Introducing Stephen Hawking E-Book

J.P. McEvoy

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

Seitenzahl: 115

Veröffentlichungsjahr: 2014

Beschreibung

'An ideal introduction [to Stephen Hawking]' - Independent 'Astonishingly comprehensive - clearer than Hawking himself' - Focus Stephen Hawking was a world-famous physicist with a cameo in The Simpsons on his CV, but outside of his academic field his work was little understood. To the public he was a tragic figure - a brilliant scientist and author of the 9 million-copy-selling A Brief History of Time, and yet spent the majority of his life confined to a wheelchair and almost completely paralysed. Hawking's major contribution to science was to integrate the two great theories of 20th-century physics: Einstein's General Theory of Relativity and Quantum Mechanics. J.P. McEvoy and Oscar Zarate's brilliant graphic guide explores Hawking's life, the evolution of his work from his days as a student, and his breathtaking discoveries about where these fundamental laws break down or overlap, such as on the edge of a Black Hole or at the origin of the Universe itself.

Leseprobe

Published by Icon Books Ltd, Omnibus Business Centre, 39-41 North Road, London N7 9DP email: [email protected]

ISBN: 978-184831-777-2

Text and illustrations copyright © 2013 Icon Books Ltd

The author and artist have asserted their moral rights.

Originating editor: Richard Appignanesi

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

Contents

Cover

Title Page

Copyright

The Luckiest Man in the Universe

The General Theory of Relativity

Newton: The Concept of Force

Four Kinds of Force in the Universe

The Principia: Describing Newton’s Universe

Newton and Hawking

The Concept of Mass

Albert Einstein, the Saviour of Classical Physics

Einstein and Hawking

Einstein’s Happiest Thought

Finding the Right Equation

The Field Equations – What do they mean?

Visualising Curved Space: the Rubber Sheet Model

The Bending of Starlight: Eclipse of 29 May 1919

Solving Einstein’s Equations: Hawking’s Starting Material

1) The Schwarzschild Geometry

The Critical Radius

2) Friedmann: the Expanding Universe

Precursor to the Big Bang: Lemaître’s Primordial Aim

3) Oppenheimer: on Continued Gravitational Collapse, 1939

1 September 1939

1942 … A Turning Point in the Story

The Death of Einstein

The Hawking Era

The Unselfish Thesis Supervisor

Something You Need to Know: What is a Singularity?

The Evolution of the Universe

1965: a Big Year for Hawking

An Unstoppable Mind

The Sixties Revolution

Dallas 1963

Something You Need to Know: the Electro Magnetic Spectrum

1963: Quasars

1965: the Cosmic Background Radiation

Something You Need to Know — Thermal Radiation

History of the Universe

Black Holes — Wheeler Gives the Media a Buzz Word

The Age of Black Holes

What is a Black Hole?

The Birth and Death of Stars

How Stars Collapse to Form White Dwarfs, Neutron Stars & Black Holes

Observational Evidence for Black Holes

The 1970s: Hawking and Black Holes

Hawking’s Eureka Moment

The Laws of Thermodynamics

Now Back to Black Holes …

Controversial Birth of a New Idea

August 1972, Les Houches Summer School on Black Hole Physics

The Uncertainty Principle & Virtual Particles

February 1974, The Rutherford- Appleton Laboratory, Oxford

Hawking and the Vatican – a Modern Day Galileo

Hawking and the Early Universe

Why Do We Need Quantum Theory?

Quantum Cosmology

Quantum Gravity or TOE

Quantum Cosmology and Complex Time

Waves and Particles: Nature’s Joke on the Physicists

The Strange World of Quantum Mechanics

Quantum Cosmology: Applying Schrödinger’s Equation to the Universe

DAMTP: 17 February 1995

Inflation

Inflation and Quantum Fluctuations

The Anthropic Principle

Hawking’s Nobel Prize

COBE: the Greatest Discovery of All Time (?)

Further Reading

Acknowledgements

Index

The Luckiest Man in the Universe

On 19 October 1994, the author of this book interviewed Stephen Hawking. He began with a question that might seem daring, if not impertinent. Did Hawking consider himself lucky?

WHAT A QUESTION! CONFINED TO A WHEELCHAIR FOR OVER TWENTY YEARS AND UNABLE TO WRITE OR SPEAK… LUCKY? WHO WOULD AGREE WITH THAT… EXCEPT POSSIBLY STEPHEN HAWKING HIMSELF!

Let’s go back a bit…

Everyone knows of Hawking’s bad luck. It began one afternoon in the spring of 1962 when he found it very difficult to tie his shoelaces. He knew something was drastically wrong with his body. That year he had talked his way into a first degree at Oxford University and was accepted as a postgraduate student at Cambridge. But he had contracted amyotrophic lateral sclerosis, ALS for short, the motor neurone disease. It is incurable and fatal. Doctors gave him two years to live.

