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'."
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.
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.
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?
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 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.
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.
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).
What's wrong with imagination, hypothesis and a simple analogy that can reach out to the masses? One might argue that your approach to science as only a set of facts based on formula is boring at best. One needs to ponder the meaning behind the formula and results. Yes, we got a number, but what is the implication of it? After all, doesn't science exist to satisfy our curiosity about the world in the first place?
Because now we have infinitely many imaginary hypotheses, and we can't resolve their differences since we have not enough facts, and ones that are ornate and humane tend to capture most attention.
But universe is made with inhumane ways, it's complex where it's not expected and it's simple where we expect more. It's never intuitive.
It's a blind alley. Doesn't help us find the exit from labyrinth.
> "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."
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.
>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"?
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.
>> 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.
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.
> 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.
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.
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 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.
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.
> 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.
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.
> But you literally need a perfectly accurate and perfectly predictive model of all mass in and around the black hole to make the shot
I think where you're going wrong is assuming that gravity acts by "distorting angles". Like, near a massive object, maybe more than 180 degrees point downwards, and less than 180 point upwards. In a black hole, then, maybe 360 degrees (minus epsilon) point downwards, and there's a peephole pointing back up. You might litter breadcumbs along that trail, or unspool some twine to find your way back.
Alas, that's not the picture we have. It's closer to the truth to say that gravity gives space a "base velocity" (downwards) equal to the escape velocity at that point. Inside the Schwartzchild radius that velocity is higher than the speed of light, and because you can't go faster than light you can't get out.
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.
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
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).
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.
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:
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.
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?
"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 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.
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.
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!
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.
> 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?
I once saw a susskind lecture about the firewall problem where he explained that to check if someone falling into a black hole was incinerated, you'd have to fire so much energy at them, you'd end up incinerating them. Physics is weird. And, apparently, kinda passive aggressive.
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?
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.
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?
> 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.
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.
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.
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?
> 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.
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.
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.
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".
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.
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[ 3.2 ms ] story [ 252 ms ] threadThe 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 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'."
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.
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.
Nonsense. By this logic, if you cross the event horizon feet-first, your head will have died of old age before it gets inside!
There is no barrier in place of event horizon, but from the POV of external observer it takes infinite time for you to dive.
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.
Of course, but when we talk about "external observer" far from the black hole, difference appears.
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 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).
But universe is made with inhumane ways, it's complex where it's not expected and it's simple where we expect more. It's never intuitive.
It's a blind alley. Doesn't help us find the exit from labyrinth.
This, itself, is a very philosophical suggestion.
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"?
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
I think where you're going wrong is assuming that gravity acts by "distorting angles". Like, near a massive object, maybe more than 180 degrees point downwards, and less than 180 point upwards. In a black hole, then, maybe 360 degrees (minus epsilon) point downwards, and there's a peephole pointing back up. You might litter breadcumbs along that trail, or unspool some twine to find your way back.
Alas, that's not the picture we have. It's closer to the truth to say that gravity gives space a "base velocity" (downwards) equal to the escape velocity at that point. Inside the Schwartzchild radius that velocity is higher than the speed of light, and because you can't go faster than light you can't get out.
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.
Free falling in your ship and suit waiting for you to be crushed to death... pretty normally
https://en.wikipedia.org/wiki/Schwarzschild_metric#Orbital_m...
Also, this applies only to circular orbits, and does not indicate that a powered ship could not maintain orbit.
http://gregegan.customer.netspace.net.au/INCANDESCENCE/Incan...
Well, guess TCP/IP is out, but maybe TV and radio broadcasts would still function.
http://gregegan.customer.netspace.net.au/PLANCK/Complete/Pla...
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.
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.
[1]: http://www.scottaaronson.com/blog/?p=2040
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!
> "Alright, a l r i g h t, a l r i…"
https://www.youtube.com/watch?v=FiTaK3Fyj0k
> 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?
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#...
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?
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.
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.
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.
That's interesting. Do you think it's better or worse in this respect than other sciences or other academic fields?
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?
> 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.
Maybe a better question is what happens when something/someone is straddling the edge of the event horizon?
Watch this talk about the firewall paradox instead, more technical but at least it makes sense!
https://www.youtube.com/watch?v=tEtt4A7WsDg
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
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.).
It's everywhere.