“Go Wondrous creature! Mount where science guides;
Go, measure earth, weigh air, and state the tides;
Instruct the planets in what orbs to run,
Correct old time and regulate the Sun
Go soar with Plato to the empyreal [heavenly] sphere.”
Alexander Pope (1734)1
Newton’s Unbroken Meditation
Isaac Newton was born on Christmas Day 1642,2 shortly after the death of his father. Newton’s mother Hannah remarried when he was three years old, and moved nearby to the home of her new husband, the wealthy and elderly clergyman, Barnabus Smith. Young Isaac stayed behind, in the house where he was born. His grandparents cared for him until his stepfather’s death eight years later, when his mother returned together with three children of her second marriage.
At the age of 12, Isaac was sent away to the Free Grammar School in Grantham, where he learned Latin grammar and lodged with the local apothecary, who sold medicines and most likely gave Isaac an interest in chemistry. Later, at age 17, he returned to the family estate in Lincolnshire, and went on to Trinity College at the University of Cambridge in June 1661.
As a youth, Newton was exposed to Anglican (Church of England) and Presbyterian forms of worship, which vied for public interest and political control of England during Newton’s early years. He was already a devout young man when entering college, and as an adult, he continued to hold an active, vigorous Christian faith and to embrace many of the local religious beliefs.
While a college student, Newton spent much of his time in religious activity, and he was not alone in this regard. All the Trinity students were required to read, critically examine, and know lengthy passages of the Bible, to attend daily sermons, and to participate in evening prayers. This was to be expected since about three quarters of the students then attending Trinity College were destined for a career in the Church of England.
Initially, Newton earned his keep at Trinity by serving the Fellows and wealthier students. He had to clean their boots, wait on tables, and empty their chamber pots. When these duties ended in 1664, Newton was elected a scholar at Trinity, but the next year the bubonic plague had spread to Cambridge and the University closed down.
Isaac therefore traveled to his ancestral farm and spent the next 18 months in intense meditation and thought. During this period he developed his theory of light and colors, began to think of gravity extending to the Moon, and realized how the forces that drive the planets must vary with distance from the Sun.
At the age of 24, Isaac came back to the University of Cambridge when it reopened in the spring of 1667, and that autumn was elected to a fellowship at Trinity College. Two years later he became Lucasian Professor of Mathematics, a position that he held for the next 32 years.
Newton just didn’t like interacting with people, and was usually indifferent to them. He declined most invitations, avoided personal contact, and never traveled outside England. He was also reluctant to publish his findings, disliked controversy, did not desire “public esteem,” and did not ask for help or invite collaboration in his investigations.
There is no evidence that the celebrated scientist ever loved a woman, and he apparently died a virgin at an age of 84. He was a lifelong bachelor who thought that sexual activity with women would corrode his spiritual purity, which had been suggested to him by a passage in the Bible.3
Newton was exceptionally curious, once sticking a long needle along the edge of his eye just to see how it worked and what would happen. On another occasion, he stared at the Sun so long that he could hardly see anything at all and was confined to his bed for days.
The great astronomer was capable of extraordinarily intense and prolonged mental concentration, and his incomparable discipline and rigorous work ethic continued throughout his life. He has attributed his significant accomplishments to this sustained thought and meditation, rather than moments of inspiration or genius.
Isaac was a detached, solitary loner, an isolated and self-contained intellect, a bit obsessed, notoriously absent-minded, famously distracted, and frequently depressed. Most of his life was spent as a reclusive Don at Cambridge, where he could work undisturbed, immersed in introspection, solitude, secrecy, and study.
Newton designed and built the earliest known reflecting telescope, which employed a mirror rather than a glass lens to gather and focus light (Fig. 2.1).4 Isaac ground the metal mirror, constructed the tube, and used the completed telescope to observe the four large moons of Jupiter and the phases of Venus. When news of the novel instrument reached London in 1671, it earned him election as a Fellow of the Royal Society. At about the same time, Newton was developing his theory of light and colors, and communicating it to the Royal Society.5 When he dispersed sunlight by passing it through a glass prism, Newton found that light is composed of different colors that were bent by the prism to different extents.
He then discovered the laws of motion and invented universal gravity, “the offspring of silence and unbroken meditation.”6 As he showed, gravity is always out there trying to pull us down. It keeps our feet on the spherical Earth, so we don’t fall off it, and enables us to rotate with the spinning planet. The atmosphere and oceans are similarly held close to the Earth by its relentless gravitational pull. And it is gravity that explains how things fall. Every object on the Earth falls in just one direction, straight down toward the ground, and any undisturbed body will fall with uniform acceleration. The further it falls the faster it moves, at the same rate regardless of its mass.
Newton thought that the primordial stuff of the world was the result of God’s existence, and that God deliberately created the ordered Cosmos by an act of will.7 He also thought that the discovery of cosmic order reveals the mind of the Divine Creator, and that finding this order and discovering God’s design was the best way to convince unbelievers of the existence of God. Newton did not, however, believe that the entire Universe was God, which would have been heretical at the time.
It has been said that Newton’s religious views might not have had all that much impact on his efforts in astronomy, since he was able to compartmentalize his interests, and that he endorsed the separation of science and religion. These views are badly mistaken. In Newton’s mind, there was considerable overlap between God and investigations of the natural world, between theology and cosmology.
Figure 2.1 Telescopes Light waves that fall on the Earth from a distant object are gathered and focused to a point by the lens (left) or the mirror (right) of a telescope.
