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Physicists War Over a Unified Theory
beggs writes: "I was looking through the New York Times and came across an article which talks about a new front in the war to find a unified theory, but this one does not come from the particle physicists, it comes from the solid state physicists. Here is a little quote for wet your appetite: 'some solid-state physicists are trying to show that the laws of relativity, long considered part of the very bedrock of the physical world, are not platonic truths that have existed since time began.'"
Challenging Particle Physics as Path to Truth
By GEORGE JOHNSON
n science's great chain of being, the particle physicists place themselves with the angels, looking down from the heavenly spheres on the chemists, biologists, geologists, meteorologists -- those who are applying, not discovering, nature's most fundamental laws. Everything, after all, is made from subatomic particles. Once you have a concise theory explaining how they work, the rest should just be filigree.
Even the kindred discipline of solid-state physics, which is concerned with the mass behavior of particles -- what metals, crystals, semiconductors, whole lumps of matter do -- is often considered a lesser pursuit. "Squalid state physics," Murray Gell-Mann, discoverer of the quark, dubbed it. Others dismiss it as "dirt physics."
Recently there have been rumblings from the muck. In a clash of scientific cultures, some prominent squalid-staters have been challenging the particle purists as arbiters of ultimate truth.
"The stakes here are very high," said Dr. Robert B. Laughlin, a Stanford University theorist who shared a Nobel Prize in 1998 for discoveries in solid-state physics. "At issue is a deep epistemological matter having to do with what physics is."
Last year Dr. Laughlin and Dr. David Pines, a theorist at the University of Illinois and Los Alamos National Laboratory, published a manifesto declaring that the "science of the past," which seeks to distill the richness of reality into a few simple equations governing subatomic particles, was coming to an impasse.
Many complex systems -- the very ones the solid-staters study -- appear to be irreducible. Made of many interlocking parts, they display a kind of synergy, obeying "higher organizing principles" that cannot be further simplified no matter how hard you try.
Carrying the idea even further, some solid-state physicists are trying to show that the laws of relativity, long considered part of the very bedrock of the physical world, are not platonic truths that have existed since time began.
They may have emerged from the roiling of the vacuum of space, much as supply-and-demand and other "laws" of economics emerge from the bustle of the marketplace. If so, then solid-state physics, which specializes in how emergent phenomena occur, may be the most fundamental science of them all.
"We're in the midst of a paradigm change," Dr. Pines said. "Ours is not the prevailing view, but I think it will turn out to be the one that lasts."
Working in this vein, one of Dr. Laughlin's Stanford colleagues, Dr. Shoucheng Zhang, recently was co- author of a paper suggesting that elementary particles like photons and gravitons, the carriers of electromagnetism and gravity, might not be so elementary after all -- they might emerge as ripples in the vacuum of space, bubbling up from the quagmire in a way that can best be explained in terms of solid-state physics.
"The idea is of course crazy, thought provoking, and somewhat anti-establishment," Dr. Zhang said. "The main idea is to apply concepts from solid-state physics to answer some big questions of the universe."
The particle physicists insist that there is plenty of mileage left in their own approach. "I strongly believe that the fundamental laws of nature are not emergent phenomena," said Dr. David Gross, director of the Institute for Theoretical Physics at the University of California at Santa Barbara. "Bob Laughlin and I have violent arguments about this."
After hearing Dr. Zhang describe his theory at a seminar last month, Dr. Gross deemed it "an interesting piece of work." He said he found the mathematics "beautiful and intriguing, and perhaps of use somewhere."
That may sound like faint praise, but the particle physicists have reason to be wary. The squalid-staters are challenging them in a debate over how the universe is made and how science should be done.
Following the method of Plato, the particle physicists are inclined to see nature as crystallized mathematics. In the beginning was a single superforce, the embodiment of an elegant set of equations they call, only a bit facetiously, the theory of everything. Then along came the Big Bang to ruin it all.
The universe cooled and expanded, the single force splintering into the four very different forces observed today: electromagnetism and the weak and strong nuclear forces, which work inside atoms, are described by quantum mechanics and special relativity. The fourth force, gravity, is described by an entirely different theory, general relativity.
The particle physicists' ultimate goal is "grand unification" -- recovering the primordial symmetry in the form of a single law -- a few concise equations, it is often said, that could be silk-screened onto a T- shirt.
This approach, in which the most complex phenomena are boiled down to a unique underlying theory, is called reductionism.
The problem, the solid-staters say, is that many forms of matter -- ranging from the exotic like superconductors and superfluids to the mundane like crystals and metals -- cannot be described in terms of fundamental particle interactions. When systems become very complex, completely new and independent laws emerge. "More is different," as the Nobel laureate Philip W. Anderson put it in a landmark paper in 1972. To the solid-staters, it would take something the size of a circus tent to hold all the equations capturing the unruliness of the physical world.
Like Aristotle, they lean toward the notion that it is the equations that flow from nature instead of the other way around. Mathematics is just a tool for making sense of it all.
