Quantum Biology and the Puzzle of Coherence

[Jim__]

15. I'm not sure why you would begin by looking at a wider context.

Even the link that you provided on top-down causation begins by talking about systems that cannot be fully analysed in terms of component level behavior:

Top-down causation refers to the effects on components of organized systems that cannot be fully analyzed in terms of component-level behavior but instead requires reference to the higher-level system itself. A sweeping and fundamental concept, it is not only a philosophical idea but also a key ingredient in the emergence and functioning of complex systems, including life and the human brain. Together with bottom-up causation, top-down causation enables genuine complexity to emerge within specific levels of the hierarchy of complexity and causation. It also links the various levels of the hierarchy in a manner that undermines any simple-minded version of reductionism. A growing literature on complexity and emergence is providing an analysis of how this happens. Nevertheless, there are some who deny that it has any significance, or even reality.

In the link that I provided, Gregory Scholes suggests a research program that may determine whether quantum coherence has always been a part of photosynthesis, or if it came about through selection, the normal development path for complex biological systems - i.e. this system may well be explainable in terms of component level behavior:

He points out that it isn't obvious why selection would favour coherence. "Almost all photosynthetic organisms spend most of the day trying to moderate light-harvesting. It is rare to be light-limited. So why would there be evolutionary pressure to tweak light-harvesting efficiency?" Fleming agrees: he suspects that quantum coherence is not adaptive, but is simply "a by-product of the dense packing of chromophores required to optimize solar absorption". Scholes hopes to investigate the issue by comparing antenna proteins isolated from species of cryptophyte algae that evolved at different times.

This seems to be a reasonable approach toward trying to understand this phenomenon.

In your posts about top-down causality, I don't see any suggested research, but rather consideration of philosophical questions. In a paper linked to from the paper referred to in the OP, they discuss the molecular configurations that can lead to the type of coherence seen in photosynthesis; and specifically with respect to a particular protein involved:

Light harvesting components of photosynthetic organisms are complex, coupled, many-body quantum systems, in which electronic coherence has recently been shown to survive for relatively long time scales despite the decohering effects of their environments. Within this context, we analyze entanglement in multi-chromophoric light harvesting complexes, and establish methods for quantication of entanglement by presenting necessary and suffcient conditions for entanglement and by deriving a measure of global entanglement. These methods are then applied to the Fenna-Matthews-Olson (FMO) protein to extract the initial state and temperature dependencies of entanglement. We show that while FMO in natural conditions largely contains bipartite entanglement between dimerized chromophores, a small amount of long-range and multipartite entanglement exists even at physiological temperatures. This constitutes the first rigorous quantication of entanglement in a biological system. Finally, we discuss the practical utilization of entanglement in densely packed molecular aggregates such as light harvesting complexes.

There is, of course, always more to learn. But in this instance, the type of research being done and being suggested would seem to be reasonable first steps toward understanding this process. It certainly does not interfere with anything being suggested at the site studying top-down causality, and any information gained may serve as fodder for further investigation of the philosphical questions.