The Roman Philosopher Lucius Anneaus Seneca (4 BCE-65 CE) was perhaps the first to note the universal trend that growth is slow but ruin is rapid. I call this tendency the "Seneca Effect."
Showing posts with label Universe. Show all posts
Showing posts with label Universe. Show all posts

Friday, June 11, 2021

The Next Ten Billion Years


This is a post that I published on "Cassandra's Legacy" in 2012. It was one of the most successful posts ever published on that blog, it was reposted, discussed, and criticized in several places, including a long rebuttal by John Michael Greer, "The ArchDruid." I commented on Greer's comments here. I think it is appropriate to repropose this rather ambitious description of the history of the universe on my new blog, "The Seneca Effect," after I explored some similar arguments in recent posts (The Great Turning Point of Humankind, Long term Perspectives of Nuclear Energy, and "Star Parasites").

So, here it is, just slightly revised and updated with respect to the initial version.

The next ten billion years

It is not surprising that we found the future fascinating; after all, we are all going there. But the future is never what it used to be and it is said that predictions are always difficult, especially those dealing with the future. Nevertheless, it is possible to study the future, which is something different from predicting it. It is an exercise called "scenario building". Here, let me try a telescopic sweep of scenario building that starts from the remote past and takes us to the remote future over a total range of 20 billion years. While the past is what it was, our future bifurcates into two scenarios; one "good" and the other "bad", all depending on what we'll be doing in the coming years.

The past 10 billion years

- 10 billion years ago. The universe is young, it has existed for less than four billion years. But it already looks the way it will be for many billion years in the future: galaxies, stars, planets, black holes and much more.

- 1 billion years ago. From the debris of ancient supernovas, the solar system has formed around a second-generation star, the Sun, about 4.5 billion years ago. The planets that form the system are not very different from those we see today. The Earth has blue oceans, white clouds, and dark brown continents. But there are no plants or animals on the continents, nor fish in the water. Life is all unicellular in the oceans, but its activity has already changed a lot of things: the presence of oxygen in the atmosphere is a result of the ongoing photosynthesis activity.

- 100 million years ago. Plenty of things have been happening on planet Earth. Starting about 550 million years ago, perhaps as a result of the ice age known as "snowball Earth," multicellular life forms have appeared. First, only in the oceans; then, about 400 million years ago, life has colonized the surfaces of the continents creating lush forests and large animals that have populated the Earth for hundreds of millions of years. That wasn't uneventful, though. Life nearly went extinct when, 245 million years ago, a giant volcanic eruption in the region we call Siberia today generated the largest known extinction of Earth's history. But the biosphere managed to survive and regrow into the cretaceous period, the age of Dinosaurs.

- 10 million years ago. The age of dinosaurs is over. They have been wiped out by a new mass extinction that took place 65 million years ago, caused perhaps by a giant asteroid hitting the Earth or, more likely, by a giant volcanic eruption in the region that, million years later, will be called "India." Again, the biosphere has survived and now it prospers again, populated with mammals and birds; including primates. We are in the Miocene period and the Earth has been cooling down over a period of several million years, possibly as the result of the Indian subcontinent having hit Asia and created the Himalayas. That has favored CO2 removal from the atmosphere by weathering. Icecaps have formed both at the North and the South poles for the first time in several hundred million years.

- 1 million years ago. The Earth has considerably cooled down during the period that we call "Pleistocene" and is now undergoing a series of ice ages and interglacials. Ice ages last for tens of thousands of years, whereas the interglacials are relatively short hot spells, a few thousands of years long. These climatic oscillations are perhaps the element that stimulated the evolution of some primate species which have developed bipedal locomotion. One million years ago, homo Erectus and homo Abilis can use fire and make simple stone tools.

