New Theory of Gravity Decouples Space & Time 575
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."
Much more mathematical detail... (Score:4, Informative)
Here's the actual article (Score:3, Informative)
ZZZTTT ! (Score:4, Informative)
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.
Excellence: Biography of Petr Hoava (Score:4, Informative)
Yet, who is Petr Hoava? He maintains a Web page [berkeley.edu] that offers the following biography.
"Petr Horava received his Ph.D. in 1991 at the Institute of Physics of the Czech Academy of Sciences in Prague. He was awarded the Robert McCormick Research Fellowship at the Enrico Fermi Institute at the University of Chicago, worked as a Research Associate at Princeton University, and won a Sherman Fairchild Senior Research Fellowship at Caltech, before joining the New High Energy Theory Center at Rutgers University in 2000 as an Associate Professor. In 1997, he was awarded the Junior Prize of the Czech Learned Society, and in 1999 he appeared on the list of top three scientists of the Czech Republic of the 90's. He joined the Physics Department at UC Berkeley in 2001."
The liberation of Eastern Europe in 1989 has unleashed an intellectual force that will advance human knowledge by leaps and bounds. 2009 is the 20th anniversary of that liberation.
Buddha bless the Eastern Europeans.
Re:String Theory (Score:4, Informative)
"String theory" is actually a collection of several competing theories and this theory appears to be another version. I can't really say for sure as the presentation on the theory seemed to me to be rather limited.
Re:ZZZTTT ! (Score:3, Informative)
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.
Re:And FTL, too (Score:5, Informative)
Actually, faster-than-light transmission of information has already been observed in science. [wikipedia.org]
Well, yes, I suppose... as long as your definition of "transmission" of information is sufficiently flexible. The quantum correlation is "transmitted" faster than light, but you can't get information out of it unless you receive the (slower than light) classical part.
Re:String Theory (Score:3, Informative)
I think it is an alternative to string theory.
From http://www.physicsforums.com/showthread.php?t=313565 [physicsforums.com] :
Compared to string theory - much simpler and works in 3+1 dimensions
Compared to LQG - the classical limit is not a problem
Re:Just wondering out loud... (Score:5, Informative)
Wrong.
Special relativity is built on two principles:
(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,
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).
Re:Not again (Score:5, Informative)
Same thing in Quantum Mechanics. They devolve into classical equations, if you set Planck's Constant to 0.
Re:Excellent! (Score:4, Informative)
The problem isn't so much with the infinities, those are perfectly allowable in math and in physics.
The gravitational pull as you approach a black hole approaches infinity
The limit of the graph 1/x as x->0 is infinite.
The problem is that other theories of quantum gravity result in infinities where we do NOT observe these infinities to exist. As a simple example (quantum mechanics is beyond me, but this gives the flavor), one of the classic theories of electrostatics states that the electric field of a point charge is inversely proportionate to the square of the distance from that charge.
However, from a quantum-mechanical standpoint, and electron has no size...it is a point particle.
This causes an issue if we take both of these results together...as you approach an electron, the electric field should approach infinity.
We know that this doesn't happen, so one of the two theories must be incomplete.
Re:Just wondering out loud... (Score:5, Informative)
Then we need a new theory.
Well, "the same in all systems" in the post above didn't refer to "at different places in the universe", but "as seen/described by different observers in the same part of the universe".
That doesn't mean we don't also assume that the laws of nature are always and everywhere the same. Indeed, that's basically always assumed.
By applying the laws we found locally to observations of distant objects, and seeing if they fit. For example, we can look at the spectra of distant stars and look if we get the same atomic spectral lines as on earth. This works great; so we know that atomic physics obviously works the same in distant stars. Also we can observe the 21cm hydrogen line everywhere in space, so atomic physics seems to apply also in between the stars.
Where we do have some problems is with large scale gravitation (what we describe with dark matter and dark energy). However, the local effects of those deviations are small enough that we couldn't measure them directly anyway, so it's also no evidence that the local laws of physics are different than the distant ones, even if those effects are to be described with modified theories.
No, it's much too small for that. To be an indication for different physics "outside" it would have to be such a large deviation that we would have to have detected the difference if it applied to Earth.
Re:And FTL, too (Score:3, Informative)
Then that wouldn't be transmitting information, now, would it?
Re:Just wondering out loud... (Score:4, Informative)
Re:And FTL, too (Score:3, Informative)
Precisely. FTL transmission of information is still impossible with current science, and we have good reason to believe it will stay that way. FTL transmission of something that's not information is definitely possible, and it doesn't violate any theories.
Re:Excellent! (Score:3, Informative)
No, but I did get a Bachelor's degree in math what seems like an infinity ago....here's what I remember.
You can add infinity to the number system just fine. In doing so you would want to preserve rules of the standard number system (e.g. a+b = b+a, (ab)c = a(bc)).
This has already been done. Hyperreal numbers make up a branch of mathematics called nonstandard analysis.
Nonstandard analysis has been used occasionally in studies of quantum physics, but it doesn't help with the infinities.
The infinities in quantum gravity are not a math problem they are a physics problem...i.e. the infinities turn up where we know they don't exist (e.g. infinite mass, infinite energy, etc). Nonstandard analysis can be useful in working with these infinities, but not in explaining them.
Re:Not again (Score:2, Informative)
It makes one wonder what he smokes...
