“In the beginning God created
the Heaven and the Earth.
And the Earth was without form,
and void; and darkness was upon
the face of the deep. And the Spirit
of God moved upon the face of the waters.
And God said, Let there be light:
and there was light.”
The Holy Bible, Genesis1
Soldier, Priest and Cosmologist
Georges Henri Joseph Édouard Lemaître was born on July 17, 1894 in the Belgian industrial town of Charleroi, the eldest son in a deeply religious, Catholic family. After attending the Sacred Heart High School in Charleroi and the College Saint Michel Preparatory School in Brussels, he entered the College of Engineering in Louvain, graduating in civil engineering in 1913. Lemaître began training as a mining engineer, but World War I (1914–1918) intervened and changed the course of his life.
The German army invaded Brussels on August 4, 1914, and Georges volunteered as a soldier in the Belgian army five days later. He spent the entire war exposed to its horrors, which included his participation in bloody house-to-house fighting and witness to the first poison gas (chlorine) attack in the history of warfare. Lemaître received the Croix de Guerre for his wartime bravery.
At the close of the war, he obtained a master’s degree in mathematics and physics at the Université Catholique de Louvain, while also studying Aristotle and Aquinas. In October 1920 he entered the Belgian Maison Saint Rombaut as a seminarian, where he fulfilled ecclesiastical studies for the Roman Catholic priesthood and maintained his mathematical interests.
Lemaître had won a scholarship from the Belgian government to study abroad, and two weeks after being ordained, in September 1923, he left for the University of Cambridge in England to work with A. S. Eddington. The following year, in 1924, he traveled to the other Cambridge, in the United States, where he studied at the Massachusetts Institute of Technology, abbreviated MIT, and interacted with Harlow Shapley at the nearby Harvard College Observatory.
While in the United States, the Belgian cleric toured the country, and met with both V. M. Slipher at the Lowell Observatory in Flagstaff, Arizona and Edwin Hubble at the Mount Wilson Observatory in California. When Lemaître returned to Belgium, he therefore knew all about Slipher’s observations of the redshifts, or outward velocities, of spiral nebulae and Hubble’s determinations of a few of their distances, which Lemaître explained by proposing the expansion of the Universe from a primeval explosion.
A Day without Yesterday
In 1917 Albert Einstein tried to apply his General Theory of Relativity to a spatially finite and eternal Universe without any motion.2 But there was a problem that was even obvious from Newton’s simpler theory of gravitation. The so-called fixed stars cannot stay at rest with respect to one another. The unrelenting gravitational attraction between individual stationary, or non-moving, stars would eventually pull them together so the entire stellar system would collapse. Einstein therefore introduced an anti-gravity repulsion term, called the cosmological constant, to keep that from happening.
The extra term represented a universal repulsive force of an unknown and undetected form of energy that permeates space and exerts an outward pressure that opposes gravity. In contrast to other physical forces, which decrease in strength with increasing distance, the cosmological repulsion was assumed to be weak over short distances and stronger at large ones. Einstein adjusted the value of this cosmological constant so that its anti-gravity force would exactly counterbalance the combined gravitational attraction of all the known stellar matter in the Universe, keeping it from collapsing and making it stay put.
At A. S. Eddington’s request, the Dutch astronomer Willem de Sitter had been submitting descriptions of the astronomical consequences of Einstein’s theory for publication in the Monthly Notices of the Royal Astronomical Society. His third paper on the subject, published in 1917, included an empty Universe that would permit movement without a cosmological constant.3
It was time to put a little matter in de Sitter’s moving world or a little motion in Einstein’s non-moving, material one, which was stressed by A. S. Eddington at the January 10, 1930 meeting of England’s Royal Astronomical Society. When news of the meeting reached Georges Lemaître, at the Université Catholique de Louvain, he wrote Eddington to remind his former teacher that he had solved the problem with an expanding model, which he had given Eddington three years earlier.
With remarkable foresight, the Belgian priest and astronomer had applied Einstein’s theory to observations of spiral nebulae, and described them by a Universe that is in a state of expansion, with all the spirals moving away from one another at high speed.4 He even derived the now-famous Hubble law in which the recession velocities of galaxies increase in proportion to their distance, two years before Hubble observed it. Others had previously used the complex theory to invent imaginary worlds, but Abbé Lemaître was the first to use it to explain the one and only true Universe that had already been observed by astronomers.
Eddington corrected his embarrassing oversight of Lemaître’s work with a letter to the journal Nature that drew attention to the work, and by sponsoring an English translation of Lemaître’s 1927 paper entitled “A Homogeneous Universe of Constant Mass and Increasing Radius accounting for the Radial Velocity of Extra-Galactic Nebulae.”5 In this explanation, space is swelling, ballooning outward, and carrying the extragalactic nebulae, or galaxies, with it, somewhat like birds riding on an otherwise unseen wind.6
Almost no one noticed Lemaître’s prophetic 1927 publication. It initially had little impact on astronomers, and was only acclaimed years later when it was realized that his work applied to the real observed Universe. Another reason for the neglect was that his paper was written in French in the obscure Annales de la Société scientifique de Bruxelles. The Belgian cleric also tended to keep his ideas to himself, and did not present his findings to the general public.
