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Quantum Mechanics Involved In Photosynthesis
Kristina at Science News writes "We all learn about photosynthesis in school: sunlight in, plant food out. Not well understood is how this process achieves its initial and uniquely high efficiency in capturing the energy of a photon. Quantum mechanics may be at work in the electron transfer process inside chloroplast, giving electrons the chance to consider many paths at once before choosing the best one."
It's been a long time since I've taken a biology class, but the way I remember it is the sunlight hits the plant and the plant makes food with it, like tacos. Also, I think some birds fuck some bees or something. It's all very confusing.
Ah, yes... I remember being told about that last part in The Talk from my parents. I was afraid to go outside for weeks.
When someone says, "Any fool can see
To be honest, the result here, while important, is entirely unsurprizing. What you're dealing with here is bound electrons, moving from say, a chlorophyll group to a tyrosine amino acid residue. There's nothing knew that electrons, in particular bound electrons (such as in an atom or molecule) can only be accurately described quantum-mechanically. Electrons move through QM 'tunneling' quite a bit, so you simply cannot accurately describe electron-transfer kinetics (which is what's going on here) without QM.
No, it does not. First off, it spells trouble that you seem to view that as a desired end result. Hardly a good way to do science. Second, there is no good reason to believe that the brain cannot be described in terms of straight-up chemistry and biochemistry. We don't know how the brain works, but that doesn't mean it's unexplainable in terms of what we already know. There are plenty of things we haven't fully understood in biochemistry, but that doesn't mean they're generally believed to be unexplainable in the current framework of things. Occam's razor would dictate that that idea should be disregarded until there is some evidence that would make it necessary. No such evidence exists.
Further, your 'philosophical' points are simply invalid. Quantum mechanics says nothing about 'free will', or philosophical determinism for that matter. Quantum mechanics can be interpreted in either way, and has; e.g. the Copenhagen interpretation is nondeterministic, whereas the Bohm interpretation is.
I work with applying quantum mechanics at the molecular level, in biochemical systems, all day long. I have yet to find anyone in my field who thinks there are macroscopic quantum-mechanical processes going on in the human body. That is not due to lack of imagination, it's due to experience with actual quantum mechanics. All chemistry is inherently quantum mechanical. Physics cannot explain an atom even, much less a molecule, with classical theory. The relationship between chemistry and biochemistry is well-understood. The quantum mechanics of chemistry is fairly well understood (due to people doing what I do). And transition in the chemical domain from what is quantum-mechanical to what is classically describable is also well understood. There is simply no physics that explains how or why quantum mechanical effects would disappear and then re-appear orders of magnitude 'upwards' on the scale of matter.
In other news, Kansas has passed legislation to allow the teaching of alternate theories of photosynthesis, including Intelligent DeShine. This theory argues that plants produce food from sunlight by the mediation of "christons", which have the mystical property of being three particles in one, allowing them to convert the sunny warmth of the 6000-year-old Sun into original sin-free gluten.
You didn't think the Eucharist was made out of wheat by accident, did you? Heathen.
"I guess the moral of the story is, don't paint your airship with rocket fuel." -- Addison Bain
As a quantum physicist, perhaps I can enlighten those of you whose ignorant "of course it's quantum physics! clearly this research is the st00p1d" comments have gained unseemly amounts of modpoints.
Yes, of course quantum mechanics is what is ultimately responsible for everything that happens in the world (at least, as far as we know, though general relativistic phenomena are so far an exception to this). However, despite this fact, it is remarkably the case that the world we perceive on our own macroscopic level does not behave in a quantum way at all, but instead seems to obey classical mechanics. Essentially what it comes down to is that at some point, things start interacting with their environment so much that they start being constantly measured, and so the quantum behaviour disappears. What is not so clear is at exactly what level the world stops being quantum and starts being classical.
In general, the cutoff seems to be somewhere around a molecule. That is although atoms and bonds between atoms are quantum effects, molecules tend be very well modeled using classical forces that were obtained from the quantum models of the bonds.
Because of this, before this research was done, a very reasonable educated guess for one to have made was that the first step of photosynthesis, where an electron essentially is knocked into walking from one part of the molecule to another, would be a classical process, since it happens on the scale of a molecule. Put another way, one might have guessed that when the electron walked from one part of the molecule to another, it did so in a classical (but non-deterministic) fashion by choosing one of the paths available to it and walking down that.
However, what this research has shown is that this is not the case. The electron in fact takes several paths at once. This was detected by performing experiments which showed that there were interference effects; this is the standard approach to take to determine whether something is quantum or classical by the following rough chain of reasoning: you can only see interference patterns when you have cancellations, and you can only see cancellations when something has taken two paths simultaneously but with the opposite phase, so ergo if you see an interference pattern then something quantum must be going on.
This is actually very remarkable because it means that nature specifically engineered a molecule that manifests quantum behaviour on a larger scale then it usually appears. This is a non-trivial thing to have done because, again, the fact that we don't usually see quantum behaviour on this scale implies that it is typically precluded by interactions with the environment, so the fact that this molecule accomplishes this means that it somehow evolved to isolate the electrons involved in photosynthesis from their environment in order to allow them to act in a quantum fashion.
It turns out that the gain from doing this is small, but notable; I didn't read the article, but I did talk to some of the people involved in this research at a couple of meetings and if recall correctly they said that according to their simulations, by doing this nature gained an efficiency of about 10% over what it would be able to get if it were only using classical phenomena. Thus, this effect is actually important for us to understand because it may give us insights into how we can engineer our own devices to use large-scale quantum phenomena to more efficiently harness energy from the sun.
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