Inflight Science E-Book

Brian Clegg

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

Seitenzahl: 262

Veröffentlichungsjahr: 2011

Beschreibung

The perfect companion to any flight - a guide to the science on view from your window seat. There are few times when science is so immediate as when you're in a plane. Your life is in the hands of the scientists and engineers who enable tons of metal and plastic to hurtle through the sky at hundreds of miles an hour. Inflight Science shows how you stay alive up there - but that's only the beginning. Brian Clegg explains the ever changing view, whether it's crop circles or clouds, mountains or river deltas, and describes simple experiments to show how a wing provides lift, or what happens if you try to open a door in midair (don't!). On a plane you'll experience the impact of relativity, the power of natural radiation and the effect of altitude on the boiling point of tea. Among the many things you'll learn is why the sky is blue, the cause of thunderstorms and the impact of volcanic ash in an enjoyable tour of mid-air science. Every moment of your journey is an opportunity to experience science in action: Inflight Science will be your guide.

Leseprobe

Previously published in the UK in 2011 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 2011 by Icon Books Ltd

ISBN: 978-1-84831-280-7 (ePub format)

ISBN: 978-1-84831-281-4 (Adobe ebook format)

Printed edition (ISBN 978-184831-241-8)

sold in the UK, Europe, South Africa and Asia

by Faber & Faber Ltd, Bloomsbury House,

74–77 Great Russell Street, London WC1B 3DA

or their agents

Printed edition distributed in the UK, Europe, South Africa and Asia

by TBS Ltd, TBS Distribution Centre, Colchester Road,

Frating Green, Colchester CO7 7DW

Printed edition published in the USA in 2011 by Totem Books

Inquiries to: Icon Books Ltd, Omnibus Business Centre,

39–41 North Road, London N7 9DP, UK

Printed edition distributed to the trade in the USA

by Consortium Book Sales and Distribution

The Keg House, 34 Thirteenth Avenue NE, Suite 101

Minneapolis, Minnesota 55413-1007

Printed edition published in Australia in 2011 by Allen & Unwin Pty Ltd,

PO Box 8500, 83 Alexander Street,

Crows Nest, NSW 2065

Printed edition published in Canada by Penguin Books Canada,

90 Eglinton Avenue East, Suite 700,

Toronto, Ontario M4P 2YE

Text copyright © 2011 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 by Marie Doherty

Contents

Title page

Copyright

List of illustrations

About the Author

Disclaimer

Dedication

At the Airport

Terminal boredom

An airport divided

Bag check

Testing the air

A lesson in detection

Body scan

Who do you think you are?

The science of superstition

Taking to the Sky

Aircraft basics

Fuelling flight

The greenhouse effect’s good side

Flying the green way

Getting moving

Big radar is watching you

Something on the air tonight

Sat nav on the flight deck

The universal language

The latest model on the runway

How Newton’s laws get you going

Joining the jet set

Rotation and climbing

Under pressure

Wing work

Control surfaces in action

Exploring the Landscape

The mystery of the fields

On the Nazca plains

Chalk marks the spot

The traces of the past

Following the water course

Fascinating fractals

The making of meanders

How does your town grow?

The infinite coast

Gravity always wins

From river to sea

Water, water everywhere

Time and tide wait for no one

On the crest of a wave

What colour is the sea?

Above the Clouds

Into the clouds

An adventure in cloud-spotting

All the way to cloud 9

No pot of gold for an endless rainbow

Over icy seas

Up into the sunlight

Voyage to the heart of the Sun

Why is the sky blue?

Why does the Sun keep shining?

Taking a trip through a quantum tunnel

Crossing flight paths

Leaving a trail in the sky

Is there life out there?

Going walkabout

Travelling through bumpy air

The flash of lightning

A static charge

Making lightning

Electricity on the move

There’s safety in metal boxes

Grounded by the ash

Volcanic eruption

In the radiation zone

Fooled by a natural high

A cosmic collision

Cabin Life

Pressure on the blood supply

Catching up with jet lag

Crossing the time zones

What jet lag is (and isn’t)

Taming jet lag

Resorting to medication

Is there a jet lag north/south divide?