Lemaître naturally wondered what the Universe has expanded from. If it is now expanding and growing larger, then a backward extrapolation implies a time when the Universe was incredibly small and in a state of high compression. Near the beginning of the expansion, he imagined, the galaxies must have been squeezed into a uniform mass of very small size, as tiny as a single atom or even the nucleus of that atom. Lemaître even supposed that all of the mass of the Universe once existed in the form of a unique atom and quantum of energy.
As he explained it in 1931:
“The present state of quantum theory suggests a beginning of the world very different from the present order of Nature.” … “We [then] find all the energy of the Universe packed in a few or even a unique quantum ... [It was] in the form of a unique atom, the atomic weight of which is the total mass of the Universe. This highly unstable atom would divide in smaller and smaller atoms by a kind of super-radioactive process.”7
This primeval atom and single, undifferentiated quantum of energy divided and subdivided into a larger and larger number of energy quanta through a process of radioactive decay. According to Lemaître, such a beginning coincided with the origin of all things, including mass, space and time.
By this time, Edwin Hubble had published, in 1929, his velocitydistance relation for spiral nebulae, and Lemaître’s paper was heralded as a brilliant synthesis of theory and observation. As he later explained, Lemaître was in part led to this conclusion by the similar billion-year lifetimes of longlived radioactive elements, such as uranium and thorium, and the expansion age of the Universe.
As the result of his imaginative interpretations of the expanding Universe, Abbé Lemaître became something of a celebrity in the 1930s, lauded by the press and scientists alike. On May 19, 1931 the New York Times, for example, reproduced almost his entire 1931 Nature article on “The Beginning of the World From the Point of View of Quantum Theory.”
Lemaître developed his concepts into a widely read book entitled The Primeval Atom: An Essay on Cosmogony, first published in French in 1946 and in English translation six years later. In this interpretation, the observable Universe began when a cold, super-dense primeval atom started to disintegrate. It resulted in the acceleration of cosmic rays, and to the eventual formation of stars and galaxies.
In this marvelously poetic and imaginative scenario, the beginning of everything occurred on a day without a yesterday, at the origin of time when the expansion of the Universe began. Since that time:
“The [subsequent] evolution of the world can be compared to a display of fireworks that has just ended: some few red wisps, ashes and smoke. Standing on a well-chilled cinder, we see the slow fading of the suns, and we try to recall the vanished brilliance of the origin of the worlds.”8
Reviving the Cosmological Constant
There was one problem with the new theory for the expanding Universe. The age of the Universe looked at first sight to be younger than geological estimates for the age of the Earth. When using Hubble’s 1929 value for the expansion rate of the Universe, the beginning of the expansion was pegged at 1.8 billion years ago. Something wasn’t quite right, for radioactive elements had been used to clock the oldest rocks on the Earth’s surface at more than twice that age.
Neither Abbé Lemaître nor A. S. Eddington were at all troubled by this age discrepancy, which could be resolved by the delayed outward thrust of a cosmological constant. As we have seen, this anti-gravity repulsion had been initially proposed by Einstein in 1917 to keep the Universe in a static, non-moving condition. After it was realized that the Universe is expanding, Einstein abandoned the cosmological constant, and stated in 1931 that the ad hoc term was “greatly detrimental to the formal beauty of the theory.” He instead collaborated with the Dutch astronomer Willem de Sitter to propose an expanding Universe described by the equations of his relativity theory without the anti-gravity term.9
Both Eddington and Lemaître nevertheless remained convinced that a non-zero cosmological constant was essential to an expanding Universe. To them, it was a real physical force that permeates the entire Cosmos. They supposed that the Universe had no definite origin in time and might have been resting in a pre-existing, immobile state before its expansion began.
Since the repulsion force of the cosmological constant increases with distance, it can overcome the gravitational attraction that holds the Universe together, and a slow expansion will then begin. Once the outward thrust gained the upper hand, the Universe would start flying apart and gradually thin out. This would lessen the overall gravitational attraction, and make the Universe less able to resist the cosmic repulsion, propelling it to faster and faster speeds as time went on.
