The strange fate of a person falling into a black hole(bbc.com)
bbc.com
The strange fate of a person falling into a black hole
http://www.bbc.com/earth/story/20150525-a-black-hole-would-clone-you
35 comments
Is that the story in which there's a discussion about whether space-time is continous or discreet, the former case allowing infinite computation as you dive into, the latter not?
I think I remember that coming up, amongst many other things.
Thank you for this morning's diversion.
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 I'm a bit out of date on this stuff, and I was never any sort of expert, but let's see: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 there. She won't see you burnt up and she certainly won't collect your ashes. The only fundamental difference between what you see and what Anne sees is that by the time she gets bored of watching, you will only have perceived a tiny amount of time passing.
2. Free fall doesn't protect you from burnination. If the horizon is surrounded by enough fire and brimstone and you free fall through it, you're still going to burn to a crisp.
3. 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.
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 there. She won't see you burnt up and she certainly won't collect your ashes. The only fundamental difference between what you see and what Anne sees is that by the time she gets bored of watching, you will only have perceived a tiny amount of time passing.
2. Free fall doesn't protect you from burnination. If the horizon is surrounded by enough fire and brimstone and you free fall through it, you're still going to burn to a crisp.
3. 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.
"This reality splitting thing sounds wrong. I've never heard of it."
It's a strange scientific truth filtered through at least one scientist filtered through at least one journalist filtered through at least one editor. The reality is stranger... even if there's no firewall, there's still only one reality, with all the observers seeing all the different things.
As for your 2, yes, it is likely there isn't a single black hole in the universe that meets our criteria for being able to "safely" fall into it, but at least in theory such a beast could exist, and barring any other unexpected existence failures, such a beast may exist in the far, far, far future. There's a lot of future and most of it is pretty boring....
It's a strange scientific truth filtered through at least one scientist filtered through at least one journalist filtered through at least one editor. The reality is stranger... even if there's no firewall, there's still only one reality, with all the observers seeing all the different things.
As for your 2, yes, it is likely there isn't a single black hole in the universe that meets our criteria for being able to "safely" fall into it, but at least in theory such a beast could exist, and barring any other unexpected existence failures, such a beast may exist in the far, far, far future. There's a lot of future and most of it is pretty boring....
I think the "current serious thought about black holes" is about quantum theoretical effects at the event horizon. Seems there are some problems with reconciling quantum entanglement at the horizon with the fact that nothing can return from beyond the event horizon apart from Hawking radiation. This results in the "Firewall Paradox" [1]. One of the proposed resolutions of the paradox is the claim that directly at the event horizon, invisible to outside observers, a kind of ultra-thin particle inferno exists due to the breakdown of entanglement. This would make it effectively impossible to enter any black hole. (I don't really understand any of this, consult wikipedia and the referenced articles for more correct explanations).
[1] https://en.wikipedia.org/wiki/Firewall_%28physics%29
[1] https://en.wikipedia.org/wiki/Firewall_%28physics%29
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?
Indeed. I never really understood how things ever actually make it through the horizon in the first place (as seen by far-away observers) in order to make the black hole grow.
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 /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"
My (also non-expert) understanding of current serious thought about black holes is that the event horizon is conjectured to be arbitrarily hot in the frame of reference of an observer hovering arbitrarily close to it. In the frame of reference of an observer falling into the black hole it's just empty space, and in the frame of reference of a distant observer the firewall is redshifted out of existence and only the Hawking temperature of the black hole is visible. But the existence of the frame of reference in which the event horizon reaches the Planck temperature suffices to justify the Schrodinger's cat style resolution of the paradox.
> 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?
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?
No, not really. This is "proper time", i.e. time as measured by the unfortunate person in the space ship who's falling in.
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
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
So I've had a question about stellar mass black holes that I can't seem to be able to get answered (the question was deleted for /r/askscience).
How does a stellar mass black hole actually form a singularity given the fact that there's gravitational time dilation? Wouldn't the heart of a black hole slow down relative to an outside observer as mass is added to it so that you never actually reach infinite density? It seems like you're fighting the upwards curve of a parabola to make that happen, and meanwhile you're releasing pressure from above via hawking radiation.
How does a stellar mass black hole actually form a singularity given the fact that there's gravitational time dilation? Wouldn't the heart of a black hole slow down relative to an outside observer as mass is added to it so that you never actually reach infinite density? It seems like you're fighting the upwards curve of a parabola to make that happen, and meanwhile you're releasing pressure from above via hawking radiation.
I reached the same conclusion years ago, and the answer is very simple (and controversial): Black holes do not exist.
If they existed they could exist, but it's impossible for them to form.
I've asked many many physicists this very same question, and none could answer me (or I've gotten hand-wavy non answers). It's like no one wants to be the first to declare this well accepted thing as non-existing.
The black holes observed by astronomers are not actually black holes, but rather super massive neutron starts. It's not possible to distinguish between these two objects, astronomers assume a black holes based on size, not based on observed phenomena.
If they existed they could exist, but it's impossible for them to form.
I've asked many many physicists this very same question, and none could answer me (or I've gotten hand-wavy non answers). It's like no one wants to be the first to declare this well accepted thing as non-existing.
The black holes observed by astronomers are not actually black holes, but rather super massive neutron starts. It's not possible to distinguish between these two objects, astronomers assume a black holes based on size, not based on observed phenomena.
I've wondered the same, found this:
http://physics.stackexchange.com/questions/21319/how-can-any...
"The objects that can be very similar to black holes are called collapsars. They are virtually indistinguishable from actual black holes after a very short time of the formation. They consist only of matter outside the radius of the event horizon of a BH with the same mass. This matter is virtually frozen on the surface like with actual BH, due to high gravity level.
Such collapsars possibly can become BHs for a short time due to quantum fluctuations and thus emit hawking radiation.
Astrophysicists do not separate such collapsars from actual black holes and call all them BHs due to practical reasons because of their actual indistinguishability."
http://physics.stackexchange.com/questions/21319/how-can-any...
"The objects that can be very similar to black holes are called collapsars. They are virtually indistinguishable from actual black holes after a very short time of the formation. They consist only of matter outside the radius of the event horizon of a BH with the same mass. This matter is virtually frozen on the surface like with actual BH, due to high gravity level.
Such collapsars possibly can become BHs for a short time due to quantum fluctuations and thus emit hawking radiation.
Astrophysicists do not separate such collapsars from actual black holes and call all them BHs due to practical reasons because of their actual indistinguishability."
In your model you get a skin forming around the event horizon. However, stuff would still be attracted to that object. This increased mass would increases the size of the event horizon. So, your hypothetical border would need to expand as matter accumulates. One of the odd things about black holes is there density decreases as their size increases. At really large scales even the 'vacuum' between galaxies is dense enough to form a black hole in a static universe.
