Thursday, 5 March 2015

Quantum Mechanics and New Perspectives on the Nature of Life (2015)

From The Philosopher, Volume CIII No. 1, 2015

Perspectives and Speculations

Lipid bilayer of the cell membrane
(Image derived from a computer model created by Wellcome images)


By Celso de Araujo Duarte

Life is a characteristic of certain things in the world around us that distinguishes them from the rest by certain features. Things such as reproduction, mobility, metabolism, growth, ability to respond to external stimulus and adaptability to the environment are often mentioned. From the earliest times, people have attributed life to animals and plants, in recognition that these have key characteristics which are absent on inert matter.

Materialist currents of thought state that life is essentially an indirect, apparent result of a complex arrangement of matter. Empedocles believed that anything in the universe is composed by a combination of the four fundamental elements - water, air, fire, earth – and living matter was composed of a specific mixture of these elements, yet Democritus thought that the essence of life resides in the soul, the psyche. During the Middle Ages, within the Western tradition, under the aegis of the Christianity, a metaphysical ingredient, the soul, became the essential condition for life.

The materialist viewpoint reemerged with Descartes, who believed the man and the animals as machines. This conception was somewhat supported by the discovery of the cell, the basic unit of life that suggested a mechanistic viewpoint.

Daniel Koshland, a biochemist based at the University of California, Berkeley, speculates about the definition of life on an essay, based on a scientific debate (in a paper entititled 'The Seven Pillars of Life. Essays on Science and Society', published in the Journal Science 295: 2215-2216). The first questions were: 'Is an enzyme alive? Is a virus alive? Is a cell alive?' Koshland concluded that, 'although everyone knows what life is there is no simple definition of life', and started a sketch of a definition: 'a living organism is an organized unit, which can carry out metabolic reactions, defend itself against injury, respond to stimuli, and has the capacity to be at least a partner in reproduction'. Still unsatisfied, he has established the pillars of life in seven words:
However, Neil Greenspan, pathologist at Case Western University, Cleveland, addressing the issue of whether or not viruses are alive, doubts if anyone knows what life is: the problem is an unsolved issue.

Our experience of nature directs us to draw out the meaning of things in subjective ways. This is not enough and instead we are attracted by the possibility of making definitions. However, these may lead us to arrive only at circular concepts, since a definition relates concepts that are already known by us, and ultimately these concepts remain essentially subjective. A failure of most definitions of life is that they define life by the characteristics of living beings. They fail to define exactly what life is.

The Emergence of Phylogeny

Walking gently through the history, we arrive to the discovery of microscopic life, and the birth of microbiology. Evidence from microbiology suggests that all organisms on Earth are genetically related, and the genealogical relationships of living things can be represented by a vast evolutionary tree: the Tree of Life. The Tree of Life then represents the phylogeny of organisms - the history of organisms as they change through time.

Specifically, with microbiology, we have the discovery of new forms of living bodies - viruses, which differ from all other living beings by the absence of cells. In addition, viruses have an uncertain phylogeny: they are an emergent class of life that starts from a common denominator, which also generated other forms of life. At the same time, viruses are themselves the precursors of other forms of life.

Controversy about the classification of viruses as living or not would not arise were it not for the discovery that they are mere aggregates of a few molecules. Yet the finding that some isolated molecules are able to replicate is certainly a decisive argument in favor of their inclusion. At the same time, it is generally accepted that a simple molecule is not alive, and a virus is scarcely any more evolved than this.

During the Twentieth century it was discovered that some diseases were caused by this kind of particles - the viruses - with a behavior like that of bacteria, albeit much smaller. Being clearly biological and with their ability to spread among victims causing biological effects, it was supposed that viruses would be the simplest form of life. However, the first crystallisation of tobacco mosaic viruses, by Wendell Stanley and fellow collaborators, led them to believe that these entities were better understood as a biochemical complex. Viruses were relegated to the class of mere inert chemical compounds. The bottom line was that viruses do not have systems for metabolic functions - the biochemical activity of life. (See perhaps, for example, the paper Are viruses alive? by L. P. Villarreal, in Scientific American.)

We arrive to the central point of the present work: to dare some considerations about the question about what is alive, in the spirit of the search for a truly generalized conception. Let us consider first what we may say about viruses being or not living, taking the law of evolution to provide a broad viewpoint? Let us appeal to the law of evolution, and work backwards from animals to the most primitive living things. And where do we arrive? Firstly, to unicellular beings; after, even simpler, as the viruses. Would we have then arrived at the last stage of life, the smallest unit of life?

The brute, inorganic matter, also shows a gradation of complexity; from complex macroscopic aggregates of molecules to small aggregates, a few atoms, and finally (or is it?) the elementary particles. We are inclined to guess that life, linked to the matter, exists on everything at different degrees of complexity, even on single molecules, atoms, elementary particles.

The existence of some elementary particles is defined by a mean lifetime, after which they decay into another. Would not it be similar to a cellular mitosis or meiosis? Elementary particles may also generate or absorb other, as an example the photon. The absorption and emission of photons may be considered like the phagocytosis and the exocytosis – energy (food) intake and excretion - despite without a metabolism. From this viewpoint, life is a very broad phenomenon. It is associated with matter and suffers a process of evolution, conditioned to cross along successive stages with increased complexity. If the life of an elementary particle is simple, it becomes more complex as part of the aggregation that forms the atom, and, in sequence, within the molecule, within the group of molecules; before then, we arrive at plants, animals and the human being.

