The Dark Energy Spectroscopic Instrument (DESI) is creating the largest 3-dimensional map of the universe.  It is designed to study the influence of dark energy on the universe's expansion over the past 11 billion years.  Since its survey start in 2021, it has mapped over 40 million galaxies and quasars.

The DESI Survey operates on the 4-meter Mayall telescope at Kitt Peak National Observatory. DESI conducts dark energy measurements using baryon acoustic oscillations and other spectroscopic techniques that map how fast matter clumps to form galaxies and other cosmic structures, a direct probe of how gravity works on the very largest scales.

Berkeley Lab is the lead DOE Lab for DESI and is responsible for the design,  construction, and data management.  Our group is active in all aspects of the science analysis. 

DESI's 2025 results challenge the standard cosmological model.

Contacts: David Schlegel, Stephen Bailey, Julien Guy, Natalie Roe, Nathalie Palanque-Delabrouille, Michael Levi, Pat McDonald, Martin White, Simone Ferraro, Alex Kim

DESI will be a transformative cosmological survey in the 2020s, mapping over 50 million galaxies and quasars and capturing a significant fraction of the available information up to redshift 1.2. This represents about 1% of the observable Universe, highlighting the opportunity for a compelling future spectroscopic roadmap for the Cosmic Frontier.

DESI-II, a proposed follow-up to DESI, will pioneer observations of galaxies both at much higher densities and at higher redshifts, opening up vast opportunities for future discoveries. 

Spec-S5, a Stage 5 spectroscopic experiment, would build out those high-density and high-redshift observations, mapping hundreds of millions of stars and galaxies in three dimensions, to address the problems of inflation, dark energy, light relativistic species, and dark matter. These spectroscopic data will complement the next generation of weak lensing, line intensity mapping and CMB experiments, allowing them to reach their full potential.

Contacts: David Schlegel, Stephen Bailey, Julien Guy, Natalie Roe, Nathalie Palanque-Delabrouille, Michael Levi, Pat McDonald, Martin White, Simone Ferraro

The Baryon Oscillation Spectroscopic Survey (BOSS) and its extension eBOSS were previous-generation galaxy redshift surveys, conducted at the Apache Point Observatory as part of the Sloan Digital Sky Survey.  LBL proposed the survey, designed the spectrographs, led the spectroscopic data processing efforts, and played key roles in science analyses.  The experience from BOSS directly led to the design and implementation of DESI.

Contacts: David Schlegel, Stephen Bailey, Julien Guy, Natalie Roe, Nathalie Palanque-Delabrouille, Pat McDonald, Martin White

The size and complexity of data generated by modern cosmological surveys make them uniquely well-suited for the application of artificial intelligence and machine learning (AI/ML) techniques. When paired with high-fidelity simulations on leading supercomputing facilities, AI/ML enables us to maximize the amount of information that can be extracted from both observational and synthetic data, often beyond the reach of traditional methods. These techniques are now integral to many aspects of cosmological analysis and experimental design.

Specific examples include spectroscopic target selection and classification, optimal methods for parameter inference, improved methods for BAO reconstruction, application of Large Language Models in cosmology, and strong gravitational lensing. 

Contacts: Uros Seljak, Simone Ferraro, David Schlegel

We are very active in the analysis of current and future LSS data, as well as the development of new techniques to maximize the amount of information that we can extract. 

Another major area of research is joint analyses of Large-Scale Structure surveys such as DESI and Rubin Observatory with the Cosmic Microwave Background. We collaborate closely with the CMB group to probe the growth and evolution of structure across Cosmic time, provide insights on the masses of neutrinos, and test our theories of how gravity works on the largest scales.

Contacts: Simone Ferraro, Pat McDonald, Uros Seljak, Martin White

The Lyman-alpha forest is a unique window to the high-redshift universe. The neutral hydrogen absorption measured along the line-of-sight of hundreds of thousands of distant quasars observed in large redshift surveys provides us with a rich data set to test fundamental physics and explore the properties of the IGM in the matter-dominated era. The group has expertise in data analysis with DESI (measuring cosmic expansion and growth of structure at z > 2) and hydrodynamical simulations (Nyx). 

Contacts: Julien Guy, Pat McDonald, Nathalie Palanque-Delabrouille

The Stage 5 Spectroscopic Instrument (Spec-S5) will be the premier instrument in the 2030s to probe dark energy, inflation physics, and the gravitational effects of dark matter within the Milky Way.  The galaxy survey will map 10X more linear modes from the early universe than the combination of DESI, Rubin Observatory and CMB maps.  Berkeley Lab is developing an innovative mirror system for Spec-S5,  as well as developing the fiber robot and CCD technologies.

Contacts: David Schlegel

Berkeley Lab has been at the forefront of developing CCDs for astronomy, specializing in the design and fabrication of thick, fully depleted p-channel CCDs. The group is developing low-read-noise CCDs using Skipper technology and Multi-Amplifier Sensing devices, reaching sub-electron read noise for read times compatible with astronomical surveys such as DESI-II and Spec-S5.  A long-term effort is underway to develop Germanium CCDs that could extend the wavelength coverage of optical spectrographs from 1.0 to 1.3 microns.

Contacts: Julien Guy, Stephen Holland

Berkeley Lab has been at the forefront of developing highly-multiplexed, robotic focal planes for mapping the universe.  For the DESI project, a robotic system was developed that simultaneously repositions 5000 optical fibers to the location of up to 5000 galaxies.  For a future Spec-S5 project, an active R&D program is developing technologies to further miniaturize such robots to increase this multiplexing. 

Contacts: David Schlegel