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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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  • Not again (Score:1, Interesting)

    by TheRealMindChild (743925) on Tuesday November 24, 2009 @04:57PM (#30218534) Homepage Journal
    Every few years, there is yet another theory that claims to be better suited for our models than Einstein's. Then they realize they overlooked something and find Einstein's idea fit better than ever.
  • 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!

  • 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?
  • 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.

  • 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?

  • by mmell (832646) <mike@the-mells.com> on Tuesday November 24, 2009 @05:21PM (#30218894) Homepage
    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?

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

    by realityimpaired (1668397) on Tuesday November 24, 2009 @05:22PM (#30218922)

    Actually, faster-than-light transmission of information has already been observed in science. [wikipedia.org]

    It's a long way from observing and indirectly influencing quantum entanglement to a Star Trek-esque subspace communication, but the fact that Quantum Entanglement exists in the first place lends credence to the notion that c is not a hard limit, or at least, that it's not a hard limit outside of the 4 dimensions that we can observe.

  • Re:And FTL, too (Score:2, Interesting)

    by megamerican (1073936) on Tuesday November 24, 2009 @05:26PM (#30218964)

    "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!

    A good scientist would be saying, "Stockholm, baby!"

    If you're a scientist looking to improve upon a theory it may be helpful to realize that something assumed by the current theory has to not be correct.

    This is what gets me as a person who loves science. There are way too many people who view religion as silly, yet their views on science are just as dogmatic.

  • 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?

  • Re:Excellent! (Score:4, Interesting)

    by mcgrew (92797) * on Tuesday November 24, 2009 @05:32PM (#30219032) Homepage Journal

    i read that some of the theory used math from helium super-fluids.

    Hoava likens this emergence to the way some exotic substances change phase. For instance, at low temperatures liquid helium's properties change dramatically, becoming a "superfluid" that can overcome friction. In fact, he has co-opted the mathematics of exotic phase transitions to build his theory of gravity. So far it seems to be working: the infinities that plague other theories of quantum gravity have been tamed, and the theory spits out a well-behaved graviton. It also seems to match with computer simulations of quantum gravity.

    As I'm no math nerd, perhaps someone who is can explain why infinity is disallowed? I finally figured out why you can't divide by zero; 10/2=5, 5/2=2.5, but if you use numbers smaller than one it is reversed; 1/.5=2, 1/.05=20, so anything divided by zero would be infinity. Is the universe infinite? If so, how can it be studied mathematically?

    I found this intrigueing:

    If Hoava gravity is true, argues cosmologist Robert Brandenberger of McGill University in a paper published in the August Physical Review D, then the universe didn't bang--it bounced. "A universe filled with matter will contract down to a small--but finite--size and then bounce out again, giving us the expanding cosmos we see today," he says. Brandenberger's calculations show that ripples produced by the bounce match those already detected by satellites measuring the cosmic microwave background, and he is now looking for signatures that could distinguish the bounce from the big bang scenario.

    I'm no physicist, but that occurred to me when I first herd of the big band theory. If so, would it bounce an infinite number of times?

  • Re:Not again (Score:4, Interesting)

    by mcgrew (92797) * on Tuesday November 24, 2009 @05:38PM (#30219106) Homepage Journal

    There are really 42 quarks. [angryflower.com]The LHC should probably be able to test this... [angryflower.com]

    (God but I love that guy's cartoons!)

  • Re:Not again (Score:5, Interesting)

    by Rand310 (264407) on Tuesday November 24, 2009 @05:38PM (#30219112)
    Yep. It's called the Correspondence Principle [wikipedia.org] when applied to quantum/classical mechanics. Basically, Newton's equations 'fall out' of Einstein's when you assume the speed of light is a big number relative to all other speeds.
    Recently, paradigms in physics have been interesting in this respect as the new perfectly subsume the prior in their limits. I am not sure that this is a tautology of science, but it is an elegant means of progression.
  • by Xaedalus (1192463) <<Xaedalys> <at> <yahoo.com>> on Tuesday November 24, 2009 @05:46PM (#30219194)
    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?
  • Re:And FTL, too (Score:5, Interesting)

    by megamerican (1073936) on Tuesday November 24, 2009 @05:50PM (#30219260)

    Remember, faster than light means time travel (&, thus, causality violations), so I can understand caution. But, I bet in reality his theory had more serious problems.

    If his theory is correct and space and time are decoupled then faster than light travel wouldn't allow you to travel back in time.

  • 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.

  • Re:Not again (Score:3, Interesting)

    by ioshhdflwuegfh (1067182) on Tuesday November 24, 2009 @05:56PM (#30219340)

    BTW, my physics is really rusty, doesn't one of Einstein's equations devolve into a newtonian equation at slow speed? Which just shows that things are truly built on top of one another.