- 100.000 years ago. The glacial/interglacial cycles continue. The hot spell called the "Eemian" period, about 114,000 years ago, has been short-lived and has given way to one of the harshest known glaciations of the recent Earth's history. But humans survive. In Europe, the Neanderthals rule, while the species that we call "homo sapiens" already exists in Africa.

- 10.000 years ago. The ice age ends abruptly to give rise to a new interglacial; the period that we call "Holocene." The Neanderthals have disappeared, pushed over the edge of survival by their "Sapiens" competitors. Climate stabilizes enough for humans to start to practice agriculture in the fertile valleys along the tropical region of Africa and Eurasia, from Egypt to China.

- 1000 years ago. The agricultural age has given rise to the age of empires, fighting for domination of large geographical areas. The human population has been rapidly growing, with the start of a series of cycles of growth and collapse that derive from the overexploitation of the fertile soil. 1000 years ago, the Western World is coming back from one of these periodic collapses and is expanding again during the period we call "Middle Ages".

- 100 years ago. The age of coal has started and has been ongoing for at least two centuries. With it, the industrial revolution has come. Coal and crude oil are the fuels that create a tremendous expansion of humankind in numbers and power. 100 years ago, there are already more than a billion humans on the planet and the population is rapidly heading for the two billion marks. Pollution is still a minor problem that goes largely unrecognized. The concentration of carbon dioxide in the atmosphere has been increasing to near 300 ppm over the 270 ppm which has been the level of the pre-industrial age. This fact is noted by some human scientists who predicted that it would cause a warming of the planet, but the long term consequences are not understood.

- 10 years ago. The fossil fuels that created the industrial age are starting to show signs of depletion and the same is true also for most mineral commodities. The attempt to replace fossil fuels with uranium has not been successful because of the difficulties involved in controlling the technology. Energy production is still increasing, but it shows signs of slowing down. The human population has reached 7 billion and keeps growing, but at reduced rates of growth. The Earth's agricultural system is in full overshoot and the population can only be fed by means of an agricultural industrial complex based on fossil fuels. The concentration of CO2 in the atmosphere has been growing fast and is now about 370 ppm. Global temperatures have been rising, too. The problem of global warming has been recognized and some efforts are being made to reduce the emissions of CO2 and of other greenhouse gases, but their concentration keeps increasing.  

Today. The world's industrial system seems to be close to stopping its growth and the financial system has been going through a series of brutal collapses. The production of crude oil has been stable during the past few years, but the overall energy production is still increasing because of the decision to extract expensive and polluting fuels out of "shales." The extraction of such fuels has been claimed to be a great success, but it seems that it has already reached its peak. The political situation is chaotic, with continuously erupting minor wars. The human population is now getting close to eight billion. The climate system seems to be on the verge of collapse, with deforestation, global warming, increased atmospheric humidity, decline of the ice caps and more. The concentration of CO2 in the atmosphere is now over 400 ppm and it keeps increasing.

The future in two scenarios

1.The "bad" scenario.

10 years from now. In 2030, the production of "conventional" crude oil has been in decline for about two decades. The enormous effort made to replace it by liquids produced using non-conventional sources, tar sands, shale oil, and other "heavy" oil sources, as well as biofuels, has been a failure. Uranium, too, has become scarce and several countries which don't have national resources have been forced to close down some of their nuclear plants. These trends are partially compensated by the still increasing production of coal; which is also used to produce liquid fuels and other chemicals that once were obtained from oil. The growth of renewable energy has stalled: there are no more resources to invest in research and development in new technologies and new plants, while a propaganda campaign financed by the oil industry has convinced the public that renewable sources produce no useful energy and are even harmful to the environment. Another propaganda campaign financed by the same lobbies has stopped all attempts of reducing the emissions of greenhouse gases. As a result, agriculture has been devastated by climate change and by the high costs of fertilizers and mechanization. The human population starts an epochal reversal of its growing trend, decimated also in reason of the increasing fraction of fertile land which is dedicated to biofuels.