Although Eddington and Lemaître agreed on the importance of this force, they had different views about the beginning of the Universe. Lemaître proposed that it began during the disintegration of his hypothetical primeval atom, but Eddington disliked the notion of an explosive beginning, which he found distasteful, and wrote: “As a scientist I simply do not believe that the present order of things started off with a bang … Philosophically, the notion of a beginning of the present order of Nature is repugnant to me,” and he subsequently asserted that: “We cannot give scientific reasons why the world should have been created one way rather than another. But I suppose that we all have an aesthetic feeling on the matter … It has seemed to me that the most satisfactory theory would be one which made the beginning not too unaesthetically abrupt.”10
Eddington then continued his disdain with: “If you prefer the view (favored by Lemaître) that the Universe started with the thunder of an explosion, there is nothing in our present knowledge to gainsay you; only it seems inartistic to give a Universe, built to contain a natural cause of expansion, an additional shove off at the start.”11 That built-in natural cause was the cosmological constant.
It was all a matter of timing. Either the expansion started at its explosive beginning in the distant past, or else the expansion was a peripheral event unrelated to the origin of the Universe, which might even have existed for an eternity. The unsettled controversy was continued in the mid-20th century in two opposing worldviews.
A Universe that Had no Beginning
Two young astronomers from Austria, Hermann Bondi and Thomas Gold, and separately the English astronomer Fred Hoyle, proposed that the expanding Universe had no specific beginning in time and might last forever. Bondi and Gold had traveled to study at the University of Cambridge in the years immediately preceding World War II (1939–1945), but did not meet until May 1940 when the English government sent them into internment in Canada as enemy aliens. They were released by the end of 1941 and sent to join the English astronomer Fred Hoyle in work on the English naval radar systems at the Admiralty Signals Establishment. After the war, in 1945, Bondi and Hoyle returned to Cambridge, while Gold stayed with naval research until 1947, when he also came back to Cambridge and joined Hermann Bondi in proposing a novel Steady State theory for the expanding Universe.
Bondi and Gold were very critical of the application of Einstein’s General Theory of Relativity to the Universe at large. As they pointed out, you could adjust the cosmological constant to accommodate almost any related observation, and the theory thereby lost its simplicity and uniqueness. In their view, any speculative theory that could never be tested by definitive observations was downright unscientific.
They therefore proposed a Universe that had no beginning, and supposed the Cosmos has always existed, presenting an unchanging Steady State on the largest scales of space and time.12 The thinning of matter caused by the continuous expansion of the Universe is, in their view, compensated for by the perpetual creation of new matter in the increasingly empty spaces of the Universe.
The Steady State hypothesis would be consistent with the supposed universality of the laws of physics, which were assumed to be applicable everywhere and at all times throughout the Universe. They proposed a perfect cosmological principle in which the Universe is unchanging in both space and time, at least when the largest possible scales are concerned.
The new hypothesis acknowledged the inescapable fact that the galaxies are moving apart, but it supposed that they have always been doing so in an eternal Universe without beginning or end. As the Universe expands, newly formed galaxies continuously fill the intergalactic voids produced when older galaxies move away from one another. The dispersal and creation of matter therefore balance each other forever in an eternal Steady State, with the expansion taking things apart as fast as new matter comes into being. If just one hydrogen atom were created in every cubic meter of space per year, on average, it would be sufficient to keep the overall Universe unchanged with time.
This creation of new matter out of the nothingness of space might seem preposterous, but to Bondi and Gold it was no harder to accept than the supposed creation of matter all at once at the beginning of time.
Fred Hoyle had a different approach to the Steady State. He thought you should get the equations first and used Einstein’s General Theory of Relativity to obtain them, without making use of the cosmological constant.13 By introducing a new term in the same way that Einstein had introduced the cosmological constant, Hoyle was able to obtain an automatic balance between the expansion of the Universe and the origin of new matter.
At this time, and probably decades before that, most astronomers had nevertheless become tired of speculations based upon Einstein’s mathematically complex theory. The behavior of galaxies and the eventual fate of their expansion could be described perfectly well by Newton’s simpler gravitational theory without any space-time curvature or a cosmological constant. The astronomers needed some definitive observations that could be applied to the Universe at large, and they eventually got it in 1965, when the remnant radiation of the Big Bang was discovered.
A Hot, Radiant Beginning
It was one thing to describe the current expansion of the Universe, and quite another to specify how the expansion began. Abbé Lemaître realized the dilemma, suggesting an explanation with:
“It remains to find the cause of the expansion. We have seen that the pressure of the radiation does work during the expansion. This seems to imply that the expansion has been set up by the radiation itself.”14
But what caused the radiation in the first place?
While working at the Johns Hopkins University in Maryland in the late 1940’s, George Gamow and his colleagues proposed that the observable Universe resulted from the detonation of a cosmic bomb. They were mainly interested in where the chemical elements came from, and suggested that they were cooked in the hot exploding oven of the infant Universe.
