The Universe Inside You E-Book

Brian Clegg

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2012

Seitenzahl: 391

Beschreibung

Built from the debris of exploding stars that floated through space for billions of years, home to a zoo of tiny aliens, and controlled by a brain with more possible connections than there are atoms in the universe, the human body is the most incredible thing in existence. In the sequel to his bestselling Inflight Science, Brian Clegg explores mitochondria, in-cell powerhouses which are thought to have once been separate creatures; how your eyes are quantum traps, consuming photons of light from the night sky that have travelled for millions of years; your many senses, which include the ability to detect warps in space and time, and why meeting an attractive person can turn you into a gibbering idiot. Read THE UNIVERSE INSIDE YOU and you'll never look at yourself the same way again.

Leseprobe

Printed edition published in the UK in 2012 by

Icon Books Ltd, Omnibus Business Centre,

39–41 North Road, London N7 9DP

email: [email protected]

www.iconbooks.co.uk

This electronic edition published in the UK in 2012 by Icon Books Ltd

ISBN: 978-1-84831-354-5 (ePub format)

ISBN: 978-1-84831-355-2 (Adobe ebook format

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This edition published in the USA in 2012 by Icon Books

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Text copyright © 2012 Brian Clegg

The author has asserted his moral rights.

No part of this book may be reproduced in any form, or by any means, without prior permission in writing from the publisher.

Typeset in Melior by Marie Doherty

Contents

Title page

Copyright

List of illustrations

Acknowledgements

Introduction

1. In the mirror

On reflection

2. A single hair

The colours of nature

Dyeing to be attractive

Worrying about hair loss

To make allies, lose your hair

Lost in space

A lousy measurement

Getting under your skin

What is stuff made of?

Battered by molecules

Empty atoms and electromagnetic bottoms

Exploring an atom’s innards

No miniature solar system

Taking a quantum leap

The charm of quarks

The messy standard model

Is it solid, liquid or gas?

The fourth state of matter

Enter the condensate

Every kind of stuff

You are what you eat

Components that pre-date the Earth

A sprinkling of stardust

3. Locked up in a cell

Cursing the pain away

A living liquid

The signs of life

Are your cells alive?

A voyage through your bloodstream

The special molecule

A company of tiny boxes

The superstar molecule

Your own special code

The invaders in your cells

Wearing your alien genes

Your trillions of tiny stowaways

A useful appendix

Bacteria don’t know the five-second rule

Worming their way into your affection

The noble leech

Aliens in the eyelashes

Seeing small

The rays that don’t stop giving

Cats and nuclear resonance

Hunting the elusive neutrino

The neutrinos light couldn’t catch

4. Through fresh eyes

In Orion’s belt

Seeing into the past

Waves or particles?

Bursting from the heart of a star

The 1,340-year star trek

The distorting lens

The Baywatch principle

Looking through a lentil

Through a glass, darkly

The messy colours of sight

Picking up the photons

From light to mind

Your artificial view of the world

Quantum reality

Through Young’s slits

Uncertainty reigns

Getting entangled

A normal whole from quantum parts

A galactic feat

Glow-in-the-dark urine

Remnants of the Big Bang?

The expanding universe

The probable Big Bang

Playing with models

The out-of-control universe

A quasar too far

Black hole myths

Building a black hole

The non-eternal sunshine

The power source of life

Is there anybody out there?

The intelligence test

We are isolated, if not alone

5. Marching on the stomach

Your inner chemistry

Reach for a chunk of rock

The evil compound of life

Adding a little fizz

Sitting at Dmitri’s table

Meet element 114

Heavy metal or noble gas?

Turning food into energy

Hot food is good food

The cup that cheers

Food of the gods

The winners’ drug

From chemical energy to moving muscle

Making work happen

The great bumble bee mystery

The elastic kangaroo

Heat on the move

No perpetual motion machines

The energy Crookes

Infinite clean energy

Entropy increases

The physics of monsters

Staying on two legs

Fidgets and knuckle-crackers

6. Feeling dizzy

Counting the senses

From compression wave to brain wave

Audible illusions

The sound of emotion

All in good taste

Flavours and taste buds

The mineral in the kitchen cupboard

Sniffing your way around

Scenting a mate

À la recherche de odeur perdu

The sense that’s everywhere

Seeing with your skin

A sense of pain

Finding your own nose

Sensing the accelerator

Weight and mass

Push me pull you

The occult force

Warping space and time

Falling and missing

No more action at a distance

Slowing your clocks

The force of creation

The force of electricity and magnetism

Going with the current

Into the nucleus

The close-up force

Travelling through time

Light gets relative

Tunnelling through time

Build your own time machine

The paradoxes of time

Breathing easier at the theme park

7. Two by two

What do you mean, attractive?

