universe-shredding energy, but possibly galaxy or star or planet shredding. And if your magic jetpack has to put out that sort of energy, I imagine that the particles in your body that are outside the event horizon are going to get a bit smashed in the attempt. Not smashed flat, smashed into exotic particles with names you’ve never heard of.
Yeah, the idea that big black holes won’t cause spaghettification means that the difference in the strength of gravitation is small over body-sized distances.
A perfect analogy is that you can certainly feel Earth’s gravity pulling you down, but you have no sense that your feet feel that gravity more than your head when you’re standing up, or that your head and feet are being squeezed together if you’re laying down.
I understand that part.
But you are at least implying that the math works out so there is no way to pass through an event horizon “slowly”.
I honestly don’t know if thats the case either way but am curious as to the answer.
No, you couldn’t. If you could, then information could get out of the event horizon. You were right when you said that, from your point of view, the horizon sweeps past you at the speed of light.
It’s not like the event horizon is a doorway, and things are one way inside and another way outside. It’s just the boundary past which nothing can escape, not even light.
But the more important point is that if you are that close to a black hole, the tidal forces are going to rip you apart. The difference between the gravity at your head and the gravity at your feet if you are that close to a black hole will leave the question about your hand as the very least of your worries.
Which shouldn’t actually be surprising, given that you’re always traveling through spacetime at c. When you think you’re sitting still, that’s when you’re moving in the time direction, and when you’re going at any other speed, you’re moving on a slant, partly in the time direction and partly in a space direction. It’s just that, in the immediate vicinity of an event horizon, your naive ideas about what precisely constitutes “space” and what constitutes “time” are a bit jumbled.
Not if it’s a large enough black hole. There’s no inherent relationship between the radius of spaghettification and the radius of the event horizon: Both increase with the size of the hole, but the radius of the event horizon grows faster than the radius of spaghettification, so that for a very large black hole, you’ll be completely through the horizon well before you get to the radius of spaghettification.
As you get close to a black hole, time itself slows down. If you travel near the speed of light, you slow down even more. There’s a children’s book called Icarus at the Edge of Time by Brian Greene that explains all of this. You can here a synopsis of the book from Robert Krulwich’s podcast.
Space is so curved inside a black hole that there is no exit. When we hear that light can’t escape, we imagine that the gravity is so strong that it pulls the light in. However, what it is really happening is that the gravity is so strong, it is bending space itself.
If you stick your hand into the event horizon of the black hole, your hand will no longer exist in this world. It’s not a matter of fighting the immense gravity, it’s that there is no way to get from point “A” inside the black hole to point “B” outside the black hole.
One thing that hasn’t been mentioned yet is that inside the event horizon, not only are stable orbits impossible, but it’s impossible to stay at a fixed distance. Given magically powered rocket boosters, you can still theoretically hover at the event horizon as long as you want. But once inside, the way spacetime is structured, it becomes impossible to hover, and everything must travel downward.
So once you stick your hand inside, you won’t be able to hang it there; it’ll immediately detach itself and fall downward.
It’s for this reason that it’s sometimes said that space and time switch places inside a black hole. It means that your position becomes time-like, where a position in space (the center of the black hole) becomes an inevitable event in your future, because all possible paths through spacetime wind up there.
I don’t have a problem with any of that, conceptually - it all seems completely consistent with the description of what an event horizon is…
What I wanted to ask was this: Does it apply to forces too? In such a scenario, can the forces binding my hand continue to interact between the atoms and molecules of me that are respectively inside and outside of the event horizon?
All forces are carried by particles, and all particles travel either at c less. Even down at the atomic level, electrons of the atoms of your submerged hand can try to exchange virtual photons with the electrons of the rest of your arm, but they’ll still be stuck beyond the event horizon. Once you dip anything inside a black hole, it might as well not even exist anymore.
Things outside can still affect things inside though, so even inside the black hole you’ll still be able to see stars and such outside. For that split second that your submerged hand is still “attached” to your arm, blood could flow into it, but not back out.
Actually, electromagnetic (and gravitational, of course) forces can cross the event horizon of a black hole. If a black hole has a charge, then it’ll exert an electromagnetic force on things outside, just like any other charge. It can’t have any higher multipoles, though, and there’s no way to change the charge of a closed system, so this still doesn’t allow for communication with the outside world.
An under-appreciated way to look at gravity is as a flow of space-time. Imagine you are in a canoe on a rapid stream. A stream whose water is accelerating, no less. The place that the current begins to flow faster than the speed of light, is the event horizon. If you’re positioned just before it, then the water is flowing at near-c and you need an extreme propeller or an amazing rope to hold your ship against the flow. But if you stick an ore into water past you, water that is moving faster than light, then that’s it. You will need greater than infinite force to pull it back. It will be torn from you.
If you make no effort at fighting the current, then you will indeed cross the event horizon at the speed of light. (An “aha” way to think of it is you’ll attain the same speed falling in as would take to get you back out.) And you will continue to accelerate towards infinite speed, which is what it will take to reach the singularity that is also infinitely far away. From the outside, though, noone can see you moving that fast, which is why they’ll never see you reaching the singularity.