## Scientists Say They Can Now Test String Theory

by Nancy Atkinson

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

“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’…

Today: Scientists find way to test String Theory

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

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.

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.

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!

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

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.

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.

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…

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

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

Woit is too conservative and curmudgeonly for me.

LC