WHAT EUCLID WILL MEASURE: BARYONIC ACOUSTIC OSCILLATIONS

When the early Universe first expanded, the formation of protons and neutrons created sound waves (bubbles) that rippled through the hot particle-radiation soup. About 300,000 years after the Big Bang, when the Universe had cooled down enough for atoms to form and light to travel freely, these waves froze in place. Over time, slightly more galaxies formed in clusters along the frozen ripples. The ripples stretched as the Universe expanded, increasing the distance between galaxies.

Euclid will study the distribution of galaxies over immense distances, teasing out these ripple patterns and determining their size. This enables us to measure accurately the accelerated expansion of the Universe and teaches us about the nature of dark energy and dark matter.