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I clearly understand what negative temperature is: if somebody squeezed an amount of energy out of a system, it's temperature drops. If somebody squeezed energy

by lisivka 10y ago

I clearly understand what negative temperature is: if somebody squeezed an amount of energy out of a system, it's temperature drops. If somebody squeezed energy from a system at arbitrary zero point at temperature scale, then system temperature is below zero: system needs energy to return back to zero. Zero point at Kelvin scale is chosen when a system has no kinetic motion. But system at 0°K still has lot of energy, which can be released. I'm talking about energy of "hot" vacuum, which causes Casimir effect. This energy can do some mechanical work even at 0°K, so system still have some energy.

jessriedel 10y ago
Your comment makes many confusing/wrong statements, but in particular this > Zero point at Kelvin scale is chosen when a system has no kinetic motion. is unambiguously wrong. The idea that temperature is monotonic function of kinetic energy is only an approximation to the fundamental definition of temperature, and that approximation isn't valid for systems that have negative temperature.
- lisivka 10y ago
  Definition of Absolute Zero from Wikipedia: > Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. > Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0. > In the quantum-mechanical description, matter (solid) at absolute zero is in its ground state, the point of lowest internal energy. It's still possible to squeeze some energy from a system past Absolute Zero as defined using Casimir effect, so it's possible to reach temperature below 0K. I know, that current interpretation of negative temperatures at Kelvin scale is different, but definition of temperature is different in that interpretation too, so let ignore it.
  - jessriedel 10y ago
    > in the classical description of thermodynamics. The "classical description of thermodynamics" is only an approximation to the fundamental definition I mentioned. I'm sorry, but I won't be able to continue this conversation.

by lisivka 10y ago

jessriedel 10y ago

Your comment makes many confusing/wrong statements, but in particular this > Zero point at Kelvin scale is chosen when a system has no kinetic motion. is unambiguously wrong. The idea that temperature is monotonic function of kinetic energy is only an approximation to the fundamental definition of temperature, and that approximation isn't valid for systems that have negative temperature.

lisivka 10y ago
Definition of Absolute Zero from Wikipedia: > Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. > Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0. > In the quantum-mechanical description, matter (solid) at absolute zero is in its ground state, the point of lowest internal energy. It's still possible to squeeze some energy from a system past Absolute Zero as defined using Casimir effect, so it's possible to reach temperature below 0K. I know, that current interpretation of negative temperatures at Kelvin scale is different, but definition of temperature is different in that interpretation too, so let ignore it.
- jessriedel 10y ago
  > in the classical description of thermodynamics. The "classical description of thermodynamics" is only an approximation to the fundamental definition I mentioned. I'm sorry, but I won't be able to continue this conversation.