Birds do it, bees do it …

You can’t make an omelette without breaking eggs

Doing it the prehistoric way

The Stone Age technology in the park

Dog as prosthetic

Genetic engineering the natural way

The mighty 23

Beyond the gene

Similarities and differences

Attack of the clones

Hello Dolly

Growing old gracefully

8. Crowning glory

What goes on inside your head

Brains weren’t made for maths

Open the door

The two-boy problem

A test of your understanding

But what does it mean?

You must remember this

Solid state versus squishy state

Remembering how it’s done

Remembering stuff

I know the face

Take down my phone number

I remember that tail from somewhere

The brain scribble

Writing with pictures

Did you hear about my mummy?

Abjads to alphabets

It sounds capital

Are you human?

Would you kill to save lives?

Trusting and ultimatums

Weighing up the options

Allowing for all the factors

It could be you

Economics gets it wrong

Did you do that consciously?

Mood swings and comfort breaks

The brain’s own painkillers

Homeopathic misdirection

The ethics of placebos

9. Mirror, mirror

Building your ancestor tower

How many colours in the rainbow?

No sudden changes

A failure to link up

The babel of towers

Proud to be ‘just a theory’

Newton gets it wrong

Evolving makes a lot of sense

What use is half an eye?

Science can always be proved wrong

The sense of wonder

Appendix: Finding out more

A single hair

Locked up in a cell

Through fresh eyes

Marching on the stomach

Feeling dizzy

Two by two

Crowning glory

Mirror, mirror

List of illustrations

Cross-section of a human hair

The structure of human skin

The letters IBM spelt out with xenon atoms

The structure of an atom

The illustration of a flea in Robert Hooke’s Micrographia

Image from a CAT scan performed on the author

Diagram showing the action of a tunnelling photon

The constellation Orion

The action of light on a mirror with dark strips on it

The chessboard optical illusion

Young’s slits

The location of the galaxy Andromeda

The electromagnetic spectrum

Pie chart of the percentages showing how small ‘ordinary stuff’ is

The periodic table

Tongue flavour map

Light crossing a spaceship

A segment of DNA spiral with a pop-out showing the CGG coding for arginine

Potential combinations of children

Acknowledgements

For Gillian, Chelsea and Rebecca.

My grateful thanks to Simon Flynn, Duncan Heath, Andrew Furlow, Harry Scoble and all at Icon for their help and support.

I’d also like to thank all the real scientists who have answered my idiot questions, including Dr Henry Gee, Professor Stephen Curry, Professor Dan Simons, Professor Arnt Maasø, Dr Mike Dunlavy, Professor Günter Nimtz, Professor Friedrich Wilhelm Hehl and Dr Jennifer Rohn.

Introduction

We are used to science being something remote, performed by experts in laboratories full of strange equipment or using vast and highly technical machinery like the Large Hadron Collider. But we all have our own laboratories in the form of our bodies – hugely complex structures that depend for their functioning on all of the many facets of science and nature.

In this book you will use the workings of your body as a tool to explore the science of the universe. Some of that exploration will be very close to home, while for some of it you will necessarily journey away from your body, to the heart of stars and beyond. These tangents always have a point, illustrating the fundamental science that underlies reality, and we will always, in the end, return to that most miraculous of constructs that is the human body.

Brian Clegg, 2012

1. In the mirror

Stand in front of a mirror, preferably full length, and take a good look at yourself. Not the usual glance – really take in what you see. You may become a little coy at this point. It’s easy to start looking for imperfections, noticing those extra centimetres on the waistline, perhaps. But that’s not the point. I want you to really look at a human being.

In this book you are going to use the human body, your body, to explore the most extreme aspects of science. It’s all there. Everything from the chemistry of indigestion to the Big Bang and the most intractable mysteries of the universe is reflected in that single, compact structure. Your body will be your laboratory and your observatory.

You can look at the whole body, treating it as a single remarkable object. A living creature. But you can also plunge into the detail, exploring the ways your body interacts with the world around it, or how it makes use of the energy in food to get you moving. Zoom in further and you will find somewhere between ten and 100 trillion cells. Each cell is a sophisticated package of life, yet taken alone a single cell is certainly not you. Go further still and you will find complex chemistry abounding – you have a copy of the largest known molecule in most of your body’s cells: the DNA in chromosome 1.

Continue to look in even greater detail and eventually you will reach the atoms that make up all matter. Here traditional numbers become clumsy; a typical adult is made up of around 7,000,000,000,000,000,000,000,000,000 atoms. It’s much easier to say 7 × 1027, simply meaning 7 with 27 zeroes after it. That’s more than a billion atoms for every second the universe is thought to have existed.