Instead of focusing on the mathematics of the early Universe, as Lemaître had before him, Gamow was interested in its physical properties. He found that conditions were relatively simple and uncomplicated in the distant past, when compared to those of today’s Universe. Since gases get hotter when they are compressed and cool when they expand, Gamow concluded that the Universe had to be incredibly hot in its earliest, most compact state, with a temperature of about 10 billion, or 1010, degrees kelvin. It was so exceptionally hot in the beginning of the expansion that radiation was indeed the most powerful thing around. As Gamow put it: “One may almost quote the Biblical statement: ‘In the beginning there was light,’ and plenty of it.”15
A single temperature would characterize the radiation, and that temperature would slowly drop as the expansion of the Universe progressed. In 1948 Ralph A. Alpher and Robert C. Herman predicted the present value of this temperature in a short paper intended to correct some mistakes in Gamow’s account of the evolution of the Universe. An ending sentence, inserted almost as an afterthought, stated that the radiation should still be around, cooled to about 5 degrees above absolute zero over the past billions of years of expansion.16 In a few years, Alpher and Herman left academia for industry — respectively to the General Electric research laboratories in 1955 and to General Motors in 1956, and at the time no one attempted to observe the relic radiation they predicted.
Although the low-temperature, residual background radiation was eventually discovered, Fred Hoyle had in the meantime developed the Steady State theory that had no relic radiation. Competition between advocates for an everlasting Universe and one with a hot beginning continued for decades.17 Astronomers were convinced that the Universe was changing over millions and billions of years, but they could not agree on whether or not it exploded from a dense, primeval state, which we now know as the Big Bang. Two outspoken proponents of these different perspectives were George Gamow and Fred Hoyle.
The Turbulent Lives of George Gamow and Fred Hoyle
Georgiy Antonovich Gamow began life on March 4, 1904 at the port city of Odessa in the Russian Empire (now in Ukraine), on the northwestern shore of the Black Sea. His parents were high-school teachers; his grandfather on his father’s side was a garrison Commander in the Russian Imperial Army, and his mother’s father was Archbishop of Odessa.
George’s early years were unsettling. His mother died, when he was just 9 years old, and during the subsequent World War I (1914–1918), his retired father had to work as a janitor so they could have something to eat.18 Some of the family silver was sold to send George to the State University in Petrograd — renamed Leningrad University in 1924 after Lenin’s death that year.
Although he rarely attended any university courses, Gamow did listen to lectures on relativity offered by Alexander Friedmann, where he learned about the possibility of expanding or contracting Universes.
In 1928, Gamow received support for a study tour to Göttingen, where he wrote his famed quantum description of the atomic nucleus19 — when he was only 24 years old. Then after returning to the Soviet Union, George married the attractive physicist Lyubov (“Rho”) Vokhminzeva, in August 1931, and the two began several attempts to leave the oppressive country. They first attempted to paddle a kayak across the Black Sea to Turkey, but poor weather ruined the attempt, and they abandoned other possibilities to defect when they realized that they would most likely be caught. After repeated attempts to obtain passports for foreign travel, the couple was eventually permitted to attend the Solvay Conference on Nuclear Physics in Brussels the fall of 1933, and they did not come back.
Marie Curie hosted the couple for two months in Paris, and they moved on to a one-month visit with Ernest Rutherford at the University of Cambridge and a stay with Niels Bohr in Copenhagen for four months. With Bohr’s encouragement, Gamow next sought work in America, and found it at the George Washington University in Washington, D.C., where he wrote important papers on the origin of the elements and organized a conference on stellar energy generation that led to solutions of the problem. As he described it, he was just waiting during most of his life, like a spider that sits in the corner of a big web, and when something exciting came he just jumped in, like a spider that quickly goes after something that is caught in his web.20
George Gamow has also been remembered for his series of books about Mr. C. G. H. Tompkins and other acclaimed books for the layperson,21 as well as his unconventional life that included a relentless mockery of science’s solemnity and an unrestrained consumption of alcohol.22
And this brings us to the other character in this colorful story, Fred Hoyle, who was born June 24, 1915 in his parent’s house in Yorkshire, England. His childhood included desperate family poverty, and an unkind teacher who regularly beat her students with a cane. She also boxed their ears with her hand, which Hoyle associated with the eventual loss of hearing in his left ear. While growing up, he acquired a lifelong disrespect for the “all-powerful and all-stupid rampaging monster called ‘law’.”23
In his adolescent years, a different sort of teacher recognized Hoyle’s insight, energy and originality, and helped him obtain a scholarship to Emmanuel College at the University of Cambridge, which he entered in 1933 with a pronounced Yorkshire accent, shabby clothes, a jobless father, and a blunt manner. He read mathematics, took the Tripos examinations, and in 1939 married Barbara Clark after just five weeks of knowing each other well enough to have a conversation. The next year Hoyle left Cambridge to help with English radar research, at a time that German aircraft were bombing London.
