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Authors: Richard Dawkins

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BOOK: The Magic of Reality
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Dust mites are too small for us to see, but the cells of which they are made are smaller still. The bacteria that live inside them – and us – in vast numbers are smaller even than that.

And atoms are far far smaller even than bacteria. The whole world is made of incredibly tiny things, much too small to be visible to the naked eye – and yet none of the myths or so-called holy books that some people, even now, think were given to us by an all-knowing god, mentions them at all! In fact, when you look at those myths and stories, you can see that they don’t contain any of the knowledge that science has patiently worked out. They don’t tell us how big or how old the universe is; they don’t tell us how to treat cancer; they don’t explain gravity or the internal combustion engine; they don’t tell us about germs, or nuclear fusion, or electricity, or anaesthetics. In fact, unsurprisingly, the stories
in
holy books don’t contain any more information about the world than was known to the primitive peoples who first started telling them! If these ‘holy books’ really were written, or dictated, or inspired, by all-knowing gods, don’t you think it’s odd that those gods said nothing about any of these important and useful things?

5

W
HY DO WE HAVE
NIGHT AND DAY,
WINTER AND
SUMMER?

 

OUR LIVES ARE
dominated by two great rhythms, one much slower than the other. The fast one is the daily alternation between dark and light, which repeats every 24 hours, and the slow one is the yearly alternation between winter and summer, which has a repeat time of a little over 365 days. Not surprisingly, both rhythms have spawned myths. The day–night cycle especially is rich in myth because of the dramatic way the sun seems to move from east to west. Several peoples even saw the sun as a golden chariot, driven by a god across the sky.

The aboriginal peoples of Australia were isolated on their island continent for at least 40,000 years, and they have some of the oldest myths in the world. These are mostly set in a mysterious age called the Dreamtime, when the world began and was peopled by animals and a race of giant ancestors. Different tribes of aborigines have different myths of the Dreamtime. This first one comes from a tribe who live in the Flinders Ranges of southern Australia.

During the Dreamtime, two lizards were friends. One was a goanna (the Australian name for a large monitor lizard) and the other a gecko (a delightful little lizard with suction
pads
on its feet, with which it climbs up vertical surfaces). The friends discovered that some other friends of theirs had been massacred by the ‘sun-woman’ and her pack of yellow dingo dogs.

Furious with the sun-woman, the big goanna hurled his boomerang at her and knocked her out of the sky. The sun vanished over the western horizon and the world was plunged into darkness. The two lizards panicked and tried desperately to knock the sun back into the sky, to restore the light. The goanna took another boomerang and hurled it westwards, to where the sun had disappeared. As you may know, boomerangs are remarkable weapons that come back to the thrower, so the lizards hoped that the boomerang would hook the sun back up into the sky. It didn’t. They then tried throwing boomerangs in all directions, in a vague hope of retrieving the sun. Finally, goanna lizard had only one boomerang left, and in desperation he threw it to the east, the opposite direction from where the sun had disappeared. This time, when it returned, it brought the sun with it. Ever since then, the sun has repeated the same pattern of disappearing in the west and reappearing in the east.

Many myths and legends from all around the world have the same odd feature: a particular incident happens once, and then, for reasons never explained, the same thing goes on happening again and again for ever.

Here’s another aboriginal myth, this time from southeastern Australia. Someone threw the egg of an emu (a sort of Australian ostrich) up into the sky. The sun hatched out of the egg and set fire to a pile of kindling wood which happened
(for
some reason) to be up there. The sky god noticed that the light was useful to men, and he told his servants to go out every night from then on, to put enough firewood in the sky to light up the next day.

The longer cycle of the seasons is also the subject of myths all around the world. Native North American myths, like many others, often have animal characters. In this one, from the Tahltan people of western Canada, there was a quarrel between Porcupine and Beaver over how long the seasons ought to be. Porcupine wanted winter to last five months, so he held up his five fingers. But Beaver wanted winter to last for more months than that – the number of grooves in his tail. Porcupine was angry and insisted on an even shorter winter. He dramatically bit off his thumb and held up the remaining four fingers. And ever since then winter has lasted four months.

I find this a rather disappointing myth, because it already assumes that there will be a winter and summer, and explains only how many months each will last. The Greek myth of Persephone is better in this respect at least.