100 years from now. In 2100, the human economic system has collapsed and the size of the economy is now a small fraction of what it had been at the beginning of the 21st century.  Resource depletion has destroyed most of the industrial system, while climate change and the associated desertification - coupled with the destruction of the fertile soil - have reduced agriculture to a pale shadow of the industrial enterprise it had become. The collapse of agriculture has caused a corresponding population collapse; now around two billion people. Most tropical areas have been abandoned because global warming has made them too hot to be habitable by human beings. The rise in sea level caused by global warming has forced the abandonment of a large number of coastal cities, with incalculable economic damage. The economy of the planet has been further weakened by giant storms and climate disasters hitting about every inhabited place. Crude oil is not extracted anymore in significant amounts and where there still exist gas resources, it is impossible to transport them at long distances because of the decay of the pipeline network and of the flooding of the ports. Only coal is still being extracted and coal-fired plants maintain electric power for reduced industrial activity in several regions of the North of the planet. Labrador, Alaska, Scandinavia, and Northern Siberia still host remnants of the old industrial society. Using coal liquefaction, it is still possible to obtain liquid fuels, mostly used for military purposes. The Earth still sees tanks and planes that exchange gunfire against each other.

1000 years from now. The industrial society is a thing of the past. Human-caused global warming has  generated the release of methane hydrates which have created even more warming. The stopping of the Oceanic thermohaline currents has transformed most of the planet into a hot desert. Almost all large mammals are extinct. Humans survive only in the extreme fringes of land in the North of the planet and in the South, mainly in Patagonia. For the first time in history, small tribes of humans live on the rapidly de-frosting fringes of the Antarctic continent, living mainly on fishing. In some areas, it is still possible to extract coal and use it for simple metallurgy that uses the remains of the metals that the 20th century civilization has left. Human beings are reduced to a few hundred million people who keep battling each other using old muskets and occasional cannons.

10.000 years from now. Human beings are extinct, together with most vertebrates and trees. Planet Earth is still reeling from the wave of global warming that had started thousands of years before. The atmosphere still contains large amounts of greenhouse gases generated by human activity and by the release of methane hydrates. The continents are mostly deserts, and the same is true for oceans, reduced to marine deserts by the lack of oxygenating currents. Greenland is nearly ice-free and that's true also for Antarctica, which has lost most of its ice. Only bushes and small size land vertebrates survive in the remote northern and southern fringes of continents.

100.000 years from now. The planet is showing signs of recovery. Temperatures have stabilized and silicate erosion removed a large fraction of the carbon dioxide accumulated in the atmosphere. Land animals and trees are growing again.

1 million years from now. The planet has partly recovered. The planetary tectonic cycles have re-absorbed most of the CO2 which had created the great burst of warming of long before. Temperature has gone down rapidly and polar ice caps have returned. The return of ice has restarted the thermohaline currents: oceanic waters are oxygenated again. Life - those species that had survived the warming disaster - are thriving again and re-colonizing the tropical deserts - which are fast disappearing.

10 million years from now. Earth is again the lush blue-green planet it used to be, full of life, animals, and forests. From the survivors of the great warming, a new explosion of life has been generated. There are again large herbivores and carnivores, as well as large trees, even though none of them looks like the creatures which had populated the Earth before the catastrophe. In Africa, some creatures start using chipped stones for hunting. In time, they develop the ability to create fire and of building stone structures. They develop agriculture, sea-going ships and ways of recording their thoughts using symbols. But they never develop an industrial civilization for lack of fossil fuels, all burned by humans millions of years before them.

100 million years from now. Planet Earth is again under stress. The gradual increase in solar irradiation is pushing the climate towards a new hot era. The same effect is generated by the gradual formation of a new supercontinent generated by continental drift. Most of the land becomes a desert - all intelligent creatures disappear. There starts a general decline of vertebrates, unable to survive on a progressively hotter planet.