"For at least some fundamental things in nature, the theory of everything is irrelevant," declared Dr. Laughlin and Dr. Pines in the Jan. 4, 2000 issue of The Proceedings of the National Academy of Sciences. "The central task of theoretical physics in our time is no longer to write down the ultimate equations but rather to catalog and understand emergent behavior in its many guises, including potentially life itself."
There may not be a theory of everything, they say, just a lot of theories of things. This is exactly the kind of squalor the particle physicists abhor.
Dr. Grigori E. Volovik, a solid- state physicist at the Helsinki University of Technology in Finland, champions an idea he calls "anti- grand unification." In a review article last year (xxx.lanl.gov/abs /gr-qc/0104046), he ventured that the universe may have begun not in a state of pristine symmetry but in one of lawlessness. The laws of relativity and perhaps quantum mechanics itself would have emerged only later on.
The notion of emergent laws is not radical in itself. A flask of gas consists of trillions of molecules randomly colliding with one another. From this disorder, qualities like temperature and pressure emerge, along with laws relating one to the other.
So take that idea a level deeper. Physicists now believe that the vacuum of space is, paradoxically, not vacuous at all. It seethes with energy, in the form of "virtual particles" constantly flitting in and out of existence. So perhaps, Dr. Volovik suggests, even laws now considered fundamental emerged from this constant subatomic buzz.
Solid-state physics offers clues to how something like this might occur. The atomic vibrations that ripple through matter are, like all quantum phenomena, carried by particles -- called, in this case, phonons.
Just as photons carry light and gravitons carry gravity, phonons carry the subatomic equivalent of sound. Like bubbles in a carbonated beverage, phonons -- physicists call them "quasi particles" -- appear only when the medium is disturbed.
In the world of solid-state physics, quasi particles abound. In some substances, like the semiconductors used to make computer chips, the displacement of an electron leaves behind a "hole" that behaves like a positively charged particle. An electron and a hole can sometimes stick together to form a chargeless quasi particle called an exciton. Other such ephemera include magnons and polarons.
Evanescent though they are, quasi particles act every bit like elementary particles, obeying the laws of quantum mechanics. This has led some mavericks to wonder whether there is really any difference at all. Maybe elementary particles are just quasi particles -- an effervescence in the vacuum.
Particularly intriguing is a phenomenon, occurring at extremely low temperatures, called the fractional quantum Hall effect. In certain substances, quasi particles appear that act curiously like electrons but with one-third the normal charge. (Dr. Laughlin won his Nobel Prize for a theory explaining this.)
Quarks, the basic building blocks of matter, also carry a one-third charge, a coincidence that has fueled speculation that emergence may be somehow fundamental to the very existence of the physical world.
A stumbling block to carrying this idea further has been that the quantum Hall effect seems to work only in two-dimensions -- on the surface of a substance. But in a paper published in the Oct. 26 issue of Science, Dr. Zhang and his student Jiangping Hu showed how to extend the phenomenon. In their scheme, the physical world would be a three-dimensional "surface" of a four-dimensional "quantum liquid" -- an underlying sea of particles that can be thought of as the vacuum.
Analyzing the ripples that would appear in such a medium, the two scientists were surprised to find that they mathematically resembled electromagnetic and gravitational waves. But there are problems with the model. At this point, the hypothetical photons and gravitons that emerge from the equations do not interact with other particles, as they do in the real world.
"The coupling is zero, so apples are weightless, as is everything else," said Dr. Joseph Polchinski, a string theorist at the University of California at Santa Barbara, who recently discussed the model with Dr. Zhang.
And there is what the theory's inventors concede is an "embarrassment of riches" -- the equations predict hordes of exotic particles that do not exist.
"The hope is that some modification of the theory, not yet specified in detail, will remove the extra fields and turn on the coupling," Dr. Polchinski said. "Whether this can be done is at this point a guess. Overall my attitude now is interest with a high degree of skepticism."
If the theory can be made to work, it may point to a new way of unifying quantum mechanics and relativity. But Dr. Zhang is careful not to oversell what he considers a work in progress.
"Our work only made a tiny step toward this direction," Dr. Zhang said, "but it seems to indicate that the goal may not be impossible to reach." At the very least, he said, his work may inspire more collaboration between particle physicists and solid-staters.
Ultimately, though, the two sides know that they are talking across a divide. Taken to its extreme, emergence suggests that all the fundamental laws, even quantum mechanics, may be secondary -- that at the base of reality is random noise.
Dr. Polchinski said he found that idea discouraging.
"To me, the history of science seems to be a steady progression toward simpler and more unified laws, and I expect to see this continue and to contribute to it. Things may take many surprising twists and turns," he said, "but we reductionists are still quite happily and busily reducing."
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I am I the only one, but is anyone else worried that when they finally find the unified theory, "The Theory that Explains Everything," that it'll wind up being Murphy's Law?
"Prepare for the worst - hope for the best."
This reminds me of pascal's image of knowledge...
