William Lane Craig once recommended physicist Nick Herbert’s book, Quantum Reality: Beyond the New Physics, as a great introduction to quantum theory.  I picked up a copy to tackle this strange and oft-misunderstood topic.

Quantum mechanics is not for the faint-hearted.  It is difficult to grasp.  Even after reading this book I still can’t say I understand quantum mechanics well enough to explain it with confidence, but at least now I have a better understanding of what I don’t understand.  Apparently I’m in good company.  Richard Feynman once said, “I think it is safe to say that no one understands quantum mechanics.”

One thing I did glean from this book is what the debate is all about.  It’s not about the quantum facts.  We know the facts well.  And it’s not even so much over quantum theory (the mathematics used to describe the quantum facts).  Rather, the debate is about the physical interpretation of quantum theory.  What is the reality of the quantum world?

There are eight different physical interpretations of quantum theory, each of which accounts for the experimental data.  As Hebert explains:

Since these quantum realities differ so radically, one might expect them to have radically different experimental consequences.  An astonishing feature of these eight quantum realities, however, is that they are experimentally indistinguishable. For all presently conceivable experiments, each of these realities predicts exactly the same observable phenomena. … At present…each of these quantum realities must be regarded as a viable candidate for ‘the way the world really is.’ They may, however, all be wrong. … Not only can physicists not agree on a single picture of what’s really going on in the quantum world, they are not even sure that the correct picture is on the list. … Physicists differ over which parts of this theory they will take seriously and which parts they will ignore as empty formalism having no counterpart in the real world.  Which different picture of quantum reality you end up with depends on what parts of quantum theory you take seriously.

If you are interested in learning more about quantum theory, its history, and what it means, get yourself a copy of Herbert’s book.