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Quantum Mechanics Still Puzzles Scientists

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Two surveys show that scientists still disagree over the foundations of quantum mechanics.

richardThe American physicist Richard Feynman is famously supposed to have once said “if you think you understand quantum mechanics, you don’t understand quantum mechanics”. Whether or not he ever actually said it, the idea that quantum mechanics poses difficulties for scientists still seems to be true today. Two surveys from quantum mechanics conferences show that there are still many foundational issues over which scientists disagree.

Quantum mechanics is the theory that describes the world at its smallest scales: individual particles of light, tiny shifts within atoms and decaying radioactive nuclei. Last year’s Nobel Prize in Physics was won by researchers working in the field of quantum mechanics. Recently, scientists have reported seeing quantum mechanical behaviour in plants.

In one sense, quantum mechanics is an excellent theory; it has been tested extensively and makes very accurate predictions for all sorts of experiments. But there is still something troubling about it. No one really knows what’s really going on behind the equations.

Because of this, quantum mechanics has various interpretations. They encompass ideas about determinism, reality, non-locality, freewill, consciousness and many worlds. The problem is that experiments cannot tell which of these interpretations is correct. And then there is the opinion that quantum mechanics needs no interpretation at all.

With all these possibilities, it is difficult to know which ones most scientists believe.

At a conference held in Austria in 2011, the organisers decided to find out. They gave a survey to each of the participants, mostly physicists but also mathematicians and philosophers, and asked questions about some of the key issues in the foundations of quantum mechanics. The answers to the 33 completed surveys were posted on the web in January 2013.

Recently, another conference, held in Germany, has done the same thing. The organisers gave the same questionnaire to the participants and collated the 76 responses. The data, published online in June 2013, show the participants are just as split over several key issues in quantum mechanics, but, interestingly, the answers are significantly different to those from the previous conference. For example, the question about the interpretation of quantum mechanics (question number 12 on the survey) received very different responses from participants at the two conferences.

The majority of participants at the first conference stated that the Copenhagen interpretation was their favourite (42%), with none choosing the de Broglie-Bohm interpretation. The participants at the second conference, however, largely chose the de Broglie-Bohm interpretation (63%) and not the Copenhagen one (4%).

The authors of the second survey are quick to point this out and suggest that it tells us more about the organisation of each conference than the quantum physics community. So although it is still difficult to tell which interpretation is held by the majority of the scientific community, it is clear that there is no overall consensus.

The survey also asked participants whether they believed that their choice of interpretation was influenced by their own philosophical preferences. Both surveys showed that most participants felt that it was. In a scientific setting, where objectiveness is usually a crucial feature, this is an intriguing answer.

One question on which the scientists largely agreed was whether conferences will still be held on the foundations of quantum mechanics in 50 years’ time. The majority of participants at both conferences answered “probably, yes”. But even if, however unlikely, quantum mechanics is completely understood by then that wouldn’t stop the small number of dedicated participants who answered “I’ll organise one no matter what”.

Maximilian Schlosshauer, Johannes Kofler, & Anton Zeilinger (2013). A Snapshot of Foundational Attitudes Toward Quantum Mechanics arXiv arXiv: 1301.1069v1
Travis Norsen, & Sarah Nelson (2013). Yet Another Snapshot of Foundational Attitudes Toward Quantum Mechanics arXiv arXiv: 1306.4646v2

Physics Today, BBC News

quantum mechanics basics, quantum mechanics news

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