Ten Tantalising Truths E-Book

John Gribbin

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2023

Seitenzahl: 164

Beschreibung

Obvious questions do not always have obvious answers. John Gribbin is known for giving us simple explanations of big concepts in science. But there is another way to probe the mysteries of the Universe and our place in it. Faced with persistent enquiries from his grandchildren, Gribbin realised that simple questions, such as 'Why is the sky blue?', sometimes require big answers, understandable in straightforward language. In answering those simple questions, he discovered that he was telling the story of our place in the Universe, from the Big Bang to the evolutionary reasons why men are, on average, bigger than women. The questions may be obvious, but the answers are sometimes surprising and highlight one of the main joys of science - discovering the unexpected. In this book, Gribbin invites the reader to join him on this voyage of discovery, where you may think you already know the answers but should be prepared to be surprised - or at least, tantalised by the truth.

Leseprobe

Praise for Six Impossible Things

‘[A]n accessible primer on all things quantum … rigorous and chatty.’

Sunday Times

‘Gribbin has inspired generations with his popular science writing, and this, his latest offering, is a compact and delightful summary of the main contenders for a true interpretation of quantum mechanics. … If you’ve never puzzled over what our most successful scientific theory means, or even if you have and want to know what the latest thinking is, this new book will bring you up to speed faster than a collapsing wave function.’

Jim Al-Khalili

‘Gribbin gives us a feast of precision and clarity, with a phenomenal amount of information for such a compact space. It’s a TARDIS of popular science books, and I loved it. … This could well be the best piece of writing this grand master of British popular science has ever produced, condensing as it does many years of pondering the nature of quantum physics into a compact form.’

Brian Clegg, popularscience.co.uk

‘Elegant and accessible … Highly recommended for students of the sciences and fans of science fiction, as well as for anyone who is curious to understand the strange world of quantum physics.’

Forbes

Praise for Seven Pillars of Science

‘[In] the last couple of years we have seen a string of books that pack bags of science in a digestible form into a small space. John Gribbin has already proved himself a master of this approach with his Six Impossible Things, and he’s done it again … [Seven Pillars of Science is] light, to the point and hugely informative … It packs in the science, tells an intriguing story and is beautifully packaged.’

Brian Clegg, popularscience.co.uk

Praise for Eight Improbable Possibilities

‘We loved this book … deeply thought-provoking and a book that we want to share with as many people as possible.’

Irish Tech News

‘[Gribbin] deftly joins the dots to reveal a bigger picture that is even more awe-inspiring than the sum of its parts.’

Physics World

‘A fascinating journey into the world of scientific oddities and improbabilities.’

Lily Pagano, Reaction

‘Gribbin casts a wide net and displays his breadth of knowledge in packing a lot into each chapter … a brief read, but one that may inspire readers to dig deeper.’

Giles Sparrow, BBC Sky at Night Magazine

Praise for Nine Musings on Time

‘The yarn of time ravels into a rich tapestry of both science and speculation, under John Gribbin’s deft hand.’

David Brin, Hugo Award-winning science fiction writer, author of The Postman, the book that inspired the Kevin Costner movie

Also by John Gribbin

Nine Musings on Time: Science Fiction, Science Fact and the Truth

About Time Travel

Eight Improbable Possibilities: The Mystery of the Moon,

and Other Implausible Scientific Truths

Seven Pillars of Science: The Incredible Lightness of Ice,

and Other Scientific Surprises

Six Impossible Things: The ‘Quanta of Solace’

and the Mysteries of the Subatomic World

In Search of Schrödinger’s Cat

The Universe: A Biography

Schrödinger’s Kittens and the Search for Reality

Einstein’s Masterwork: 1915 and the General Theory of Relativity

13.8: The Quest to Find the True Age of the Universe

and the Theory of Everything

With Mary Gribbin

Richard Feynman: A Life in Science

Science: A History in 100 Experiments

Out of the Shadow of a Giant: How Newton Stood

on the Shoulders of Hooke and Halley

On the Origin of Evolution: Tracing ‘Darwin’s Dangerous Idea’

from Aristotle to DNA

Published in the UK and USA in 2023 byIcon Books Ltd, Omnibus Business Centre,39–41 North Road, London N7 9DPemail: [email protected]

ISBN: 978-183773-100-8ebook: 978-183773-112-1

Text copyright © 2023 John and Mary Gribbin

The authors have asserted their 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.

