The universe and everything in it roared to life with the Big Bang approximately 13.8 billion years ago. It has continued expanding ever since. While we have a good understanding of the early universe, its fate billions of years into the future poses an equally puzzling question. Would gravity eventually collapse everything back together in the Big Crunch, or would our cosmological balloon continue expanding forever? The actual situation, as it turns out, is quite unexpected. In 1998, scientists determined the universe’s rate of expansion is accelerating. This Nobel Prize-winning discovery answered a big question, but catalyzed an even bigger one – how can this be happening?

Fascinated by this mystery, Dr. Katrin Heitmann, Physicist and Computational Scientist in the High Energy Physics Division at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, dedicates her career to understanding the mechanisms propelling the unexpected behavior of the cosmos. Her efforts in the field of computational cosmology also extend to her work as Computing Coordinator for the Large Synoptic Survey Telescope Dark Energy Science Collaboration.

Like many mysteries facing modern researchers, the questions Dr. Heitmann seeks to answer are perplexing. “The universe we can observe with traditional scientific methods represents about five percent of its total composition. It’s a bit unsettling to think we do not have a clear understanding of the dark matter and dark energy comprising ninety-five percent of the cosmos – what we often refer to as the Dark Universe,” said Dr. Heitmann. “Understanding the nature of these elusive cosmological building blocks means that we must develop comprehensive mathematical models, using available data, to simulate the structures in the universe and how they evolve.”

Cosmological simulations

Dr. Heitmann’s models and simulations run atop the specialized Hardware/Hybrid Accelerated Cosmology Code (HACC) developed in partnership with her colleagues at Argonne. HACC is the only cosmology code suite designed from the ground up for enormous-scale simulations regardless of a supercomputing system’s architecture. Dr. Heitmann, with the HACC team, also maintains responsibility for CosmoTools, the tool set involved with HACC’s analysis library.

“Naturally, the success of our work is dependent on obtaining the best data from which to create our mathematical models for dark energy’s impact on the expansion of the universe,” noted Dr. Heitmann. “Even some of the most advanced imaging devices, like the Hubble Space Telescope, cannot obtain enough sky area for our simulations. We need to cast the net wider. Using existing cosmological survey data obtained from satellites, telescopes, and ground-based antennae, we have access to optical data and also information extracted from other wavelengths, including gamma rays, microwaves, and radio waves.”

Combined, the mix of data creates a more holistic view of the universe, which in turn helps Dr. Heitmann and her team hone their models and simulations to mirror observations of our universe’s behavior.

Additional surveys, starting in 2022 using the National Science Foundation’s (NSF) and DOE’s Large Synoptic Survey Telescope (LSST) based in Chile, will augment existing cosmological data with more massive data sets captured at high resolution. Mapping billions of galaxies, each with billions of stars, represents a considerable undertaking. Using a mirror over 25 feet wide, LSST will capture 15 terabytes of data each night for over ten years, ultimately creating the most comprehensive survey of our universe. The resulting information will make essential contributions to Dr. Heitmann’s work, offering the nuanced details needed to understand the nature of the “Dark Universe,” and hone a mathematical model to emulate it.

Embracing HPC

Utilizing the massive data sets, which describe our ever-growing universe, necessitates the speed and scale of the world’s most powerful high-performance computing (HPC) systems.

“Many years ago, the desire to understand the nature of the Dark Universe captured my curiosity. In 2000, I joined the team at Los Alamos National Laboratory and had the opportunity to use the Roadrunner HPC system for cosmological research in 2008. At that time, Roadrunner represented cutting edge performance for demanding computational tasks. As our simulation and data requirements increased in size, though, that system had trouble keeping up with us,” she said.“More recently, Argonne National Laboratory’s Mira and Theta systems advanced work in important ways. Today, we use the Summit system at Oak Ridge National Laboratory. Summit offers remarkable performance in the 200 petaflop range, but our future simulations will benefit from even greater speed than the fastest supercomputers existing today.”

Moving to exascale computing with Aurora

In 2021, Aurora, one of the first exascale[*] computing systems in the United States, will arrive at Argonne National Laboratory. Based on the Cray Shasta architecture, with the underlying support of future Intel Xeon Scalable processors, a new X^e GPU architecture which will serve as an acceleration companion to the Xeon processors, and over 10 petabytes of memory, Aurora’s performance will exceed an exaflop which equates to a billion-billion calculations per second.

In preparation for Aurora’s deployment, the Argonne Leadership Computing Facility’s (ALCF) Early Science Program (ESP) awarded pre-production time on the system to researchers crossing a diverse array of scientific disciplines including health sciences, energy, chemistry, particle physics, and cosmology. The ESP project teams, including Dr. Heitmann’s, will be among the first researchers in the world to use an exascale system. In the process, they will pave the way for other scientific applications to run on Aurora.

“In the past, our simulations were done in smaller volumes. Simulations performed on Mira seemed fast at the time, but performing more extensive cosmological simulations faced practical limits due to computing power and memory. The Summit system can accomplish in one day the type of computations which took Mira several days. However, Aurora will exceed Summit’s speed by a factor of five. That level of performance will give us the ability to use more resolving models to achieve greater insights, at higher resolution, and in a much shorter timeframe,” noted Dr. Heitmann. “We’re very excited that our team will have early access to Aurora’s extreme-scale performance and run our simulations at a truly universal scale.”

Discoveries ahead

Over the next decade, especially with the forthcoming Aurora supercomputer, Dr. Heitmann anticipates critical discoveries in the field of computational cosmology she helps pioneer. “Our big hope for our research is obtaining is a deeper understanding of the Dark Universe – something we know little about today,” she said. “In ten years, we hope to have a deeper knowledge of the ninety-five percent of our universe we cannot observe directly. With new data, optimized models, and detailed simulations which reflect our direct observations of the universe’s growth, we will have a much better comprehension of how all the components of our cosmos fit together. I deeply enjoy what I do, and it’s very fulfilling to contribute to an understanding of – quite literally – the big picture.”

[*]  Editor’s note: Neither Intel nor the DOE has indicated publicly whether Aurora is expected to reach 1 exaflops Linpack performance, which we consider the minimum threshold for “exascale computing.”

About the Author

Rob Johnson spent much of his professional career consulting for a Fortune 25 technology company. Currently, Rob owns Fine Tuning, LLC, a strategic marketing and communications consulting company based in Portland, Oregon. As a technology, audio, and gadget enthusiast his entire life, Rob also writes for TONEAudio Magazine, reviewing high-end home audio equipment.

Feature image caption: The Helix Nebula is a large planetary nebula located in the constellation Aquarius. Source: NASA photo with artistic rendering (via Shutterstock)