A new phase in the quantum consciousness debate

Posted by Simon Raggett on 14 November 2009 | 3 Comments

Tags: Consciousness, quantum coherence, quantum entanglement

The debate over the possible existence of quantum coherence and entanglement in the brain and their connection to consciousness may have been moved into a new phase by the discovery that quantum coherence (the wave as opposed to particle state of quanta) has a functional role in the transfer of energy within proteins, the basic building blocks of living cells (1. Engel et al, 2007). Most importantly, this discovery undermines the central argument against quantum consciousness, which has been the claimed impossibility of quantum coherence being sustained for any useful period in biological matter. At the same time, it moves the discussion of what sort of coherent features could support consciousness on from a phase of more-or-less pure theorising, to a phase in which ideas can be related to features that have been shown to exist in biological matter.

In the nearly three years since Engel's study was published in Nature, there has been almost no discussion of the possible significance of his findings in relation to consciousness. Anyone familiar with consciousness studies inn the last ten years, where the very mention of quantum consciousness produces a braying chorus of 'fringe' or 'pseudoscience', will not be surprised by the absence of constructive comment from that quarter. Engel and other researchers in the field of quantum coherence in protein are not involved in researching consciousness, and would probaly not improve their chance of funding, if they suggested there was any connection to consciousness. More disappointing is the relative lack of discussion within the very limited realm of quantum consciousness studies.

Possibly the most interesting models for quantum consciousness are those that make use of Penrose's idea of objective reduction (OR), in which it is proposed that the self-collapse of quanta, that are sufficiently isolated from the environment, from the quantum wave to the classical particle state, gives access to understanding/consciousness as a fundamental property of spacetime. Some quantum consciousness models have the same limitation as classical models of consciousness, in that there is no particular reason why a particular quanta or quantum feature should suddenly produce consciousness just because it happens to be in the brain. An OR model allows consciousness/understanding located in the fundamental structure of spacetime to interact with the sensory inputs of the brain.

For objective reduction models, it is vital that such reduction not only occurs in the brain, but occurs within a timescale that has some relevance for neural functioning. In OR models, it is important that the collapse or reduction occurs within a timescale that could be relevant to neural processing. A single quanta in isolation might not spontaneously collapse or decohere for millions of years. Some more substantial quantum system is needed to make this model of quantum consciousness plausible. This is where the possibility of the entanglement of many quanta, giving a feature with a larger total amount of energy, and thus a longer time to reduction becomes interesting.

Engel et al studied photosynthesis in green sulphur bacteria. Unpromising as this may sound, much the same principles apply across all multicellular living tissues. and this means that the nature of processing in photosynthetic protein could be relevant to what happens in neurons. The photosynthetic complexes (chromophores) in the bacteria are tuned to capturing light, and transmitting its energy to long-term storage areas. It should be stressed that in this system, photons (the light quanta) only provide the initial excitation, and that the coherence and entanglement discussed here involves electrons in the protein.

It is the energy transfer mechanism that is of intererest, Traditionally this had been analysed in terms of classical physics. However, the Engel study documented the dependence of the energy transport on the spatially extended properties of the wave function of the photosynthetic complexes. Engel views the system as performing a single quantum computation, sensing many states simultaneously, and selecting the correct answer. This process is analogous to Grover's algorithm. The involvement of quantum coherence explains the extreme efficiency of the system.

It is interesting that the timescale of the quantum coherence observed was much longer than would normally be predicted for a protein environment, with a duration of at least 660 femtoseconds (fs) (femtosecond=10^-15 seconds), nearly three times as long as the normally predicted time of only 250 fs. In the latter case rapid destruction of the coherence would prevent if from influencing the system. The delay from 250 to 660 fs suggests some kind of protection of coherence in protein, which has been studied in other recent papers, and is analogous to the screening or shielding argued for in some theories of quantum consciousness.

Engel's paper considered the possibility that the system discussed involved quantum entanglement as well as coherence. In a 2009 paper, (2. Sarovar et al) the authors examined the subject of possible quantum entanglement in the photosyntetic complexes discussed above. Entanglement carries the possibility of a large number of particles acting as a single quantum feature, and having an extended time to objective reduction that could have some bearing on neural processing. The Sarovar paper starts from the position of quantum coherence between the spatially separated chromophore molecules found in these systems. The entanglement examined is the non-local correlation between the electronic states of spatially separated chromophores. Coherence is a necessary and sufficient state for entanglement to exist. The coherence properties of the photosynthetic complex reflect the interplay of the protein with the decoherence effects of the environment. Ishizaki and Fleming (2009) (3.) developed an equation that allows modelling of this system. Where this deals with the first sites to be excited by the light energy, the initial entanglement rapidly decreases to zero, but then increases again after about 600 fs. This is thought to be a function of the entanglement of the initial sites being transported and localised at other sites, but then remaining coherent at those other sites, from which fresh entanglement can subsequently resurge. Interestingly, the timescale of entanglement between different sites in the photosynthetic complex is much longer than for coherence. The coherence is 660 fs or greater, while entanglement can last for 5 picoseconds (picosecond=10^-12 seconds) at a relatively low temperature of 77 Kelevin or 2 picoseconds at room temperature. The authors regard this as remarkable in the conditions of biological matter. This latter study is only the result of modelling, but is considered to be experimentally verifiable. Other studies appear to confirm the existence of picosecond timescales for entanglement in chromophores.

Following on the recent papers discussed above, the debate on quantum coherence in living tissues has moved to a new stage. We now have definite evidence of functional quantum coherence in living matter, and also modelling that makes it likley that there is also quantum entanglement in living matter. In looking for a possible mechanism for quantum consciousness, the principle of Occam's razor suggests that we should work with existing evidence, rather than more speculative possibilities. In the present state of knowledge, the findings concerning photosynthetic protein appear to be a more promising basis than other models that require longer times to collapse, or physical aspects that are not involved in the structures studied here.

Refererences:-

1.) Engel et al (2007)  -  Evidence for wavelike transfer of energy through quantum coherence in photosynthetic systems  -  Nature, 446, pp. 782-6

2.) Sarovar, M. et al (2009)  -  Quantum entanglement in photosynthetic light harvesting complexes  -  arXiv0905.3787v1 [quant-ph]

3.) Ishizaki, A. & Fleming, G. (2009)  -  On the adequacy of the Redfield equation and related approaches to the study of quantum dynamics in electronic energy transfer  -  Journal of Chemical Physics

4.) Cia, J. et al (2009)  -  Dynamic entanglement of oscillating molecules  - arXiv:0809.4906v1