To Newton, the goal of natural philosophy was to understand God, the Divine Creator of the rationally ordered Universe, through knowledge of “His most excellent contrivances of things and final causes,” and close scrutiny of His works in Nature. God’s existence, Newton proclaimed, could not be denied in the face of the grandeur of this observable Universe.
In December 1692, he wrote Richard Bentley that he had written his renown Principia in order to promote a belief in God among thoughtful men, and:
“When I wrote my treatise about our System, I had an eye upon such Principles as might work with considering men for the belief of a Deity and nothing can rejoice me more then to find it useful for that purpose.”8
Bentley, an English classical scholar and theologian, was then presenting a series of popular lectures using Newtonian physics to demonstrate the existence of an intelligent Creator, and to use the origin and state of the natural world to challenge atheism.
In his General Scholium, added to the second edition of the Principia in 1713, Newton wrote:
“This most beautiful system of Sun, planets, and comets, could only proceed from the counsel and dominion if an intelligent and powerful Being… He [God] is eternal and infinite, omnipotent and omniscient… All that diversity of natural things which we find suited to different times and places could arise from nothing but the ideas and will of [such] a Being necessarily existing.”9
He likened all of infinite space to God’s presence everywhere, and identified time with God’s eternity. For Newton, God is present in every imaginable place and is forever there. This would enable Him to make worlds of several sorts in different parts of the Universe and at different times. His Divine power was indeed required for the growth of new systems out of old ones.
Newton urged everyone to devote themselves to reading and study of the Bible He began an intensive, passionate study of theology as a young man around 1670, and devoted exceptional efforts to understand the Divine until the end of his life in 1727. Newton never doubted the existence of God, and had a robust faith that gave meaning to his life and work. He nevertheless questioned some practices of religion that he found contrary to his reason and to his exhaustive studies of ancient Scriptures and the early history of the Church.
His examination of the oldest extant Greek copies of Holy Scripture suggested that certain passages had been added around the 4th century after the birth of Christ. According to Newton, these false passages corrupted the true faith and misrepresented Jesus Christ. Although Christ was divine and worthy of worship, had died on the Cross and then been resurrected, he was not God himself, not equal to God. This meant to Newton that the doctrine of the Trinity, with the strict equality of the Father, Son and Holy Spirit, was not correct, and that he did not agree with Kepler’s claim that the Cosmos has the Trinity embedded in it.
Newton’s secrecy and habit of almost never publishing his extensive writings turned out to be a good thing, at least as far as his beliefs were concerned. If his denial of the Trinity had been published and became widely known, then Newton would have been immediately dismissed from the College of the Holy and Undivided Trinity at the University of Cambridge, and may have never written the Principia or acquired subsequent fame and position. His private beliefs were contrary to the faith of the Anglican Church, and would have also made Newton ineligible for his subsequent government positions at the Royal Mint in London.
At the time of Newton’s election as the Lucasian Professor of Mathematics at the University of Cambridge, in 1669, the Fellows of Trinity College were required to become ordained priests in the Church of England within seven years. Although he was a sincere member of the Church, and publically participated in its religious services and practices throughout his life, Newton was not prepared to give up his academic freedom and take Holy Orders. Fortunately, the English king, Charles II, issued a royal decree in 1675, just when Newton’s seven years was about to elapse, which exempted the Lucasian Professor from needing to take Holy Orders.
Newton wanted to purge Christianity of irrationalities, which he thought had been introduced by the Roman Catholic Church, and he disagreed with many Catholic practices, as many did in the English society of the time. Like Martin Luther and other participants in the Protestant Reformation, Newton thought that Catholics had perverted the true faith by the use of indulgences, compulsory confession, and the introduction of idolatrous beliefs and practices that appeal to superstition and mystery. To Newton, this false idolatry included the magical use of the sign of the cross, the cult of the Virgin, the worship of Christ as God, the veneration of saints and their relics, and the supremacy of the Pope.
Perhaps because of his unprecedented scientific discoveries, Newton has often been portrayed as a man of incessant reason; a person solely dedicated to science or natural philosophy as it was then called. This is far from the truth. He devoted significant time and effort to other subjects including alchemy, theology, the early Christian Church, and interpretations of Biblical prophecy. Newton also spent much of his life trying to understand the origin of the elements and the eternal mysteries of health and human death by examining what he considered to be mystical clues left by God.
The renowned economist John Maynard Keynes, who purchased most of Newton’s alchemical papers, wrote that Newton’s deepest instincts were “occult and esoteric,” and that he was “the last of the magicians” who “looked on the whole Universe and all that is in it as a riddle, as a secret. By concentration of mind, the riddle, he believed, would be revealed to the initiate.”10
In his lifetime, Newton’s contemporaries viewed his scientific achievements with awe and admiration, and he became the most famous of men, celebrated as a great and rare genius. Upon his death in 1727 he was buried with ceremonious pageant and great pomp in Westminster Abbey, London, when two dukes, three earls and the Lord Chancellor carried the coffin. His elaborate tomb, erected in 1731, includes symbols of his discoveries — a prism, a reflecting telescope, and the Sun, planets and comets.
The Principles
When the English astronomer Edmond Halley visited Newton at the University of Cambridge in August 1684, Halley asked him about the unsolved problems of planetary movements around the Sun. Newton replied that he had already found a solution but mislaid it.11
Newton had confirmed Kepler’s conclusion that a planet moves in an elliptical orbit under the influence of a force originating at a focus of the ellipse, and that the force must decrease in strength as the inverse square of the distance from that focus. Since the Sun was at the focus of the elliptical planetary orbits, it must exert a gravitational force on the planets that varies with distance from the Sun in that way. Such a decrease of the Earth’s gravitational force with distance from the Earth also explains the Moon’s orbital motion.
