Quantum entanglement. Image courtesy Discovery News.

Cosmology, Physics

Scientists Say They Can Now Test String Theory

1 Sep , 2010 by


The idea of the “Theory of Everything” is enticing – that we could somehow explain all that is. String theory has been proposed since the 1960’s as a way to reconcile quantum mechanics and general relativity into such an explanation. However, the biggest criticism of String Theory is that it isn’t testable. But now, a research team led by scientists from the Imperial College London unexpectedly discovered that that string theory also seems to predict the behavior of entangled quantum particles. As this prediction can be tested in the laboratory, the researchers say they can now test string theory.

“If experiments prove that our predictions about quantum entanglement are correct, this will demonstrate that string theory ‘works’ to predict the behavior of entangled quantum systems,” said Professor Mike Duff, lead author of the study.

String theory was originally developed to describe the fundamental particles and forces that make up our universe, and has a been a favorite contender among physicists to allow us to reconcile what we know about the incredibly small from particle physics with our understanding of the very large from our studies of cosmology. Using the theory to predict how entangled quantum particles behave provides the first opportunity to test string theory by experiment.

But – at least for now – the scientists won’t be able to confirm that String Theory is actually the way to explain all that is, just if it actually works.

“This will not be proof that string theory is the right ‘theory of everything’ that is being sought by cosmologists and particle physicists,” said Duff. “However, it will be very important to theoreticians because it will demonstrate whether or not string theory works, even if its application is in an unexpected and unrelated area of physics.”

String theory is a theory of gravity, an extension of General Relativity, and the classical interpretation of strings and branes is that they are quantum mechanical vibrating, extended charged black holes.The theory hypothesizes that the electrons and quarks within an atom are not 0-dimensional objects, but 1-dimensional strings. These strings can move and vibrate, giving the observed particles their flavor, charge, mass and spin. The strings make closed loops unless they encounter surfaces, called D-branes, where they can open up into 1-dimensional lines. The endpoints of the string cannot break off the D-brane, but they can slide around on it.

Duff said he was sitting in a conference in Tasmania where a colleague was presenting the mathematical formulae that describe quantum entanglement when he realized something. “I suddenly recognized his formulae as similar to some I had developed a few years earlier while using string theory to describe black holes. When I returned to the UK I checked my notebooks and confirmed that the maths from these very different areas was indeed identical.”

Duff and his colleagues realized that the mathematical description of the pattern of entanglement between three qubits resembles the mathematical description, in string theory, of a particular class of black holes. Thus, by combining their knowledge of two of the strangest phenomena in the universe, black holes and quantum entanglement, they realized they could use string theory to produce a prediction that could be tested. Using the string theory mathematics that describes black holes, they predicted the pattern of entanglement that will occur when four qubits are entangled with one another. (The answer to this problem has not been calculated before.) Although it is technically difficult to do, the pattern of entanglement between four entangled qubits could be measured in the laboratory and the accuracy of this prediction tested.

The discovery that string theory seems to make predictions about quantum entanglement is completely unexpected, but because quantum entanglement can be measured in the lab, it does mean that there is way – finally – researchers can test predictions based on string theory.

But, Duff said, there is no obvious connection to explain why a theory that is being developed to describe the fundamental workings of our universe is useful for predicting the behavior of entangled quantum systems. “This may be telling us something very deep about the world we live in, or it may be no more than a quirky coincidence”, said Duff. “Either way, it’s useful.”

Source: Imperial College London

By  -        
Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.



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Beckler
Member
Beckler
September 1, 2010 7:26 AM

“But, Duff said, there is no obvious connection to explain why a theory that is being developed to describe the fundamental workings of our universe is useful for predicting the behavior of entangled quantum systems.”

What? Is it a possible theory of everything or not? If so, then presumably quantum entanglement is included? Wait, let me quickly check the definition of ‘everything’…

Dave Finton
Member
September 1, 2010 8:37 AM

Today: Scientists find way to test String Theory

4 Months From Now: Scientists disprove string theory. TOE advocates are found inconsolable.

TerryG
Member
September 1, 2010 9:01 AM

Utter quackery! Experimentally attributing the phenomena of quantum entanglement or water being wet or exit signs being on the way out etc. to an extra-dimensional theory such as String theory requires an extra-dimensional laboratory. Good luck with that.
Maybe it’s still early days, but even as a theory of last resort, String theory still looks like specious reasoning thus far. Keep working on it.

