Wednesday, September 19, 2012

Heisenberg in Question

Have you ever heard the story about Heisenberg driving on the autobahn? He's speeding along, and he gets pulled over. The police officer says, "Do you have any idea how fast you were going?!" And Heisenberg says, "No. But I know exactly where I was!"

Some of you may have released a slight chuckle at this clearly fictional story. It's a joke about Heisenberg's uncertainty principle, which says that if you measure a quantum particle's momentum, its position will be overwhelmed by uncertainty. And vice versa. So you can measure properties of quantum particles, but you can't measure all of them.

But it turns out this common explanation of the uncertainty principle, isn't quite true. It is possible, with very advanced methods, to measure a quantum particle such that you do not disrupt it to the point of inducing the uncertainty principle.

Don't worry: Heisenberg's principle is safe. Measurement induced uncertainty is not actually at the heart of the uncertainty principle. Uncertainty in a system may come from different places, and may in fact be intrinsic to the system (meaning, electrons in your body may not exist in a definite position, even if you don't measure them. Uncertainty is a natural part of life for quantum particles). So the uncertainty principle still defines the uncertainty of a quantum system, but that uncertainty may not necessarily come from someone measuring it.

This is a subtle point, and I try to clarify it in this week's podcast, with the help of Dr. Aephraim Steinberg of the University of Toronto. Go have a listen: it could make you rethink this pillar of quantum mechanics, and remind you that uncertainty is just a part of quantum life.

Dr. Steinberg would like to thank his collaborators on this work: Lee A. Rozema, Ardavan Darabi, Dylan H. Mahler, Alex Hayat, and Yasaman Soudagar. And, the physicists who's work led to this new experiment: Dr. Masanao Ozawa at the Graduate School of Information Science in Sendai, Japan; Dr. Weissman et. al. at the Centre for Quantum Dynamics in Queensland, Australia; and Dr. Yuji Haswgawa et. al. at the Vienna University of Technology, in Vienna, Austria.

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