8 ms·

Our universe within a larger universe? So suggests wormhole research (2010)

60 points by coderdude 14y ago

pdonis 14y ago
A red flag: the paper is using isotropic coordinates, which don't cover the region inside the horizon (which would be the region including the wormhole if it's present); they only cover the exterior region. That makes me suspicious that whatever result the paper claims to be deriving is a mathematical artifact of the coordinates being used, and does not reflect the actual physics. Looking at the figures on the ScienceDirect page... http://www.sciencedirect.com/science/article/pii/S0370269310003370 http://www.sciencedirect.com/science/article/pii/S0370269310... ...the second figure bears this out; it shows the worldline of an object going through the wormhole (A-B-C-D) as disconnected, which is physically invalid; it violates local energy conservation. So I've got to conclude that the paper's claimed result is not physically valid. Note: The ScienceDirect page claims that "B and C are the same event", but you can't just claim that arbitrarily; you have to show that it's physically valid. I strongly doubt that the paper can do that, for reasons which are too long to fit in the margin of this post. :-)
- sillysaurus 14y ago
  you have to show that it's physically valid. I strongly doubt that the paper can do that, for reasons which are too long to fit in the margin of this post. I'd love to hear about it if you have some time.
  - pdonis 14y ago
    I'll try to give the short version. Look at the Figure 2 diagram on the ScienceDirect page. That is a diagram of a solution to the Einstein Field Equation, which is the central equation of General Relativity. In that diagram, B and C are not the same event; the curve A-B-C-D is disconnected. That's not physically valid as it stands. The paper, as far as I can tell, is claiming that it is somehow physically possible for the curve A-B-C-D to be connected, so that it can be a physically valid worldline for an observer. For that to be the case, we would have to be able to obtain another solution to the Einstein Field Equation by cutting the Figure 2 diagram along the "southwest-northeast" diagonal (the one on which B and C lie), and sliding one half of the diagram along that diagonal until B and C coincide. I strongly doubt that the spacetime described by the resulting diagram is a solution of the Einstein Field Equation; and if it isn't, then the paper's claim is incorrect. [Edit: someone downthread posted a link to an arxiv preprint of the paper; I'll take a look and respond further there.]
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    - pdonis 14y ago
      cutting the Figure 2 diagram along the "southwest-northeast" diagonal (the one on which B and C lie), and sliding one half of the diagram along that diagonal until B and C coincide. After reading through the paper, that I think the transformation the author intends is somewhat different than what I described: what he is doing is cutting the Figure 2 diagram along the diagonal containing B and C, then flipping the top half over so that C coincides with B. This is not a valid solution of the vacuum Einstein Field Equation (neither is the transformed spacetime I originally described, where the top half is "slid" along the diagonal), which the original spacetime diagrammed in Figure 2 (before any transformations to move C around) is. But the author is claiming that it is a solution if we put an infinitely dense sheet of lightlike radiation on the diagonal. This may be true mathematically speaking (I haven't verified it), but that doesn't make it physically reasonable. So I still think the paper's claims are not physically valid; they may describe a mathematically consistent solution, but it's not something that would ever happen in the real universe.
- kevin_rubyhouse 14y ago
  I see comments like this all the time - where people with a strong background find faults in scientific articles and such written online. Why do these articles get things wrong so often? In this case I think you're saying the paper itself should not have been using isotropic coordinates. Is this because of different schools of thought in this higher realm of physics? Or... what?
  - pdonis 14y ago
    Why do these articles get things wrong so often? Different journals have different standards of rigor. I believe Physics Letters B, where this paper was published, is one of the less rigorous ones. They might also be more inclined to publish speculative papers, figuring that it's better to publish it and let someone else publish a refutation if it's wrong, as opposed to refusing to publish it in the first place. In this case I think you're saying the paper itself should not have been using isotropic coordinates. I suspect that the use of isotropic coordinates misled the paper's author, yes. I can't know for sure since I can't read the paper itself (it's behind a paywall). [Edit: someone downthread posted a link to an arxiv preprint; I'll take a look and respond further there.] Is this because of different schools of thought in this higher realm of physics? This could be a factor--it certainly is in some cases--but I'm inclined to think that in this case it's more a matter of a less rigorous journal being willing to publish a speculative paper, as above.
