Quantum effects Photosynthesis

[offroff]

I would like to hear some thoughts about the quantum effects that seem to be an important part of the photosynthesis (http://www.lbl.gov/Science-Articles/Archive/PBD-quantum-secrets.html" ).

According to the scientists who made this discovery it seems that the photon tests all possible paths and then the most effective one is chosen. If that theory is correct it seems to contradict all popular interpretations of QM. (am I right?)

Or does anyone believe that an effect like this can be explained with any of the common interpretations (many worlds for example).

Is there any discussion at all that tries to explain what's going on in the photosynthesis? I assume there are no definitive answers right now but I would like to hear your comments and if anyone has good links, please share.

 

[offroff]

I need some help here because I might be totally wrong and I don't want to believe in false ideas. I think the photosynthesis result is totally incompatible with some of the most common interpretations. It seems pretty obvious to me. But I shouldn't be right about that, so can someone please tell me I'm wrong so I'll be forced to study more?

 

[pallidin]

I read the article.
How the heck did you jump from advanced studies of photosynthesis to contradicting quantum mechanics?
The article supports QM.

 

[offroff]

The scientists say that the most effective path is "chosen", whatever that means. But if there are more than one possible path then there should be some randomness involved and the most effective one shouldn't be "chosen" all the time.

But alright I guess I need to study more but this is pretty new stuff and I haven't seen a discussion about it anywhere. It's hard to understand when no one even tries to explain what's going on.

 

[pallidin]

Your in the right place for your questions!
Hopefully those more knowledgeable than I can respond...

 

[offroff]

When they talk about the classical view I think they refer to earlier theories of the photosynthesis (Maybe http://fias.uni-frankfurt.de/symposium/papers/schulten.pdf" ). Then they didn't know about this wave-like state that keeps its coherence for a very long time.

 

[Bob S]

It is important to remember that about 29 eV is required to photosynthesize a single monosaccharide molecule (C₆H₁₂O₆; glucose, fructose), and this seems to require at least 24 visible-light photons (~4000 to 7000 Angstroms) in a few milliseconds. A sugar molecule cannot be synthesized in a few femptoseconds by a single photon.

Bob S

 

[SpectraCat]

The scientists say that the most effective path is "chosen", whatever that means. But if there are more than one possible path then there should be some randomness involved and the most effective one shouldn't be "chosen" all the time.

My speculation is that this is consistent with QM, because the states they are talking about have such long lifetimes. Thus the higher energy pathways experience much more drastic decoherence, and only the lowest-energy one is observed to any significant extent, as I explain in more detail below.

This can be rationalized using the classical quantity of "action" .. the full definition of action is complicated, but it's physical significance can be appreciated by noting that the partial derivative of the action wrt time yields the total energy, whereas the partial derivative with respect to position (i.e. the gradient), is the classical momentum.

Anyway, any system in classical physics, when presented with a choice of pathways, will always take the one for which the integrated action over the pathway is the lowest .. this is "Hamilton's principle of least action". In QM, the actions of relative paths represent their phase-lengths, and thus Hamilton's principle can be rephrased as, "in a QM system, the probability that a system will follow an available pathway is inversely related to the action of that pathway." Thus, in QM, the classical path (i.e. the one of least action), is the *most probable pathway* .. however other paths will also be sampled with probability weights corresponding to the relative difference between their actions from the action of the classical (i.e. preferred) path.

Now, this next statement is more speculative on my part, and I am not sure it is correct without reading about this particular case in more detail. I believe that what is going on in the photosynthetic system is that the system is approaching the classical limit ... that is, the long-lived nature of the coherent state implies that the actions for all paths except the classical one become sufficiently large that only the minimum-action pathway survives to any appreciable extent.

 

[offroff]

SpectraCat, I think your explanation makes a lot of sense so thank you, I can believe that for the time being.