Posted on 03/07/2010 2:11:48 PM PST by LibWhacker
Cutting the threads of the spacetime fabric and reinstating the aether could lead to a theory of quantum gravity.
If there’s one thing Einstein taught us, it’s that time is relative. But physicist Petr Hořava is challenging this notion and tearing through the fabric of spacetime in his quest for a theory of quantum gravity. His work may also resurrect another entity that Einstein had seemingly buried—the aether.
Physicists have spent decades searching for a way to reconcile the seemingly incongruous twin foundations of modern physics: quantum theory, which deals with the infinitesimally small, and Einstein’s theory of gravity, general relativity, which deals with the vast cosmos. This effort has led to a dazzling array of candidate theories—including superstring theory, loop quantum gravity, and doubly special relativity—but none have succeeded in unambiguously bridging the quantum-gravity divide. The problem: When you try to do the math to work out the strength of forces on the quantum-gravitational scale, your calculations return a maddening proliferation of infinite answers that have no physical meaning.
Now Hořava, at the University of California, Berkeley, claims to have found a solution that is both simple and—in physics terms, at least—sacrilegious. To make the two theories gel, he argues, you need to throw out Einstein’s tenet that time is always relative, never absolute.
Hořava’s controversial idea is based on the fact that the description of space and time in the quantum and relativistic worlds are in conflict. Quantum theory harks back to the Newtonian concept that time is absolute—an impassive backdrop against which events take place. In contrast, general relativity tells us that space and time are fundamentally intertwined; two events can only be marked relative to one another, and not relative to an absolute background clock. Einstein’s subjective notion of time is well accepted and is the hallmark of Lorentz invariance, the property that lies at the heart of general relativity.
"Lorentz invariance is not actually fundamental to a theory of quantum gravity," says Hořava. "But the problem so far has been that many cosmologists are wedded to the concept."
Good Gravitons
By restoring the absolute nature of time at very high energies, such as those in the early universe where quantum gravity would be important, Hořava can treat variations in space and time differently. The upshot of this is that in your calculations at very short distances you do not get such dramatic spatial variations as you do in general relativity, taming the infinities that frustrate other candidate theories of quantum gravity. This makes it possible to describe gravity on the quantum level using a well-behaved graviton—the hypothesized quantum particle thought to mediate gravity, just as the photon mediates the electromagnetic force (arxiv.org/abs/0901.3775).
So far Hořava’s potential resolution of a decades-long physics stalemate has been creating a buzz. Last year, five of the top ten cited academic papers in high energy physics dealt in some form with Hořava’s model.
"The existence of an absolute time might ensure that the usual framework of quantum mechanics can survive even the most exotic regimes of quantum gravity," says physicist Ted Jacobson at the University of Maryland, College Park.
Surprisingly, Hořava’s trick is fairly commonplace in the laboratory. Condensed matter scientists looking at complex real-world systems, such as superconductors at low temperatures, have been using the idea that space and time are not on the same footing for years. Cosmologists do not usually take the lead from their condensed-matter cousins because of "sociological barriers," but the groups should look to each other for inspiration more often, says Hořava. He borrowed ideas from condensed matter models when developing his theory of quantum gravity. "In some condensed matter systems, relativistic behaviour and Lorentz invariance only emerge at lower energies," he says.
But while condensed matter physicists have shown that their models can recover relativistic behaviour as required at low energies, the big question is whether Hořava gravity can successfully morph back into the classical theory of relativity, in a way that agrees with all observations. In principle, general relativity should emerge at lower energies and larger distances. In other words: Look at a patch of the universe with infinitely powerful glasses and you would see that time and space are distinct from one another. Zoom out and the picture blurs, restoring Einstein’s more familiar spacetime fabric.
Knife-Edge
There is some support that this emergence does indeed happen from computer simulations of quantum gravity carried out by Jan Ambjørn of the Niels Bohr Institute at the University of Copenhagen and his colleagues. Ambjørn’s simulations showed that at short distances, the familiar four-dimensional spacetime of our macroscopic universe seems to shrink to just two dimensions—one space and one time. Hořava believes that his theory can explain how those spatial dimensions disappeared.
According to Hořava, this vanishing point marks the knife-edge at which general relativity breaks down and his theory of gravity comes into play. As the fabric of spacetime rips, space and time start to stretch at different rates. The stronger constraints on short distance spatial variations mean that space now stretches only a third as quickly as time, effectively reducing the familiar three spatial dimensions into just one.
Since Hořava first proposed his theory in 2009, other researchers have used it to answer important cosmic questions about the nature of the Big Bang, dark matter and dark energy. Jacobson, however, feels there is much work still to be done before the theory can be widely accepted. "Hořava’s paper triggered a feeding frenzy, but most workers outside that frenzy remained wisely sceptical," he says.
