Quantum Rebellion?

The New Scientist’s July 24th issue has its feature article titled ‘Quantum Rebellion’ with the intriguing byline ‘Nothing exists till it is measured’. Since the archive is subscribers-only, I couldn’t read the article or the editorial. Till now.

The article concerns a double-slit experiment, conducted by a researcher at Harvard, Shariar Afshar. Before reading further, familiarize yourself with the Principle of Complementarity, if you haven’t already.

Basically, the experiment shows light displaying wave and particle aspects at the same time, in violation of complementarity. Supposedly, and I’m not too qualified to render this judgement myself, this falsifies the Copenhagen interpretation and the Many-Worlds interpretation as well.

If the experiment is valid and verified, what conclusions can conservatively be drawn?

I’m not sure this is quite so revolutionary as the title suggests (but then again, that’s what New Scientist does every week to sell copies, and good luck to them!). As the discussion below the article admits:

My own view of how to interpret QM is that M Theory will hopefully provide a rather more rigorous formulation of Many Worlds which does not quite appeal to the infinite for each electron or photon, while avoiding the problems inherent in the simple hidden variable interpretation.

Elsewhere, someone rebutted that the sci.physics.research poster misconstrued the experiment:

Then I’m afraid I must admit I’m in over my head here! I’ll leave the discussion to those more capable than I.

No one?

An update:

How is this any different from the Schrodinger’s Cat paradox?

Wait. Wavicle action at the same time? This… this does change things, and seriously, insofar that… okay. Insofar that it is not "This is true, but this is true, and both are true, as long as you don’t measure it. If you measure it like a particle, it is a particle, if you measure it like a wave, it is a wave. But it will never be both at the same time, that is, it is indeterminately both until measured.

If it is measured, and measured as both a wave and particle at the same time, a lot of fairly basic quantum mechanics theories are wrong, I think, because it’s no longer… uhm, deterministic? It is not one or the other but both at once, a different sort of particle.

I think that article does physics a disservice by describing Bohr’s “principle of complimentarily” (that something can be a wave or a particle but not both at the same time) as the orthodox view. It simply isn’t precise enough to be useful. This principle can be interpreted as a summary or a simplification of the actual laws particles obey, but I doubt many practicing physicists would accept it as a perfectly true statement about the way they think the world works.

In standard quantum theory, a particle is considered to be a wave packet: a combination of an infinite number of waves of continuously varying frequency. It’s possible for a packet to be relatively confined to a single spot in space (“particle-like”), or for it to travel coherently, with little dispersion in momentum (“wave-like”). There are an infinite number of possible states that match neither of these descriptions, or both, to varying degrees; but for a wave packet to have an arbitrarily precise position it must have an arbitrarily imprecise momentum, and vice versa. This behavior is perfectly described by the ordinary mathematics of wave propagation (leaving complications accompanying “measurement” out of it).

A quick search for “uncertainty principle wave packet” gave me this page which appears to describe the orthodox view reasonably well.

In short, the result of this experiment is exactly what one would expect based on the rules of quantum mechanics. All it does is demonstrate in an obvious way that Bohr’s principle cannot be exactly true, but that shouldn’t surprise anyone with detailed knowledge of the theory.

This is over my head, as well. So, I’ll post another clarification on the supposed significance of this experiment.