Typesetting by SJmagic DESIGN SERVICES, India

Printed and bound in the UK

CONTENTS

PREFACE

Tantalising Questions

QUESTION 1

Why Is the Sky Dark at Night?

QUESTION 2

How Far Away Are the Most Distant Things We Can See?

QUESTION 3

How Old Is the Sun?

QUESTION 4

How Do We Know Einstein Was Right?

QUESTION 5

Where Did Everything Come From?

QUESTION 6

How Fast Do Continents Move?

QUESTION 7

What Is Inside the Earth?

QUESTION 8

Why Does Blood Taste Salty Like the Sea?

QUESTION 9

Why Are Men Bigger than Women?

QUESTION 10

Why Is the Sky Blue?

ABOUT THE AUTHOR

John Gribbin’s numerous best-selling books include In Search of Schrödinger’s Cat, The Universe: A Biography, 13.8: The Quest to Find the True Age of the Universe and the Theory of Everything, and Out of the Shadow of a Giant: How Newton Stood on the Shoulders of Hooke and Halley.

His most recent book is Nine Musings on Time: Science Fiction, Science Fact, and the Truth About Time Travel. His earlier title, Six Impossible Things: The ‘Quanta of Solace’ and the Mysteries of the Subatomic World, was shortlisted for the Royal Society Insight Investment Science Book Prize for 2019. He is an Honorary Senior Research Fellow at the University of Sussex and was described as ‘one of the finest and most prolific writers of popular science around’ by the Spectator.

For William, Beatrice and Florence: my chief inquisitors

tantalising:

possessing a quality that arouses or stimulates desire or interest

Merriam-Webster Dictionary

PREFACE

Tantalising Questions

When I wrote my book Six Impossible Things, I did not anticipate it being the beginning of a series. But it seemed to strike a chord with people who wanted simple answers to big questions in science, such as the nature of quantum reality, the emergence of life on Earth and the origin of the Universe. Having done my best to tackle these issues with Seven Pillars of Science and Eight Improbable Possibilities, I felt that was enough of a good thing and signed off the series of short books (as I thought) by indulging in something completely different – my fascination with time, time travel and science fiction – in the form of Nine Musings on Time. But other people had different ideas. In particular, our grandchildren began to ask deceptively simple questions, which required a great deal of thought to answer accurately. I realised that this was a reversal of the procedure I had used in tackling my series of three short books – instead of providing simple answers to big questions, I was giving them big answers to simple questions. And if they were asking those questions, maybe other people would be interested in the answers. So I began to put together ten of the questions (theirs) and answers (mine), with no intended theme except that they are all genuine questions that I have been asked by the younger members of the family over the past couple of years. As I planned the structure of the book, though, I realised that the questions form a natural progression in terms of the place of the Earth in the Universe, and the place of people on our planet, so that is more or less the order in which the answers appear here. The questions are, of course, originally much older than my inquisitors, and some of the answers are almost as old as the questions. But if you think you know the answers, you may be in for a surprise or two. Which to me is a feature of what Richard Feynman called ‘the pleasure of finding things out’. Obvious questions do not always have obvious answers, which is part of the fun of science. I hope you have fun with these examples. If you do, make the most of them, because I have at present no plans to write a book called Eleven Intriguing Possibilities, not least because I cannot think of eleven suitable topics for discussion. But if you can think of any, feel free to send an email to [email protected]; one should never say ‘never again’.

John Gribbin, June 2022

QUESTION

Why Is the Sky Dark at Night?