PS: In reality black holes are molded by the full general relativity equation which most physicists don't actually understand. Much like how most programmers don't understand how GPU drivers work in detail.
PS: In reality black holes are molded by the full general relativity equation which most physicists don't actually understand. Much like how most programmers don't understand how GPU drivers work in detail.
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 picture above which is surely realistic."
He simply skips right past the impossible point: "the radius of the star drops below the Schwarzschild radius". It will take that Sun an infinite amount of time to do that. Any conclusions you draw after that point are unscientific.
He draws all sort of conclusions from the diagram, without ever showing that his diagram is actually true.
There was some talk of how to be a stationary observer near the black hole you must keep accelerating, but a: I fail to see how that explains the infinite time, and b: who said I have to be near the black hole to look at it?
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 picture above which is surely realistic."
He simply skips right past the impossible point: "the radius of the star drops below the Schwarzschild radius". It will take that Sun an infinite amount of time to do that. Any conclusions you draw after that point are unscientific.
He draws all sort of conclusions from the diagram, without ever showing that his diagram is actually true.
There was some talk of how to be a stationary observer near the black hole you must keep accelerating, but a: I fail to see how that explains the infinite time, and b: who said I have to be near the black hole to look at it?
> 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.
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.
> 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.
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.
> just a massive gravitational field
There is no massive gravitational field inside a star.
There is no massive gravitational field inside a star.
In the exact center, no. But there certainly is everywhere else in the star.
After all, if there was no massive gravitational field, what's causing it to collapse? You can't have it both ways.
After all, if there was no massive gravitational field, what's causing it to collapse? You can't have it both ways.
Thank you both for this interesting discussion, helped me grasp a few things.
Astrophysicists aren't insisting that black holes have singularities on the insides (just speculating that there are objects that are well described as a gravity well with an event horizon).
Astrophysicists do not see an event horizon. All they see is massive gravity.
Yeah, that's why I said "speculating", and they will also say that they are speculating, if you ask them to be careful.
(edited for clarity)
(edited for clarity)
Indeed you won't ever be able to ever see something fall into it, but when you get down to it that's just because the light will take an infinitely long time to reach you. There are coordinate systems that are able to describe stuff falling past the event horizon in finite time, you just won't be able to see this happening until you fall into it yourself.
My question isn't along the lines of how visible it is to an outside observer, it's more of how can a singularity itself form? It seems like you can't reach infinite density in finite time given gravitational time dilation.
It only takes "infinite" time in that particular coordinate system, it takes finite time in other coordinate systems, such as one where you're in orbit around the black hole.
It takes a finite amount of proper time (time experienced by the particle) to reach the singularity.
[deleted]
Are there such coordinate systems that "describe stuff falling bast the event horizon in finite time"? How does that not violate general relativity?
To the first, yes. For example http://en.wikipedia.org/wiki/Lema%C3%AEtre_coordinates is one.
To the second, when we talk about "coordinates" in GR, we're talking about parametrizing a volume of space-time. Given one parametrization, it is possible to create another parametrization that blows up at any particular spot - not because space-time is weird there - but because you picked a bad coordinate system.
The existence of parametrizations that carry through the event horizon demonstrate that the singularity at the event horizon in Schwarzschild's original metric is not a real problem for GR.
However the singularity at the middle of the black hole is a spot where GR breaks down. It is widely believed that a theory that combines GR and QM will make that singularity impossible.
To the second, when we talk about "coordinates" in GR, we're talking about parametrizing a volume of space-time. Given one parametrization, it is possible to create another parametrization that blows up at any particular spot - not because space-time is weird there - but because you picked a bad coordinate system.
The existence of parametrizations that carry through the event horizon demonstrate that the singularity at the event horizon in Schwarzschild's original metric is not a real problem for GR.
However the singularity at the middle of the black hole is a spot where GR breaks down. It is widely believed that a theory that combines GR and QM will make that singularity impossible.
Thank you! This will require some study.
According to general relativity those coordinate systems are equivalent. Well apart from the fact that the "classical" coordinate system isn't able to describe the inside of the black hole. For an example see the Kruskal coordinate system [1].
[1] https://en.wikipedia.org/wiki/Kruskal%E2%80%93Szekeres_coord...
[1] https://en.wikipedia.org/wiki/Kruskal%E2%80%93Szekeres_coord...
Matter gets added to the hole even though an outsider never sees it fall in. This should lead to the increase of the schwarzchild radius . It has been proved by Penrose that once the mass falls inside its horizon, the singularity is inevitably formed in its center: http://www.quantum-gravitation.de/media/2d2cde3ec9c38fffffff...
I wouldn't think it could matter to an outside observer whether the mass inside an event horizon had converged to a point of infinite density or not, there just needs to be enough mass collapsed to an area small enough to create an event horizon.
If the outside observer were to cross the event horizon to check whether there was a singularity in the middle, they'd approach the same frame of reference, no longer be affected by the time dilation, and find the singularity.
/notaphysicist
If the outside observer were to cross the event horizon to check whether there was a singularity in the middle, they'd approach the same frame of reference, no longer be affected by the time dilation, and find the singularity.
/notaphysicist
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?
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 wouldn't change despite density not being infinite. However that thought experiment is newtonian thinking, not GR, so perhaps flawed)
Edit: I assume "singularities" are a red herring here and you're also thinking that as the mass approaches whatever density is required for an event horizon, time slows to zero for the outside observer so no event horizon happens either, but that would leave mass on and around the smaller-or-proto-event-horizon so you get the situation from the link guard-of-terra posted "He also said that the black-hole-with-an-essentially-undetectable-object-just-outside-its-event-horizon is a very good approximation to a black hole of a slightly larger mass.". So perhaps for outside observers, black holes are just very good approximations of black holes - unless you go in for a closer look, in which case you find they are real black holes.
(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 wouldn't change despite density not being infinite. However that thought experiment is newtonian thinking, not GR, so perhaps flawed)
Edit: I assume "singularities" are a red herring here and you're also thinking that as the mass approaches whatever density is required for an event horizon, time slows to zero for the outside observer so no event horizon happens either, but that would leave mass on and around the smaller-or-proto-event-horizon so you get the situation from the link guard-of-terra posted "He also said that the black-hole-with-an-essentially-undetectable-object-just-outside-its-event-horizon is a very good approximation to a black hole of a slightly larger mass.". So perhaps for outside observers, black holes are just very good approximations of black holes - unless you go in for a closer look, in which case you find they are real black holes.
> (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 wouldn't change despite density not being infinite. However that thought experiment is newtonian thinking, not GR, so perhaps flawed)
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.
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.
No, singularities aren't a red herring here, they are very muchthe core of what I'm asking. I don't really care that much about the event horizon (at least for this specific question : ) ).
