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

• nilkn 12y ago
  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 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 interesting result that only applies in a fringe variation of accepted modern theory. Perhaps someone with actual training in physics can comment in more detail.
  • tjradcliffe 12y ago
    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.
    • otakucode 12y ago
      >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...
      • tjradcliffe 12y ago
        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.
        • deleted 12y ago
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  • swamp40 12y ago
    Perhaps people don't take it seriously because it sounds a lot like "double secret probation"?
• filearts 12y ago
  "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?
  • phn 12y ago
    I had never head of anything like this. Does that mean that space and time are somehow discrete instead of continuous?
    • marktangotango 12y ago
      This idea kind of ties into the idea of a 'computable' universe: I'm no expert but this article gives some ideas[1]. [1] http://en.wikipedia.org/wiki/Digital_physics#Criticism http://en.wikipedia.org/wiki/Digital_physics#Criticism
    • jarin 12y ago
      For all practical purposes, they kind of appear to be: https://en.wikipedia.org/wiki/Planck_length https://en.wikipedia.org/wiki/Planck_length https://en.wikipedia.org/wiki/Planck_time https://en.wikipedia.org/wiki/Planck_time
    • tjradcliffe 12y ago
      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.
      • PaulHoule 12y ago
        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.
• mrfusion 12y ago
  Would this imply hawking radiation doesn't exist? Can we no longer use black holes as a potential energy source?
  • lxc 12y ago
    Hawking radiation is fake
  • jaideepsingh 12y ago
    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.
    • tjradcliffe 12y ago
      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.
  • tjradcliffe 12y ago
    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.
• RickHull 12y ago
  Where is it that space does not exist? The headline seems like a contradiction in terms.
  • Retra 12y ago
    It's probably just a 'dumbing down for journalism' title.
  • Florin_Andrei 12y ago
    Your question, actually, is self-contradictory. "Where" already assumes space.
    • 0942v8653 12y ago
      I believe that was the point. The article title makes the same mistake.
• mrfusion 12y ago
  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?
  • Retra 12y ago
    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.
• PaulHoule 12y ago
  As 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.
  • Steuard 12y ago
    Counterargument to "the Planck scale is blown up to be visible": The expanding universe itself has (or very probably has) stretched by a factor starting to push into "practical infinity" territory since the Big Bang. (As I recall, common models of cosmic inflation require a minimum of 60 "e-foldings" of expansion in the first moments of the universe's existence: a factor of 10^26 or so, not counting the considerable expansion since then.) By that argument, we ought to be dangerously close to "voiding the warranty" on spacetime already, everywhere in the universe. As far as I know, the notion that curved space can "enlarge the Planck-scale granularity of spacetime" is not a universal feature of quantum gravity theories. It's not even clear to me what that would mean. (I've only seen one or two string theory talks that suggested such a thing, for instance, and most of the experts in the audience seemed fairly convinced that the idea had no compelling basis in our context. I don't recall whether that's a feature of LQG.)
• givan 12y ago
  Having so little evidence and information about the phenomena http://en.wikipedia.org/wiki/Black_hole#Observational_evidence http://en.wikipedia.org/wiki/Black_hole#Observational_eviden... the entire theory around black holes is a mathematical model that probably has nothing to do with the real phenomena.
  • tjradcliffe 12y ago
    Absence of information in Wikipedia isn't very good evidence that there isn't very much evidence. Black holes can be observed in multiple ways: 1) radiation from infalling matter 2) gravitational lensing 3) dynamics of orbiting objects Remember: we not see the moon by its own light. We see the moon by the light it reflects from the sun. That reflected light is a direct causal consequence of the moon's existence, and we quite properly take it as such... even though the moon emits no light of its own. No one, to the best of my knowledge, has ever suggested we ought to treat the evidence for the Moon as scanty or inadequate on this basis. So the fact that the radiation we see from black holes originates from the heat of infalling matter, which is a direct causal consequence of the black hole's existence, should constitute similarly strong evidence. Lensing and dynamical measurements are also quite direct, strong and compelling. There exist compact bodies with more than 1.4 solar masses, which is the limit for nuclear matter (we would have to be wrong about quite a lot of nuclear physics for this to be otherwise.) The question is: what is the best theory to describe black holes, given we know based on this deep and broad evidence that they exist? Currently we have a rough combination of GR and quantum theory, and while the theory has issues, the claim it "probably has nothing to do with the real phenomenon" is minimally plausible.
• mattbgates 12y ago
  This article looks like one big paradox that shouldn't actually exist.
• memracom 12y ago
  Could it be that when space and time get stretched beyond the Planck interval, then the black hole ceases to exist at all beyond that point? In other words, the center of a black hole is non-existence itself. Looking at it from the time angle, we all blink in and out of existence constantly. But when time and space gets stretched too far, it becomes impossible to blink back into existence, as if the process runs out of gas if the out-of-existence time period is too long.