Newton was also probably aware of Kepler’s Astronomiae Pars Optica (The Optical Part of Astronomy), published in 1604, in which Kepler reasoned that the intensity of light decreases with the inverse square of the distance. As either gravity or light move away from their source and fill the increasing volume of space, they get weaker in the same way and exhibit a similar decrease in either force or intensity.
Encouraged by Halley, Newton spent 18 months of intense labor to redo his work and write his great treatise, the Philosophiae naturalis principia mathematica, or the Mathematical Principles of Natural Philosophy, commonly known as the Principia. It was presented to the Royal Society, which withdrew from publishing it owing to insufficient funds, so in 1687 Halley saw the book through the press and was paid for his work by the Royal Society in the form of 50 copies of Francis Willughby’s De Historia piscium (The History of Fishes) instead of 50 pounds.
The first Book I of the Principia concerned The Motion of Bodies, where Newton described space and time and introduced the concepts of mass, force, and quantities of motion, including parameters known today as centrifugal force, momentum and inertia. As the title Principia, or Principles, suggests, a few simple natural laws could be used to describe any moving object, from a tossed stone to the Moon, comets, and planets. If the object was at rest, it stayed at rest, and if it was moving in empty space, it continued in motion at the same speed and in the same straight direction, unless it was compelled to change that state by external forces impressed on it. The new motion would be proportional to the motive force impressed, and would be in the direction of the force.
In Book II Newton examined the effects of a Resisting Medium on a body’s motion, such as air, water, or friction.
The last Book III entitled De mundi systemate (On the System of the World) unified the Earth and Heavenly bodies through the principle of universal gravitation. It discussed the consequences of gravity to known worlds, especially for astronomical observations, and described how the unseen powers of gravitation thread their way across space, guiding material objects along invisible but determined paths. When combined with the rules of motion, universal gravitation describes the movement of cosmic objects everywhere in the Universe.
Since the Earth’s gravitational force is present even at the top of the highest mountains, Newton imagined that it extends all the way to the Moon. He demonstrated that this force, diminished by distance to the Moon, pulls it into ceaseless motion around the Earth.
This is the universal force of gravity that operates between all bodies and pulls any two material objects together. The attraction is centered in each object, increases with their mass, and strengthens with proximity, as the inverse square of the distance. [Mass is an intrinsic aspect of an object, different from its weight that alters with distance from the main source of gravity, but back in Newton’s time, mass and weight were assumed to be equal.]
How did Newton arrive at the concept of universal gravitation? He emphasized that his laws were discovered by observations and experiment, and not by rational deduction, uncertain conjectures, or complex mathematics. It was enough that these laws allowed successful predictions to be made for observed phenomena. In the second edition of his Principia, published in 1713, he therefore famously wrote:
“I have not as yet been able to deduce from phenomena the reason for these properties of gravity, and I do not feign hypotheses [hypotheses non fingo]… And it is enough that gravity really exists and acts according to the laws that we have set forth and is sufficient to explain all the motions of the Heavenly bodies and of our sea.”12
In other words, Newton explained how material bodies move; he subsequently attributed the why they move to God.
In old age, he also told a few friends of watching an apple falling in his orchard, which reminded him of the power of gravity whose pull influences the motion of all falling bodies. Newton noted that the Moon resembles a projectile fired from the Earth and constantly falling toward it, but moving so fast that it always keeps the same mean distance from the Earth. If the Moon moved any faster, it would travel out into space, never returning to the Earth, and if the Moon moved any slower, the Earth’s gravity would pull it to the ground.
Like our Moon, the planets travel along curved trajectories, and in this case Newton proposed that it is the Sun’s unseen gravitational force that guides the planets in their motion. If left to themselves, the planets would not move in a closed path, and instead travel along straight-line paths. But they are not “left to themselves” because an external force is exerted on them by the Sun. The relentless pull of the Sun’s gravity holds the planets in their rounded paths, keeping them balanced and suspended rather than falling into the Sun or moving off into interstellar space.
The motions of comets soon provided a demonstration of this universality.
Return of the Comet
Unlike the planets, the comets can appear almost anywhere in the sky, remain visible for a few weeks or months, and then vanish into darkness. For centuries, no one knew where comets came from, where they went, or when they might be expected to appear.
The unexpected arrival of the awe-inspiring comets seemed to upset the natural order of the eternal, unchanging Heavens. Their appearance was thought to foretell wars and other disasters on Earth, such as the assassination of Julius Caesar, the Norman conquest of England, and the Turkish conquest of Constantinople. As Shakespeare declared:
“When beggars die there are no comets seen;
The Heavens themselves blaze forth the death of princes.”13
The mystique, fear, and superstition associated with comets were largely removed by Edmond Halley in his Astronomiae Cometicae Synopsis of 1705.14 He compiled a large number of previously recorded observations of comets from old and rare sources, and used them to calculate each comet’s orbit using Newton’s theory of gravity. Halley found that twenty-four bright comets seen in previous centuries moved around the Sun in very elongated, elliptical orbits as Newton had speculated.
