Tag Archives: John Preskill

Nobel Laureates on the QM Interpretation Mess

Update:  Perusing the web I noticed that John Preskill [not yet a Nobel laureate 🙂 ] also blogged on the same survey.  Certainly another prominent voice to add to the mix.


In the LinkedIn discussion to my earlier blog post that was lamenting the disparate landscape of QM interpretation, I had Nobel laureate Gerard ‘t Hooft weighing in:

Don’t worry, there’s nothing rotten. The point is that we all agree about how to calculate something in qm. The interpretation question is something like: what language should one use to express what it is that is going on? The answer to the question has no effect on the calculations you would do with qm, and thus no effect on our predictions what the outcome of an experiment should be. The only thing is that the language might become important when we try to answer some of the questions that are still wide open: how do we quantize gravity? And: where does the Cosmological Constant come from? And a few more. It is conceivable that the answer(s) here might be easy to phrase in one language but difficult in another. Since no-one has answered these difficult questions, the issue about the proper language is still open.

His name certainly seemed familiar, yet due to some very long hours I am currently working, it was not until now that I realized that it was that ‘t Hooft.  So I answered with this, in hindsight, slightly cocky response:

Beg to differ, the interpretations are not more language, but try to answer what constitutes the measurement process. Or, with apologies to Ken, what “collapses the wave function”: The latter is obviously a physical process. There has been some yeoman’s work to better understand decoherence, but ultimately what I want to highlight is that this sate of affairs, of competing QM interpretation should be considered unsatisfactory. IMHO there should be an emphasis on trying to find ways to decide experimentally between them.

My point is we need another John Bell.  And I am happy to see papers like this that may allow us to rule out some many world interpretations that rely on classical probabilities.

So why does this matter?  It is one thing to argue that there can be only one correct QM interpretation, and that it is important to identify that one in order to be able to develop a better intuition for the quantum realities (if such a thing is possible at all).

But I think there are wider implications, and so I want to quote yet another Nobel laureate, Julian Schwinger, to give testament to how this haunted us when the effective theory of quantum electrodynamics was first developed (preface selected papers on QED 1956):

Thus also the starting point of the theory is the independent assignment of properties to the two fields, they can never be disengaged to give those properties immediate observational significance. It seems that we have reached the limits of the quantum theory of measurement, which asserts the possibility of instantaneous observations, without reference to specific agencies.  The localization of charge with indefinite precision requires for its realization a coupling with the electromagnetic field that can attain arbitrarily large magnitudes. The resulting appearance of divergences, and contradictions, serves to deny the basic measurement hypothesis.

John Bell never got one of these, because of his untimely death.