“March with air.” This is how cosmologist Mark Devlin of the University of Pennsylvania describes the Chajnantor Plateau, in northern Chile. A surreal and extreme landscape, five kilometers high, without vegetation and surrounded by even higher volcanic peaks. By the way, there is not much air: here you have to make do with half the amount of oxygen at sea level. Altitude sickness is constantly lurking.
Yet here, at an altitude of 5,200 meters at the foot of the Cerro Toco volcano, a new observatory will be put into use one of these days. Not to explore planets or stars, but to hunt for the very first birth cry of the universe. “The Simons Observatory is the latest step in our search for signals from the newborn universe,” said cosmologist Daan Meerburg of the University of Groningen.
The observatory looks like a messy jumble of sheds, barracks and containers. In between are three ‘small’ telescopes with lenses of fifty centimeters and one colossal instrument with a diameter of six meters, which has not yet been completed. Sixty thousand tiny detectors, cooled to a tenth of a degree above absolute zero, will soon capture every individual ‘light particle’ of the cosmic background radiation – the ‘reverberation’ or ‘echo’ of the Big Bang.
High and dry
The newborn universe was filled with high-energy radiation. Thanks to fourteen billion years of cosmic expansion, that dazzling glow has been diluted, cooled and ‘stretched’ into barely perceptible microwave radiation. If you want to learn more about the birth of the cosmos, about 13.8 billion years ago, you must study this most ancient ‘light’ in detail. “These are incredibly difficult measurements,” says Devlin, one of the two directors of the new observatory.
Sixty thousand tiny detectors, cooled to a tenth of a degree above absolute zero, will soon capture every individual ‘light particle’ of the cosmic background radiation – the ‘reverberation’ or ‘echo’ of the Big Bang
Microwave radiation is absorbed by water vapor (that is why food heats up so quickly in a microwave oven). A ‘big bang telescope’ must therefore be as high as possible: then you are above most of the water vapor in the Earth’s atmosphere. High and dry is the motto, and the Chajnantor plateau in Chile’s Atacama Desert is therefore ideally suited. For this reason, the international Alma observatory was built here more than ten years ago and Japanese astronomers recently put a new large infrared telescope into use there.
A telescope in space is of course even better – then you won’t be bothered by any disturbances at all. More than thirty years ago, it was an American artificial moon that studied the cosmic microwave background radiation in detail for the first time. Then minute temperature variations were discovered, of about one ten-thousandth of a degree. These are the result of small density differences in the newborn universe – the subtle concentrations of matter from which entire galaxies later clumped together.
Later artificial moons, such as the European Planck space telescope, have carried out these measurements in much more detail. This way you can compare the properties of the newborn universe with what it looks like now. And then it turns out that in addition to ‘normal’ matter, there must also be a lot of mysterious dark matter (of which only the gravitational influence is noticeable). Moreover, it turns out that the expansion of the universe has been accelerating for about five billion years, as a result of an equally mysterious form of dark energy.
Swirl pattern
Enough remaining riddles, and the new Simons Observatory takes it one step further. Because what happened in the first tiny fraction of a second after the universe was created? Was there really an extremely short period of cosmic ‘inflation’, during which our observable universe doubled in size at least eighty times? It is a popular hypothesis, about which nothing is known with certainty. But if it’s true, the empty space must have been made to vibrate vigorously. And those antediluvian gravitational waves would later have left their traces in the cosmic background radiation.
That is why cosmologists like Devlin have been looking for that ‘fingerprint’ for a quarter of a century: a unique polarization pattern of the already very weak signal. Polarization means that the radiation waves have a preference for one particular vibration direction. And the gravitational waves we are looking for reveal themselves because the direction of polarization varies in a very specific way across the starry sky, in a kind of swirl pattern.
This subtle effect cannot be measured with relatively small satellites; you need larger telescopes on the ground for that. “The detectors we use are already one hundred percent efficient,” says Meerburg, who is an advisor to one of the analysis working groups of the Simons Observatory. “So the only way to become even more sensitive is to use more detectors.” Planck Space Telescope had 52; the Simons Observatory sixty thousand.
