Is Light a Particle or a Wave According to Quantum Theory?

[Ken G]

You are certainly right that the meaning of the words is crucial. Many people interpret the meaning of "wave/particle duality" along the lines of "sometimes it's a particle, sometimes it's a wave, it depends on the question we ask." They reject that, for good reason, because quantum mechanics is not sometimes one thing and other times something different, it's a very consistent approach to answering questions. But when I talk about "wave/particle duality", all I mean is "when we think about what used to be thought of as particles and their trajectories, we often forget that waves can do that too. And when we think about what we used to think of as waves and what they do, we did not realize that particles can do all those things too. Hence, the discovery is that particles and waves were never two completely different things, that was wrong. They are different aspects of the same things, aspects that show up everywhere we look."

Of course, others are free to say "neither the particle concept, nor the classical wave concept, are correct in quantum field theory," and that's fine-- conceptual entities like "particles" and "waves" that are defined in one theory are never defined the same way in some very different theory. But the concepts themselves are still of great value, in any of these theories-- the idea that entities show up in discrete bundles of fixed mass or energy is all one needs to mean by the "particle" notion, and that outcomes can exhibit interference is all one needs to mean by the "wave" notion, for those notions to be tremendously valuable. Perhaps you are looking for more specific meanings of what these things are, but every theory defines them for its own purpose.

 

[Feeble Wonk]

Perhaps you are looking for more specific meanings of what these things are, but every theory defines them for its own purpose.

Thanks Ken. Yes, I was hoping (not realistically) for a more specific description. But you're right, of course. Each QT interpretation would give me a different answer. I realize that, and accept it... but not without a great deal of frustration.