At war’s end in 1945, Hoyle returned to Cambridge, where he spent nearly three decades at the Institute of Astronomy and proposed novel solutions to many significant problems such as the nuclear fusion reactions in stars, the formation of giant stars, the synthesis of elements within stars, and the origin and nature of the Universe.
Fred Hoyle’s remarkable creative output included popular astronomy books and lectures, entertaining radio and television broadcasts, and his science fiction classics, The Black Cloud and A for Andromeda, which helped make Julie Christie a star.
Hoyle became a very public figure as the result of a series of talks on astronomy in the spring of 1949 for the British Broadcasting Corporation, abbreviated BBC. On Saturday evenings millions of listeners tuned into the popular radio broadcasts, which were widely circulated the following year in a short book entitled The Nature of the Universe. After ten years of marriage, Hoyle and his wife could now use the lecture payments and book income to buy their first refrigerator.
During his radio broadcast on March 28, 1949, the intelligent and sarcastic Hoyle presented the Steady State theory of the continual creation of matter as the only sensible cosmology, and coined the term Big Bang as an expression of derision, without credit to A. S. Eddington who had called it a Bang two decades earlier. Eddington thought such an event was unaesthetic, and Hoyle dismissed the unreasonable assumption that matter was created “in one Big Bang at a particular time in the remote past.”24 The Big Bang, he supposed, was an unscientific theory that could never be challenged by direct appeal to observations. The cynical Hoyle also wondered about the scientific credibility of a theory that had been conceived by a Priest and endorsed by a Pope.
Fred Hoyle had a feisty contempt for bureaucracy and orthodox behavior, and regularly spoke out to say just what was on his mind. His combative, pugnacious attitude did not fit in with the traditional, polite behavior of English society, and led to numerous disagreements with his colleagues. They included three decades of public arguments and corrosive relationships with Martin Ryle, the Nobel-prize-winning Cambridge radio astronomer.25 Their disagreements may have reflected a difference between Hoyle’s impoverished family background and Ryle’s privileged one — his father was physician to King George VI.
Fred Hoyle did not like religion, and was widely regarded as an atheist. When discussing the beliefs of Christians during one of his BBC radio broadcasts he declared:
“In their anxiety to avoid the notion that death is the complete end of our existence, they suggest what is to me an equally horrible alternative. … [They] offer an eternity of frustration, [and] have so little to say about how they propose eternity should be spent.”26
Although the dogmas and miracles in religion were troubling to Hoyle, he retained a religious awe of the Universe and life in it, and had a strong spiritual affinity with a greater power that we do not understand. He sensed that our minds participate in a cosmic intelligence that was somehow involved in the establishment of the Universe and the physical laws that govern it.
As an example, the manufacture of carbon inside stars involves the simultaneous collision of not two helium nuclei but three of them, an exceedingly unlikely situation. Unless the carbon nucleus resonated at a specific energy level, there would not be enough carbon for life to exist. In effect, the resonance increases the cross section for a collision and makes it more likely to occur, like the greater possibility of throwing a ball against a house instead of a tree trunk.
In early 1953, Hoyle visited William Fowler’s laboratory at the California Institute of Technology and boldly suggested that there had to be such a resonance of the carbon nucleus, whose energy ought to be at about 7.69 MeV. Ward Whaling, a junior member of Fowler’s team, thought there might be something to Hoyle’s proposal, and persuaded Fowler to let him look for the effect with equipment no one else was using. When the prediction was verified, Hoyle’s name was included on the announcement, but omitted in the published version.27
In his autobiographical note for the Nobel Foundation in 1983, Fowler drew attention to Hoyle’s important role in our understanding of elementproducing nuclear reactions in stars, stating that: “The grand concept of nucleosynthesis was first definitely established by Hoyle in 1946. After Whaling’s confirmation of Hoyle’s ideas I became a believer.”
Although Fowler probably meant his belief in stellar nucleosynthesis, his team’s discovery of the excited state of carbon was nevertheless important in turning Hoyle’s attention to Design by a Creator God. Hoyle had been involved in the Steady State hypothesis for the expanding Universe, and at the time he was criticized for atheism, but the discovery of his predicted resonance seems to have changed his mind about all that.
When discussing the unlikely origin of carbon, Hoyle commented in 1959 that:
“If this were a purely scientific question and not one that touched on the religious problem, I do not believe that any scientist who examined the evidence would fail to draw the inference that the laws of nuclear physics have been deliberately designed.”28
And when writing about the remarkable energy level of the carbon nucleus in subsequent decades, he reaffirmed that: “A ‘super-intellect’ has monkeyed with physics, as well as with chemistry and biology;”29 and that:
“Either our existence is a freakish accident, or the laws of physics were deliberately arranged by some agent to permit our existence.”30
On New Years Day 1972 Hoyle received a knighthood from Queen Elizabeth II for his service to astronomy, and in the same year his disagreements with the entrenched scientific bureaucracy and political University figures led to his resignation from the Plumian Professorship at the University of Cambridge. In the meantime, he declared that there might be something wrong with his Steady State theory.
