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which is also the reason why Einstein addressed him as plain Herr Weber, rather than Herr Professor Weber.

      As a result of this battle of wills, Weber did not write the letter of recommendation that Einstein required to pursue an academic career. Consequently, Einstein spent the next seven years after graduation as a clerk in the patent office at Berne, Switzerland. As it turned out, this was not such a terrible predicament. Instead of being constrained by the mainstream theories promulgated at the great universities, Einstein could now sit in his office and think about the implications of his teenage thought experiment—exactly the sort of speculative deliberations that Herr Professor Weber would have pooh-poohed. Also, Einstein’s prosaic office job, initially ‘probationary technical expert, third class’, allowed him to squeeze all of his patenting responsibilities into just a few hours each day, leaving him plenty of time to conduct his personal research. Had he been a university academic, he would have wasted day after day dealing with institutional politics, endless administrative chores and burdensome teaching responsibilities. In a letter to a friend, he described his office as ‘that secular cloister, where I hatched my most beautiful ideas’.

      These years as a patent clerk would prove to be one of the most fruitful periods of his intellectual life. At the same time, it was a highly emotional time for the maturing genius. In 1902, Einstein experienced the deepest shock of his entire life when his father fell fatally ill. On his deathbed, Hermann Einstein gave Albert his blessing to marry Mileva Marić, unaware that the couple already had a daughter, Lieserl. In fact, historians were also unaware of Albert and Mileva’s daughter until they were given access to Einstein’s personal correspondence in the late 1980s. It emerged that Mileva had returned to her native Serbia to give birth, and as soon as Einstein heard the news of their daughter’s arrival he wrote to Mileva: ‘Is she healthy and does she already cry properly? What kind of little eyes does she have? Who of us two does she resemble more? Who is giving her milk? Is she hungry? And is she completely bald? I love her so much and I do not even know her yet!… She certainly can cry already, but will learn to laugh only much later. Therein lies a deep truth.’ Albert would never hear his daughter cry or watch her laugh. The couple could not risk the social disgrace of having an illegitimate daughter, and Lieserl was put up for adoption in Serbia.

      Albert and Mileva were married in 1903, and their first son, Hans Albert, was born the next year. In 1905, while juggling the responsibilities of fatherhood and his obligations as a patent clerk, Einstein finally managed to crystallise his thoughts about the universe. His theoretical research climaxed in a burst of scientific papers which appeared in the journal Annalen der Physik. In one paper, he analysed a phenomenon known as Brownian motion and thereby presented a brilliant argument to support the theory that matter is composed of atoms and molecules. In another paper, he showed that a well-established phenomenon called the photoelectric effect could be fully explained using the newly developed theory of quantum physics. Not surprisingly, this paper went on to win Einstein a Nobel prize.

      The third paper, however, was even more brilliant. It summarised Einstein’s thoughts over the previous decade on the speed of light and its constancy relative to the observer. The paper created an entirely new foundation for physics and would ultimately lay the ground rules for studying the universe. It was not so much the constancy of the speed of light itself that was so important, but the consequences that Einstein predicted. The repercussions were mind-boggling, even to Einstein himself. He was still a young man, barely twenty-six years old when he published his research, and he had experienced periods of enormous self-doubt as he worked towards what has become known as his special theory of relativity: ‘I must confess that at the very beginning when the special theory of relativity began to germinate in me, I was visited by all sorts of nervous conflicts. When young I used to go away for weeks in a state of confusion, as one who at the time had yet to overcome the state of stupefaction in his first encounter with such questions.’

      Figure 21 Albert Einstein pictured in 1905, the year he published his special theory of relativity and established his reputation.

      One of the most amazing outcomes of Einstein’s special theory of relativity is that our familiar notion of time is fundamentally wrong. Scientists and non-scientists had always pictured time as the progression of some kind of universal clock that ticked relentlessly, a cosmic heartbeat, a benchmark against which all other clocks could be set. Time would therefore be the same for everybody, because we would all live by the same universal clock: the same pendulum would swing at the same rate today and tomorrow, in London or in Sydney, for you and for me. Time was assumed to be absolute, regular and universal. No, said Einstein: time is flexible, stretchable and personal, so your time may be different from my time. In particular, a clock moving relative to you ticks more slowly than a static clock alongside you. So if you were on a moving train and I was standing on a station platform looking at your watch as you whizzed by, then I would perceive your watch to be running more slowly than my own watch.

      This seems impossible, but for Einstein it was logically unavoidable. What follows in the next few paragraphs is a brief explanation of why time is personal to the observer and depends on the travelling speed of the clock being observed. Although there is a small amount of mathematics, the formulas are quite simple, and if you can follow the logic then you will understand exactly why special relativity forces us to change our view of the world. However, if you do skip the mathematics or get stuck, then don’t worry, because the most important points will be summarised when the mathematics is complete.

      To understand the impact of the special theory of relativity on the concept of time, let us consider an inventor, Alice, and her very unusual clock. All clocks require a ticker, something with a regular beat that can be used to count time, such as a swinging pendulum in a grandfather clock or a constant dripping in a water-clock. In Alice’s clock, the ticker is a pulse of light that is reflected between two parallel mirrors 1.8 metres apart, as shown in Figure 22(a). The reflections are ideal for keeping time, because the speed of light is constant and so the clock will be highly accurate. The speed of light is 300,000,000 m/s (which can be written as 3 × 10⁸m/s), so if one tick is defined as the time for the light pulse to travel from one mirror to the other and back again, then Alice sees that the time between ticks is

      Alice takes her clock inside a train carriage, which moves at a constant velocity down a straight track. She sees that the duration for each tick remains the same—remember, everything should remain the same because Galileo’s principle of relativity says that it should be impossible for her to tell whether she is stationary or moving by studying objects that are travelling with her.

      Meanwhile, Alice’s friend Bob is standing on a station platform as her train whizzes past at 80% of the speed of light, which is 2.4 X 10⁸m/s (this is an express train in the most extreme sense of the word). Bob can see Alice and her clock through a large window in her carriage, and from his point of view the light pulse traces out an angled path, as shown in Figure 22(b). He sees the light pulse as following its usual up-and-down motion, but for him it is also moving sideways, along with the train.

      In other words, in between leaving the lower mirror and arriving at the upper mirror, the clock has moved forward, so the light has to follow a longer diagonal path. In fact, from Bob’s perspective, the train has moved forward 2.4 metres by the time the pulse has reached the upper mirror, which leads to a diagonal path length of 3.0 metres, so the light pulse has to cover 6.0 metres (up and down) between ticks. Because, according to Einstein, the speed of light is constant for any observer, for Bob the time between ticks must be longer because the light pulse travels at the same speed but has farther to travel. Bob’s perception of the time between ticks is easy to calculate:

      Figure 22 The following scenario demonstrates one of the main consequences of Einstein’s special theory of relativity. Alice is inside her railway carriage with her mirror-clock, which ’ticks’ regularly as the light pulse is

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