Halley went further, and predicted that at least one bright comet had been seen more than once during several trips around the Sun and that it would be seen again. He had found that the observed trajectories of the comets seen in 1456, 1531, 1607 (noted by Kepler and Shakespeare), and 1682 were very similar, and concluded that they were four apparitions of the same comet, which appeared at 76-year intervals when coming close to the Sun. Halley predicted that the bright comet would return in 1758, and if that happened he hoped that it would be remembered that an Englishman had predicted its reappearance. He was criticized for placing the date of the comet’s return so far in the future that he would most likely not be alive to see it. [Halley died in 1742 at the age of 85.] But the comet came as predicted, and was re-discovered on Christmas night in the expected year, the first comet to arrive on schedule and now the most celebrated of the comets, bearing Halley’s name (Figs. 2.2, 2.3).
The earliest apparition of Halley’s comet, established with confidence from Chinese chronicles, dates back to 240 BC. Since then, all thirty-two of its passages near the Sun have been retraced in the ancient or modern records of astronomers. Halley’s comet has now moved away from the Sun into cold icy darkness where it cannot be seen, but it is heading back toward us along an elongated orbit that will bring it into sight in 2061. The Sun’s heat will then vaporize the outer parts of the small icy world to enlarge it and perhaps form an extended tail that could be as long as the distance between the Earth and the Sun.
Figure 2.2 Comet Halley in 1759 AD This Korean record of comet Halley was made during the comet’s first predicted return in 1759 AD. (Courtesy of Il-Seong Na, Yonsei University, Seoul.)
Figure 2.3 Comet Halley in 1910 The head region or coma of comet Halley observed on 8 May 1910 with the 1.5-meter (60-inch) telescope on Mount Wilson, California. The comet’s tail flows to the left, away from the Sun. (Courtesy of the Hale Observatories.)
The development of telescopes in the 19th and 20th centuries resulted in the discovery of many comets that cannot be seen with the unaided eye. When their orbits were determined it was found that they are all tiny invisible denizens of the outer Solar System, residing far away but still within the Sun’s gravitational embrace. They spend most of their unseen life in icy hibernation far from the Sun, and only become visible when a passing star tosses them into the realm of the inner planets, where the Sun’s heat vaporizes their surface ice and they grow large enough to reflect visible amounts of sunlight. Up to 200 billion of them are thought to move about the Sun in the remote unseen darkness, some of them halfway to the nearest star.15
Newton the astronomer thought that God’s intervention was needed to prevent the Sun and stars from being pulled together by gravity, and that the observed laws of Nature, which incidentally proved the existence of such an all-powerful God, did not prohibit such “miracles”. To Newton, all motion would eventually run down and stop, and everything in the currently observable material world would inevitably wear out in time and cease to exist. But the free and powerful “Lord God,” who has a “propensity for action,” could correct the situation at all times anywhere in the observable Universe.
This active God, this Divine Will, was required to sustain the Universe and to assure the renewal of systems in it. So the Universe was not only created by the will of God; it is also preserved, governed, maintained and continued by God’s active intervention, according to his will and wishes.
Throughout much of his adult life, Newton also provided interpretations of Biblical prophecies that he found in ancient Greek versions of The Revelation of St. John the Divine. He thought that God’s dominion over a fallen people explained the plague and barbaric invasions of Europe, and that things did not look good for Catholics or believers in the strict Trinity at the future Second Coming, which would bring Christ’s judgment over all the kingdoms of the Earth.
A Universal Truth
It was the prediction of the existence of Neptune that convinced astronomers, and just about anyone else, of the far-reaching power of universal gravitation. Another remote planet, Uranus, had been accidentally discovered in 1781; by William Herschel who initially thought it was a comet.16 Uranus had been detected by professional astronomers and mistaken for a star on no less than 22 occasions during the century that preceded the realization that it was a planet. These additional observations were combined with the post-discovery ones to determine Uranus’ trajectory and calculate its future position. Before long it was found that the planet was wandering from its predicted path.
A large, unknown world, located far beyond Uranus, was evidently producing a gravitational tug on the planet, causing it to deviate from the expected location. Two astronomer-mathematicians, John Couch Adams in England and Urbain Jean Joseph Le Verrier in France, independently specified the location of the planet by using Newton’s theory of gravitation to explain the observed motions of Uranus.17
Adams, a recent graduate from the University of Cambridge, finished his work first, deriving a precise position of the planet in mid-1845. He left a summary of his results with the then Astronomer Royal, George Biddell Airy, who did not feel compelled to look for the unknown world. Le Verrier finished his best calculations about a year later, and, unlike Adams, published his results. The two astronomers had arrived at nearly identical locations for the unseen planet.
When Le Verrier’s memoir reached Airy, he persuaded James Challis, Professor of Astronomy at the University of Cambridge, to make a search for the undiscovered planet. For a variety of reasons, Challis began the investigation slowly, and Le Verrier had in the meantime sent his results to the Berlin Observatory where Johann Gottfried Galle and his student Heinrich Louis d’Arrest found the planet.18 They identified it on the first night of their search, on September 23, 1846, using a 0.23-meter (9-inch) refractor; it was located within a degree of both Adams’ and Le Verrier’s predicted positions. Only later did Challis realize that he had previously observed the planet twice when beginning his own search.
The discovery of the new planet, named Neptune after the Roman god of the sea, was acclaimed as the ultimate triumph of Newtonian science. It resulted from mathematical calculations, based on Newton’s theories, of the effects of a previously unknown planet whose gravity was pulling Uranus from its predicted place. If proof were needed, this achievement certified the validity of gravitational theory.
This verification provided the foundation and impetus for all of science to come. Universal scientific laws are thought to apply anywhere throughout the observable Cosmos. Given present circumstances, these laws can be used to predict what will happen in the future. For astronomers, these universal and eternal physical truths are always present, even if they are as yet undiscovered.
