What is the Dark Energy Survey (DES) and what is its purpose?

DES is a large astronomical survey designed to study dark energy by collecting data from hundreds of millions of galaxies to understand the universe's expansion and its possible drivers.

How many galaxies did DES observe, and over what years?

DES compiled information from about 669 million galaxies observed over 2013 to 2019.

What was unique about DES's latest results?

DES combined four different dark energy probes in a single experiment for the first time, yielding tighter and more trustworthy conclusions.

Why is combining multiple probes advantageous in cosmology?

Because the four methods are very different, their combination reduces model degeneracies and increases confidence in the results.

What future observatory is mentioned as a beneficiary of DES methods?

The Vera C. Rubin Observatory (formerly LSST) is highlighted as a facility that could perform similar work with methods DES helped develop.

The Dark Energy Survey | Investigating how the universe expands

Fermilab

Science & Technology3 min read2 min video

Jan 23, 2026|14,480 views|609|32

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Key Moments

TL;DR

DES unites four probes to pin down dark energy and guide future surveys.

Key Insights

The universe's expansion is accelerating, driven by dark energy which makes up about 70% of the universe's energy density.

The Dark Energy Survey (DES) collected data from 669 million galaxies over billions of light-years (2013–2019).

For the first time, DES combined four independent dark energy probes in a single analysis, improving robustness and precision.

Using multiple probes helps break degeneracies and strengthens constraints on cosmological models and gravity theories.

The results pave the way for future surveys, including the Vera C. Rubin Observatory, to further probe dark energy and gravity.

A Century of Clues: The Expanding Cosmos

The story begins with a century of observations showing galaxies receding from us, a clear sign that the universe is expanding. Early expectations were that gravity would slow this expansion over time. However, empirical work culminated in 1998 with the surprising discovery that the expansion is not slowing but accelerating. This acceleration led to the attribution of a mysterious component called dark energy, which now appears to dominate the energy budget of the universe. Dark energy is estimated to make up about 70% of the mass-energy density of the cosmos, yet its nature remains one of the deepest mysteries in physics. Understanding dark energy requires precise measurements of cosmic expansion and the growth of structure over cosmic time, which motivates large surveys like DES.

DES: Mapping the Cosmos with a Massive Galaxy Sample

The Dark Energy Survey (DES) ran from 2013 to 2019 and collected data on roughly 669 million galaxies lying billions of light-years away. The breadth and depth of this catalog enable multiple cosmological probes to be studied, including the distribution of galaxies, the bending of light by gravity (weak lensing), and the counts of galaxy clusters, all of which are sensitive to dark energy and the laws of gravity on large scales. The sheer scale of DES makes it possible to trace both the geometry of the universe and the growth of cosmic structures across a substantial fraction of cosmic history.

Four Probes, One Analysis: A New Milestone in Cosmology

In the latest results, DES combined four distinct dark energy probes within a single analysis for the first time. These probes—traditionally including weak gravitational lensing, galaxy clustering, Type Ia supernovae, and galaxy cluster counts—offer complementary ways to detect the imprint of dark energy on both the expansion history and the growth of structure. Each method has different systematics and sensitivities, so their combination provides a more complete and robust picture. This multi-probe approach marks a significant step toward a more holistic understanding of the cosmos.

Sharper Constraints, Fewer Degeneracies

By blending independent observational pathways, the DES analysis helps break degeneracies between geometry (the expansion rate) and growth (how structures form over time). The result is tighter constraints on the behavior of dark energy and on possible modifications to gravity. The combined data narrow the range of viable models, making it more feasible to distinguish between a cosmological constant, dynamic dark energy, or alternative theories of gravity. The approach also demonstrates how cross-checks across diverse observables strengthen confidence in cosmological inferences.

From DES to Rubin Observatory: A Roadmap for the Future

DES not only advances current knowledge but also charts the path for the next generation of cosmological surveys. The methodologies developed—especially the multi-probe combination and careful handling of systematics—are being carried forward to the Vera C. Rubin Observatory (formerly LSST) and its planned analyses. This continuity ensures that the insights gained from DES can be amplified with larger datasets and deeper observations, enabling more rigorous tests of dark energy models and alternative gravity theories as the next phase of cosmology unfolds.

Mentioned in This Episode

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Common Questions

Astronomers noted the expansion about a hundred years ago, and in 1998 they discovered that this expansion is accelerating, which led to the dark energy interpretation.