Timeline for What is the "lowest energy"?
Current License: CC BY-SA 4.0
6 events
| when toggle format | what | by | license | comment | |
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| Dec 16, 2018 at 19:09 | comment | added | GiorgioP-DoomsdayClockIsAt-90 | What wikipedia says is that the uncertainty principle may help to understand why, when the system gets the minimum of energy there is still some irreducible kinetic energy. But this has nothing to do with absolute zero. Things go the other way round: at absolute zero the system has to get the minimum energy. Due to quantum mechanics such minimum energy state is not the state with zero kinetic energy. what is wrong is to add the implication no zero energy -> no zero temperature. The thermodynamic temperature is not proportional to the kinetic energy at low temperatures. | |
| Dec 16, 2018 at 18:04 | comment | added | cxx | I am using it to justify exactly that. My intent was to make it clear that there is a difference between the classical minimum and the quantum minimum, which is why we give it a name. Also, I still don't understand why the uncertainty principle doesn't prevent a system from reaching absolute zero. Wikipedia seems to agree with me. | |
| Dec 16, 2018 at 17:29 | comment | added | GiorgioP-DoomsdayClockIsAt-90 | Think of a particle of mass $m$ in a potential well which could be approximated, close to the minimum, by a harmonic potential $\frac{1}{2}( m \omega^2 x^2 - \hbar \omega)$. By construction its lowest eigenvalue is zero. The corresponding eigenstate is a minimum uncertainty wavefunction . Moreover, since the system is in an eigenstate, the variance of the energy vanishes, Therefore, all the measurements of energy will return zero. The argument you are citing is usually used to justify a value of the minimum energy higher than the minimum of the potential energy. | |
| Dec 16, 2018 at 16:42 | comment | added | cxx | @GiorgioP Thank you for pointing out my mistake. Unfortunately, I always thought that this was the case, and I don't understand why it shouldn't be. Is it completely wrong, absolutely and utterly? Could you enlighten me? | |
| Dec 16, 2018 at 8:48 | comment | added | GiorgioP-DoomsdayClockIsAt-90 | Writing that it is not possible to get absolute zero because the system has to satisfy the uncertainty principle is completely wrong. Absolute zero does correspond to the minumum of energy whatever it is. It has nothing to do with energy being zero. One very good reason is that the energy is always definite within an arbitrary constant. | |
| Dec 16, 2018 at 0:28 | history | answered | cxx | CC BY-SA 4.0 |