B00B7H7M2E EBOK, page 20
Though it might seem that such a mystery as Jansky’s hiss would have made headlines, his work received little attention even within the astronomy community. The one exception to this apathy was Grote Reber, an eccentric bachelor and ham radio operator in Wheaton, Illinois, who read about Jansky’s radio hiss in Popular Astronomy magazine. Reber proceeded to cash in his savings and design and construct his own device in his mother’s back yard to listen to radio signals coming from the sky. Reber’s telescope was a dish 30 feet (nine metres) in diameter. Astronomer Jesse Greenstein of Yerkes Observatory, when he later saw the back-yard telescope, called Reber ‘the ideal American inventor. If he had not been interested in radio astronomy, he would have made a million dollars.’
In the 1940s, Greenstein tried to get Reber a position at the University of Chicago. That fell through when the University agreed to have Reber only if his pay and research support came from Washington, and Reber refused to go to the bother of explaining to bureaucrats precisely how the money for new telescopes would be used. Except for Reber, until the 1950s there was virtually no interest in radio astronomy in the United States.
Astronomers elsewhere in the world were quicker, after the development of radar during World War II, to appreciate the potential advantages of studying radiation in a part of the electromagnetic spectrum outside the visual range. In 1946 a radar signal was bounced off the Moon, and in the years that followed, the Jodrell Bank radio telescope in England led the world in mapping radio sources in space. Following close behind were Cambridge University and a team in Australia. Particularly intense sources of radiation in the radio range of the spectrum became known as ‘radio stars’ and ‘radio galaxies’.
A problem in early radio astronomy – and one reason it drew little interest at first from optical astronomers – was that radio telescopes like Reber’s couldn’t measure a source’s position in the sky accurately enough to find out which visible object was emitting the radio waves. In order to accomplish that, there needed to be a hundred-fold improvement in resolution, and that meant a telescope about a kilometre in diameter. Radio waves come in a large range of lengths, but they are all longer than waves in the visible part of the spectrum, and their length is the problem. A radio telescope doesn’t give good resolution unless it is quite a bit larger than the length of the radio waves it’s receiving. Studying shorter radio waves only helps a little. The much shorter waves in the visible part of the spectrum allow optical telescopes to achieve resolution with relative ease. Radio astronomers finally solved this problem in 1949 by using networks of small telescopes linked to a receiving station which combines the signals. Such a network or array is a ‘radio interferometer’.
England and Australia continued to dominate the field. In 1950 Martin Ryle of Cambridge University and his co-workers discovered evidence of radio emissions from four nearby galaxies including Andromeda. Ryle was an advocate of Big Bang theory, and as he and his colleagues continued to map the distribution of radio sources across the sky, their findings supported that theory. They discovered that radio galaxies are much more abundant in the far distance than they are nearby. Since the further we peer into space the further back in time we are looking, Ryle’s radio telescopes were showing him the universe at a much earlier stage, and his discovery indicated that the density of radio galaxies was greater then than it is today. It’s reasonable to think this should be the case if this is an expanding universe in which everything on the large scale is moving away from everything else and used to be much more closely crowded together.
In 1954, owing largely to the influence of Greenstein, by then a professor at the California Institute of Technology, the National Radio Astronomy Observatory was built in West Virginia and a radio interferometer was constructed near Yosemite National Park in California under the aegis of Cal Tech. But before that, even during the years when radio astronomy was virtually nonexistent in the United States, the Bell Telephone Company had continued to carry on research having to do with radio communications. It was at Bell Labs in New Jersey, where Jansky had first investigated the radio hiss from space in the 1930s, that the discovery took place that most scientists considered the clincher for the Big Bang theory.
