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."

Possible to make unlimited energy?

[UbuntuDupe]

The Wikipedia article [wikipedia.org] goes to great lengths to explain how the demon can't violate the 2nd law -- that it must delete information, which increases entropy. Okay. But what keeps it from violating the 1st law: that energy is conserved?

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]

Off Topic - But WTF is Opinion Center Intel

[Ranger]

Today, I see this Opinion Center with Intel under it. I check my Preferences to see if I can select other Opinion Centers or turn it off. I can't. So I go and take a look. It's a paid advertiser section. That's fine, but please label it for what it is, a Paid Sponsor Section. It's not an opinion center.

Mabye there's a place to make a comment or complaint about this, but it wasn't obvious so I posted it here.

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 [wikipedia.org] 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 [ed.ac.uk]) 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.

Re:Possible to make unlimited energy?

[Stile 65]

You're correct, but creating and keeping a gradient also requires energy. That energy is given to the rotaxane molecules in the form of photons.

How it works

[baby_robots]

I am currently working towards a PhD in this subject. I think that the first thing to realize is that he has not yet made a motor. He has molecular ratchet as proof of concept towards a molecular motor.
          In layman's terms this is how the ratchet works. First, the molecule is essentially a dumbbell with a ring around it. The ring can move freely back and forth across the dumbbell, but prefers to be at either end. The dumbbell can be bent only near one end, which prevents the ring from moving. The ring catalyzes the transition from bent to strait, to allow motion. The thing is, is that the ring needs to be next to the bend for a significant amount of time to unbend the dumbbell.
            So, when the ring is next to the bend, it can straiten it temporally to move across. When it is far away, it can no longer move across the bend, and since the second binding site is far away from the bend, it is stuck there. If you have two dumbbells looped end-to-end with one ring, then you would have a molecular motor. The ring is acting as "Maxwell's Daemon" to allow movement across the system.

Here's a link to the actual journal article if you care to read: http://www.nature.com/nature/journal/v445/n7127/pd f/nature05452.pdf [nature.com]

Re:Possible to make unlimited energy?

[Dilaudid]

The reason the wiki article goes on about the second law (entropy increases) is because the first law (energy is conserved) is seen as being fairly obvious, e.g. a ball will never bounce higher than the level it was dropped from, and the first law applies both forwards and backwards in time. The second law is weird, since it is time inhomogeneous (entropy increases when time goes forward, and therefore would decrease as time goes backwards), and it seems to be more a statistical result than a scientific one.

It's interesting to note that the first law, conservation of energy, is not true within General Relativity within any bounded region, due to the existence of gravitational waves. Here's an article about it http://math.ucr.edu/home/baez/physics/Relativity/G R/energy_gr.html/ [ucr.edu]. I provide only this as evidence that I'm not talking out of my arse - I could understand GR once, many years ago, but not now.