a conference on the foundations of quantum mechanics in Vienna. It was a very interesting and well organized event. The food was good, the staff efficient, and everybody got a conference bag with an umbrella.
I don’t normally have a lot to do with quantum foundations, especially not since I left Perimeter Institute. And so I learned many new things and got feedback on my paper. It was a useful meeting for me – but it was also a little strange.
Most of the feedback I got was people telling me they don’t believe in superdeterminism, wanting to know why I believe in it, not that I’m sure I do. Discussions turned towards final causes and theology. I’m a phenomenologist, I heard myself saying, I couldn’t care less what other people believe, I want to know how it can be tested. Faintly, I heard an echo of a conversation I had with Joao Magueijo at PI some years ago. Boy, I thought back then, does this guy get explosive when asked about his beliefs. Now I think he must have been spending too much time with the quantum foundations folks. Suddenly I’m very sympathetic to Joao’s attitude.
Quantum foundations polarizes like no other area in physics. On the one hand there are those actively participating who think it’s the most important thing ever but no two of them can agree on anything. And then there’s the rest who thinks it’s just a giant waste of time. In contrast, most people tend to agree that quantum gravity is worthwhile, though they may differ in their assessment of how relevant it is. And while there are subgroups in quantum gravity, there’s a lot of coherence in these groups (even among them, though they don’t like to hear that).
As somebody who primarily works in quantum gravity, I admit that I’m jealous of the quantum foundations people. Because they got data. It is plainly amazing for me to see just how much technological progress during the last decade has contributed to our improved understanding of quantum systems. May that be tests of Bell’s theorem with entangled pairs separated by hundreds of kilometers, massive quantum oscillators, molecule interferometry, tests of the superposition principle, weak measurements, using single atoms as a double slit, quantum error correction, or the tracking of decoherence, to only mention what popped into my head first. When I was a student, none of that was possible. This enables us to test quantum theory now much more precisely and in more circumstances than ever before.
This technological progress may not have ignited the interest in the foundations of quantum mechanics but it has certainly contributed to the field drawing more attention and thus drawing more people. That however doesn’t seem to have decreased the polarization of opinions, but rather increased it. The more attention research on quantum foundations gets, the more criticism it draws.
“Shut up and let me think” is the title of an essay by Pablo Echenique-Robba which you can find on the arxiv at 1308.5619 [quant-ph]. In his personal account Pablo addresses common arguments for why research on quantum foundations is a waste of time. I’ve encountered most of these and I largely agree with his objections. But let me add some points Pablo didn’t mention.
I do have my issues with much of what I’ve seen in quantum foundations. To begin with, most of it seems to be focused on non-relativistic quantum mechanics. That’s like trying to improve the traffic in NYC by breeding better horses. If you can’t make it Lorentz-invariant and second quantized I don’t know why I should think about it. More important, I can’t fathom what most of the interpretation-pokers are aiming at. It’s all well and fine with me to try to find another formulation for the theoretical basis of quantum theory. But in the end I want to see either exactly what the observable differences are or I want to see a proof of equivalence. Alas, there seems to be a lot of talk about, well, interpretations which do neither one nor the other. Again the phenomenologist lacks the motivation to think about it.
Despite these reservations I think that research on the foundations of quantum mechanics is of value, again for a reason that Pablo did not address in his paper, so I want to add.
I’ve been educated in the “shut up and calculate” philosophy with my profs preaching Feynman’s mantra that nobody understands quantum mechanics, so don’t bother trying. Needless to say I, as probably most students, was not so much deterred as encouraged by this, so we dug a little into the literature. If you dig, it gets into philosophy very quickly. That’s not necessarily a bad thing, but most students come around to realize they wanted to study physics, not philosophy, and they move on to calculate. I’m among those who feel comfortable with a mathematical framework that “just” delivers results and that can be used to describe nature. To me science is “just” about making good models.
But those who are criticizing research on the foundations of quantum mechanics on the ground that everything has been understood are dismissing a way to arrive at an improved description of nature, and they are dismissing it based on unjustified arrogance about their superior motives.
Science progresses by evaluating the use of models about nature in the form of specific hypotheses. What we call ‘scientific method’ are procedures that have proved efficient in creating good hypotheses and tests thereof. Not only do these methods change (hopefully improve) over time, what constitutes a ‘good’ hypothesis also depends on beliefs and social dynamics. In the end what matters is not how somebody arrived at a hypothesis, but whether it works. That’s the essence of scientific progress.
The action principle, gauge-symmetry, and unification, for example, have proved dramatically useful in the construction of theories. And that they have been useful in the past is a good reason to employ them in the future search for improved theories. The same goes for naturalness. A theory that isn’t ‘natural’ is typically believed to be incomplete and in need of improvement or at least additional explanation. Yet all that says is that it’s a criterion which researchers draw upon to arrive at better theories. There’s no proof that this will work. It’s a reasonable guess, that’s all. How reasonable depends on your attitude, your beliefs and on whether you think it’ll land you a job.
And so some may guess there is something to be gained by poking around on the foundations of quantum mechanics. You might not believe that the reasons for their interest are good reasons, much like I don’t believe in naturalness and others don’t believe in a theory of everything. But in the end it doesn’t matter. In the end what matters is not what motivated people to study some research question, but only whether it led to something.
My support for quantum foundations thus comes from a live-and-let-live attitude. Maybe studying the foundations of quantum theory will improve our understanding of the fundamental nature of reality. Maybe it won’t. I don’t understand most of their motivations. But then they don’t understand mine either.
Those who are dismissing quantum foundations as a waste of time I want to ask to consider the consequences of this research in fact revealing a different theory underlying quantum mechanics, one that allows us to manipulate quantum processes in novel ways. The potential is enormous. It’s not a stone that should be left unturned.
I’ll shut up now and let you think.