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Black holes do not exist where space and time do not exist, says new theory

phys.org

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Re: Black holes do not exist where space and time do not exist, says new theory

#11

Post by tjradcliffe »

phn wrote: post #4
filearts wrote: post #3

"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?

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 that level.

Re: Black holes do not exist where space and time do not exist, says new theory

#12

Post by tjradcliffe »

nilkn wrote: post #2

I've never heard of "gravity's rainbow". It seems that it's what happens when one derives general relativity using "doubly special relativity" instead of normal special relativity. I hadn't heard of "doubly special relativity" either. http://en.wikipedia.org/wiki/Doubly_special_relativity It seems to have been around for at least ten years but perhaps never gained much traction. In short, this seems like it may be an…

This isn't a "fringe" variation in any but the sociological sense. I hadn't heard of either of these ideas until today, but my first thought was, "Yeah, that makes sense" (I'm a physicist, but not a gravity person.)

If you believe in the Planck scale (and almost everyone does) then incorporating it into SR as an "observer independent maximum energy" that is comparable to the usual "observer independent maximum velocity" is a very natural thing to do.

The theory might not have got much play, but this result will definitely increase interest because the black hole information paradox is a pain. However: the amount of interest a theory gets does not reflect the likelihood that it is correct. Caloric was once a very popular idea. Currently string theory is. Tomorrow maybe "extra special relativity" will be.

Re: Black holes do not exist where space and time do not exist, says new theory

#13

Post by tjradcliffe »

mrfusion wrote: post #5

Would this imply hawking radiation doesn't exist? Can we no longer use black holes as a potential energy source?

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 those scales, something that looks very much like the event horizon still exists. The time taken to fall into a black hole will still be very long, just not infinite. Presumably the details of the theory show how this happens, which is the interesting bit. It's one thing to say "Hey, maybe the horizon is smooth or doesn't exist at small scales!" but to be useful the theory has to show how reality will actually behave if that is the case.

With regard to using black holes as power sources: if we have the technology to do that we'd be unlikely to need black holes as power sources.

Re: Black holes do not exist where space and time do not exist, says new theory

#15

Post by otakucode »

tjradcliffe wrote: post #12
nilkn wrote: post #2

I've never heard of "gravity's rainbow". It seems that it's what happens when one derives general relativity using "doubly special relativity" instead of normal special relativity. I hadn't heard of "doubly special relativity" either. http://en.wikipedia.org/wiki/Doubly_special_relativity It seems to have been around for at least ten years but perhaps never gained much traction. In short, this seems like it may be an…

This isn't a "fringe" variation in any but the sociological sense. I hadn't heard of either of these ideas until today, but my first thought was, "Yeah, that makes sense" (I'm a physicist, but not a gravity person.) If you believe in the Planck scale (and almost everyone does) then incorporating it into SR as an "observer independent maximum energy" that is comparable to the usual "observer independent maximum veloci…

>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 personally think spacetime is quantized, but the only physicists pursuing the consequences of such an idea tend to be the fringe ones...

Re: Black holes do not exist where space and time do not exist, says new theory

#16

Post by mrfusion »

tjradcliffe wrote: post #13
mrfusion wrote: post #5

Would this imply hawking radiation doesn't exist? Can we no longer use black holes as a potential energy source?

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…

Re power source, I think the idea is you have a small, quickly evaporating black hole (electrically charge so you can hold it in place?)

And you feed matter into it, and immediately get radiation back due to hawking radiation equivalent to e=mc^2 of the matter you dropped in?

Re: Black holes do not exist where space and time do not exist, says new theory

#17

Post by swamp40 »

nilkn wrote: post #2

I've never heard of "gravity's rainbow". It seems that it's what happens when one derives general relativity using "doubly special relativity" instead of normal special relativity. I hadn't heard of "doubly special relativity" either. http://en.wikipedia.org/wiki/Doubly_special_relativity It seems to have been around for at least ten years but perhaps never gained much traction. In short, this seems like it may be an…

Perhaps people don't take it seriously because it sounds a lot like "double secret probation"?

Re: Black holes do not exist where space and time do not exist, says new theory

#18

Post by mrfusion »

tjradcliffe wrote: post #13
mrfusion wrote: post #5

Would this imply hawking radiation doesn't exist? Can we no longer use black holes as a potential energy source?

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?

Re: Black holes do not exist where space and time do not exist, says new theory

#19

Post by tjradcliffe »

jaideepsingh wrote: post #10
mrfusion wrote: post #5

Would this imply hawking radiation doesn't exist? Can we no longer use black holes as a potential energy source?

For using black holes as a potential energy source, we have to find it first. There are a lot of potential candidates for black holes (binary stars, center of our galaxy), but we still haven't seen any direct evidence of their existence.

It isn't clear what "direct evidence" would be. We have the kind of perfectly ordinary evidence that is used to infer the existence of everything from the Higgs to neutrons: we see consequences of an entity that fits with a particular theoretical description.

The fundamental piece of evidence for black holes is the existence of compact objects with more than 1.4 solar masses. This is direct evidence. These things exist.

We know they can't be neutron stars because there is an upper limit on their mass due to nuclear physics. We therefore infer they are black holes (fully gravitationally collapsed objects) because "maybe the aren't" is not a compelling counter-argument.

If you're going to ask for "direct evidence" you need to be extremely clear what you mean, and your definition really should be such that the evidence we have for the existence of neutrons or muons counts as "direct". Otherwise, you will be in a position of insisting that we have a kind of evidence for black holes that we don't have for almost anything else, which is not something anyone is going to take seriously.

Re: Black holes do not exist where space and time do not exist, says new theory

#20

Post by tjradcliffe »

otakucode wrote: post #15
tjradcliffe wrote: post #12

Earlier quoted context omitted.

This isn't a "fringe" variation in any but the sociological sense. I hadn't heard of either of these ideas until today, but my first thought was, "Yeah, that makes sense" (I'm a physicist, but not a gravity person.) If you believe in the Planck scale (and almost everyone does) then incorporating it into SR as an "observer independent maximum energy" that is comparable to the usual "observer independent maximum veloci…

>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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