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Information and energy

  1. Nov 23, 2013 #1
    "Physicists in Japan have shown experimentally that a particle can be made to do work simply by receiving information, rather than energy."

    It seems to be something like a demonstration of Maxwell's Demon.


    My question is:

    Can the conversion of information into energy work in reverse? In other words, can energy be converted to information? How would that work? Does it actually happen?
  2. jcsd
  3. Nov 23, 2013 #2
    In this case information and entropy are equivalent.
    They converted thermal energy into an energy form of lower entropy i.e. lowering the entropy and therefore the information content of the box. But the total amount of energy staid the same. So claiming that they converted information to energy is misleading. They didn't create any energy. However they were only able to do so because they increased the entropy of the rest of the universe. The camera, computer, etc. created many orders of magnitude more entropy/information than was lost in the box.

    And about converting energy to information - that's very simple. Just connect a battery to a resistor. Electric energy has low entropy, thermal energy posesses high entropy. So in that way you can convert an energy form of low information content into one with high information content.
  4. Nov 23, 2013 #3

    I am not claiming any violation of 2nd Law or anything like that.

    I am asking about the reverse - converting energy to information.

    If it can go one way, it ought to go the other way too.

    It looks to me like converting electrical energy to thermal enegy is just moving one form of energy to another - no net change information.
  5. Nov 23, 2013 #4
    But that's exactly what the article is about. Converting one form of energy to another.
    They converted thermal energy to kinetic energy and electric potential energy. And they reduced the entropy in the box as a result. The article just uses the word information instead of entropy to make it sound more interesting.
    If you connect a resistor to a battery you do the opposite, converting electric into thermal energy.
    And yes, there is a net change in information. At least when you define information in the physical sense.
  6. Nov 24, 2013 #5
    So the statement in the article that clearly makes a distinction between information and energy is wrong? Notice the "rather than energy" part of the statement.

    ""Physicists in Japan have shown experimentally that a particle can be made to do work simply by receiving information, rather than energy."
  7. Nov 24, 2013 #6
    I think, that information is an attribute of energy.
    For example computers use two different energy levels (for 0 and 1), to store and transfer information.
    So information is an energy state, and I don't think that we can change information without changing the energy state.
  8. Nov 24, 2013 #7
    The "rather than energy" I think is intended to mean that there is no direct thermal contact and direct energy transfer. Since exchange of information at a constant temperature is an entropy change at constant temperature, there is an energy transfer. I believe this is generalized even when temperature is not constant, but I don't know for sure.

    I don't think that "wrong" is the best word, but maybe a bit misleading. If you have two systems and when they exchange information in a particular manner the energy balance changes in a particular way, doesn't it make sense to say that they have exchanged energy?

    I don't know about this particular experiment, but one of my professors was doing a lot of theoretical work on Maxwell's Demon and working to show that any receipt of information requires an exchange of energy. I know that he published a fairly well received article showing that every quantum measurement (exchange of information) implies an exchange of energy.
  9. Nov 24, 2013 #8
    What gives you that idea? Information and energy are of course two very different concepts. Information and entropy however are the exact same thing in the context of this experiment.
  10. Nov 24, 2013 #9
    This is the statement in the article:

    ""Physicists in Japan have shown experimentally that a particle can be made to do work simply by receiving information, rather than energy."

    And here's another statement in the article:

    "The breakthrough in the latest work is to have quantified the conversion of information to energy."

    The article talks about converting information into energy. Your comment was:

    "But that's exactly what the article is about. Converting one form of energy to another."
  11. Nov 24, 2013 #10
    Yes, the article is about converting one form of energy into another. Thermal energy into kinetic and electric energy. The physicists were able to do that by extracting information from the box (i.e. lowering the boxes entropy). But no information disappeared in this experiment and no energy was created either.
  12. Nov 24, 2013 #11
    Erm does that mean that information and energy are like mass and energy? Sorry for the dumb questions probably totally unrelated I don't mean interchangable but then again they must be if they are doing this experiment. But yea as einstein said mass=energy does information perhaps equal energy or is that way off or I mean can it be changed to energy. Btw I aint even sure what information is it probably shows. Seems like this abstract thing to me where the charges, spins and other such things are somehow stored.
    Last edited: Nov 24, 2013
  13. Nov 24, 2013 #12

    That is what I am asking too. The article specifically mentions "information energy equivalence".

    The energy comes from the information not from another form of energy. They even calculated the energy value of a bit of information and estimated they could exploit about a a quarter of it.

    But what I am also asking is that if you can convert information to energy then can you do the reverse. I am not meaning that energy may somehow involved in gain or loss of information, which I think is well-understood.
  14. Nov 24, 2013 #13
    Of course if you thought about it logically it is all information. As in the universe is keeping books on what is occuring, as in the changes well maybe not keeping accounts due to conservation laws it has no call to do so. Yea man this kinda thing would only seem to heighten those physical axioms.
  15. Nov 24, 2013 #14
    What they calculated was how much high entropy energy (e.g. heat) you can convert to low entropy energy (e.g. electricity) per bit of information/entropy.
    This is closely related to Carnot's theorem, but more fundamental.
    They did not convert information to energy.
    Their experiment is a form of Maxwell's demon
    Read that article. It explains that stuff quite well.
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