Arno Penzias was born to a Jewish family in Munich. When he was six years old, he and his brother and parents were among the last Jews to get out of Nazi Germany, arriving as impoverished immigrants in the United States in the winter of 1940. Penzias received his undergraduate physics degree from the City College of New York and went on to Columbia University for his PhD. In 1961 he took a job at Bell Labs, where two years later he was joined by Texan Robert Wilson. Wilson had at first favoured the Steady State theory over the Big Bang. He was strongly impressed with Fred Hoyle, who had been a visiting professor at Cal Tech when Wilson was a graduate student there. In 1963, a year after completing his PhD, Wilson crossed the country to the east coast to work at Bell Labs.
At Bell there was a large, horn-shaped antenna designed for use with the Echo I communications satellite. In the spring of 1964, Penzias and Wilson were using the antenna to study noise levels that were hampering the satellite’s transmission. Scientists working with the antenna had to make adjustments and limit themselves to signals that were stronger than the ‘noise’. It was an annoyance that was possible to ignore, but Penzias and Wilson chose not to. They noticed that the noise remained the same regardless of which direction they pointed the antenna. If the Earth’s atmosphere itself were the source of the noise, an antenna pointed towards the horizon should pick up more noise, for it faces more of that atmosphere than an antenna pointed straight up. Penzias and Wilson concluded that the noise had to be coming either from beyond the Earth’s atmosphere or from the antenna itself. Pigeons nesting in the antenna were evicted and their droppings cleared away. That didn’t help.
Penzias and Wilson were unaware of theoretical predictions that had been made back in the late 1940s and also of current work going on in England, Russia and a few miles away from them in Princeton, New Jersey. In the 1940s, Russian-born physicist George Gamow, who had defected to the West in 1933, and Americans Ralph Alpher and Robert Herman had theorized about the early universe, running Friedmann’s equations backwards towards the event with which the universe began. Their prediction was that there ought to be left-over radiation surviving from about 1,000 years after the origin of the universe. At that time, if Big Bang theory had it right, the universe was very hot, but by now the temperature of the radiation should have cooled to about five degrees above absolute zero. The prediction wasn’t tested, for such radiation would not be easy to observe.
The idea that this radiation might indeed exist, and questions about its temperature, were still around in the early 1960s. In 1964, while Wilson and Penzias were tidying the pigeon droppings, Fred Hoyle and a colleague, Roger Taylor, in England were attempting to calculate what the background temperature of the universe would be today if it began in a Big Bang. And in the Soviet Union Yakov Borisovich Zel’dovich had concluded that given the abundances of hydrogen, helium and deuterium observed today, the universe must have begun in a hot Big Bang and its background temperature currently must be a few degrees above absolute zero. Soviet researchers had written papers about current radio astronomy measurements and what they implied about the background radiation, and they had even suggested that the most likely antenna in the world to be able to detect this radiation was the Bell Labs antenna in Holmdel.
Robert Dicke at Princeton was working along the same lines. Born in Missouri in 1916, he was of Hoyle’s generation. He was educated at Princeton and at Rochester University, then worked on radar at the Massachusetts Institute of Technology (MIT) during World War II and after that joined the Princeton faculty. On and off through the years Dicke had considered the problems of the background temperature of the universe and the as yet undetected background radiation. In 1964, he set P.J.E. Peebles, a young researcher at Princeton, to work figuring out how the temperature might have changed over time in an expanding universe that had originated with a hot Big Bang. When Peebles had finished his calculations, Dicke gave two other researchers the job of setting up an antenna on the roof of the Princeton physics lab to try to detect the predicted radiation. It was at this juncture that Dicke received a phone call from Arno Penzias and Robert Wilson.
It so happened that Bernard Burke, another radio astronomer, had heard about Penzias and Wilson’s puzzle, and he also knew (as they did not) of the work being done by Dicke. Burke proceeded to bring Dicke, Penzias and Wilson together, and they soon concluded that Penzias and Wilson had found by accident the radiation that Dicke had been hoping to discover.