Imagine two neutron stars colliding and forming a black hole. Now imagine the particle inside one of these that's closest to where the singularity's point would be upon formation. How does that singularity form given that the actual compaction that creates it also continually keeps pushing the goal post farther away due to gravitational time dilation.
Imagine two neutron stars colliding and forming a black hole. Now imagine the particle inside one of these that's closest to where the singularity's point would be upon formation. How does that singularity form given that the actual compaction that creates it also continually keeps pushing the goal post farther away due to gravitational time dilation.
Is there any time dilation in the same reference frame as where the singularity is forming?
(I'm running on rules of thumb rather than a genuine understanding of GR: I would normally answer "no", but "frame of reference" might not be a useful concept where a singularity is forming)
It is kinda neat that the only time where a singularity has formed is contained within the place where the singluarity formed. That isn't even yo dawg.
(I'm running on rules of thumb rather than a genuine understanding of GR: I would normally answer "no", but "frame of reference" might not be a useful concept where a singularity is forming)
It is kinda neat that the only time where a singularity has formed is contained within the place where the singluarity formed. That isn't even yo dawg.
> 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?
Isn't it just in the future of every particle within the event horizon (perhaps arbitrarily far from the particle's perspective, and necessarily infinitely far from any outside observer's perspective.)
Isn't it just in the future of every particle within the event horizon (perhaps arbitrarily far from the particle's perspective, and necessarily infinitely far from any outside observer's perspective.)
I've been wrestling with this same problem, and can't find a satisfying answer. One problem I have with the usual description of a black hole is that the singularity is at the center. But it seems to me that if the escape velocity is the speed of light at the Schwarzschild radius, then the singularity should be there. More of a spherical asymptote than a point mass in the center.
This is a simple explanation: http://motls.blogspot.co.at/2008/11/why-can-anything-ever-fa...
>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"?
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"?
Better yet, black holes are known to emit Hawking radiation. If the event-horizon-crosser (let's call him "Matt" to be consistent with the article's "Anne") figured out some way to manipulate how that radiation is emitted (perhaps with some comic-book-esque "freeze ray" to selectively lower temperatures within the black hole with Morse or binary encoding?), Matt could send messages to Anne to the effect of "I AM ALIVE. BLACK HOLES ARE AWESOME.", thus unifying the two realities (or (inclusively) violating one or more models of the universe) if Anne knows to inspect Hawking radiation emissions.
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.
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.
Given the initial split in realities, Anne would create a new parallel universe when she placed your ashes in the black hole, one in which they exist outside the black hole and in a parallel universe where they exist inside the black hole, but this is not the same parallel universe you are experiencing, but a parallel parallel universe. Essentially, 2 instances of the black hole.
The theory very explicitly does not posit a "split in realities" or "parallel universes" or anything of the sort. It says there is quantum information both inside the black hole and outside it, and this is ok because they're supposedly causally disconnected from one another.
> The instant you entered the black hole, reality would split in two.
From the 3rd paragraph. However, yes the alternate universe comes into existence when you reach the singularity.
Still, if you can exist both inside and outside, then your ashes can exist in both places alongside living you without causing a paradox because you simply will not exist in the same space as you ashes that will arrive very much later anyway as time slows at the edge of the black hole. You are more likely, having read the article, to have a post-life crises knowing that outside the black hole you are dead.
From the 3rd paragraph. However, yes the alternate universe comes into existence when you reach the singularity.
Still, if you can exist both inside and outside, then your ashes can exist in both places alongside living you without causing a paradox because you simply will not exist in the same space as you ashes that will arrive very much later anyway as time slows at the edge of the black hole. You are more likely, having read the article, to have a post-life crises knowing that outside the black hole you are dead.
Reality only splits in two in the sense that the observer-dependent reality of the person falling into the black hole and the observer-dependent reality of the person remaining outside of it can no longer exchange information anywhere except inside of the black hole's event horizon.
The half of your light cone that extends into the future remains entirely within that event horizon. The outside observer's cone can remain outside of it only as long as she avoids crossing the event horizon.
Even if the outside observer decide to jump in just seconds after you, it is possible that the physics inside the event horizon would prevent her from ever catching up with you to compare notes, or even sending you a message. You could send a message with modulated x-rays, and she might pick them up with a VLF antenna. She might reply with a deep infrared laser and accidentally cook your brains with cosmic rays. Assuming a steep spacetime gradient as you approach the singularity, everything sent inward would be severely blueshifted, and everything sent outward severely redshifted.
There might even be a sort of Zeno's Paradox inside, where once you cross the event horizon, there's another event horizon beyond that, such that anything that much closer to the singularity than you are can never communicate with you, in the same way that you can never communicate with the universe outside the first event horizon.
The half of your light cone that extends into the future remains entirely within that event horizon. The outside observer's cone can remain outside of it only as long as she avoids crossing the event horizon.
Even if the outside observer decide to jump in just seconds after you, it is possible that the physics inside the event horizon would prevent her from ever catching up with you to compare notes, or even sending you a message. You could send a message with modulated x-rays, and she might pick them up with a VLF antenna. She might reply with a deep infrared laser and accidentally cook your brains with cosmic rays. Assuming a steep spacetime gradient as you approach the singularity, everything sent inward would be severely blueshifted, and everything sent outward severely redshifted.
There might even be a sort of Zeno's Paradox inside, where once you cross the event horizon, there's another event horizon beyond that, such that anything that much closer to the singularity than you are can never communicate with you, in the same way that you can never communicate with the universe outside the first event horizon.
> There might even be a sort of Zeno's Paradox inside, where once you cross the event horizon, there's another event horizon beyond that, such that anything that much closer to the singularity than you are can never communicate with you, in the same way that you can never communicate with the universe outside the first event horizon.
Isn't every step in from the event horizon effectively an event horizon? If all the mass of a black hole is effectively at the singularity in the center, and escape velocity is the speed of light at the event horizon, won't there be no point within the event horizon where escape velocity is less than the speed of light, such that at any point within the event horizon, no point farther from the event horizon is within the future light cone of that point.
Isn't every step in from the event horizon effectively an event horizon? If all the mass of a black hole is effectively at the singularity in the center, and escape velocity is the speed of light at the event horizon, won't there be no point within the event horizon where escape velocity is less than the speed of light, such that at any point within the event horizon, no point farther from the event horizon is within the future light cone of that point.
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 the event horizon, can there be someone close enough to the singularity that I can never catch up?"
Communication isn't much of a problem for two people falling into a black hole one after another if they're close enough. The messages from the person lower down don't "go up", they just go down more slowly than the person higher up. If they're too far apart, though, this might not work.
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 the event horizon, can there be someone close enough to the singularity that I can never catch up?"