A moving experience

Relatively interesting

Galileo’s big idea

In the jet stream

The special one

Anti-ageing flights

A nice cup of tea

Hearing food

Technology in Flight

Following your course on the map

Projecting the world

At the bleeding edge of technology

Keeping the screen flat

Bartholin’s crystal wonder

Giving light the liquid crystal twist

Taking your hi-tech with you

The view from the flight deck

Following the guidance of inertia

Tracking your way through the air

Einstein’s accelerating revelation

The feeble force

Gyroscopic gyrations

Distant Views and Back to Earth

Viewing the distant mountain peaks

As old as the hills

It’s cold on them thar hills

The icing on the mountain

Around the bend with a siphon

The vacuum solution

Meeting the night sky

A view of Venus

The amazing Moon

The changing face of the man in the Moon

Welcome to the galaxy

The street light fantasia

The amazing eye

Making up a picture of the world

Eyes wide

First touch on the runway

Final steps

Picture credits

List of illustrations

1. The electromagnetic spectrum

2. A transformer

3. The undercarriage of an Airbus A-380

4. The greenhouse effect

5. A tug in action

6. Producing lift in a sheet of paper

7. Features of an aircraft wing

8. A crop circle

9. The Nazca lines

10. The Uffington white horse

11. Estimating distance

12. Old Sarum

13. River meanders

14. An evolved settlement

15. A planned settlement

16. Contours of a rugged coastline

17. A Koch curve

18. The Ganges river delta

19. The tides

20. Waves breaking near the shore

21. Cumulus clouds

22. A thunderhead cumulonimbus

23. Stratocumulus clouds

24. Cirrus clouds

25. Contrails

26. A storm on an aircraft radar

27. Forked cloud-to-ground lightning

28. Pico do Fogo volcano

29. Seatback entertainment

30. A polarizing filter

31. An aircraft flight deck

32. Light bends in an accelerating spaceship

33. Mountain peaks

34. An annular solar eclipse

35. The phases of the Moon

About the author

Brian Clegg is a science writer (website: www.brianclegg.net). He runs www.popularscience.co.uk, and his most recent book wasArmageddon Science(St Martin’s Press, 2010).

Disclaimer

The experiments in this book are designed to be safe, and many of them can be done on board an aircraft. Those that are better carried out at home are clearly indicated. When carrying out any experiments in the air, make sure that you don’t disturb other passengers or distract the cabin crew. Any experiments that could cause damage, danger or disturbance are clearly marked asnot to be performedand are theoretical examples only. The publisher accepts no responsibility for any damage, injury or loss arising from any of the experiments contained in this book, theoretical or otherwise.

For Gillian, Chelsea and Rebecca

At the Airport

Terminal boredom

You’re sitting in the terminal, waiting for the flight. A whole mix of conflicting emotions could be vying for attention: boredom, excitement and fear included. Boredom often wins. Flying may be the quickest way to get to a distant destination, but it includes a lot of waiting around.

Even if you’re a seasoned traveller, though, there’s something special about taking to the air, an excitement that’s often triggered by the scent of kerosene on the tarmac, or the sound of an aircraft engine starting up. And there’s an element of fear – because however much you enjoy flying, there’s something highly unnatural about being suspended in a metal and plastic tube seven miles up, with only science and technology to keep you alive.

If you don’t like flying (and I don’t), a little science might help by providing some very reassuring statistics. The risk of being killed in a plane crash in any particular year is 1 in 125 million passenger journeys. This makes it three times safer on any particular journey than travelling by train – and when did you ever worry about that? The equivalent risk for a car is 1 in 10 million – twelve times as dangerous. You’re more likely to have a fatal accident during six hours spent in the workplace than you are during six hours on a plane. There’s only so much reassurance you can get from statistics – but flying is incredibly safe.

Our focus will be on what you see and experience on board an aircraft, but it’s quite possible that boredom will kick in as you wait in the terminal. You can only do so many trips round the duty-free shops, or drink so many coffees. So let’s take a brief look at some of the extreme technology you might encounter on the ground before taking to the air.

An airport divided

Airports have a strict divide between groundside and airside. To get from one to the other, particularly when flying internationally, you will face a barrage of technology aimed at identifying you and checking that you aren’t carrying anything dangerous. If airlines were permitted, they would also weigh you as you pass through (this was done in the early days of flight). Plane loading is very sensitive to weight and airlines have to rely on average weights to know how much load the passengers are contributing.

