— Christopher Shea, American writer and editor, Is Scientific Truth Always Beautiful?, The Chronicle of Higher Education, Jan 28, 2013.
The Asymmetry of Life
Image courtesy of Ben Lansky
“Look into a mirror and you’ll simultaneously see the familiar and the alien: an image of you, but with left and right reversed.
Left-right inequality has significance far beyond that of mirror images, touching on the heart of existence itself. From subatomic physics to life, nature prefers asymmetry to symmetry. There are no equal liberties when neutrinos and proteins are concerned. In the case of neutrinos, particles that spill out of the sun’s nuclear furnace and pass through you by the trillions every second, only leftward-spinning ones exist. Why? No one really knows.
Proteins are long chains of amino acids that can be either left- or right-handed. Here, handedness has to do with how these molecules interact with polarized light, rotating it either to the left or to the right. When synthesized in the lab, amino acids come out fifty-fifty. In living beings, however, all proteins are made of left-handed amino acids. And all sugars in RNA and DNA are right-handed. Life is fundamentally asymmetric.
Is the handedness of life, its chirality (think chiromancer, which means “palm reader”), linked to its origins some 3.5 billion years ago, or did it develop after life was well on its way? If one traces life’s origins from its earliest stages, it’s hard to see how life began without molecular building blocks that were “chirally pure,” consisting solely of left- or right-handed molecules. Indeed, many models show how chirally pure amino acids may link to form precursors of the first protein-like chains. But what could have selected left-handed over right-handed amino acids?
My group’s research suggests that early Earth’s violent environmental upheavals caused many episodes of chiral flip-flopping. The observed left-handedness of terrestrial amino acids is probably a local fluke. Elsewhere in the universe, perhaps even on other planets and moons of our solar system, amino acids may be right-handed. But only sampling such material from many different planetary platforms will determine whether, on balance, biology is lefthanded, right-handed, or ambidextrous.”
— Marcelo Gleiser, The Asymmetry of Life, § SEEDMAGAZINE, Sep 7, 2010.
“One of the deepest consequences of symmetries of any kind is their relationship with conservation laws. Every symmetry in a physical system, be it balls rolling down planes, cars moving on roads, planets orbiting the Sun, a photon hitting an electron, or the expanding Universe, is related to a conserved quantity, a quantity that remains unchanged in the course of time. In particular, external (spatial and temporal) symmetries are related to the conservation of momentum and energy, respectively: the total energy and momentum of a system that is temporally and spatially symmetric remains unchanged.
The elementary particles of matter live in a reality very different from ours. The signature property of their world is change: particles can morph into one another, changing their identities. […] One of the greatest triumphs of twentieth-century particle physics was the discovery of the rules dictating the many metamorphoses of matter particles and the symmetry principles behind them. One of its greatest surprises was the realization that some of the symmetries are violated and that these violations have very deep consequences. (…) p.27
Even though matter and antimatter appear in equal footing on the equations describing relativistic particles, antimatter occurs only rarely. […] Somehow, during its infancy, the cosmos selected matter over antimatter. This imperfection is the single most important factor dictating our existence.(…)
Back to the early cosmos: had there been an equal quantity of antimatter particles around, they would have annihilated the corresponding particles of matter and all that would be left would be lots of gamma-ray radiation and some leftover protons and antiprotons in equal amounts. Definitely not our Universe. The tiny initial excess of matter particles is enough to explain the overwhelming excess of matter over antimatter in today’s Universe. The existence of mattter, the stuff we and everything else are made of, depends on a primordial imperfection, the matter-antimatter asymmetry. (…) p.29.
