Imagine peering into the vast cosmos and realizing that everything we know—our planet, stars, and even our own existence—makes up just a tiny fraction of the universe's true makeup. That's the mind-blowing reality fueling the Dark Energy Spectroscopic Instrument (DESI) project, and it's about to get some well-deserved spotlight!
After dedicating five years to creating a breathtaking 3D map of the heavens, covering distances from our earthly vantage point all the way out to roughly 11 billion light-years, the team behind DESI is taking a well-earned break to bask in recognition from their scientific colleagues.
Come January, DESI—a collaborative effort involving researchers from over 70 global institutions, including Yale University—will be honored with the American Astronomical Society's prestigious 2026 Lancelot M. Berkeley Prize for outstanding contributions to astronomy. This award celebrates not just DESI's achievement in producing the most extensive 3D universe map ever made, but also its ambitious quest to unravel the mysteries of dark energy.
Dark energy, you see, is this elusive, invisible force that scientists believe makes up about three-quarters of the universe's total mass-energy. Unlike the stars and galaxies we can see twinkling in the night sky, dark energy doesn't give off light or any detectable radiation. Our clues about it come from clever indirect approaches, like studying how distant galaxies are spread out in three-dimensional space. Think of it like trying to understand a hidden room in a house by observing shadows cast through the walls—it's tricky, but that's the detective work of cosmology!
And this is the part most people miss: the sheer scale of what DESI has accomplished. Enter DESI, stage left. By harnessing the power of the 4-meter Mayall Telescope at Kitt Peak Observatory in Arizona, DESI can capture light from up to 5,000 galaxies at once, plotting the positions of over 30 million galaxies and quasars across a full third of the entire sky. For beginners wondering what a quasar is, it's like a super-bright, ancient beacon powered by a supermassive black hole—kind of like the universe's own supercharged lighthouse.
The project is overseen by the U.S. Department of Energy's Lawrence Berkeley National Laboratory, bringing together a dedicated team of 750 researchers from around the world.
“DESI has exceeded expectations so far,” shared Charles Baltay, the Eugene Higgins Professor Emeritus of Physics and Astronomy at Yale's Faculty of Arts and Sciences and a founding member of the DESI initiative. “In fact, we're a bit ahead of our timeline.”
Other Yale-affiliated contributors to the DESI team include Nikhil Padmanabhan, an associate professor in physics and astronomy within the Faculty of Arts and Sciences; David Rabinowitz, a recently retired senior research scientist in physics; and Xinyi Chen, a 2024 Ph.D. graduate now at Ohio State University. Baltay and Rabinowitz are also part of Yale's Wright Lab.
In a recent conversation, Baltay put DESI into historical perspective, highlighting Yale's role in the experiment. The interview below has been edited for clarity.
What core scientific puzzle drives DESI?
Charles Baltay: It's the biggest question out there—what is the universe really composed of?
The cosmos contains far more stuff than what meets the eye. All the familiar elements—humans, worlds, subatomic particles, every page in every library—add up to maybe a paltry 4% of the universe's total matter. The remaining 96% remains a total enigma, and that's where we stand today.
Can you imagine anything more thrilling than uncovering the universe's hidden ingredients?
How does charting galaxies in 3D aid this quest?
Baltay: During the mapping, DESI searches for echoes of the universe's early intense heat, known as baryon acoustic oscillations—these are like ripples from the Big Bang's first 400,000 years. By measuring these oscillations, we can examine how galaxies are positioned and how they group together, then compare our findings with Lambda CDM, the dominant model explaining the universe's structure.
For those new to this, think of baryon acoustic oscillations as the universe's original sound waves, frozen in time, helping us measure cosmic distances like a cosmic ruler.
The Dark Energy Spectroscopic Instrument has crafted the biggest 3D map of the universe yet. Take a virtual journey through millions of mapped galaxies using DESI's data. (Credit: DESI collaboration and Fiske Planetarium, CUBoulder)
What discoveries has DESI uncovered thus far?
Baltay: It's reinforced the need for fresh physics theories to match what we're seeing.
Over two decades ago, my colleague Saul Perlmutter—a Nobel laureate from 2011—demonstrated that the universe's expansion isn't decelerating, as classic physics predicts, but speeding up.
This points to dark energy acting like a sort of anti-gravity, forcing everything apart. As we dig into all five years of DESI's data, we're eager to see if it hints that dark energy might vary over time. Early results from the first year suggest it could be evolving, rather than being the fixed cosmological constant proposed by Einstein.
How game-changing would such a finding be?
Baltay: It represents a monumental crossroads that could shape research for the coming decades.
In many ways, it's reminiscent of a century ago, when physics seemed solid and predictable—almost dull. Then came the revelation of atoms behaving unexpectedly, paving the way to quantum mechanics and relativity.
What role has Yale played in DESI?
Baltay: We engineered, constructed, and implemented DESI's Fiber View Camera, a crucial component for the entire operation.
This camera's job is to precisely align 5,000 optical fibers on the telescope's focal plane with targeted galaxies, enabling the capture of spectra needed to gauge distances to objects billions of light-years away. This lets us build a 3D picture of 30 million galaxies.
It took three or four years to refine, but without it, the whole experiment would grind to a halt.
On a personal level, how rewarding is witnessing DESI's triumphs and its promise for grasping dark energy?
Baltay: You invest years hoping to contribute to something groundbreaking—and this might just be that historic project.
Centuries back, Aristotle gazed at the heavens and declared the universe unchanging, with motionless stars. Later, Einstein saw his general relativity clashing with that view, introducing the cosmological constant as a countering force.
Then in 1929, Edwin Hubble revealed the universe's expansion, implying it should eventually slow. That notion held until 1999, when Perlmutter revived the cosmological constant concept.
Now, DESI is poised to potentially confirm if dark energy fluctuates over time, proving it's not Einstein's unchanging constant. We're living in an exhilarating era.
But here's where it gets controversial: If DESI's data truly shows dark energy changing, does that mean we have to toss out Einstein's elegant cosmological constant entirely, or could there be a way to tweak our understanding without rewriting physics from scratch? Some scientists argue this could open doors to new theories, while others fear it might complicate cosmology even further. What do you think—could this be the next big paradigm shift, or just a tweak in our models? Share your thoughts in the comments; I'd love to hear if you side with tradition or embrace the unknown!
