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Space Science

New Theory of Gravity Decouples Space & Time 575

Posted by kdawson
from the paging-hal-clement dept.
eldavojohn writes "Petr Horava, a physicist at the University of California in Berkeley, has a new theory about gravity and spacetime. At high energies, it actually snips any ties between space and time, yet at low energies devolves to equivalence with the theory of General Relativity, which binds them together. The theory is gaining popularity with physicists because it fits some observations better than Einstein's or Newton's solutions. It better predicts the movement of the planets (in an idealized case) and has a potential to create the illusion of dark matter. Another physicist calculated that under Horava Gravity, our universe would experience not a Big Bang but a Big Bounce — and the new theory reproduces the ripples from such an event in a way that matches measurements of the cosmic microwave background."
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New Theory of Gravity Decouples Space & Time

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  • And FTL, too (Score:5, Interesting)

    by Geoffrey.landis (926948) on Tuesday November 24, 2009 @05:01PM (#30218576) Homepage

    Special relativity, of course, forbids sending information faster than light. A theory supplanting the space-time unification of General Relativity would also supplant special relativity, and hence might not have that limitation. Here's an inteersting tidbit from the article: "Gia Dvali, a quantum gravity expert at CERN, remains cautious. A few years ago he tried a similar trick, breaking apart space and time in an attempt to explain dark energy. But he abandoned his model because it allowed information to be communicated faster than the speed of light."

    I'd call that a feature, not a bug!

    • Re:And FTL, too (Score:5, Insightful)

      by mea37 (1201159) on Tuesday November 24, 2009 @05:15PM (#30218770)

      Whether it's a feature or a bug depends on whether it reflects reality.

      It's strange to me that Dvali would abandon his model for allowing FTL propagation of information unless he experimentally checked the conditions in question to see if information really could propagate FTL in those cases. I have to assume he did not - lacking clarification on the matter I'm left to assume that the conditions were not something simple he could test no a whim.

      Without the experimental results, it's meaningless to call such an artifact in the model "good" or "bad".

      • by Anonymous Coward on Tuesday November 24, 2009 @05:50PM (#30219256)

        I have to assume he did not - lacking clarification on the matter I'm left to assume that the conditions were not something simple he could test no a whim.

        Wow. Anyone else see that? From my location, the n arrived before the o; however, the parent clearly typed them in order (o before n) in our reference frame, so I think we've just witnessed information traveling faster than light! Woohoo!

      • by khallow (566160) on Tuesday November 24, 2009 @06:10PM (#30219526)

        It's strange to me that Dvali would abandon his model for allowing FTL propagation of information unless he experimentally checked the conditions in question to see if information really could propagate FTL in those cases.

        Sorry, my bad. I have to be the one who checks for FTL propagation, union rules. I'll get to it after I finish my "get laid" project. I'm particularly hopeful. Just the other day, I made eye contact for 1.3 seconds with what I assume to be the female of our species. I think I can get that up to 10 seconds without breaking any laws of the legal kind. It's very promising progress here.

      • Re: (Score:3, Insightful)

        by markov_chain (202465)

        Whether it's a feature or a bug depends on whether it reflects reality.

        Clearly with FTL travel it cannot reflect reality, so it must be false.

    • Re:And FTL, too (Score:5, Interesting)

      by Culture20 (968837) on Tuesday November 24, 2009 @05:19PM (#30218836)

      "But he abandoned his model because it allowed information to be communicated faster than the speed of light."
      I'd call that a feature, not a bug!

      Exactly! "Oh no, my theory doesn't match the theory it's replacing!" Well, experiment, dummy! Did Einstein say "oh no, my theory allows light rays to bend and makes C the absolute speed!"? No! He got together with other scientists in 1919 and watched starshine bend around an eclipse.

      • Re:And FTL, too (Score:5, Interesting)

        by PuckSR (1073464) on Tuesday November 24, 2009 @05:51PM (#30219274)

        Actually, HE DID!

        He added the cosmological constant to his general theory of relativity, because if he followed his models...it indicated that the universe was expanding.
        Einstein didn't like the idea that it was expanding(because it didn't fit the current thinking), so he added the cosmological constant to his equations to make the universe "static".

        so, even Einstein fell prey to conventional wisdom and thinking.

  • by ErikTheRed (162431) on Tuesday November 24, 2009 @05:05PM (#30218648) Homepage

    Does this theory suck or is there some pull to it? It just seems so weighty to me.

