While there’s a growing unease about the trajectory of science funding in the U.S., the government has recently pulled its support for a critical cosmological initiative. This project, known as CMB-S4 or Cosmic Microwave Background Stage 4, was designed to probe the remnants of the big bang and provide unprecedented insights into the universe’s nascent stages. Planned for construction in the remote locales of Antarctica and Chile, the initiative was first proposed in 2013 and had since been a top contender for funding, earmarked with an estimated budget of $900 million, to be shared between the U.S. Department of Energy and the National Science Foundation (NSF).

On July 10, however, in a succinct, unsigned memo, the two sponsoring agencies stated their joint decision to discontinue their backing for the CMB-S4 project.

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“The outlook was bleak,” remarked John Carlstrom from the University of Chicago, who is the lead researcher of the project. The agencies had previously cautioned against launching substantial new initiatives amid financial uncertainties, leaving the future of the project ambiguous.

With the withdrawal of federal funding, the project is effectively dead. This abrupt termination follows prolonged concerns about the deteriorating condition of scientific infrastructure in Antarctica, compounded by both agencies’ reluctance to initiate major new projects in the current economic climate.

The decision is a significant setback not only for scientific advancement but also for the U.S’s leadership in global science, according to Hitoshi Murayama, a physicist at the University of California, Berkeley, and chair of the Particle Physics Project Prioritization Panel. The project had achieved top rankings in various reviews, including the 2021 Decadal Survey on Astronomy and Astrophysics 2020 (Astro2020).

“If they’re indeed pulling the plug, it’s a scientific tragedy,” stated Joel Parriott, director of external affairs and public policy at the American Astronomical Society. “It’s devastating for everyone involved.”

Ripples in the Dark

The universe came into existence about 13.8 billion years ago, setting the stage for cosmic evolution that eventually led to the emergence of intelligent life capable of investigating its origins.

“What kind of universe allows for intelligent beings who can explore the initial moments and understand the evolution of everything?” posed Carlstrom.

One of the most intriguing aspects of the universe’s early seconds is the theory of cosmic inflation—an exponential expansion that would have left behind spacetime ripples known as primordial gravitational waves. These waves would appear today as faint, swirling patterns in the cosmic microwave background (CMB) radiation—a pervasive glow filling the cosmos. CMB-S4 aimed to detect these swirls and provide definitive evidence of cosmic inflation.

“There are several indicators that would support the inflation theory, some of which we’ve already observed,” noted Jo Dunkley, an astrophysicist at Princeton University. “Detecting the tensor fluctuations—these gravitational waves—would be a much stronger proof than what we currently possess.”

Since its discovery in 1965, the CMB has been a crucial tool for cosmologists to peer back in time and analyze the conditions of the early universe. Despite decades of research, the potential to uncover new knowledge from this ancient light remains largely untapped. With CMB-S4 and other future observatories, scientists hoped to achieve breakthroughs in understanding the energies of the universe’s inception, the nature of dark energy, and the formation of the earliest cosmic structures.

“The CMB offers a unique window into physics beyond our current reach,” stated David Spergel, a theoretical astrophysicist and president of the Simons Foundation. “To conclusively detect or discount those inflation-marked swirls, deep, detailed observations of the CMB are necessary—a task ideally suited for space missions, which, while costly, avoid Earth’s atmospheric challenges.”

Antarctica, despite its harsh conditions, provides one of the few earthly vantage points suitable for such detailed cosmic observations. “The South Pole, in particular, offers a unique advantage,” noted Rachel Mandelbaum, a physicist at Carnegie Mellon University. “As the Earth rotates, the same section of sky remains in view.”

This makes the Amundsen-Scott South Pole Station an ideal location for CMB-S4, which would have featured a new large microwave telescope and several smaller telescopes equipped with cutting-edge detectors, capable of scanning roughly 3% of the sky with unparalleled sensitivity.

Additionally, the project planned to install two new six-meter telescopes at Cerro Toco in Chile’s Atacama Desert—a site already noted for its stable, dry conditions and minimal atmospheric distortion. These telescopes would have complemented the existing facilities, enhancing our ability to survey the cosmos and understand the darker, unseen forces at play.

In total, CMB-S4 would have featured 550,000 detectors across its two sites, offering an unmatched opportunity to explore the earliest light of the universe and its profound mysteries.

“The amount of science still to be gleaned from the CMB is staggering,” expressed Suzanne Staggs, a physicist at Princeton University and co-director of the Simons Observatory. “It’s a phenomenal resource for understanding the early universe.”

Given its robust scientific backing and multiple endorsements from leading panels, CMB-S4 seemed poised for eventual realization. “This project has undergone nearly every conceivable review and emerged with high acclaim,” Parriott remarked.

Initially, the team was optimistic about starting construction soon. However, delays began accumulating, leading to a series of disheartening realizations.

The Big Chill

Despite its scientific importance, the fate of CMB-S4 may have been sealed long ago. The primary challenge was its proposed location at the South Pole, where extreme conditions make it difficult to build and maintain sophisticated scientific facilities. Antarctica, being the coldest, driest, windiest, and most remote continent, rapidly degrades infrastructure.

