Quantum weirdness; essay says not so weird (Introduction)

by David Turell , Monday, February 23, 2015, 18:42 (3561 days ago) @ dhw

With enough system correlations it all works just fine:-http://nautil.us/issue/21/information/is-your-theory-of-everything-pure-enough-"And just like that, we have come to an idea at the heart of quantum mechanics, called the Purification Principle. It states that if one takes into consideration a sufficient number of systems, it is always possible to find a level of description where all systems are in a pure state. The Purification Principle is a sieve that separates physical theories that can aspire to fundamental status, from those that are merely effective. After all, fundamental theories of nature should describe phenomena in a self-contained way, making predictions that cannot be altered by the presence of information hiding elsewhere.-"What about quantum mechanics? It turns out that not only is it a fundamental theory, but it is the only standard theory that can satisfy Purification while allowing for the idea of probabilities in nature. This is the central result of a 2011 paper by Mauro D'Ariano, Paolo Perinotti, and myself, and it brings us to a fork: Either the outcome of every event is predetermined, or quantum theory must be the correct description of the natural world.1 In other words, only in a quantum world can the notion of randomness—and hence information—play a role in the fundamental laws of physics. For if every event was predetermined, the outcomes of all experiments should be independent of the information possessed by any agent.-"Physicists can take heart from quantum information theory. When quantum mechanics was first formulated, it seemed that physics had lost something. To classical physicists, it was as though the beautiful clockwork universe of Galileo and Newton had been shrouded with a cloud of indeterminacy. But quantum information has been the joyful discovery that quantum mechanics is not only a theory of limits, but also a theory of new opportunities, such as secure quantum cryptography and super-fast quantum computers. From this angle, quantum theory does not look any longer like “physics with something less,” but instead like “information theory with something more.” That “something more” is provided—we believe—by the Purification Principle, which lets us harness randomness in ways that were undreamt of in the classical world of Galileo and Newton."