Maxwell's Demon Soon A Reality?

DMiax writes "Reuters reports that a group of scientists from University of Edimburgh may have realized a nanomolecular engine - a Maxwell's Demon. The device selects and traps other molecules based on their direction of motion. Physicist James Maxwell first imagined the nano-scale device in 1867, and the research team cites him as the basis for their understanding of how lights, heat, and molecules interact. The device is powered by light, and may spur advances in nano-scale technology to new heights in coming years."

Comments

It's neat, but it's not Maxwell's Demon

[Control Group]

Maxwell's Demon was a thought experiment about the possibility of violating the second law of thermodynamics, not a thought experiment about sorting molecules. The idea was that the entropy of the system could be decreased by the demon selectively moving fast molecules from one side of the box to the other, thereby concentrating heat.

This tech is certainly a mechanism for such sorting, but it's powered by external light, so the entropy of the system has not decreased and the second law isn't violated. So, while it's mechanically similar to Maxwell's Demon, it's dissimilar in concept (or should I say, "in spirit" - we're talking about demons, after all).

Of course, TFA doesn't have Leigh claiming that they've come up with Maxwell's Demon, just that he "credits Maxwell for establishing the fundamentals for understanding how light, heat and molecules behave."

None of this is to say that this isn't an impressive feat, and of obvious value in terms of furthering the science/technology of nanomachines, but calling it Maxwell's Demon is missing the whole point of the original thought experiment.

[this text added to waste time between hitting reply and submit]

Not actually a Maxwell Demon...

[kebes]

Let's get the pedantic "This is not actually a Maxwell Demon" comments out of the way first. The original thought experiment of Maxwell's Demon was to suggest a hypothetical creature/device/demon that could watch molecules and make decisions based on what those molecules were doing. By watching the motion of molecules, the demon could open/close a flap and thus sort molecules by kinetic energy. This would allow the demon to generate a hot gas out of nowhere, without any energy input. This would thus contradict thermodynamics (which states that entropy always increases, etc.).

The reason that such a demon cannot be created is that the very act of making an observation (of a gas molecule's trajectory, for instance), requires the usage of energy. And on the scale we're talking about, that usage of energy is exactly the 'work' you are doing to raise the temperature of the gas in sorting the molecules. Thus no such thing as a maxwell demon can be made, and thermodynamics is intact.

This most recent report, as stated, requires an input of energy to move/sort molecules. Thus it doesn't violate thermodynamics and it's not really a Maxwell Demon. The article seems a bit confused on this issue, stating:

As Maxwell had predicted long ago, it does not need energy because it is powered by light.

I would content that the light is an input of energy, and thus saying "it does not need energy" is rather silly.

In any case, the actual research (see David Leigh's page) is about photo-activated molecular shuttles: molecules that switch between well-defined states with input of light. You can thus trap or move other molecules using light. Certainly one step towards the much-anticipated "nanotechnology" but not quite the fine control of molecular positions one would imagine when using the term "Maxwell Demon."

Re:Light coming in?

[Control Group]

Pretty much, yes. The idea of Maxwell's Demon was to violate the second law of thermodynamics - once you include an external power source, its entropy increase has to be included in the system, and now you've just got a heat pump. Doing it on the nanoscale is Really Neat(tm), but it's not Maxwell's Demon.

But then, TFA doesn't have Leigh saying that it is Maxwell's Demon, just that he credits Maxwell with furthering science.