Everything that an astronomer observes must obey the natural laws that apply to its particular situation. No exceptions are permitted. You cannot break the law in astronomy, where the truth prevails and no one can lie, at least for very long. All new discoveries, and every explanation of them, must be verifiable, and they are always subject to question and doubt.
In order to obtain objective, repeatable, and verifiable physical truths, astronomers cordon off and scrutinize a tiny portion of the vast and largely unknown Cosmos. This closed-off part is assumed to be isolated from all external influences, and every prediction about them is hedged with the proviso “other things being equal” or “no unexpected external forces allowed.” As a result, the astronomers’ truths are always qualified by boundary conditions, and their knowledge of the Universe is forever limited and never complete.
Towards the end of his life, Isaac Newton humbly recognized these limits to current knowledge, exclaiming: “I have been like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.”19
In the memorable words of the 20th century Chilean poet Pablo Neruda: “In this net it’s not just the strings that count but also the air that escapes through the meshes.”20 The astronomers’ nets are always open to unknown possibilities that might be revealed by future observations. Their lives are often driven by a continual quest for these unseen, mysterious things, and they are always carrying us beyond the existing boundaries of current astronomical vision, sometimes beyond the limits of known natural laws.
The unexpected behavior of the planet Mercury provides an early example of this ongoing quest. Instead of returning to its starting point to form a closed ellipse in one orbital period, Mercury moves slightly ahead in a winding path that was first described by LeVerrier in 1859, when he attempted to use Newtonian gravitation to account for observations of the planet’s transits in front of the Sun. LeVerrier subsequently attributed the mysterious motion to the gravitational pull of an unknown planet orbiting the Sun inside Mercury’s orbit and moving ahead of it. The hypothetical planet named Vulcan was never reliably detected.
As we shall next see, the cause of Mercury’s unexplained motion remained a mystery until 1915 when Albert Einstein described how gravity works. According to his explanation, massive objects produce a curvature in nearby space-time, and that bending, twisting and distortion is gravity. The prediction of consequences of this curvature made him famous and still does.
Einstein’s Cosmic Religious Feeling
Albert Einstein was born on March 14, 1879 at Ulm, in southern Germany, but after the age of four grew up in Munich. As a child of four or five, Einstein’s father showed him a compass needle that “did not fit into the usual explanation of how the world works,” leading him to conclude that “there must be something deeply hidden behind everything.”21 A mysterious and unseen agent was making the compass needle move without touching it, and that unknown something inspired awe and wonder in Einstein.
Albert also had a deep, lifelong love of music. He played the violin, and his favorite composers included Bach, Mozart, and Vivaldi. Einstein often thought in music, daydreamed in it, and saw his life in terms of music.22
The Einstein family moved to Milan, Italy in 1894, but Albert stayed in Munich to finish high school, and then went to Switzerland to continue his education. After failing his college entrance exams at the Zurich Federal Polytechnic School, he went to a high school in Aarau, the German speaking part of Switzerland, which enabled him to enroll in 1896 in a four-year course at the Zurich Polytechnic that was designed to produce high school teachers. [In 1911 the school was given its current name Eidgenössische Technische Hochschule, or ETH for short.]
At Zurich, Einstein began life-long friendships with Michele Besso and Marcel Grossman, and also became romantically entangled with Mileva Maric, a fellow student at the Polytechnic. In 1901, they had a child out of wedlock, a daughter, whose real name and fate remain unknown. She was probably put up for adoption, but Einstein never saw her. Albert married Mileva in a civil ceremony in 1903 without the presence of a rabbi or priest, and to the discontent of both sets of parents. [His family was Jewish, and she was a member of the Greek Orthodox Church.] Two sons were born to the couple, Hans in 1904 and Eduard in 1910.
In 1900 Einstein graduated from the Zurich Polytechnic with a diploma to teach mathematics and physics in high school. He applied for a job as a university lecturer and was turned down, and then as a high school teacher and was rejected again. After two years of failure to find a job, Marcel Grossman’s father helped Einstein obtain a job in Bern at the Swiss patent office, where he stayed for the next seven years.
Einstein evaluated patent applications for electromagnetic devices, which he enjoyed, and it left him time to write scientific papers, which he contributed to the Annalen der Physik. These papers were written without any significant contact with the physics community, and they attracted little notice amongst them. After all, an unknown clerk in a Swiss patent office wrote them.
But then, in 1905, Einstein published a wide-ranging series of original ideas that could not be ignored, and after that his professional career began to rise. He moved from university teaching as a Privatdozent in Bern in 1908, to Associate Professor at the University of Zurich in 1909, to Full Professor at the University of Prague in 1911, and on to Full Professor at the ETH in 1912.
In 1913, Einstein was offered a Full Professorship without teaching obligations at the University of Berlin, under the aegis of the Prussian Academy of Science, which he held for the next eighteen years. He apparently had enough of teaching, and also his unhappy marriage. Mileva and their two sons remained in Zurich, and after five years apart, the couple divorced.
In late 1915, Einstein completed his General Theory of Relativity, which explained an unexpected aspect of Mercury’s motion as the result of the Sun’s curvature of nearby space, and predicted that this curvature would cause the bending of starlight passing near the Sun. After the effect was observed during a solar eclipse in 1919, Einstein became a legend, almost overnight.
