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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."
We all learn about photosynthesis in school: sunlight in, plant food out.
Huh, apparently some of us learned about it differently than others. I seem to recall it having to do with water and carbon dioxide in and some extra oxygen left over?
Also, I think someone beat you to the punch back in 2007 when we covered this story the first time and we covered that part about the birds using quantum effects in 2008.
My work here is dung.
Quantum mechanics isn't some tool in nature's toolbox. QM is a way that humans describe all natural phenomena when we explain details of how it all works. QM is a universal framework for describing all the actions of everything that exists.
If scientists are coming up with a new QM description of a physical process like photosynthesis, it's not because they're just discovering that QM is involved. It's because they're figuring out how to describe the process in terms of QM.
In other news, physics turns out to be involved in how the brain works.
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make install -not war
Parent is 100% on the mark. Nearly everything involving chemistry is governed by quantum mechanics, including the molecular bonds and photon absorption which are core to photosynthesis.
It is not new at all that quantum tunneling is an important mechanism in the electron transport chain. The iron-sulfur centers are optimally positioned to optimize the tunneling rate of electrons between them. They knew about this several years ago, when I learned this in an undergrad biophysics class.
I actually read TFA and from what I understand, plant is using quantum computing to solve sort of Traveling Salesmen Problem (TSP) in constant time. TSP belongs to the class of NP-complete problems. Thus, it is assumed that there is no efficient algorithm for solving TSP problems on non-quantum computer.
839*929
Is it just me or is everything now being explained through Quantum Mechanics?
No it is not just you. Practically everything is explained through QM. The only exception being gravity which we think is governed by QM if only we can find the right model.
While its is arguable that they do a good job explaining it, results that came out about 6 months ago suggest that incoming light can be directed to reaction centers through means of doing a quantum computation for the light to determine where the reaction center is. The ratio of antennas to reaction centers is about 300:1 which would make the photoharvisting step lossy if it wasn't for this quantum computation. The efficiency is well over 95% for the initial light harvisting step.
I thought this was obvious after learning about photodiodes in electronics class.
It's not about the quantum nature of the absorption of the photon and its conversion to an excited electron state.
It's about the efficient propagation of that excited electron state, once created, from one molecule to another until it gets to a place where it can be used. "Picking the path" in a non-random way, without losing energy in the process, seems to be using quantum weirdness as well.
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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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There is a common misconception that quantum computers can solve NP-complete problems in polynomial time. That is not known to be true, and is generally suspected to be false.[24]
'Nondeterministically' guessing the answer won't be enough. There is a class called BPP that concerns those algorithms classically, quantum computing goes further, but might still not be able to solve NP-complete problems fast. You say "an NP problem is one that can be solved in polynomial time", but you either meant that the answer can be checked in polynomial time or that you know P=NP. In the last case large amounts of fame and money are waiting on you.
Obviously quantum mechanics is involved in the root of all physical processes, but that is not what this article is about. This is saying that quantum coherences across the biological molecule contribute to the efficient energy transfer. The reason this is of note is that a biological molecule of this size should be too big to exhibit such quantum effects. The idea is not that quantum mechanics is needed to explain the photon->energy conversion process, which is inherently quantum mechanical. The idea is that plants have somehow harvested some advantages of quantum mechanics to perform rudimentary biological processes (like transferring energy) during evolution. You are looking at the smallest piece of the equation when this article is talking about a higher order biologic process instead.