The obvious answer is that the side of the Earth that is experiencing night is turned away from the Sun, and we are looking out into the cold, dark Universe. But why is the Universe cold and dark apart from a sprinkling of stars? As far as we know, the first person to think seriously about this puzzle was the Englishman Thomas Digges, one of the inventors of the telescope. In 1576, Digges suggested that the Universe is infinitely big and infinitely old, rejecting the ancient idea of the Earth surrounded by a series of ‘crystal spheres’. He realised that in an infinite Universe full of stars, you ought to see a star in every direction you looked, with no dark spaces in between, but he reasoned that the very distant stars were simply too faint to be seen. But in 1610, Johannes Kepler realised that this argument would not wash.

Kepler turned the argument on its head. He said that in an infinite Universe full of stars, you would indeed see a star in every direction, so the dark night sky must tell us that the Universe is not infinite. He said that there must be an edge, or wall, around the Universe, and when we look through the gaps between the stars, we are looking at that wall. This almost fits in with the modern idea that our Milky Way Galaxy is an island of stars floating in dark space. If you imagine standing in a small grove of trees, you can look out through the gaps between the trees to the outside world, but in an infinite forest, everywhere you look you will see a tree. Unfortunately for this analogy, there are other galaxies out there, so the whole argument can be brought up to date by saying that everywhere we look beyond the Milky Way, we should see another galaxy.* I shall continue to talk about stars, because that is the way the story developed, but bear in mind that the argument applies with equal force to a Universe full of galaxies.

The person who first expressed the puzzle clearly in scientific terms was the Swiss astronomer Jean-Philippe Loys de Chéseaux, in the 1740s. The big difference between his approach and earlier speculations was that he put real numbers into the calculation. He estimated the distances to stars by guessing that they were all the same actual brightness as the Sun and working out how far away they would have to be to look so faint. Then he worked out how big the disc of the Sun would look to us at those distances. Finally, he worked out that if stars were spread out more or less evenly through the Universe in the same density as they are in our part of the Universe, these discs would all be overlapping, so the entire sky would be as bright as the Sun, once we looked out to a distance equivalent, in modern terms, to 1015 (a million billion) light years. His conclusion was that either stars are not distributed evenly in this way – that there must be an ‘edge’ to our grove of astronomical trees – or that something happens to hide the light from very distant stars. De Chéseaux suggested that light gets fainter and fainter as it travels across space to us. He was wrong (or at least, partially wrong, as I shall explain), but at least he tried to explain the puzzle.

A modern update to de Chéseaux’s argument makes it even more powerful for the mathematically inclined (if you are not mathematically inclined, skip this paragraph). Imagine the Earth at the centre of a large (potentially infinite) series of thin ‘shells’ (thin by astronomical standards, that is), like onion skins. If each shell is the same thickness, then at any distance r, the volume of a shell, is proportional to r2.* If stars are distributed evenly through the Universe, the number of stars in each shell is proportional to the volume, so it also goes up as r2. But the light we receive from each star goes down in proportion to r2 (it is proportional to 1/r2). So the factors of r2 cancel out, and every shell contributes the same brightness to the night (or day!) sky. Of course, some of the light from very distant shells gets blocked by stars in nearer shells, so once again, the sky should ‘only’ be as bright as the surface of the Sun.

De Chéseaux ought to have been the person who got his name attached to this scientific puzzle, but in fact it has gone down in history as ‘Olbers’ Paradox’, which is doubly annoying because the German astronomer Heinrich Olbers did not think of it first, and it is not a paradox. But so it goes.

Olbers came up with his variation on the theme in 1823. It was very similar to de Chéseaux’s idea, but he suggested that the light from distant stars doesn’t just get tired on its way to us but is absorbed by dust in space. The snag, which he missed, is that if there is dust in space absorbing energy from the stars, the dust will heat up, eventually becoming as hot and bright as the stars themselves. So in an infinitely large, infinitely old Universe, the puzzle of the dark night sky still exists.