Communication isn't much of a problem for two people falling into a black hole one after another if they're close enough. The messages from the person lower down don't "go up", they just go down more slowly than the person higher up. If they're too far apart, though, this might not work.
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 the singularity decreases will be detectable as a pseudoforce in that reference frame.
The first jumper writes a note on a baseball and throws it at the second. The second also writes a note on a baseball and throws it at the first.
The concern for the first jumper is not whether the baseball can be thrown back to the top of the radio mast, but 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.
The other thing to consider is that both fallers will "see" multiple images of the other, and of themselves, because there is a direct light path, the light path that twists around once, the light path that twists around twice, and so on. Images further away will be lower, slower, and older. If you aimed correctly, you could send messages to your older self, but I'm not entirely certain if your older self could reply.
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 the singularity decreases will be detectable as a pseudoforce in that reference frame.
The first jumper writes a note on a baseball and throws it at the second. The second also writes a note on a baseball and throws it at the first.
The concern for the first jumper is not whether the baseball can be thrown back to the top of the radio mast, but 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.
The other thing to consider is that both fallers will "see" multiple images of the other, and of themselves, because there is a direct light path, the light path that twists around once, the light path that twists around twice, and so on. Images further away will be lower, slower, and older. If you aimed correctly, you could send messages to your older self, but I'm not entirely certain if your older self could reply.
> 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.
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.
Which would also imply that you cannot communicate with a person who jumped in right after you did. I think your model does not account for the jumper having mass and his communication photons being massless.
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.
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.
> Which would also imply that you cannot communicate with a person who jumped in right after you did
That doesn't follow at all. It's conceivable we could drop three things into a black hole one after another, and at some point the first two could send a message to each other, and so could the last two, but the first and last could not (in a situation similar to the cosmological horizon.)
> the entire outside universe presents an infinitesimally small target
No. There is literally no direction you could fire a photon that could take it out of the black hole. You can talk to someone falling behind you only because they can "fall onto" your transmissions. Light cannot go uphill at all.
That doesn't follow at all. It's conceivable we could drop three things into a black hole one after another, and at some point the first two could send a message to each other, and so could the last two, but the first and last could not (in a situation similar to the cosmological horizon.)
> the entire outside universe presents an infinitesimally small target
No. There is literally no direction you could fire a photon that could take it out of the black hole. You can talk to someone falling behind you only because they can "fall onto" your transmissions. Light cannot go uphill at all.
If you can communicate with someone who jumped in one second after you, you could communicate with your younger self via a gravity-warped path that has the same distance as the direct distance between you and the second jumper.
There are no one-way trapdoors with massless particles. If a photon can get in, an anti-photon (aka a photon) following the reverse trajectory (including moving backward through time) can get out. It seems almost tautological, but the photon doesn't really care which way the time arrow points, and can't tell whether it is coming or going.
The warping of spacetime is such that no photon crossing the event horizon from the outside can return to the outside. All straight light paths between any arbitrary point on the event horizon and any arbitrary point inside it do not intersect any other point on the event horizon. If your point of origin is inside the event horizon, you can fire a photon out of it. But you literally need a perfectly accurate and perfectly predictive model of all mass in and around the black hole to make the shot. A single neutron unaccounted for could bend the spacetime that the photon traverses in such a way that it misses the event horizon. So for all practical purposes, you cannot ever be certain if your photon made it out or not, especially after your first second beyond the event horizon.
There's also the little matter that your photon, if it does make it out, may have done so billions of years later, and possibly with a wavelength longer than the diameter of the event horizon, which might make it appear as though it were radiating from the event horizon itself, rather than somewhere inside. It would convey no information across. It would probably look exactly like the Hawking radiation.
There are no one-way trapdoors with massless particles. If a photon can get in, an anti-photon (aka a photon) following the reverse trajectory (including moving backward through time) can get out. It seems almost tautological, but the photon doesn't really care which way the time arrow points, and can't tell whether it is coming or going.
The warping of spacetime is such that no photon crossing the event horizon from the outside can return to the outside. All straight light paths between any arbitrary point on the event horizon and any arbitrary point inside it do not intersect any other point on the event horizon. If your point of origin is inside the event horizon, you can fire a photon out of it. But you literally need a perfectly accurate and perfectly predictive model of all mass in and around the black hole to make the shot. A single neutron unaccounted for could bend the spacetime that the photon traverses in such a way that it misses the event horizon. So for all practical purposes, you cannot ever be certain if your photon made it out or not, especially after your first second beyond the event horizon.
There's also the little matter that your photon, if it does make it out, may have done so billions of years later, and possibly with a wavelength longer than the diameter of the event horizon, which might make it appear as though it were radiating from the event horizon itself, rather than somewhere inside. It would convey no information across. It would probably look exactly like the Hawking radiation.
>> The instant you entered the black hole, reality would split in two.
Ah, I'd assumed this meant that "you" would split in two, both copies being "in the same universe". I don't know enough about the physics to know which is meant.
Ah, I'd assumed this meant that "you" would split in two, both copies being "in the same universe". I don't know enough about the physics to know which is meant.
I think this is begging the question.
I really don't understand this sentence:
> So Anne takes her bit, A, and puts it through her handy entanglement-decoding machine, which spits out an answer: either B or C.
(Note: I have a Ph.D. in Math and half a major in Physics that include a few quantum mechanics curses (for example, with the Sakurai book))
What is a entanglement-decoding machine? You cant use entanglement to send information. Just repeat after me: You cant use entanglement to send information. This is one of the most common misunderstandings about entanglement.
When you make the measurement and get the collapse, you only get a random value (with a weighted probability). It's not possible to use that to get information about B or C.
> So Anne takes her bit, A, and puts it through her handy entanglement-decoding machine, which spits out an answer: either B or C.
(Note: I have a Ph.D. in Math and half a major in Physics that include a few quantum mechanics curses (for example, with the Sakurai book))
What is a entanglement-decoding machine? You cant use entanglement to send information. Just repeat after me: You cant use entanglement to send information. This is one of the most common misunderstandings about entanglement.
When you make the measurement and get the collapse, you only get a random value (with a weighted probability). It's not possible to use that to get information about B or C.
half a major in Physics that include a few quantum mechanics curses
I'm sure you meant "courses" but I like it more the way you wrote it.
I'm sure you meant "courses" but I like it more the way you wrote it.
The article doesn't say that information from B or C is useful. All it explains is only 2 particles can be entangled with each other. So either A is entangles with B or it is entangled with C, not both. Which means that either Anne's reality is correct, or yours. The whole thing about the decoding machine is just described to oversimplify it for the benefit of the masses.