There’s a whole lot going on inside that apparently simple form that you see standing in front of you in the mirror.

On reflection

In a moment we’ll plunge in to explore the miniature universe that is you, but let’s briefly stay on the outside, looking at your image in the mirror. Here’s a chance to explore a mystery that puzzled people for centuries.

Stand in front of a mirror. Raise your right hand. Which hand does your reflection raise?

As you’d expect from experience, your reflection raises its left hand.

Here’s the puzzle. The mirror swaps everything left and right – something we take for granted. Your left hand becomes your reflection’s right hand. If you close your right eye, your reflection closes its left. If your hair is parted on the left, your reflection’s hair is parted on the right. Yet the top of your head is reflected at the top of the mirror and your feet (if it’s a full-length mirror) are down at the bottom. Why does the mirror switch around left and right, but leave top and bottom the same? Why does it treat the two directions differently?

Here’s a chance to think scientifically. There are three things influencing how the mirror produces your image. The way light travels between you and the mirror, the way that you detect that light (with your eyes) and, finally, the way that your brain interprets the signals it receives. We will explore all of these aspects of your body in more detail later in the book, but one significant point may leap out immediately as you think about the process of seeing your reflection. Your eyes are arranged horizontally. You have a left and a right eye, not top and bottom eyes. Could this be why the switch only happens left and right?

Sadly, no. It’s a pretty good hypothesis, but in this case it’s wrong. That’s not a bad thing; much of our understanding of science comes from discovering why ideas are wrong. Let’s try a little experiment that will help clarify what is really happening.

Experiment – On reflection

Hold up a book (or magazine) in front of you, closed, with the front cover towards you. Look at the book in the mirror. What do you see? Be as precise as possible. List everything that you can say about the reflected book. Does this help explain why the mirror works the way it does?

Do try this yourself first, but here’s what I see:

The book in the mirror is printed in mirror writing, swapped left to right.The reflected book is as far behind the mirror as my book is in front of it.The book’s colours are the same in the mirror as they are on my side.The front cover of the book in the mirror is the back cover of my book.

Just take a look at that last statement. If I simply consider the book in the mirror to be an ordinary book then, as I look at it, my book’s back cover has become the mirror book’s front cover. Lurking here is the explanation of the mirror’s mystery. It doesn’t swap left and right at all. It swaps back and front.

In effect, what the mirror does is turn an image inside out. The back of my book becomes the front of the book in the mirror. Put the book down and look at your own reflection again. Imagine that your skin is made of rubber and is detachable. Take off that imaginary skin, move it straight through the mirror and, without turning it round, turn it inside out. The point of your nose, which was pointing into the mirror is now pointing out of the mirror. The parts of you that are nearest the mirror are also nearest in the reflection. Your entire image has been turned inside out.

In reality there is no swapping of left and right, so you don’t have to explain why the mirror handles this differently from top and bottom. The reason we have the illusion of a left-right switch is down to your brain. When you see your reflection in a mirror your brain tries to turn the reflection into you. It makes a fairly close match if it rotates you through 180 degrees and moves you back into the mirror. This half turn flips left and right. But the key thing to realise is that it’s not the mirror that performs a swap of left and right, it is your brain, trying to interpret the signals it receives from the mirror.

Now, with the mirror’s mystery solved, let’s start our exploration of the universe by taking a look at a single, rather unusual part of your body. We are going to investigate a human hair.

2. A single hair

Take a firm hold of one of the hairs on your head and pull it out. No one said science was going to be entirely painless. If you want to make this less stressful, get a hair from a hairbrush. If you are bald, get hold of someone else’s hair – but ask first! Now, examine what you’ve got. It’s a long, very narrow cylinder, flexible yet surprisingly strong considering how thin it is.

Take as close a look at the hair as you can. If you can lay your hands on a microscope, use that, but otherwise use a magnifying glass.

That strand of hair is going to start us off on everything from philosophy to physics. Dubious about just how philosophical hair can be? Consider this: you are alive and that hair is an integral part of you (or at least it was until you pulled it out). Yet the hairs on your body are dead – they are not made up of living cells. The same is true of fingernails and toenails. So you are alive, but part of what goes to make ‘you’ is dead.

Remember that next time a TV advert is encouraging you to ‘nourish’ your hair. You can’t feed hair. You can’t make it healthy. It’s dead. Deceased. It has fallen off its metaphorical perch. Worried that your hair is lifeless? Well, don’t be. That’s how it is supposed to be. It’s quite amazing just how many hair products are advertised using the inherently meaningless concept of ‘nourishing’.

We’re talking about a single hair, but of course you have (probably) got many more than one on your head. A typical human head houses around 100,000 hairs, though those with blonde hair will usually have above the average, and those with red hair rather fewer. Looking at that individual hair, the colour that provides this distinction doesn’t stand out the same way it does on a full head of hair, but it’s still there.

