Amid simmering anxiety about the future of federally funded science, the U.S. government has quietly withdrawn support for cosmology’s next premier project, an experiment that would have given us the best read yet of the strangest chapter in our cosmic origin story.
Called CMB-S4—or Cosmic Microwave Background Stage 4—the project would have used a suite of new radio telescopes, constructed in Antarctica and Chile, to search the big bang’s faint, ancient afterglow for new clues about the universe’s earliest moments. First conceived in 2013 and repeatedly ranked as a top priority by the nation’s astronomers and physicists, the project carried an estimated $900-million price tag, which was set to be roughly split between U.S. Department of Energy and the National Science Foundation (NSF).
Yet in a terse, unsigned statement to project leaders on July 10, the two agencies declared they had “jointly decided that they can no longer support the CMB-S4 project.”
“We knew things weren’t looking good,” says John Carlstrom of the University of Chicago, the project’s principal investigator. “They had warned us that it was not the time to start any big projects, given all the budget areas and all the uncertainty. But whether they would continue to drag us out or have a clean break or try to do something—that was unknown.”
Without federal support, Carlstrom says, the project is essentially canceled. Although abrupt, the decision follows years of concern about the decay of U.S. Antarctic scientific infrastructure, exacerbated by hesitations from both agencies about starting big new projects in the face of ongoing federal budget uncertainty.
Still, the decision “is a tremendous loss for science and also for the U.S. as the leader in science. It’s a big blow to the community,” says Hitoshi Murayama, a physicist at the University of California, Berkeley, and chair of the once-a-decade Particle Physics Project Prioritization Panel, which in 2023 ranked CMB-S4 as the highest priority for construction. The project also received a high ranking in 2021 from the U.S. astronomy and astrophysics community via a similar but separate process, the Decadal Survey on Astronomy and Astrophysics 2020 (Astro2020).
“If the agencies are really saying it’s over, scientifically, that’s awful,” says Joel Parriott, the American Astronomical Society’s director of external affairs and public policy. “And for the people involved, that’s devastating.”
The universe burst into existence some 13.8 billion years ago, and the unfolding sweep of cosmic evolution eventually led to us.
“What kind of universe created intelligent beings that can go and look at the first instants and understand how everything evolved?” Carlstrom says.
Perhaps the most curious aspect of that beginning is the wealth of circumstantial evidence suggesting that in the first minuscule moments after the big bang, the universe underwent an almost inconceivably exponential expansion—a ballooning so violent it shook the fabric of the newborn cosmos. This “cosmic inflation” would have left indelible ripples in spacetime called primordial gravitational waves. Today they would be visible as subtle, swirly fingerprints in the big bang’s relict radiation. Known as the cosmic microwave background, or CMB, that radiation is a diffuse light that permeates all of space. CMB-S4’s flagship objective was to detect those signature swirls in the CMB and clinch the case for cosmic inflation.
“There are a few different signatures that would be consistent with inflation, and some of them we’ve already seen,” says Jo Dunkley, an astrophysicist at Princeton University. “But the tensor fluctuation—these gravitational waves—they would be much stronger evidence than we currently have.”
First observed in 1965, the CMB has become a treasure trove for cosmologists, who use it to look back in time and study the characteristics of the very early universe. But even after 60 years of observations, we’ve only scratched the surface of what’s possible to see in this faint light. With CMB-S4 and other next-generation observatories, scientists have aimed for multiple breakthroughs, ranging from precisely measuring the energies at play in the first instants of creation to constraining the properties of dark energy, the still-mysterious force that drives the universe’s accelerating expansion. Along the way, almost as a bonus, advanced CMB studies could also reveal new particles, clarify the nature of known ones (such as neutrinos) and identify the earliest seeds of sprawling galaxy clusters and other large-scale cosmic structures.
“The CMB is a way that we might learn about physics at scales that are completely inaccessible in any other way,” says David Spergel, a theoretical astrophysicist and president of the Simons Foundation.
To definitively detect—or rule out—those inflation-scrawled swirls, scientists need to make very deep and detailed observations of the CMB. That’s something best done from space, above Earth’s turbulent, troublesome atmosphere, following in the footsteps of a few earlier CMB-focused satellites from NASA and the European Space Agency. Today such a mission would cost billions of dollars, however, and wouldn’t be amenable to upgrades or enduring operations. The quest to seek out the swirls of the cosmos from Earth has always been a challenging endeavor. However, with the right conditions and technology, it is not only feasible but also more cost-effective. One of the few places on our planet where this is possible is Antarctica, specifically at the South Pole.
