New study suggests researchers can now test the 'theory of everything'

http://www.physorg.com/news202553083.html

September 1, 2010

Researchers discover how to conduct first test of 'untestable' string theory

(PhysOrg.com) -- Researchers describe how to carry out the first

experimental test of string theory in a paper published tomorrow in

Physical Review Letters.

String theory was originally developed to describe the fundamental

particles and forces that make up our universe. The new research, led

by a team from Imperial College London, describes the unexpected

discovery that string theory also seems to predict the behaviour of

entangled quantum particles. As this prediction can be tested in the

laboratory, researchers can now test string theory.

Over the last 25 years, string theory has become physicists' favourite

contender for the 'theory of everything', reconciling 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.

"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," said Professor

Mike Duff FRS, lead author of the study from the Department of

Theoretical Physics at Imperial College London.

"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,"

added Professor Duff.

Professor Duff recalled sitting in a conference in Tasmania where a

colleague was presenting the mathematical formulae that describe

quantum entanglement: "I suddenly recognised 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."

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 at last

researchers can test predictions based on string theory. 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 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", concluded Professor Duff.

"Either way, it's useful."

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.

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.

Professor Duff and his colleagues realised 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 realised 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.

More information: M. J. Duff FRS et al., “Four-qubit entanglement from

string theory.” Physical Review Letters 2010. http://prl.aps.org …

/i10/e100507

Provided by Imperial College London

http://www.physorg.com/news202553083.html

September 1, 2010

Researchers discover how to conduct first test of 'untestable' string theory

(PhysOrg.com) -- Researchers describe how to carry out the first

experimental test of string theory in a paper published tomorrow in

Physical Review Letters.

String theory was originally developed to describe the fundamental

particles and forces that make up our universe. The new research, led

by a team from Imperial College London, describes the unexpected

discovery that string theory also seems to predict the behaviour of

entangled quantum particles. As this prediction can be tested in the

laboratory, researchers can now test string theory.

Over the last 25 years, string theory has become physicists' favourite

contender for the 'theory of everything', reconciling 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.

"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," said Professor

Mike Duff FRS, lead author of the study from the Department of

Theoretical Physics at Imperial College London.

"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,"

added Professor Duff.

Professor Duff recalled sitting in a conference in Tasmania where a

colleague was presenting the mathematical formulae that describe

quantum entanglement: "I suddenly recognised 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."

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 at last

researchers can test predictions based on string theory. 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 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", concluded Professor Duff.

"Either way, it's useful."

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.

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.

Professor Duff and his colleagues realised 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 realised 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.

More information: M. J. Duff FRS et al., “Four-qubit entanglement from

string theory.” Physical Review Letters 2010. http://prl.aps.org …

/i10/e100507

Provided by Imperial College London