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SPIDER: Hunting for signals in universe’s oldest light

Balloon-borne telescope may help answer physicists’ most pressing questions
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Just a few weeks ago, on the very first day of 2015, researchers at the scientific McMurdo Station in Antarctica finally saw the successful launch of a balloon-carried telescope that has been in the works for over six years.

The project, which is called Spider, is one of the many enterprises in a recent surge in cosmologists’ hunt for the elusive “B-Mode polarization,” which is a signal in the primordial light from the early universe. This is also known as the Cosmic Microwave Background (CMB), which may hold the final proof of many current unresolved theories that are fundamental to contemporary physics.

The balloon, which successfully rose to its final height of 35 kilometres above the surface of Antarctica, will be nearing the end of its 20 day round-trip of the continent, where it has been taking advantage of the high altitude to collect as much unobstructed data of the very weak CMB signal as possible.

When Spider returns to the ground near its landing point of the McMurdo research station, its team — which includes Jamil Shariff, a PhD candidate at the Department of Physics and Astrophysics — is eager to finally be able to analyze the data and find whether or not it has discovered the long-hunted and highly specific patterns that so many cosmologists currently seek.

“What Spider is searching for specifically are particular patterns in the CMB polarization directions across the sky,” Shariff said in an email sent from the McMurdo station, written in between monitoring the device, “These patterns, characterized by ‘swirling,’ are known as B-modes.”

If the B-mode polarization is found, its discovery will act as a confirmation of the 30-year-old “inflation theory,” which states that the early universe underwent an extremely quick accelerating expansion at an age of almost one decillionth of a second, and inflated from an infinitesimally small size to something large enough to fit perhaps in the palm of your hand. This theory is an incredibly specific prediction for something that happened so long ago.

As it turns out, inflation theory would help explain some of physicists’ most fundamental unanswered questions. One of these questions addresses the problem of why the universe looks the way that it does.

“Inflation neatly resolves some outstanding questions in standard Big Bang cosmology,” Shariff explains, continuing, “So far, inflationary models are able to reproduce a universe in remarkable agreement with the observed properties of our universe.”

Additionally, the detection of the B-modes would be an indication of the existence of what are known as “primordial gravity waves,” and may help physicists develop a completely consistent quantum theory of gravity, which would help us fill even more gaps at the heart of our understanding of how the universe works.

In order to find these evasive polarization patterns, Spider is equipped with six telescopes that are sensitive to microwave light in two different frequency ranges.

“At the focus of each telescope is a camera whose several-hundred pixels consist of state-of-the-art detectors known as bolometers,” Shariff says, adding, “These bolometers act as very sensitive thermometers, changing temperature in response to variations in the amount of CMB light shining on them. That’s how we’re able to image the sky.”

In order to measure something as cold as the background temperature of space (which is just a few degrees above absolute zero), the telescopes and detectors need to be cooled as well, which is done by enclosing them entirely in a large vessel of liquid helium. This entire contraption — along with a whole host of GPS devices, gyroscopes, and various other sensors and machinery — must stay afloat and point in the right direction for the duration of the flight. This requires a pointing-control system, in which Shariff himself has had a hand in almost every aspect of the design.

“I guess you can say that I am the guy on the team who knows the best how to ‘drive the telescope,’” Shariff says.

After the recovery of the data, Shariff expects a one- or two-year process for it to be analyzed and the results released. In the meantime, there is already funding for a second flight. Improvements based on lessons learned from the current project will help Spider 2 bring us even closer to the goal of detecting primordial B-modes, if they are present.