After-Glow of the Big Bang
In 1965 Fred Hoyle recanted the Steady State theory and withdrew his objections to the Big Bang hypothesis, even though he never did think it was right.31 What led Hoyle to renounce his previous outspoken support of the Steady State? The 3-degree relic background radiation of the Big Bang was discovered that year, and it was not predicted by the continual creation theory. The background radiation instead provided strong observational evidence for a dense, primeval origin of the observed Universe.
The discovery of this faint after-glow of the Big Bang was an unexpected outcome of experiments designed for other purposes at the Bell Telephone Laboratories. Their engineers had invented a horn-reflector antenna to detect weak microwave signals from a satellite by rejecting radiation from the ground surrounding the antenna. It was the most sensitive antenna that existed in the world at the time, and it worked just fine in tests carried out in 1962 with instruments aboard Telstar, the first working communications satellite.
These tests demonstrated the feasibility of transmitting signals from a place on Earth to an overhead satellite and back. But within one year the Communications Satellite Corporation, abbreviated Comsat, had been created, and the Bell Telephone Laboratories’ parent company, the American Telephone and Telegraph Corporation, was legislated out of the international communications-satellite business to avoid a monopoly. So the Bell Telephone Laboratories had this superb horn antenna and detection equipment that were no longer needed, and Arno A. Penzias and Robert W. Wilson decided to use them to make accurate measurements of the intensity of several extragalactic radio sources at a microwave wavelength of 7.34 centimeters or a frequency of 4080 MHz.
Bell Telephone Laboratories hired Arno and Bob with the understanding that they would help with satellite communication, and would be free to work half time on astronomy. They both also had Ph.D. degrees with an astrophysics thesis, and realized there was too much unexpected noise interfering with the detected microwave radiation of known cosmic objects.
They found a persistent, ubiquitous, unvarying and totally unanticipated noise source that contributed an antenna temperature of 3 degrees kelvin, or just three degrees above absolute zero, the coldest possible temperature. The unexpected noise was equally strong in all directions, wherever they pointed the antenna, and independent of the time of the day and of the year. Even a seemingly empty part of space emitted the persistent radiation, and it had no dependence on the location of any known cosmic radio source.
Penzias and Wilson only thought about a cosmological explanation for their result after coming in contact with Princeton Professor Robert H. Dicke, who visited them with his coworkers at the Bell Telephone Laboratories Crawford Hill research facility near Holmdel, New Jersey, located just 40 kilometers (25 miles) from Princeton. The two groups agreed to the publication of two adjacent letters in the Astrophysical Journal. The Bell Telephone Laboratories scientists would report on their serendipitous discovery observations in a one-page report, with the modest title A Measurement of Excess Antenna Temperature at 4080 MHz,32 while the Princeton group would write about their possible cosmological interpretations of it in a companion paper, which had a more ambitious title of Cosmic Blackbody Radiation.33 It argued that the ubiquitous and unvarying noise was the first definitive evidence for the Big Bang.
Sometime between the submission and publication of both papers, Walter Sullivan obtained copies and announced the discovery on the front page of the New York Times. The headline, on May 21, 1965, read: Signals Imply a ‘Big Bang’ Universe, which told it all. It is this newspaper article that apparently led Robert Wilson to take the cosmology interpretation seriously.
The Nobel Prize in Physics for 1978 was half-awarded to Arno A. Penzias and Robert W. Wilson “for their discovery of cosmic microwave background radiation”.
It is now generally accepted that the three-degree radiation is the faint, cooled after-glow of the Big Bang. This remnant radiation is now known as the three-degree cosmic microwave background radiation. It is called a background radiation because it originated before the stars and galaxies were formed and lies behind them. The galaxies are moving away from the background, like a flock of startled birds in the sky.
We are immersed within the radiation and participating in the explosion. The American poet Robinson Jeffers, whose brother was an astronomer at Lick Observatory, has captured the essence of this Great Explosion with:
“Nothing can hold them down; there is no way to express that explosion; all that exists
Roars into flame, the tortured fragments rush away from
each other into all the sky, new Universes
Jewel the black breast of night; and far off the outer nebulae
like charging spearmen again
Invade emptiness.”
