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.
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.
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."
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.
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
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?
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.
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/ 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"
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?
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 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'."
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.
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).
This, itself, is a very philosophical suggestion.
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...
Can't you? Why can't Anne "gather up your ashes" and send them into the black hole, where you can inspect them? Shouldn't that go against the "no cloning theorem"?
Similarly, the black hole will eventually evaporate (unless it indefinitely maintains an intake of matter to counteract evaporation due to the Hawking-radiation-induced loss of mass). While it's highly unlikely that Matt will be emitted in one piece (let alone alive at all), he'll eventually be emitted as Hawking radiation as that evaporation occurs. If Anne's still around when the black hole evaporates, she could then collect and inspect Matt's "ashes" (more like escaped thermal radiation) and possibly get some idea of what happened if she can somehow reconstruct Matt from those emissions.
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#...
> 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.
I'm sure you meant "courses" but I like it more the way you wrote it.
> 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.
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.).
> "Alright, a l r i g h t, a l r i…"
> 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?
http://gregegan.customer.netspace.net.au/PLANCK/Complete/Pla...
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.
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.
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.
> 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.
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?
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.
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.
Maybe a better question is what happens when something/someone is straddling the edge of the event horizon?
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.
Watch this talk about the firewall paradox instead, more technical but at least it makes sense!
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?
I want technical details about ship which can deliver human near the event horizon.