From this viewpoint, life is a very broad phenomenon. It is associated to matter and suffers a process of evolution, conditioned to cross along successive stages, with increased complexity . . .

Now quantum mechanics states that elementary particles have a dualistic nature: that they can take on either the characteristics of particles or of waves. How could we conceive life on a class of beings whose constitution is not well defined, ambiguous, dual? Firstly, only our paradigmatic conceptions would prohibit us to accept life under such conditions - at least as a hypothesis. Secondly, this dual nature is yet present on all the living beings at the quantum level of their subatomic constituents. Finally, quantum mechanics gives us a model for the reality, not the real panorama of reality. Following Bohr, another creator of quantum mechanics:
There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature..., Every sentence I utter must be understood not as an affirmation, but as a question.

(Niels Bohr, as quoted in the Bulletin of the Atomic Scientists Vol. 19, No. 7, September 1963).
Of course, we could argue that the result of the decay of an elementary particle is not a similar particle, and this does not occur with living beings: the decay of a neutron into a proton, an electron and a neutrino should have equivalents as an elephant giving birth to a giraffe, a duck and a sparrow. However, this concern reveals our attachment to the paradigm that living organisms can only generate similar ones. By the way, in termites, ants and bees, there is a differentiation among workers, soldiers, etc. A physicist would argue: however, the new generations consist of the beings of the same species. Making the parallel, protons and neutrons are baryons, electrons and neutrinos are leptons. The parallel is flawed. Again, this thinking reveals an attachment to paradigms (note that both classifications of living species and elementary particles are human inventions - albeit very founded and consistent in many aspects).

Now consider the probabilistic (quantum) character of the physical magnitudes associated to the elementary particles. This probabilism reflects a statistical law that previews tendencies. The behavior of a given single particle follows one of the previewed possibilities. The present status of quantum mechanics does not go beyond this limit. Would not be this an open door to interpret that each particle follows its own trajectory on a dynamical space of phases - and so that this could be interpreted as free will that sign individuality of the particle? This would break the deterministic principle in nature in the essence of matter (yet also broken by the quantum mechanics itself), and if we prefer, this indeterminacy can be seen as a characteristic of life at the subatomic scale.

Clinamen is the Latin name given by Lucretius to the unpredictable deviation of atoms, in the atomistic doctrine of Epicurus. According to Lucretius, this deviation occurs at no time or place fixed:
When atoms move straight down through the void by their own weight, they deflect a bit in space at a quite uncertain time and in uncertain places, just enough that you could say that their motion has changed. But if they were not in the habit of swerving, they would all fall straight down through the depths of the void, like drops of rain, and no collision would occur, nor would any blow be produced among the atoms. In that case, nature would never have produced anything.

('The Atomic Swerve' from De Rerum Natura by Lucretius)
It is this indeterminacy that, according to him, provides the free will that living things have throughout the world. Summarising then, the elementary particles:
• exchange energy with the environment;
• follow a law of minimization of energy causing an increase of entropy on the surrounding medium;
• have a characteristic average lifetime, defined by spontaneous decay (or by annihilation with another particle);
• generate other particles.
Yet are not these properties similar to that of living beings? Why should we think that the life scale finishes at (or before) viruses? We could speculate about what we would find continuing backwards on the scale of life, in size and complexity. Would we reach to a limit? Moreover, what would we find along the opposite direction of increasing complexity?

Finally, in this last paragraph I employed the word complexity. Yet perhaps, this word is not quite adequate to describe the real panorama. A bacterium seems to be nothing compared to the complexity of a horse; however, an endless compendium could be written about a single bacterium. And then, the simplicity of a bacterium is apparent. The true picture is that we have different levels or planes of complexity, whose mutual comparison enables us to set up a criterion of hierarchy of complexity (maybe this hierarchy is an illusion, a mere invention of the man - made to meet a better comprehension): each level has its own inherent complexity.

From this perspective, we would see a holographic scale of complexity in life. The complexity of the horse, made of cells; that of the cells made of organelles - specialised subunit within a cell that have specific functions; and on then to molecules, atoms, et cetera. It is in exactly the same way that the bacterium is complex since it too is made of organelles, and these by molecules, and all their ever-diminishing elements. And thus, eventually we arrive at an infinite scale of planes of complexity within each and every living being.

Contact details: Dr. Celso de Araujo Duarte is Professor of the Dept. of Physics, Federal University of Paraná, Brazil


1 comment:

  1. In the book The Quark and The Jaguar: Adventures on Simple and Complex, Murray Gel-Mann explores some interesting aspects. One question people from Santa Fé Institute of new Mexico ( are asking is what is the smallest living thing possible, considering the minimum energy required to keep life ? Reading your article I get the impression that without a better definition of What is Life ? from the physical point of view, there is no hope for a general answer, however if we define some limits to the question with some plausible and well understood question than some very interesting answers may help a better understanding. Congratulations for the inspiring paper