Gustavo Niz at the University of Nottingham, UK, notes that physicists have found that in its original form, Hořava theory has plenty of "pathologies" and does not recover general relativity. "However, the idea behind the model is encouraging and scientists have ideas on how to cure all these secondary problems," he says.
Among those attempting to fix the original model are Diego Blas and Sergei Sibiryakov at the Swiss Federal Institute of Technology (EPFL) in Lausanne, and Oriol Pujolas at CERN near Geneva. Their work has revealed a flaw in the model: Minor variations in the initial conditions used in calculations in Hořava gravity can give dramatically different results (arxiv.org/abs/0909.3525). The culprit is a unique and unstable "breathing mode" in which space can locally expand or contract, wreaking havoc with your answers. To address this problem, they’ve modified Hořava’s initial proposal, making it harder for this breathing mode to develop. They have dubbed their formulation "extended Hořava gravity."
“In my view, the extended version of Hořava gravity is the only currently viable approach and needs to be extensively analysed,” says Jacobson.
Einstein’s Aether?
Jacobson’s own current research, funded by FQXi, examines the short distance structure of space and the quantum vacuum as space expands. He is also now looking at connections between Hořava gravity and an earlier modification of relativity, dubbed "Einstein-aether theory" that he had proposed a decade back.
Nineteenth-century physicists believed light waves must move through an "aether"—a medium that permeates all of space, allowing light to propagate just as sound waves move through air. However, a series experiments by Michelson and Morley failed to find any evidence that Earth moves through an aether. Einstein’s theory of relativity was the final nail in the aether’s coffin, because it explained that light moves through a vacuum.
Jacobson does not believe that the nineteenth-century aether exists. However, within Einstein-aether theory—in contrast to general relativity—there is a preferred time that can be used as an absolute reference to mark events against. It is as if spacetime were filled with a fluid—an aether—which defines a "rest frame" at each event.
Like Horava’s theory, Einstein-aether theory breaks Lorentz invariance and may lead to a viable mechanism for producing gravitons. To get from the general Einstein-aether theory to extended Horava gravity, you simply assume that the aether rest frame arises from an absolute time.
Jacobson has shown that some of the tests proposed to confirm or rule out Einstein-aether theory over the years could also falsify Hořava gravity (http://arxiv.org/abs/1001.4823). "The list of potential experimental signatures includes everything gravitational: from modified orbits to gravitational radiation—there is a new type of gravity wave in Hořava theory from the breathing mode—to the structure of neutron stars and black holes, and perhaps even more exotic stuff," says Jacobson.
For now though, Hořava remains modest, and is glad that others are examining his work. "My papers present the basic idea but don’t present a full theory yet," he says. "It is still unclear which of the possible different trajectories is best."
LOL!
Have you seen some of the latest experiments in this?
parsy, who is getting night terors
“Nobody said this stuff was simple... “
So, are like you saying at 56, its probably too late for me to try to discover a unified theory?
I suspect it is, myself. I got this book on Lorentz Contractions, by mistake(I got the name wrong-—it was supposed to be a Lamaze contractions thing. Which is why I think some of my ex’s thought it was OK to slap me around with various forms of cookware, including, but not limited to, cast iron skillets-—) but I digress.
Anyway, I felt too embarrassed to take it back, so I tried reading it, I mean how hard could it be, I did well in fractions and long division. Where was I going on this??
parsy, who thought he had something to add to the conversation but must have been wrong...my wave function hasn’t collapsed yet
Near as I can tell, the unified theory HAS been discovered and the author of the real deal version of it is this Ralph Sansbury. Moreover, the whole thing gets back to classical physics and all the magical shit we’ve been hearing about all our lives goes out the window, including big bangs, black holes, dark matter, dark energy, string theory, and every other bit of all that rubbish.
One other neat sort of a google search for spare time is ‘dayton miller’. Turns out, if you do the Michelson/Morley experiment at high enough altitudes (to get a tad further away from the planet’s cog) and with sensitive enough equipment, it does not fail. That obviates the entire motivation for relativity.
I will start googling. What about all the little sub atomic particles, the bosons, mesons, gluons, stickons, quarks etc...
Gut instinct said that was way too many particles to have to come together (what is it like 38 or something, now) all across the universe without loose clouds of leftover sub-atomic particles floating around all over the place.
parsy, who is opening a new tab on Sansbury
I was afraid Pavarotti was invading your dreams.
There was a young fellow named Bright
who traveled much faster than light
He set out one day
in a relative way
and returned on the previous night!
Cheers!
My question is this - - is there anything that can’t be cut in half?
That is, is there any limit to smallness?
LOL! I love limericks! I just wrote this one.
Herr Schrodinger bought him a kitty.
To show to the Quantum committee.
He bought him some locks,
Put the cat in the box
And the next thing you knew, the cops were cuffing him for animal abuse, PETA burned his house down, and Schrodinger got run out of the city.
parsy, who says, Poor Schrodinger is still wondering what would happened if...