Einstein brought an “other worldly” order to the Universe. He was a new Moses come down from the mountain to bring the law and a new Joshua controlling the motion of heavenly bodies. He spoke in strange tongues, and the stars demonstrated the truth of his sacred message.23
For the rest of his life, Einstein basked in international fame; abruptly ended his creative scientific work; and became more noted for his support of social justice, his defense of the weak and oppressed, and important political activities.
As an example, when Adolf Hitler came to power, Einstein was in the United States, where he settled down as a Professor at the Institute for Advanced Study in Princeton, New Jersey, while also becoming a citizen of the United States in 1940. The preceding year Einstein sent a letter to the United States President Franklin D. Roosevelt alerting him to the possibility of setting up a nuclear chain reaction by which “extremely powerful bombs of a new type may thus be constructed.”24 He suggested that Hitler’s forces might be developing such weapons, and recommended that the United States begin making one. This helped lead to the Manhattan Project in which the best scientific minds in the country moved to Los Alamos, New Mexico and created the first atomic bomb.
Einstein did not lead a lonely life, thanks to the loving care of his cousin Elsa Löwenthal. They married in 1919, and parted without children on Elsa’s death in 1936. But Einstein never did get along well with women. In 1955, shortly after the death of his friend Michele Besso, he wrote to the Besso family, stating: “What I most admired in him as a human being is the fact that he managed to live for many years not only in peace but also in lasting harmony with a woman — an undertaking in which I twice failed rather disgracefully.”25
He instead spent his entire life in understanding and explaining how the natural world works. As Einstein expressed it: “Out yonder there was this huge world, which exists independently of us human beings and which stands before us like a great, eternal riddle, at least partially accessible to our inspection and thinking. The contemplation of this world beckoned like a liberation.”26
Einstein had an unshakeable conviction that there is a hidden order and unity in nature, which the probing mind can partially comprehend. As he expressed it, we have “a knowledge of the existence of something we cannot penetrate, [manifesting itself in] our perceptions of the profoundest reason and the most radiant beauty, which only in their most primitive forms are accessible to our minds — it is this knowledge and this emotion that constitute true religiosity; in this sense, and in this alone, I am a deeply religious man.”27
Einstein did not believe in the personal God who cares for human beings and directly interacts with them, rewarding the righteous, punishing the wicked, and providing comfort after death. But he considered himself a very devout man, with a deep and profound belief in “his God, his Lord.” To him, the Divine is not isolated from the physical world, but instead revealed by it.
Throughout his life, Einstein was enlivened by this “cosmic religious feeling” that included an awe, admiration, and wonder for the Universe itself, for its subtlety, beauty, and elegance. In his own words:
“The individual feels the futility of human desires and aims, and the sublimity and marvelous order which reveal themselves both in Nature and in the world of thought. Individual existence impresses him as a sort of prison, and he wants to experience the Universe as a single significant whole. … In my view, it is the most important function of art and science to awaken this feeling and keep it alive in those who are receptive to it.”28
And on another occasion: “The fairest thing we can experience is the mysterious. It is the fundamental emotion that stands at the cradle of true art and true science. He who knows it not and can no longer wonder, no longer feel amazement, is as good as dead, a snuffed out candle.”29
Throughout his life, Einstein was a man apart, a lone traveler. As he confessed in 1930: “I have never belonged to my country, my home, my friends, or even my immediate family, with my whole heart. ... I have never lost a sense of distance and a need for solitude.”30 This independence of mind, this apartness, led to that amazing sequence of papers in 1905 that jump-started his career and transformed our understanding of light, space, time, mass and energy.31 He then moved on to gravity.
Einstein Discovers how Gravity Works
We can’t see the force of gravity, and Newton didn’t know how it was exerted. Its unseen hand was supposed to operate everywhere across the space between all bodies that do not touch each other. Newtonian gravity therefore resembled a mystic, occult quality, a ubiquitous presence.
Einstein amended Newton’s laws to explain how gravity works. He supposed that a massive body like a star bends nearby space-time into the curvature of an embrace, giving it a shape and form. Gravity works by this bending, twisting and distortion of space-time. In effect, mass tells nearby space-time how to curve and curved space-time tells neighboring matter how to move. But such curvature effects are only noticeable in extreme conditions near a very massive, cosmic object like a star, and the differences between Newton’s and Einstein’s theories of gravity are indistinguishable in ordinary circumstances on the Earth.
The new theory arose because of an exceedingly tiny, unexplained aspect of the planet Mercury’s motion around the incredibly massive Sun. Instead of returning to its starting point in one orbital period, Mercury moves slightly along a path that can be described as a rotating ellipse (Fig. 2.4). As a result, the point of Mercury’s closest approach to the Sun, the perihelion, advances by a small amount, just 43 seconds of arc per century, beyond that which can be accounted for by planetary perturbations using Newton’s theory of gravitation.
Figure 2.4 Mercury’s motion Instead of always tracing out the same ellipse, the orbit of Mercury pivots around the focus occupied by the Sun. Albert Einstein explained this movement by extending Newton’s theory of gravity to include the Sun’s curvature of nearby space-time.
Although discovered by the French mathematician Urbain Jean Joseph Leverrier in 1859,32 the unexplained motion of Mercury remained a mystery for more than half a century, until 1915 when Einstein identified its cause in his General Theory of Relativity.33 He showed that Mercury is directed along a path in curved space-time. It is something like watching the slow arc of a bird gliding on unseen winds.