Making such an estimate has, at least once, caused problems. The plane, taking off from a German airport, struggled to get away from the runway and only just managed to claw its way into the air. It later turned out that there was a coin fair on in the city, and many of the passengers were coin dealers with their pockets crammed with new acquisitions, because they didn’t want to risk their new purchases being stolen from the hold baggage. All this unexpected spare change pushed the passengers’ weight well above the expected average. Added up over the entire aircraft, there was so much extra load that the plane didn’t respond as the pilots expected it to, causing a few worrying moments on take-off.

Bag check

Your first encounter with interesting technology is likely to be the security scanners. Your hand baggage is put on a conveyor belt that carries it through a powerful X-ray machine. That name ‘X-ray’ is not because of some special scientific naming convention, it’s just that when discoverer Wilhelm Roentgen first came across rays that would pass through solid objects he called them X-rays (or ratherX-Strahlen) to show that they were unknown and mysterious. They were officially renamed Roentgen rays, but everyone liked Roentgen’s original nickname for them, and it stuck.

In reality, X-rays aren’t particularly mysterious – they are nothing more or less than light, but light of a colour that is far outside the spectrum that we can see. All light is ‘electromagnetic radiation’, a special interaction between electricity and magnetism that comes in a huge range of ‘colours’. As well as visible light there is radio, microwaves, infra-red, ultra-violet, X-rays and gamma rays – all exactly the same kind of stuff but with varying amounts of energy (see illustration 1. below). We now know that light is made up of tiny particles called photons (more on these later). X-rays consist of much higher-energy photons than visible light. If you prefer to think of light as a wave, as it was probably described to you at school, then X-ray waves have a shorter wavelength (the distance in which the wave makes a complete wiggle) than visible light.

1. The electromagnetic spectrum: visible light forms a small segment near the middle.

When ordinary light hits an object like a suitcase that isn’t transparent, the photons of light are absorbed. This happens because the energy in the photon is sucked up by one of the particles that make up the suitcase. Every object we see around us is made up of atoms, and each atom consists of a very small central part, the nucleus, which contains over 99 per cent of its weight, surrounded by a fuzz of tiny particles called electrons. When a photon of light meets an electron, the electron can consume the energy in the photon. This leaves the electron buzzing around with more energy than it started with.

This process of an electron absorbing or giving off the energy of a photon of light is called a quantum leap, a term that has come to mean a large, significant change, even though a real quantum leap is an absolutely tiny difference.

Once the electron has absorbed the energy of the photon, it’s as if it were teetering on top of a high wall. Before long, that extra energy shoots back out in the form of a new photon, and the electron drops back to having less energy. We don’t know in which direction a particular photon will shoot off, but over time some will head towards your eyes. It’s these photons, pumped out by the electrons in an object, that allow you to see it.

X-rays are made up of photons too, and as with all other forms of light, they travel at 300,000 kilometres per second, but each photon has a lot more energy than a photon of ordinary light, enabling it to smash past the electrons in an object’s atoms with much less interaction. This means that X-rays can penetrate many substances that stop ordinary light dead.

In the process of battering through matter, the X-rays can cause damage to the molecules (molecules are just collections of atoms that are joined together) that make up an object. Each cell in the human body contains huge molecules of DNA that contain the instructions for how the cell should behave. If these molecules, or other important chemicals in the cell, are damaged by the impact of X-rays, the changes can increase the chances of cancer forming. This is why medical X-rays have to be used with care, keeping doses to a minimum. Before the 1960s this wasn’t appreciated. You still saw X-ray devices in shoe shops, for example, where you could peer through and see your toe bones wriggling around inside the shoe.

Inanimate objects are less susceptible to damage (though photographic film can be fogged), so baggage X-ray machines are considerably more powerful than most medical X-rays. Those big scanners you now find in airports use a wide band of X-rays, some more powerful than others. After passing through your bag and its contents, the X-rays reach detectors, working on a similar principle to a digital camera. There are two sets of sensors, one behind the other, separated by a metal shield. The weaker X-rays are stopped by the metal shield, so register only on the front detectors, but the more powerful X-rays blast on through the shield, so are spotted by both.

This distinction between the two strengths of X-ray is used to produce different-coloured images on the operator’s screen. This way the picture will distinguish between ‘soft’ matter like plants, plastic or explosives – which are usually coloured orange by the scanner – and less penetrable matter, which will let only the more powerful X-rays through – typically coloured green. The result is to give more depth to the image and to distinguish at a glance between the different types of material within your baggage.

