As the 19th century ended, scientists could be happy they’d solved most mysteries of the physical world: electricity, magnetism, gases, acoustics and statistical mechanics, all had fallen before them. They had discovered the X-ray, the electron, and radioactivity, invented the ohm, the watt, the Kelvin, the joule, and the amp. Many people believed there was nothing left for science to do.
English
Last updated
Sun, 30-Jun-2024
Relativity and the Expanding Universe
As the 19th century ended, scientists could be happy they’d solved most mysteries of the physical world: electricity, magnetism, gases, acoustics and statistical mechanics, all had fallen before them. They had discovered the X-ray, the electron, and radioactivity, invented the ohm, the watt, the Kelvin, the joule, and the amp. Many people believed there was nothing left for science to do.
J. Willard Gibbs is perhaps the most brilliant person that most people have never heard of. Nearly scientifically invisible, he passed almost all his life in a three-block area from the Yale campus. From 1871, when he joined the university, to his death in 1903, his courses attracted an average of one student a semester. His written work was difficult to follow. But in 1875–78, Gibbs produced a series of papers that dazzlingly explained the thermodynamic principles of, well, nearly everything: gases, surfaces, solids, chemical reactions, electrochemical cells, sedimentation, and osmosis. What Gibbs did was show that thermodynamics didn’t apply only to heat and energy at the scale of the steam engine, but also at the atomic level of chemical reactions.
In Cleveland, Ohio, in the 1880s, a physicist named Albert Michelson started a series of experiments that produced curious and disturbing results that would have great effects for much of what followed. What Michelson did was cast doubt on a longstanding belief in something called ether, a stable, invisible, weightless and, unfortunately, wholly imaginary medium. Invented by Descartes, trusted by Newton, and admired by nearly everyone since, ether was central to nineteenth-century physics as a way of explaining how light traveled across the emptiness of space. It was needed in the 1800s because light and electromagnetism were seen as waves, which is to say types of vibrations. Vibrations must occur in something; so, ether.
Born in 1852 on the German–Polish border to a family of poor Jewish merchants, Albert Michelson came to the United States with his family and grew up in a mining camp in California’s gold rush country, where his father ran a dry goods business. Too poor to pay for college, he traveled to Washington, D.C., and waited by the front door of the White House so that he could walk beside President Ulysses S. Grant when the President exercised every day. Grant agreed to get him a free place at the U.S. Naval Academy. It was there that Michelson learned his physics.
Ten years later, Michelson became interested in trying to measure something called the ether drift – a kind of wind produced by objects as they moved through space. Newton suggested that the speed of light varied depending on whether the observer was moving toward the light or away from it, but no-one had figured out a way to measure this. It occurred to Michelson that for half the year the Earth is traveling toward the Sun and for the other half away from it. If you took careful measurements at opposite seasons and compared light’s travel time between the two, you’d have your answer.
Michelson persuaded Alexander Graham Bell to provide the money to build a sensitive instrument of Michelson’s called an interferometer, which could measure the velocity of light with precision. By 1887 they had their results. They were not at all what the two scientists expected to find. The speed of light was the same in all directions and at all seasons. It was the first hint in two hundred years that Newton’s laws might not apply all the time everywhere. The Michelson outcome became probably the most famous negative result in the history of physics.
Scientists would soon find themselves where everything was strange. Science was moving from a world of macrophysics, where objects could be seen and held and measured, to one of microphysics, where events happen with unimaginable speed on scales far below the limits of imagination. We were about to enter the quantum age, and the first person to push on the door was the German Max Planck.
In 1900, Planck created a new ‘quantum theory,’ which posited that energy is not a continuous thing like flowing water but comes in individual packets, which he called quanta. This was a new concept, and a good one. In the short term it would provide a solution to the puzzle of the Michelson experiments as it demonstrated that light needn’t be a wave after all. In the longer term it would lay the foundation for the whole of modern physics. It was, at all events, the first clue that the world was about to change.
But a new age came in 1905, when in a German physics journal a series of papers appeared by a young Swiss bureaucrat who had no access to a laboratory or library. His name was Albert Einstein, and in that one eventful year he wrote five papers, of which three were among the greatest in the history of physics, one examining the photoelectric effect by Planck’s new quantum theory, one on the behaviour of small particles in suspension, and one outlining a special theory of relativity.