The NSF, responsible for managing the U.S. Antarctic program, has been aware for over a decade that the facilities there desperately need upgrades. “If you haven’t been following this closely, you might think this is a broad government retreat from projects,” explained Mitch Ambrose, director of science policy news at the American Institute of Physics. “But the issues with Antarctic infrastructure have been building for a long time in the context of CMB-S4.”

In 2011, the White House and NSF convened a panel to assess the logistical challenges of maintaining U.S. scientific presence in Antarctica. The panel’s findings underscored the dire state of the infrastructure and the critical need for capital investment—a situation described as unsustainable for any successful operation.

“Continuing as is was not an option,” the report stated, highlighting such problems as a warehouse where forklifts could fall through the floor and buildings where snow blew inside through large gaps.

Following this, a report by the U.S. National Academy of Sciences echoed the need for significant infrastructure improvements. NSF began planning some upgrades, but then the COVID-19 pandemic hit, disrupting access to the sites and exacerbating supply chain issues, which significantly increased costs.

“Much of that planning went completely off track during the pandemic,” said Parriott. “It’s quite disheartening to see what has become of the U.S. Antarctic program.”

Since then, NSF has struggled to implement the necessary upgrades, casting a shadow over projects like CMB-S4. In 2023, NSF paused new projects at the South Pole, and by May 2024, it definitively informed the CMB-S4 team that the South Pole was no longer a viable option due to sinking buildings, inadequate electrical power, and insufficient housing for essential personnel. This led NSF to officially halt the project’s progression to its next design phase.

“When I first heard the news a year ago, I was utterly shocked,” said Staggs.

Subsequently, NSF and the DOE questioned whether CMB-S4 could proceed without the South Pole, asking if focusing solely on Chile might be feasible.

Charting a New Course

On June 4, the collaboration proposed a modified plan to both agencies, suggesting a path forward in Chile at about half the original cost. By building one large telescope and a smaller array of dishes at Cerro Toco and leveraging data sharing and collaborations with the South Pole Telescope, the Simons Observatory, and others, the team believed it could still meet its scientific goals, albeit more slowly and with less certainty.

“In the June proposal, we planned to scale back and collaborate with other experiments, which would allow us to construct fewer facilities. We hoped to have telescopes operational by 2032 and to combine results around 2040 or 2041,” Carlstrom explained. “When we began this project in 2013, I thought we’d be operational by 2020, and I could retire by 2025.”

Staggs, co-director of the Simons Observatory, mentioned that leaders of both projects had met several times over the past year to discuss the revised plans.

“Even before the need to shift to Chile became apparent, we anticipated that the two projects would eventually operate very closely, at least in terms of day-to-day operations, though specific details had not yet been worked out,” Staggs said. “We were hoping to start on that collaboration about now, especially given the news that CMB-S4 would need to relocate.”

Despite these plans, under severe budgetary constraints and with a ledger filled with fixed costs for maintaining existing facilities, along with a backlog of other projects waiting for construction, the agencies decided to withdraw their support.

“The agencies faced really tough choices,” Ambrose remarked. “There’s a significant tension here: the scientific community strongly desires this project, yet the agencies are unwilling to proceed.”

Knocked back by this setback, the scientists involved in CMB-S4 are now focusing on finding alternative paths forward.

“The quest for primordial gravitational waves will continue; it just won’t progress as quickly as we had hoped,” Spergel stated. “I hope this becomes an opportunity to reconsider how we conduct this science and not a step back from pursuing truly exciting and impactful research.”

In a statement to Scientific American, a DOE spokesperson affirmed that “the scientific case for CMB exploration remains strong and compelling” and indicated that the agency “intends to continue supporting CMB research,” which is a key aspect of the DOE’s high-energy physics program. This includes exploring opportunities for near-term enhancements to existing experiments at the South Pole and in Chile. (The NSF declined to comment.)

“If there were no ongoing projects, the situation would be different,” Dunkley added. “We’ll have to see how developments unfold: What extent of upgrades or continuation of existing projects can be achieved?”

One potential solution, according to Spergel, is to maximize construction in Chile to advance as much science as possible from that location and then consider shifting focus to the South Pole if necessary.

Another less frequently mentioned possibility among U.S. researchers is the potential need to relinquish leadership in CMB studies to other countries. For example, Japan’s space agency is spearheading the development of LiteBIRD, a space-based CMB mission set for launch in the early 2030s. Additionally, China’s Ali Cosmic Microwave Background Polarization Telescope (AliCPT) on the Tibetan Plateau has recently completed the first phase of construction, with scientific observations soon to commence. The U.S. is involved in both projects, primarily through hardware contributions from the federal National Institute of Standards and Technology, but plays only a supporting role. Despite ongoing U.S. support for CMB experiments in Chile, the definitive confirmation of cosmic inflation’s role in our universe’s early history may ultimately come from other nations.

“We’ll get there eventually,” Carlstrom said. “It’s just going to be much more challenging without the South Pole, and without substantial new equipment wherever we are, including in Chile.”