    - jacquesm 14y ago
      > I can't know for sure since I can't read the paper itself (it's behind a paywall). That sounds familiar.
    - Osmium 14y ago
      I think you might be doing Physics Letters B a bit of a disservice there. I'm not saying it's the best, but it's certainly reputable and there are a lot worse...
  - twiceaday 14y ago
    Isotropic coordinates have a discontinuity at the event horizon. It is therefore invalid to make any assumptions about worldlines inside the event horizon. However it is possible to use coordinates that do not have discontinuities. If the papers intent was to consider what happens to world lines as they cross the event horizon the paper should not have used isotropic coordinates.
- pkirk 14y ago
  Fermat, is that you?
- gjm11 14y ago
  The paper (at http://arxiv.org/abs/0902.1994 http://arxiv.org/abs/0902.1994) does offer some justification for the identification of B and C, or rather points at the work of someone else who allegedly does so. "The completeness of the particle's geodesic in the spacetime of the Einstein-Rosen bridge in the Kruskal coordinates can be explained if we note that both coordinate pairs (-U,-V) and (U,V) mathematically correspond to the same coordinates r,t. Rindler suggested that both coordinate pairs (-U,-V) and (U,V) physically represented the same coordinates r,t, i.e. region III is identical with region I, and (interior) region IV is identical with region II; the Kruskal spacetime is elliptic. In order to represent the Einstein-Rosen bridge in the Kruskal coordinates, we need to impose Rindler's elliptic identification of event antipodes only on the line V=U, i.e. only the two antipodal future event horizons are identical. After the particle reaches the event horizon of an Einstein-Rosen black hole at point B, it moves from point C, which is identical with point B, to point D, which is related to point A via the transformation (2) of the isotropic radial coordinate r. As the particle moves from point C to D, the proper time tau increases, while the coordinate time t decreases (runs in the reverse direction with respect to observers in region I). This reversion does not cause any problems, because it occurs after t -> infinity, so observers in region I never see it." I know approximately nothing about general relativity so shan't attempt to comment on the physics of this, but I have to say that there are a bunch of stylistic features that to me strongly suggest an author who isn't thinking very clearly. A bit of googling for the Rindler reference brings up a snippet from "300 years of gravitation" by Hawking and Israel: "Since it is, indeed, 'hard to believe that every mass point should have the effect of splitting the universe in two, thus necessitating a second copy of ours' (Rindler, 1965), the elliptic interpretation was resurrected six years later, with varying degrees of reservation, independently by a number of authors (...), but was soon abandoned. Quite apart from the conical singularity there were obvious problems with causality which proved to be insurmountable." With, again, the caveat that I know scarcely anything about general relativity, my understanding of this is that the bit about not splitting the universe in two is a reason in favour of this "elliptic interpretation" (saying that certain pairs of points in a particular model are actually the same physical point) but that for other reasons -- that singularity, and the "obvious problems with causality" -- the interpretation was abandoned. In the particular context of Popławski's paper, it seems like that singularity might correspond to something with some physical significance, and the causality problems -- IIUC, the point is that if you identify (u,v) with (-u,-v) everywhere then it's easy to make closed timelike loops, so that you could keep going "forward" in time and end up back where you started -- might not matter because the black hole is "in the way" of all the loops you could make. It all seems a bit dodgy, though -- but, I repeat, I don't know anything and you probably shouldn't take much notice of anything I say.
- fargolime 14y ago
  Worse, wormholes contradict general relativity's own postulate, the equivalence principle, as shown by rock-solid logic here: http://finbot.wordpress.com/2008/03/05/no-black-holes/ http://finbot.wordpress.com/2008/03/05/no-black-holes/ Wormholes provide an endless stream of grant money, careers and tenure. That's why we still read about them. Einstein spent a decade trying to refute his own theory about them and black holes. (It's a throwaway account so I won't see the unscientific replies.)
