Causality of the Heisenburg Uncertainty Principle

[Deathby]

I understand that its been proved that simple locality and causality does not apply to quantum physics, but is there some (known) reason why the heisenburg uncertainty principle works? I know that if we try to measure one property, other properties become less precise, but why does that happen? I read something about it having to do with the Shroedinger wave function, but I couldn't really make head or tail of it.

[atinymonkey]

Shroedingers cat is the usual example given.

 

 

[swansont]

Conjugate variables (momentum/position and energy/time) are Fourier transforms of each other in QM. The uncertainty is inherent in that. e.g. the transform of a delta function (exact value for one variable) is a constant over all space (no knowledge of the other variable)

 

The operators for these variables don't commute, so the physical interpretation of that is that measuring one property changes the other one.

[Obnoxious]

Schrodinger's poor little cat has been put through so much abuse. Only a sick, sick man would put a cat next to deadly radioactive chemicals just for the hell of it.

 

Anywho, it happens because the only way we can detect where something is, is by recieveing something from it, normally, we fire off the something too (usually it is light). Because we fire off the beam to detect it, we invariably alter the velocity and of the object, we know the location at the second the beam returns, but the velocity is lost. It works the other way too based upon similar logic.

[soulestada]

Schrodinger's poor little cat has been put through so much abuse. Only a sick' date=' sick man would put a cat next to deadly radioactive chemicals just for the hell of it.

 

[/quote']

 

Exactly what I have always thought whenever I hear/read about his "thought experiment"---a sick thought for a sick man. Brilliant, yes, but how well is the rest of his mind..?

Sorry, that's all I have to contribute.

[jdurg]

Obnoxious explained it perfectly. In order to observe something, we have to make contact with that 'something' in some manner or another. Generallys speaking, for large objects like people, buildings, cars, etc. the observation takes place via light waves. We see light that is bounced off of the object and into our eyes which allows us to see the object. The objects are so huge in comparison to the thing being used to observe it that there is no visible effect on its position or momentum.

 

When you get to a subatomic level, however, those objects aren't huge in comparison to the light wave. As a result, the act of observing the object causes it to move substantially. Observing an electron using an electromagnetic wave is akin observing a moving car by firing a 2 ton rock at it. When you make contact, you'll know exactly where the car is, but after contact is made the position and momentum of the car are changed significantly. Therefore, you won't be able to know where it will be a short time later.