:)
Where knowledge is symbolized by the sphere's volume and the unknown by the sphere's surface. Therefore as knowledge grows, so does the unkown (although the volume grows faster than the surface, total wisdom will be never achieved.)
(or if the sphere is a balloon, science grows until it explodes
Speaking as part of the community, the physics world is not at all portrayed accurately in this article. Nearly every physicist sees value in every subset of physics. Think nuclear physics is dead? I happen to know a few nuclear physicists who are still active in research. No-one I know refers to solid-staters as "squalid-staters". There is worthwhile research still in every discipline of physics, even solid state and particle physics.
I think what we have here is a case of journalistic hype used to make the a mountain out of a molehill. I do not think that anyone can deny that there has not been advances in the understanding of any field.
Ciao
nahtanoj
This isn't quite correct. You are right that in changing the speed of light you are only redefining the time unit. (One second is how long a photon takes to travel a certain distance.) In everyday work, (yes- I am a physicist) I choose units where c is one. It makes things so much easier.
What the physicists are measuring isn't the speed of light - it is the dimensionless constant alpha. Since alpha is dimensionless, you cannot renormalise changes in it by changing the size of your units. (Alpha is a measure of the strength of the electromagnetic (and electroweak) force.)
Quantum mechanics is the thing we know least about. We have tested general relativity to fourteen decimal places, but QED (quantum electrodynamics) has only been tested to ten decimal places. Quantum is a theory filled with ad-hoc rules. GR is increadibly simple. It wouldn't surprise me at all if quantum field theory was shown to be a suitable limit of what happens to gravational waves once non-linear effects become important, and once you start running into the effects of compactified dimensions.
You are forgetting something. Before the great paradigm shifts in the history of physics (Newton, Einstein, Bohr, etc.), there was always evidence that something was wrong with prevailing theory. Scientists on the front lines weren't "comfortable", they noticed things like the "ultraviolet catastrophe" and the precise spectra of atoms and knew something was wrong.
Today we know that general relativity and quantum mechanics don't work together, but we aren't sure how to fix it (though string theorists try hard).
Eventually it's conceivable that we'll write down some basic laws and then millenia will pass without any evidence that something is still wrong. While you're right that it's impossible to prove that these laws are correct, scientists are very diligent about trying to find holes and if none are found, then everyone will believe we finally know the truth. And perhaps we actually will.
Mathematics is entirely artificial. It's based on rules and premises that we pretty much made up. You can prove things in math because it's a self-contained problem set, and you're looking at it from the outside with an omniscient view.
When you didn't invent the framework of the problem, it tends to be harder to prove a solution.
That said, you may never be able to prove a Unified Theory, because you can't ever be certain you've described every aspect of the problem set. But you can disprove a physical theory (or at least show it to be lacking) simply by finding a counterexample.
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To quote (by memory) from the Hitchhikers' guide:
There's a theory saying that, if we ever figure out the Universe, it will be immediately replaced by something even more complicated. There's another theory saying that already happened.
I remember reading an article some time ago in which a scientist proposed that Quantum Physics could actually be a natural corollary of General Relativity (where each particle is some kind of "ripple" in the space-time continuum), and that the mathematics of this could make sense if the requirement for Causality ("cause must happen before effect") were dropped from General Relativity.
His proposal suggested that quantum coupling (where two particles can become intertwined based on an earlier interaction) was caused by some kind of ripple-effect going back in time from the observed particle to the time that the original interaction happened.
He was able to explain many other aspects of Quantum Physics the same way, although he claimed that the mathematics was so complex that only the simplest of interactions had been formally proved to match between his model and QP - most of his theory, including the explanation of coupling, was hand-waving.
I always thought that this theory seemed one of the most elegant I've ever heard - no need to introduce new hypothetical particles like Strings, no need to assume that all the complexities of the Standard Model are fixed, absolute and arbitrary. Just take General Relativity, drop Causality, and look at what emerges.
I've often wondered whether this guy's theory ever went anywhere. It seems to have something in common with the theory proposed in this article - that QP is just an "emergent behavior" from GR. The difference is that the article seems to propose that there is no underlying rule at all except chaos and GR itself emerged from that; this guy proposed that GR was fundamental and QP was the emergent behavior.
Anyone know anything about this theory or know where the original article might be? Did this guy have any success or get any recognition? Has his theory been actually disproved, or simply ignored?
Stuart.
i never liked the big bang theory. it stinks of creationism. ... i'm no cosmologist. but the big bang stinks of creationism to me ...
So, let me get this straight. You are rejecting a reasonable theory which fits the observed behaviours simply because it conflicts with your religious (or anti-religious) beliefs?
Isn't that what people accuse religious folks of daily?
You aren't being logically consistant. You rail against anything with any hint of taint from our human experience, but at the same moment your rejection is based in how you feel about the existing theories. Stinks of creationism is a very visceral reaction to what you insist should be a completely rational debate.
Face it. You have a philosophy guiding your argument as well. That philosophy is Nihilism and your post stinks of it.