3 ms·

Its obvious to us 150 years later because we are very familiar with the idea that processing data needs energy, its as natural an idea to us as plugging in a ph

Its obvious to us 150 years later because we are very familiar with the idea that processing data needs energy, its as natural an idea to us as plugging in a phone. It wasn't so obvious in 1867.

engineer_22 5y ago
I don't think you give Maxwell enough credit.
- codeulike 5y ago
  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.
philipswood 5y ago
That's the thing: it doesn't! (i.e. Processing data doesn't need energy - more correctly "work") In the limit, you can process information adiabatically.(*) i.e. you can perform a computation without heat exchange, and you can perform computations reversibly. Maxwell's demon as a thought experiment is actually quite a deep and subtle probe into the boundary between information and thermodynamics. What you CAN'T do adiabatically or reversibly is clear or set bits and throw away their initial state. In theory you could make a classical mechanical turing machine that could perform a computation for an arbitrarily small amount of work, but to prepare a blank tape for it (or to configure a tape into a known configuration) will take a certain minimal expenditure of work. * Ignoring Quantum Physics for now The Wikipedia page for Reversible Computing might be a place to start reading if you're interested in following up.

Its obvious to us 150 years later because we are very familiar with the idea that processing data needs energy, its as natural an idea to us as plugging in a phone. It wasn't so obvious in 1867.

engineer_22 5y ago

I don't think you give Maxwell enough credit.

codeulike 5y ago
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.

philipswood 5y ago

That's the thing: it doesn't! (i.e. Processing data doesn't need energy - more correctly "work") In the limit, you can process information adiabatically.(*) i.e. you can perform a computation without heat exchange, and you can perform computations reversibly. Maxwell's demon as a thought experiment is actually quite a deep and subtle probe into the boundary between information and thermodynamics. What you CAN'T do adiabatically or reversibly is clear or set bits and throw away their initial state. In theory you could make a classical mechanical turing machine that could perform a computation for an arbitrarily small amount of work, but to prepare a blank tape for it (or to configure a tape into a known configuration) will take a certain minimal expenditure of work. * Ignoring Quantum Physics for now The Wikipedia page for Reversible Computing might be a place to start reading if you're interested in following up.