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Name: phoebe
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Date: 1999 

Re: Heisenberg's uncertainty principle Does the position/velocity concept pertain only to electrons and to other sub-atomic particles, or, can it apply to other measurable things in the real world like trains or planes? This may sound idiotic, but in Greene's book, he says the "ideas directly apply to all constituents of nature." Are man-made things considered "con- stituents of nature"? Probably not...I'm not a scientist...clearly.

Yes, the uncertainty principle applies to all objects. There is no distinction between natural and man-made things. However, it works so that the uncertainty in the product of position and momentum is a constant small number. For small objects like electrons, this can mean a considerable uncertainty in its position, or in its velocity. However, momentum is the product of mass and velocity. For more massive objects, a small uncertainty in momentum makes for very little uncertainty in velocity. For all practical purposes, uncertainty is insignificant for macroscopic objects.

Richard E. Barrans Jr., Ph.D.

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