DESI’s Hubble diagram plots a characteristic pattern – baryon acoustic oscillations, or BAO “bubbles” – at different ages of the universe. The amount of dark energy determines how fast the universe grows, and therefore the size of the bubbles. The solid line is how big Lambda CDM predicts the bubbles will be, while the dashed line shows the prediction from a different model where dark energy evolves with time. DESI will gather more data to determine which model is a better description of the universe.

A simplified explanation of the different parts of DESI’s Hubble diagram.

This artist’s rendering shows light from quasars passing through intergalactic clouds of hydrogen gas. Researchers can analyze the light to learn about distant cosmic structure.

As light from a distant quasar passes through gas in space, certain wavelengths of light are absorbed. Plotting the absorption lines reveals the “Lyman-alpha forest” (emphasized here in brown and green) and provides information about the distant clouds of gas between us and the quasar.