[ExI] The subjectivity of entropy, the role of the observer...==> Rational metaethics

Eliezer Yudkowsky sentience at pobox.com
Fri Feb 29 15:23:59 UTC 2008

On Thu, Feb 28, 2008 at 8:54 PM, Lee Corbin <lcorbin at rawbw.com> wrote:
>  Almost all the time, I stick with this idea:  Temperature of a
>  gas is the mean kinetic energy of its molecules.

Aren't there vibrational degrees of freedom that also contribute to
kinetic energy, and isn't that why different materials have different
specific heats? I.e., what matters is kinetic energy per degree of
freedom, not kinetic energy per molecule? So you actually do have to
think about a molecule (not just measure its kinetic energy per se) to
determine what its temperature is (which direction heat will flow in,
compared to another material), even if you know the total amount of
heat - putting the same amount of heat into a kilo of water or a kilo
of iron will yield different "temperatures".

But the more important point: Suppose you've got an iron flywheel
that's spinning very rapidly. That's definitely kinetic energy, so the
average kinetic energy per molecule is high. Is it heat? That
particular kinetic energy, of a spinning flywheel, doesn't look to you
like heat, because you know how to extract most of it as useful work,
and leave behind something colder (that is, with less mean kinetic
energy per degree of freedom).

If you know the positions and speeds of all the elements in a system,
their motion stops looking like heat, and starts looking like a
spinning flywheel - usable kinetic energy that can be extracted right

Eliezer Yudkowsky
Research Fellow, Singularity Institute for Artificial Intelligence

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