1960s Dr. Who [wikia.com] by the looks of things. Man, I'd forgotten about those...
Not faith - belief (Score:4, Informative)
You do NOT need faith to believe that the universe is anything. Ordered, structured, causal, etc. A good scientist believes these things because there is evidence of order, causality, etc.
To not have faith is to not believe in something for which there is no evidence.
One does not need faith to look forward to the future doing something chaotic because of the belief (through prior observation) that those kind of things (earth turning into a carnivore butterfly) just does not happen.
Science and faith are NOT intrinsically linked. Science and belief ARE. Science and faith are two completely separate things.
Re:Here's the actual article (Score:3, Informative)
Bullshit.
I just pressed "Preview" on this comment and it took 18 seconds to display.
I'm not posting anonymously.
The second time pressing it takes 1 second.
Re:Excellent! (Score:2, Informative)
Actually for electrodynamics the problem is completely solved. Basically the idea is that around the electron the vacuum polarization causes the field to me modified, so what you see as electron isn't actually the "naked" electron, but the electron plus vacuum polarization. So if you get closer to the electron (or equivalently, are scattering at higher energies), you have to modify the coupling constant (that is, basically the charge). The procedure is called renormalization and can remove the infinities from the theory.
The problem with General Relativity is that if you quantize it, you cannot get rid of the infinities through renormalization.
Re:And FTL, too (Score:3, Informative)
Wait. What? I truly don't understand this. If you are transmitting something, and this something "arrives" at its destination, couldn't information have been encoded in this something?
If you can't encode information into it, are you really transmitting something? *Headache*
No, you got it. What you're transmitting is "something." It's not matter, it's not energy, and you can't encode information on it.
Re:And FTL, too (Score:3, Informative)
Each of the entangled particles just relies on local information that it carries with it and which was generated at the moment of entanglement.
Please see Bell's Theorem (from over forty years ago) and the experiments based on it for the reasoning as to why this is (at the very least) extremely unlikely.
Re:Not again (Score:3, Informative)
Yes, and our current problem in physics is that we have two forks of Newtonian Physics. In one branch, we fixed the description of gravitation, in the other branch we fixed the description of subatomic particles. Both branches are very successful in their respective area. Now we try to merge those branches, however it turns out that the patches are not compatible, and we don't know what is the right way to combine them.
Re:Excellence: Biography of Petr Hoava (Score:3, Informative)
Einstein was an Eastern European. As were most of the other scientists coming up with what Einstein brought together in Relativity. Soviet physicists were mostly Eastern European, and came up with quite a lot of advances in physics.
No he wasn't - Western Germany/Italy/Switzerland are hardly 'Eastern Europe'. Nor were the others: Poincaré (France), Planck (Germany), Bohr (Denmark), Lorenz (Netherlands), Schwarzschild (Germany), Lemaitre (Belgium)... (Not that Eastern Europeans weren't well represented in sciences, they just have very little to do with the early history of relativity.)
Re:Not again (Score:3, Informative)
Haven't we proven enough of our theories about this world that we know for certain things are stable to a known degree?
Not to be contrarian, but we haven't proven any of our theories at all.
First, you do not know what is occurring in every place in the universe. No number of experiments will ever prove a theory to be true because you cannot perform the test at every conceivable place in the universe. This is why Francis Bacon stated that the proper scientific method should be falsification. You only have to find one place where a theory comes up short to prove it wrong, but time constraints say that you can never prove that it is right. This is what modern science is based upon.
More importantly to his post, however, is the fact that we have no deductive reason to assume that the future will replicate the past. The GP says
Pointing out that it's worked before is just begging the question
He is referring to the problem of induction http://en.wikipedia.org/wiki/Problem_of_induction [wikipedia.org]
This is not "fancy footwork," it is a many centuries old philosophical problem brought up by David Hume. You cannot state "X happened in the past, therefor it will happen in the future" without using "X happened in the past" as your reason for believing "X will continue to happen."
Essentially, you cannot prove induction correct without being inductive. "The ice I've touched has been cold, therefor all ice is cold" is not deductive reasoning.
This is, for all intents and purposes, a genuine criticism of the scientific method. "All ice I've ever touched is cold" may be true, but "All ice is cold" is completely false. http://arstechnica.com/science/news/2007/03/turing-water-into-very-hot-ice-very-very-quickly.ars [arstechnica.com] http://uk.reuters.com/article/idUKN1621607620070516 [reuters.com]
This is the sort of thinking that science employs, however. Now, his point is not that science is not useful, nor is it that science is wrong. He is simply stating that inductive thinking is programmed into us, and that there is no good deductive logic which led us to it. You see neither causality nor time, these concepts exist inside of you -- i.e. Science is a byproduct of being an ape, not a byproduct of logic itself.
Re:Spooky action at a distance? (Score:2, Informative)
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.
Isn't that just the 'hidden variables' [wikipedia.org] interpretation of quantum physics, which from my limited knowledge I think was eperimentally proven false?
From my understanding, there really is nothing in the envelope until you look inside it - that's what makes the in-sync states of the atoms, even when seperated by distances greater than c*t, 'spooky'. Communication may not be possible, but it is still very weird from our classical perspective.
Re:Excellent! (Score:3, Informative)
BTW, if you get a correct answer about the nature of the universe, let me know.
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