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marked as duplicate by Chris White, Qmechanic Apr 4 '13 at 16:06

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Possible duplicates: physics.stackexchange.com/q/24068/2451, physics.stackexchange.com/q/54184/2451 and links therein. –  Qmechanic Apr 3 '13 at 23:32
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I sense that the mathematical derivation of the uncertainty principle may not be a sufficient explanation... :) But if you're interested, look at the answer here: Heisenberg Uncertainty Principle scientific proof

Think about how we look at something in macro space - we shine a light on it, such as with a microscope, and see what reflects back. In the case of a very small particle, this light could be as small as one photon - but one photon has enough momentum to push the object we're examining when they collide. So if we want to know where a particle is in space, we bounce a photon off of it - but this accelerates the particle, so now its momentum is "uncertain" (or changed). Likewise if we want to know what its momentum is - now its position has changed.

Whatever technique is used to measure a quantity (photons are just an example), it necessarily has an impact on the subject of that measurement. Thus it is impossible to measure these quantities simultaneously to a degree of precision which exceeds the uncertainty principle's limitations.

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The uncertainty principle is much more than just the statement of the observer effect. –  Andrew Gibson Apr 4 '13 at 1:50
I know this question closed, however let me add a comment. If that measurement "would happen" the system would return reverse time to its past in order to "have it avoided"! It sounds crazy but so it would. –  al-Hwarizmi Jun 29 '13 at 14:35
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You've probably heard the observational reason for the uncertainty principle which basically states that if you measure either position or momentum very accurately your measurement changes the other. That's a really nice hand-wavy explanation but the uncertainty principle is fundamental to waves and is not about measurement.

Check out the Wikipedia article on this. The second paragraph states:

[...] the uncertainty principle actually states a fundamental property of quantum systems, and is not a statement about the observational success of current technology

The article goes on to spell out in detail why this is so.

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