There is uncertainty in* measuring* the position and momentum of a particle *simultaneously* and to *arbitrary precision* and this is expressed by the famous Heisenberg uncertainty principle. This is a true fact but the amazing thing is that this uncertainty does not arise from practical limitations of the measuring device. Actually, at the deepest level, the uncertainty principle has nothing to do with taking measurements. It is a law of nature!

Forget about momentum, even the position of a particle cannot be specified precisely. If I understand correctly, the position of the particle you measure might be different from what I measure (even if you and I measure with same device which can measure with arbitrary precision ). In a mathematical sense, the position of this particle is actually a probability distribution. The *act of observing* is the most crucial and provides with an instantiation of the position. These instantiations, of course, need not be the same.

It was startling for me when this whole new interpretation sinked in. Such an interpretation has many philosophical implications as well but it is best not to go down that lane. This rambling is a result of two videos I watched today :-

1) http://www.metacafe.com/watch/883107/quantum_physics_explains_law_of_attraction/

2) The amazing series of lectures by Prof.V.Balakrishnan (balki), at IITM on youtube, http://www.youtube.com/watch?v=TcmGYe39XG0&feature=PlayList&p=0F530F3BAF8C6FCC&index=0

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Varma I do not understand one bit. How is the position different if we are measuring with the same scale.

Uncertainty is inherent in nature. Basically, the position of any object (electrons, protons, you, me etc) is not deterministic but stochastic. By observing, one only samples from this stochastic distribution. The sample you get might be different from what I get.

It seems electrons behave differently when you observe them. In a double-slit experiment, when no “person” is observing we get one diffraction pattern but when someone observes we get a different pattern. Hard to believe but this uncertainty is at the heart of quantum physics. This is what I understood from the videos posted in the blog.