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posted by martyb on Friday March 24 2017, @05:27AM   Printer-friendly
from the can't-even-quit-the-game dept.

In 1912, chemist Walther Nernst proposed that cooling an object to absolute zero is impossible with a finite amount of time and resources. Today this idea, called the unattainability principle, is the most widely accepted version of the third law of thermodynamics—yet so far it has not been proved from first principles.

Now for the first time, physicists Lluís Masanes and Jonathan Oppenheim at the University College of London have derived the third law of thermodynamics from first principles. After more than 100 years, the result finally puts the third law on the same footing as the first and second laws of thermodynamics, both of which have already been proved.

To prove the third law, the physicists used ideas from computer science and quantum information theory. There, a common problem is to determine the amount of resources required to perform a certain task. When applied to cooling, the question becomes how much work must be done and how large must the cooling reservoir be in order to cool an object to absolute zero (0 Kelvin, -273.15°C, or -459.67°F)?

The physicists showed that cooling a system to absolute zero requires either an infinite amount of work or an infinite reservoir. This finding is in agreement with the widely accepted physical explanation of the unattainability of absolute zero: As the temperature approaches zero, the system's entropy (disorder) approaches zero, and it is not possible to prepare a system in a state of zero entropy in a finite number of steps.

https://phys.org/news/2017-03-physicists-impossible-cool-absolute.html

[Abstract]: A general derivation and quantification of the third law of thermodynamics


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  • (Score: 1, Informative) by Anonymous Coward on Friday March 24 2017, @06:56AM (1 child)

    by Anonymous Coward on Friday March 24 2017, @06:56AM (#483549)

    Apparently less than zero is still possible though:

    That a system at negative temperature is hotter than any system at positive temperature is paradoxical if absolute temperature is interpreted as an average kinetic energy of the system. The paradox is resolved by understanding temperature through its more rigorous definition as the tradeoff between energy and entropy, with the reciprocal of the temperature, thermodynamic beta, as the more fundamental quantity. Systems with a positive temperature will increase in entropy as one adds energy to the system. Systems with a negative temperature will decrease in entropy as one adds energy to the system.

    https://en.wikipedia.org/wiki/Negative_temperature [wikipedia.org]

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  • (Score: 1, Informative) by Anonymous Coward on Friday March 24 2017, @07:50AM

    by Anonymous Coward on Friday March 24 2017, @07:50AM (#483559)

    actually the problem comes from trying to define temperature for a system that is not at thermodynamic equilibrium.
    For any system that is at thermodynamic equilibrium, you can define a temperature using statistical physics, and it will be positive.
    You can then derive the relationship between the temperature and the entropy (and other thermodynamic quantities).
    If you then use these relations for a system outside of equilibrium, then you get "negative temperatures".