U of M builds telescope to peer into infant universe

CSE physicist leads team to South Pole

September 25, 2019

In the instant of its birth, the universe threw the mother of all tantrums, and this winter, University of Minnesota physicists are going to the South Pole to catch it in the act.

The team, led by College of Science and Engineering Professor Clem Pryke and colleagues at Harvard, Stanford, and Caltech, are installing a new composite telescope—the BICEP Array—they hope will capture gigantic ripples in the fabric of space called gravitational waves.

These perturbations were generated in an early, infinitesimally brief period of the universe’s life. Called the inflation epoch, it created our entire observable universe from a tiny subatomic speck. The inflation epoch holds a critical place in cosmology, the science of how the universe originated. Pryke and his colleagues want to confirm that the universe’s mind-bogglingly quick expansion—in just 10^-32 seconds—actually occurred by finding its signature in the sea of microwave-length light waves that pervade the sky.

When completed, the BICEP Array will comprise four telescopes, each scanning a different part of the microwave spectrum in search of a telltale feature known as B mode polarization.

“If we find it, it will be the smoking gun for inflation,” said Pryke, a physicist with the Minnesota Institute for Astrophysics.

The telescopes—also called receivers—of the BICEP Array will join several other similar telescopes already at the Pole. To minimize “noise” signals, the receivers operate at 0.25 degrees above absolute zero.

“The first receiver will arrive at the South Pole in mid-November and must be up and running by mid-February, when flights to Antarctica stop for the season,” Pryke said.

Pryke and his graduate students have tested receivers in the high bay of the University’s Physics and Nanotechnology Building on the Twin Cities campus, focusing on optimizing the mount, the cooling system, and the ability of all the various pieces of equipment to work well together. One researcher, Nathan Precup, will be stationed at the Pole for a year to operate the array. (For a peek a Precup’s life, visit his “Daily Antarctic Photo” webpage.)

A short history of light

The universe began with the Big Bang some 13.8 billion years ago. First came the extremely brief Planck epoch, followed immediately by the equally brief inflation epoch. Inflation produced all kinds of particles and disturbances, including the sought-after gravitational waves, which propagated through the newly expanded cosmos.

About 380,000 years later, the universe had cooled enough for the first true atoms to condense, opening up a path for light to travel freely.

That first light persists today as the cosmic microwave background (CMB) radiation, “an echo of the Big Bang” that fills the sky. The CMB was stretched to microwave wavelengths as the universe continued to expand.

If they were present, these gravitational waves will have produced a swirliness in the polarization pattern of the CMB—the so-called B-mode—that should be detectable when scanning large swaths of sky. (The polarization pattern refers to how the vibrations of light waves are oriented with respect to their direction of movement through space.)  

A mirror in time

Einstein’s theory of general relativity predicts the existence of gravitational waves. They have been observed emanating from cataclysmic mergers between two black holes and two ultra-dense neutron stars, but not from inflation. Finding gravitational waves produced by inflation would bring physics closer to its holy grail: a theory of everything that describes the four fundamental forces of nature.

Many physicists believe that during the Planck epoch, the universe was in an incredibly high energy state, and only one force existed. But it promptly split into four, which became electromagnetism, two forces that govern the atomic nucleus, and gravity.

Currently, quantum mechanics describes the first three, but theorists have been unable to bring gravity into the fold.

The lenses of the BICEP Array may become a mirror for the behavior of gravity before it split from the other forces, during a window of time “as close as we’re likely to get” to the Planck epoch, Pryke said.

Story by Deane Morrison

The BICEP Array is funded by the National Science Foundation.

Video credit: UMN Ph.D. student Mike Crumrine

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