Two things Albert Einstein did not like about quantum theory were its inherent uncertainty and its assertion that particles can remain weirdly linked even when separated by great distances. The former he dismissed with the phrase 鈥淕od does not play dice,鈥� and the second he called 鈥渟pooky action at a distance鈥�.
Now a pair of physicists says that these two strange effects are intimately linked 鈥� and that uncertainty itself limits how 鈥渃onnected鈥� separate particles can be.
When two distant particles that are quantum mechanically linked, or entangled, are measured, the results are more similar than predicted by classical physics. 鈥淣ature is non-local,鈥� says of the University of Bristol. 鈥淭his is arguably the most important lesson of quantum theory.鈥�
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But these non-local links are not as influential as they might conceivably be. Popescu and colleague , now at Ben Gurion University in Israel, calculated 15 years ago that the laws of physics could allow even stronger coordination between distant systems, leading physicists to wonder why quantum theory doesn鈥檛 go as far as it could.
of the University of Cambridge in the UK and of the National University of Singapore suggest they鈥檝e found a clue. The secret, they suggest, lies in another famous property of the quantum world 鈥� its inherent uncertainty.
鈥楨ven spookier鈥�
In quantum theory, states of a quantum system can never be defined with precision. The uncertainty principle, for example, implies that any effort to measure the position of an electron entails giving up precise knowledge of its velocity, or vice versa.
Using information theory, a core tool of computer science that quantifies how much information is contained in any structure, Oppenheim and Wehner studied how the amount of uncertainty in a theory should influence the possibilities it presents for nonlocal connections.
Hypothetical theories containing no uncertainty, they found, could feature coordination between distant systems as strong as the limit calculated by Popescu and Rohrlich. 鈥淨uantum mechanics could be even spookier,鈥� says Oppenheim. 鈥淏ut Heisenberg鈥檚 uncertainty principle gets in the way.鈥�
The results do not suggest what underlying physical mechanism would link uncertainty to non-locality. But because the results rest only the ideas of information theory, they should hold not only for quantum theory, but for any conceivable future theory as well, the authors say.
鈥淭his is a very original and important idea,鈥� says Popescu. But he cautions that it is probably not the final word on why quantum theory is not more non-local than it is. 鈥淭his work doesn鈥檛 finally solve the problem,鈥� he says. 鈥淏ut it goes in a very new direction鈥�, adding to other possible explanations that physicists have explored in recent years.
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