And perhaps alluding to Lemaître’s fireworks Universe, Jeffers’ poem includes the lines:
“No wonder we are so fascinated with fireworks
And our huge bombs: It is a kind of homesickness perhaps for
the howling fireblast that we were born from.”34
Confirming the Discovery
Dicke’s research group had been preparing to look for the relic radiation when they were scooped by Penzias and Wilson, so they were able to quickly detect it with their own equipment, and a host of instruments were also sent aloft in high-altitude balloons to get a clear view of the background radiation. Within a decade, the observed spectrum looked very much like that expected from a thermal radiator, or black body, and convinced nearly everyone that it might have cosmological implications. In 1982 Robert Wilson, for example, recalled: “We felt that, at least until they [the theoreticians] had a chance to think about our results, we shouldn’t go out on a theoretical limb that we couldn’t support. For me, the last nail in the coffin of the Steady-State theory wasn’t driven in for quite a while — not until the black body curve was really verified.”35
Nevertheless, more definitive observations had to be carried out from a satellite with instruments specifically designed to study the cosmic background radiation. They would determine if it has a precise black body spectrum or only an approximation of one, and might detect the temperature fluctuations from place to place that were needed to explain the visible lumpiness of the distribution of galaxies that eventually formed.
Children of the Space Age
On October 4, 1957, the Soviet Union used an intercontinental ballistic missile to launch the first artificial Earth satellite, named Prosteyshiy Sputnik 1, the first simple satellite. In shocked response, the United States Congress established the civilian National Aeronautics and Space Administration, abbreviated NASA, to exercise control over activities in space devoted to peaceful purposes for the benefit of all mankind. But threats to world peace also preoccupied Congress, so the very act that established NASA assigned the Department of Defense responsibility for military interests in space. The Space Age had thus begun, triggered by a Cold War rivalry between the United States and the Soviet Union to gain superiority in rocket, satellite, and space technology.
The competition was won when NASA’s Apollo flights carried men to the Moon, which demonstrated the superiority of American purpose and technology in space. Over 500 million people around the world watched the televised landing of Apollo 11 on July 20, 1969, when Neil A. Armstrong took the first human step on the Moon. Although public interest in NASA’s space program, and congressional funding of its activities, diminished when the Soviet Union fell apart and American commercial interests and other government agencies gained access to space, NASA’s responsibility for space vehicles was nevertheless extended to include rockets, the Space Shuttle, space platforms, and space telescopes such as the Hubble Space Telescope and the Spitzer Space Telescope.
Two young astronomers grew up and matured in this climate, experiencing the Cold War and NASA’s triumphs. These children of the Space Age are John C. Mather, born on August 7, 1946, and George Smoot, born on February 20, 1945. They both played key roles in the development, launch and use of a NASA satellite devoted to the study of the cosmic background radiation from above the Earth’s obscuring atmosphere. It is named the COsmic Background Explorer, abbreviated COBE.
Out in space, the instruments aboard COBE were not hampered by looking through our planet’s atmosphere. The satellite was always surrounded in every direction by the pervasive cosmic microwave background radiation, which emitted far more microwave energy than all the stars and galaxies put together.
Mather’s instrument was specifically designed to measure the radiation spectrum, or distribution of radiation intensity as a function of wavelength, to see if it precisely describes the black body spectrum of a perfect thermal radiator. Such a black body absorbs all thermal radiation falling upon it and reflects none — hence the term “black.” It radiates energy at a wide range of wavelengths, but with an intensity that is greatest at a wavelength that depends on the temperature. The expansion of the Universe would preserve the black body spectrum of the cosmic background radiation for all time. No process can destroy its shape, but the location of maximum intensity will stretch to longer and longer wavelengths as time goes on and the radiation gets colder.
In the present epoch, with a temperature of about 3 degrees above absolute zero or 3 degrees kelvin, the black body radiation intensity peaks at a wavelength of 0.001 meters, or 1 millimeter. Unfortunately, the Earth’s atmosphere absorbs cosmic radiation at this short wavelength.
Mather and John Boslough have provided a fascinating description of the long, trying ordeal involved in doing science from space, particularly with COBE.36 During the previous twenty-five years, each instrument on COBE had been preceded by numerous tests of earlier versions lofted in high-altitude balloons or rockets. That involved the dedicated, hard work of large teams of scientists, engineers and managers who faced scientific, technological and bureaucratic obstacles. Even lawyers were involved.
Instruments designed for NASA’s specific scientific objectives have to win a peer-reviewed Announcement of Opportunity, with stiff competition from other proposals. Once the COBE proposal won, the travail had just begun, as the launch vehicles were changing and the instruments needed to be reconfigured. Altogether the COBE venture was quite a different kettle of fish from Penzias and Wilson’s unexpected discovery, and there was nothing serendipitous about it. True experimenters, the COBE team was hunting for something that might or might not be there, and they were careful to confirm their results before announcing them.
On January 13, 1990, less than two months after COBE went into orbit but a quarter of a century after the discovery of the background radiation, John C. Mather reported the combined results of the first COBE spectral measurements at an American Astronomical Society meeting near Washington, D.C. The spectrum fit the Planck black body curve with error bars of 1%. Later work using the whole data set improved the precision to one part in 20,000 (Fig. 13.1), establishing a temperature of precisely 2.725 degrees kelvin, with an uncertainty of 0.001 degrees kelvin.37 The presentation caused the audience to break into a standing applause, which you usually see only at the end of a beautiful performance of music.
