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There's a couple of things going on here. Absolute zero does exist theoretically. In a quantum system, you can describe a system in it's lowest energy state and that's absolute zero. Whether you can reach that in an experiment or not is another question.The Fermi energy is just the energy of the highest quantum state in lowest-energy configuration of some system. Fermions can't occupy the same states, so if you have 100 energy levels of increasing energy and 50 Fermions, the lowest energy state will have levels 1-50 occupied, and the Fermi energy will be given by the 50th energy level.
I think you're confused on what zero-point energy is. From wikipedia, "Zero-point energy is the lowest possible energy that a quantum mechanical physical system may have; it is the energy of its ground state." It does exist and agrees with what I said above about the Fermi energy. I'm not sure where this idea of all motion ceasing comes from. Zero-point energy states can definitely have non-zero momentum. Not to tout my credentials too much, but I have studied Fermi-Dirac statistics and the Fermi energy in graduate level physics coursework, so I'm quite sure what I'm saying about them is correct. I think this was the book we used, if that helps.
So, how far from 0K do you think 170nK is?
Think about what the ''zero'' in zero-point means. Go back to when we believed you could cool the system to absolute temperatures. We cannot cool our system to an absolute freezing temperature. We can only get so close, and then it evades us. There is always thermodynamics in a system. I can settle with ''ground state'' this is very true. I don't settle with the terminology that we can make soemthing reach a zero-point temperature. That is false.
Actually, I'm referring to temperatures that have been created by scientists in labs.EDIT: I was merely pointing out that, despite your assertion - "Absolute zero is like one of those mythical fairytales your grandma reads you at night. It doesn't exist."While I agree we will probably never get all the way there, we have created temperatures that come remarkably close to 0K, so I would not exactly describe it as a fairytale. As we reached 0.00000017K about fifteen years ago, it's perhaps being pedantic to say 0K does not exist.At what temperature do you think we might declare victory?
Quote from: QuantumClue on 01/02/2011 12:42:34Think about what the ''zero'' in zero-point means. Go back to when we believed you could cool the system to absolute temperatures. We cannot cool our system to an absolute freezing temperature. We can only get so close, and then it evades us. There is always thermodynamics in a system. I can settle with ''ground state'' this is very true. I don't settle with the terminology that we can make soemthing reach a zero-point temperature. That is false.Having a personal dislike for the terminology is different than having a legitimate beef with the science. Your personal opinion is unlikely to change scientific consensus on the terminology:1) Zero-point energy means essentially the quantum ground state, which is not necessarily zero-energy.2) Absolute zero is taken to be the case of a system in it's lowest energy state, which is not zero-momentum (which is classically zero movement).3) The Fermi energy is the energy of the highest quantum particle when a system is at absolute zero. This doesn't have to be physically achievable, but it is a theoretical and physical limit on the system.All these are perfectly well defined and are theoretical as well as physical limits, regardless of whether you can obtain them in a lab--no matter how much you cool something you can get as close as you want to absolute zero without passing it, the same with the Fermi energy.
You do realize it exists as a limit, which is perfectly well defined?