1 billion years from now. The Earth has been sterilized by the increasing solar heat. Only traces of single-celled life still survive underground.

10 billion years from now. The sun has expanded and it has become so large that it has absorbed and destroyed the Earth. Then, it has collapsed in a white dwarf. The galaxy and the whole universe move slowly toward extinction with the running down of the energy generated by the primeval big bang.


2.The "good" scenario

Ten years from now. In 2030, fossil fuel depletion has generated a global decline in production. That, in turn, has led to international treaties directed to ease the replacement of fossil fuels with renewable energy. Treaties are also enacted with the purpose of minimizing the use of coal. The production and the use of biofuels for industrial machinery has been forbidden everywhere and treaties force producers to direct all the agricultural production towards food for humans. The existing nuclear plants make full use of the uranium in the warheads that had been accumulated during the cold war. Research on nuclear fusion continues, with the hope that it will provide useful energy in 50 years. Even with these actions, global warming continues and agriculture is badly damaged by droughts and erosion. Population growth stops and widespread famines occur. Governments enact fertility reduction measures in order to contain the population. The economy thrives, stimulated by the demand for renewable plants.

A hundred years from now. The measures taken at the beginning of the 21st century have borne fruit. Now, almost 1% of the surface of the planet is covered by solar panels of the latest generations which produce energy with an efficiency of the order of 50%. In the north, wind energy is used, as well as energy from ocean currents, tides, and waves. The production of renewable electrical energy keeps growing and it has surpassed anything that was done in the past using primitive technologies based on fossil fuels. No such fuels are extracted any longer and doing so is considered a crime punishable with re-education. The industrial economy is undergoing rapid changes, moving to abandon the exploitation of dwindling resources of rare metals, using the energy available to exploit the abundant elements of the Earth's crust. The human society is now completely based on electric energy, also for transportation. Electric vehicles move along roads and rails, electric ships move across the oceans and electric airships navigate the air. The last nuclear fission plants have been closed for lack of uranium fuel around 2050, they were not needed anymore. Research on nuclear fusion continues with the hope that it will provide usable energy in 50 years. Despite the good performance of the economy, the ecosystem is still under heavy stress because of the large amounts of greenhouse gases emitted into the atmosphere during the past centuries. Agriculture is still reeling from the damage done by erosion and climate change. The human population is in rapid, but controlled, decline under the demographic measures enacted by governments. It is now less than 4 billion humans and famines are a thing of the past.  With the returning prosperity, humans are restarting the exploration of space that they were forced to abandon at the start of the 21st century.

1000 years from now. In the year 3000 A.D. the ecosystems of the planet have completely recovered from the damage done by human activities during the second millennium. A sophisticated planetary control system manages solar irradiation by means of space mirrors and the concentration of greenhouse gases by means of CO2 absorbing/desorbing plants. The planet is managed as a giant garden, optimizing its biological productivity. The Sahara desert is now a forest and the thermohaline currents pump oxygen to the northern regions, full of life of all kinds. The solar and wind plants used during the previous millennium have been mostly dismantled, although some are still kept as a memory of the old times. Most of the energy used by humankind is now generated by space stations which capture solar energy and beam it to the ground in forms easily usable by humans. Research in controlled fusion energy continues in the hope that it will produce usable energy in 50 years. Humans are now less than one billion, they have optimized both their numbers and their energy use and they need enormously less than they had needed in the more turbulent ages of one thousand years before. The development of artificial intelligence is in full swing and practically all tasks that once had been in the hands of humans are now in the "hands" of sophisticated robotic systems. These robots have colonized the solar system and humans now live in underground cities on the Moon. The new planetary intelligence starts considering the idea of terraforming Mars and Venus. The first antimatter powered interstellar spaceships have started their travel to faraway stars.