    It's easy to get Newtonian physics from Relativity. The hard part was to get Relativity knowing just Newtonian physics. Ergo, things are not just built on top of one another, but it's more like building beneath of what you don't know.

  • Re:And FTL, too (Score:2, Interesting)

    by acid_andy (534219) on Tuesday November 24, 2009 @05:56PM (#30219356)
    I'm by no means an expert on this stuff but I think the time travel / causality argument is also a consequence of Einstein's equations. In special relativity he states time slows down for a moving body by a factor of sqrt(1 - (v/c)^2) compared to a stationary observer, so the moving body is effectively travelling into the future for all velocities less than c. Travelling into the future shouldn't violate causality though. The problem is if you plug a value greater than c into the velocity. Then (v/c)^2 becomes bigger than 1 resulting in an apparently negative passage of time for the moving body - hence apparent time travel into the past. The thing is its hard to see how the equation is useful for those values when it also predicts increasing mass approaching infinity at the speed of light. If special relativity does hold true up to the speed of light then it does prevent a craft accelerating past it. If it doesn't hold true, then the negative time factor presumably also won't necessarily apply - preserving causality? I don't know whether general relativity sheds any more light on this. I doubt it.
  • Re:And FTL, too (Score:5, Interesting)

    by HTH NE1 (675604) on Tuesday November 24, 2009 @06:04PM (#30219440)

    You have two things quantumly entangled. You tickle either one, they both laugh. But if can only observe one at a time, if one laughs without being tickled, you don't know whether it was because the other was tickled or if it laughed spontaneously until you observe the other being tickled. There's no way to confirm the laughter as FTL information from the future unless and until you observe the future.

    It may be that they only both laugh when you can observe them both. Your observation entangles them and bridges the FTL transmission classically.

    I'd like to see the experiment where they're entangled, one is dropped through a black hole's event horizon, and you observe the result on the other. Time compression should have an interesting effect on the half-life of the retained entangled one until it crosses the EH.

  • 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 boristhespider (1678416) on Tuesday November 24, 2009 @06:10PM (#30219534)

    No, that's not actually the starting point of special relativity and it's got really nothing to do with general relativity.

    Special relativity, if you wish to formulate it like that, comes from postulating that the velocity of light as seen from unaccelerated frames of reference is always the same -- this is *not* the same as saying that nothing travels faster than light; that is, instead, a result of this hypothesis.

    General relativity, ultimately, comes from stating that the fact that all objects regardless of mass fall under gravity with the same acceleration isn't an accident. If you think about it, this is an absolutely unnatural situation. Imagine any force -- any actual force. Then the heavier an object is, the less it accelerates for a given force. Simple physics. Gravity doesn't do that. What other force doesn't? Well, centrifugal force. And as people who've never studied anything in rotating reference frames are fond of pointing out, centrifugal force does not exist -- centrifugal force is a fictional force. The hallmark of a fictional force is that it imparts an equal acceleration on all objects. If one assumes that this is due to the fundamental nature of gravity, then by some relatively straightforward reasoning (tied to some not-so-straightforward differential geometry) one is lead to something that resembles general relativity, a "metric" theory of gravity that explains gravity as the manifestation of geometry in some manner.

    (General relativity itself is then found by postulating, based chiefly on the sheer simplicity of it, some equations tying the metric to the distribution of matter, known as the Einstein equations.)

    In general relativity, the fact that nothign can travel faster than light is, firstly, not actually absolutely true due not least to ambiguities in how to define distance and time in arbitrary curved reference frames and, secondly, linked chiefly to the geodesics that particles travel on. A "spacelike" (FTL) geodesic cannot become a timelike (slower than light) geodesic, at least not in a non-pathological spacetime. (I've never seen a spacetime where this could happen, but I'll never say never just in case I'm wrong...)

  • Re:Not again (Score:2, Interesting)

    by osu-neko (2604) on Tuesday November 24, 2009 @06:12PM (#30219546)
    I prefer to say one will prove to be a better model. I suppose "more accurate" works too, although it begs the question of what "accurate" means in the context. Scientists of course understand that means it produces correct predictions more often, but laymen are likely to interpret it to mean something more vis a vie it's status as a "description" of reality. Which may indeed be true, but ultimately that's a philosophical question, not a scientific one. In science, the "better description of reality" is "better" only in the sense that it produces better predictions. "Closer to the truth" is a question outside the scientific realm. "Right" is right out...
  • Re:And FTL, too (Score:3, Interesting)

    by Have Brain Will Rent (1031664) on Tuesday November 24, 2009 @06:16PM (#30219598)
    (Without looking at the Wikipedia article) It seems to me that the alternate explanation usually given for this is that there are hidden variables which encode the state information we see as entanglement so there is no communication after the particles separate. Each of the entangled particles just relies on local information that it carries with it and which was generated at the moment of entanglement.
  • by Anonymous Coward on Tuesday November 24, 2009 @06:20PM (#30219650)

    This can't possibly be correct. Don't you remember? The science is already settled! Whew - boy, glad that's over (hand wiping)!

