14 August 2004
From New Scientist Print Edition.
Alastair Rae, Birmingham, UK
The results of Shahriar Afshar's experiment are just what would be predicted from a
conventional quantum-mechanical analysis of the experimental set-up. As all the
leading interpretations of quantum physics (including those referred to in the article)
are designed to predict the same experimental results as conventional quantum
theory, none of them can be logically falsified by this experiment.
To imply that complementarity means that light must always be 100 per cent a wave
or 100 per cent a particle is a gross oversimplification. More correctly, the state of a
quantum system can often be represented as a combination or "superposition" of
complementary descriptions, such as "wave" and "particle".
The closer it is to one of these the further it is from the other, but in general neither description is correct.
Given this, we can see that Afshar's experiment, rather than refuting
complementarity, actually exemplifies it in a rather elegant way.
Also, whatever the weaknesses of Bohr's approach to quantum physics, it is quite
wrong to imply that he identified observation or measurement as a conscious human
act, such as looking at oneself in a mirror. For Bohr, observation meant the recording
of results by apparatus undergoing irreversible changes such as occurs when a
The foundations of quantum physics are puzzling and controversial and really do not need further obfuscation.
University of Birmingham
From issue 2460 of New Scientist magazine, 14 August 2004, page 24