Space, Time and Einstein

An Introduction

J.B. Kennedy

• Publisher: Routledge
• Year: 2014
• ISBN:
  9781317489436
• Edition: 1
• Topic: Storia
• Subtopic: Storia antica

This introduction to one of the liveliest and most popular fields in philosophy is written specifically for a beginning readership with no background in philosophy or science. Step-by-step analyses of the key arguments are provided and the philosophical heart of the issues is revealed without recourse to jargon, maths, or logical formulas. The book introduces Einstein's revolutionary ideas in a clear and simple way, along with the concepts and arguments of philosophers, both ancient and modern that have proved of lasting value. Specifically, the theories of the ancient Greek philosophers, Zeno, Euclid and Parmenides are considered alongside the ideas of Newton, Leibniz and Kant as well as the giants of twentieth-century physics, Einstein and Lorentz. The problems at the heart of the philosophy of space and time, such as change, motion, infinity, shape, and inflation, are examined and the seismic impact made by relativity theory and quantum theory is assessed in the light of the latest research. The writing is lucid and entertaining, allowing a beginning readership to grasp some difficult concepts while offering the more experienced reader a succinct and illuminating presentation of the state of the debate. "Space, Time and Einstein" shows the reader the excitement of scientific discovery and the beauty of theory in the search for answers to these fundamental questions.

Part I
Einstein's revolution

Chapter 1
From Aristotle to Hiroshima

Cup your hands together and peer down between your palms.

What is between them?

One answer is “air”. But we think of air as composed of separate molecules, like isolated islands. What lies between the molecules?

Nothing?

The distances between the molecules differ. Could there be more “nothing” between some, and less “nothing” between others? Could nothing really exist?

The empty space does seem to be nothing. It is tasteless, colourless and weightless. It does not move, and the gentlest breeze can pass through it without resistance.

This is our first question. What is between your cupped palms? Is it space, a vacuum, a place? Is it there at all? Is it something or nothing?

Now pause silently for a moment until you can feel the blood pulsing through your hands. Time is flowing. Your brain is sensitive to the physical passage of time and as each second or so passes it rouses itself and decides to stimulate your heartbeat, sending blood coursing down through your palms.

Does time flow invisibly through the space between your palms, as blood flows through your fingers or as a river flows past it banks? Can you feel time flowing there? Is that the right metaphor?

Does time flow more slowly and more quickly, or at a steady rate? If steady, then steady compared to what? Does it flow at a speed of one hour per . .. hour?

If no body moves through a space does time still flow there? Can time proceed without change? This is our second question. What is the flow of time? Is it happening there in the empty space between your palms, or in the space your brain occupies? Is time the same as physical change, or is it the cause of change?

These questions about space and time seem idle at first. It is not clear even how to begin, how to get a grip on them. But we have learned otherwise.

Consider one time and place. On 6 August 1945, early on a bright sunny morning in the city of Hiroshima, tea was being made in offices, children were being bundled off to school and a lonely, propeller-driven plane buzzed unnoticed through the sky above. When the atom bomb fell, the furious, boiling ball of fire killed some one hundred thousand human beings at once. The city centre disappeared, rivers and criss-crossing canals were vaporized and buildings were blown apart for miles. Pedestrians walking across a distant bridge were suddenly sooty silhouettes on scarred concrete. Many more who at first survived the initial blast soon died horribly as their flesh peeled from their bones, and their organs were eaten away by the radiation.

The atom bombs dropped on Hiroshima and Nagasaki, like those still poised and ready in missile silos around the world today, stand as emblems of the power – of the depth and the danger – of our new ideas about space and time. The basic theory of the bombs is given by Albert Einstein’s famous equation that says that ordinary matter can be converted into tremendous explosions of pure force and energy. The following chapters will trace Einstein’s surprisingly simple theories, showing how new ideas about time led to new ideas about energy, and give instructions for constructing an atomic bomb. But here we should pause to contemplate the power of ideas, the possibility that seemingly idle questions may have far-reaching consequences.

Modern answers to the two questions above mix great tragedy and great beauty, and are known as the “philosophy of space and time”. This subject has played a central role in European philosophy since the time of the ancient Greeks. It is sometimes traditional to divide philosophy – the “love of wisdom” – into three branches according to the three leading questions:

• What is there? What exists? What is reality composed of? Does it include atoms, space, ghosts, souls, Beauty, God?
• What can we know? Which sorts of knowledge are reliable? Can we trust our senses? Who should we believe? What is truth?
• What should we do? What is good or evil? Is our aim successful survival or saving our souls? Should we tell lies? Should we be guided by reason or emotion, or both?