This all-pervasive hum of radiation, coming at equal intensity from all over the sky, has been likened to a faded photograph of the universe as it existed about 300,000 years after the Big Bang. It is the oldest ‘photograph’ we have, and the most direct evidence that the universe was once much hotter and denser than it is now. The radiation has cooled with the expansion of the universe and been red-shifted so greatly that it reaches us in the microwave range of the spectrum at a temperature of about three degrees above absolute zero, a little cooler than the five degrees Gamow, Alpher and Herman had predicted in the 1940s.
What is the source of the radiation? According to Big Bang theory, the universe in its early stages was everywhere filled with electromagnetic radiation. This radiation wasn’t in the visible part of the spectrum. It was far too hot for that, in the trillions of degrees. As space expanded, stretching the wavelengths of the radiation, it shifted through the spectrum. The universe gradually cooled, but until it was about 300,000 years old the radiation was still too energetic to allow electrons and protons to bind together and form atoms. If an electron began to orbit a proton it was knocked out of orbit by a photon – a particle of electromagnetic radiation. At about the 300,000-year mark, everything had cooled off enough so that photons no longer had the energy to knock electrons away from protons. Electrons and protons could form hydrogen nuclei and atoms, and photons could move about more freely. Physicists call this the ‘decoupling’ of radiation and matter. With that change, radiation (photons) streamed in all directions, and it is that radiation, red-shifted all the way across the spectrum to the microwave range, that we detect today as the cosmic microwave background radiation. Though that radiation began its journey longer ago and further away than anything else we observe, you don’t need special equipment to detect it. The snow on a TV screen that appears when a station isn’t broadcasting consists in part of this radiation, this dim afterglow of the Big Bang cataclysm.
It’s an interesting bit of astronomy trivia that Wilson and Penzias were not actually the first to detect and measure the cosmic microwave background radiation. In 1961, another engineer at Bell Labs, Ed Ohm, had also tried to figure out what was causing the ‘noise’. Eliminating everything that could be explained away, he found that it was the equivalent of radiation at a temperature of about three degrees above absolute zero. Unfortunately for Ohm, he didn’t find the problem as annoying as Wilson and Penzias did, and he didn’t pursue it or suspect its significance. No one put him in touch with anyone who knew of the theoretical predictions. It was Wilson and Penzias who shared a Nobel Prize for the discovery.
Why wasn’t this discovery made sooner? Gamow, Alpher, Herman or Dicke probably could have discovered the cosmic microwave background radiation earlier had they tried. As it was, it took a combination of a private corporation – American Telephone and Telegraph (AT&T) – far-sighted enough to fund less practical science and attract such researchers as Wilson and Penzias, the stubborn curiosity of these two men themselves – who unlike Ohm weren’t satisfied until they got to the bottom of a mystery – and a serendipitous meeting of observation and theoretical understanding when those almost were ships passing in the night.
From the early 1960s, everything seemed to fall into place for those who favoured Big Bang theory. The discovery that quasars – which theorists think are probably an early stage of galaxy formation – exist only at enormous distances from Earth was more support. According to Steady State theory, galaxies are periodically dying and being replaced by new galaxies made from new matter. If that were so, and if quasars are part of the process of galaxy formation, they ought to be fairly evenly distributed near and far throughout the universe. The fact that they are not argues against the Steady State and in favour of the Big Bang. Quasars’ distance from us in space (and, by virtue of that fact, in time) means they only existed when the universe was much younger than it is now, indicating that this particular stage of galaxy formation occurred only in the distant past, hasn’t happened again in later periods of the universe’s history, and isn’t still going on today. The universe is not repeating itself.
Astronomers and physicists have also continued to study the cosmic microwave background radiation for clues about how the universe has evolved. In 1973, Paul Richards and colleagues at Berkeley undertook balloon experiments to find out whether the spectrum of the background radiation was the spectrum that Big Bang theory predicted. They found that it was.