Persephone was the daughter of the chief god Zeus. Her mother was Demeter, fertility goddess of the Earth and the harvest. Persephone was greatly loved by Demeter, whom she helped in looking after the crops. But Hades, god of the underworld, home of the dead, loved Persephone too. One day, when she was playing in a flowery meadow, a great chasm opened up and Hades appeared from below in his chariot; seizing Persephone, he carried her down and made her the queen of his dark, underground kingdom. Demeter was so
grief-stricken
at the loss of her beloved daughter that she stopped the plants growing, and people began to starve. Eventually Zeus sent Hermes, the gods’ messenger, down to the underworld to fetch Persephone back up to the land of the living and the light. Unfortunately, it turned out that Persephone had eaten six pomegranate seeds while in the underworld, and this meant (by the kind of logic we have become used to where myths are concerned) that she had to go back to the underworld for six months (one for each pomegranate seed) in every year. So Persephone lives above ground for part of the year, beginning in the spring and continuing through summer. During this time, plants flourish and all is merry. But during the winter, when she has to return to Hades because she ate those pesky pomegranate seeds, the ground is cold and barren and nothing grows.

What
really
changes day to night, winter to summer?

Whenever things change rhythmically with great precision, scientists suspect that either something is swinging like a pendulum or something is rotating: going round and round. In the case of our daily and seasonal rhythms, it’s the second. The seasonal rhythm is explained by the yearly orbiting of the Earth around the sun, at a distance of about 93 million miles. And the daily rhythm is explained by the Earth’s spinning round and round like a top.

The illusion that the sun moves across the sky is just that – an illusion. It’s the illusion of
relative movement
. You will have met the same kind of illusion often enough. You are in a
train
, standing at a station next to another train. Suddenly you seem to start ‘moving’. But then you realize that you aren’t actually moving at all. It is the second train that is moving, in the opposite direction. I remember being intrigued by the illusion the first time I travelled in a train. (I must have been very young, because I also remember another thing I got wrong on that first train journey. While we were waiting on the platform, my parents kept saying things like ‘Our train will be coming soon’ and ‘Here comes our train’, and then ‘This is our train now’. I was thrilled to get on it because this was
our
train. I walked up and down the corridor, marvelling at everything, and very proud because I thought we
owned
every bit of it.)

The illusion of relative movement works the other way, too. You think the other train has moved, only to discover that it is your own train that is moving. It can be hard to tell the difference between apparent movement and real movement. It’s easy if your train starts with a jolt, of course, but not if your train moves very smoothly. When your train overtakes a slightly slower train, you can sometimes fool yourself into thinking your train is still and the other train is moving slowly backwards.

It’s the same with the sun and the Earth. The sun is not really moving across our sky from east to west. What is really happening is that the Earth, like almost everything in the universe (including the sun itself, by the way, but we can ignore that), is spinning round and round. Technically we say the Earth is spinning on its ‘axis’: you can think of the axis as a bit like an axle running right through the globe from North
Pole
to South Pole. The sun stays almost still relative to the Earth (not relative to other things in the universe, but I am just going to write about how it seems to us here, on Earth). We spin too smoothly to feel the movement, and the air we breathe spins with us. If it didn’t, we would feel it as a mighty rushing wind, because we spin at a thousand miles an hour. At least, that is the spin speed at the equator; obviously we spin more slowly as we approach the North or South Pole because the ground we’re standing on has less far to go to complete a circuit round the axis. Since we can’t feel the spinning of the planet, and the air spins with us, it’s like the case of the two trains. The only way we can tell we are moving is to look at objects that are not spinning with us: objects like the stars and the sun. What we see is the relative movement, and – just as with the trains – it looks as though we are standing still and the stars and the sun are moving across our sky.

A famous thinker called Wittgenstein once asked a friend and pupil called Elizabeth Anscombe,

‘Why do people say it was natural to think that the sun went round the Earth rather than that the Earth turned on its axis?’

Miss Anscombe answered,

‘I suppose because it looked as if the sun went round the Earth.’

‘Well,’ Wittgenstein replied, ‘what would it have looked like if it had looked as if the Earth turned on its axis?’

You try and answer that!