  • Re:And FTL, too (Score:3, Interesting)

    by 4D6963 (933028) on Tuesday November 24, 2009 @06:27PM (#30219750)

    Well, I know what you mean, you might make the house of cards of our theories fall by pulling that one out, but it doesn't mean that it shouldn't be tried, as long as the impossibility of FTL information travel isn't definitely proven. For all we know, a theory might smoothly remove it without disturbing anything too much, you know, a bit like this new theory being talked about doesn't disturb too much some of the seemingly unreconcilable properties of relativity and quantum mechanics by distinguishing in the scales involved.

  • Re:And FTL, too (Score:3, Interesting)

    by 4D6963 (933028) on Tuesday November 24, 2009 @06:38PM (#30219878)

    Not to make the discussion drift off topic, but at the core people who hold religious dogmas and scientists share the same brain structure as we all do, and there are instincts in us that work the same way as when you spray chimp with cold water when they reach for the Holy Banana until quickly no one touches it, even those who were not sprayed, even when the last chimp to be sprayed left the place a long time ago.

    What I mean is, we tried hard for about a century to find cracks in Einstein's theories, and while there are many things that are wrong with it (i.e. you can't marry it with quantum mechanics too well), all attempts to disprove his predictions have failed, which gives us room to hold some aspects of his theories as scientific dogma, the impossibility of FTL information transmission being possibly one of them. That is, we act like we know for sure about that when really we don't, it's just that so far there's nothing that really goes against that assumption.

    For the fellow coders out there, that's a bit like when you thoroughly test and verify a function to make sure it's bug free, but yet much later find out it caused a bug, and you wasted much time looking for a cause for it where it was not. Sorry, can't think of any car analogy.

  • Re:Excellent! (Score:2, Interesting)

    by hrimhari (1241292) on Tuesday November 24, 2009 @06:42PM (#30219916) Journal

    As I'm no math nerd, perhaps someone who is can explain why infinity is disallowed? I finally figured out why you can't divide by zero; 10/2=5, 5/2=2.5, but if you use numbers smaller than one it is reversed; 1/.5=2, 1/.05=20, so anything divided by zero would be infinity. Is the universe infinite? If so, how can it be studied mathematically?

    I'm no math nerd either, but what I remember is that since it has no end (infinite), you can't add or subtract from it because it still has no end after that. That's all fine, but irrational numbers don't exist, yet we use them in arithmetic. I don't know why we just can't use infinity the same way and do magic tricks like:

    oo - oo = 0
    oo / oo = 1
    etc.
    (Note: oo = infinity. &infin; and &#8734; not supported on Slashdot.)

    Any math lord reading this thread?

  • Re:Not again (Score:3, Interesting)

    by ShieldW0lf (601553) on Tuesday November 24, 2009 @06:46PM (#30219962) Journal

    Religions, which is what you're talking about when you say faith, are software that runs in a cluster of human beings. They mutate all the time... you turn your head, there's another one popping up, the bastard stepchild of a few predecessors. Some religions will destroy the hardware they run on before they ever propagate. The Davidians, for example. Others will propagate through a population quickly, but lead that population to extinction in a few generations. A few will endure, supporting their populations growth and infecting or destroying the populations running another religion.

    This is not made up airy-fairy bullshit that some simpleton believes for no reason. This is evolution at work. These old religions have demonstrated their reliability, because the people who believe in them are not dead.

    The evidence indicates that the vast majority of ideas that are "modern" and "novel" and "progressive" will lead the population that embraces them to extinction.

    http://en.wikipedia.org/wiki/Evolutionary_psychology [wikipedia.org]

  • by jpmorgan (517966) on Tuesday November 24, 2009 @07:01PM (#30220188) Homepage

    Spooky action at a distance doesn't need any finagling to get around lightspeed, because spooky action at a distance doesn't involve any communication. It's already compatible with general relativity (at least, insofar as any quantum theory is compatible with relativity).

    A flawed, but illustrative example that should explain why this is so: imagine you have a friend who is flipping a coin... if it comes up heads, he writes an X on two sheets of paper, if it comes up tails, he writes a checkmark on both instead. Both are immediately sealed inside envelopes and mailed to opposites sides of the planet. If you open one letter and see an X, you instantly know the other has an X also. That doesn't require any communication.

