Friday, July 20, 2007

Quantum Biology Goes Mainstream

I’m very interested to learn of any discoveries regarding the utilization of non-trivial quantum effects in biological systems. (I wish I could follow developments more effectively then just the occasional internet search.)

Anyway, back in April a paper in Nature appeared discussing the meaningful role quantum coherence plays in photosynthesis. Here is the press release from the research team at the Berkeley Lab. Here is a short piece in Scientific American (Access to the Nature paper requires subscription -- a related paper in Science followed in June.)

This seems like a big deal to me – this is a central topic in biology – and until now biologists incorrectly assumed only classical mechanisms were being used.

If natural selection made use of quantum coherence in this case, it seems likely we should find it exploited elsewhere by living things.


10 comments:

Michael said...

Sweet.

I think the reason this will be generally seen as cool but not earth-shaking is that we're talking about coherence for all of 660 femtoseconds. I think the typical way to ignore quantum theory is to think of it as defining rules of chemistry. Then the "practical" theory is like chemistry plus classical mechanics plus local noise and we can forget about all that pesky philosophical talk about entanglement and measurement and Deepak Chopra. So I'm saying this may be seen as a little addendum about (bio)chemistry, which everyone is willing to admit is quantum.

If we get up to microns, or milliseconds, then quantum biology might really go a bit more mainstream.

Actually, I can think of one at least one experimental paper that does make a claim on that scale, called (according to my memory) "Quantum interaction of human erythrocytes." They watched blood cells randomly walking around and concluded they were aggregating non-randomly. This result was related to quantum field theoretical predictions from Del Giudice and Vitiello, which predicted the aggregation phenomenon should be enhanced by the presence of long chains of polar molecules; which was also reported in the experimental paper.

I don't know how to search for subsequent "debunkings" of these findings, if there were any, but the experimental paper refs are below.

There is a big and confusing literature about em interactions with living cells, including claims of weak coherent em radiation of cellular processes like neurotransmitter release or calcium sequestration or cell reproduction. You've already looked into Popp's apparent proof that biophotons emitted by all living matter are coherent and correlated with biological functions like the reproductive cycle (supporting a quantum model by Frohlich). Vitiello or Del Giudice also reported experimental evidence of a superconducting state in living matter analogous to a Josephson junction. (I confess I didn't understand it.)

All these later effects I guess could still be construed as nonfunctional or epiphenomenal, but the blood cell effect, if true, would seem to be big enough to be mainstream...but I haven't heard much about it lately...

I found a few refs in case you're interested:

1.
Rowlands S, Sewchand LS, Enns EG. A quantum mechanical interaction of human erythrocytes.
Can J Physiol Pharmacol. 1982 Jan;60(1):52-9.

2.
Sewchand LS, Roberts D, Rowlands S.
Transmission of the quantum interaction of erythrocytes.
Cell Biophys. 1982 Dec;4(4):253-9.

3.
Rowlands S, Sewchand LS, Skibo L.
Conversion of albumin into a transmitter of the ultra long-range interaction of human erythrocytes.
Cell Biophys. 1983 Sep;5(3):197-203.

Michael said...

Steve,

Sorry I'm spewing words all over your lovely site, but two more thoughts:

1. In BioSystems 51 (1999): 15-19, Matsumo predicted that the actin-myosin muscle mechanism is quantum coherent. (Mae-won Ho might have mentioned or also predicted this in her book.) I don't know whether there are experimental data that speak to this.

2. Re: our discussion of pan-intentionality or panpsychism... The characterization of the photosynthetic mechanism as using the basic principle of quantum computation, in which multiple alternatives are explored simultaneously, suggests the basis for a quantum panpsychism. Similarly, I've mentioned how the quantum path integral is "like" a mind considering alternatives and choosing optimally (ie to minimize the physical action). Maybe we can define our quantum panpsychism in terms of a mapping between physical action and something like psychological "effort" or maybe "suffering." This would give us a basis for relating the "motivation" of plants and electrons to our own...but again I won't go there...