Lawrence B. Crowell
Member
Lawrence B. Crowell
September 1, 2010 11:24 AM
I think people should read the paper http://arxiv.org/PS_cache/arxiv/pdf/1005/1005.4915v2.pdf Four-qubit entanglement from string theory L. Borsten, D. Dahanayake, M. J. Duff, A. Marrani and W. Rubens Of course this paper is typical of Duff’s papers, in that it is dense with group theory. If you are familiar with Young Tableaux calculations then this is paper is tractable. The paper involves coset constructions of gauge groups and moduli for certain symmetries, in particular U duality. U duality involves compositions of S and T duality. S duality involves a dualism between a gauge charge q and its magnetic-like corresponding charge g (electric and magnetic charges, but the latter do not exist at low energy) according to a Bohr-Sommerfeld rule qg =… Read more »
GekkoNZ
Member
September 1, 2010 12:29 PM

TERRYG: huh?

Making sense, you are not. All I see is a kneejerk emotional ( some would say, emorage ) response to the article, while actually explaining nothing.

A Theory made a prediction. Scientists can test that prediction to see if the Theory works for *that* prediction. No claims beyond testing that prediction were made.

*please* read the article carefully before emoraging in the comments section.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
September 1, 2010 1:57 PM
Well, you would think that a unique prediction would test the theory. But it has happened before, when string theory was born it was the only theory explaining strong interactions in the atomic nucleus (say). The next year (IIRC) QCD, a more predictive theory, came around and did the same. And of course predicting black hole entropy is not unique for string theory (and here never was). Similarly string theory predicts quark-gluon plasma and solid state system properties that AFAIU no other theory does. But here the predictions are not fundamental but of the “convenient math” type. Hopefully this sticks. he classical interpretation of strings and branes is that they are quantum mechanical vibrating, extended charged black holes… Read more »
Torbjorn Larsson OM
Member
Torbjorn Larsson OM
September 1, 2010 2:15 PM
@ Beckler: What? Is it a possible theory of everything or not? If so, then presumably quantum entanglement is included? Wait, let me quickly check the definition of ‘everything’… Exactly, I suspect you know this: “Theory of Everything” is the misnomer the ellipsis hint at. It is a fundamental theory, in fact perhaps of everything gravity and field, but would both add on other theory and need add ons. (Add ons for emergent phenomena like chemistry or solid state physics which is likely impossible to practically predict from fundamental principles.) Actually there is a better (simpler, massively predictive) contender for “TOE” in the sense implied by the misnomer, which is the quantum mechanics it relies on. All systems… Read more »
IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
September 1, 2010 2:31 PM

If anyone here smells burning rubber, don’t worry; it’s just the insulation of my synapses overheating as a result of reading that paper provided by LBC above! wink

William928
Member
William928
September 1, 2010 3:11 PM

I anyone else having trouble understanding what LBC wrote above? Waaaaaaaay over my head! An interesting article, however.

Lawrence B. Crowell
Member
Lawrence B. Crowell
September 1, 2010 3:35 PM
if you want to make contact, get a hold of a quantum mechanics text, or look up Pauli matrices — which is what those sig symbols stand for. Also look up the Born rule in quantum mechanics. If you follow what I wrote then you will understand the basic idea of quantum entanglements. The coset stuff that Duff et al. wrote is far more abstract and deep, and as i read it I agree with the conclusion. As for practical experimental physics the biggest problem is in detecting entanglements at such high energy. Normally to set up entangled states and to do experiments you need things to be very cold, or to work with massless particles such as… Read more »
William928
Member
William928
September 1, 2010 4:23 PM

Lawrence,
I hope you didn’t misunderstand my post above. I wasn’t implying that your writing didn’t make sense; simply that from my lay perspective it was difficult to understand. I much appreciate that you take the time to provide your expertise on a number of subjects offered at UT. The reason I come to this site is my love of astronomy, and to learn. Your comments, while at times a bit over my head, foster additional research and learning on my part.