A similar but smaller instrument at the geographic South Pole came in 2014 with the claim that the polarization signal had been found. It later turned out that the scientists had not corrected sufficiently for the presence of dust in our Milky Way Galaxy – which also causes polarization. That’s why it’s good that a number of teams are working on it, Devlin explains. “If only one team comes up with a new claim, no one is going to believe it.”
According to Brian Keating of the University of California San Diego, the scientific project leader of the Simons Observatory, the South Pole team does have a significant lead, “but hopefully we will catch up in time. There is certainly competition, but the two observatories are complementary rather than competitive.”
An even more sensitive project, called CMB-S4, is planned for the next decade, with collaborating telescopes both in Chile and at the South Pole.
Microwave radiation is absorbed by water vapor. A ‘big bang telescope’ must therefore be as high as possible: then you are above most of the water vapor in the Earth’s atmosphere.
At 2,835 meters, the South Pole is not as high as the Chajnantor plateau, but due to the low temperature the air is still much drier. On paper it is therefore an even better place to study the cosmic microwave background radiation in detail, says Meerburg. But yes, also much more extreme, and above all more difficult to reach. “If I need a crane at the South Pole, I have to plan it years in advance,” says Devlin. Moreover, only half of the sky is visible at any time from the South Pole, while from Northern Chile you can study 80 percent of the universe in the course of a year.
Background radiation measurements have been made from the Chajnantor plateau since the beginning of this century, with increasingly larger and more sensitive instruments and usually funded by the American National Science Foundation. The Simons Observatory was created thanks to a gift of more than $40 million from the private Simons Foundation (hence the name), founded by mathematician and hedge fund manager Jim Simons and his wife Marilyn. “Simons, who celebrated his 86th birthday last week, brought together a number of teams in 2015,” says Keating. “The best minds in this research area are now working together, with the same goal in mind.”
Because although all kinds of other astronomical research will also be conducted with the Simons Observatory, the most important question remains what the birth of the universe looked like and whether the idea of cosmic inflation holds up. To find out, the coming years will involve a hunt for the special spiral-like patterns in the polarization of the echo of the Big Bang.
Malfunction
These patterns could already be found by the three small telescopes (that number will be expanded to six in the near future). Unfortunately, there are all kinds of cosmic interference signals that cloud the image. The precision measurements with the large telescope make it possible to filter out the effects very accurately. “That did not happen enough in 2014,” says Devlin. “You don’t want that to happen again, so we really need to be sure that we can measure and eliminate any form of noise and distortion.”
No one knows when this will happen, and whether the breakthrough will be achieved in Chile or at the South Pole. “It just depends on who you ask,” says Meerburg. “The South Pole is a better site, but we could win because we have many more detectors and therefore much higher sensitivity and image sharpness.” Keating also hopes and expects that the ‘enormous leap in technological possibilities’ will ultimately be the deciding factor.
If not, we will have to wait for the future CMB-S4 observatory, with three large and eighteen small telescopes, spread over the two unique locations. This should make the measurements six times more efficient, says Devlin. He expects to continue shuttling between comfortable Philadelphia and the Mars-like Chajnantor Plateau for the time being. “The view from Cerro Toco is spectacular. Yes, the conditions are very extreme, but I am quite used to it.”
Cosmic background radiation
The cosmic background radiation was discovered more or less by chance in 1964 by the American radio engineers Arno Penzias and Robert Wilson, who received the Nobel Prize for Physics in 1978. They were trying to determine the origin of a disturbing noise signal in a large antenna used for satellite communications. It was a weak microwave radiation that was observed continuously and from every direction in the same strength.
Initially they thought pigeon droppings in the colossal antenna were the cause, but even after a thorough cleaning the signal remained present. Only after consultation with the research group of physicist Robert Dicke did it become clear that it was the ‘echo of the Big Bang’ – the enormously weakened remnant of the energy that filled the newborn universe.
The discovery of the cosmic background radiation is still seen as the strongest ‘evidence’ for the correctness of the big bang theory. Precision research into the background radiation provides information about the events just after time zero.