  - Osmium 14y ago
    Because of course a blog titled "Solutions to 5 Major Problems in Physics" wouldn't be talking out of its own ass. Among other things claimed to be solved on there are problems related to dark energy and quantum gravity. Perhaps the sarcastic tone is too much, but "peer review" (flawed though it may be) exists for a reason. If there's a paper, you should link that instead, and if there isn't a paper then maybe that tells you something. There's too much crap on the Internet and it makes it far too easy for a layman to be led astray by almost-but-not-quite logic. I don't know if your link is an example of that or not, but I've seen far too many blogs that claim to have solved some big mystery that's alluded great minds for the last several decades, but yet somehow their work remains unpublished.
    - tuppol 14y ago
      So you didn't even read the content of his link, but somehow you felt entitled to dismiss it on the basis that... on what basis, exactly? That no information that wasn't pre-approved by a certified, "well-respected" expert is worth considering? Science doesn't work like that. Academia does.
      - pdonis 14y ago
        Have you read the content of his link? I have; its reasoning is invalid.
        genwin 14y ago
Xcelerate 14y ago
I am frequently bothered by the misuse of the word "universe". It is defined as the totality of all that exists -- that we can observe. So if there is anything out there, which we didn't think existed before, but we now suspect does exist, well... it's just part of our same old universe.
- dmayle 14y ago
  I'm not an astrophysicist, so hopefully one can chime in, but my understanding is that 'universe' == the x,y,z,t continuum. Anything outside of that is a different 'universe'. If you can imagine a place that requires alternate dimensions in order to access (e.g. klein bottle), you would be traveling through a different 'universe' (though it is possible that a passage through other universes could lead back to our own). If, however, the other place has a different x,y,z,t continuum, even if there is a passage between the two (wormhole), it's still a different universe. EDIT: (Appending this) Also, if you think of the word universe, it means one totality (uni=one, verse=totality). So, if you want to refer to all that can exist, you probably want to say 'omniverse'.
  - yk 14y ago
    I think the concept of outside the universe or inside of it are not developed in a sufficiently rigorous way to really define what a universe is. However in some theories objects appear were it is actually quite natural to speak of an universe and something else. For example there is a unique way to extend the Schwartzschild space time [1] such that all geodesics either terminate in the singularity or go to infinity. But if you do this, then a region of the spacetime appears, that is 'on the other side' of the black hole. And there is no way to communicate with this region of spacetime, since all geodesics leading to it are space like, that is they would require (local) superluminal travel. It is therefore sometimes called a parallel universe. It is similar in certain string theories, that patches of spacetime with different physical laws appear, this is then called the landscape. Or the multiverse in some cosmological models, where a far away region may appear, which is vastly different from or 'local' universe, that is in this case everything we can possibly observe. So I think that it is quite possible that a theory of quantum gravity will have some object which we will call a universe, but until we have such a theory the appearance of anything outside of the universe marks highly speculative physics. [1] That is the spacetime describing a black hole.
Aardwolf 14y ago
And that larger universe is yet within another larger universe! We must go deeper.
- evanb 14y ago
  http://inception.davepedu.com/ http://inception.davepedu.com/
gjm11 14y ago
(This is from April 2010.) As usual, phys.org have simply reproduced someone else's press release and made a bunch of the words in it link to other phys.org pages. The original press release is at http://newsinfo.iu.edu/news/page/normal/13995.html http://newsinfo.iu.edu/news/page/normal/13995.html and differs from the phys.org version only in not being blogspam. An arXiv preprint of the paper in question is at http://arxiv.org/abs/0902.1994 http://arxiv.org/abs/0902.1994; I think it's actually identical to the version published in Phys. Lett. B. There's a bit more information on Popławski's Wikipedia page: http://en.wikipedia.org/wiki/Nikodem_Pop%C5%82awski http://en.wikipedia.org/wiki/Nikodem_Pop%C5%82awski.
drucken 14y ago
Could you not prove this (or at least go a long way to do it) just by finding a "white hole"?
- mvzink 14y ago
  I am probably totally misunderstanding all this, but it sounds like the big bang is the white hole.