Testing the air

It’s also possible that your bags will be subjected to a sniffer, hunting down explosives by their smell. Like many substances, explosives are to some extent volatile. This means that some of the molecules making up the chemicals within the explosive evaporate at room temperature and waft into the air. Molecules in solids and liquids are always bouncing around, and some bounce with more energy than the rest, managing to escape. This is the process that makes it possible for us to smell anything, whether we’re sniffing the bouquet of a glass of wine, or appreciating the tempting odour of baking bread. It’s also why a pool of water will eventually evaporate, even at room temperature.

Sometimes the sniffer will be a dog. Arguably, the dog is the oldest piece of highly developed technology still in active use. It might seem bizarre to call a dog ‘technology’. Yet dogs have been consciously moulded into distinct breeds with specific functions in mind. They were the first autonomous technology – they function on their own, as opposed to a similarly ancient device like a hand axe that had to be powered by a human being. Now we have dogs that provide a wide range of functions, from guide dogs and sheepdogs to the owners of the extremely sensitive noses that can pick out the presence of explosives.

Of course the production of this remarkable piece of technology didn’t originate with the intention of creating such a flexible helper. The chances are it all started by accident, when wolves began to hang around human camps. Although wolves don’t deserve a lot of the bad press they get – they rarely attack human beings, for instance – they would have been irritating scavengers that early man had to make an effort to see off, to stop them stealing the remains of hunted animals.

It’s easy to imagine those first, tentative steps away from the wolf’s role as enemy. Perhaps it was a cold winter, and a wolf crept close to a fire to keep warm. Maybe while it was there some other predator attacked the camp – the wolf, ever the pack animal, jumped to the defence of the humans, fighting alongside them. It was rewarded with a gift of meat. Wolf cubs that were more docile, more easily fitting with a human ‘pack’, were the ones more likely to stay around and more likely to be fed and encouraged. Over the years this selection became conscious and gradually the modern dog emerged.

What had been a natural process was transformed into genetic engineering, just as much as any GM crop. The dog is not a natural animal. It’s as much a human-made piece of technology as a table that started off as a ‘natural’ piece of wood. Without doubt, the dog is one of the most impressive things our early ancestors made. Forget Stonehenge – it’s a toy by comparison. Okay, it gave a handful of people some astronomical information, and it’s pretty – but it hasn’t been used for thousands of years. The dog is a piece of Stone Age technology, developed 35,000 years before Stonehenge, that is still going strong in airports around the world.

The security team might also use an electronic sniffer, which breaks down the chemicals in the air using one of a number of possible processes, most frequently gas chromatography. Here a gas carries the air up a tube, past various substances that the molecules in the air can interact with. Different molecules latch onto different substances within the tube. This splits out the components of the odour, so the machine can quickly produce a chart showing just what’s in the substance it’s sniffing. Different substances will have recognizable ‘signatures’ in the shape of their charts.

A lesson in detection

While your bags are being checked, you will have to pass through one of those intimidating arches that always make you feel nervous and guilty. These are metal detectors, similar technology to the hand-held devices used to hunt for treasure in a field, but here deployed to searchyoufor metal. Although there are a number of variants, they all use the same basic process, called induction. If you have an electric toothbrush that charges by sitting on a plastic stand with no visible metal connectors, you already have a very obvious induction device in your home.

The idea for induction came out of a fundamental discovery made by the great Victorian scientist Michael Faraday. He discovered that moving a wire carrying electricity, or changing the rate at which the current flowed, produces magnetism. Similarly, moving or changing magnetism produces electricity. That’s how electric motors and generators work.

In the toothbrush, a coil of wire in the charger sends out a changing electromagnetic field that produces a current in wires in the toothbrush. ‘Electromagnetic’ just means electrical and/or magnetic – electricity and magnetism are all part of the same phenomenon. And this ‘field’ is a field of force. This is a concept that Faraday dreamed up. He had seen how iron filings line up on a piece of paper held over a magnet, producing curved lines that seem to map out the magnet’s invisible power. Faraday imagined these lines filling the space around a magnet.

Move a wire through a magnetic field and the wire hits line after line of the field, like a child’s hand slapping a series of iron railings, transforming magnetism into electricity. There’s no difference between moving a magnet next to a wire and moving a wire through a magnetic field – in both cases the result is a relative movement between the wire and the magnetic field, encouraging electrically-charged electrons to move in the wire. It’s the same mechanism that appears in every generator.

