4 ms·
"It is literally impossible to turn heat, by itself, into anything useful. That's the 2nd law of thermodynamics" That's not quite true/relevant. Matter can be
by benj111 7y ago
"It is literally impossible to turn heat, by itself, into anything useful. That's the 2nd law of thermodynamics"
That's not quite true/relevant.
Matter can be turned into energy, energy can be turned into matter, theoretically at least. More practically a Stirling engine or peltier will turn heat into electricity, and filament bulbs did a good enough job of turning heat into light.
Plus you can still cheat the 2nd law locally. I can heat my house in winter for example, it isn't just a slow uniform slide to the heat death of the universe.
- AlexandrB 7y ago> That's not quite true/relevant. It’s actually extremely true and relevant. > Matter can be turned into energy, energy can be turned into matter, theoretically at least. None of these conversions are 100% efficient. The second law effectively puts limits on the efficiency of heat engines[1] that depend on the difference between “hot” and “cold” in the engine. At low temperature differences, the theoretical efficiency is extremely poor[2] and the practical efficiency is even worse. Peltiers are not exempt from this either. [1] https://en.m.wikipedia.org/wiki/Carnot_cycle https://en.m.wikipedia.org/wiki/Carnot_cycle [2] https://en.m.wikipedia.org/wiki/Heat_engine#Efficiency https://en.m.wikipedia.org/wiki/Heat_engine#Efficiency
- benj111 7y agoI'm not saying any of it is efficient, just not 'literally impossible'.
- knodi123 7y agoI said "heat, by itself", not just "heat". And I stand by what I said. It is fundamentally correct. The state of entropy of the an isolated system will always increase over time. Yes, you can bring in other things, like an outside system or additional useable energy, but that only disproves the misquoted version of my statement.