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We’ve all come across the mind-blowing weirdness of quantum mechanics; that it makes its predictions in probabilistic rather them deterministic form, that it does not allow unknown states to be copied and that one quantum object can instantly influence another regardless of the distance between them, but not in a way that allows faster-than-light communication.

That’s one helluva a theory and 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.

Perhaps. The problem with this argument is that the new rule so far gives no insight into the nature of quantum mechanics (or information) and seems to have no predictive power. That’s not going to be much use to anybody.

The truth is that this team is not the first to consider the role that information plays in quantum mechanics.

There are no shortage of theorists who recognise the problem of understanding the nature of information as the outstanding mystery of our era.

Various teams are wrestling with the problem of producing a quantum version of Shannon’s Theory of Communication which describes how a classical message created at one point in space can be recreated at another. The problem is how to describe in very general terms the rules that govern how a quantum message created at one point in space can be recreated at another.

Others are attempting to redraw the laws of quantum mechanics in terms of quantum information alone.

Roy Frieden at the University of Arizon in Phoenix, has already derived the laws of physics, including the Schrodinger equation, using the powerful idea of Fisher information (although the method has not produced the kind of predictions needed to make it mainstream).

All this work stems from the growing realisation that it is not the laws of physics that determine how information behaves in our Universe, but the other way round. The implication is extraordinary: that somehow, information is the ghostly bedrock of our Universe and from it, all else is derived. That really is mind-blowing.

Ref: arxiv.org/abs/0905.2292: A New Physical Principle: Information Causality

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