As the tabloid press and the paperback biographies would have us believe, Hawking spent the next several months in deep depression in his university digs, drinking and listening to Wagner. To add to his bitterness, he was told that he would not have the famous cosmologist Fred Hoyle (b. 1915) as his research adviser, the reason he chose Cambridge in the first place.

But immediately his luck began to change. A young woman, Jane Wilde, he met on New Year’s Eve 1962 had taken a genuine interest in him, and the Cambridge Physics Department had assigned him to Dennis Sciama (b. 1926), one of the best-informed and most inspiring research advisers in the world of relativistic cosmology.

Once it is accepted that Stephen William Hawking’s physical capabilities were severely limited by the tragic disease of ALS, a whole series of fortunate events seemed to have taken place in the early 1960s which enabled him to fulfil his destiny as one of the leading cosmologists of modern times.

First of all, for the profession he had chosen – theoretical physics – the only facility he absolutely needed was his brain, which was completely unaffected by his illness. He had met a helpful partner in Jane Wilde and been presented with a sympathetic thesis adviser, Sciama.

Soon he would meet Roger Penrose (b. 1931), a brilliant mathematician working on black holes, who would teach him radically new analytical tools in physics. Penrose would help him solve a research problem that would not only save his doctoral dissertation but also bring him directly into mainstream theoretical physics.

The help of these three people at such a critical time in Hawking’s life is perhaps more than anyone can hope for.

He had another appointment with destiny at about the same time. A theory which had been developed almost fifty years earlier – Einstein’s general theory of relativity – was only just being widely applied to practical problems in cosmology. It seems that predictions based on this theory were so bizarre that it had taken decades for it to be accepted. Now in the early 1960s, a golden age of research in cosmology based on general relativity was about to begin. Fate had waited for Stephen Hawking. The secretly ambitious – though by then slightly crippled – theoretical physicist was ready. He didn’t know how long he had to live … but he was certainly in the right place at the right time.

MAYBE HE WAS LUCKY.

Stephen Hawking is called a relativistic cosmologist. This means he studies the Universe as a whole (cosmologist) and uses mainly the theory of relativity (relativistic).

As Hawking has spent his entire career as a theoretical physicist – from the early 1960s to the mid 1990s – working with Einstein’s general relativity, it might be a good idea to know what it’s about.

The General Theory of Relativity

Berlin, November 1915. Albert Einstein (1879-1955) had just completed his theory of general relativity, a mathematical structure in which curved space and warped time are used to describe gravitation. All modern cosmology began two years later, when Einstein published a second paper called Cosmological Considerations in which he applied his new theory to the entire Universe.

General relativity is difficult to master, but the relatively few people who understand the theory agree it is an elegant, even beautiful theory of gravitation.

Describing a set of equations as beautiful doesn’t help much in understanding how Einstein’s theory differs from that of Isaac Newton (1642-1727). But an example of how each of the two theories describes gravity in the same physical situation might do the trick.

Why does a, cosmologist have to study gravitation?

Cosmology is the study of the whole Universe and much of the subject is based on wide-sweeping hypotheses. Gravitation determines the large-scale structure of the Universe or, more simply, keeps the planets star and galaxies together. It is the most important concept for work in this field.

Until recently, the subject of cosmology was considered to be a pseudo-science reserved for retired emeritus professors. But in the last three decades, more or less coinciding with Hawking’s career, two major developments have changed the subject dramatically.

THE COMPLETE STORY TAKES IN NEWTON, THEN EINSTEIN, THEN HAWKING FIRST, NEWTON.

First, major breakthroughs in observational astronomy – reaching out to the most distant galaxies – have made the Universe a laboratory to test cosmological models

Second, Einstein’s general relativity has been proven over and over again to be an accurate and reliable theory of gravitation throughout the entire Universe.

Remember, physics is a cumulative subject. New theories are built on previous ones, keeping the ideas that stand up to experimental test and discarding those that don’t. Our final goal is to understand the contributions of Stephen Hawking who has taken Einstein’s gravitation theory to its ultimate limit.

It is important to understand the notion of partial theories. For example, Newton’s Law of Gravitation is very accurate only when gravity is weak – and must be replaced by Einstein’s general relativity in strong gravitational fields. Similarly, relativity must be replaced by quantum mechanics when examining interactions on a microscopic scale, such as the big bang singularity, or at the edge and centre of a black hole. Hawking is generally recognized as the theoretician with the best chance of combining general relativity and quantum mechanics to produce quantum gravity, ill-named by the media as Theory of Everything.

Newton: The Concept of Force

Newton introduced the concept of a gravitational force of attraction and stated that the mutual pull of attraction between two objects is proportional to the mass of each object (i.e. the amount of matter the object contains) and inversely proportional to the square of distance between them.