  • by Lord Grey (463613) * on Tuesday November 24, 2009 @05:08PM (#30218682)
    ... in a presentation [ksc.re.kr] from the 30th Workshop on Gravitation and Numerical Relativity at Jungwon University. It's a PDF version of a PowerPoint deck, so it's not exactly easy to read.
  • String Theory (Score:5, Interesting)

    by Statecraftsman (718862) * on Tuesday November 24, 2009 @05:09PM (#30218694) Homepage
    So does this compete with string theory or have a chance modifying it to an eventual theory of everything?
  • by Anonymous Coward on Tuesday November 24, 2009 @05:13PM (#30218734)
    http://arxiv.org/abs/0901.3775 [arxiv.org] PS Slashdot has the slowest comment preview of any website I know.
  • ZZZTTT ! (Score:4, Informative)

    by mbone (558574) on Tuesday November 24, 2009 @05:14PM (#30218764)

    it fits some observations better than Einstein's or Newton's solutions. It better predicts the movement of the planets (in an idealized case)

    Oh. In an idealized case. Imaginary physics. Of course, in the actual case, it does not (it requires patching to allow for non-spherical planets).

    At any rate, there are at present no known relativistic measurements that are not consistent with General Relativity, so I am not clear where the "better than" comes from.

    And, from the standpoint of a General Relativist, the stubborn desire of the particle physicists to have a flat spacetime at high enough energies, no matter what, seems, well, quaint.

    • Re: (Score:3, Informative)

      by wizardforce (1005805)

      It isn't the expectation of a flat space-time at quantum scales that is the problem, it is the infinities and negative probabilities that are the trouble. Relativity is wrong at some level; this much is pretty well established. The real tricky part is welding our understanding of space-time with quantum physics in a signle theory without breaking everything.

  • by czarangelus (805501) <iapetus@nOSpaM.gmail.com> on Tuesday November 24, 2009 @05:19PM (#30218844)
    1. Gravity is still spooky action at a distance with no causal mechanism defined.

    2. I don't think time, as in "time lines" or some kind of unidirectional movement through a medium exists. Now exists, hypostatized out of a past (which stops existing when it stops being now) and which in turn hypostatizes the future (which does not exist.)

    3. Electromagnetism is the dominant force in the heavens as it is on Earth.

    4. Stars are organisms and they reproduce through fission.

    5. Galaxies are powered by vast electric circuits; beads on a string.
  • by DaveV1.0 (203135) on Tuesday November 24, 2009 @05:19PM (#30218846) Journal

    Sounds to me like this is just an hypothesis as there doesn't appear to much experimental evidence supporting it. This is an extraordinary claim and so need extraordinary proof.

    And, the interchanging of hypothesis and theory by scientific magazines is a bad thing. If scientists, science fans, and science writers do not use the words correctly how are we to defend the difference when creationists come around misusing the words?

    • Re: (Score:3, Insightful)

      by MontyApollo (849862)

      The theory of special relativity and of general relativity existed before there was any experimental proof.

      I think when you are dealing with theoretical physics, if you can get a mathematical model to "work," then it is a theory. Like String Theory.

  • by mmell (832646) <mike.mell@gmail.com> on Tuesday November 24, 2009 @05:21PM (#30218894)
    Einstein's theories of relativity basically start by saying something to the effect of "Let us assume the speed of light to be the fastest anything can travel. If we assume this, then..."

    Sounds like this guy's saying "Let us assume the speed of light is not necessarily the fastest anything can travel. If we assume this, then..."

    The reason for Einstein's initial assumption is that we have never to date observed anything which has moved faster than light. Then again, would we know such a thing if we observed it, and have we actively looked for such a thing? If so, how have we looked?

    • by maxwell demon (590494) on Tuesday November 24, 2009 @05:57PM (#30219362) Journal

      Einstein's theories of relativity basically start by saying something to the effect of "Let us assume the speed of light to be the fastest anything can travel. If we assume this, then..."

      Wrong.
      Special relativity is built on two principles:

      • The speed of light is the same in all inertial systems
      • The laws of physics look the same in each inertial system

      (actually, if you take Maxwell's equation into account, the first is just a special case of the second). Especially it does not postulate that there's nothing faster than light. Rather,

      • it is a result of SR that anything slower than light cannot be accelerated to a speed faster than light (you'd need infinitely much energy to get it just to the speed of light)
      • any action which goes faster than light would violate causality, so if in addition to SR we also assume causality, FTL cannot exist.

