Earth as a Lovely and Placid Place

Earth as a Lovely and Placid Place

The Earth is a lovely and more or less placid place. Things change, but slowly. We can lead a full life and never personally encounter a natural disaster more violent than a storm. And so we become complacent, relaxed, unconcerned. But in the history of Nature the record is clear. Worlds have been devastated. Even we humans have achieved the dubious technical distinction of being able to make our own disasters, both intentional and inadvertent. On the landscapes of other planets where the records of the past have been preserved, there is abundant evidence of major catastrophes. It is all a matter of time scale. An event that would be unthinkable in a hundred years may be inevitable in a hundred million. Even on the Earth, even in our own century, bizarre natural event have occurred.

In the vast spaces between the planets there are many objects, some rocky, some metallic, some icy, some composed partly of organic molecules. They range from grains of dust to irregular blocks the size of Nicaragua or Bhutan. And sometimes, by accident, there is a planet in the way. The Tunguska Event was probably caused by an icy cometary fragment about a hundred meters across – the size of a football field – weighing a million tons, moving at about 30 kilometers per second, 70,000 miles per hour.

Could an asteroid trigger a nuclear war? Earth is a Placid Place. Photo: Elena

If an impact such as Tunguska Event occurred today it might be mistaken, especially in the panic of the moment, for a nuclear explosion. The cometary impact and fireball would simulate all effects of a one-megaton nuclear blast, including the mushroom cloud, with two exceptions: there would be no gamma radiation or radioactive fallout. Could a rare but natural event, the impact of a sizable cometary fragment trigger a nuclear war? A strange scenario: a small comet hits the Earth, as millions of them have, and the response of our civilization is promptly to self-destruct. It might be a good idea for us to understand comets and collisions and catastrophe a little better than we do. For example, an American Vela satellite detected an intense double flash of light from the vicinity of the South Atlantic and Western Indian Ocean on September 22, 1979.

Early speculation held that it was a clandestine test of a low yield (two kilotons, about a sixth the energy of the Hiroshima bomb) nuclear weapon by South Africa or Israel. The political consequences were considered serious around the world. But what if the flashes were instead caused by an impact of a small asteroid or a piece of a comet? Since airborne overflights in the vicinity of the flashes showed not a trace of unusual radioactivity in the air, this is a real possibility and underscores the danger in an age of nuclear weapons of not monitoring impacts from space better than we do.

Tunguska Event

Tunguska Event

In the early morning hours of June 30, 1908, in Central Siberia, a giant fireball was seen moving rapidly across the sky. Where it touched the horizon, an enormous explosion took place. It leveled some 2,000 square kilometers of forest and burned thousands of trees in a flash fire near the impact site. It produce3d an atmospheric shock wave that twice circled the Earth. For two days afterward, there was so much fine dust in the atmosphere that one could read a newspaper at night by scattered light in the streets of London, 10,000 kilometers away.

The government of Russia under the Czars could not be bothered to investigate so trivial an event, which, after all, had occurred far away, among the backward Tungus people of Siberia. It was ten years after the Revolution before an expedition arrived to examine the ground and interview the witnesses. These are some of the accounts they brought back:

Early in the morning, when everyone was asleep in the tent, it was blown up into the air, together with the occupants. When they fell back to Earth, the whole family suffered slight bruises, but Akulina and Ivan actually lost consciousness. When they regained consciousness they heard a great deal of noise and saw the forest blazing round them and much of it devastated.

I was sitting in the porch of the house at the trading station of Vanovara at breakfast time and looking towards the north. I had just raised my axe to hoop a cask, when suddenly… the sky was split in two, and high above the forest the whole northern part of the sky appeared to be covered with fire. At that moment I felt a great heat as if my shirt had caught fire. I wanted to pull off my short and throw it away, but at that moment there was a bang in the sky, and a might crash was heard. I was thrown on the ground about three sajenes away from the porch and for a moment I lost consciousness. My wife ran out and carried me into the hut. The crash was followed by a noise like stones falling from the sky or guns firing. The Earth trembled and when I lay on the ground I covered my head because I was afraid that stones might hit it. At that moment, when the sky opened, a hot wind, as from a cannon, blew past the huts from the north. It left its mark on the ground.

