3 ms·

Maxwell was a giant obviously but with his thought experiment of the Demon (which he quite casually came up with in a letter to a friend) he suspected that he h

Maxwell was a giant obviously but with his thought experiment of the Demon (which he quite casually came up with in a letter to a friend) he suspected that he had successfully poked holes in the second law - to "show that the 2nd Law of Thermodynamics has only statistical certainty" as he put it. So he thought the law was a statistical guide that could be gotten around in special circumstances. It took the thinkers of the time a long time to realise that tracking all the molecules would need energy. Whereas if you re-state the thought experiment using todays technology - "imagine a device that tracks all the molecules and opens a hatch to only let the fast ones through" its obvious to us - with our modern conception of processing - that such a device would need a fair bit of juice. Source: https://archive.org/details/lifescientificwo00knotuoft/page/214/mode/2up?view=theater https://archive.org/details/lifescientificwo00knotuoft/page/...

chriswarbo 5y ago
> its obvious to us - with our modern conception of processing - that such a device would need a fair bit of juice It wouldn't. The hatch itself could operate with no net energy lost/gained, e.g. using a counterweight to cancel out the momentum. Any required calculations could be carried out with a reversible computer, e.g. a billiard ball computer. This way, once our computation is finished, we just can just run it in reverse to get back any energy that was spent (e.g. anything that needed charging during the computation, will get discharged on the way back; and likewise for any lifting, pushing, etc.). The only thing which requires energy is resetting the device. This cannot be done reversibly, since it has to 'forget' whether the hatch got opened or not; i.e. reset(opened) -> init and reset(closed) -> init, so we can't "undo" the 'reset' operation to recover any energy it used.

chriswarbo 5y ago

> its obvious to us - with our modern conception of processing - that such a device would need a fair bit of juice It wouldn't. The hatch itself could operate with no net energy lost/gained, e.g. using a counterweight to cancel out the momentum. Any required calculations could be carried out with a reversible computer, e.g. a billiard ball computer. This way, once our computation is finished, we just can just run it in reverse to get back any energy that was spent (e.g. anything that needed charging during the computation, will get discharged on the way back; and likewise for any lifting, pushing, etc.). The only thing which requires energy is resetting the device. This cannot be done reversibly, since it has to 'forget' whether the hatch got opened or not; i.e. reset(opened) -> init and reset(closed) -> init, so we can't "undo" the 'reset' operation to recover any energy it used.