[ExI] fermi question alive and well

John Clark johnkclark at gmail.com
Sat Mar 30 20:04:55 UTC 2019

On Sat, Mar 30, 2019 at 1:05 PM BillK <pharos at gmail.com> wrote:

> > *Heat is incredibly useful, especially in the depths of space.*

The usefulness of heat, that is to say the ability to extract work out of
it, depends on how hot it is. The closer that heat comes to the temperature
of deep space, 2.7 degrees Kelvin, the less useful it is. The equation for
efficiency in extracting work out of heat is 1-Tc/Th when Tc is the
temperature of your cold heat sink (which is never less than 2.7 K) and Th
is the temperature of your hot heat source. If those 2 temperatures are
same then the efficiency is precisely zero.  And that means zero work

> > There could be a whole civilisation living off that 'waste heat'!

If they're still extracting work out of it then it's not waste heat, but
you can be absolutely certain if they are extracting work out of it then
they *WILL *produce waste heat. The point is after you've finished using
energy it is not destroyed but is converted to a higher entropy form that
is much more difficult to obtain work from.

 John K Clark

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