Tunguska Event: A giant fireball explosed in the air, it’s all we are certain about it. Image: Princess and Butterfly Wings on Mythical Horse by © Megan (Elena)

When I sat down to have my breakfast beside my plough, I heard sudden bangs, as if from gun-fire. My horse fell to its knees. From the north side above the forest a flame shot up… Then I saw that the fir forest had been bent over by the wind and I thought of a hurricane. I seized hold of my plough with both hands, so that I would not be carried away. The wind was so strong that it carried off some of the soil from the surface of the ground, and then the hurricane drove a wall of water up the Angara. I saw it all quite clearly, because my land was on a hillside.

The roar frightened the horses to such an extent that some galloped off in panic, dragging the ploughs in different directions, and others collapsed.

The carpenters, after the first and second crashes, had crossed themselves in stupefaction, and when the third crash resounded, they fell backwards from the building onto the chips of wood. Some of them were so stunned and utterly terrified that I had to calm them down and reassure them. We all abandoned work and went into the village. There, whole crowds of local inhabitants were gathered in the streets in terror, talking about this phenomenon.

I was in the fields… and had only just got one horse harnessed to the harrow and begun to attach another when suddenly I heard what sounded like a single loud shot to the right. I immediately turned round and saw an elongated flaming object flying through the sky. The front part was much broader than the tall end and its color was like fire in the day-time. It was many times bigger than the Sun, but much dimmer, so that it was possible to look at it with the naked eye. Behind the flames trailed what looked like dust. It was wreathed in little puffs, and blue streamers were left behind from the flames… As soon as the flame had disappeared, bangs louder than shots from a gun were heard, the ground could be felt to tremble, and the window panes in the cabin were shattered.

I was washing wool on the bank of the River Kan. Suddenly a noise like a fluttering of the wings of a frightened bird was heard… and a kind of swell came up the river. After this came a single sharp bang so loud than one of the workmen fell into the water.

This remarkable occurrence is called the Tunguska Event. Some scientists have suggested that it was caused by a piece of hurtling antimatter, annihilated on contact with the ordinary matter of the Earth, disappearing in a flash of gamma rays. But the absence of radioactivity at the impact site gives no support to this explanation. Other postulate than a mini black hole passed through the Earth in Siberia and out the other side. But the records of atmospheric shock waves show no hint of an object booming out of the North Atlantic later that day.

Perhaps it was a spaceship of some unimaginably advanced extraterrestrial civilization in desperate mechanical trouble, crashing in a remote region of an obscure planet. But at the site of the impact there is no trace of such a ship. Each of these ideas has been proposed, some of them more or less seriously. Not one of them is strongly supported by the evidence.

The key point of the Tunguska Event is that there was a tremendous explosion, a great shock wave, an enormous forest fire, and yet there is no impact crater at the site. There seems to be only one explanation consistent with all the facts: In 1908 a piece of comet hit the Earth.

Is Cosmos Knowable?

Is Cosmos Knowable?

Plato and Aristotle were comfortable in a slave society. They offered justifications for oppression. They served tyrants. They taught the alienation of the body from the mind (a natural enough ideal in a slave society); they separated matter from thought; they divorced the Earth from the heavens – divisions that were to dominate Western thinking for more than twenty centuries.

Plato, who believed that “all things are full of gods”, actually used the metaphor of slavery to connect his politics with his cosmology. He is said to have urged the burning of all the books of Democritus (he had a similar recommendation for the books of Homer), perhaps because Democritus did not acknowledge immortal souls of mortal gods or Pythagorean mysticism, or because he believed in an infinite number of worlds. Of the seventy-three books Democritus is said to have written, covering all of human knowledge, not a single book survived. All we know is from fragments, chiefly on ethics, and second-hand accounts. The same is true of almost all the other ancient Ionian scientists.

