Wouldn't something like the uncertaintity principle mean information is destroyed all the time?
I don't see how you can find an earlier state from knowing the current state since you can't know position and momentum, right?
Black holes do not exist where space and time do not exist, says new theory
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Re: Black holes do not exist where space and time do not exist, says new theory
#22Earlier quoted context omitted.
On a quick read before I've entirely finished my morning coffee, Hawking radiation will still exist. The argument seems to go like this: 1) the event horizon in GR is infinitely sharp 2) gravity's rainbow implies nothing can be infinitely sharp (because that requires space and time to exist on scales below the Planck scale) 3) therefore gravity's rainbow implies the event horizon does not exist at those scales Above…
I didn't see what about your explanation says why hawking radiation would still exist? It's caused by particle-anti particle pairs being created with one on each side of the event horizon, no?
When I first posted that response I was thinking that the scale that mattered was the compton wavelength of the particles being emitted, but having actually finished my coffee now I'm no longer so sure. My point was that so long as the horizon is sufficiently fine on the scale of the particle's compton wavelength then hawking radiation can still be emitted, even granted the horizon is not infinitely fine. This may be correct, or not.
Re: Black holes do not exist where space and time do not exist, says new theory
#23Wouldn't something like the uncertaintity principle mean information is destroyed all the time? I don't see how you can find an earlier state from knowing the current state since you can't know position and momentum, right?
The uncertainty principle doesn't imply that any information is being destroyed, it implies that there is a limit to the amount of information you have. Position and momentum are things that you derive from the available information. You just can't use the same limited pool of information to derive the both in a way that would use more information than you have.
>I don't see how you can find an earlier state from knowing the current state since you can't know position and momentum, right?
State has little to do with position and momentum directly, but the underlying information. We use those concepts to indirectly refer to state, but state is more fundamental. Information arises from a correlation between states, and position and momentum are different measures of this correlation.
Re: Black holes do not exist where space and time do not exist, says new theory
#24Where is it that space does not exist? The headline seems like a contradiction in terms.
It's probably just a 'dumbing down for journalism' title.
Re: Black holes do not exist where space and time do not exist, says new theory
#25Earlier quoted context omitted.
>If you believe in the Planck scale (and almost everyone does) What? The idea that spacetime is quantized is most definitely not widely accepted. Spacetime is presumed to be continuous by basically every mainstream physicist (though most will admit that we don't have conclusive evidence either way, we only know that spacetime is not quantized down to a certain scale (which is short of the planck length by a good deal…
I should have said "take seriously" rather than "believe in". Most people take the notion seriously, for some value of "seriously". It's not a binary state.
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Re: Black holes do not exist where space and time do not exist, says new theory
#26"In gravity's rainbow, space does not exist below a certain minimum length, and time does not exist below a certain minimum time interval" Does this imply that neither space nor time can go below the given threshold independently? I.e.: could a situation be imagined where time remains above the minimal interval, but space is below? Also, would those answers be different depending on the observer's time / position?
I had never head of anything like this. Does that mean that space and time are somehow discrete instead of continuous?
Discrete is probably not the best way of looking at it; instead, think of it as the smallest scale across which space can change. From this perspective, it's not possible to discern between a quantized and continuous spacetime.
Re: Black holes do not exist where space and time do not exist, says new theory
#27As a physics PhD I feel like an idiot for accepting the theory of the classical black hole.
If you write the equations for the space around a black hole in the straightforward way you see a singularity at the event horizon. You can make a coordinate change that makes this singularity go away, but then you get the classical black hole singularity where there is either an "end of time" or an infinitely dense point or ring.
Physicists believed that this coordinate transformation was valid but it is not because it infinitely stretches space/time which at some point will blow up the Planck scale to be visible, at which point something completely indescribable happens -- it might be something like DSR or it might be different, but you void any warranty on the space time continuation, so the classical black hole is science fiction.
The obvious semiclasicalization is for the infinitely dense singularity to become a highly dense object which has some dimensions on the length of the Planck scale, but no model of quantum black hole using actual quantum gravity looks like that at all.
We don't have a "complete" theory of quantum gravity but we do have a number of competing partial theories, and we can already make some strong conclusions, such as holography, that are generic to many or any QG models. Underlying this are principles such as unitarity (unitarity is pretty much the one thing you need to make QM work) that means no information is lost when stuff falls in a black hole and that can't be reconciled with the mass being concentrated all in one place.
Re: Black holes do not exist where space and time do not exist, says new theory
#28"In gravity's rainbow, space does not exist below a certain minimum length, and time does not exist below a certain minimum time interval" Does this imply that neither space nor time can go below the given threshold independently? I.e.: could a situation be imagined where time remains above the minimal interval, but space is below? Also, would those answers be different depending on the observer's time / position?
So does discrete space and time also solve zenos paradox? (or was that already solved classically?)
Re: Black holes do not exist where space and time do not exist, says new theory
#29Earlier quoted context omitted.
I had never head of anything like this. Does that mean that space and time are somehow discrete instead of continuous?
They have a scale. They are not "discrete" in the sense that pixels are discrete because there is no grid (no orientation, no preferred direction, etc). Think of it like the resolution of a microscope: you can only see objects down to scales of 1 micron, say. That doesn't make what you are looking at discrete at the 1 micron level. It makes it blurry (invisible, or in the case of space and time, non-existent) below t…
How it shows up depends on the model. Superstrings are objects of (usually) Planckian size, so if the particles are the size of the "grain" then that is one way a scale could manifest.
In other models like loops quantum gravity you can only ask questions about loops in space and not about points so that is another way the scale manigests.
Re: Black holes do not exist where space and time do not exist, says new theory
#30Where is it that space does not exist? The headline seems like a contradiction in terms.
Your question, actually, is self-contradictory. "Where" already assumes space.