Near the bottom of the article:
> One clue might lie in Anne's decoding machine. Figuring out which other bit of information A is entangled with is an extraordinarily complicated problem. [...] In 2013 they calculated that, even given the fastest computer that the laws of physics would allow, it would take Anne an extraordinarily long time to decode the entanglement. By the time she had an answer, the black hole would have long evaporated, disappearing from the universe and taking with it the threat of a deadly firewall.
The "machine" is an oversimplification, but I don't understand the equivalent experiment that can distinguish between B and C.
Also, there are more complicated situations. You can entangle 3, 4, ... or more particles http://en.wikipedia.org/wiki/Multipartite_entanglement
Usually the discussions are only about entanglement of 2particles, because that is weird enough, but the math for more particles is just a little more complicated.
> One clue might lie in Anne's decoding machine. Figuring out which other bit of information A is entangled with is an extraordinarily complicated problem. [...] In 2013 they calculated that, even given the fastest computer that the laws of physics would allow, it would take Anne an extraordinarily long time to decode the entanglement. By the time she had an answer, the black hole would have long evaporated, disappearing from the universe and taking with it the threat of a deadly firewall.
The "machine" is an oversimplification, but I don't understand the equivalent experiment that can distinguish between B and C.
Also, there are more complicated situations. You can entangle 3, 4, ... or more particles http://en.wikipedia.org/wiki/Multipartite_entanglement
Usually the discussions are only about entanglement of 2particles, because that is weird enough, but the math for more particles is just a little more complicated.
Somewhat related: there is a short story by Greg Egan, "The Planck Dive", describing a voyage (without return) into a black hole, in a scientifically not too absurd way. You can read it online:
http://gregegan.customer.netspace.net.au/PLANCK/Complete/Pla...
http://gregegan.customer.netspace.net.au/PLANCK/Complete/Pla...
Have yet to read this but huh – manually responsive web design!
That's actually really interesting. Imagine having a feature like this built into browsers for dealing with long articles and text. Yes, we have 'zoom' but that typically breaks things at a certain point. Easily swapping the background and even the left/right bias of the text is a pretty neat tool to include, even though it isn't that intuitive on the site.
"That's the thing about black holes. They're not just annoying obstacles for space travellers. They're also theoretical laboratories that take the subtlest quirks in the laws of physics, then amplify them to such proportions that they can't be ignored."
I also use this strategy to think about philosophy and science. People often think that because they are extremes, they are not relevant. However, they are as relevant! And they force us to think outside our natural instinct.
I also use this strategy to think about philosophy and science. People often think that because they are extremes, they are not relevant. However, they are as relevant! And they force us to think outside our natural instinct.
This was very confusing, and a prime example of the horrors of popularisation.
Watch this talk about the firewall paradox instead, more technical but at least it makes sense!
https://www.youtube.com/watch?v=tEtt4A7WsDg
Watch this talk about the firewall paradox instead, more technical but at least it makes sense!
https://www.youtube.com/watch?v=tEtt4A7WsDg
"In a big enough black hole, you could live out the rest of your life pretty normally"
Free falling in your ship and suit waiting for you to be crushed to death... pretty normally
Free falling in your ship and suit waiting for you to be crushed to death... pretty normally
As the article alluded to we are in many ways free falling and waiting to be crushed to death. It's just we are free falling through time rather than space.
It depends on what you mean by "inside" a black hole. If this means "inside the event horizon", well, if the black hole is big enough, you can put yourself in orbit around it relatively easily, you'll just never be able to achieve escape velocity. If you take the Earth for example, a geosync orbit has a velocity of 3.07km/s, whereas escape velocity is 11km/s
There aren't any stable orbits within the event horizon of a black hole (due to General Relativity):
https://en.wikipedia.org/wiki/Schwarzschild_metric#Orbital_m...
https://en.wikipedia.org/wiki/Schwarzschild_metric#Orbital_m...
Not so, only one of the two solutions is unstable:
https://en.wikipedia.org/wiki/Schwarzschild_geodesics#Circul...
Also, this applies only to circular orbits, and does not indicate that a powered ship could not maintain orbit.
Also, this applies only to circular orbits, and does not indicate that a powered ship could not maintain orbit.
Those orbits are all outside the event horizon. Inside it, all you can hope to do is fall inward as slowly as possible.
BTW most of what I know about black hole physics is from Greg Egan's novel "Incandescence". Which covers quite a lot of science for a work of fiction (and overall extremely inspiring).
http://gregegan.customer.netspace.net.au/INCANDESCENCE/Incan...
http://gregegan.customer.netspace.net.au/INCANDESCENCE/Incan...
Assuming you still have an internet connection... why not? :)
Well, guess TCP/IP is out, but maybe TV and radio broadcasts would still function.
Well, guess TCP/IP is out, but maybe TV and radio broadcasts would still function.
Light (read: any electromagnetic wave) cannot escape a black hole beyond the event horizon. Therefore this wouldn't work.
Just have Anne toss you DVDs of Game of Thrones from outside the event horizon.
Netflix would have to get really creative with their business model to support those subscribers.
Couldn't Anne just beam an electromagnetic wave of TV/radio into the black hole to you, though? Nothing will be escaping the black hole.
but it can go in. You can still watch TV
I always assumed the differing 'views' of what would happen crossing into a black hole was a product of the interplay of the equivalence principle and 'relativity of simultaneity' that Special/General relativity already accounts for.
I had thought that upon reaching the event horizon the outside observer sees time 'stand still' because no light from your continued motion the other side of the event horizon can reach them, effectively freezing the observers view. Or thought of another way, the curvature of spacetime at the event horizon reaches the equivalent velocity of c due to the extreme warping of spacetime, so light can't escape and 'time' stops for the observers view of the freefaller because light can't get to them, the freefallers then image freezes and slowly fades.
Special relativity says the relativity of simultaneity is pronounced at high % of c, would it not be pronounced in an extreme gravitation field? A gravitational field is equivalent to acceleration so...
If the curvature of spacetime at the event horizon has an equivalent velocity inwards of c, thereby preventing light escaping, would this not lead the outside observer to see one thing and the freefallers to experience another which special relativity's relativity of simultaneity explains?
I say this becaue the light cone escaping the black hole must experience high gravitational fields (i.e equivalence principle) and the free faller continues on their geodesic experienceing 'no' force (save for tidal forces which in the case of a large black hole won't spegetify them just yet).
So the _outside_ observer is seeing the effect of the freefaller and the freefallers observable light cone experiencing the equivalence principle which necessarily would cause relativity of simultaneity to become more pronounced. At the event horizon, with an equivalent spacetime curtavure of velocity c, surely this would mean that the outside observer would see no more regardless of what the freefaller observs and all that would be accounted for by relativity of simultaneity.
I guess I thought of it as applying relativity of simultaneity to a gravitational field (by way of the equivalence principle) and not just velocity as the train thought experiment did.
Is this line of reasoning incorrect - I'm assuming it is - why?