For each question, the corresponding branch of philosophy is:

• Metaphysics – the study of reality
• Epistemology – the study of knowledge
• Ethics – the study of good and evil, of values

The philosophy of space and time is part of metaphysics. Some people mistakenly think that the word “metaphysics” means “after or beyond physical science”, but the word is really an historical accident. Historians explain that Aristotle (384–322BCE) wrote many books, which were kept in a chest after his death in 322BCE. A later editor bound them together into volumes and gave each volume a title. One dealt with “Physics”, and was so entitled. The next dealt with more basic questions but had no title. It came to be called “the book that came after the one entitled Physics”, and this name, “After-the-Physics” or “Metaphysics” (“meta” being Greek for “after”), has stuck through the ages. Aristotle would have probably preferred to call it “First Philosophy”, simply because it dealt with the most basic and general questions that could be asked. It was thus a deeper continuation of physics, not a separate subject.

This is important because the philosophy of space and time deals with many ideas that are part of modern physical science: it is not “after” or “beyond” physics. Here, there is no dividing line between philosophy and science.

In fact, the division between philosophy and science may have been a temporary aberration. A little history will help explain this. What we call “science” in the modern sense grew from a small movement in the 1600s led by a few philosophers, aristocrats and mechanics. At that time the new vogue in studies of nature was simply known as “philosophy”. Only some two centuries later, when the trend had caught on and attracted many investigators, was a need felt for some new name for the discipline. “Science” slowly came to have the sense of a study of nature that emphasized experiment and mathematics. The word “scientist” was not coined until 1863.

These new terms signalled a novel and peculiar split between philosophy and the emergent “science”; suddenly there were two disciplines and two communities of thinkers, where before there had been one loose community of philosophers. Crudely put, the philosophers withdrew from experimenting and observing the world while scientists tried to restrict themselves to measurement, calculation and deduction. Philosophers thought in their armchairs: scientists looked through their telescopes and microscopes. The split widened so much in the twentieth century that some people complained that Europe had “two cultures”: the humanities were separate and isolated from the sciences.

There are now healthy signs that this split is healing, and the philosophy of space and time is one area where philosophy and science are converging and overlapping again. After all, both are studying the same world. One reason for this convergence is an extraordinary and unexpected crisis in our understanding of space and time. Physicists had been optimistic that Einstein’s theories were both correct and fundamental. Now there is a widespread sense that, although his theories make many correct predictions, they are somehow wrong and mistaken. Just as Einstein overthrew earlier physics, we may now be on the verge of a new revolution. The new problems are so surprising and so deep that ambitious philosophers have invaded physics and thoughtful physicists have begun raising broad and searching metaphysical questions again. The quantum theory of matter, the new theory of gravitation (“quantum gravity”), astronomy and attempts at unified theories of physics are all throwing up challenges to our understanding of space and time. These are deep enough to be called philosophical.

It is an exciting moment to study the philosophy of space and time. We possess deep and beautiful theories that seem right and illuminating, and make many verifiable predictions. We also know now that they are not fundamentally correct, but we do not understand why. We do not understand how to proceed.

Chapter 2
Einstein in a nutshell

Two theories of relativity

There are two Einsteins. For most of the world, Einstein (1879–1955) is a cult figure: the pre-eminent icon of genius. With his wispy, wild grey hair, missing socks and other-worldly idealism, he has replaced the wizards of earlier times in the popular mind. This Einstein is dangerous, a stereotype with a life of its own that distorts both the man behind it and the nature of the science that so shapes our world.

Among physicists, Einstein is at times remembered as a grumpy, cutting and arrogant fellow with little patience for family or colleagues. He so annoyed his teachers at university that he failed to secure a job in academia, and had to scramble to find low-paying work in the Swiss patent office (although some say that being Jewish hurt his chances too). During his twenties in Berne, Einstein was a fashionable man about town. His wit and violin playing brought him many dinner invitations, and he formed a reading group with friends to study the work of Kant, Schopenhauer and other philosophers. In 1905, his miracle year, he published several unrelated papers. One was good enough to win a Nobel prize, and another revolutionized our views of space and time. The 25-year-old patent clerk had remade physics in his own image.