We are flawed by ancient contradictions. Image: © Megan Jorgensen (Elena)

In the recognition by Pythagoras and Plato that the Cosmos is knowable, that there is a mathematical underpinning to nature, they greatly advanced the cause of science. But in the suppression of disquieting facts, the sense that science should be kept for small elite, the distaste for experiment, the embrace of mysticism and the easy acceptance of slave societies, they set back the human enterprise. After a long mystical sleep in which the tools of scientific inquiry lay moldering, the Ionian approach, in some cases transmitted through scholars at the Alexandrian Library, was finally rediscovered.

The Western world reawakened. Experiment and open inquiry became one more respectable. Forgotten books and fragments were again read. Leonardo and Columbus and Copernicus were inspired by or independently retraced parts of this ancient Greek tradition. There is in our time much Ionian science, although not in politics and religion, and a fair amount of courageous free inquiry. But there are also appalling superstitions and deadly ethical ambiguities.

Alien Culture

It was in Alexandria, during the six hundred years beginning around 300 B.C., that human beings, in an important sense, began the intellectual adventure that has to led them to the shore of space. But of the look and feel of that glorious marble city nothing remains. Oppression and the fear of learning have obliterated almost all memory of ancient Alexandria, whose population was marvelously diverse. Macedonian and later Roman soldiers, Egyptian priests, Greek aristocrats, Phoenician sailors, Jewish merchants, visitors from India and sub-Saharan Africa – everyone, except the vast slave population – lived together in harmony and mutual respect for most of the period of Alexandria’s greatness.

The city of Alexandria was founded by Alexander the Great and constructed by his former bodyguard. Alexander encouraged respect for alien cultures and the open-minded pursuit of knowledge.

According to legend – and it does not much matter whether it really happened – he descended beneath the Red Sea in the world’s first diving bell. He encouraged his soldiers and generals to marry Indian and Persian women. He respected the gods of other nations and he collected exotic lifeforms, including an elephant for Aristotle, his teacher.

Is it not worthy of tears that, when the number of worlds is infinite, we have not yet become lords of a single one? (Alexander the Great, when asked why he wept on hearing there was an infinite number of worlds, from On the Tranquility of the Mind, by Plutarch). Image : © Megan Jorgensen (Elena)

Anaxagoras

Anaxagoras

Anaxagoras was an Ionian experimentalist who flourished around 450 B.C. and lived in Athens. He was a rich man, indifferent to his wealth but passionate about science. Asked what was the purpose of life, he replied, “the investigation of the Sun, the Moon, and the heavens”, the reply of a true astronomer. He performed a clever experiment in which a single drop of white liquid, like cream, was shown not to lighten perceptibly the contents of a great pitcher of dark liquid, lie wine. There must, he concluded, be changes deducible by experiment that are too subtle to be perceived directly by the senses.

Anaxagoras was not nearly so radical as Democritus. Both were thoroughgoing materialists, not in prizing possessions but in holding that matter alone provided the underpinnings of the world. Anaxogaras believed in a special mind substance and disbelieved in the existence of atoms. He thought humans were mere intelligent than other animals because of our hands, a very Ionian idea.

He was the first person to state clearly that the Moon shines by reflected light, and he accordingly devised a theory of the phases of the Moon.

The prevailing belief was that the Sun and Moon were gods. Anaxagoras held that the Sun and stars are fiery stones. We do not feel the heat of the stars because they are too far away. This doctrine was so dangerous that the manuscript describing it had to be circulated in secret, an Athenian samizdat. It was not in keeping with the prejudices of the time to explain the phases or eclipses of the Moon by the relative geometry of the Earth, the Moon and the self-luminous Sun. Aristotle, two generations later, was content to argue that those things happened because it was the nature of the Moon to have phases and eclipses – mere verbal juggling, an explanation that explains nothing.

