Sydney Brenner's 10-on-10

The Chronicles of Evolution

Shuzhen Sim, Benjamin Seet

• Éditeur: WILDTYPE BK
• Année: 2018
• ISBN:
  9789811197161
• Sujet: Biological Sciences
• Sous-sujet: Evolution

Humans now wield a greater influence on the planet than any other species in history, and human-developed technologies like genetic engineering and artificial intelligence stand poised to overtake biological evolution. Just how did we arrive at this unique moment in human history, 14 billion years after the birth of the universe Sydney Brenner's 10-on-10: The Chronicles of Evolution brings together 24 prominent scientists and thinkers to trace the story of evolution through ten logarithmic scales of time. Through expert insights, this unique volume considers how humans found our place in the cosmos, and imagines what lies ahead.

Published by Wildtype Books and distributed by World Scientific Publishing Co.

Contents:

• Life In The Habitable Zone (John D Barrow)
• From Clay To The Code Of Life (Hyman Hartman)
• Stepping Up To Life (Jack W Szostak)
• When Cells Get Creative (Giulia Rancati and Norman Pavelka)
• Finding Strength In Numbers (Detlev Arendt)
• There And Back Again (Per Ahlberg)
• Conquest Of The Land And Sea (Byrappa Venkatesh)
• A Salute To Our Placoderm Pioneers (John A Long)
• Warming Up To Mammals (Harris Lewin)
• All In The Family (Francis Thackeray)
• Lessons From Our Inner Neanderthal (Svante Pääbo)
• Wired For Intelligence (Terrence Sejnowski)
• Getting Smart About Learning (Atsushi Iriki)
• More Than Just Small Talk (Tecumseh Fitch)
• The Logic Of Cultural Evolution (Roland Fletcher)
• Going With The (Information) Flow (Sander van der Leeuw)
• Lingo With A Life Of Its Own (N J Enfield)
• How We Became Modern (W Brian Arthur)
• The Creative Destruction Of Evolution (Stefan Thurner)
• The Challenge Of The Anthropocene (J Stephen Lansing)
• Difficult Questions In Evolution (Eörs Szathmáry)
• An Evolving View On Evolution (Gerd B Müller)
• The Humble View From Inside Evolution (Helga Nowotny)
• Epilogue (Sydney Brenner)

Readership: Science enthusiasts, history buffs, students, educators, scientists, social scientists, researchers.

Artist’s impression of star formation in the early universe.

Chapter 1

LIFE IN THE

HABITABLE ZONE

Complexity in the cosmos

We live in an epoch of cosmic history which not only allows our very existence, but also offers us a unique and precious opportunity to understand the universe.

……

John D. Barrow

For thousands of years, philosophers, astronomers and scientists thought of the universe as rather like a stage setting—a fixed, unchanging space within which the planets, stars and other heavenly bodies had been set in motion.

Albert Einstein changed all this in 1915 with his theory of general relativity, which showed that space and time are in fact dynamic entities whose structure, rate of change and shape of flow are shaped by the material contents of the universe. Instead of a fixed stage, space is more like a trampoline, shaped by the movement of mass and energy upon it.

I like to think of cosmology before Einstein as a branch of art history. You could paint any picture you like of the universe—it could be cubical, it could be a giant cosmic pyramid, it could be a succession of turtles placed one on top of the other—and no one would have been able to prove otherwise. But what Einstein also did was to turn cosmology into a science, by providing a set of mathematical equations whose solutions (and there are an infinite number of them) describe entire universes.

Fortunately for us, our universe is very well approximated by particular solutions of Einstein’s equations which show relatively simple behaviour, thus allowing us to make testable predictions about the nature of the cosmos and converge on the best solution of Einstein’s equations. We have since learned a lot about how the universe evolved from a simple past into the complexity of galaxies, stars and planets we see today; along the way, we have also found unexpected connections between the properties of the universe and those conditions needed for life to exist and persist within it.

……

A UNIQUE INTERVAL

After Einstein, work by Georges Lemaître, Edwin Hubble, Milton Humason and others demonstrated that the universe is indeed in a state of overall change—it is expanding all the time, like a great lump of raisin bread dough in an oven. The raisins moving away from each other as the dough expands are the great clusters of galaxies that trace the cosmic expansion.

We therefore exist in a unique interval of cosmic history that can be thought of as a habitable zone in time, after the stars were formed but before they all go out.

If we ran the clock back some 14 billion years, to a time just seconds after the Big Bang, we would find a universe many thousands of times smaller and hotter than the one we know today. Under these extreme conditions, only protons, electrons, photons and other elementary particles could exist.

Only after several hundred thousand years of expansion would the universe cool sufficiently for protons to catch hold of electrons, thus forming atoms and, subsequently, simple molecules. Over the next few billion years, some of this matter would accumulate still more matter, condensing (through complex processes we still do not completely understand) into stars, galaxies, galaxy clusters and ultimately planetary systems, including our own solar system.

From here on, the long-range forecast is rather bleak. Over the next 100 billion years, all stars, including the sun, will eventually exhaust their fuel and die, turning the universe into a great cosmic cemetery of dead worlds. We therefore exist in a unique interval of cosmic history that can be thought of as a habitable zone in time, after the stars were formed but before they all go out.

