151–160 of 164 posts
Thought it was weird in Interstellar that Cooper survived getting pulled into the black hole. Interesting that surviving is one of the 2 possibilities.
But yeah, what I'd love to know is how he got out. Did it leave him behind when it evaporated (due to Hawking radiation)? Is Cooper a "particle" in that context that was emitted as Hawking radiation?
Crazy stuff.
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> For sufficiently large black holes you can peacefully pass beyond the horizon (unless there's something else going on, like a firewall). The article addresses this by pointing out that the "tidal forces" in question are only noticeable for smaller black holes (at which point "spaghettification" - which is, by the way, the formal technical term for this phenomenon - occurs); for larger ones, spaghettification forces…
You're right, I glossed over that the article does address that point. So I retract that criticism. I'm honestly at this point just exceedingly skeptical of mostly everything I read about theoretical physics unless it's coming directly from an expert.
Black holes are fuckin' weird.
I don't think this article is representative of current serious thought about black holes. I'm a bit out of date on this stuff, and I was never any sort of expert, but let's see: 1. This reality splitting thing sounds wrong. I've never heard of it. Ignoring quantum effects, if you fall into a black hole and survive crossing the horizon, Anne will see you get closer and closer to the horizon, but she won't see you get…
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The distance between fallers determines the energy requirements for communication. The lower person will also experience slower time than the higher. The analogy is as follows: Two BASE jumpers leap from the top of an infinitely tall radio mast in a vacuum, one after the other. They are in free-fall, so do not directly experience the effects of gravity, but the increase in the gravitational field as the distance to t…
> The concern for the first jumper is ... whether it can be thrown hard enough and accurately enough for the second to ever reach it. The concern for the second is whether the first can catch his ball without exploding like a paper sack full of wet spaghetti. This is just a practical difficulty. There might actually be stronger constraints in play -- the two jumpers might be causally disconnected from one another ent…
The reason the photons cannot escape is not because they are affected by the gravity, but because the space they must traverse is stretched and twisted to such an extent that to an observer inside the event horizon, the entire outside universe presents an infinitesimally small target that is receding rapidly. Anything you might manage to shoot out would be indistinguishable from the Hawking radiation coming from the event horizon.
On a closer scale, you could probably communicate uphill, but the conversation would be like an ent talking to a chipmunk. At some point, you simply can't target your uphill counterparty accurately enough, or with enough bandwidth to hold their interest.
>there is no paradox, because no one person ever sees your clone. Anne only sees one copy of you. You only see one copy of you. You and Anne can never compare notes. Can't you? Why can't Anne "gather up your ashes" and send them into the black hole, where you can inspect them? Shouldn't that go against the "no cloning theorem"?
Similarly, the black hole will eventually evaporate (unless it indefinitely maintains an intake of matter to counteract evaporation due to the Hawking-radiation-induced loss of mass). While it's highly unlikely that Matt will be emitted in one piece (let alone alive at all), he'll eventually be emitted as Hawking radiation as that evaporation occurs. If Anne's still around when the black hole evaporates, she could then collect and inspect Matt's "ashes" (more like escaped thermal radiation) and possibly get some idea of what happened if she can somehow reconstruct Matt from those emissions.
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> You incorrectly assume that when the star collapses there is already an event horizon I made no such assumption. You don't need an event horizon to dilate time, just a massive gravitational field, and something resisting it. When the sun collapses either the outer layers experience a repulsive force of some kind from below (a bounce perhaps, which is already theorized for supernovas, or maybe neutron degeneracy), o…
> just a massive gravitational field There is no massive gravitational field inside a star.
After all, if there was no massive gravitational field, what's causing it to collapse? You can't have it both ways.
I don't think this article is representative of current serious thought about black holes. I'm a bit out of date on this stuff, and I was never any sort of expert, but let's see: 1. This reality splitting thing sounds wrong. I've never heard of it. Ignoring quantum effects, if you fall into a black hole and survive crossing the horizon, Anne will see you get closer and closer to the horizon, but she won't see you get…
Based on your point 1, if time (on the outside) seems to speed up infinitely for the person falling into the black hole, and if the black hole will eventually evaporate due to hawking radiation, then wouldn't the black hole appear to completely evaporate prior to crossing the event horizon?
I /think/ what's going on is that, from the outside, you never really see a big black hole. Instead, you see what is, for all practical purposes, a big black hole, but really it's an exceedingly dense band of stuff, red-shifted to the point of invisibility, around the horizon. Of course, once you go close enough to inspect it for real, you get caught up in the time dilation enough that it looks more and more like a real black hole. If you go through the horizon, everything that ought to have preceeded you through the horizon already has, and it all makes sense.
The math for this is quite hairy [1] and I suspect that we're mostly limited to numerical simulations. The closed-form steady-state black hole metrics are gnarly enough as is.
[1] Terrible pun -- look up the "no-hair theorem"
I don't think this article is representative of current serious thought about black holes. I'm a bit out of date on this stuff, and I was never any sort of expert, but let's see: 1. This reality splitting thing sounds wrong. I've never heard of it. Ignoring quantum effects, if you fall into a black hole and survive crossing the horizon, Anne will see you get closer and closer to the horizon, but she won't see you get…
> If I remember my old problem set correctly, a black hole big enough for you to live your life in would be truly huge. IIRC the supermassive black hole at the center of the Milky Way would give you about 0.1 ms before you hit the singularity. Would that be from the point-of-view of the one crossing the event horizon or from the point-of-view of the observer? If that 0.1ms is from the POV of the latter, then - due to…
The observer outside never sees you hit the event horizon in the first place, so I'm not sure it's well-defined to talk about how long an outside observer thinks it takes you to hit the horizon once you've crossed the singularity.
Incidentally, one thing the article got right is that time and space are kind of switched inside the black hole. Once you cross the horizon, the singularity is no longer something that's radially inward from you. Instead the singularity is in your future, kind of like tomorrow is in my future. This is part of why you can't escape. Once you're inside, it makes no sense to fire your rockets to push yourself backwards in time. In fact, firing your rockets just makes it worse. You'll accelerate, and the resulting time dilation will actually /reduce/ the perceived time before you hit the doom in your future.
This is a big difference between GR black holes and toy classical black hole models. In a classical black hole (a point mass and an "event horizon" around it where the escape velocity exceeds the speed of light), you can try to throw something outside the horizon, and it might escape the horizon, but it's guaranteed to fall back in unless someone catches it or it has rockets and can continue propelling itself outward. In a real GR black hole, you can't cross the horizon from the inside in the first place. Despite this, if you squint a bit, the toy classical model predicts the Schwarzchild radius correctly
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Sure, it doesn't matter really to an outside observer, I just threw that in to hit home the time dilation aspect. You seem to be assuming a preexisting singularity. My question is how does that singularity get there if the compaction itself that would form the singularity continually pushes the goal post down the line?
No I'm not assuming a preexisting singularity, I'm assuming (possibly incorrectly) that you needn't reach infinite density for an event horizon. i.e. a singularity doesn't need to have formed, and you couldn't tell whether one had anyway. (My thinking is that if the mass of the singularity was redistributed evenly into a small sphere in the center of the black hole, the gravitational strength around the black hole wo…
Update: It turns out I was describing something like the "Schwarzschild radius", confirming that in GR you don't need a singularity for a black hole - the mass just needs to be compacted into a volume smaller than a sphere of the Schwarzschild radius.
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interstellar was more a pile of nonsense than Science.
Have you read the book? That's solid science and contains good explanations on why things were done the way they were done.