Quantum Mechanics is quite possibly the sexiest, most mysterious thing to come out of 20^{th} century physics. Almost a century of evidence has confirmed that the world is fundamentally ambiguous and yet deeply predictable, that physics is best described probabilistically, and that however alien this seems the world wouldn’t work without it. Quantum Mechanics raises deep philosophical questions about the nature of reality, some of the most interesting of which are still unanswered to this day.

And I am (for the moment, at least) not the best person to ask about these questions. Because while I specialize in Quantum Field Theory, that actually means I pay very little attention to the paradoxes of Quantum Mechanics.

It all boils down to the way calculations in quantum field theory work. As I described in a previous post, quantum field theory involves adding up progressively more complicated Feynman Diagrams. There are methods that don’t involve Feynman Diagrams, but in one way or another they work on the same basic principle: to take quantum mechanics into account, add up all possible outcomes, either literally or through shortcuts.

That may sound profound, but in many ways it’s quite mundane. Yes, you’re adding up all possibilities, but each possibility is essentially a mundane possibility. There are a few caveats, but essentially each element you add in, each Feynman Diagram for example, looks roughly like the sort of thing you could get without quantum mechanics.

In a typical quantum field theory calculation, you don’t see the mysterious parts of quantum mechanics: you don’t see entanglement, or measurements collapsing the wavefunction, and you don’t have to think about whether reality is really real. Because of that, I’m not the best person to ask about quantum paradoxes, as I’ve got little more than an undergraduate’s knowledge of these things.

There are people whose work focuses much more on quantum paradoxes. Generally these people focus on systems closer to everyday experiments, atoms rather than more fundamental particles. Because the experimentalists they cooperate with have much more ability to manipulate the systems they study, they are able to probe much more intricate quantum properties. People interested in the possibility of a quantum computer are often at the forefront of this, so if you’ve got a question about a quantum paradox, don’t ask me, ask people like WLOG blog.

A final note: there are many people (often very experienced and elite researchers) who, though they might primarily be described as quantum field theorists, have weighed in on the subject of quantum paradoxes. If you’ve heard of the black hole firewall debate, that is a recent high-profile example of this. The important thing to remember is that these people are masters of many areas of physics. They have taken the time to study the foundations of quantum mechanics, and have broadened their horizons to the tools more commonly used in other subfields. So while your average grad student quantum field theorist won’t know an awful lot about quantum paradoxes, these guys do.

Lucas VieiraMaybe that is because the typical field theorist will not ask the right questions for the foundations of QM. You could certainly ask what happens if slow moving particles whose spin are entangled are accelerated to high energies.

Also, the field theorest deals mostly with pure states, whereas the information theories must look at mixed states.

You can always think of QM though, from the point of view of effective field theory, or as a one dimensional quantum field theory.

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