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The feeling I get from reading the article is the theory is highly speculative. Could be just this line: "‘loop quantum gravity’ — a theoretical attempt that ha

by Oculus 12y ago

The feeling I get from reading the article is the theory is highly speculative. Could be just this line: "‘loop quantum gravity’ — a theoretical attempt that has yet to find experimental support"

Argorak 12y ago
Considering that the Higgs Boson was theorized about in 1964 and finally proven in an experiment in 2012: this seems to be the way of theoretical physics. ;)
- lisper 12y ago
  The difference is that the Higgs was a necessary logical consequence of the Standard Model. Quantum loop gravity is purely speculative, much like string theory. In the case of QM versus GR we have the very weird situation where we have two theories that are logically incompatible with each other, so we know at least one of them must be wrong. And yet neither one has ever made a prediction that has ever been falsified by experiment, so we have no guidance from nature regarding which theory is wrong or how. That's the reason that the theoretical physicists seem to be grasping at straws, and everyone is a little disappointed that the LHC hasn't done anything surprising.
  - chunky1994 12y ago
    While I agree with what you are saying, I'd like to add a bunch of addenda (caveats?). The Higgs mechanism was one possible model which the standard model required, the others have now obviously been disproven thanks to the LHC. If no one had proposed this particular model, we'd still be wondering how fundamental particles gained mass and have another unexplained experimental result with the peak at 125 GeV from the data at the LHC. Similarly, GR and QM are both extremely well tested, however GR has dark matter and energy to deal with, and we still have no real idea what that is. This could potentially point to GR being wrong, however none of us are able to come up with another theory of gravity that could incorporate this and be better than GR at this stage. If a theory of quantum gravity (or just gravity) came along that could explain dark matter quite effectively then it would be hailed as a better theory than GR. The reason string theory and loop quantum gravity are considered completely speculative is because their predictions are so far beyond our grasp that even in the relatively far future we still have no way of confirming or denying either of them. Had they predicted things that could've been confirmed within the next century or so, I'm sure we'd all be rallying to try and confirm them. They aren't speculative so much so because we don't know which of GR or QM is wrong, but because their testability is quite precarious at this point.
  - mtdewcmu 12y ago
    I think it's not so much that the Higgs was logical; the difference with Higgs is that the Higgs was conceived as something testable from the start (I'm assuming, but it doesn't seem like a big leap, considering that particle physics has always been driven by experiments). The really big problem with untestable ideas is that they are not even science. Untestable ideas about physics are more like a peculiarly abstruse art form practiced by physicists.
  - trhway 12y ago
    >In the case of QM versus GR we have the very weird situation where we have two theories that are logically incompatible with each other, so we know at least one of them must be wrong nope. Incompatible are only stretches of the theories into the areas where conditions contradict basic assumptions of the theories. QM assumes fixed space-time which we know isn't true, so the QM can be true only where the difference between fixed space-time and real one is negligeable, ie. small scale/local effects. (And even at the small scale, assumption of the fixed space-time may be very limiting - who knows, may be powerful forces at local level do "bad" things to space-time too and this would be an explanation for the things like non-separability of quarks or a for a lot of others "strange" effects observed at quantum level). GR is about real, non-fixed space-time and disregards any forces/interactions other than gravitation. Thus it is not correct when applied at local scales where other interactions overpower gravitation. Thus stretching GR into small scale just makes a wrong physical theory the same way as stretching QM into GR space makes for a wrong theory too.
    - lisper 12y ago
      What you say is true, but it is also true that they are logically incompatible. GR assumes that matter is precisely localized and QM assumes that it is not. They can't both be right (and in fact we know that GR is wrong about this). So, for example, GR predicts that the interior of a black hole contains a singularity at a precise location, while QM (via the Heisenberg uncertainty principle) says that this is impossible.
- Iftheshoefits 12y ago
  Theoretical physics encompasses far more than speculative hypotheses with no experimental support (and in some cases without a way to even describe accurately any experiment which might lend support). A majority of theoretical physics (including some areas mistaken to be "purely theoretical") consists of work where there exists the means to experimentally support (or falsify) hypotheses right now, or at least construct experiments which could do so. They tend to be less glamorous than string theory or loop quantum gravity, though, and so they don't get as much attention.
jerf 12y ago
Loop quantum gravity is in competition with the much more popular String Theory, which is also "a theoretical attempt that has yet to find experimental support". The Grand Unified Theories all fit in that bucket. It's important to keep that in mind, but since there isn't a GUT that does have "experimental support" we can't really demand that at this point....
- webkike 12y ago
  String Theory is only more popular because there are ted talks on it and thus people who shouldn't hold an opinion on the matter do.
mindcrime 12y ago
Could be just this line: "‘loop quantum gravity’ — a theoretical attempt that has yet to find experimental support" As @jerf points out here as well, LCG has as much experimental support as any of the other competing GUT hypotheses... which is to say, none. This whole "thing" about the lack of experimental support and lack of testable / falsifiable assertions in physics (especially String Theory) is explored at length in two pretty interesting books: Not Even Wrong[1] by Peter Woit and The Trouble With Physics[2] by Lee Smolin. [1]: http://www.amazon.com/Not-Even-Wrong-Failure-Physical/dp/0465092764 http://www.amazon.com/Not-Even-Wrong-Failure-Physical/dp/046... [2]: http://www.amazon.com/The-Trouble-With-Physics-Science/dp/061891868X http://www.amazon.com/The-Trouble-With-Physics-Science/dp/06...