We have seen how the weak interactions violate a series of internal symmetries: charge conjugation, parity, and even the combination of the two. The consequences of these violations are deeply related to our existence: they set the arrow of time at the microscopic level, providing a viable mechanism to generate the excess of matter over antimatter. […]The message from modern particle physics and cosmology is clear: we are the products of imperfections in Nature. (…)
It is not symmetry and perfection that should be our guiding principle, as it has been for millennia. We don’t have to look for the mind of God in Nature and try to express it through our equations. The science we create is just that, our creation. Wonderful as it is, it is always limited, it is always constrained by what we know of the world. […] The notion that there is a well-defined hypermathematical structure that determines all there is in the cosmos is a Platonic delusion with no relationship to physical reality.(…) p. 35.
The critics of this idea miss the fact that a meaningless cosmos that produced humans (and possibly other intelligences) will never be meaningless to them (or to the other intelligences). To exist in a purposeless Universe is even more meaningful than to exist as the result of some kind of mysterious cosmic plan. Why? Because it elevates the emergence of life and mind to a rare event, as opposed to a ubiquitous and premeditated one. For millennia, we believed that God (or gods) protected us from extinction, that we were chosen to be here and thus safe from ultimate destruction. […]
When science proposes that the cosmos has a sense of purpose where in life is a premeditated outcome of natural events, a similar safety blanket mechanism is at play: if life fails here, it will succeed elsewhere. We don’t really need to preserve it. To the contrary, I will argue that unless we accept our fragility and cosmic loneliness, we will never act to protect what we have. (…)
The laws of physics and the laws of chemistry as presently understood have nothing to say about the emergence of life. As Paul Davies remarked in Cosmic Jackpot, notions of a life principle suffer from being teleologic, explaining life as the end goal, a purposeful cosmic strategy. The human mind, of course, would be the crown jewel of such creative drive. Once again we are “chosen” ones, a dangerous proposal. […] Arguments shifting the “mind of God” to the “mind of the cosmos” perpetuate our obsession with the notion of Oneness. Our existence need not be planned to be meaningful.” (…) p.49.
Unified theories, life principles, and self-aware universes are all expressions of our need to find a connection between who we are and the world we live in. I do not question the extreme importance of understanding the connection between man and the cosmos. But I do question that it has to derive from unifying principles. (…) p.50.
My point is that there is no Final Truth to be discovered, no grand plan behind creation. Science advances as new theories engulf or displace old ones. The growth is largely incremental, punctuated by unexpected, worldview-shattering discoveries about the workings of Nature. […]
Once we understand that science is the creation of human minds and not the pursuit of some divine plan (even if metaphorically) we shift the focus of our search for knowledge from the metaphysical to the concrete. (…) p.51.
For a clever fish, water is “just right“ for it to swim in. Had it been too cold, it would freeze; too hot, it would boil. Surely the water temperature had to be just right for the fish to exist. “I’m very important. My existence cannot be an accident,” the proud fish would conclude. Well, he is not very important. He is just a clever fish. The ocean temperature is not being controlled with the purpose of making it possible for it to exist. Quite the opposite: the fish is fragile. A sudden or gradual temperature swing would kill it, as any trout fisherman knows. We so crave for meaningful connections that we see them even when they are not there.
We are soulful creatures in a harsh cosmos. This, to me, is the essence of the human predicament. The gravest mistake we can make is to think that the cosmos has plans for us, that we are somehow special from a cosmic perspective. (…) p.52
We are witnessing the greatest mass extinction since the demise of the dinosaurs 65 million years ago. The difference is that for the first time in history, humans, and not physical causes, are the perpetrators. […] Life recovered from the previous five mass extinctions because the physical causes eventually ceased to act. Unless we understand what is happening and start acting toghether as a species we may end up carving the path toward our own destruction. (…)” p.56
— Marcelo Gleiser is the Appleton Professor of Natural Philosophy at Dartmouth College, A Tear at the Edge of Creation, Free Press, 2010.
☞ Symmetry in Physics - Bibliography - PhilPapers
☞ The Concept of Laws. The special status of the laws of mathematics and physics, Lapidarium notes
☞ Universe tag on Lapidarium notes