When Einstein found that his calculations agreed with the unexplained observations of Mercury, it changed his life. He wrote to his friend Michele Besso that: “My wildest dreams have been fulfilled,” and subsequently confessed that “for a few days, I was beside myself with joyous excitement,” and that it “had given him palpitations of the heart, with a feeling that something actually snapped in him.”34
Like any good scientist, Einstein realized that his General Theory of Relativity had to be verified by definitive tests of other consequences, and in the very paper that explained Mercury’s unexpected motion he predicted that the curvature of space-time would also deflect starlight from a straight-line path.35 Newton had previously speculated that massive bodies might bend nearby light rays if light has mass; but when Einstein took curvature into account the expected deflection was doubled, to 1.75 seconds of arc for a light ray grazing the Sun’s edge.
Einstein’s novel concepts of 1915 were made during World War I, that began on July 28, 1914 and lasted until the armistice of November 11, 1918. The war pitted Great Britain and its allies against Germany, and as the result of the warfare the English people suffered extraordinary hardship and loss of life. There were wide-spread anti-German feelings in England, and communications with enemy scientists were forbidden. So, it is quite amazing that the General Theory, which was conceived and published by a German scientist, became known to English astronomers who arranged to test it during the darkest days of the war.
One of the principal actors in this drama was the Quaker astronomer A. S. (Arthur Stanley) Eddington, who opposed any war and advocated international cooperation amongst astronomers. He therefore wrote in 1916 that “the pursuit of truth, whether in the minute structure of the atom or the vast system of the stars, is a bond transcending human differences — to use it as a barrier fortifying national feuds is a degradation of the fair name of science.”36
It was Willem de Sitter, in the neutral Netherlands, who sent Eddington articles in English about the new amendments to Newton’s gravitation theory, which were then published in England’s Monthly Notices of the Royal Astronomical Society.37 As the result of Eddington’s informal expositions and a major presentation given in his Report on the Relativity Theory of Gravitation (London: Fleetway Press 1918) many English astronomers learned of the new concept. And already in 1917, the Astronomer Royal, Frank Dyson, was actively seeking support for an expedition to test Einstein’s light-bending predition during a total solar eclipse on May 29, 1919.38
If Einstein was right, the curvature of space-time would bend the light of stars passing nearly behind the Sun and spread their apparent positions apart like a gigantic magnifying lens (Fig. 2.5). The effect could be established by comparing the observed positions of adjacent stars seen near the Sun during a solar eclipse with those seen long before or after and far from the Sun’s location in the sky. When near the Sun the observed separations between the stars are greater than when the stars are far away from the Sun.
Figure 2.5 The Sun bends starlight The massive Sun creates a curvature in nearby space-time, which bends the path of starlight passing near it.
In June of 1918 there was the possibility that Eddington might be sent to jail due to his refusal to participate in the Great War. That’s when the Scottish astronomer Frank Dyson came to the rescue of his old friend and former colleague at the Royal Greenwich Observatory. Dyson, with connections to the Admiralty as Astronomer Royal, testified before Eddington’s Appeals Tribunal, stating that Eddington was uniquely qualified to carry out distant, important eclipse observations the next year. On hearing that such an eclipse might not be seen again for a very long time, the Tribunal declared that Eddington’s work continued to be of national importance and provided him a 12-month exemption on the condition that he participate in the eclipse expedition, which he did. By that time, the war was over, and the issue of Eddington’s military service vanished without a review of his concientious objection.
Interest ran high in Britain, and funding was obtained for a joint Greenwich Observatory — Royal Society expedition to measure the deflection of starlight during the total solar eclipse of May 29, 1919, when stars could be seen near the darkened Sun.
English expeditions were sent to observe it from the small Principe Island off the coast of West Africa and from Sobral, Brazil. In the last evening before sailing to Principe, E. T. Cottingham, who was to accompany Eddington, asked Dyson what would happen if they found twice Einstein’s predicted deflection. Sir Frank replied: “Then Eddington will go mad and you will have to come home alone.”39
Clouds and rainy weather interferred with the eclipse observations from Principe, and telescope difficulties compromised the Sobral ones. Measurements were made of the separation of stellar positions on photographs taken during the eclipse from both locations, and compared to those obtained long before when the same region of the sky was nowhere near the Sun. Deflections were observed, and they favored Einstein’s explanation of how gravity works, but the imprecise measurements did not confirm it with complete definitive confidence.
In his report given at a joint meeting of the Royal Society and the Royal Astronomical Society,40 on November 6, 1919, Dyson nevertheless declared that there was no doubt that they verified Einstein’s law of gravitation, and it turned out that his confidence was ultimately justified. The Sun’s curvature of nearby space-time has now been measured with increasingly greater precision for nearly a century, confirming Einstein’s prediction to two parts in a hundred thousand, or to the fifth decimal place.
The apparent confirmation of the bending of starlight by the Sun in 1919 brought Einstein international recognition and capitulated him into the public limelight. Members of the press were present when Dyson announced the eclipse results, and the headlines of the London Times on the next day read “Revolution in Science — New Theory of the Universe — Newtonian Ideas Overthrown.” Half way down the page was a second heading: “Space Warped.” Two days later, the New York Times called Einstein’s theory one of the greatest, perhaps the greatest, achievement in the history of human kind.
Einstein resembled ancient prophets and saints who could understand what others could not, and tell them about it. He gave them something to believe in, and these new things were not the way they used to be. Time was no longer exact; space was curved and warped; light had weight; and stars were not where they were supposed to be. Invisible gravitational waves might even be rippling unseen throughout space.