The colours of nature

The colour in hair comes from two variants of a pigment called melanin. One, pheomelanin, produces red colours. Blonde and brown hair colourings are due to the presence of more or less of the other variant of the pigment, eumelanin. This is the original form of hair pigment – red hair is the result of a mutation at some point in the history of human development.

As we become older, the amount of pigment in our hair decreases, eventually disappearing altogether. Grey and white hairs don’t have any melanin-based pigment inside. In effect they are colourless, but the shape of the hair and its inner structure has an effect on the way that the light passes through it, producing grey and white tones.

Cross-section of a human hair

The inner structure of hair isn’t particularly obvious when you hold a single strand in your hand and look at it with the naked eye, but under a microscope it becomes clear that there is more going on than just a simple filament of uniform material. In effect your hairs have three layers: an inner one that is mostly empty, a middle one (the cortex) that has a complex structure that holds the pigments and can take in water to swell up, and an outer layer called the cuticle which looks scaly under considerable magnification, and which has a water-resistant skin.

On the end of the hair, where you have pulled it out of your scalp, there may be parts of the follicle, the section of the hair usually buried under your skin. The follicle is responsible for producing the rest of the structure and is the only part of the hair that is alive.

Dyeing to be attractive

The idea that the colouring of your hair is produced by melanins assumes it has its natural hue, but many of us have changed our hair colour using dyes at one time or another. Dyes use a surprisingly complex mechanism to carry out the superficially simple task of changing a colour. It’s not like slapping on a coat of paint – the process of dyeing hair owes more to the chemist’s lab than the beauty salon.

In a typical permanent dyeing process, a substance like ammonia is used to open up the hair shaft to gain access to the cortex. Then a bleach, which is essentially a mechanism for adding oxygen, is used to take out the natural colour. Any new colouration is then added to bond onto the exposed cortex. Temporary dyes never get past the cuticle; they sit on the outside of the hair and so are easily washed off.

Worrying about hair loss

Almost every human being has hairs, but compared with most mammals we are very scantily provided. Not strictly in number – we have roughly the same number of hairs as an equivalent-sized chimpanzee – but the vast majority of these hairs are so small as to be practically useless.

Next time you are cold or get a sudden sense of fear, take a look at the skin on your arms. You should be able to see goose bumps or goose pimples. This hair-related (indeed, hair-raising) phenomenon links to the fact that our ancestors once were covered in a thick coat of fur like most other mammals.

When you get goose bumps, tiny muscles around the base of each hair tense, pulling the hair more erect. If you had a decent covering of fur this would fluff up your coat, getting more air into it, and making it a better insulator. That’s a good thing when you are cold, at least if you have fur – now that we’ve lost most of our body hair, it just makes your skin look strange without any warming benefits.

Similarly, we get the bristling feeling of our hair standing on end when we’re scared. Once more it’s a now-useless ancient reaction. Many mammals fluff up their fur when threatened to make themselves look bigger and so more dangerous. (Take a dog near to a cat to see the feline version of this effect in all its glory. The cat will also arch its back to try to look even bigger.) Apparently we used to perform a similar defensive fluffing-up, but once again the effect is now ruined by our relatively hairlessness. We still feel the sensation of having our hair stand on end, but get no benefit in added bulk.

Our lack of natural hairy protection struck me painfully when out walking my dog recently. It was a cold day and I was under-dressed for the weather in a short sleeved shirt. I was shivering and my trainers were soaked from the wet grass, so that I squelched as I walked. When passing through the fence from one field to the next, I managed to brush against a rampant clump of nettles, stinging both my arms.

But the dog, with her thick fur coat and hard padded feet, was impervious to both the weather and the vegetation. She seemed much better prepared to survive what nature could throw at her than I was.

I wondered why human beings are so badly equipped to cope with the discomforts and dangers of the natural world. We know that our distant ancestors had good, thick coats of protective fur, just as the apes still do today. (Present-day apes like chimpanzees and gorillas aren’t our ancestors, but it’s a mistake that’s still often made in describing them.) It seems counter-intuitive that the early humans should have lost that helpful fur.

Of course, it’s a misunderstanding to think that evolution has our best interests in mind. Evolution doesn’t have a mind, or any concept of what is good or bad for us. Evolution usually works by gradual selection of subtle variants that enhance the survival and reproduction capabilities of individual members of species. It doesn’t take an overview and think ‘That’s good, I’ll keep that’. Even so, it seemed unlikely that there was any evolutionary benefit in losing the warmth and protection of that natural fur coat.

