At what scale do we start to see quantum phenomena? Is it picometers? Is it a femtometer?

There´s no fixed scale at which quantum effects become evident, less a scale at which you can see them. You can easily make the interference pattern resulting from a double-slit experiment as large as a meter or more. Typically, at the scale of a few atomic diameters (roughly 10^-9 m) you cannot neglect quantum mechanical effects anymore but you cannot reverse that statement: Many properties of solid objects -even large ones- are of quantum mechanical origin, like magnetism and the mechanism of valence and conduction bands in metals and semi-metals.

There´s no fixed scale at which quantum effects become evident

 

I hear you.

 

 

Typically, at the scale of a few atomic diameters (roughly 10^-9 m) you cannot neglect quantum mechanical effects anymore

 

But this is what I was getting at - at what scale can you just not ignore quantum mechanics. Thanks

But this is what I was getting at - at what scale can you just not ignore quantum mechanics. Thanks

 

If the deBroglie wavelength (h/p) is on the scale of your observation, your probably can't ignore QM.

If the deBroglie wavelength (h/p) is on the scale of your observation, your probably can't ignore QM.

 

Please forgive my ignorance, but what is the deBroglie wavelength?

wavelegnth of a particle

 

wavelegnth = plancks constant/momentum

 

usually very very tiny

Ah. So in other words, it doesn't matter at what scale you're studying the wavelength at, it will always display "quantum effects" so to speak.

 

That is something to consider, so thanks for that.

 

Do physicists have a clear-cut way of decided what phenomena can be studied more or less ignoring quantum mechanics and what phenomena cannot?

Ah. So in other words, it doesn't matter at what scale you're studying the wavelength at, it will always display "quantum effects" so to speak.

 

That is something to consider, so thanks for that.

 

Do physicists have a clear-cut way of decided what phenomena can be studied more or less ignoring quantum mechanics and what phenomena cannot?

 

Its usually very obvious if you need to take into account quantum mechanics. Ie if you are dealing with things molecule sized or smaller, its safe to say quantum effects can play a role. With things above that size you just can't measure any difference.

I belive the largest particle seen to exhibit wave-particle duality is a buckyball being passed through two slits.

 

But as swansont said. if the debroglie wavelength is the same order of magnitude of what you are studying the chances are QM will have some noticable effect.

I belive the largest particle seen to exhibit wave-particle duality is a buckyball being passed through two slits.

Ha, I just posted that in another thread, then came here and was going to repeat it, to find you beat me to it! Like he said, largest particle to show wave-particle duality is a buckminsterfullerene (Carbon-60).

Speaking of seeing and taking quantum phenomena into account, are we nearing the scale in consumer electronics such as PCs where you can no longer ignore the Casimir effect in the design?