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How Uncertain Was Heisenberg?

I want to continue our little expedition into the world of quantum weirdness by turning to the Heisenberg Uncertainty Principle.

The Uncertainty Principle basically states there's an intrinsic limit on the accuracy of simultaneous measurements of certain pairs of variables. If, for example, you want a perfect measurement of an electron's position and its velocity at the same time, you can't get them.


If you get an infinitely accurate measurement of where the electron is, then you are infinitely ignorant of, and can't know, how fast it's moving. If you get an infinitely accurate measurement of how fast the electron is moving, then you are infinitely in the dark about its position.

Compare this with Newtonian (also called "classical") physics, where I can — in principle — know and follow every particle and all their properties with infinite precision. (Yes, I am neglecting Chaos Theory, for now).

The Uncertainty Principle has nothing to do with sloppy tools. It's not your cheap ruler or radar gun that makes the results inherently uncertain. It's nature. The fundamental limit on knowledge of a physical system is, well, fundamental. Nature has set this boundary, not the budget of the NSF.

In my eyes the principle says something even weirder. In a sense, the Uncertainty Principle says that, at the quantum level, things don't have properties. At least they don't have properties the way we think that classical objects do.

You think your dog has a weight. You think your car has a length. You think of these properties as being inherent to the world and the objects we find in it. But the Uncertainty Principle says that, at some level, the world turns fuzzy and the idea of properties as perfectly objective, knowable attributes gets a little ... um ... fuzzy.

You can keep up with more of what Adam Frank is thinking on Facebook and on Twitter @AdamFrank4. His latest book is About Time: Cosmology and Culture at the Twilight of the Big Bang.

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