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iwonder...
18th May 2010 - 09:16 PM
Why do quantum mechanical rules only apply to small particles? Why does the wave function collapse when mass increases?

I can't seem to find the answer to this basic question. Maybe you can help?
dhruv8890
19th May 2010 - 10:21 PM
Quantum mechanical rules don't apply to "small" things not as a matter of size, but as a matter of small energy differences b/w states. At a small (lengthwise) scale, the system has very tiny differences of energy b/w its superposable states.
Ron
20th May 2010 - 08:38 PM
A very blunt analogy was explained to me once.
When trying to measure Velocity, the longer the sample, the more accurate the Velocity. When trying to measure position, the smaller the sample, the more acurate the position.
Just a thought,
Peace,
Ron
AlexG
20th May 2010 - 10:49 PM
QUOTE (dhruv8890+May 19 2010, 05:21 PM)
Quantum mechanical rules don't apply to "small" things not as a matter of size, but as a matter of small energy differences b/w states. At a small (lengthwise) scale, the system has very tiny differences of energy b/w its superposable states.

No, actually it is an matter of size. It's a corollary of the uncertainty principle. The smaller the area of space examined, the more accurately position is known, and so the less accurately momentum is known.
prometheus
24th May 2010 - 06:02 AM
The answer to the OP, "Why do quantum mechanical rules only apply to small particles?" is simply that the scale of quantum effects is given by h-bar. if h-bar was different we would see quantum effects at a different scale.

I'm not sure I understand the question "Why does the wave function collapse when mass increases?" Perhaps you could elaborate on what you mean?
light in the tunnel
24th May 2010 - 01:40 PM
QUOTE (AlexG+May 20 2010, 10:49 PM)
No, actually it is an matter of size. It's a corollary of the uncertainty principle. The smaller the area of space examined, the more accurately position is known, and so the less accurately momentum is known.

Ron's statement made sense. If you would take a long exposure of a few particles, the pattern would be more likely to be tighter than if you took the same length exposure of many particles.

Your statement is just saying that if you narrow down where you're looking, a smaller range of point locations is included in the area.
AlexG
24th May 2010 - 06:34 PM
QUOTE
Your statement is just saying that if you narrow down where you're looking, a smaller range of point locations is included in the area.


Yes. And when you narrow down where you're looking, you define the possible values for position more accurately. The smaller the area you consider, the more inaccurately you can measure the momentum, and the wider the range of possible values there can be.

This, and the Pauli exclusion principle, is the source of 'electron degeneracy pressure, which prevents neutron stars from completely collapsing into black holes.

Wiki on electron degeneracy pressure.

QUOTE (->
QUOTE
Your statement is just saying that if you narrow down where you're looking, a smaller range of point locations is included in the area.


Yes. And when you narrow down where you're looking, you define the possible values for position more accurately. The smaller the area you consider, the more inaccurately you can measure the momentum, and the wider the range of possible values there can be.

This, and the Pauli exclusion principle, is the source of 'electron degeneracy pressure, which prevents neutron stars from completely collapsing into black holes.

Wiki on electron degeneracy pressure.

Ron's statement made sense. If you would take a long exposure of a few particles, the pattern would be more likely to be tighter than if you took the same length exposure of many particles.


When Ron said 'the smaller the sample', he was talking about the physical space examined, not the number of particles.
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