10.000 years from now. There are now less than a billion human beings on Earth who live in splendid cities immersed in the lush forest that the planet has become. Some of them work as a hobby on controlled nuclear fusion which they hope will produce usable energy in about 50 years. The New Intelligence has now started terraforming Mars. It involves similar methods as those used for controlling the Earth's climate: giant mirrors and CO2 producing plants that control the Martian atmosphere, increasing its pressure and temperature. The terraforming of Venus has also started with similar methods: giant screens that lower the planetary temperatures and flying plants that transform CO2 into oxygen and solid carbon. That will take a lot of time, but the New Intelligence is patient. It is also creating new races of solid-state beings living on the asteroids and orbiting around the Sun. The exploration of the galaxy is in progress, with spaceships from the solar system now reaching a "sphere" of about a thousand light-years from the sun.

100.000 years from now. About 500 million humans live on Earth - mostly engaged in art, contemplation, and living fully human lives. Some of them still engage in experiments that are supposed to produce controlled nuclear fusion after 50 years or so. Mars is now colonized by Earth's plants, which are helping to create an atmosphere suitable for life; it is now a green planet, covered with oceans and lush forests. Several million human beings live there, protected from cosmic radiation by the planetary magnetic field artificially generated by giant magnetic coils at the planet's poles. The temperature of Venus has been considerably lowered, although still not enough for life to take hold of its surface. The exploration of the galaxy is in full swing. Other galactic intelligences are encountered and contacted.

A million years from now. Venus, Earth and Mars are now lush and green; all three full of life. Mercury has been dismantled to provide material for transforming the solar system into a single intelligence system that links a series of creatures. There are statites orbiting around the sun, solid-state lifeforms living on asteroids and remote moons, ultra-resistant creatures engineered to live in the thick atmosphere of Jupiter and of the other giant planets. Humans, living on the green planets, have become part of this giant solar network. The other extreme of the Galaxy has been now reached by probes coming from the solar system.

10 million years from now. The New Intelligence is expanding over the Galaxy. The Green planets are now the place of evolution tests and the re-created Neanderthals now live on Mars, whereas dinosaurs have been recreated on a Venus where the planetary control system has recreated conditions similar to those of the Jurassic on Earth.

In 100 million years from now. Controlling temperatures over the three green planets of the Solar System has become a complex task because of the increasing solar radiation. Mirrors are not enough anymore and it has been necessary to move the planets farther away from the sun. The statites that form the main part of the solar intelligence now surround the sun almost completely in a series of concentric spheres.

In a billion years from now. The solar radiation has increased so much that it has been necessary to move the green planets very far away. One year lasts now as 50 of the "natural" Earth years as they were long before. But these are no problems for the Solar Intelligence, now just part of the Galactic intelligence. The three green planets. Venus, Earth, and Mars are three jewels of the Solar System.

In ten billion years from now. The sun has collapsed in a weak white dwarf and all the planets that orbit around it are frozen solid. The Galaxy has lost most of its suns and the universe is entering its last stage of expansion which will lead it to become a frozen darkness. The Galactic Intelligence looks at a galaxy that is by now a pale shade of its old glory. The Intelligence says, "Let there be light" And there is light.

(this text was inspired by Isaac Asimov's story "The Last Question")


Sunday, June 6, 2021

Star Parasites: Carbon-Based Life and the Future of the Universe

  The universe is enormous, and yet it seems to follow certain patterns. What we are seeing today is the result of the dissipation of the enormous energy burst that came with the big bang, some 14 billion years ago. The dissipation occurs in steps, as it is typical of dissipative systems, forming a trophic chain of energy stocks that has some parallels with the kind we know in Earth's ecosphere. In this giant chain of beings, our role seems to be of "star parasites," growing on the light emitted by a star which, from the viewpoint of the star, is waste. Above: an image obtained by the Chandra X-ray telescope. This region shows hundreds of supermassive black holes, each one in a galaxy far beyond our own. (source: Ethan Siegel).


