We still don’t know if the wavefunction is physically real

Nature has a piece claiming that a newly-published paper shows that the quantum mechanical wavefunction is physically real, as opposed to merely encoding information about our knowledge of the state of a system. As I mentioned back in the fall, I can’t see how the published result shows anything like this.

The paper shows that a certain class of hidden-variable theories would lead to predictions that differ from standard quantum mechanics, and hence that experiments can in principle tell the difference between these theories and quantum mechanics. But that doesn’t show that the wavefunction is real, unless you believe that this particular class of hidden-variable theories is the only thing that the wavefunction-isn’t-real camp could possibly believe. There’s certainly no evidence that this is the case.

Personally, I’m not sure the question of whether the wavefunction is “physically real” is meaningful. I am pretty sure that, even if it is, this paper doesn’t resolve it.


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Ted Bunn

I am chair of the physics department at the University of Richmond. In addition to teaching a variety of undergraduate physics courses, I work on a variety of research projects in cosmology, the study of the origin, structure, and evolution of the Universe. University of Richmond undergraduates are involved in all aspects of this research. If you want to know more about my research, ask me!

2 thoughts on “We still don’t know if the wavefunction is physically real”

  1. At the link you mention one can read:

    The authors have some heavyweights in their corner: their view was once shared by Austrian physicist and quantum-mechanics pioneer Erwin Schrödinger, who proposed in his famous thought experiment that a quantum-mechanical cat could be dead and alive at the same time. But other physicists have favoured an opposing view, one held by Albert Einstein: that the wavefunction reflects the partial knowledge an experimenter has about a system. In this interpretation, the cat is either dead or alive, but the experimenter does not know which.

    Didn’t Schrödinger trot out his cat as a type of reductio-ad-absurdum argument to argue against the interpretation of the wave function as something real? Einstein is portrayed as having an alternative view, whereas what actually happened was that Einstein and Schrödinger were in one camp and almost everyone else in the other.

    Schrödinger’s cat is thus perhaps a case of irony which has been lost in the mists of time. (Something similar happened in some of Aldous Huxley’s books—though not Brave New World—in that some things which he intended to paint a picture of an undesirable society are now held in esteem by his modern-day intellectual colleagues and, to some extent, vice-versa.)

  2. Part of Nature’s business is to sell magazines. So they will trumpet specific studies if they have popular appeal. I disagree with the notion that whether the wavefunction is real or not has no meaning. What the univerise is, how it works, and even why it works the way it does is what drives me personally has an lay person studying these ideas. Also, Scientific American published an interesting article entitled, “Quantum Flip-Floppers: Photon Findings Add to Mystery of Wave-Particle Duality” that is very interesting. Should take a look.

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