In the toothbrush charger, nothing is moving, but the electrical current keeps changing direction (this is alternating current), making the lines of force shoot out from the charger and pull back in again. When a wire is positioned in the way of these moving lines of force it cuts through them, just as the moving wire does in a generator. There is no direct contact between the wires in the charger and the wires in the toothbrush. Instead it’s magnetism generated by the changing electrical field that carries the power from the coil to generate electricity in the toothbrush. Similarly, devices called transformers that are used to drop voltage (you’ll have several in your home in chargers and power supplies for mobile phones and electronic gadgets) do so by having a pair of coils of different size, where a changing current in one induces a current in the other via magnetic induction. (See here for a definition of voltage.)

In the arch of a metal detector, there will be several coils of wire. The flow of electricity in these generates a magnetic field, which produces electric currents in any metal objects nearby. These currents generate magnetism in their turn, which finally produces electricity in a detection coil. The metal objects might be coins in your pocket, a belt buckle, or a weapon in your jacket. More recently, since shoes have been used to carry dangerous items, it’s normal to take your shoes off to have them X-rayed, as the detectors can’t cope with items at floor level, though some modern metal detectors can scan shoes, making the process less irritating.

2. A transformer changes electrical voltage via magnetic induction.

Body scan

There’s an increasing possibility at airports of being subjected to a whole body scan. These scanners offer similar facilities to a strip search, in that all kinds of items carried anywhere about the body can be detected, but the process is quicker, taking only a few seconds, and feels less intrusive. It has been said that such scanners produce a nude image of the individual, and as such violate privacy, but in reality this is an exaggerated concern. The result is unrecognizable – more like a computer model of a human body than anything real.

There are two types of these scanners, both using non-visible forms of light. Some employ high-energy (short-wavelength) radio, while others use a form of X-ray. Small health concerns have been raised in some quarters about both of these. The radio version uses a frequency that is quite close to microwaves, and though there’s no known evidence of a health risk from these radio signals, there are some concerns that the small levels of heating caused in human bodies might have a negative effect.

X-rays are known to carry a risk, but the approach in an X-ray scanner is totally different from a traditional medical X-ray. Full body scanners use a process called backscatter X-ray. Here, instead of passing through you, the X-rays pass through your clothes but are bounced back from your body to detectors all around you. These are very low-dose X-rays. You will be exposed to around 50 times as much damaging radiation for each hour you are in the air (we’ll come back to this natural radiation later on) as you will receive from a backscatter scan. Overall the health risk is very low, and the process is significantly less unpleasant than an intimate body search.

Who do you think you are?

We now know that you are safe, but we might not be sure who you are. On international flights, after security, you will pass through border controls. Here, increasing use is being made of biometrics to identify individuals. Many passports contain a tiny chip that can be loaded up with your biometric data. These are simply measurements that can be checked on the day you travel to see if you really are the person your passport says you are.

Although in principle any aspect of your body could be used for biometrics (ear size, for instance), in practice most systems use one or more of face recognition, fingerprint recognition and iris recognition. Retinal scans, popular in spy movies, where an image is taken of the inside of your eyeball, have been avoided because the process feels too scary and intrusive. Few people, it seems, fancy having a laser blasted into their eye.

The idea of using fingerprints to recognize individuals is the most familiar technique, even if it does have unfortunate criminal associations. The first practical use of fingerprints seems to have been by Sir William Herschel, grandson of the astronomer of the same name. In the 1850s, he used them when working in India as a way to make clear identification on legal documents. By the 1890s they were starting to be used in criminal cases, with police departments building up libraries of prints, classified by shapes to make identification easier. From the beginning, though, matching a fingerprint found at a crime scene to an entry in a library was a tedious business.

Using fingerprints for biometric identification is much simpler as there’s no need to search through a vast database. Instead it’s just a matter of comparing the biometric data held on the passport with measurements taken on the day. Fingerprint identification technology picks up differences between the ridges and valleys in the skin of the fingertip, using a number of possible detection methods from a simple scan or the pattern of heat given off to electrical capacitance (the technology used on an iPhone touch screen). The whole print isn’t stored – instead, key points in the pattern are identified, and compared with the stored data.