Nowadays, we are obsessed with the idea that we need to "produce energy." That is, of course, a wrong way to express the concept. Energy can't be produced: the first principle of thermodynamics tells us that. Energy can only be transformed from a kind of energy to another. And even that is not correct. You can only transform energy going in a specific direction, it is dictated by the second principle of thermodynamics. All you can do, and you can do no more, is to transform high energy potentials into low energy potentials. This is called "potential dissipation." 

An example: what we do when we claim that we "produce energy" is, mostly, to combine atmospheric oxygen with those long-chain carbon and hydrogen molecules that we call "fossil fuels," stored inside Earth's crust. The dissipation process starts with the chemical energy potential stored in crude oil (or gas, or coal), then it goes on in steps, always downhill, until we are left with low-temperature heat, plus water and carbon dioxide. What we covet from this transformation is heat that we then use to run engines and do more things. These intermediate steps we can call "dissipative structures," a term proposed for the first time by Ilya Prigogine.

Can we go back? It is possible, but we can't trick nature and go against the second principle. It is a steep uphill road that of recombining water and carbon dioxide to form again long-chain carbon molecules. We can only achieve that by dissipating an even higher potential, solar light. It is done all the time by plants, it is called "photosynthesis." It is the process that, long ago, created the carbon compounds we are so busy burning nowadays.

This is what makes us "star parasites." We, like the whole Earth's ecosystem, live by dissipating the potential of our star, the sun, and using the energy flow to build dissipative structures: plants, animals, and everything human-made. More correctly, we should say that we are "commensals," a technical term for those parasites that do not compete with their host for resources. From the viewpoint of the star, light is just waste discarded into space. We just intersect a minimal fraction of it and we re-emit it in a slightly lower potential form, infrared light. 

But how about the Sun? Is it a parasite of anything? Not in the same way, but the second principle of thermodynamics holds for the Sun, too. The potential that the Sun is dissipating originated long ago, with the big bang. At that time, an enormous energy potential was accumulated in a very small space. When the big bang came, this energy started being dissipated, a process that has been lasting for 14 billion years and is continuing now. As the universe expands, it cools down. Far from the enormous temperatures of its early life, the universe is now down to just 2.725 degrees Kelvin -- close to the absolute zero. In terms of radiative potential, it is by now dead. Too cold to create new dissipative structures.

But the universe can still create dissipative structures because matter can accumulate into gravity pits. These accumulations concentrate gravitational energy, creating new forms of potential dissipation. Stars are formed by accumulating a vast mass of interstellar dust in a relatively small space. Eventually, a star reaches conditions of temperature and pressure so high that it can start another process of dissipation, turning matter into energy. It is the fusion of hydrogen nuclei into helium ones, a process that, as far as we know, can happen only inside the depth of star cores. It is what makes us star parasites. There are surely other carbon-based lifeforms that do the same around other stars of our galaxy and other galaxies. (image from ESA)

Hydrogen fusion is not the only large-scale energy dissipation process in the universe. There is a sort of "trophic chain" out there, with entities that can be seen as existing at higher trophic levels. Black holes are predators that can devour anything that comes close to them, including stars, and turn it into more internal matter. Neutron stars can be eaten by black holes, but they can eat stars, too. 

Stars themselves have a life of their own. Most of them tend to become brighter and larger as they get older and consume their hydrogen stock. If they are very large, they end their life with the spectacular explosions called "supernovae." The remnant may be a neutron star or a black hole. The debris ejected into space will eventually coalesce to form a new star -- an "offspring" of the old one. So, stars reproduce but, as far as we know, all the information stored in the old star disappears in the cloud of gas that forms as a result. So, there is no transmission of information from a generation of stars to another and no evolution in the Darwinian sense (*). 