      However, you can describe hypothetical faster-than-light particles in SRT (so-called tachyons; those cannot be decelerated to below the speed of light), and AFAIK there have been experiments to look for them. Note however that as soon as you add quantum mechanics to the picture, even with tachyons no information can be transmitted faster than light (local disturbances in he quantum tachyon field only propagate with light speed).

      General relativity adds the equivalence principle (locally you cannot distinguish between gravitation and acceleration) and the demand of general covariance (the equations must look the same regardless of choice of coordinates, even if those don't correspond to an inertial system).

    • by rewt66 (738525) on Tuesday November 24, 2009 @06:49PM (#30220006)
      Well, Einstein assumed that because of the null result of the Michaelson-Morley experiment. He didn't just guess it out of the blue...
  • Ow! (Score:4, Insightful)

    by necro81 (917438) on Tuesday November 24, 2009 @05:22PM (#30218924) Journal
    It took me long enough to get my head around the intertwining of space and time in relativity. Now you're telling me that they might also be decoupled in special circumstances.

    Ow! My brain hurts.
  • by perrin (891) on Tuesday November 24, 2009 @05:32PM (#30219026)

    From the linked article, it seems the theory both predicts the heat death of the universe (continued accelerated expansion) and that our universe started from a "Big Crunch" scenario (gravity had pulled everything back again). This seems quite strange (although of course nature can be quite strange at times). Anyone know this theory any better and can provide some enlightenment?

    • So let's say our universe is expanding (doesn't matter if it's this theory or mainstream Big Bang). We already know there's volume beyond the visible edges of our universe. What if there's another universe expanding towards us, accelerating into heat death, and then its edges hit our own? Wouldn't that Big Smack be a Big Crunch? And thus another universe is born?
  • by darkharlequin (1923) on Tuesday November 24, 2009 @05:49PM (#30219232) Homepage Journal
    In one day, and they are both in California. I am stuck here in New Jersey. New Jersey is Hell. When people die, they don't go under the ground, they just pop up somewhere in Newark. See, us citizens of New Jersey are immortal because if we are killed, we just pop up back again in New Jersey. Its just really hard to navigate around Newark, so that's why you don't see us again..................
  • by migla (1099771) on Tuesday November 24, 2009 @05:55PM (#30219332)

    My hypothesis about gravity:

    Everything is growing. We can't see anything growing, because our rulers and tapemesures and everything is growing. That's gravity: Just the growing earth pushing against your growing feet. Gravity at a distance is just objects growing towards each others (the void doesn't grow). Come to think of it. It's probably a bad hypothesis. It couldn't explain a slingshot effect, could it? Nevermind.

  • by asdf7890 (1518587) on Tuesday November 24, 2009 @05:56PM (#30219342)
    But does it also predict that time is an illusion, lunch-time doubly so? If not then there is still room for a more refined theory.
  • by 4D6963 (933028) on Tuesday November 24, 2009 @06:08PM (#30219500)

    Gia Dvali, a quantum gravity expert at CERN, remains cautious. A few years ago he tried a similar trick, breaking apart space and time in an attempt to explain dark energy. But he abandoned his model because it allowed information to be communicated faster than the speed of light.

    How do we know for sure that it's impossible? How can we test against it to conclude it's definitely an impossibility? We surely haven't found any way to achieve that, but given that all theories are still in the balance, how do we know for sure there's no way we possibly could?

    This being said, nice to see a theory that's more intuitive than usual, that attempts to explain dark matter and dark energy by revising how things work rather than claiming there's a bunch of invisible mysterious things at work, and that does so without adding a bucketload of new unperceptible dimensions and weird vibrating strings that no one can prove. Ah, and give an alternative to the ailing theory of Big Bang.

    And nice to see that it took SciAm's commenters less time than Slashdot users to make the discussion drift into some crap about religion. Maybe we're not that bad after all.

  • by mpsmps (178373) on Tuesday November 24, 2009 @08:42PM (#30221276)

    Remember the saying that science proceeds by successive approximation to the truth.

  • by Ralph Spoilsport (673134) on Tuesday November 24, 2009 @10:40PM (#30222142) Journal
    The universe is a giant plutonium atom. Archimedes told me so.

Recursion is the root of computation since it trades description for time.

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