Gravity Makes Waves
Astronomers had to wait a very long time before the confirmation of Einstein’s 1916 prediction of gravitational radiation. The vibrations are so weak and their interaction with matter so feeble that Einstein questioned whether they would ever be detected. As it turned out, orbiting neutron stars and merging black holes can produce detectable gravity waves. These ripples carry away energy from their source, and stretch and compress the space they pass through.
The existence of gravity waves wasn’t demonstrated until 1974, when the two American radio astronomers Russell A. Hulse and Joseph H. Taylor, Jr. decided to replace the strip-chart method of discovering radio pulsars with digital computer techniques that provided the signal processing needed for a sensitive pulsar search. Their extensive survey using the 305-meter (1000-foot) Arecibo radio telescope in Puerto Rico resulted in the discovery of the first known pulsar with a companion.41
The pulsar’s period of just 0.059 seconds rhythmically increases and decreases by very small amounts every 7.75 hours, as the result of its orbital motion about another neutron star that does not emit detectable radio pulses. As Hulse and Taylor predicted, precise timing of the radio pulses permits measurements of the relativistic orbital parameters and the masses of the pulsar and its silent companion. They weighed in at 1.44 and 1.39 times the mass of the Sun, as would be expected for two neutron stars.
After routine computer analysis of about 5 million pulses during a four-year period, Taylor and his colleagues found that the orbital period was slowly becoming smaller. The two stars were drawing closer and closer together, approaching each other at the rate of about 1 meter per year. This is the change expected if the orbital energy of the two neutron stars is being carried away by gravitational waves.42 It demonstrated the existence of gravitational waves and opened up new possibilities for the study of gravitation — for which Hulse and Taylor received the 1993 Nobel Prize in Physics.
Direct detections of gravitational waves, with measurements of their waveforms, were announced on February 11, 2016 and June 15, 2016,43 about a century after Einstein’s prediction. Two identical instruments known as an Advanced Laser Interferometer Gravitational-Wave Observatory, abbreviated LIGO, were used to sense the distortions that occur when gravitational waves pass through these detectors and the underlying ground. One LIGO instrument is located in Washington State and the other in Louisiana, and gravity waves have to be observed in each of them to confirm a single detection. Each detector has the shape of a giant L with two perpendicular legs that are both four kilometers long. Laser light is sent back and forth through the two legs by multiple reflections from mirrors located at the ends of each leg, but canceling each other out at the place where they meet.
When a gravitational wave passes through the observatory, there is a change in the relative length of the two legs, and the laser beams are no longer synchronized on arrival. An oscillation is then detected that resembles the chirp of a bird with a rapidly increasing pitch or “ring-down,” from 35 to 250 cycles per second.
The two chirp-like signals have each been attributed to the coming together of two black holes that have merged into a single, larger black hole. In the first detection, one black hole was about 36 times the mass of the Sun, and the other about 29 solar masses; in the second detection, the merging black holes were about 14.2 and 7.5 solar masses. When they got near enough to each other, each pair spiraled together into a black hole, which weighed about 62 solar masses in the first instance and 20.8 times the mass of the Sun in the second one.
The change in the length of the legs was exceedingly small, by much less than the diameter of a proton, but the result is a very big deal. More than a thousand scientists are now working on the $1-billion LIGO experiment. Some people have dedicated their entire working life to it, from its construction to first run in 2002 and eventual success 14 years later. And despite the tiny observed signal, the black-hole merger that caused it temporarily radiated an enormous energy in the form of gravitational waves, more than all the stars in the observable Universe emitted as light in the same time.
You might say that it is about time that gravitational waves were detected. Einstein predicted their existence almost exactly 100 years before the LIGO result. Joe Weber was trying to detect them more than half a century ago, and in 1971 Stephen W. Hawking, the theoretical physicist and cosmologist at the University of Cambridge predicted they would be generated by colliding black holes.44 Subsequent experiments using massive detectors similar to Weber’s indicated his reported detection was a false alarm. As recently as 2014, reputed observations of gravitational-wave signatures in the cosmic microwave background, by BICEP2, were also discounted. But this time around, there is not one but two LIGO detectors that are widely separated on the Earth, and the fact that they both “heard” the same faint chirps gives added confidence in the result.
Rainer Weiss, Barry Barish, and Kip Thorne received the 2017 Nobel Prize in Physics “for decisive contributions to the LIGO detector and the observation of gravitational waves.”
The European Gravitational Observatory has constructed an interferometer gravitational-wave detector, named Virgo, near Pisa, Italy; it began joint observations with LIGO in 2017. Both the two LIGO and the Virgo instruments have directly detected gravitational waves on several occasions; the radiation has been attributed to either the collision of a pair of neutron stars or to a binary black hole merger. Future experiments may provide additional insight to massive, binary black holes, confirm that gravitational waves travel at the speed of light, and even measure the rate of expansion of the Universe.
Walking in the Midst of Wonder
The man who predicted that gravity bends the path of light, and that unseen gravitational waves ripple through space, was driven by his belief in the rational, intelligible order of Nature, which we only partly see and must be humbled by. Whenever this motivation is absent, he thought, science degenerates and becomes uninspired.
Einstein also supposed that there is much more to human life than scientific knowledge, a rejuvenating dimension implied in his letter to Queen Elizabeth of Belgium. It includes: “As always, the springtime Sun brings forth new life, and we may rejoice because of this new life and contribute to its unfolding; and Mozart remains as beautiful and tender as he always was and always will be. There is, after all, something eternal that lies beyond reach of the hand of fate and all human delusions.”45
Astronomers have similarly tapped into something eternal, which normally operates beyond the range of known perception. We all walk in the midst of this wonder.