The first hint for the correct explanation of the puzzle came from the American writer Edgar Allen Poe, in an essay, ‘Eureka’, published in 1848. But this really was only a hint at a potential answer, in the middle of a lot of metaphysical musing (some good, some bad), and Poe does not deserve quite as much credit as he is sometimes given. Nevertheless, it is worth looking at the good bits of what he said, which, with hindsight, can be seen as pointing in the right direction.

He starts out well enough, clearly expressing the nature of the puzzle:

A very slight inspection of the Heavens assures us that the stars have a certain general uniformity, equability, or equidistance, of distribution through that region of space in which, collectively, and in a roughly globular form, they are situated.

And:

All observation of the firmament refutes – the conception of the absolute infinity of the Universe of stars.

But it soon becomes clear that he is refuting the idea of an infinity of stars, not an infinity of space.

He successfully points out that because light travels at a finite speed it takes a long time to travel across space to us from a distant star or from what he calls ‘nebulae’, which we now know to be other galaxies:

Since the light by which we recognize the nebulæ now, must be merely that which left their surfaces a vast number of years ago, the processes at present observed, or supposed to be observed, are, in fact, not processes now actually going on, but the phantoms of processes completed long in the Past.

This is an important insight. Because light travels at a finite speed, we see objects as they were when the light left them. Even light from the Sun takes just over eight minutes to reach us. So telescopes are in a sense time machines, giving us views of more ancient times the further out we look. With this understood, by isolating one passage in ‘Eureka’, Poe can be made to seem quite prescient:

Were the succession of stars endless, then the background of the sky would present us an uniform luminosity, like that displayed by the Galaxy – since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all. That this may be so, who shall venture to deny?

Unfortunately, in the next sentence in his essay, without actually denying this, he says:

I maintain, simply, that we have not even the shadow of a reason for believing that it is so.

If Poe had omitted that sentence, he could rightly have been credited with the idea that the sky is dark at night because the Universe is not old enough to have been filled with starlight.

His own explanation of the puzzle of the dark night sky comes a little later in the essay and echoes the ideas of Kepler. Poe refers to:

Those frequent gaps in the Heavens, where our utmost scrutiny can detect not only no stellar bodies, but no indications of their existence: – where yawning chasms, blacker than Erebus, seem to afford us glimpses, through the boundary walls of the Universe of Stars, into the illimitable Universe of Vacancy, beyond.

Which is simply the old idea of an isolated astronomical grove with eternal emptiness beyond.

It was this idea of an eternity of space and time that left the mystery of the dark night sky unexplained (and largely ignored) until well into the 20th century. Things started to change at the end of the 1920s, when the Belgian cosmologist Georges Lemaître and the American astronomer Edwin Hubble (with help from fellow astronomer Milton Humason) independently discovered that light from distant galaxies has been stretched to longer wavelengths on its way to us. This is the famous ‘redshift’, so-called because red light has longer wavelengths than blue light – more about this phenomenon in the answer to Question 2. It soon became established that this shift happens because space itself is expanding, or stretching, carrying galaxies away from one another. It is not a result of galaxies moving through space, but a stretching of space itself, in line with the equations of the general theory of relativity (which could have been used to predict the effect, but that is another story).

Edgar Allan Poe

Unknown author; Restored by Yann Forget and Adam Cuerden, Public domain, via Wikimedia Commons

Lemaître pointed out that if the Universe is expanding in this way today, then long ago, all the stars in all the galaxies must have been squashed together in one lump at the beginning of the process of expansion, what we now call the Big Bang. Astronomers argued about whether there really had been a Big Bang up until the 1960s, when a combination of factors (one of which I will discuss shortly) provided clinching evidence in favour of the idea. Subsequent observations of the rate at which the galaxies are being carried apart, and other data, tell us that the Big Bang happened 13.8 billion years ago. What happened before that, if there was a ‘before’, is still up for debate. But the Universe as we know it is only 13.8 billion years old, so there cannot be any stars older than that, and there has not been enough time for the stars, even in an infinite Universe, to fill the sky with starlight.