The same would seem to be valid for neutron stars, whose destiny is normally to become black holes. Then, black holes are supposed to evaporate over extremely long times by the slow emission of Hawking radiation, again losing all the information that may have been contained inside. (image below from NASA)

That's not the end of the great trophic chain. There is another energy dissipation mechanism: the decay of heavy radioactive nuclides, uranium and thorium. It generates energy that plays a fundamental role in keeping hot, at about 6000 K, the molten core of our planet. It probably does the same for billions of Earth-like planets of our galaxy. This heat is nearly impossible to detect at interstellar distances because it appears as very low temperatures at the surface, probably around a few tens of degrees K. Nevertheless, compared with the background temperature of the universe, Earth-like planets shine.

The decay of heavy nuclides is slow and not very spectacular, but it is fundamental for carbon-based life. A geologically active nucleus generates enough heat to keep the inner layers of Earth hot enough to create the structures we call "hydrothermal vents" at mid-ocean ridges. It is believed that life started at these undersea vents exploiting geothermal energy much before it ventured to the surface and learned how to exploit solar light. Then, life needs a constant supply of carbon dioxide, which is provided by outgassing from the hot mantle. A cold, solid nucleus would not be able to outgas anything and, in such case, the carbon dioxide in the atmosphere would be consumed by reacting with surface silicates and disappear in a few million years at most. A hot inner Earth doesn't just provide CO2 by outgassing. It actively controls its atmospheric concentration by removing carbon by silicate erosion and transporting it to the mantle by the subduction process that takes place at the edges of the crustal plates. And subduction can happen only because of the presence of convective currents in the semi-molten mantle.

So, no radioactive elements, no life. Or, at least, the lifetime of the ecosphere would be much shorter than it is, probably too short to generate complex, multicellular lifeforms.

There is more about radioactive elements: they have a trick that makes them go off in a burst of rapid energy dissipation. It is the neutron-catalyzed reaction that occurs for a sufficiently high concentration of a "fissile" nuclide. In the whole universe, only one fissile nuclide exists in significant amounts: the 235 isotope of uranium: most uranium and the other long-lived radioactive element, thorium, are not fissile, but "fissionable." They can undergo fission, but cannot sustain a chain reaction. 

Even though U(235) is rare, with its half-life of about 700 million years, in very ancient times it was less rare than it is nowadays. So, geological phenomena could accumulate a sufficiently large amount of it to generate a natural chain reaction. It happened at least once in Earth's history, some 2 billion years ago in Oklo, in the area we call today "Gabon," in Africa. Nothing spectacular happened at that time: the chain reaction went on and off several times, generating some heat over a few hundred thousand years. Probably, the place was rich of hot springs at the time, but there were no people who could have enjoyed them. Not even animals existed, they were to appear only one billion and a half years later. So this natural uranium reactor had little or no effect on the ecosystem. 

We don't know if other Oklo-like reactors existed on Earth but, if they existed, they must have been marginal phenomena (even though some people propose the rather improbable theory that the Moon was created in a nuclear explosion). What we know is that, in recent times, the creatures called "humans" managed to process minerals from Earth's crust in such a way to concentrate heavy nuclei at levels where chain fission could be maintained for a certain time. They even managed to "breed" fissile nuclei out of fissionable ones. The flow of energy created in this way is small, a few percent of the energy that humans are generating from fossil fuels, infinitesimal in comparison to the output of a star. But it is there. Could it become much larger in the future and became a significant mechanisms of energy dissipation in the universe? 

It is an especially interesting point because, as far as we know, the only way to run a nuclear chain reaction on a large scale is by having intelligent beings actively control it. We can say that since there is at least one such civilization in the universe (us) and there is no reason to think we are alone. The consequence is that carbon-based sentient beings might use the energy created by fission chain reaction to engage in major feats of planetary engineering and interstellar travel.