I don't think anyone actually using the term "quantum panpsychism" has actually taken this step of proposing a specific psycho-physical mapping. Except for the guy who says painful quantum amplitudes are suppressed. Do you know of any other?

Michael said...

Absolutely my last post! (today)

The following paper by Behera et al might be considered "only theoretical," but is very nice as a concrete, intuitive example of how the neural system could use a quantum system for computation, and it claims to describe eye saccade data better than classical models:

http://www.arxiv.org/abs/q-bio.NC/0407001

In a charitable mood, or in twenty years, we might even consider this to be experimental evidence...

It's a short paper; I'm curious whether it provokes any ideas or associations in you.

Steve said...

Thank you for these references. I've got my reading assignment!

Steve said...

I think the model in that last paper seems plausible and intuitively appealing. I guess the difference between this sort of paper and the photosynthesis work is that one is a model and the other actually detects the phenomenon. And the problem is that detecting a quantum phenomenon you've predicted is usually going to be very hard.

I see that on Arxiv if I search the "quantitative biology" papers with key words like "quantum" I find a few more papers to look at...

Blue Devil Knight said...

I think biologists have few preconceptions about what 'level' is most relevant to explain the phenomenon they are studying. They assume that at the very least, they will have to go down to the level of individual cells and the molecular denizens therein (i.e., proteins, nucleic acids), often down to single electrons (e.g., the electron transport chain)! It is rightly treated as an empirical question how far 'down' you have to go to explain what you are interested in.

What biologists will tend to not like are philosophical arguments about what the substrate 'must' be. They want data, and will happily follow wherever it leads...

To add another example, Bialek worked on quantum effects to explain certain protein function a while ago:
[37.] Vibrationally enhanced tunneling as a mechanism for enzymatic hydrogen transfer. WJ Bruno & W Bialek, Biophys. J. 63, 689–699 (1992).

The transfer of hydrogen atoms or ions is central to a wide variety of biological processes. There has long been interest in the possibility that these reaction proceed by quantum tunneling, but the evidence was murky at best. In many enzymes the hydrogen transfer
reactions show anomalous isotope effects, as expected for tunneling, but also substantial temperature dependencies, as expected for thermal activation. In this work we considered a scenario in which (classical) protein motions could enhance the quantum tunneling
of hydrogen in enzymatic reactions by causing fluctuations in the shape of the barrier. In the semiclassical limit we showed that almost any reasonable model in this class leads to a very simple phenomenology that fits the puzzling pattern of temperature dependent kinetic isotope effects. New experiments have provided yet stronger evidence for the importance
of protein enhanced tunneling, and current theoretical activity is concentrated
on detailed quantum chemical calculations that embody the basic scenario proposed in our work. I found it very pleasing to see how biology could exploit this interplay between classical and quantum dynamics.

Blue Devil Knight said...

I should be clear that the paragraph after the Bialek citation is from his web site where he gives a little commentary on some of publications.

Steve said...

Thanks very much, Blue Devil Knight, for your comment and the reference. I'm sure you're right about biologists following the trail whereever the data lead. I had this fear, based on no real knowledge, that looking for quantum effects might be viewed in the academy as "fringe-y" and therefore possibly neglected.
Best regards,
- Steve

Michael said...

Though I generally agree with BDK's comments about the open-mindedness of biologists, looking for MACROscopic quantum effects in biology IS decidedly "fringey."

Steve, have you checked out "The Emperor of Scent," a book about a "rogue theory of smell"? I have not read it, but I think it is tied in to a theory that protein interactions are better explained in terms of vibrational resonances than in terms of the traditional "lock-and-key" binding model. That model might be the kind you're looking for... I haven't had a chance to investigate it myself yet, but I'll see if I can dig up the name of the main person associated with it...

Revlin said...

In other words, plants are employing the basic principles of quantum mechanics to transfer energy from chromophore (photosynthetic molecule) to chromophore until it reaches the so-called reaction center where photosynthesis, as it is classically defined, takes place. The particles of energy are behaving like waves. "We see very strong evidence for a wavelike motion of energy through these photosynthetic complexes," Engel says.

Dude...BitTorrent!

Excuse my highly non-scientific remark.