The first won its author a Nobel Prize and explained the nature of light (and also helped to make television possible). The second provided proof that atoms existed – a fact that had, surprisingly, been unclear. The third changed the world.
Einstein was born in southern Germany in 1879 and grew up in Munich. Little in his early life suggested the greatness to come. Famously he didn’t learn to speak until he was three. In the 1890s, his father’s electrical business failed and the family moved to Milan, Italy, but Albert, by now a teenager, went to Switzerland to continue his education, though he failed his college entrance exams on the first try. In 1896 he gave up his German citizenship to avoid going into the army and entered the Zurich Polytechnic Institute on a four-year course designed to produce school science teachers. He was a bright but not outstanding student.
In 1900 he graduated and within a few months was beginning to publish papers. At the same time he fell in love with another student, a Hungarian named Mileva Maric. In 1901, unmarried, they had a daughter who was quietly adopted. Einstein never saw his child. In between, in 1902, Einstein took a job with the Swiss patent office, where he stayed for the next seven years. He enjoyed the work: it was challenging enough to engage his mind, but not so challenging as to distract him from his physics. This was the background against which he produced the special theory of relativity in 1905.
It was and is one of the most extraordinary scientific papers ever published. It had no notes or quotations, contained almost no mathematics & made no mention of any work that influenced or came before it. It was as if Einstein reached his conclusions by thinking alone, without the opinions of others.
In simple terms, what his famous equation, E = mc2 says is that mass and energy are two forms of the same thing: energy is liberated matter; matter is energy waiting to happen. Since c2 (the speed of light times itself) is a truly enormous number, what the equation is saying is that there is a huge amount of energy in every material thing.
An average-sized adult contains no less than 7 x 1018 joules of potential energy: enough to explode with the force of thirty very large hydrogen bombs. Everything has this kind of energy trapped within it. We’re just not very good at getting it out.
Among much else, Einstein’s theory explained how radiation worked: how a lump of uranium could throw out constant streams of high-level energy without melting like an ice cube. (It could do it by converting mass to energy extremely efficiently – E = mc2.) It explained how stars could burn for billions of years without racing through their fuel. In a simple formula, Einstein gave geologists and astronomers the luxury of billions of years. Above all, the special theory showed that the speed of light was constant and supreme. Nothing could overtake it. It also solved the problem of ether by making it clear that it didn’t exist. Einstein gave us a universe that didn’t need it.
Einstein’s papers attracted little notice. Having just solved several of the deepest mysteries of the universe, Einstein applied for jobs as a university lecturer and high school teacher and was rejected. So he went back to his job as a civil servant, but of course he kept thinking.
When the poet Paul Valéry once asked Einstein if he kept a notebook to record his ideas, Einstein looked at him with mild but genuine surprise. “Oh, that’s not necessary,” he replied. “It’s so seldom I have one.” Einstein’s next idea was one of the greatest that anyone has ever had.
In 1907, or so it has sometimes been written, Albert Einstein saw a workman fall off a roof and began to think about gravity. According to Einstein himself, he was simply sitting in a chair when the problem of gravity occurred to him. Actually, what occurred to Einstein was something more like the beginning of a solution to the problem of gravity, since it was clear to him from the start that one thing missing from the special theory was gravity. What was “special” about the special theory was that it dealt with things moving uninterrupted. But what happened when a moving thing – light, above all – met an obstacle like gravity? It was a question that would keep him busy for most of the next decade and lead to a 1917 paper, ‘Cosmological Considerations on the General Theory of Relativity.’ The theory of relativity of 1905 was an important piece of work, of course, but if Einstein hadn’t thought of it, someone else would have, probably within five years. But the general theory was something else. Without it, it is likely that we should still be waiting for the theory today.
The world suddenly discovered Einstein at the end of World War I. Almost at once his theories of relativity developed a reputation for being impossible for an ordinary person to understand. It did not help that New York Times decided to send its golf journalist to conduct an interview with Einstein. He got nearly everything wrong. Among the more lasting mistakes in his report was that Einstein had found a company with enough courage to publish a book that only twelve men “in all the world could comprehend.” In fact, the problem with relativity wasn’t that it involved a lot of differential equations and other complicated mathematics (though it did – even Einstein needed help with some of it), but that it was just so much against common sense.