NOW DON’T PANIC IT’S A VERY SIMPLE EQUATION! I CALL THIS MY LAW OF UNIVERSAL GRAVITATION. “IF THE MASS OF ONE OR THE OTHER OF THE TWO OBJECTS DOUBLES! THE FORCE DOUBLES! BUT IF THE DISTANCE BETWEEN THE TWO OBJECTS IS DOUBLED, THE FORCE IS REDUCED BY A FACTOR OF FOUR, DUE TO THE SQUARED TERM IN THE DENOMINATOR. “THUS THE FORCE DECREASES RAPIDLY AS THE TWO OBJECTS ARE MOVED A PART.”

Gravitation is the weakest force in nature as seen by the magnitude of the gravitational constant Gin practical units:

A Newton is a scientific unit of force, equal to about a quarter of a pound.

Four Kinds of Force in the Universe

The Electromagnetic Force: keeps atoms together and is the basis for all chemical reactions.

The Strong Nuclear Force: binds the neutrons and protons together in the nucleus. This force is important in nuclear reactions like fission and fusion.

The Weak Nuclear Force: determines radioactive decay, i.e. the spontaneous emission of alpha and beta particles from inside the nucleus.

The Gravitational Force: responsible for large-scale structure of the Universe, the formation of galaxies, stars, and planets.

The four known forces separate and become individually distinct during the earliest moments of the Universe.

When two Sumo wrestlers (mass about 135 kilograms) get close to each other in the ring (say a metre apart), the force pushing them towards each other is minuscule … about 10,000 times less than the pull necessary to pick up one square of toilet tissue! To convert the answer to pounds multiply Newtons by 0.225.

But the force pulling each of them towards the floor is much larger. That’s because the other object attracting each downwards is the Earth, whose mass (5.98 x 1024 kilograms) must be put in the numerator of Newton’s equation. The Earth’s radius (6.37 x 106 metres) goes in the denominator. Try the calculation yourself with an electronic calculator and don’t forget the conversion factor to get your answer in pounds.

The Principia: Describing Newton’s Universe

Newton was chiefly concerned with the force of gravity between the Sun and planets, i.e., the solar system. The immediate impetus for the publication of his theory of gravitation, the Principia, arose from a discussion at the Royal Society in 1684 between the astronomer Edmond Halley (1656-1742), the architect Sir Christopher Wren (1632-1723) and Newton’s arch rival Robert Hooke (1635–1703).

WE THINK AN INVERSE SQUARE LAW OF ATTRACTION IMPLIES ELLIPTICAL ORBITS FOR THE PLANETS. BUT WE CAN’T PROVE IT. I CAN BUT I’M KEEPING MY PROOF SECRET!

I’LL JOURNEY TO CAMBRIDGE AND ASK NEWTON’S OPINION… WELL, I’M OFF TO ST PAULL’S TO BUILD MY CATHEDRAL.

AN INVERSE SQUARE LAW DOES INDEED PRODUCE ELLIPTICAL ORBITS A RESULT WHICH I’VE DEMONS TRATED MATHEMATICALLY. THIS IS VERY EXCITING! CAN YOU SHOW IT TO ME?

EH WELL… I CAN’T FIND THE CALCULATION.

Halley returned to London frustrated, but 3 months later he received a 9-page paper in Latin, De Motu Corporum or On the Motion of Bodies in Orbit, in which Newton described the elliptical paths of the planets in terms of his Law of Gravitation and his Laws of Motion. This was the precursor of his world-famous Principia (1687) which presented a complete mathematical description of his ideas.

Newton and Hawking

The media often compares Stephen Hawking with other famous physicists like Newton and Einstein, much to the alienation of scientists and, in particular, historians of science. No single individual will ever dominate his era as Newton did, whereas Hawking is one of a small group of élite scientists at the cutting-edge of today’s cosmology.

Yet, some of these comparisons are very interesting.

Newton spent his entire scientific career at Cambridge with his residence and laboratories at Trinity College. Hawking has been at Cambridge since his postgraduate student days in 1962, except for a few sabbatical years abroad.

They have both attempted to explain the observable physical Universe using theories of gravity: Newton using his own theory, and Hawking using mainly Einstein’s general relativity.

Both have held the same distinguished position at Cambridge, the Lucasian Chair of Mathematics.

The wide range of applications for the gravitation law which Newton presented in the Principia is quite extraordinary. The theory was an immediate success and found to be applicable to all motion in the solar system, including the Moon and comets as well as the planets. It was so accurate that it was used to discover the planet Neptune, which could not even be seen with the telescopes available at the time.

BUT I’M WORRIED! QUIET! YOU DON’T EXIST YET!