Physicists looking for a way to test their theory about strings might make more progress by tangling them up.
String theory--which describes particles of matter and force as tiny vibrating loops or strands--has extended its reach to the quantum behavior known as entanglement. Repurposing string theory math allowed physicists to solve a hard problem involving this strange feature at the heart of quantum mechanics. In doing so, the new study, reported online September 2 in Physical Review Letters, also points out a way to test whether the co-opted string theory equations are correct.
"String theory has not had a lot of success in making falsifiable predictions," says study coauthor Michael Duff of Imperial College London. "But in the field of quantum information theory, it can."
One hallmark of quantum information is that particles carrying it can interact in a way that makes them "entangled," so that measuring one seems to instantaneously affect the other, even at great distances. In recent years, Duff and colleagues have noticed similarities between string theory and equations for entangled particles.
In a paper published last year, the physicists noted that string theory math describing black holes is similar to the equations for a group of three entangled particles. The new study tackles the more difficult problem of how four pieces of quantum information, called qubits, behave when entangled. Because experiments disagree, physicists aren't sure how many ways four qubits can be entangled. The answer, according to string theory, is 31. …