I had thought that upon reaching the event horizon the outside observer sees time 'stand still' because no light from your continued motion the other side of the event horizon can reach them, effectively freezing the observers view. Or thought of another way, the curvature of spacetime at the event horizon reaches the equivalent velocity of c due to the extreme warping of spacetime, so light can't escape and 'time' stops for the observers view of the freefaller because light can't get to them, the freefallers then image freezes and slowly fades.
Special relativity says the relativity of simultaneity is pronounced at high % of c, would it not be pronounced in an extreme gravitation field? A gravitational field is equivalent to acceleration so...
If the curvature of spacetime at the event horizon has an equivalent velocity inwards of c, thereby preventing light escaping, would this not lead the outside observer to see one thing and the freefallers to experience another which special relativity's relativity of simultaneity explains?
I say this becaue the light cone escaping the black hole must experience high gravitational fields (i.e equivalence principle) and the free faller continues on their geodesic experienceing 'no' force (save for tidal forces which in the case of a large black hole won't spegetify them just yet).
So the _outside_ observer is seeing the effect of the freefaller and the freefallers observable light cone experiencing the equivalence principle which necessarily would cause relativity of simultaneity to become more pronounced. At the event horizon, with an equivalent spacetime curtavure of velocity c, surely this would mean that the outside observer would see no more regardless of what the freefaller observs and all that would be accounted for by relativity of simultaneity.
I guess I thought of it as applying relativity of simultaneity to a gravitational field (by way of the equivalence principle) and not just velocity as the train thought experiment did.
Is this line of reasoning incorrect - I'm assuming it is - why?
> Is this line of reasoning incorrect - I'm assuming it is - why?
You're trying to reason about black holes with special relativity, rather than general relativity. Special relativity explicitly ignores acceleration (and equivalently, gravitation). You mention the equivalence principle, which is relevant, but "spacetime curtavure of velocity c" makes no sense, because the curvature leads to acceleration, not velocity directly.
You're trying to reason about black holes with special relativity, rather than general relativity. Special relativity explicitly ignores acceleration (and equivalently, gravitation). You mention the equivalence principle, which is relevant, but "spacetime curtavure of velocity c" makes no sense, because the curvature leads to acceleration, not velocity directly.
Well that was sort of the point really, I was seeing how special relativity's relativity of simultaneity would work in an accelerated reference frame from the point of view of both observers.
Intuitively (dangerous I know) it seemed that just because you're accelerating, that doesn't mean relativity of simultaneity wouldn't apply.
I assumed the equivalence principle would be relevant because thinking about simulaneity of relativity in an accelerated reference frame (like an accelerating train at high c) would mean any outcome of the thought experiment would likely be transferable to relativity of simultaneity in a gravitational field, seeing as path through curved spacetime and acceleration is 'equivalent' (with caveats).
Spacetime curtavure of velocity c - this is clumsy language but c behaves differently right? It's a constant, so unlike a helicopter hovering above the earth, spacetime's curvature must 'equal' c at the event horizon i.e. cause it to travel on a curved path back towards the singularity, or at least cause it to orbit on the event horizon.
In this sense I was thinking about spacetime itself as the thing that was accelerating and the light was stationary at the event horizon, which is just a mental analogue really and likely unhelpful.
Intuitively (dangerous I know) it seemed that just because you're accelerating, that doesn't mean relativity of simultaneity wouldn't apply.
I assumed the equivalence principle would be relevant because thinking about simulaneity of relativity in an accelerated reference frame (like an accelerating train at high c) would mean any outcome of the thought experiment would likely be transferable to relativity of simultaneity in a gravitational field, seeing as path through curved spacetime and acceleration is 'equivalent' (with caveats).
Spacetime curtavure of velocity c - this is clumsy language but c behaves differently right? It's a constant, so unlike a helicopter hovering above the earth, spacetime's curvature must 'equal' c at the event horizon i.e. cause it to travel on a curved path back towards the singularity, or at least cause it to orbit on the event horizon.
In this sense I was thinking about spacetime itself as the thing that was accelerating and the light was stationary at the event horizon, which is just a mental analogue really and likely unhelpful.
Articles like these are great reminders to question everything you think you know.
I find this "new age" mentality annoying.
Yes there are things we don't know, but we should try to come up with precise questions, not to ponder about the meaning of black holes in philosophical way.
Start small, figure things out.
Yes there are things we don't know, but we should try to come up with precise questions, not to ponder about the meaning of black holes in philosophical way.
Start small, figure things out.
It's not really a new age mentality at all (I wouldn't classify myself as that at all). If anything, it's a strictly scientific mindset.
It's more of a reminder to think that even when we start to understand some incredible things, there's still a TON out there we DON'T know.
I think that's where the cool revelations come in, when you start to understand how much out there you don't know much about. That's where the wonder starts (which tends to bring up some of those specific questions).
It's more of a reminder to think that even when we start to understand some incredible things, there's still a TON out there we DON'T know.
I think that's where the cool revelations come in, when you start to understand how much out there you don't know much about. That's where the wonder starts (which tends to bring up some of those specific questions).
> "Yes there are things we don't know, but we should try to come up with precise questions, not to ponder about the meaning of black holes in philosophical way."
This, itself, is a very philosophical suggestion.
This, itself, is a very philosophical suggestion.
[deleted](1)
They are also useful in questioning the validity of what the author has written.
The entire article basically said "what happens? we don't know. here's a few possibilities." It's hypothesis used as a way to explain what potentially might be happening.
mostly they are a reminder that it's GR's 100th anniversary
What do we know about the nature of entanglement? Does it make sense to talk about entanglement between regions inside and outside of an event horizon? Couldn't it be the case that entanglement too breaks down somehow at the event horizon?
It'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 the second you cross the event horizon. This is well-known to be false. For sufficiently large black holes you can peacefully pass beyond the horizon (unless there's something else going on, like a firewall).
> 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.
[0]: https://en.wikipedia.org/wiki/Spaghettification
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.
[0]: https://en.wikipedia.org/wiki/Spaghettification
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.
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.
To be fair, I'm pretty skeptical of stuff about black holes even when they do come from experts, since there's so much contradiction between general relativity and quantum mechanics in this particular context, and experts more well-versed in one field over the other will try to use that field's explanations over the other's.
Black holes are fuckin' weird.
Black holes are fuckin' weird.
Interesting read, but I must say I was a bit disappointed by the ending. Resolving the paradoxon relies on the computational complexity of finding out with which other particle it is entangled with? Somehow that doesn't feel right.
Thought it was weird in Interstellar that Cooper survived getting pulled into the black hole. Interesting that surviving is one of the 2 possibilities.
Dude, spoilers! :)
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.
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.
