String theory was originally developed to try and describe the fundamental particles and forces that make up our universe.  Over the last 25 years, string theory has become some physicists' contender for a 'theory of everything', reconciling particle physics with cosmology - a puzzle that tormented Einstein for the last 30 years of his life.

It contends that the subatomic particles found in nature, such as electrons and quarks, may not be particles at all but instead tiny vibrating strings.      String theorists said our universe is 10-dimensional but during the big bang, 6 of those 10 dimensions curled up into a tiny ball and the remaining '4' (they count time as a dimension even though it relies on the other three dimensions) expanded explosively, providing us with the universe we know and love, including the cast of "Jersey Shore".

How did these six dimensions compactify?  There's no mathematical basis for topology and properties of these higher-dimensional universes.  Where do strings come from?  No one knew so what we ended up with were multiple 'string theories', which means it stands a chance of not being a theory at all.   Some even proposed M-theory (11-dimensions) to get away from focusing on strings entirely.(1)

There's no shortage of instances where theory, deduction or inference have survived being falsifiable just fine and later been proven to be correct but in a modern science world a half dozen 'theories of a theory' won't get much traction outside people who want funding.

An upcoming article in Physical Review Letters says it can change all that and make string theory experimental.  Their reasoning?   They say string theory seems to predict the behavior of entangled quantum particles and since that prediction can be tested in the laboratory, they can now test string theory - predicting how entangled quantum particles behave provides the first opportunity to test string theory by experiment because quantum entanglement can be measured in the lab.(2)

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 but if it checks out, it will be an interesting insight.

"This will not be proof that string theory is the right 'theory of everything' that is being sought by cosmologists and particle physicists. 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," says professor Mike Duff, lead author of the study from the Department of Theoretical Physics at Imperial College London.  "If experiments prove that our predictions about quantum entanglement are correct, this will demonstrate that string theory 'works' to predict the behaviour 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.  Either way, it's useful."

Article: M. J. Duff , L. Borsten, D. Dahanayke , W. Rubens, A. Marrani, 'Four-qubit entanglement from string theory', arXiv:1005.4915v2 and Physical Review Letters 2010 (in press)


(1) String theory

String theory, and its extension M-theory, are mathematical descriptions of the universe. They have been developed, over the last 25 years, by theoreticians seeking to reconcile the theories of general relativity and quantum mechanics. (The former describes the universe at the level of cosmology – the very large, while the latter describes the universe at the level of particle physics – the incredibly small). One of the major bugbears, especially of M-theory, is that it describes billions of different universes and ‘anything’ can be accommodated in one or other of the M-theory universes. Researchers have no way of testing which of the answers that string/M-theory gives us is ‘right’. Indeed, they all may be right and we live in one universe among an infinite number of universes. So far no one has been able to make a prediction, using string theory, that can be tested to see if it is correct or not.

(2) Qubit (quantum bit) entanglement

Under very precisely controlled conditions it is possible to entangle the properties of two quantum particles (two quantum bits, or qubits), for example two photons. If you then measure the state of one of these entangled particles, you immediately affect the state of its partner. And this is true if the particles are close to one another or separated by enormous distance. Hence Einstein’s apposite description of quantum entanglement as ‘spooky action at a distance’. It is possible to entangle more than two qubits, but calculating how the particles are entangled with one another becomes increasingly complex as more particles are included.

Duff and colleagues say they 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.