60 points by coderdude 14y ago

A red flag: the paper is using isotropic coordinates, which don't cover the region inside the horizon (which would be the region including the wormhole if it's present); they only cover the exterior region. That makes me suspicious that whatever result the paper claims to be deriving is a mathematical artifact of the coordinates being used, and does not reflect the actual physics. Looking at the figures on the ScienceDirect page... http://www.sciencedirect.com/science/article/pii/S0370269310003370 http://www.sciencedirect.com/science/article/pii/S0370269310... ...the second figure bears this out; it shows the worldline of an object going through the wormhole (A-B-C-D) as disconnected, which is physically invalid; it violates local energy conservation. So I've got to conclude that the paper's claimed result is not physically valid. Note: The ScienceDirect page claims that "B and C are the same event", but you can't just claim that arbitrarily; you have to show that it's physically valid. I strongly doubt that the paper can do that, for reasons which are too long to fit in the margin of this post. :-)

sillysaurus 14y ago
you have to show that it's physically valid. I strongly doubt that the paper can do that, for reasons which are too long to fit in the margin of this post. I'd love to hear about it if you have some time.
- pdonis 14y ago
  I'll try to give the short version. Look at the Figure 2 diagram on the ScienceDirect page. That is a diagram of a solution to the Einstein Field Equation, which is the central equation of General Relativity. In that diagram, B and C are not the same event; the curve A-B-C-D is disconnected. That's not physically valid as it stands. The paper, as far as I can tell, is claiming that it is somehow physically possible for the curve A-B-C-D to be connected, so that it can be a physically valid worldline for an observer. For that to be the case, we would have to be able to obtain another solution to the Einstein Field Equation by cutting the Figure 2 diagram along the "southwest-northeast" diagonal (the one on which B and C lie), and sliding one half of the diagram along that diagonal until B and C coincide. I strongly doubt that the spacetime described by the resulting diagram is a solution of the Einstein Field Equation; and if it isn't, then the paper's claim is incorrect. [Edit: someone downthread posted a link to an arxiv preprint of the paper; I'll take a look and respond further there.]
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  - pdonis 14y ago
    cutting the Figure 2 diagram along the "southwest-northeast" diagonal (the one on which B and C lie), and sliding one half of the diagram along that diagonal until B and C coincide. After reading through the paper, that I think the transformation the author intends is somewhat different than what I described: what he is doing is cutting the Figure 2 diagram along the diagonal containing B and C, then flipping the top half over so that C coincides with B. This is not a valid solution of the vacuum Einstein Field Equation (neither is the transformed spacetime I originally described, where the top half is "slid" along the diagonal), which the original spacetime diagrammed in Figure 2 (before any transformations to move C around) is. But the author is claiming that it is a solution if we put an infinitely dense sheet of lightlike radiation on the diagonal. This may be true mathematically speaking (I haven't verified it), but that doesn't make it physically reasonable. So I still think the paper's claims are not physically valid; they may describe a mathematically consistent solution, but it's not something that would ever happen in the real universe.
kevin_rubyhouse 14y ago
I see comments like this all the time - where people with a strong background find faults in scientific articles and such written online. Why do these articles get things wrong so often? In this case I think you're saying the paper itself should not have been using isotropic coordinates. Is this because of different schools of thought in this higher realm of physics? Or... what?
- pdonis 14y ago
  Why do these articles get things wrong so often? Different journals have different standards of rigor. I believe Physics Letters B, where this paper was published, is one of the less rigorous ones. They might also be more inclined to publish speculative papers, figuring that it's better to publish it and let someone else publish a refutation if it's wrong, as opposed to refusing to publish it in the first place. In this case I think you're saying the paper itself should not have been using isotropic coordinates. I suspect that the use of isotropic coordinates misled the paper's author, yes. I can't know for sure since I can't read the paper itself (it's behind a paywall). [Edit: someone downthread posted a link to an arxiv preprint; I'll take a look and respond further there.] Is this because of different schools of thought in this higher realm of physics? This could be a factor--it certainly is in some cases--but I'm inclined to think that in this case it's more a matter of a less rigorous journal being willing to publish a speculative paper, as above.
  - jacquesm 14y ago
    > I can't know for sure since I can't read the paper itself (it's behind a paywall). That sounds familiar.
  - Osmium 14y ago
    I think you might be doing Physics Letters B a bit of a disservice there. I'm not saying it's the best, but it's certainly reputable and there are a lot worse...
- twiceaday 14y ago