So, what if you built a shell around the black hole so that no new radiation whatsoever could reach the black hole, and then dumped enough matter into the black hole to absorb all the Hawking radiation orbiting it, and then jumped in. What would Anne see since you are no longer incinerated (she's inside the shell too)?
Also, the article says that for the laws of quantum physics to be preserved, no information can be lost, which is why one clone['s ash] must remain outside the event horizion. But why doesn't the ash fall in the black hole after the one clone gets incinerated, thereby being permanently lost?
Also, the article says that for the laws of quantum physics to be preserved, no information can be lost, which is why one clone['s ash] must remain outside the event horizion. But why doesn't the ash fall in the black hole after the one clone gets incinerated, thereby being permanently lost?
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There are minimal tidal forces for very large black hole. You would not be torn apart approaching or crossing the event horizon then. You would be unable to leave or signal out of the hole.
Note the observable universe has an event horizon 13.8B years in time or 92GLY wide in space which we cannot communicate across. Some speculate the observable universe may also have the mass-energy of a black hole with an event horizon of that size. But the observable universe is not a singularity with all the mass-energy concentrated at a infinitely small "center". So in conclusion the observable universe SOME of the characteristics of being inside a black hole, but not all of them.
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I guess I've always misunderstood blackholes. I was under the impression that they were simply a vacuum created as a by product of the every expanding "space". Sure they are sucking things up and growing, but space is always expanding.
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....
What would happen if Anne was holding a rope attached to you?
Maybe a better question is what happens when something/someone is straddling the edge of the event horizon?
Maybe a better question is what happens when something/someone is straddling the edge of the event horizon?
From her perspective, you and the rope would burn up against the fire wall
sounds cool, except before you even got close close to the black hole you would be ripped apart by the tidal forces.
http://en.wikipedia.org/wiki/Spaghettification
> The point at which tidal forces destroy an object or kill a person will depend on the black hole's size. For a supermassive black hole, such as those found at a galaxy's center, this point lies within the event horizon, so an astronaut may cross the event horizon without noticing any squashing and pulling, although it remains only a matter of time, as once inside an event horizon, falling towards the center is inevitable. For small black holes whose Schwarzschild radius is much closer to the singularity, the tidal forces would kill even before the astronaut reaches the event horizon.
> The point at which tidal forces destroy an object or kill a person will depend on the black hole's size. For a supermassive black hole, such as those found at a galaxy's center, this point lies within the event horizon, so an astronaut may cross the event horizon without noticing any squashing and pulling, although it remains only a matter of time, as once inside an event horizon, falling towards the center is inevitable. For small black holes whose Schwarzschild radius is much closer to the singularity, the tidal forces would kill even before the astronaut reaches the event horizon.
That is the best word for a scientific phenomenon, ever.
Most of theoretical science and science fiction is complete bullshit. They use some analogy and run with their wild imagination to create anything utterly non nonsensical. The space time fabric etc is just an analogy to avoid people from the real mathematical equations of relatively and what people did with it created whole shit load of theoretical science around that analogy.
Relevant xkcd: https://xkcd.com/895/
This article reeks of phlogiston
I think we are in a black hole already. We just don't know it yet. :D
There is actually a recent theory that says this is the case (in a way): http://scitechdaily.com/universe-may-emerged-black-hole-high... .
Falling into a black hole is booooring.
I want technical details about ship which can deliver human near the event horizon.
I want technical details about ship which can deliver human near the event horizon.
LOL, Is it great news on hackernews ?
And if you ever start to think Doctor Who is a wishy-washy-weeny, someone once pissed him off and he did this to them. Moral of the story: don't fuck with time lords.
You can only get inside black hole after time ends.
That's because universe-time stops at the horizon.
The moment you fall in, Anne is dead eternally long ago.
Also, you are incinerated by a billion years of starlight per your second, including energetic particles I guess.
You will observe the end of universe and death of everything in it before diving.
The moment you fall in, Anne is dead eternally long ago.
Also, you are incinerated by a billion years of starlight per your second, including energetic particles I guess.
You will observe the end of universe and death of everything in it before diving.
If that were the case, wouldn't that mean that the moment a black hole is formed, it would never become any larger? How have super-massive black holes formed in less than 14 billion years?
This is a very interesting question and I'm unaware of a definite answer.
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.
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.
Well, it has to be slightly more complicated than that. After all you are going to be emitted as hawking radiation a lot earlier than the end of the universe.
Large black holes have life expectancy so much larger than universe age that it's not even funny. They're not going anywhere AFAIK. No, you will stay there and watch.
"The power in the Hawking radiation from a solar mass black hole turns out to be a minuscule 9 × 10−29 watts. It is indeed an extremely good approximation to call such an object 'black'."
"The power in the Hawking radiation from a solar mass black hole turns out to be a minuscule 9 × 10−29 watts. It is indeed an extremely good approximation to call such an object 'black'."
Larger than the current life of the universe, not necessarily longer than the end of the universe, though that really depends on your model of how it'll all end. Some do involve black holes gradually boiling away to radiation being the last things being left.
Maybe there would be an eternity of black holes boiling / protons decaying. I doubt that since something ought to lose stability in the long run.
If spacetime continues to accelerate its expansion, a black hole at the future end of time might be like suddenly dropping the air pressure over a boiling pot of water--or maybe more like popping a blackhead pimple by stretching the skin on either side of it.
I am not a theoretical physicist, though, so whenever I think too hard about how that would actually work, I give myself a headache and need a good lie-down in a very dark room.
I am not a theoretical physicist, though, so whenever I think too hard about how that would actually work, I give myself a headache and need a good lie-down in a very dark room.
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> The moment you fall in, Anne is dead eternally long ago.
Nonsense. By this logic, if you cross the event horizon feet-first, your head will have died of old age before it gets inside!
Nonsense. By this logic, if you cross the event horizon feet-first, your head will have died of old age before it gets inside!
It is not so, as the relative time difference between your feet and head is very small (for large black holes).
There is no barrier in place of event horizon, but from the POV of external observer it takes infinite time for you to dive.
There is no barrier in place of event horizon, but from the POV of external observer it takes infinite time for you to dive.
> the relative time difference between your feet and head is very small
If there's nothing significant going on between your head and your feet, there's nothing significant between your head and an "external observer" two metres above your head.
Say Anne is falling in behind you, and she either decides to "back out at the last minute" or just keep falling with you. As you fall, time is passing more or less the same for the both of you, so we can just go by your clock: You cross the event horizon at t=0, she makes her decision at t=1, and she either crosses at t=2 or doesn't cross at all.
Now, if Anne "backs out", her clock does diverge sharply from yours as she stops her fall and accelerates away from the event horizon, but this clock divergence happens after you've crossed the event horizon, not as you cross it or before.
If there's nothing significant going on between your head and your feet, there's nothing significant between your head and an "external observer" two metres above your head.
