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Atoms at Absolute 0

by claytonh4
Tags: absolute 0, atom, cold atoms, electron, subatomic
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claytonh4
#1
Apr29-12, 04:37 PM
P: 77
Hi everyone, I'm in high school right now so sorry if this question seems stupid or blatantly obvious to most of you, but at absolute zero, I understand atoms in a material cease to move and lose all kinetic energy between atoms, but what about the atom on a subatomic level? I know electrons in an electron cloud are constantly moving around the nucleus at their respective energy levels, but it would seem to me that if you have subatomic kinetic energy, some of that would transfer outward or at least cause friction giving the atom itself thermal or kinetic energy and therefore wouldn't be absolute zero. Can electrons stand still like that if such a temperature was attainable?? Or can they drop energy levels at that temperature to make their energy negligible or what? Thanks!
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Drakkith
#2
Apr29-12, 09:15 PM
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Electrons are not little spheres moving in an orbit around the nucleus. They exist as a standing wave instead. Absolute zero is the lowest possible state that a material can be in, but even at this point these waves still exist. Since they are in the lowest state, there would be no kinetic energy to transfer around.
sambristol
#3
Apr29-12, 11:44 PM
P: 84
Don't worry about asking 'stupid' questions they are usually the best and most fundamental ones. In fact your question opens up a whole new set of ideas quantum mechanics.

Near absolute zero quantum mechanics effects become very obvious. For a start the atoms cant have zero energy (on average) they still have a small amount given by the uncertainty principle. This 'zero point energy' was key to understanding the behaviour of materials at low temps and added greatly to exploiting them.

As with all thermal problems you can just about forget the bound electrons as their binding energy is much much more than thermal energies even at the melting point of metals. 'Free electrons' such as the conduction electrons in metals do have to be considered even at low temps even then they are still subject to the uncertainty principle

The best experimental way to look for this is to measure the specific heat capacity at low temps, as you reduce the temp various 'modes' such as rotation of molecules 'drop out' because the termal energy is below the energy required to make them happen - so heat capacity reduces but it never gets to zero. Specific Heat Capacity is just the thermal energy you need to add to a unit mass of a substance to raise its temp by 1 degree (in whatever units you are using)

Einstein tackled this problem and got it wrong. Debye had a better approach using a very early form of quantum mechanics and (almost got it right)

Hope this helps

Regards

Sam

jay.yoon314
#4
May1-12, 03:48 AM
P: 22
Atoms at Absolute 0

Quote Quote by claytonh4 View Post
Hi everyone, I'm in high school right now so sorry if this question seems stupid or blatantly obvious to most of you, but at absolute zero, I understand atoms in a material cease to move and lose all kinetic energy between atoms, but what about the atom on a subatomic level? I know electrons in an electron cloud are constantly moving around the nucleus at their respective energy levels, but it would seem to me that if you have subatomic kinetic energy, some of that would transfer outward or at least cause friction giving the atom itself thermal or kinetic energy and therefore wouldn't be absolute zero. Can electrons stand still like that if such a temperature was attainable?? Or can they drop energy levels at that temperature to make their energy negligible or what? Thanks!
That's a really good question.

I'll try to answer it to the best of my ability.

There is a quantity called the Boltzmann factor that gives you the "weight" of a particular distribution of discrete quantum energy levels at any given temperature T. In the case that T = 0 K, there will be a probability of zero that even a single atom out of a collection of N atoms, where N can be arbitrarily large, will be in an excited state; that is, in any other state other than the ground state. This result is found, specifically, by dividing the Boltzmann factor by something called the "partition function."

Said in plain English, at absolute zero, all atoms in any collection of atoms will be pretty much guaranteed to be found in their ground states without exception. Since an electron's ground state has a nonzero amount of energy, the answer to your question lies in whether that ground state energy consists of, in part or in whole, of kinetic energy. If the ground state energy of an electron in an atom does have a kinetic component either in part or in whole, then the answer would be no (the kinetic energy of the electron can never be zero), but if this is false, and the ground state has no kinetic component, then the answer would be yes (it can be zero).
claytonh4
#5
May1-12, 06:32 PM
P: 77
Thanks everyone for your answers! I've always heard of the uncertainty principle but never really knew where it could be applied and what it really meant by wave/particle duality. Now I know!
Thanks!


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