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Old Feb 23rd 2018, 02:00 AM   #1
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Uncertainty Principle

"Misconception – You cannot simultaneously measure both the position and the momentum of a particle.

Correct Physics – This is the wrong phrasing of Heisenberg’ s Uncertainty Principle (HUP), which actually states that the position and momentum are not simultaneously determined. This has a very different meaning than what is stated above. Uncertainty is a property of the quantum state and not determined by how measurements are done. No matter how a measurement is taken one cannot change the inherent uncertainty determined by the quantum state of the system."
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I still maintain that you cannot simultaneously measure both the position and the momentum of a particle. Simple, unless and until you take the measurement of the position or velocity there is a situation like that of the quantum cat. The cat is both dead and alive untill you open the box.

When you apply Heisenberg Uncertainity Principle you are opening the box.

Last edited by topsquark; Feb 23rd 2018 at 03:15 PM.
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Old Feb 23rd 2018, 06:20 AM   #2
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Avito,

PMB is quite correct in that 'determination' includes not only 'measurement' but also calculation, divine inspiration or any other method.

You are correct in that it also means that determination implies 'opening the box' insofar as the HUP does not apply to events that have not yet happened.
On the other hand the HUP applies to calculations that are purely theoretical ie to 'thought experiments'.

I will leave you to consider the situation 100 years after sealing the cat into the box, with the box still sealed, when the cat is most definitely dead and unmoving (momentum = exactly 0) yet his position is known exactly.
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Old Feb 23rd 2018, 10:28 AM   #3
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From his general phrasing,
I am guessing that Avito's native language is not English
This must make understanding our descriptions of some of the subtleties of Physics difficult.
(it is difficult enough when English is your native language)

Measuring requires that something is done to the particle in order to obtain the measurement.
No mater how delicately the particle is "touched" by the measuring equipment, the properties of the particle will unavoidably be changed.

This is NOT the uncertainty principle.

The statement of the uncertainty principle indicates that the position and the momentum of the particle are not mutually independent properties of the particle.

There is an inherent and fundamental uncertainty in the properties of the particle.
The strangest feature is that different interactions with the particle will experience that uncertainty in different ways;
either as an uncertainty in position, or as an uncertainty in momentum, or as an uncertainty in both.
Actually it is always an uncertainty in both, but one can "choose" to improve precision of the knowledge of one only by reducing the precision of the knowledge of the other.
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Last edited by Woody; Feb 23rd 2018 at 10:42 AM.
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Old Feb 23rd 2018, 09:59 PM   #4
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Originally Posted by avito009 View Post
I still maintain that you cannot simultaneously measure both the position and the momentum of a particle.
"I still maintain" is not a legitimate argument in physics. There are basically two valid methods of argument in any branch of science. Either one proposes a law of physics which is justifiable from observation or one uses the already established laws to derive a conclusion.

To date there is no valid reason to justify the notion of the simultaneous measurement of two conjugate observations such as position and measurement. Even if the uncertainty principle related to simultaneous measurement it still doesn't imply that conjugate variables can't be simultaneous measurements. At best it would imply only that they can't be measured with absolute precision

Originally Posted by avito009 View Post
Simple, unless and until you take the measurement of the position or velocity there is a situation like that of the quantum cat. The cat is both dead and alive untill you open the box.
That has to do with determinacy, not uncertainty. And the situation was proposed to demonstrate that a macroscopic system doesn't have a quantum state, i.e. that the notion is nonsense.

Originally Posted by avito009 View Post
When you apply Heisenberg Uncertainity Principle you are opening the box.
Incorrect. But would you like to present an argument to that effect?
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Old Feb 23rd 2018, 10:05 PM   #5
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Originally Posted by Woody View Post
The strangest feature is that different interactions with the particle will experience that uncertainty in different ways; ...
A particle doesn't experience uncertainty. Uncertainty is a property of the quantum state of a particle. Its not meaningful to apply it to a measurement. Uncertainty is merely the standard deviation of a set of data.
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Old Feb 25th 2018, 09:56 AM   #6
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I agree Pmb!

different interactions with the particle will experience that uncertainty
was poor choice of wording on my part.

Perhaps "exhibit" or "demonstrate" or possibly "reveal" rather than "experience"
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