Say Anne is falling in behind you, and she either decides to "back out at the last minute" or just keep falling with you. As you fall, time is passing more or less the same for the both of you, so we can just go by your clock: You cross the event horizon at t=0, she makes her decision at t=1, and she either crosses at t=2 or doesn't cross at all.
Now, if Anne "backs out", her clock does diverge sharply from yours as she stops her fall and accelerates away from the event horizon, but this clock divergence happens after you've crossed the event horizon, not as you cross it or before.
"there's nothing significant between your head and an "external observer" two metres above your head."
Of course, but when we talk about "external observer" far from the black hole, difference appears.
Of course, but when we talk about "external observer" far from the black hole, difference appears.
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How can something that doesn't really exist such as space and time possibly be warped? Physicists need to get a grip and understand that their model of the universe is completely wrong. There is no space or time and the universe has no shape.
> How can something that doesn't really exist such as space and time possibly be warped?
Think of a surface of a ball: it locally looks flat, but globally is pretty warped. This is an example of a warped 2-dimensional space. The spacetime is just 4-dimensional analogue.
http://en.wikipedia.org/wiki/Manifold
Think of a surface of a ball: it locally looks flat, but globally is pretty warped. This is an example of a warped 2-dimensional space. The spacetime is just 4-dimensional analogue.
http://en.wikipedia.org/wiki/Manifold
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 would not expect a Berkeleyan Idealist to complain on every article about nuclear fusion because they do not believe that atoms exist.
If space and time "do not exist", it seems like speaking of them as if they do would be a useful shorthand, in any case (Provided that they yield a useful model, which they seem to.).
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 would not expect a Berkeleyan Idealist to complain on every article about nuclear fusion because they do not believe that atoms exist.
If space and time "do not exist", it seems like speaking of them as if they do would be a useful shorthand, in any case (Provided that they yield a useful model, which they seem to.).
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.
"Matter contained in space contained in space" might be a problem, but "matter contained in space and space existing directly" should be ok, especially if your alternative is "matter existing directly".
> If space does indeed exist, it must be somewhere
It's everywhere.
It's everywhere.
What a coincidence that I finish watching interstellar and the minute I check my phone this is the number one post. Maybe I made that happen.
Surprisingly, they only snuck in one Interstellar reference, and it was pretty vague:
> "Alright, a l r i g h t, a l r i…"
https://www.youtube.com/watch?v=FiTaK3Fyj0k
> "Alright, a l r i g h t, a l r i…"
https://www.youtube.com/watch?v=FiTaK3Fyj0k
Ha, and here I thought maybe it was a reference to "Hey Ya"
By my count, there are three.
> What happens here, no one knows. Another universe? Oblivion? The back of a bookcase? It's a mystery.
The back of a bookcase. That might also be a reference.
> Let's start by asking your space companion — we'll call her Anne — who watches in horror as you plunge toward the black hole, while she remains safely outside.
Perhaps the outside observer's last name is Hathaway?
> What happens here, no one knows. Another universe? Oblivion? The back of a bookcase? It's a mystery.
The back of a bookcase. That might also be a reference.
> Let's start by asking your space companion — we'll call her Anne — who watches in horror as you plunge toward the black hole, while she remains safely outside.
Perhaps the outside observer's last name is Hathaway?
Talk about the moral decay of theoretical physics...
This is just like one of those miller lite ads where somebody smacks a beer bottle on the table and on the TV they see a mix of dog racing and bikini mud wrestling.
The trouble is that it is so hard to get established that the field is dominated by old fogies; as a kid in the 80s I was aware of this contradiction but it was censored from the physics literature. Instead the greybeards were worried about the information paradox which turned out to be no paradox at all.
This is just like one of those miller lite ads where somebody smacks a beer bottle on the table and on the TV they see a mix of dog racing and bikini mud wrestling.
The trouble is that it is so hard to get established that the field is dominated by old fogies; as a kid in the 80s I was aware of this contradiction but it was censored from the physics literature. Instead the greybeards were worried about the information paradox which turned out to be no paradox at all.
Nobody prevents you from postulating your own theory, but those almost always turn out "tinfoil hats".
The trouble is that it is so hard to get established that the field is dominated by old fogies...
That's interesting. Do you think it's better or worse in this respect than other sciences or other academic fields?
That's interesting. Do you think it's better or worse in this respect than other sciences or other academic fields?
I recently saw the movie Interstellar starring Matthew McConaughey. It answers the question of what happens if you fall into a blackhole and it involves a bookcase, I don't want to spoil it for those who haven't seen it.
Edit: Seems the people downvoting me are a bit sensitive and don't have a sense of humour. Sorry to anyone who was somehow offended.
Edit: Seems the people downvoting me are a bit sensitive and don't have a sense of humour. Sorry to anyone who was somehow offended.
Very interesting if you want some more background is the book 'the science of Interstellar'.
interstellar was more a pile of nonsense than Science.
This is not an insightful response. Of the people I know who watched the movie, those who objected the most to the science were those with little scientific training. (Similar to a relative of mine who is certain that we will "never" have self-driving cars...) If you are knowledgeable, and have specific objections, those might be more insightful.
Nah. Someone should've realized Miller's world was a bad idea before they went down there and made the whole thing a screw up.
Oh, or what about the fact that they "solve" Gravity and decide to leave Earth. HELLO, YOU NOW HAVE INFINITE ENERGY! YOU CAN FIX ANY PROBLEM WITH BRUTE FORCE!
Oh, or what about the fact that they "solve" Gravity and decide to leave Earth. HELLO, YOU NOW HAVE INFINITE ENERGY! YOU CAN FIX ANY PROBLEM WITH BRUTE FORCE!
Well considering they were looting really old Indian Air Force drones for parts at the beginning, and they have giant self-sustaining luxury habitats at arbitrary points in the Solar system at the end, I'd say energy utilization has increased a bit.
Have you read the book? That's solid science and contains good explanations on why things were done the way they were done.
I haven't read the book, but from what I gather[1], the explanations were not all good. Getting to and from Miller's world should have required absurd amounts of energy. But as extreme luck would have it, there were "intermediate-mass black holes" positioned ever-so-conveniently to make those trips possible (along with some other stuff). Cherry-picking the physics you like and papering over the rest with a series of extremely implausible coincidences isn't good science or good storytelling.
[1]: http://www.scottaaronson.com/blog/?p=2040
[1]: http://www.scottaaronson.com/blog/?p=2040
BONUS EDIT: here's a Greg Egan short story about transhumans diving into a black hole and trying to do physics on the way down: http://gregegan.customer.netspace.net.au/PLANCK/Complete/Pla...
also here's his page explaining the physics in the story: http://gregegan.customer.netspace.net.au/PLANCK/Planck.html#...