There are two problems with fingerprints. One is the need to capture a shape that can vary quite significantly over time, and that distorts depending on both the amount of pressure used and the position of the fingertip on the sensor. The other is the technique’s criminal associations. It’s very difficult to get someone to give a fingerprint without them feeling guilty. By contrast, iris recognition has none of those negative connotations.

The iris is the coloured bit around the pupil of your eye, which, on close examination, has a very detailed pattern of fine lines heading out from the centre like the spokes of a wheel. This unique pattern is captured by a camera and can provide an effective match to the data on the passport that isn’t influenced by transparent materials like a pair of glasses. And there’s no need to come into direct contact with the detection device.

Of the three options, face recognition is the ideal technology, because it can be undertaken remotely without the individual having to stop at a booth to give a fingerprint or an iris photograph. But as yet it isn’t reliable enough to be the sole method of identification. Face recognition can be applied to a flow of people (though obviously it requires the face to be visible) or more practically for security, it can be performed unobtrusively in the background at any point an individual stops to speak to an official.

There are a number of ways that face recognition can work – picking up the locations of main facial features, taking a 3D scan of the face shape, or working more like fingerprint recognition on aspects of skin texture – but all are susceptible to variation, whether from an individual growing a beard or even from major changes in expression. The technology is a work in progress, but it provides a powerful extra check that is likely to become the dominant recognition mechanism as systems get better. Like it or not, your face says a lot about you.

The science of superstition

When the gate has been announced, and you’ve had enough of relative freedom, it’s time to make your way to the holding pen that is the gate lounge. Gates are traditionally numbered, and you will usually find that gate 13 is missing. Although few people truly suffer from triskaidekaphobia – an irrational fear of the number 13 – the number is still often regarded as unlucky, something airlines and airports are enthusiastic to avoid.

The science of superstition is very much tied in with our perception of chance. Our brains just aren’t wired well to cope with probability. You can see this with the way we react to clusters of events. Imagine something that happens randomly across the country, anything from outbreaks of disease to people falling over. How would you expect those random things to be distributed? Our natural response is to expect them to be spread out evenly. But that is totally wrong.

Just imagine tipping a tin of ball bearings onto a flat, empty floor. What would you think if, when the balls stopped moving, they were evenly distributed in a grid, each the same space from the other? You’d think something was making them do it – there must be magnets under the floor, or some other trickery. The natural thing is for there to be places where there are clumps of ball bearings and others where there are gaps. These clumps are known as clusters.

Experiment – Clustering cash

The chances are you don’t have a tin of ball bearings about your person, and even if you did, you’d probably get arrested for scattering them across the floor of the plane. But you can get a similar effect with a handful of coins, though it’s still best to wait until you get back home before you do this. Hold the coins in your hand about waist height and drop them. While in principle they could all fall nice and evenly, the chances are high that you will get clusters in their distribution.

Exactly the same thing happens with any randomly distributed event. But traditionally when, say, a number of farmers in the same area had cattle go ill, it was assumed that there had to be a cause for this clustering. The problems would be blamed on the local witch. Now, clusters of non-transmitted illnesses are often blamed on phone masts or nuclear power stations.

If such illnesses were random, we would expect them to form clusters; but it’s very natural to look for a local cause, and, where there’s a source of concern nearby, to assume that it’s responsible. Not all clusters are random – a cluster of asbestosis victims near an asbestos factory, for example. But we can’t assume that the apparent threat causes the problem. There are very effective statistical techniques to check on causality that need to be applied before jumping to conclusions.

Although people have put forward many explanations for the fear of 13, linking it to Judas as the 13th person at the Last Supper, or to the way 13 is the outrider number on collections of 12, like the 12 signs of the zodiac, there is very little evidence to support these theories. It’s more likely that the number 13 was associated naturally with a cluster of bad events. Perhaps a farm failed after a sow had 13 piglets. Then, by coincidence, someone died on the 13th of the month. As a few coincidences built up, 13 would become the number everyone loved to hate.

Irrational though any fear of 13 is, airlines and airports don’t take any chances of scaring their passengers, so there’s unlikely to be a flight 13 or a gate 13. This avoidance is taken one step further at Heathrow’s Terminal Four. Sometimes, when gate 13 is missed out, there’s a tendency to consider gate 14 unlucky because ‘it’s really gate 13’. To prevent this from happening, gate 12 is at one end of the Terminal Four building while gate 14 is at the other end. As you never see the two gates side by side, it’s not obvious that gate 13 isn’t there, so no one worries about using gate 14.