……

OLD IS GOLD

The very fact that we exist in this zone is inextricably linked to some of the universe’s most fundamental properties, chief among them its extreme age.

As far as elements go, the early universe was almost exclusively made up of hydrogen and helium, with only minute traces of everything else. Carbon, oxygen and all the other heavier elements that make up life today did not appear ready-made at the beginning of the universe, but were forged in the furnaces of dying stars, where helium atoms combined via nuclear reactions into beryllium, then beryllium and helium into carbon, and carbon and helium into oxygen. By a remarkable quirk of the nuclear constants of nature, this production of carbon goes unusually quickly, but its burning away into oxygen is impeded.

These reactions, which yielded the basic building blocks of biochemistry, took billions of years to complete. Thus, we shouldn’t be surprised to find ourselves in a universe that is 14 billion years old, since younger ones could not contain all the right starting ingredients needed for biochemical complexity.

Neither should the size of the universe surprise us; its immensity is simply a reflection of its age. In fact, we could not exist in a universe that is significantly smaller than the one we find ourselves in. While a universe the size of the Milky Way, with its billions of stars and planets, might seem a sufficiently large setup for life to emerge, it would be little more than a month old—barely enough time for you to pay off your credit card bill, let alone evolve complex life.

People often point to the vastness of the cosmos to argue that life surely must exist somewhere other than Earth. While this might very well be the case, the truth is that the universe would still have to be as big as it is in order to support even one lonely outpost of life.

……

THE PARADOX OF LIFE

The universe’s enormous age and size have several other interesting consequences. For one, the universe is exceedingly empty—if you spread out all the matter it contains, you would find yourself with just one atom per cubic metre of space. This low density of matter explains why planets, stars and galaxies are separated by such astronomical distances, and why the universe is not swarming with nearby civilisations.

For another, since temperature falls in proportion to size, the expanding universe is now a very cold place, clocking in at just under three degrees above absolute zero.

US astronomer and cosmologist Edwin Hubble at his telescope in 1924. Hubble and others demonstrated that the universe is constantly expanding, like dough in an oven.

To develop the broad-brush ingredients required for biochemical complexity, the universe must be old, big, almost empty, cold and dark.

Finally, despite the seemingly unending number of stars it displays, the universe appears dark at night. This is curious, because surely every line of sight out into the universe should end on the surface of a star, just like a look into the forest reveals a wall of trees. The whole sky should look like the surface of the sun all the time, and there should be no night. This ‘dark sky paradox’, which first puzzled 17^th and 18^th century astronomers like Edmund Halley, can be resolved if we consider that the expansion of the universe has reduced the density and temperature of matter so much that there is just not enough energy to illuminate the sky today.

Thus, we are faced with a curious, philosophically interesting set of consequences—to develop the broad-brush ingredients required for biochemical complexity, the universe must be old, big, almost empty, cold and dark. Paradoxically, these properties, which do not sound at all conducive to the evolution of living things, turn out to be absolutely necessary for the creation of the building blocks of life upon which evolution can act.

……

THE GREAT INFLATION

From its very beginning, a universe must expand at a certain rate in order to become habitable. If it expands too fast, falling far short of a threshold known as the critical density, matter will never cluster into stars and galaxies. On the other hand, if it expands too slowly and exceeds the critical density, it will collapse to a ‘Big Crunch’ before any celestial bodies can form.

Remarkably, our universe is expanding such that its density agrees with the critical density to within a factor of two percent today (making it what cosmologists call a critical universe, and what I like to call a ‘British compromise’ universe). Since any deviation from the critical value steadily increases with time, for this level of proximity to the critical expansion rate to be observed today, the starting speed of the universe must have been astoundingly finely tuned—it cannot have deviated from the ideal speed required for critical density by more than about one part in 10³⁵.

That our universe seems to be balanced on a knife edge is not the only bizarre thing about it. The expansion of the universe is also isotropic, meaning that it proceeds at the same rate in every direction. In addition, the universe is extremely smooth, but not completely so—it has a graininess level of one part in 10⁵, just lumpy enough for stars and galaxies to form. Had the universe been just ten times more or less grainy, it would host no habitable regions.

In 1981, theoretical physicist Alan Guth proposed the idea of cosmic inflation, which offered an explanation for the universe’s perplexing precision and uniformity. According to this theory, the universe went through a brief, explosive period of accelerated expansion beginning as early as 10^-35 of a second after the Big Bang, growing from the size of an atom to cosmic proportions within a split second.

Though over in the blink of an eye, inflation would have many far-reaching consequences. For one, it would drive the speed of expansion up dramatically, launching the universe on the trajectory that drives it so close to the critical density that even 14 billion years later it is still tantalisingly close to the critical divide. For another, no matter how complicated, chaotic or turbulent the expansion of the universe was pre-inflation, the acceleration would drive away nearly all deviation from smoothness, leaving a slightly grainy universe whose expansion is perfectly isotropic in every direction to very high precision.

……

BUBBLES OF POSSIBILITY

What cosmic inflation—now regarded as the standard working model for the birth of the universe—also means is that the whole of the visible universe grew from an infin...