Such a spectrum could not have happened in the Universe as it is now. Atoms, interstellar material, planets, stars and galaxies all now have a very different temperature than the background radiation. And to put it another way, the observed spectrum is proof that the observable Universe did expand from a very hot, dense state in the past, when matter and radiation were at the same temperature.
It took more than two more years for significant results to be accumulated by the second (of three) COBE instruments. George Smoot announced them at the April 23, 1992 meeting of the American Physical Society, but a press release had been issued two days earlier from his home institution, the Lawrence Berkeley Laboratory in California. That caused a considerable uproar, since Smoot had broken his signed policy agreement involving prior approval of all papers and press releases by both the full COBE science team and NASA officials. His attempts to garner credit for himself appalled everyone involved; but the discomfort was partly alleviated by Smoot’s subsequent letter of apology.
Figure 13.1 Background spectrum The intensity of the cosmic microwave background radiation plotted as a function of wavelength. Pioneering measurements are compared to the expected spectrum of a three-degree black body and radiation from our Galaxy (bottom). The full spectrum at millimeter wavelengths (top) was obtained from instruments aboard the COsmic Background Explorer, abbreviated COBE, in late 1989. It corresponds to a black body with a temperature of 2.725 degrees kelvin.
After subtracting out the known microwave emission of the Milky Way and using mathematical averaging techniques on about 100 million observations, the COBE team found that the temperature varies ever so slightly over large angular sizes.38 The sensitive instrument detected minute temperature differences no larger than a hundred-thousandth, or 10-5, of a degree kelvin. These fluctuations in the background radiation must have provided the beginning seeds from which today’s material Universe of stars and galaxies grew. Otherwise they wouldn’t exist.
This was a very important finding. The observed temperature fluctuations portray ripples in the fabric of space-time that existed prior to the formation of the first stars and galaxies, which had to coalesce out of the low-level fluctuations. Mather and Smoot were jointly awarded the 2006 Nobel Prize in Physics “for their discovery of the black body form and anisotropy of the cosmic microwave background radiation.”
The COBE instrument only probed the largest angular scales, and there was much to be learned by observing smaller scales and by measuring the temperature fluctuations with much greater sensitivity. In the subsequent decade more than 20 experiments from the ground and balloons provided sharper focus for localized regions of the background radiation. Nevertheless another satellite experiment was still needed that would scan the entire sky with enormously improved accuracy, precision, and sensitivity.
At about this time, NASA was faced with intense public scrutiny, having launched the Hubble Space Telescope with a faulty mirror, lost the billion dollar Mars Observer spacecraft, and blown up at least one Space Shuttle. So NASA administrator Daniel S. Goldin decided to cut the losses, and to begin doing things “better, faster and cheaper” using mid-sized rockets to launch inexpensive missions within a year or two of approval.
Charles L. “Chuck” Bennett, at the Goddard Space Flight Center, and David T. Wilkinson, at Princeton, formed a small team of experts to design a spacecraft instrument that could measure angular variations in the temperature of the background radiation within the budget cap of $70 million in 1994 dollars. This cost threshold was raised to $95 million in the late 1990’s when two other “cheaper” missions failed, but still a relatively low-cost payload; it did not include the launch costs of about $55 million and the operations costs of about $1.5 million per year.
For a two-decade period beginning in 1993, Bennett led team efforts for the design, proposal, operations, and findings of the key mapping instrument known as the Microwave Anisotropy Probe, or MAP for short. It was approved in mid-1996, and launched on June 30, 2001, with a name change in early 2003 to WMAP, or Wilkinson Microwave Anisotropy Probe to honor Wilkinson after his death.
Figure 13.2 Map of the young Universe An all-sky view of the three-degree cosmic microwave background radiation emitted from the Universe just 390,000 years after the Big Bang that occurred 13.7 billion years ago. These temperature fluctuations provided the seeds from which galaxies subsequently grew. (Courtesy of the NASA/COBE and NASA/WMAP Science Teams.)
The most detailed and precise map yet provided for the background radiation was obtained from WMAP (Fig. 13.2). The observed temperature fluctuations were used to infer the gravitational pull that caused them, and to reliably tell us what the young Universe was made of, how dense it was, and what forces were at play at the time.39
They have shown that the amount of “ordinary” matter, the baryonic kind that makes up atoms, is a small fraction of the total material content of the Universe, and that dark, invisible non-baryonic matter is about five times more abundant than ordinary baryonic matter. Moreover, the combined gravitational pull of both kinds of matter is not enough to stop the expansion of the Universe in the future. The time of the Big Bang explosion that gave rise to the expanding Universe was also dated to 13.7 billion years ago, provided that the Universe has been expanding at a constant rate for all that time.