Simons Observatory Begins Hunt for Echoes of the Big Bang in Universe’s Oldest Light

The hunt is on. From a vantage point high in the Chilean Andes, cosmologists with the Simons Observatory have begun searching for evidence of what happened in the minuscule fraction of a second that followed the Big Bang.

The observatory, which just completed its main construction phase, will make some of the most precise measurements ever taken of the oldest light in the universe. That light, known as the cosmic microwave background (CMB), originated about 380,000 years after the Big Bang and holds secrets of the universe’s birth.

“We’re taking the search for cosmic inflation to a new level,” says Simons Observatory co-director Suzanne Staggs of Princeton University. “Our instrument sensitivity breaks new ground for the field.”

Physicists predict that a period of rapid expansion of the newborn universe, called inflation, generated ripples in the fabric of space-time. Those ripples would have led to giant swirling patterns in the polarization of the CMB light called ‘B-modes.’ Despite decades of CMB observations, the swirls elude detection.

Their discovery would provide an unprecedented window into how the universe came to be and offer confirmation of the inflation theory, says observatory co-director Mark Devlin of the University of Pennsylvania. “A detection of primordial B-modes will tell us about the state of the universe in the first instants after its birth,” he says.

Humans have long gazed at the stars, wondering how the universe came to be, says observatory principal investigator Brian Keating of the University of California, San Diego. “With the Simons Observatory, we stand on the brink of uncovering answers rooted not in mere speculation but in the most precise and expansive data ever gathered by the world’s most advanced telescopes,” he says. “We are not just observing the cosmos; we are unlocking the secrets of our origins.”

A Cosmic Merger

The Simons Observatory team came from two earlier CMB projects: the Atacama Cosmology Telescope and the Simons Array. In 2014, mathematician and Simons Foundation co-founder Jim Simons proposed the collaboration as a way of creating a supergroup of top-tier CMB researchers.

“He brought together teams with a variety of expertise but a common goal,” Staggs says. The completion of the observatory’s main construction coincided with Simons’ 86th birthday on April 25, she notes. Sadly, Simons died a few weeks later on May 10.

The Simons Foundation is the primary funder of the observatory, which is named after Jim Simons and foundation co-founder and chair Marilyn Simons. Planned extensions have already been funded by the U.S. National Science Foundation, U.K. Research and Innovation and the Japan Society for the Promotion of Science.

Additional funding comes from the Heising-Simons Foundation, six founding institutions — Princeton University; the University of California, Berkeley, with Lawrence Berkeley National Laboratory; the University of California, San Diego; the University of Chicago; and the University of Pennsylvania — and additional collaborating institutions worldwide. In total, the collaboration includes more than 350 researchers from more than 35 institutions.

The Hunt

One of the primary science goals of the Simons Observatory is to help sleuth out what happened in the first decillionth of a second after the Big Bang (that’s a trillionth of a trillionth of a billionth of a second). In that fleeting moment, physicists believe the universe grew 100 trillion trillion times larger. That’s comparable to a bacterium growing to the size of a galaxy. Quantum fluctuations in the newborn universe ballooned into the cosmic distribution of matter we see in the modern universe. Those same mechanisms also generated ripples in space-time called primordial gravitational waves.

While the proposed inflationary period was a critical moment in the universe’s history, we can’t see that far back in time. The early universe was too hot and dense for light to travel very far. Only after 380,000 years did things cool off enough for light to move unimpeded through the universe. That light is the cosmic microwave background, which we see throughout the sky.

While the CMB originated hundreds of thousands of years after the inflationary period, the light was influenced by what came before it. The primordial gravitational waves created during inflation would have altered the CMB’s appearance.

Like the light passing through a pair of polarized sunglasses, light from the CMB can have a preferred orientation, or ‘polarization.’ Scientists have already spotted small variations in the CMB’s polarization caused by the early universe’s matter distribution. The gravitational waves from inflation would also have left subtle patterns called B-modes in the CMB’s polarization. Detecting those B-modes would provide unprecedented insights into the universe’s earliest moments.

“We are hot on the trail of a possible signal generated during the first billionth of a trillionth of a trillionth of a second after the Big Bang,” says Simons Observatory collaboration spokesperson Arthur Kosowsky of the University of Pittsburgh. “No one is sure if that signal remains large enough to see today, but we have a shot. Seeing it would be like winning the physics lottery — the science payoff would be immense.”

Mapping the CMB

The Simons Observatory comprises three 0.4-meter small-aperture telescopes (SATs) and one 6-meter large-aperture telescope (LAT), which together will offer unprecedented sensitivity to the polarization patterns in the CMB. As of late April 2024, two of the SATs are calibrated and taking measurements, with the third SAT slated to come online in the coming months and the LAT early next year.

The Simons Observatory’s size and innovative use of new technology enable it to make detailed maps of the CMB at several times the rate of previous efforts. Together, the observatory’s four telescopes will have 60,000 detectors gathering data — more than every other CMB experiment combined. Additionally, the observatory’s superconducting detectors operate at just 0.1 degrees Celsius above absolute zero, thanks to the same cooling tech used in quantum computers. Such low temperatures reduce the amount of noise in the collected data, enabling higher-sensitivity CMB maps.

“I am thrilled by how well our instruments are performing,” says Simons Observatory founding member Jeff McMahon of the University of Chicago. “I am even more excited by the scientific data these telescopes are starting to produce.”

The three SATs will together study a patch covering 20 percent of the southern-hemisphere sky, and the LAT will map 40 percent of the sky at a finer resolution. By combining the telescopes’ power with innovative software and data analysis, the Simons Observatory team will filter out noise from sources such as our galaxy’s dust to improve the chances of spotting the sought-after B-modes.

Later, after about four years of operation, the observatory will get an upgrade — including 30,000 additional detectors — thanks to a grant awarded by the U.S. National Science Foundation to Devlin and Staggs. After the upgrade, the observatory will finish out its planned 10 years of measurements.

“Ten years might seem like a long time, but if you were to use the current capability, it would be 60 years before you would reach our planned sensitivity,” Devlin says.

Additional telescopes funded by Japan and the United Kingdom are scheduled to go live at the Simons Observatory in 2026, doubling the number of SATs.

Exciting Science

While there’s no guarantee that the observatory will detect the telltale swirls during its runs, Staggs says, “the lack of detection would itself give us information about what happened in the extremely early universe — an epoch we have scarcely any other hope of probing.”

In addition to the B-mode hunt, the observatory will provide fresh insights into the universe’s age, the distribution of dark matter, the motions of our solar system’s asteroids, the mass of ghostlike particles called neutrinos, and more. “There’s so much to be excited about,” says Simons Observatory founding member Kam Arnold of the University of California, San Diego.