TerryG
Member
September 2, 2010 2:10 AM

Hello GekkoNZ
We embrace theories closer when they pass lots of tests. Relativity theories account for orbital effects, gravitational lensing, frame dragging, time dilation etc. and if they are ever observed, gravity waves. Similarly QM is successful in describing a whole bunch of stuff and there are even attempts to commercialise it with quantum computing, quantum cryptography etc.
While a unique prediction would test Mr Duffs theory, he rightly allows the possibility of “no more than a quirky coincidence”. Hence, more (some might say a lot more) work is required. Good luck to him.
No doubt UT will keep us in the loop and thanks as always LC for the write up.

Lawrence B. Crowell
Member
Lawrence B. Crowell
September 2, 2010 4:23 AM
The story of Ludwig Boltzmann comes to mind. He founded his theory of statistical mechanics on the atomic theory. At the close of the 19th century the idea was highly controversial, where Ernst Mach opposed the theory on positivist grounds. Nobody had found any experimental evidence for atoms, though the chemists used the idea to make sense of chemical calculations. String theory is in a similar situation, where the tests of the core concept have not yet come about. There are several possible tests of string theory that are fairly direct. The first is with AdS or BTZ amplitudes at high energy, where some AdS/QCD evidence has already been found at RHIC. This amounts to detecting back hole… Read more »
Olaf
Member
Olaf
September 2, 2010 8:45 AM

I also read that if we are lucky, then one of the dimensions might be as big as 0.7mm and within this range the gravity would not follow the inverse square law if string theory would be correct. Finding this would also give a clue that string theory might be onto something. The question is how to you measure the gravity formula at 0.7 mm scale…

jimhenson
Guest
jimhenson
September 2, 2010 6:36 PM
2 and 3 entangled qubits proved in lab fully applies fits perfectly for black holes. 4 qubits doesn’t quite apply for the universe theory of everything, because there will be many more then the 4 proven entangled cubits to possibly discover. Using Lie Algebra three-dimensional geodesics motion that we perceive is stationary D=4 is the “4th dimension of time” which is Supergravity after a further time-like reduction to D=3. What causes this time-like reduction could be that complex qubits appear automatically by black holes. Four Qubits relates to D=4 STU blackholes. Four Qubits is : large/small values of CHARGES, Absolute zero TEMP or not, Zero or not zero ENTROPY, and ORBITS nilpotent or semisimple : this leads to… Read more »
Lawrence B. Crowell
Member
Lawrence B. Crowell
September 2, 2010 12:57 PM
This is based on the Randal-Sundrum idea, which has some merit. I tend to think that in D = 10, with six extra dimensions gravity will depart from Newtonian 1/r^2 into 1/r^8 at around 1TeV of energy or 10^{-16}cm. This fixes the scale for Planck physics from 1TeV at the IR low energy scale up to 10^{16}TeV at the UV high energy scale. The scale of this interaction involves a power law on the string parameter, which for higher powers means a fairly small number is reduced a lot. For gravity to exhibit behavior departing from 1/r^2 of Newton some additional things have to be going on. It requires that two of the six compactified dimensions renormalize at… Read more »
Olaf
Member
Olaf
September 2, 2010 2:19 PM
We live in existing times. I don’t like Dr. Michio Kaku on his string theories. He is making it popular but he is still guessing and give claims that might be completely false when tested to reality. I would love string theory to be true, but I am also realistically that it can be completely wrong direction and have no problems to dispose it when it proves to be wrong. Experimental evidences is what I base on. LBC sometimes my brains gets fried trying to read your math stuff, but that is actually good since it forces me into a deeper understanding of the material instead of the basic stuff you find elsewhere. For those that are interested… Read more »
Lawrence B. Crowell
Member
Lawrence B. Crowell
September 2, 2010 2:56 PM

The |+> and |-> states are up and down. Or it could be polarized up and side — which ever is the case it just signifies two different states. In quantum mechanics we do also have

= 1 = and = 0,

which means these are orthogonal (perpendicular) vectors in an abstract vector space of states. Here the vector space is two dimensional — a plane with unit vectors that point to a circle centered around the origin.

LC

Jean Tate
Member
September 3, 2010 12:51 PM

Lee Smolin (“Not Even Wrong”) has an interesting blog entry on this paper, interesting as much for the comments of String Theory mavens (e.g. Ed Witten) as for his own comments: http://www.math.columbia.edu/~woit/wordpress/?p=3127

Lawrence B. Crowell
Member
Lawrence B. Crowell
September 6, 2010 5:52 AM

Woit is too conservative and curmudgeonly for me.

LC

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