Chapter 2.1 Einstein in a nutshell Two theories of relativity

CHAPTER 2 Einstein in a nutshell - Two theories of relativity
CHAPTER 2 Einstein in a nutshell – Two theories of relativity

Space, Time and Einstein

J. B. Kennedy

PART I – Einstein’s revolution

CHAPTER 2.1 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 inter- nationalism 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 measure- ments 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 between two sorts of scientific theories. Constructive theories begin by listing the basic things in the world, and build up or construct larger, high-level things from these. The fully developed model is then used to make predictions. Philosophers would say that such a theory begins with an ontology, and draws consequences from it.

In contrast, Einstein said, special relativity is a principle theory. He meant that the theory begins by listing a few high-level assumptions or isolated facts that are not supported by any model, and then uses these to make predictions. The truth of the predictions would justify the assumptions or justify relying on the facts, even if they are not clearly supported by a deeper picture of the world. A principle theory can seem very mysterious when the predictions it makes are unexpected. When a magician pulls a rabbit out of an ordinary looking hat we seek for some deeper explanation of what happened.

A principle theory does not offer deeper explanations.

The special theory of relativity is a principle theory. This chapter introduces the principles and facts that Einstein used to make his startling predictions. At the end of the chapter we take a first glance at what could make all this true, and attempt to go deeper than Einstein’s principles.

The general theory of relativity builds on and generalizes the special theory of relativity, but does not explain its principles.

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