pasar explanation....

heat is low "quality energy", once energy is in this form, you can't convert it back to say nuclear energy.........

which also means, the universe will eventually be a very cold place................the sun and all the stars will expend all its energy through fusion, giving out heat, light, magnetic energies.....once gone, then that's it. No more work can be done.....

pasar explanation....

heat is low "quality energy", once energy is in this form, you can't convert it back to say nuclear energy.........

which also means, the universe will eventually be a very cold place................the sun and all the stars will expend all its energy through fusion, giving out heat, light, magnetic energies.....once gone, then that's it. No more work can be done.....

a photon will still be a photon in space until it interacts with matter

What potential energy the star has would have been converted to all other forms of energy, making the star devoid of anything.....it would just be a hunk of matter approaching zero kelvins it will just be a boring place. If you look at stars that are towards the end of their lives...the fact that radio telescopes can still see them tells you that they are still dimly radiating EM waves, eventually that will also stop and it won't be detectable.

key word is work........energy and work have the same physical units of course...that's your law.

Thermal physics became a discipline in the 1800s because of the industrial revolution. Engineers and physicists formulated ways to exploit energy through machines to do work and very rapidly, they understood that the "process" only/mostly moves one way in order for work to be done. of course, you can still reverse the process but that would entail doing useful work on the system to restore it in its original state......so really, doesn't make economic or physical sense to do so.