Einstein’s 1905 theory of space and time is now called the special theory of relativity. The word “relativity” refers to relative speeds and other relations. The theory was “special” in a negative sense: it applied only to a restricted special case and was not general. It has become most well known for predicting that mass can be converted directly into energy, and thus provided the theory behind atomic bombs. During the decade after 1905, Einstein struggled to broaden his theory. It was a time of frustration and false trails, of Herculean labours and wasted years. Finally, in 1916, he published his even more radical general theory of relativity. The special theory overthrew the classical physics of Isaac Newton (1642–1727), which had reigned for some 200 years, and the general theory overthrew Euclid’s geometry, which had been considered a model of certain knowledge for more than 2000 years.

As Europe lay in ruins after the end of the First World War, an English astronomer sought observations that might confirm Einstein’s radical theories. Arthur Eddington believed that a British effort to support the theories of a Swiss-German would demonstrate the internationalism of science, and promote healing among the shattered nations. He mounted an expedition to South Africa, where a total eclipse was predicted in 1919. Einstein had predicted that measurements of starlight bending around the darkened Sun would test his theory. Eddington’s crude photographs made Einstein a celebrity. The results were telegraphed around the world and newspapers announced that we had entered the Age of Relativity.

Einstein became a professor of physics in Berlin, the fashionable capital of interwar Germany and a centre of modernist movements in art, literature and politics. He enjoyed his celebrity, socializing at black-tie dinners with the high and mighty, and used his fame to advance pacifism and international socialism. As the economy worsened, however, he became a lightning rod for anti-Semitic threats. A wave of frightened scientists, intellectuals and artists were then emigrating to the USA, and transforming it into a leader in scientific research. Einstein moved with his family in 1933 and took up a position at the Institute for Advanced Study at Princeton. In 1939, as the Nazis advanced across Europe, Einstein sent a now famous letter to President Roosevelt appealing for urgent research into atomic weapons. Together with pressure from their allies in Britain, this led the USA to collaborate with Britain on a huge, incredibly expensive crash programme, the Manhattan Project, which constructed the bombs dropped on Japan four years later.

In 1948 Einstein turned down an offer to become the first president of Israel, and continued his quiet life of research at Princeton. Younger physicists had moved on to more exciting developments, and at times regarded Einstein as a scientific has-been who failed to keep up with them.

Today we live in the golden age of astronomical exploration. Using the Hubble Telescope and a host of other satellites, ultra-sensitive detectors and high-speed computers, we have learned more about the universe during the past two decades than during all of history. If anything, the pace of discovery is even now accelerating. And all this is Einstein’s golden age too. His ideas guide these explorations, and provide the basic framework underlying theories of the Big Bang, black holes and the birth of stars and galaxies. All the same, however, experiments now strongly suggest that Einstein’s most basic views on space and time were somehow wrong: that they were fruitful half-truths. A storm of work in the foundations of physics, quantum gravity and cosmology has made this an era that once again is posing the deepest questions about space and time. Like Newton before him, Einstein now faces the prospect of being overthrown by new and deeper theories. These are exciting times.

The following chapters introduce Einstein and his special theory of relativity in a very simple way, and concentrate on two themes. First, they pinpoint the daring, conceptual leaps that lay at the heart of Einstein’s theory. Einstein was not a great mathematician, and his discoveries all begin with creative insights that can be understood and appreciated without jargon. For philosophers, these flights of genius are enduring monuments to the beauty and power of thought. Secondly, the chapters return constantly to the heated controversy now surrounding the interpretation of Einstein’s theories. Despite the myriad of successful predictions they produce, there is now real uncertainty about why his theories work, and therefore about his grand revisions in our ideas about space and time.

This approach is unusual. Most introductions to relativity hide the ongoing debates and concentrate on expounding the technical features of Einstein’s theory. Here, the mathematics is set aside and we stay close to the phenomena, to the concrete predictions and observable implications of the theory. Thus we penetrate to the conceptual core of theory, and therefore to its philosophical heart.

Later in his life, Einstein distinguished betw...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Dedication
• Contents
• Preface and acknowledgements
• Part I: Einstein's revolution
• Part II: Philosophical progress
• Part III: Frontiers
• Appendix A: Spacetime diagrams
• Appendix B: Symmetry and Lorentz's minority interpretation
• Appendix C: Simple formulas for special relativity
• Appendix D: Websites
• Appendix E: Guide to further reading
• Index