I think they are having problems with dipoles.
parsy, who thinks we may just be thick energy
Well... In case you didn't already know, let me preface my comment with a qualifier; I'm a theoretical physicist.
Here is the essence of the gravitational section of a unified theory that I have been working on for well over 30 years:
There is no such thing as a "graviton particle." Gravity is the result of resisting movement through the fabric (or, aether, if you will) of spacetime. The more mass that is located in a point of space, the more it resists movement through time. This creates a multidimensional gravity well in the fabric of spacetime.
Of course, there exists another multidimensional stream which is "pushing" (as it were) the mass through spacetime. But, I don't wish to get into that as I have yet to publish that paper...
"Nineteenth-century physicists believed light waves must move through an "aether"—a medium that permeates all of space, allowing light to propagate just as sound waves move through air. However, a series experiments by Michelson and Morley failed to find any evidence that Earth moves through an aether. Einstein’s theory of relativity was the final nail in the aether’s coffin, because it explained that light moves through a vacuum. "
Yeah, this is where modern quantum physics started to go wrong. They assumed that this "aether" existed in phase with our own dimension and neglected to take into account its multidimensional aspects. Had they avoided that mistake... Well, the mind boggles at the potential discoveries we would be enjoying right now...
Anyway, if you like theoretical physics, here is a link to "Einstein-Aether Theory" that Jacobson co-authored:
Cheers
May I ask a dumb question? What if the sun, with all its mass, were shaped like a cube, instead of a sphere. What would orbits look like? What would happen at the interfaces/sides of the cubes as a planet transit-ed that point?
parsy, who has been trying to keep the shortest distance stuff he read in Bertrand Russells(?) book on relativity. (Dang I wish I had my books with me!!!)
Could there be no such thing as half a dipole?
Hmm. The first line isn’t actually a link.
I think they call them monopoles, and as yet, they don’t seem to be able to create them. Take a bar magnet, it has a north and south pole. Keep cutting the magnet in half and you never get to either north or south. At least, that’s how I remember it.
parsy, who is still using crayons and safety scissors on this stuff
Newton’s theory viewed gravity as instantaneous while Einstein’s theory viewed it as traveling at the speed of light.
I believe in 2003, or thereabouts, it was announced by a physicist here at the University of Missouri (go Tigers!) that the speed of gravity had finally been measured and it was consistent with Einstein’s theory. However, his methodology and conclusions are still controversial.
Okay, I just Googled it. His name is Sergei Kopeiken. Here’s an article you can read that pretty much encompasses the debate:
http://www.space.com/scienceastronomy/gravity_speed_030116.html
And, here is Kopeiken’s rebuttal:
http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0311/0311063v6.pdf
It’s a great read when you have some time.
Cheers
Whether one is ever created or not, there would be such a thing as a half a monopole, wouldn't there?
bump for later read
What an interesting thought experiment you posit!
Well, to begin with, it is not in the nature of gravity to allow a massive cube with the mass of the Sun to exist...
But, I suppose that one could grow a giant diamond sun cube that might somehow withstand the natural tendencies of the gravitational forces collapsing the sharp edges and corners. But, I digress... Back to the question at hand:
A hypothetical “diamond sun cube” would exhibit the same gravitation constant as a spherical object of equal mass and would not alter the orbits of the planets orbiting around it...
However, since gravity is dependent on the distance from the center of the object, if you were able to don some hyper-asbestos space suit, grab a scale, and walk out onto the “surface” of the “diamond sun cube” then you would weigh more when you walked on the face of the cube than you would if you were walking at the corners of the cube.
Remember, at the corners, you are farther from the center gravitational point of the cube than you are when on the face of the cube. Newton’s formula for the Force of gravity is:
F=GMm/r^2.
We can apply this formula to our cubic sun.
The value of r (radius) is the distance from the center of the sun, M is the mass of the sun, and m is your mass. Ignore the “G” for this discussion.
As r goes up, F (Force) goes down.
Basically, the amount of gravitational pull due to mass from corner to corner is largely offset by the increased distance you are from the center of the cube.
It’s kind of a counter-intuitive concept, but that’s the math behind it.
Cheers
Thank you. I think you are saying the center of the cube is more or less where the effect would be measure from. So, if there were a planet, like Mercury in close orbit, and assume in an orbit perpendicular to a face of the suncube....
Would gravity be stronger at the center of each face and then weaken as the planet approached the interface of the sides, and how would this affect the orbit? Would it tend to flare out a little at each of the four corners?
And, may we assume that the suncube is not rotating as it is actually a big square block of neutron star or something, because I understand that rotating gassy things like the Sun would tend to sphere up?
For some reason I just keep thinking one would get a basically circular orbit with four rounded corner points.
parsy, who isn’t asking you to spend a lot of time on this.
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