Just because evolution deals us a set of cards it doesn’t mean that everything we receive in our genetic hand is beneficial. There doesn’t have to be an obvious evolutionary advantage just because we have developed a certain trait. It’s just as likely to be a side effect of another evolutionary development. For example, many birds have wings that are easily snapped, because the bones are thin and hollow. Having weak bones isn’t a good thing in itself – on the contrary, it’s bad for survival. However, it is necessary to reduce the bird’s weight enough for it to be able to fly.

There are various possibilities as to why it made evolutionary sense to lose the majority of our hair. It might have been due to the need to sweat more as our ancestors moved from the forest to the savannah – it’s easier to sweat with less hair, exposing more skin for sweat to evaporate. Equally it could have been a response to the increase in parasites (though all the great apes are afflicted with these). Most exotically it has been suggested that early humans were partly aquatic, and less body hair made for a sleeker swimmer (though many semi-aquatic mammals are hairy). But the explanation that works best for me is that the loss was an accidental side effect, like those precariously thin bird bones.

To make allies, lose your hair

Around 100,000 years ago our distant ancestors went through the final changes that made them into modern humans. That was the end of our evolution to date. We are the same biological species now as they were back then. There have been plenty of tiny changes at the genetic level, but as a species we are essentially the same. We have the same potential for physical strength, for longevity, for attracting the opposite sex, for thinking and more.

Those many thousands of years ago, our predecessors had undergone huge evolutionary changes from the common ancestor they shared with chimpanzees and the other great apes. The pre-humans had lost most of their hair, leaving a delicate, thin skin exposed. They had shifted from a four-legged gait to walking upright. Their brains had grown out of all proportion with their bodies, leaving them bulgy-headed and top heavy (quite possibly unattractive features at the time). Their mouths had become smaller, making their teeth less effective as a biting weapon. The big toe had ceased to be an opposing digit that could be used to grip a tree branch.

Taken together, these alterations made the pre-humans more vulnerable to attack by predators. Their naked, unprotected skin was pathetically easy for claws and teeth to rip through. Compared with the smooth, four-footed pace of other apes, their tottering movements on two legs were painfully clumsy – a rabbit could easily outrun this strange unstable creature. The adaptations that came through in pre-humans don’t seem to make any sense except as side effects. Put them alongside the change of behaviour that may have triggered them, and they were an acceptable price to pay.

These physical modifications of pre-humans are likely to have been an indirect result of an environmental upheaval. As the global climate underwent violent change, our ancestors were pushed out of the protective forests into the exposed world of the savannah. Facing up to starkly efficient predators, they were forced to change behaviour or become extinct. Back then, most pre-humans could not function well in large groups. This is still the case with most of our close relatives. The chimpanzee, for example, is incapable of forming large, cooperative bands. Get more than a handful of males together and the outcome is bloody carnage as battles for supremacy break out.

The pre-humans who first straggled onto the savannah around five million years ago were probably much the same. But the fast, killing-machine predators of the day – from the terrifying sabre-toothed dinofelis and the lion-sized machairodus to the more familiar hyena – made sure that things changed. The most likely pre-humans to survive were those with a natural tendency to cooperate. Our ancestors began to live in larger groups, giving them the ability to take on a predator and win, where a small band would be torn to pieces. And this change of behaviour may well have brought with it as side effects all the physical oddities that we observe in modern man.

The characteristics that repressed aggression and enhanced the ability to cooperate are typical of juvenile apes. Our primate cousins’ inability to function in large groups only appears with maturity. The individuals amongst our predecessors who were more likely to survive on the savannah, those with the immature ability to get on with their fellows rather than tear them to pieces, were also the least physically developed. The eventual outcome was lack of hair on most of the body, a large head, a small mouth and even the upright stance – all features of the early part of the primate lifecycle that have normally disappeared by the time an individual matures.

As an aside, this mechanism of selecting for cooperative behaviour and getting an infant-like version of the animal is something humanity has since managed to produce repeatedly in its domestic animals. The dog, for example, has much more in common with a wolf cub than with the mature wolf that it was bred from. This is not just a matter of theory. In a fascinating long-term experiment between the 1950s and the 1990s, Russian geneticist Dmitri Belyaev selectively bred Russian silver foxes for docile behaviour and showed just how early man managed to turn the wolf into a dog.

Over 40 years – an immensely long experiment, but no time in evolutionary terms – the fox descendants began to resemble domesticated dogs. Their faces changed shape, becoming more rounded. Their ears no longer stood upright, but drooped down. Their tails became more floppy. Their coats ceased to be uniform in appearance, developing colour variations and patterns. They spent more time playing, and constantly looked for leadership from an adult. As they became more cooperative, they took on the physical appearance and the behaviour patterns of overgrown fox cubs.

