Uncertainty Principle question

[stockr21]

Warning: My understanding of physics is minimal let alone Quantum Mechanics so please excuse (but feel free to correct) my misunderstandings.

My understanding of the Uncertainty Principle is that because photons have to hit a particle so that we can view it, we can never be certain of position and velocity. The greater we care to know the position, the higher intensity light waves must be fired at the particle, which in turn affect the velocity.

My question, is that just because we cannot know, should this mean that particles do not have both a definite velocity and position?

Secondly, is it possible in the future that though greater understanding and discoveries of other laws of physics and the universe that we could determine the velocity and position because we no longer have to use a photon to "view" the particle, but can know where it is through some other method? Possibly similar our abilities to assume black holes and dark matter exist because we see their gravitational effects on visible matter?

Again, bear with me if I'm making some dramatic errors in my assumptions of the Uncertainty Principle. Thanks so much for the help!

 

[Drakkith]

I've read two ways of looking at this. One is that your method of observation ALWAYS alters something with whatever you are observing.

The other is that observation doesn't really do anything, it is actually the particles themselves that are ALWAYS uncertain, even when you aren't observing them.

I am unsure which one is correct.

 

[khemist]

From wikipedia:

"the principle implies that it is impossible to determine simultaneously both the position and the momentum of an electron or any other particle with any great degree of accuracy or certainty. This is not a statement about researchers' ability to measure the quantities. Rather, it is a statement about the system itself. That is, a system cannot be defined to have simultaneously singular values of these pairs of quantities. The principle states that a minimum exists for the product of the uncertainties in these properties that is equal to or greater than one half of ħ the reduced Planck constant (ħ = h/2π)."

http://en.wikipedia.org/wiki/Uncertainty_principle

 

[jtbell]

The uncertainty principle is a statement about the properties of QM wavefunctions or states, and is derived from more fundamental principles without any reference to any particular measurement process.

One way to do it is to start with the assumption that a particle with a precise momentum p is associated with a wave that has wavelength \lambda = h / p (de Broglie's formula), and a particle with an uncertainty in momentum \Delta p is represented by a sum (superposition) of many waves with different wavelengths that are in that range of momentum. The resulting wave has a peak (a "wave packet") with a width in position \Delta x. It can be shown using the mathematics of Fourier analysis that no matter what the "shape" of this packet is, it must satisfy the relationship

\Delta x \Delta p \ge \frac{h}{4\pi}

For a qualitative example of this wave addition, see this post.

 

[Drakkith]

The uncertainty principle is a statement about the properties of QM wavefunctions or states, and is derived from more fundamental principles without any reference to any particular measurement process.

Got it!