A new physical principle: Information Causality. In recent years physicists have discovered an entire class of theories that do the same kind of thing. The question is which one do we choose?

A few can be ruled out because they simplify various computational tasks in implausible ways. But the rest have seemed more or less equivalent. Until now.

Marcin Pawlowski at the University of Gdansk in Poland and a few pals say that the addition of a single additional consideration, quickly and easily separates the non-physical theories from the physical ones.

The idea is based around information and can be stated simply. The rule is this: the sending of “m” classical bits causes an information gain of, at most, “m” bits.

It sounds bewilderingly simple and perhaps it is. Pawlowski and co say that without this principle, non-physical theories allow extra information to be sent. They point out that the rule applies only to classical bits. In the real quantum world, extra infromation can be sent using the ideas of super dense coding.

The team say because the idea distinguishes between physical and non-physical versions of quantum mechanics, it must be a fundamental property of the universe.

Source: ArXiv blog

Abstract: Quantum physics exhibits many remarkable features. For example, it gives probabilistic predictions (non-determinism), does not allow copying of unknown states (no-cloning), its correlations are stronger than any classical correlations but information cannot be transmitted faster than light (no-signaling). However, all the mentioned features do not single out quantum physics. A broad class of theories exist which share all of them with quantum mechanics and allow even stronger than quantum correlations.

Here, we introduce the principle of Information Causality, stating that communication of m classical bits causes information gain of at most m bits. We show that this principle is respected both in classical and quantum physics, and that all stronger than quantum correlations violate it. We suggest that Information Causality, being a generalization of no-signaling, is one of the foundational properties of Nature.