To get back to humans, in the process of becoming more cooperative, and so more infantile (neotenous in the scientific jargon), the pre-humans lost the majority of their hair, leaving us with the largely hairless appearance we have today. Except, of course, on our heads. Head hair can be lush in the extreme, and unlike the rest of our body hair (and that of other mammals) it just keeps on growing.

As with our general lack of hair, there are several possible explanations for this. It’s quite possible that originally all our hair stayed at a roughly fixed length, but over time natural selection moved us towards head hair that continued to grow. This could be because those with a mutation causing head hair to keep growing had better protected brains. Or it could have been a side effect of wearing clothes, leaving the head most in need of furry protection. Or it could have provided a shield against the full impact of the noonday Sun, which can be formidable (as anyone with a bald patch can testify). Or there might be another, quite different explanation.

Tracing back the ‘reason’ for an evolutionary trait like this is notoriously difficult because we can’t directly observe what happened or do an experiment to test a particular theory. It’s a bit like news analysis saying that the stock market fell ‘because of lack of confidence in the government’, or for some other reason. No one really knows for certain why the market reacted this way, and similarly no one can prove why humans developed a particular trait. It is inevitably a matter of conjecture.

Lost in space

But given that we are now largely hairless, in some circumstances, clothing is a survival essential. Whether you are venturing under the sea or to the North Pole, your clothing is part of your equipment. And perhaps the greatest example of clothes-as-protection is when someone is out in space. Your body was never intended to be exposed to the extremes of space. The temperature is impossibly cold, as low as –270°C. There is no atmosphere. It’s literally like nothing on Earth. Yet astronauts regularly make spacewalks protected only by specialist clothing.

It is possible to survive in space briefly without the right protection. Hollywood loves showing what would happen to a human being exposed unprotected, and can get it wonderfully wrong. The most ludicrous example is in the 1990 Arnold Schwarzenegger movie Total Recall, based on a Philip K. Dick story, where, expelled from the protected environment of a city on Mars, human beings inflate grossly before their heads explode messily.

Mars actually has a slight atmosphere (around one per cent of Earth’s atmospheric pressure), and even in space this sort of inflation and explosion caused by low pressure isn’t going to happen. There would be some discomfort as gas escaped from body cavities, but there is no danger that your head would inflate like a balloon.

It is true, though, that you would experience some liquids boiling. The lower the pressure, the lower the boiling point of anything, and in space – with no pressure to speak of – you will get an unpleasant drying up of the eyes as water boils away. Some fiction assumes your blood will boil in your veins, too – a horrible way to go – but according to NASA the pressure of your skin and circulatory system is enough to stop this happening.

Another worry is that you would freeze instantly in the very low temperatures of space. But bear in mind how a vacuum flask keeps its contents piping hot. Heat can only travel through a vacuum as light. We get our heat from the Sun in the form of light, which can happily cross empty space. Admittedly our bodies do glow with infrared – they do give off a degree of (invisible) light. But most of the heat we usually lose is passed on by conduction. The heat in our skin – atoms jiggling around with thermal energy – is passed on to the atmosphere, so our atoms jiggle a bit less, and the atmospheric atoms jiggle a bit more. That can’t happen in a vacuum.

You would lose heat, but not very quickly. In practice, the thing that is going to kill you in space is simply the lack of air to breathe, and this will take a number of seconds. NASA has even experienced what would happen, when in 1965 a test subject’s suit sprang a leak in a vacuum chamber. The victim (who survived) stayed conscious for around fourteen seconds in the airless chamber. According to NASA, the exact survival limit isn’t known, but would probably be one to two minutes.

There’s no doubt, then, that clothes can be important survival aids. Yet most of us, in everyday life, only have to cope with environments where plenty of other animals manage perfectly well with a bit of fur and some hardened skin on the feet. As naturists demonstrate, wearing clothes is often a social decision rather than an essential protection, and it’s a decision we’ve been making for a long time. Woven cloth dates back at least 27,000 years – we know this because clay has been found at an ancient settlement at Pavlov in the Czech Republic with the imprint of woven cloth on its surface.

This isn’t the oldest evidence for clothes we have, though. Bone needles have been found at Kostenki, a village in Russia, dating back around 40,000 years. These seem to have been used to stitch together animal skins to provide clothing. But the best clues to just how long we have been wearing clothes comes from the humble­ louse.

A lousy measurement

When Robert Hooke published Micrographia (see page 51), probably the most delight and revulsion came from his fold-out illustration of a louse. Seen magnified they are truly evil-looking parasites, specialist bloodsuckers that live on their host’s skin, taking sips from the blood beneath. As many people with children at junior school know, the head louse is very fussy about sticking with its preferred environment around the base of head hairs. You don’t find head lice straying to other parts of the body. But it does have a cousin that’s less picky.

