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Cosmology is entering a potentially transformative period, and the Dark Energy Spectroscopic Instrument (DESI) stands at its centre. Recognized by the 2026 Gizmodo Science Fair, the DESI Collaboration has produced the largest high-resolution three-dimensional map of the universe, giving scientists an unprecedented record of cosmic history and new reasons to question their standard assumptions about dark energy.

Installed on the Mayall 4-meter telescope at Kitt Peak National Observatory in Arizona, DESI uses 5,000 remotely controlled, pencil-sized robotic positioners. Each robot directs an optical fibre toward a specific galaxy, allowing the instrument to collect thousands of spectra during every exposure.

Spectroscopy reveals how quickly objects are moving away from Earth and helps determine their distances, enabling astronomers to reconstruct the universe’s expansion over time.

DESI completed its planned five-year survey in April 2026, observing more than 47 million galaxies and quasars and over 20 million stars. Its map reaches across approximately 11 billion years of cosmic history and contains about six times as many galaxy and quasar measurements as all previous surveys combined.Because light takes time to travel, observing distant galaxies is equivalent to looking into the past: the farther away the galaxy, the earlier the stage of cosmic history that DESI records.

The universe has been expanding since the Big Bang. Gravity from ordinary matter tends to slow that expansion, so a universe containing only matter and gravity would be expected gradually to decelerate. However, observations of distant Type Ia supernovas in 1998 indicated that cosmic expansion is accelerating rather than slowing.

Scientists therefore proposed the existence of “dark energy,” a name for whatever produces this acceleration, although the term identifies an effect rather than explaining its underlying nature.

The simplest explanation is the cosmological constant, represented by the Greek letter lambda, \Lambda. In this model, dark energy is constant through space and time and constitutes roughly 70% of the universe’s total content. Its persistent repulsive effect causes the expansion of space to accelerate.Yet the cosmological constant is a description of the observed behaviour, not a complete physical explanation of what dark energy actually is.

DESI’s first three years of data produced an unexpected result. Although the observations broadly fit the standard cosmological model, the best-fitting parameters appeared to suggest that dark energy may change over cosmic time rather than remain constant.

This possibility would mean that the cosmological constant is incomplete and that dark energy might instead involve an evolving field, a new form of physics, or some presently unknown feature of gravity.

The evidence is intriguing but not yet strong enough to count as a definitive discovery. Independent observations and further analysis are required before scientists can conclude that dark energy truly evolves. The full five-year dataset should improve the precision of the test; the first comprehensive dark-energy results are expected in 2027.

DESI’s importance lies not only in its extraordinary scale but also in the openness of its data. Researchers worldwide can use the survey to test competing models of cosmic expansion, investigate galaxy formation, study dark matter, and examine the universe’s possible ultimate fate.

DESI will continue observations into approximately 2028 and is expected to expand its map before a later observing phase continues the project’s work.

Reference

Lee, G. (2026, October 1). The Largest 3D Map of the Universe is Shaking Cosmology to Its Foundations. Gizmodo.

About Coram Deo

Coram Deo — before the face of God. This blog reflects on Scripture, world events, science, music, psychology, and the human mind — always through the lens of Christian faith. All of life is lived before the face of God.