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Does Anyone Know What Quantum Theory Means?

By Andrew Zimmerman Jones, Daniel Robbins

Some physicists hope that a “theory of everything,” perhaps even string theory, may provide clear explanations for the underlying physical meaning of quantum physics. Among them, Lee Smolin has cited string theory’s failure to explain quantum physics as a reason to look elsewhere for a fundamental theory of the universe — a view that is certainly not maintained by the majority of string theorists.

Quantum physics is based on experimental evidence, much of which was obtained in the first half of the 20th century. The odd behavior has been seen in laboratories around the world, continually agreeing with the theory, despite all common sense.

The really strange behavior occurs only on small scales; when you get to the size of cats, the quantum phenomena seems to always take on a definite value. Still, even today, the exact meaning of this strange quantum behavior is up in the air — something that doesn’t trouble most modern physicists who work on these problems.

Most string theorists believe that what matters is that quantum physics works (that is, it makes predictions that match experiment) and the philosophical concerns of why it works are less important. All of the interpretations of why quantum physics work yield the same experimental predictions, so they are effectively equivalent.

Einstein spent the last 30 years of his life railing against the scientific and philosophical implications of quantum physics. This was a lively time of debate in physics, as he and Niels Bohr sparred back and forth. “God does not play dice with the universe,” Einstein was quoted as saying. Bohr replied, “Einstein, stop telling God what to do!”

A similar era may be upon us now, as theoretical physicists attempt to uncover the fundamental principles that guide string theory. Unlike quantum theory, there are few (if any) experimental results to base new work on, but there are many Einsteinian critics — again, on both scientific and philosophical grounds.

Even with a firm theory that clearly works, physicists continue to question what quantum physics really means. What is the physical reality behind the mathematical equations? What actually happens to Schrödinger’s cat? Some physicists hope that string theory may provide an answer to this question, though this is far from the dominant view.

Still, any successful attempt to extend quantum physics into a new realm could provide unexpected insights that may resolve the questions.