The human body louse evolved from the head louse between 50,000 and 100,000 years ago. We don’t have ancient lice to work this out from, but this timing can be estimated by looking at the variations in the DNA of the two creatures – the more difference, the longer ago the division between head and body lice occurred.

This is of interest when thinking about the history of clothing because it’s thought that the body louse was only able to develop once we started wearing clothes. Before then, the uncovered skin was too exposed. Interestingly, this 50,000 to 100,000 year timescale corresponds well with the timing of the move of humans out of Africa into colder climates, which could have been the spur that brought on the use of clothing.

Getting under your skin

Underneath your clothes, your body is covered in skin. Like hair, skin relies on melanin-based pigments to get its colouring. Also like hair, the outer layer of your skin is dead. The tiny flakes that contribute to the dust around your house fall off from this surface. Immediately below that dead layer called the stratum corneum (like the cornea in the eye, this ‘corneum’ comes from the Latin for horn, cornu) are two further layers, protective squamous cells and basal cells. The basal cells rise to the surface where they die, to form the outer coating, and they also play host to a different kind of cell, melanocytes, which produce skin pigments.

The more melanin the melanocytes pump out, the darker your skin. The normal state of your skin will have evolved to match the amount of ultraviolet in the light where your ancestors lived. Ultraviolet sits on the spectrum of light between visible light and x-rays – it is energetic enough to cause damage to the DNA inside your cells, if it can penetrate the outer layers of skin. Humans with a history of low exposure to ultraviolet – in the northern hemisphere – tend to lose melanin from the original African levels of their common ancestors.

The structure of human skin

This reduction in protection might not seem to have any advantage, merely adding risk if you get exposed to more sunlight (for example by emigrating to Australia), but in practice it was beneficial. This is because, despite the risk, the body needs some ultraviolet to get through, as it is used to produce the essential vitamin D. This is a vitamin that is relatively uncommon in food and that we need to avoid conditions like rickets. In northern climates, where there isn’t as much sunlight, the early settlers needed more ultraviolet to be allowed through.

This led to paler skin in northern areas, and what melanin the northerners were left with can often clump together to make dark patches, forming freckles and moles. Even in areas where sunlight tends to be weak, levels of ultraviolet can vary, so the skin has a mechanism – tanning – to deal with varying strength of UV. When the skin is exposed to strong sunlight, the melanocytes go into overdrive, producing more melanin and darkening the skin, thereby allowing it to absorb more ultraviolet and preventing damage to the lower layers.

What is stuff made of?

Keratin, the main structural material of the outer layers of both your skin and your hair, is a protein. And a protein is a molecule, a collection of atoms. If you go back to the hair you pulled from your head and start to zoom in, taking in more and more detail, you will eventually get down to the fundamental building blocks of the universe. To understand how your body is constructed, we have to ask what is ‘stuff’ (including your hair) made of?

The Ancient Greeks had two theories. The dominant idea was that everything was made up from four ‘elements’ – earth, air, fire and water. However, a small but vocal opposition thought that if you took stuff and cut it into smaller and smaller pieces you would eventually get to the limit of that cutting. The remaining piece would be uncuttable or a-tomos: they thought everything was made up of atoms. This idea stayed on the back burner for almost 2,000 years, until in the early 1800s, English scientist John Dalton devised modern atomic theory, suggesting that the different elements were made up of different types of small particle called atoms, each type unique to an element.

These elements were not the Ancient Greek four, but chemicals that could not be made out of others. Gases like hydrogen and oxygen, metals like iron and lead, and other substances like carbon and sulfur (for UK readers who think this word looks odd, this is now the standard worldwide chemical spelling for sulphur). Yet even at the start of the twentieth century, most scientists believed that atoms were just a useful concept to make chemistry work, rather than actual entities. It was only with work started by Albert Einstein in 1905 that atoms were finally considered to be real.

Battered by molecules

Atoms are a bit like small children – they are never entirely still. If you look at a glass of water sitting on a table, the water seems motionless. Yet within it, the water molecules are frantically (if randomly) rushing around. Einstein realised that an effect first observed by Scottish botanist Robert Brown in 1827 could be explained by the clumsiness of these energetic molecules.

Brown had spotted that the pollen grains of an evening primrose plant danced around in a drop of water when watched under a microscope. At first, Brown thought this was because there was some kind of life force in the pollen, but the same thing happened with ancient pollen and with stone dust and soot. It wasn’t life in the pollen, but the activity of the water itself that created this ‘Brownian motion’. Einstein realised that it was the water molecules randomly bashing into the pollen grains that caused the movement, and went on to give a mathematical basis for the theory. A little later, in 1912, French physicist Jean Perrin performed a wide range of experiments proving for the first time that atoms and molecules exist.