In essence what relativity says is that space and time are not absolute, but relative to both the observer and to the thing being observed, and the faster one moves the more pronounced these effects become. We can never accelerate ourselves to the speed of light, and the harder we try (and faster we go) the more distorted we will become, relative to an outside observer. Bertrand Russell, the British philosopher and mathematician, used this image. He asked the reader to imagine a train one hundred metres long moving at 60% the speed of light. To someone standing on a platform watching it pass, the train would appear to be only eighty metres. If we could hear the passengers on the train speak, their voices would sound slow, like music played too slow. Even the clocks on the train would seem to be running at only four-fifths of their normal speed.
However, people on the train would have no sense of this. To them, everything on the train would seem normal. It would be we on the platform who looked strangely slowed down. It is all to do, you see, with your position relative to the moving object.
So if the ideas of relativity seem weird, it is only because we don’t experience these sorts of interactions in normal life. However, we all commonly see other kinds of relativity, for instance with sound. If you are in a park and someone is playing loud music, you know if you move to a distant spot the music will seem quieter. That’s not because the music is quieter, of course, but simply that your position has changed. To something small or slow – a snail, say – the idea that speakers could seem to two observers to produce two different volumes of music simultaneously might seem incredible.
The most challenging of all the concepts in the general theory of relativity is the idea that time is part of space. Our instinct is to regard time as eternal, absolute – nothing can disturb it. In fact, according to Einstein, time is ever-changing. It even has shape. It is connected with the three dimensions of space in a strange dimension known as spacetime.
Spacetime is usually explained by asking you to imagine something flat but flexible – a mattress, say – on which there’s an iron ball. Its weight causes the material to bend slightly. This is similar to the effect that a huge object such as the Sun has on spacetime: it stretches and curves it. Now if you roll a smaller ball across the mattress, it tries to go in a straight line according to Newton’s laws of motion, but as it nears the massive object and the bend in the material, it rolls downward, drawn to the huge object. This is gravity – the bending of spacetime.
Every object that has mass creates a little bend in the cosmos. So, the universe. Gravity in this view is no longer so much a thing as a result, not a ‘force’ but a byproduct of the bending of spacetime. In some sense, gravity does not exist; what moves the planets and stars is the distortion of space and time.
Of course the sagging mattress analogy can take us only so far because it doesn’t include the effect of time. But then our brains can take us only so far because it is so nearly impossible to imagine a dimension comprising three parts space to one part time.
Among much else, Einstein’s general theory of relativity suggested that the universe must be either expanding or contracting. But Einstein was not a cosmologist, and he accepted the general belief that the universe was fixed and eternal. He dropped into his equations something called the cosmological constant, to counterbalance the effects of gravity. Einstein called it “the biggest blunder of my life.”
At about the same time in Arizona, an astronomer, Vesto Slipher, was taking spectrographic readings of distant stars and discovering that they appeared to be moving away from us. The universe wasn’t static. The stars Slipher looked at showed unmistakable signs of a Doppler shift, the same mechanism behind that distinctive stretched-out yee-yummm sound cars make as they speed past on a racetrack. The phenomenon also applies to light, and in the case of receding galaxies it is known as a red shift (because light moving away from us shifts toward the red end of the spectrum; approaching light shifts to blue).
Slipher was the first to notice this effect with light and to realize its importance for understanding the movement of the cosmos. Unfortunately no-one much noticed him. Slipher was unaware of Einstein’s theory of relativity, and the world was equally unaware of Slipher. So his finding had no impact.
Glory instead would pass to Edwin Hubble, born in 1889, ten years after Einstein, in the US. His father was a successful insurance executive, so life was always comfortable, and Edwin was a strong and gifted athlete, charming, smart, and good-looking. According to his own accounts, he also managed to rescue drowning swimmers, lead frightened men to safety across the battlefields of France, and surprise world-champion boxers with knockdown punches. It all seemed too good to be true. It was. Hubble was a liar.
