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Randomness

Poll of quantum physicists shows agreement, disagreement and something in between

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Science is not a democracy. Nature’s laws are not subject to the whims of popular vote. A scientific theory succeeds by providing logical explanations for puzzling phenomena and making correct predictions about the outcomes of new experiments. It doesn’t matter how many scientists believed in the theory beforehand (or even afterward, for that matter).

In fact, revolutionary new theories are seldom very popular. As Max Planck, the founder of quantum theory, once noted, sometimes a theory doesn’t get widely accepted until its opponents die. Nevertheless, in certain scientific matters it’s worth knowing what most experts think. Sometimes the math is clear, and experimental results indisputable, but their implications are charged with ideological controversy. Mainstream expert judgment on such matters usually offers a better path to wisdom than wishful thinking based on philosophical predisposition.

Yes, all the above could be alluding to climate change. But quantum mechanics, the math of the microworld, is more fun and less likely to elicit hate mail. And a new paper has provided actual data about what mainstream quantum physicists think about how to interpret their math.

It’s curious. It has been more than 80 years since the mathematical framework of quantum mechanics was formulated. It has been about three decades since the first modern experiments confirmed the most outrageous consequences of quantum math. Yet physicists still argue about it, some contending that the onetime consensus interpretation (named for Copenhagen, where the Danish physicist Niels Bohr developed it), should be abandoned. But apparently the Copenhagen interpretation still gets more support from experts than any of the alternatives.

It’s not easy to concisely describe the Copenhagen interpretation, but it essentially contends that reality at the atomic level is ill defined. An electron has no actual “real” position, for instance, until a measurement determines where it is. And its location cannot be predicted precisely — you can compute only probabilities for where it will be. Electrons can be either waves or particles depending on the nature of the experimental apparatus used to observe them. In other words, for some things in the subatomic world there’s no preexisting objective reality independent of observation. Or something like that.

Einstein rejected these ideas, proclaiming that God doesn’t play dice and that the moon exists whether or not a mouse is looking at it. But he didn’t have much of a case. At a conference of quantum physicists (plus a few philosophers and mathematicians) held last year, 64 percent of 33 respondents to a questionnaire declared that Einstein was wrong. None said he was correct. A few suggested he might turn out to be right someday, and others said “we’ll just have to wait and see.”

As for Bohr’s views, 27 percent said he was wrong, 30 percent said he was correct or ultimately would be and 30 percent voted for waiting and seeing. When asked to name their favorite interpretation, 42 percent said Copenhagen, far more than any of the other choices.

And 64 percent of the respondents concurred with the statement that randomness is a fundamental concept in nature, about half agreeing that randomness is irreducible — there is, in other words, no way to explain reality without it.

One proposal to eliminate God’s dice throwing, known as Bohmian quantum mechanics for the physicist David Bohm, was preferred by no one.

Another interpretation, championed by some experts, is the many worlds interpretation. An observation doesn’t fix an electron’s position from among multiple possibilities, this view holds. Rather an observation sends the observer off into one branch of the universe corresponding to one result, while all the other possibilities are equally real in other branches. This interpretation got 18 percent of the votes in the survey, conducted by physicists Maximilian Schlosshauer, Johannes Kofler and Anton Zeilinger and reported recently in a paper online at arXiv.org.

Of course, such surveys are mostly just for fun — the views of a particular group of experts at one conference don’t necessarily reflect the entire quantum physics community. What’s more interesting than the numerical results is their diversity. Quantum physics remains, after decades of debate, one of the most baffling theories science has ever produced. Knowledgeable people cannot agree on what to make of it. They can’t even agree on whether it matters to agree. (A favorite slogan of many physicists encountering such discussions is “shut up and calculate.”)

But it appears that the arguments have in fact been fruitful. Efforts to probe the foundations of quantum physics beginning about three decades ago produced a new strain of quantum research called quantum information theory. It has not only illuminated quantum philosophy but has also led to potential practical applications, from crack-proof secret codes to powerful new breeds of computers and communications systems.

So it’s probably good for quantum people to continue probing their discipline’s foundation. They might uncover some new inventions, or dig up some fuel for even more controversy.

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