Didn't Patrick Hayden write a paper about this stating it was essentially an unphysical situation in the lifetime of the universe? I seem to remember this from the fundamental physics prize lectures....
The strange fate of a person falling into a black hole
141–150 of 164 posts
Re: The strange fate of a person falling into a black hole
#142Earlier quoted context omitted.
The answer is both simple and controversial: They have not. Black holes do not exist because they take an infinite amount of time to form. See the thread elsewhere on this page.
You're making some awfully assertive statements for not having proved your case. Dismissal of all answers as "hand-wavy" does not actually make your non-argument more compelling.
The concept is known as "eternally collapsing objects", and has survived peer review just as much as any other concept discussed here.
http://en.wikipedia.org/wiki/Magnetospheric_eternally_collap...
This is actually something that is verifiable, given time, since traditional black holes may not sustain their own magnetic field, but MECOs can.
Re: The strange fate of a person falling into a black hole
#143Earlier quoted context omitted.
Do you have a line of reasoning for that? Models which take spacetime to be able to be warped, /to my understanding/, make what are currently the predictions which are most matched by experiment. I don't know why one would suppose that space and time do not exist, other than as some philosophical idea, but even if one does suppose that, it still appears to work well to model the universe as if they do exist. One woul…
The reasoning is very simple - If space does indeed exist, it must be somewhere, because everything that exists is somewhere, but space can't be anywhere, because if it's somewhere it must be contained in space. How can something be contained within itself? It can't.
> If space does indeed exist, it must be somewhere
It's everywhere.
Re: The strange fate of a person falling into a black hole
#144Earlier quoted context omitted.
I don't think that's quite what they meant by that. In silly "outside universe coordinates", inside the black hole you can define a "minimum inwards speed" as a function of distance from the singularity. This is how fast a photon will go towards the singularity if fired directly away from it. It's zero at the event horizon, and it increases as you go in. Now, what (I think) logfromblammo was saying was, "If I'm at th…
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 entirely (that is, their forward light cones might intersect only at the singularity.) I have no idea whether that's possible, though.
> If you aimed correctly, you could send messages to your older self, but I'm not entirely certain if your older self could reply.
Any message has to be received "lower" than where it was sent, so all messages go from younger selves to older selves.
Re: The strange fate of a person falling into a black hole
#145Earlier quoted context omitted.
Not true: http://motls.blogspot.co.at/2008/11/why-can-anything-ever-fa...
That explained nothing whatsoever. I'll even quote: "At some moment, the radius of the star drops below the Schwarzschild radius - that's where the yellow and orange lines intersect. At this moment, the star is pretty much doomed. Right now I am not sure whether one can generally prove that the event horizon becomes inevitable at this point but I am sure that it is going to be there in a moment according to the pictu…
> It will take that Sun an infinite amount of time to do that (drops below the Schwarzschild radius). Any conclusions you draw after that point are unscientific.
Not true. You incorrectly assume that when the star collapses there is already an event horizon, somewhere. But it isn't. The event horizon will only form at some particular proper time, and at that time most (but not all) of the stellar mass will be trapped by the horizon and will form a singularity (interestingly all the trapped matter will reach the singularity at the same proper time).
This is all very clearly explained here: http://www.aei.mpg.de/~rezzolla/lnotes/mondragone/collapse.p...
Related physics stack-exchange answer: http://physics.stackexchange.com/a/28837
I don't want to sound rude, but you really need to understand GR. The seminal work on the subject is "The Mathematical Theory of Black Holes" by Subrahmanyan Chandrasekhar, you need to know GR very well to be able to understand it, but the pdf I linked is comparatively much simpler on the GR and the mathematics required.
Re: The strange fate of a person falling into a black hole
#146Earlier quoted context omitted.
That explained nothing whatsoever. I'll even quote: "At some moment, the radius of the star drops below the Schwarzschild radius - that's where the yellow and orange lines intersect. At this moment, the star is pretty much doomed. Right now I am not sure whether one can generally prove that the event horizon becomes inevitable at this point but I am sure that it is going to be there in a moment according to the pictu…
> It will take that Sun an infinite amount of time to do that (drops below the Schwarzschild radius). Any conclusions you draw after that point are unscientific. Not true. You incorrectly assume that when the star collapses there is already an event horizon, somewhere. But it isn't. The event horizon will only form at some particular proper time, and at that time most (but not all) of the stellar mass will be trapped…
> 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), or the outer layers accelerate to nearly the speed of light, either way they dilate time, and from the POV of an outside observer take an infinite amount of time to collapse.
Because of this dilation the rate of light output (as seen from outside) will drop and the sun will "turn off" - i.e. it will look [almost] identical to a black hole, except without the physics breaking singularity or event horizon.
One visible effect will be extreme red-shift of the light, which will look (to us) like a very distant object hubble-red-shifted by distance/time.
Re: The strange fate of a person falling into a black hole
#147It's hard to say exactly why as I'm not a scientist, but I find the credibility of this piece extremely suspect. It seems to be making a number of sensational claims (splitting of reality?) and I don't get the feeling that the author understands this material on anything other than a completely amateur level. Also, this seems to commit the famous mistake of thinking that you will be ripped to shreds by tidal forces t…
> 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 are too small to even be felt.
The Wikipedia article on spaghettification [0] has more details. The mechanics are similar to those of a body's Roche limit (the point where the tidal forces of one body will disintegrate a satellite body held together only by its own gravity; i.e. the reason why the gas giants tend to have rings).
Granted, my own understanding of astrophysics isn't a whole lot better than an amateur level, either, but the article doesn't seem all that inconsistent with how people who do have expertise in astrophysics have described these sorts of things.
Re: The strange fate of a person falling into a black hole
#148I 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 relativistic time dilation - that could easily add up to one or more lifetimes for the event-horizon-crosser, no?
Re: The strange fate of a person falling into a black hole
#149Earlier quoted context omitted.
> It will take that Sun an infinite amount of time to do that (drops below the Schwarzschild radius). Any conclusions you draw after that point are unscientific. Not true. You incorrectly assume that when the star collapses there is already an event horizon, somewhere. But it isn't. The event horizon will only form at some particular proper time, and at that time most (but not all) of the stellar mass will be trapped…
> 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.
Re: The strange fate of a person falling into a black hole
#150It's hard to say exactly why as I'm not a scientist, but I find the credibility of this piece extremely suspect. It seems to be making a number of sensational claims (splitting of reality?) and I don't get the feeling that the author understands this material on anything other than a completely amateur level. Also, this seems to commit the famous mistake of thinking that you will be ripped to shreds by tidal forces t…
> 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.