Even more support for the theory, also in the early 1970s, came from studies of the spectra of other galaxies to measure the abundances of various elements in them. Big Bang theory had predicted that about 25 per cent of the mass of all the elements making up the universe should be helium 4. The studies showed that prediction was on target. So did measurements within the Galaxy. Predictions of abundances of other elements such as deuterium, helium 3 and lithium also turned out to be what the theory prescribed.
While it looked increasingly likely that Steady State theory would go the way of Tycho Brahe’s valiant last-ditch efforts to save the Earth-centred universe, the Big Bang theory wasn’t entirely problem-free either. Two stumbling blocks were the ‘horizon problem’ and the ‘flatness problem’.
The ‘horizon problem’ stems from the observation that the cosmic microwave background radiation is very homogeneous, the same in all directions in areas too far separated for radiation ever to have passed from one to the other even at the earliest moments. The intensity of radiation is so close to identical in those remote areas that it seems they must have exchanged energy and come to equilibrium. The question is: how?
The ‘flatness problem’ is the problem of why the universe has not either long ago collapsed again to a Big Crunch or else experienced such runaway expansion that gravity wouldn’t have been able to pull any matter together to form stars. Neither has happened or seems to be happening at the moment. Yet having a universe somehow poised between those possibilities is so unlikely as to boggle the imagination.
A revised history of the Big Bang universe called ‘inflation theory’ proposed to solve both those problems. The idea emerged in the late 1970s, when Alan Guth, then a young physicist at the Stanford Linear Accelerator, reached the conclusion that the universe might early on have undergone a period of stupendous growth before settling down to the expansion rate it has today. Guth knew immediately that he’d hit upon a good thing. ‘SPECTACULAR REALIZATION’ he wrote in his notebook, and drew two concentric boxes around the letters.
Guth proceeded to work out a process which, at a time less than 10-30 seconds after the Big Bang (that number as a fraction is 1 as the numerator and 1 followed by 30 zeros as the denominator), could have caused gravity to become an enormous repulsive force. Instead of pulling matter back and slowing the expansion of the universe, it would, during a period lasting only an unimaginably small fraction of a second, have accelerated the expansion, causing violent, runaway inflation in the dimensions of the universe from a size smaller than a proton in the nucleus of an atom to about the size of a golf ball. When the inflationary period ended, the universe would continue to expand, but in the more sedate, familiar fashion.
Inflation theory helps the horizon problem by allowing the visible universe to have emerged from a region so tiny that it had an opportunity to reach equilibrium before it inflated. When it comes to the flatness problem, the theory says that out of an infinite number of possible universe stories – those that have the universe collapsing, those that have it expanding forever to thin oblivion, and the one in which it is perfectly poised between the two – the universe actually can be expected to be a universe perfectly balanced, expanding forever but at a continually decreasing rate, not collapsing and not eternally thinning out. Big Bang theory before inflation theory had not been able to help the universe walk that tightrope. But Guth and others who have contributed to the development of inflation theory explain that any imbalance between the expansive energy resulting from the Big Bang and the contracting force of gravity would have been wiped out by this period of runaway inflation, leaving the universe in that extremely unlikely and highly desirable condition of flatness. Highly desirable because that is the only sort of universe that eventually allows intelligent life to emerge.
To visualize the version of inflation theory that has the most to offer in this regard, first imagine the universe before the period of inflation begins, again using a balloon as an analogy. Inflate the balloon a little. That represents the expansion of the universe before the inflationary period. Pause to mark a tiny red dot on the surface of the balloon. Next attach the balloon to one of those machines that inflates balloons rapidly and turn the machine on at maximum force. That inflates the balloon to a truly remarkable size. The tiny red dot itself will have become huge. Imagine now that it isn’t the whole balloon that represents all we observe and ever will observe of the universe. It is the red dot. Inflation theory asks us to believe that what we normally call ‘the universe’ is similarly only a tiny fraction of everything there is.