Of course, we are not seeing anything like that in the universe. This is the essence of the so-called "Fermi Paradox," often understood as meaning that humans are the only technological civilization existing in the universe. In a previous post, I argued that the explanation is the result of two conditions. One is that energy production by controlled nuclear fusion is not possible outside stars, so it is not available to planetary civilizations. The other is that the amounts of radioactive elements available in the solar system are too small to provide sufficient energy to sustain a civilization for a long time. Not even fissionable elements are sufficiently abundant to create more that a transient "flare" of energy dissipation that then would rapidly decline before a civilization could engage in a sustained effort of interstellar exploration.

With the fissile/fissionable resources available, humans, or their extrasolar colleagues, could at most engage in a limited, local interstellar exploration program before running out of energy. More than that, we lack the capability to control what we are doing and it is likely that we'll soon be destroyed by the pollution we ourselves are generating, while at the same time doomed by the depletion of the mineral resources needed to keep civilization going. Or that we'll blow out ourselves using those chain fission reactions we are so proud of. Fortunately, it seems that some 50 years ago we missed the chance we had to embark in a dangerous and ultimately futile nuclear energy program. Now, it is probably too late to gather the resources that would be necessary. Given the current situation, dreams of galactic empires seem to be a little premature.

If we are lucky, we'll just fall back to our normal role of star parasites, after having run out of other forms of potentials to dissipate. That might not be such a bad destiny, considering that the flow of solar energy arriving on our planet is several thousand times larger than the flow of primary energy produced nowadays. But solar energy, although abundant, may not be easy to convert into forms that can power a starship.

So, are carbon-based civilizations destined to remain forever stuck to their home planets? Not necessarily. The universe is not static, it keeps changing albeit at a very slow pace and the availability of fissile materials may be different in the future. We saw that all that is happening in the universe nowadays is the result of the dissipation of the original energy of the big bang. Nuclear fission is no exception. The existence of radioactive nuclei is the result of processes believed to take place mainly in supernova explosions, although it seems that large amounts can also be created in the processes called "kilonovae," the fusion of two neutron stars that generates a black hole. Fissionable nuclei have a half-life of the order of billions of years, so that the universe (14 billion years old) is being progressively enriched with them. 

So, maybe there is a threshold at some moment in the future in which Earth-like planets will be normally endowed with sufficiently large resources of radioactive materials that carbon-based lifeforms might be able to engage in the exploration, and maybe even the colonization, of the galaxy. They might even be able to overcome the limitations of planetary resources by scooping heavy nuclides from the dust around neutron stars or black holes. Maybe we need to wait a few billion years but, from the viewpoint of the universe, a few billions of years are nothing.

This kind of reasoning is, of course, very tentative, but surely fascinating. The universe as a dissipation system appears as a thermodynamic machine. And when you deal with a machine, you can't avoid wondering what is its purpose. Why the universe is the way it is? Why do radioactive elements exist? Why is carbon-based life so dependent on their existence? Why do they exist in the small amounts that we see nowadays? Is the future accumulation of radioactive nuclei planned for some purpose? Are carbon-based civilizations destined to use this energy, someday? Are they supposed to be "filtered" by the danger of the power of nuclear fission? It is a theme that Isaac Asimov already explored in his 1957 short story "The Gentle Vultures.

Surely, we need to avoid the mistake of the fleas that think that the dog was created for them. But, who knows? The flea God may be more powerful than what we can imagine.


(*) It has been hypothesized that DNA-like structures could exist inside stars, formed by the combination of "cosmic strings" and "magnetic monopoles." But, for what we can say, these lifeforms cannot move out of their stars and maybe they can't even perceive the existence of the universe outside. Something similar holds for neutron stars, despite the attempt by Robert Forward in his novel "Dragon's Egg" (1980) to imagine living beings composed of neutronium. Black holes, then, tend to destroy information and have an extremely long life. Of course, there may exist things we can't even remotely imagine in the universe but for the time being that seems to be a safe assumption. Incidentally, I went back to read Forward's novel and I found it incredibly boring. Times are changing and the novel is by now an obsolete art form.