Rachel Mandelbaum, a physicist at Carnegie Mellon University, highlights the exceptional conditions at the South Pole that make it an ideal location for astronomical observations. Due to the Earth’s rotation, observers at the pole can continuously gaze at the same patch of sky, providing a stable and unobstructed view. This unique feature makes the Amundsen-Scott South Pole Station a prime candidate for hosting projects like CMB-S4.
CMB-S4, short for Cosmic Microwave Background Stage 4, is a cutting-edge project that aims to explore the cosmic microwave background, the oldest light in the universe. With a new five-meter aperture microwave telescope and an array of smaller telescopes equipped with state-of-the-art detectors, CMB-S4 will delve deep into the mysteries of the universe. The project plans to cover approximately 3 percent of the sky, offering unprecedented sensitivity and clarity in its observations.
In addition to the South Pole, CMB-S4 intends to set up two six-meter telescopes on the summit of Cerro Toco in Chile’s Atacama Desert. This high-altitude site, known for its dry and stable atmosphere, is already home to the Simons Observatory, conducting similar cosmological studies. The inclusion of these additional telescopes will enable CMB-S4 to conduct nightly observations of vast regions of the sky, mapping out visible matter and unraveling the secrets of the dark universe.
The allure of CMB-S4 lies in its potential to shed light on cosmic inflation, the rapid expansion of the universe in its early stages. With 550,000 detectors spread across its two sites, the project is poised to make groundbreaking discoveries in the field of cosmology. Suzanne Staggs, a physicist at Princeton University and co-director of the Simons Observatory, emphasizes the significance of the cosmic microwave background in understanding the origins of the universe.
Despite the scientific promise and strong support for CMB-S4, the project has faced numerous challenges. The harsh conditions of Antarctica, with its extreme cold, dryness, and remoteness, pose significant obstacles to building and operating sophisticated scientific facilities. The National Science Foundation (NSF), which oversees U.S. research in Antarctica, has long been aware of the aging infrastructure at its research stations and the need for upgrades.
In recent years, logistical and financial constraints, exacerbated by the COVID-19 pandemic, have hindered progress on infrastructure improvements in Antarctica. This has led to the suspension of new projects at the South Pole, including CMB-S4. NSF’s decision to restrict access to the South Pole in 2024 due to safety concerns and insufficient resources has dealt a major blow to the future of the project.
As the fate of CMB-S4 hangs in the balance, the scientific community is left grappling with the missed opportunity to unravel the mysteries of the cosmos. The setbacks faced by the project serve as a stark reminder of the challenges inherent in conducting cutting-edge research in extreme environments. Despite the obstacles, scientists remain undeterred in their quest to unlock the secrets of the universe, hoping for a brighter future for astronomical exploration. The National Science Foundation (NSF) has officially declined to move the CMB-S4 project toward its next design milestone, leaving scientists shocked and scrambling to chart a new course for their research. This decision came after NSF and the Department of Energy (DOE) raised concerns about the feasibility of the project at the South Pole site. The agencies posed a simple question to the CMB-S4 collaboration: Could the project proceed without the South Pole site? What if Chile was the only option?
In response, the collaboration submitted a proposal outlining a new plan that would shift the project to Chile at a reduced cost. By constructing one large telescope and a smaller array of dishes at Cerro Toco, and leveraging collaborations with other observatories, such as the Simons Observatory, the CMB-S4 team believed they could still achieve their scientific goals, albeit at a slower pace.
The revised plan, submitted in June, aimed to have telescopes operational by 2032, with combined results expected by 2040 or 2041. This timeline was a far cry from the initial expectations set in 2013, but the scientists remained determined to push forward with their research.
Despite the challenges and budgetary constraints, the CMB-S4 team remained hopeful about the future. They saw the shift to Chile as an opportunity to collaborate more closely with other projects and maximize the scientific potential of their work.
However, with mounting pressures and competing priorities, NSF and DOE ultimately decided to withdraw their support for the project. This decision left the scientific community reeling, but also determined to find alternative paths forward.
While the future of CMB research may be uncertain, scientists are exploring options to continue their work. Some suggest focusing on upgrades to existing experiments in Chile, while others propose collaborating with international efforts in countries like Japan and China.
Despite the setbacks, researchers remain optimistic about the potential for groundbreaking discoveries in the field of cosmology. As they navigate through this challenging period, they are committed to pushing the boundaries of science and unraveling the mysteries of the universe. The world of technology is constantly evolving, and one of the most exciting advancements in recent years has been the development of artificial intelligence (AI). AI has the potential to revolutionize countless industries, from healthcare to finance to transportation. But what exactly is AI, and how does it work?
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