Anaxagoras was convicted and imprisoned for the religious crime of impiety – because he had taught the Moon was made of ordinary matter. But those were ancient times. Have we changed? (Quotations from Megan Jorgensen). Image: © Megan Jorgensen (Elena)

Anaxagoras also thought that the Moon has mountains (right) and inhabitants (wrong). He held that the Sun was so huge that it was probably larger than the Peloponnesus, roughly the southern third of Greece. His critics thought this estimate excessive and absurd.

Anaxagoras was brought to Athens by Pericles, its leader in its time of greatest glory, but also the man whose actions led to the Peloponnesian War, which destroyed Athenian democracy. Pericles delighted in philosophy and science, and Anaxagoras was one of his principal confidants. There are those who think that in this role Anaxagoras contributed significantly to the greatness of Athens. But Pericles had political problems. He was too powerful to be attacked directly, so his enemies attacked those close to him.

Anaxagoras was convicted and imprisoned for the religious crime of impiety – because he had taught the Moon was made of ordinary matter, that it was a place, and that the Sun was a red-hot stone in the sky. Bishop John Wilkins commented in 1638 on theses Athenians: “Those zealous idolators counted it a great blasphemy to make their God a stone, whereas notwithstanding they were so senseless in their adoration of idols as to make a stone their God”. Pericles seems to have engineered Anaxagoras’ release from prison, but it was too late. In Greece the tide was turning, although the Ionian tradition continued in Alexandrian Egypt two hundred years later.

Ocean of Truth

Ocean of Truth

Isaac Newton, in his mid-forties, was described by his servant as follows: “I never knew him to take any recreation or pastime either in riding out to take the air, walking, bowling, or any other exercise whatever, thinking all hours lost that were not spent in his studies, to which he kept so close that he seldom left his chamber unless to lecture at term time… where so few went to hear him, and fewer understood him, that offtimes he did in a manner, for want of hearers, read to the walls.

Students both of Kepler and of Newton never knew what they were missing.

Newton discovered the law of inertia, the tendency of a moving object to continue moving in a straight line unless something influences it and moves it out of his path. The Moon, it seemed to Newton, would fly off in a straight line, tangential to its orbit, unless there were some other force constantly diverting the path into a near circle, pulling it in the direction of the Earth. This force Newton called gravity, and believed that it acted at a distance.

The great ocean of truth lay all undiscovered before me (Isaac Newton). Image: © Meg Jorgensen (Elena)

There is nothing physically connecting the Earth and the Moon. And yet the Earth is constantly pulling the Moon toward us. Using Kepler’s third law, Newton mathematically deduced the nature of the gravitational force (sadly, he does not acknowledge his debt to Kepler in his masterpiece the Principal. But in a 1686 letter to Edmund Halley, he says of his law of gravitation: “I can affirm that I gathered it from Kepler’s theorem about twenty years ago”). He showed that the same force that pulls an apple down to Earth keeps the Moon in its orbit and accounts for the revolutions of the then recently discovered moons of Jupiter in their orbits about that distant planet.

Things had been falling down since the beginning of time. That the Moon went around the Earth had been believed for all of human history. Newton was the first person ever to figure out that these two phenomena were due to the same force. This is the meaning of the word “universal” as applied to Newtonian gravitation. The same law of gravity applies everywhere in our universe.

It is a law of the inverse square. The force declines inversely as the square of distance. If two objects are moved twice as far away, the gravity now pulling them together is only one-quarter as strong. If they are over ten times farther away, the gravity is ten squared, 10(2) = 100 times smaller. Clearly, the force must in some sense be inverse – that is, declining with distance. If the force were direct, increasing with distance, then the strongest force would work on the most distant objects, and we can suppose all the matter in the universe would find itself careering together into a single cosmic lump. No, gravity must decrease with distance, which is why a comet or a planet moves slowly when far from the Sun and faster when close to the Sun. The gravity it feels is weaker the farther from the Sun it is.