    A slightly less flawed, and still illustrative extension: Now instead of a coin flip, you have a machine do it based on the decay of a mass of cesium, and you have a perfect envelope which protects against quantum decoherence. The same situation applies, as soon as you open one envelope you know what is contained in the other. The only difference this time is that the letters were entangled and in a superposition of states. However, it's the same mechanism, and no communication is required.

  • Re:Excellent! (Score:3, Interesting)

    by Jarjarthejedi (996957) <christianpinch@ g m a i l . c om> on Tuesday November 24, 2009 @07:11PM (#30220310) Journal

    Uh, because that would be incorrect? One infinity is not necessarily equal to another, not to mention infinity isn't a number, nor is it a constant or variable. It's a concept, and you can't add, subtract, multiple or divide concepts, so you can't do anything like that to infinity.

    There's a calculus theory whose name escapes me that allows you to solve for what X/Y equals when X and Y are both infinite functions using their derivatives. I remember taking tests where we basically had lim (x->oo, y->oo) of (x+10)/(y^2) and we had to determine what it equaled. Sure you could simplify that to oo/oo and then say it equals 1, but you'd get that question wrong.

  • Re:Not again (Score:2, Interesting)

    by tomthegeek (1145233) on Tuesday November 24, 2009 @07:27PM (#30220516) Homepage

    Thanks for making the point more clear. We can't predict the future so we can't know if in ten feet the road will vanish beneath me or that my electrons won't go flying off into space. Fair enough.

    Haven't we proven enough of our theories about this world that we know for certain things are stable to a known degree? Or is it like the "law" of gravity, not proven but correct according to a large body of evidence? Do you mean to say that we know no absolutes?

  • Re:Not again (Score:3, Interesting)

    by radtea (464814) on Tuesday November 24, 2009 @10:49PM (#30222188)

    You *must* presuppose that the future is relevantly like the past for empiricism to have any meaning in any context; it's pretty much an irreducible problem.

    Who must what?

    That is, you--who who exist and are persistent in time with a unique personal identity and live in a causal world that is persistent in time and full of a diversity of phenomena that are identifiable by you and persistent in time--must, to engage in the act of disagreeing with the self-consistency and sturdiness of the logical foundations of empiricism, must presuppose--as a condition of entering into the discourse--the very conditions that you for some reason want to say must be uniquely presupposed by empiricists.

    That is, you are saying, "I completely accept these conditions without dispute and can raise no argument or question against them, but I demand that empiricists justify them, even though I don't demand the same thing of anyone else, including myself."

    What you are claiming is a problem with empiricism is actually nothing more than a universal and rather uninteresting form of scepticism, and anyone who raises it seriously immediately rules themselves out of bounds by the simple fact of not having applied their own argument to their own utterance first.

  • Re:Not again (Score:2, Interesting)

    by focoma (865351) <focoma@gmail.com> on Tuesday November 24, 2009 @11:47PM (#30222552) Homepage
    Your use of argumentum ad ignorantiam is... interesting. Would you, perhaps, claim that agnostics use argumentum ad ignorantiam when they say that we cannot prove or disprove the existence of God?
  • Re:Not again (Score:3, Interesting)

    by ultranova (717540) on Wednesday November 25, 2009 @03:37AM (#30223546)

    The catch is, eventually one will be right, and explain things that are out of the scope of Einstein's theories or more accurately explain in-scope things.

    Assuming, of course, that Einstein's theories are actually incorrect. This particular theory, for example, sets of my bullshit detector because it claims that the nature of reality suddenly changes totally in large enough energies - not just some field, but space and time itself.

    Or do you believe we are at the pinnacle of the field, and can achieve no more?

    Frankly, yes: I don't think that Einstein's theories will ever be proven wrong. They fit too many phenomenom perfectly, predict too much, and when you really come down to it, are too fundamentally simple: General Relativity is really just taking the notion that all observers are equal and examining the logical consequences.

    The only reason these "Einstein was wrong" -theories keep on popping up is because it's difficult to get the math of quantum mechanics and General Relativity to work together. I suspect that's mainly because of our insufficiently advanced mathemathics, rather than physics, and possibly also inappropriate use of Heisenberg uncertainty principle (which is why you get infinite energies input into GR in the first place). It could also be that the universe simply is chaotic in the fundamental level, and only looks stable at large scale because uncertainty becomes averaged out.

    In any case, since the article doesn't bother to actually describe the theory, it's impossible to say for sure. But I'm not holding my breath.

"Only the hypocrite is really rotten to the core." -- Hannah Arendt.

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