This is cool. But it should be noted that it has already been proven that there is a minimum amount of entropy associated with a single irreversible bit flip, and as a result Maxwell's demon cannot actually violate the second law of thermodynamics.
That's the trouble with exciting phrases like "This seems to violate the second law of thermodynamics". It is known that Maxwell's demon does not violate anything, and the article does explain this later. But that's not quite the point.
It's direct empirical support for the idea that "there is energy in information", and it demonstrates how even supposedly tried-and-trusted science is still subject to empirical validation.
This is the part I never understood about Maxwell's Demon:
> If the demon itself doesn’t use up any energy (which can be done), entropy would decrease, right?
Would anyone care to explain? Energy isn't spent moving the door around? (Particularly since the demon has to make sure the fast-moving molecules don't go right back through it... though I suppose with a sufficiently large box for fast-moving molecules, this may not happen...)
One nice way to think about is to imagine a very light but strong door, and very massive particles. The energy it would take to move the door back and forth would be trivial compared to the energy of the system.
You can even use a reversible process (e.g. the doors on a spring so the energy put into it to close the door is regained by letting the spring's energy reopen it) to make it use effectively zero energy.
Then all the "energy" in the system is in the demon's observation of the system, and not in the actual mechanics of opening and closing the door.
Energy is a tricky thing, and you have to pay really close attention to the concept in physics class or you'll miss out on it, because it is not at all intuitive. As non-intuitive things go it's actually not that difficult to understand, but it doesn't match with our experience, because our bodies are set up in such a way that even doing nothing requires a certain amount of exertion, and our intuitive attempts to match "exertion" to "energy" produces very bad results.
How much energy does it cost to suspend an object one mile in the air, without it moving up or down? None. The problem is not one of energy, it's of an inability to counter the force of gravity. A hovering helicopter is indeed using a lot of energy, but 0% of the energy is doing work against gravity, it's all going other places.
How much energy does it take to keep an already-in-orbit object in orbit? None. Motion isn't energy. (It can't be, that would crack relativity wide open.)
How much energy is it to work against gravity and go uphill? X. How much energy is it to work against gravity and go back downhill to the same location? -X. Whats the net energy used against gravity? 0. Again, if we try to do this with our bodies, we are using lots of energy to do it, you can trace the chemical energy going out of the ATP and being used for things, but if you sum it all up after a round trip it is all going to things other than gravity; every joule of gravitational potential energy you gained going uphill was precisely returned to you on the return trip.
So yes, Maxwell's Demon can, in principle, use no energy manipulating the door. It'll need a bit to open and close it, but since we're in a thought experiment, whichever direction is increasing the potential energy of the system, it will get 100% of it back moving the other way if you set it up with a force to work against, like a 100% perfect spring. (Or it is balanced, moving across the set point, and since it's 100% efficient we never lose any.) Movement is not energy.
You are referring to Landauer’s principle with the "minimum amount of entropy associated with a single irreversible bit flip". While it is proven (or "trivial" if you believe some scientists on the subject), its applicability to all possible computation systems is not clear.
"The bead is driven as a mini-rotor, with a information-to-energy conversion efficiency of 28%."
What exactly are the units of information in this case? The statement doesn't make much sense as I think the OP just took the quote out of context.
A simpler way to visualize what's going on: imagine your trained dog picks up a ball and tosses it up in your hands and you catch it. Now the ball is 1.5 meters higher off the ground than it was before. E = m * g * h = 1 kg (it's a heavy ball, all right?) * 9.8 m/s^2 * 1.5 m = 14.7 J. That's 14.7 J you got for free. But the dog expanded more energy than that to pick up the ball, overcome gravity and air resistance and toss it up. The total system (= you + ball + dog) lost energy and increased entropy.
I may be missing the point here... but this seems like a simple feedback system, just with a slightly more complex energy exchange (i.e. the experimenters observation and action) which hides the fact and allows it to be presented as a "paradox".
In actual fact this is just bad reporting, really. The experiment is about showing energy exists in information, which it seems to do successfully.
My reply:
One of the benefits of relying on crowdsourcing for quality judgements (i.e. using people to determine what content goes on your site), is that by and large the system takes care of itself - good stuff generally floats upwards and bad stuff generally floats downwards. The advantage of this is that the system can respond to current events much much more quickly than any kind of curated medium. Many stories are 'broken' in places like hackernews and reddit long before mainstream media catch the story.
One of the downsides is that the system does have a fair dose of randomness. A story with 50 votes is not necessarily worth half a story with 100 votes. Likewise, some stories will get missed - perhaps the right people weren't looking at the new queue when it was submitted, or perhaps another high-profile story was taking up people's attention.
This is the tradeoff you make; increased reaction time for reduced recall. I.e. hackernews and sites like it feature fresher content with the drawback that some stories don't make it.
Fortunately, this system takes care of the drawback by virtue of the fact that if an important story is somehow missed, the chances are it will be submitted again by a different user and have another chance to rise.
Which is exactly what happened here. The system works, it self-corrected the omission of this story. How cool is that!
Which is exactly what happened here. The system works,
And one of important parts of that system is RiderOfGiraffes letting us know when the dupe-filter has failed, and pointing us to previous discussions, when they exist.
Yeah, I did take a look... I felt that it added nothing to the conversation. What's the problem with dupes? 2 sets of insightful conversations instead of one? So? Obviously if more than a few dupe stories get through then that's something to be solved technically. But one or two dupe stories on the homepage now and then? So?
Compare with a huge history of comments saying nothing other than "this is a dupe [link]". especially when the link has no comments attached to it.
edit: example on an "A humble programmer" submission they wrote this comment http://news.ycombinator.com/item?id=1895032 linking to ten other submissions of the same article, none of which had any interesting comments, and all of which had exactly the same content for the link. What's the point in that?
I can totally see the point in saying "there's some interesting discussion over here [link]", but it seems mostly his efforts to de-dupe add nothing of value.
Similar to a bead in an electric field, reversing entropy to climb up an energy hill through the magic of information. I guess that makes us all Daemons?