In 1919, aged thirty, Hubble moved to California and took up a job at the Mount Wilson Observatory. Swiftly, and unexpectedly, he became the most outstanding astronomer of the twentieth century.
It is worth pausing for a moment to consider just how little was known of the cosmos at this time. Astronomers today believe there are perhaps 140 billion galaxies in the visible universe. That’s a much bigger number than just saying it would suggest. If galaxies were peas, it would be enough to fill a large auditorium. In 1919, when Hubble first put his head to a telescope, the number of these galaxies known to us was one: the Milky Way. Hubble quickly showed how wrong that belief was.
Over the next decade, Hubble looked at two of the most fundamental questions of the universe: how old is it, and how big? To answer both it is necessary to know two things – how far away galaxies are and how fast they are flying away from us. The red shift gives the speed at which galaxies are retiring, but doesn’t tell us how far away they are to begin with. For that you need what are known as “standard candles” – stars whose brightness can be calculated and used as standards to measure the brightness (and relative distance) of other stars.
Hubble’s luck was to come along soon after Henrietta Swan Leavitt. Leavitt worked at the Harvard College Observatory as a computer, as they were known. Computers spent their lives studying photographic plates of stars and making computations – hence the name. It was little more than a chore, but it was as close as women could get to real astronomy in those days. Leavitt noticed that a type of star, known as a Cepheid, pulsated with a regular rhythm – a kind of heartbeat. Cepheids are rare, but at least one of them is well known to most of us, the Pole Star.
We now know that Cepheids beat because they are elderly stars that have moved past their main phase and become red giants. The chemistry of red giants, put simply, means that they burn their remaining fuel in a way that produces a very rhythmic, reliable brightening and dimming. Leavitt’s genius was to realize that by comparing the relative magnitudes of Cepheids at different points in the sky you could work out where they were in relation to each other. It was the first time anyone had come up with a way to measure the large-scale universe.
Combining Leavitt’s cosmic yardstick with Vesto Slipher’s handy red shifts, Hubble now began to measure selected points in space with a fresh eye. In 1923 he showed that a distant wisp in the Andromeda constellation known as M31 wasn’t a gas cloud but a blaze of stars, a galaxy in its own right, a hundred thousand light-years across and at least nine hundred thousand light-years away. The universe was vaster – vastly vaster – than anyone had supposed. In 1924 he produced a landmark paper showing that the universe consisted not just of the Milky Way but of lots of independent galaxies, many of them bigger than the Milky Way and much more distant.
This finding would have made Hubble’s reputation, but he now turned to working out just how much vaster the universe was, and made an even more striking discovery. He began to measure the spectra of distant galaxies. He worked out that all the galaxies in the sky (except our own local cluster) are moving away from us. Also, their speed and distance were proportional: the further away the galaxy, the faster it was moving. The universe was expanding, quickly and evenly in all directions. So, it must have started from some central point. Far from being the stable, fixed, eternal void that everyone had always believed, the universe had a beginning. It might therefore also have an end. The wonder, as Hawking noted, is that no-one had the idea of the expanding universe before. A static universe would collapse in on itself. There was also the problem that if stars burnt indefinitely in a static universe they’d have made the whole impossibly hot.
Hubble was a better observer than thinker and didn’t appreciate the importance of what he found. Instead, a Belgian priest named Georges Lemaître brought together the two strands in his own “fireworks theory,” which suggested that the universe began as a geometrical point, a “primeval atom,” which exploded and had moved apart ever since. It was an idea that predated the modern Big Bang.
Hubble died of a heart attack in 1953. One last small oddity about him. For mysterious reasons, his wife refused a funeral and never revealed what she did with his body. For a memorial you must look to the sky and the Hubble Space Telescope, launched in 1990 and named for him.
If you want to watch some videos on this topic, you can click on the links to YouTube videos below.
If you want to answer questions on this article to test how much you understand, you can click on the green box: Finished Reading?
Videos :
1. Josiah Willard Gibbs (10:00)
7. General theory of Relativity (3:00)
8. General theory of Relativity 2 (8:00)
Study any topic, anytime. explore thousands of courses for the lowest price ever!