  Isotropic coordinates have a discontinuity at the event horizon. It is therefore invalid to make any assumptions about worldlines inside the event horizon. However it is possible to use coordinates that do not have discontinuities. If the papers intent was to consider what happens to world lines as they cross the event horizon the paper should not have used isotropic coordinates.
pkirk 14y ago
Fermat, is that you?
gjm11 14y ago
The paper (at http://arxiv.org/abs/0902.1994 http://arxiv.org/abs/0902.1994) does offer some justification for the identification of B and C, or rather points at the work of someone else who allegedly does so. "The completeness of the particle's geodesic in the spacetime of the Einstein-Rosen bridge in the Kruskal coordinates can be explained if we note that both coordinate pairs (-U,-V) and (U,V) mathematically correspond to the same coordinates r,t. Rindler suggested that both coordinate pairs (-U,-V) and (U,V) physically represented the same coordinates r,t, i.e. region III is identical with region I, and (interior) region IV is identical with region II; the Kruskal spacetime is elliptic. In order to represent the Einstein-Rosen bridge in the Kruskal coordinates, we need to impose Rindler's elliptic identification of event antipodes only on the line V=U, i.e. only the two antipodal future event horizons are identical. After the particle reaches the event horizon of an Einstein-Rosen black hole at point B, it moves from point C, which is identical with point B, to point D, which is related to point A via the transformation (2) of the isotropic radial coordinate r. As the particle moves from point C to D, the proper time tau increases, while the coordinate time t decreases (runs in the reverse direction with respect to observers in region I). This reversion does not cause any problems, because it occurs after t -> infinity, so observers in region I never see it." I know approximately nothing about general relativity so shan't attempt to comment on the physics of this, but I have to say that there are a bunch of stylistic features that to me strongly suggest an author who isn't thinking very clearly. A bit of googling for the Rindler reference brings up a snippet from "300 years of gravitation" by Hawking and Israel: "Since it is, indeed, 'hard to believe that every mass point should have the effect of splitting the universe in two, thus necessitating a second copy of ours' (Rindler, 1965), the elliptic interpretation was resurrected six years later, with varying degrees of reservation, independently by a number of authors (...), but was soon abandoned. Quite apart from the conical singularity there were obvious problems with causality which proved to be insurmountable." With, again, the caveat that I know scarcely anything about general relativity, my understanding of this is that the bit about not splitting the universe in two is a reason in favour of this "elliptic interpretation" (saying that certain pairs of points in a particular model are actually the same physical point) but that for other reasons -- that singularity, and the "obvious problems with causality" -- the interpretation was abandoned. In the particular context of Popławski's paper, it seems like that singularity might correspond to something with some physical significance, and the causality problems -- IIUC, the point is that if you identify (u,v) with (-u,-v) everywhere then it's easy to make closed timelike loops, so that you could keep going "forward" in time and end up back where you started -- might not matter because the black hole is "in the way" of all the loops you could make. It all seems a bit dodgy, though -- but, I repeat, I don't know anything and you probably shouldn't take much notice of anything I say.
fargolime 14y ago
Worse, wormholes contradict general relativity's own postulate, the equivalence principle, as shown by rock-solid logic here: http://finbot.wordpress.com/2008/03/05/no-black-holes/ http://finbot.wordpress.com/2008/03/05/no-black-holes/ Wormholes provide an endless stream of grant money, careers and tenure. That's why we still read about them. Einstein spent a decade trying to refute his own theory about them and black holes. (It's a throwaway account so I won't see the unscientific replies.)
- Osmium 14y ago
  Because of course a blog titled "Solutions to 5 Major Problems in Physics" wouldn't be talking out of its own ass. Among other things claimed to be solved on there are problems related to dark energy and quantum gravity. Perhaps the sarcastic tone is too much, but "peer review" (flawed though it may be) exists for a reason. If there's a paper, you should link that instead, and if there isn't a paper then maybe that tells you something. There's too much crap on the Internet and it makes it far too easy for a layman to be led astray by almost-but-not-quite logic. I don't know if your link is an example of that or not, but I've seen far too many blogs that claim to have solved some big mystery that's alluded great minds for the last several decades, but yet somehow their work remains unpublished.
  - tuppol 14y ago
    So you didn't even read the content of his link, but somehow you felt entitled to dismiss it on the basis that... on what basis, exactly? That no information that wasn't pre-approved by a certified, "well-respected" expert is worth considering? Science doesn't work like that. Academia does.
    - pdonis 14y ago
      Have you read the content of his link? I have; its reasoning is invalid.
      - genwin 14y ago