If the Earth is spinning at a thousand miles an hour, why, when we jump straight up in the air, don’t we come
down
in a different place? Well, when you are on a train travelling at 100 mph, you can jump up in the air and you still land in the same place on the train. You can think of yourself as being hurled forwards by the train as you jump, but it doesn’t feel like that because everything else is moving forwards at the same rate. You can throw a ball straight up on a train and it comes straight down again. You can play a perfectly good game of ping-pong on a train, so long as it is travelling smoothly and not accelerating or decelerating or going fast around a corner. (But only in an enclosed carriage. If you tried to play ping-pong on an open truck the ball would blow away. This is because the air comes with you in an enclosed carriage, but not when you are standing on an open truck.) When you are travelling at a steady rate in an enclosed railway carriage, no matter how fast, you might as well be standing stock still as far as ping-pong, or anything else that happens on the train, is concerned. However, if the train is speeding up (or slowing down), and you jump up in the air, you will come down in a different place! And a game of ping-pong on an accelerating or decelerating or turning train would be a strange game, even though the air inside the carriage is dead still relative to the carriage. We’ll come back to this later, in connection with what it is like when you throw things about in an orbiting space station.

Working round the clock – and the calendar

Night gives way to day, and day gives way to night, as the part of the world we happen to be standing on spins to face the
sun
, or spins into the shade. But almost as dramatic, at least for those of us who live far from the equator, is the seasonal change from short nights and long, hot days in summer to long nights and short, cold days in winter.

The difference between night and day is dramatic – so dramatic that most species of animal can thrive either in the day or in the night but not both. They usually sleep during their ‘off’ period. Humans and most birds sleep by night and work at the business of living during the day. Hedgehogs and jaguars and many other mammals work by night and sleep by day.

In the same way, animals have different ways of coping with the change between winter and summer. Lots of mammals grow a thick, shaggy coat for the winter, then shed it in spring. Many birds, and mammals too, migrate, sometimes huge distances, to spend the winter closer to the equator, then migrate back to the high latitudes (the far north or far south) for the summer, where the long days and short nights provide bumper feeding. A seabird called the Arctic tern carries this to an extreme. Arctic terns spend the northern summer in the Arctic. Then, in the northern autumn, they migrate south – but they don’t stop in the tropics, they go all the way to the Antarctic. Books sometimes describe the Antarctic as the ‘wintering grounds’ of the Arctic tern, but of course that’s nonsense: by the time they get to the Antarctic it is the southern summer. The Arctic tern migrates so far that it gets two summers: it has no ‘wintering grounds’ because it has no winter. I’m reminded of the joking remark of a friend of mine who lived in England during the
summer
, and went to tropical Africa to ‘tough out the winter’!

Another way some animals avoid the winter is to sleep through it. It’s called ‘hibernation’, from
hibernus
, the Latin word for ‘wintry’. Bears and ground squirrels are among the many mammals, and quite a lot of other kinds of animals, that hibernate. Some animals sleep continuously through the whole winter; some sleep for most of the time, occasionally stirring into sluggish activity and then sleeping again. Usually their body temperature drops dramatically during hibernation and everything inside them slows down almost to a stop: their internal engines just barely tick over. There’s even a frog in Alaska which goes so far as to freeze solid in a block of ice, thawing out and coming to life again in the spring.

Even those animals, like us, that don’t hibernate or migrate to avoid the winter have to adapt to the changing seasons. Leaves sprout in spring and fall in autumn (which is why it’s called the ‘fall’ in America), so trees that are a lush green in summer become gaunt and bare in winter. Lambs are born in spring, so they get the benefit of warm temperatures and new grass as they are growing. We may not grow long, woolly coats in winter, but we often wear them.

So we can’t ignore the changing seasons, but do we understand them? Many people don’t. There are even some people who don’t understand that the Earth takes a year to orbit the sun – indeed, that’s what a year is! According to a poll, 19 per cent of British people think it takes a month, and similar percentages have been found in other European countries.

Even among those who understand what a year means,
there
are many who think the Earth is closer to the sun in summer, more distant in winter. Tell that to an Australian, barbecuing Christmas dinner in a bikini on a baking hot beach! The moment you remember that in the southern hemisphere December is midsummer and June is midwinter, you realize that the seasons can’t be caused by changes in how close the Earth is to the sun. There has to be another explanation.

BOOK: The Magic of Reality
10.37Mb size Format: txt, pdf, ePub
ads

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