How does the universe work?

Understanding the Forces That Shape the Cosmos

The universe is vast, dynamic, and filled with mysteries still waiting to be uncovered. Since the early 20th century, scientists have known that the universe is expanding—but in the 1990s, they made a remarkable discovery: the expansion is accelerating. This surprising result revealed the influence of dark energy, a force that now appears to make up nearly 70% of the universe and drives its continued acceleration.

At the same time, observations show that galaxies contain far more mass than can be accounted for by visible matter alone. This invisible substance—known as dark matter—makes up roughly 25% of the universe and acts as the framework on which galaxies and galaxy clusters form. Together, dark energy and dark matter dominate the cosmos, shaping its structure and evolution.

The Nancy Grace Roman Space Telescope, launching in fall 2026, will investigate these unseen forces with unprecedented depth and precision—shedding new light on the nature of dark energy, dark matter, and the large-scale structure of the universe. NASA also collaborates with international missions such as ESA’s Euclid, combining global expertise to advance our understanding of the hidden universe.

Through these efforts, NASA’s Astrophysics Division continues to explore the fundamental forces that shape everything we see—helping humanity understand not only how the universe works, but why it continues to evolve in such extraordinary ways.