Remarkably, individual atoms can now both be manipulated and experienced visually. In 1989 a team working at IBM was the first to use a type of electron microscope that can manipulate as well as view, in order to move an individual atom. Two months later they arranged 35 atoms of the element xenon to spell out the initials IBM.

The letters IBM spelt out with xenon atomsPhotograph courtesy of Press Association Images

A little earlier, in 1980 Hans Dehmelt of the University of Washington isolated a single barium ion (an ion is just an atom with electrons missing, or extra electrons added, giving it an electrical charge). When illuminated by the right colour of laser light, that individual barium ion was visible to the naked eye as a pinprick of brilliance floating in space. You might argue that you couldn’t ‘see’ the ion, just light that was reflected by it – but then that’s all that ever happens when we see something.

Empty atoms and electromagnetic bottoms

The atoms that make up your body are not only very small, they are also mostly composed of empty space. If you could squeeze all the matter in your body together, removing the gaps, it would pack into a cube less than 1/500th of a centimetre on each side.

One of the wonders of the cosmos is the neutron star, a star in which the atoms have collapsed, losing all that empty space. In a single cubic centimetre of neutron star material – a chunk little more than the size of a sugar cube – there are around 100 million tons of matter. The entire star, heavier than our Sun, occupies a sphere that is roughly the size across of the island of Manhattan.

There is no danger of the atoms in you or your hair collapsing like a neutron star – without the massive gravitational pull of the star they remain stable. Collections of such atoms make up molecules like the keratin in your hair. The atoms stay together because of electromagnetism, one of the four forces of nature we will meet in more detail in Chapter 6. A molecule can be made up of a single element, like oxygen, the gas we breathe, which comes in molecules of paired atoms. Or it can be a compound, linking different elements, anything from simple sodium chloride – common salt – to the complex molecules, found in living organisms, like keratin.

The atoms that everything is composed from never touch each other. The closer together they get, the greater the repulsion between the electrical charges on their component parts. It’s like trying to bring like poles of two intensely powerful magnets together. This is even the case when something appears to be in contact with something else. When you sit on a chair, you don’t actually touch it. Your body floats an infinitesimal distance above, suspended by the repulsion between atoms.

It may be quite a while since you’ve played around with magnets. Get hold of a couple and remind yourself how remarkable the interaction between them really is.

Somehow the repulsion when you bring two of the same pole together seems more magical than attraction. Yet this is exactly what is happening every time one piece of matter ‘comes into contact’ with another. The interaction is electrical rather than magnetic, but it’s a similar electromagnetic repulsion to the one you feel between the magnets that stops the atoms in your bottom slipping between the atoms of the chair.

Exploring an atom’s innards

It wasn’t long after atoms were proved to exist in 1912 that it turned out that the name was inaccurate. Atoms aren’t ‘uncuttable’. They have component parts. Scientists were already aware that there were negatively charged particles called electrons that could be pulled out of atoms. At first these were assumed to be scattered through a mass of positive material, like plums in a plum pudding (a description provided by British physicist J.J. Thomson). But a walrus-moustached New Zealander working in Cambridge proved things were different.

Ernest Rutherford had the idea of firing other particles into an atom and seeing how they reacted – a bit like throwing a ball at an invisible structure and using the way the ball is influenced by what it hits to work out what that structure is like. The ‘ball’ he used was an alpha particle, a particle that had recently been discovered shooting out of radioactive elements. (It was later identified as the nucleus of a helium atom.) Alpha particles made tiny flashes when they hit screens painted with fluorescent material. By crouching in the dark it was possible for Rutherford’s assistants to spot the paths of particles that were deflected to the sides as they were shot at a piece of gold foil.

With the kind of inspiration that makes all the difference in science, Rutherford and his team also looked for alpha particles that reflected off the atoms in the gold straight back towards the source – and occasionally one did. This was totally unexpected. Rutherford said it was like firing an artillery shell at a piece of tissue paper and having it bounce back at you. He realised it meant that atoms must have a small, very dense, positively charged core to repel the positive alpha particles. Rutherford established for the first time the familiar picture of an atom being like a solar system with a positive nucleus at the centre (he borrowed the word ‘nucleus’ from biology). The nucleus was the equivalent of the Sun and the negatively charged electrons were the planets of this tiny solar system.

Thomson’s plum pudding was no more. The nucleus was so much smaller than the whole atom it was described as being like a fly in a cathedral, around 100,000 times smaller than the atom as a whole. The nucleus was made up of positively charged particles called protons, making up 99.9 per cent of the mass of the atom. For each proton an electron flew around the outside, balancing up the electrical charge, leaving the atom neutral.