Xcelerate 14y ago

I am frequently bothered by the misuse of the word "universe". It is defined as the totality of all that exists -- that we can observe. So if there is anything out there, which we didn't think existed before, but we now suspect does exist, well... it's just part of our same old universe.

dmayle 14y ago
I'm not an astrophysicist, so hopefully one can chime in, but my understanding is that 'universe' == the x,y,z,t continuum. Anything outside of that is a different 'universe'. If you can imagine a place that requires alternate dimensions in order to access (e.g. klein bottle), you would be traveling through a different 'universe' (though it is possible that a passage through other universes could lead back to our own). If, however, the other place has a different x,y,z,t continuum, even if there is a passage between the two (wormhole), it's still a different universe. EDIT: (Appending this) Also, if you think of the word universe, it means one totality (uni=one, verse=totality). So, if you want to refer to all that can exist, you probably want to say 'omniverse'.
- yk 14y ago
  I think the concept of outside the universe or inside of it are not developed in a sufficiently rigorous way to really define what a universe is. However in some theories objects appear were it is actually quite natural to speak of an universe and something else. For example there is a unique way to extend the Schwartzschild space time [1] such that all geodesics either terminate in the singularity or go to infinity. But if you do this, then a region of the spacetime appears, that is 'on the other side' of the black hole. And there is no way to communicate with this region of spacetime, since all geodesics leading to it are space like, that is they would require (local) superluminal travel. It is therefore sometimes called a parallel universe. It is similar in certain string theories, that patches of spacetime with different physical laws appear, this is then called the landscape. Or the multiverse in some cosmological models, where a far away region may appear, which is vastly different from or 'local' universe, that is in this case everything we can possibly observe. So I think that it is quite possible that a theory of quantum gravity will have some object which we will call a universe, but until we have such a theory the appearance of anything outside of the universe marks highly speculative physics. [1] That is the spacetime describing a black hole.

Aardwolf 14y ago

And that larger universe is yet within another larger universe! We must go deeper.

evanb 14y ago
http://inception.davepedu.com/ http://inception.davepedu.com/

gjm11 14y ago

(This is from April 2010.) As usual, phys.org have simply reproduced someone else's press release and made a bunch of the words in it link to other phys.org pages. The original press release is at http://newsinfo.iu.edu/news/page/normal/13995.html http://newsinfo.iu.edu/news/page/normal/13995.html and differs from the phys.org version only in not being blogspam. An arXiv preprint of the paper in question is at http://arxiv.org/abs/0902.1994 http://arxiv.org/abs/0902.1994; I think it's actually identical to the version published in Phys. Lett. B. There's a bit more information on Popławski's Wikipedia page: http://en.wikipedia.org/wiki/Nikodem_Pop%C5%82awski http://en.wikipedia.org/wiki/Nikodem_Pop%C5%82awski.

drucken 14y ago

Could you not prove this (or at least go a long way to do it) just by finding a "white hole"?

mvzink 14y ago
I am probably totally misunderstanding all this, but it sounds like the big bang is the white hole.