0
$\begingroup$

Sounds absolutely ridiculous, for vacuum is no 'material' in strict sense. But special relativity tells me that length may be contracted or expanded. I find no problem in extending this idea, that space itself may be compressed or expanded, and if it's so, why can't we devise a piston and cylinder like setup where piston moving in and out compresses/decompresses the vacuum/empty space, atleast this is possible theoretically to build a heat engine with vacuum acting as the working material. Is this even possible? If yes, then in what domain , I mean, if not classical then in relativistic or quantum physics? Moreover, will it be an ordinary heat engine or will it supercede , in terms of efficiency? Any suggestions are welcome.

$\endgroup$
  • $\begingroup$ Vacum has no specific heat, i.e. temperature changes won't produce heat. $\endgroup$ – TheAverageHijano Feb 14 at 9:16
1
$\begingroup$

Maybe, if you consider light pressure, vacuum HAS a temperature; light pressure from a thermal background could, ideally, expand a volume (by pushing a light sail) while lessening (by Doppler-shifting the thermal light toward the red) the temperature of the vacuum.

The practical problem, though, is that equilibrium of radiation in a vacuum doesn't happen on short timescales. No human lifespan will ever see the photon/photon interactions in any real volume cause a return to equilibrium spectrum after a disturbance. You cannot expect to ever see a second cycle of such an engine, because unlike an 'ideal' gas of weakly-interacting particles, a vacuum is a gas of noninteracting photons.

The temperature of 'the vacuum' is measurable, and that tells us of the conditions at the creation of the universe, because it hasn't been re-heated since. Dust can be heated by starlight, but not vacuum.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.