Euclid science: five mysteries Euclid will help solve

Peering into the Universe beyond our galaxy, ESA’s Euclid will try to untangle the mysteries of the cosmic web to address five fundamental questions in cosmology:

• What is the structure and history of the cosmic web? 
• What is the nature of dark matter and dark energy? 
• How has the expansion of the Universe changed over time? 
• Is our understanding of gravity complete? 

95% of the Universe appears to be made up of unknown “dark” matter and energy. Scientists estimate that dark matter makes up 25% of the Universe and dark energy 70%. Dark matter and energy affect the motion and distribution of visible sources, but do not emit, absorb or reflect any light. Scientists do not know yet what these entities actually are or whether our current understanding of how gravity behaves on the very large scale is completely correct. Revealing the nature of dark matter and dark energy, and testing the behaviour of gravity over the largest distances, are among the most compelling challenges of cosmology and fundamental physics today.

Euclid is ESA’s space telescope designed to explore the dark Universe. The mission will create the largest, most accurate 3D map of the Universe ever produced across 10 billion years of cosmic time. Euclid will explore how the Universe has expanded and how large-scale structure is distributed across space and time, revealing more about the role of gravity and the nature of dark energy and dark matter.