by Oculus 12y ago

Argorak 12y ago

Considering that the Higgs Boson was theorized about in 1964 and finally proven in an experiment in 2012: this seems to be the way of theoretical physics. ;)

lisper 12y ago
The difference is that the Higgs was a necessary logical consequence of the Standard Model. Quantum loop gravity is purely speculative, much like string theory. In the case of QM versus GR we have the very weird situation where we have two theories that are logically incompatible with each other, so we know at least one of them must be wrong. And yet neither one has ever made a prediction that has ever been falsified by experiment, so we have no guidance from nature regarding which theory is wrong or how. That's the reason that the theoretical physicists seem to be grasping at straws, and everyone is a little disappointed that the LHC hasn't done anything surprising.
- chunky1994 12y ago
  While I agree with what you are saying, I'd like to add a bunch of addenda (caveats?). The Higgs mechanism was one possible model which the standard model required, the others have now obviously been disproven thanks to the LHC. If no one had proposed this particular model, we'd still be wondering how fundamental particles gained mass and have another unexplained experimental result with the peak at 125 GeV from the data at the LHC. Similarly, GR and QM are both extremely well tested, however GR has dark matter and energy to deal with, and we still have no real idea what that is. This could potentially point to GR being wrong, however none of us are able to come up with another theory of gravity that could incorporate this and be better than GR at this stage. If a theory of quantum gravity (or just gravity) came along that could explain dark matter quite effectively then it would be hailed as a better theory than GR. The reason string theory and loop quantum gravity are considered completely speculative is because their predictions are so far beyond our grasp that even in the relatively far future we still have no way of confirming or denying either of them. Had they predicted things that could've been confirmed within the next century or so, I'm sure we'd all be rallying to try and confirm them. They aren't speculative so much so because we don't know which of GR or QM is wrong, but because their testability is quite precarious at this point.
- mtdewcmu 12y ago
  I think it's not so much that the Higgs was logical; the difference with Higgs is that the Higgs was conceived as something testable from the start (I'm assuming, but it doesn't seem like a big leap, considering that particle physics has always been driven by experiments). The really big problem with untestable ideas is that they are not even science. Untestable ideas about physics are more like a peculiarly abstruse art form practiced by physicists.
- trhway 12y ago
  >In the case of QM versus GR we have the very weird situation where we have two theories that are logically incompatible with each other, so we know at least one of them must be wrong nope. Incompatible are only stretches of the theories into the areas where conditions contradict basic assumptions of the theories. QM assumes fixed space-time which we know isn't true, so the QM can be true only where the difference between fixed space-time and real one is negligeable, ie. small scale/local effects. (And even at the small scale, assumption of the fixed space-time may be very limiting - who knows, may be powerful forces at local level do "bad" things to space-time too and this would be an explanation for the things like non-separability of quarks or a for a lot of others "strange" effects observed at quantum level). GR is about real, non-fixed space-time and disregards any forces/interactions other than gravitation. Thus it is not correct when applied at local scales where other interactions overpower gravitation. Thus stretching GR into small scale just makes a wrong physical theory the same way as stretching QM into GR space makes for a wrong theory too.
  - lisper 12y ago
    What you say is true, but it is also true that they are logically incompatible. GR assumes that matter is precisely localized and QM assumes that it is not. They can't both be right (and in fact we know that GR is wrong about this). So, for example, GR predicts that the interior of a black hole contains a singularity at a precise location, while QM (via the Heisenberg uncertainty principle) says that this is impossible.
Iftheshoefits 12y ago
Theoretical physics encompasses far more than speculative hypotheses with no experimental support (and in some cases without a way to even describe accurately any experiment which might lend support). A majority of theoretical physics (including some areas mistaken to be "purely theoretical") consists of work where there exists the means to experimentally support (or falsify) hypotheses right now, or at least construct experiments which could do so. They tend to be less glamorous than string theory or loop quantum gravity, though, and so they don't get as much attention.

jerf 12y ago

Loop quantum gravity is in competition with the much more popular String Theory, which is also "a theoretical attempt that has yet to find experimental support". The Grand Unified Theories all fit in that bucket. It's important to keep that in mind, but since there isn't a GUT that does have "experimental support" we can't really demand that at this point....

webkike 12y ago
String Theory is only more popular because there are ted talks on it and thus people who shouldn't hold an opinion on the matter do.

mindcrime 12y ago

Could be just this line: "‘loop quantum gravity’ — a theoretical attempt that has yet to find experimental support" As @jerf points out here as well, LCG has as much experimental support as any of the other competing GUT hypotheses... which is to say, none. This whole "thing" about the lack of experimental support and lack of testable / falsifiable assertions in physics (especially String Theory) is explored at length in two pretty interesting books: Not Even Wrong[1] by Peter Woit and The Trouble With Physics[2] by Lee Smolin. [1]: http://www.amazon.com/Not-Even-Wrong-Failure-Physical/dp/0465092764 http://www.amazon.com/Not-Even-Wrong-Failure-Physical/dp/046... [2]: http://www.amazon.com/The-Trouble-With-Physics-Science/dp/061891868X http://www.amazon.com/The-Trouble-With-Physics-Science/dp/06...