Physics Help Forum Principle of uncertanties

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 Jul 16th 2008, 09:57 PM #1 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 Principle of uncertanties As we all know, when we are making observations by eyes, photons must have reached the object we would like to observe ahead of any images seen by us. However, this would force the quanta inside to be changed into another stage. Does it mean that we can never know the "true" property of matter? Could there be something other than light which can be used for observation?
Jul 17th 2008, 06:17 AM   #2

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 Originally Posted by werehk As we all know, when we are making observations by eyes, photons must have reached the object we would like to observe ahead of any images seen by us. However, this would force the quanta inside to be changed into another stage. Does it mean that we can never know the "true" property of matter? Could there be something other than light which can be used for observation?
The Heisenberg Uncertainty principle applies for any pair of "conjugate" varaibles. The origin of the principle is rooted in the Mathematics that Quantum Physics is based on. The physical interpretation of the principle is that we can only measure one of the conjugate pairs with absolute precision. The measurement technique is typically direct, as in the case of a position measurement, but does not have to be. Another way to consider the Uncertainty principle is to think of it as a consequence of the probabilistic nature of Quantum Physics.

The usual example used to explain the Uncertainty principle is to measure the position of a particle with increasing precision by "looking" at the particle. In order to "see" the particle better we have to apply photons of higher and higher energy, so we have less and less of an idea of the exact momentum of the particle.

As far as the nature of the particles we are studying, we would have severe difficulties in observing them directly anyway. Most theories have the fundamental particles in nature as point particles so we couldn't see them anyway. Even if this is not correct the size of these particles must be orders of magnitude smaller than an atomic nucleus and so would take us (probably at least) generations to be able to look at anyway. And even if that is true, it is likely that a fundamental particle's radius is on the scale of theorized quantum fluctuations of space-time and so would be unobservable anyway.

-Dan
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Jul 17th 2008, 09:59 AM   #3
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I believe Topsquark gave you an excellent answer.
However, related to
 Could there be something other than light which can be used for observation?
I think electrons can be used to "see" objects, this is the case in electron microscopes. Nevertheless, it doesn't solve the problem "photons must have reached the object we would like to observe ahead of any images seen by us. However, this would force the quanta inside to be changed into another stage."
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