What is dark energy?

Dark energy is the name scientists give to the unknown force that appears to be pushing the universe apart at an ever-increasing rate. In the late 1990s, astronomers studying distant supernovae discovered that the expansion of the universe is not slowing down under gravity as expected, but speeding up. To explain this, physicists proposed dark energy, a form of energy spread throughout empty space that produces a kind of repulsive pressure. It is estimated to account for roughly 68 percent of the total energy of the universe, while dark matter makes up about 27 percent and ordinary matter only around 5 percent. Despite its dominance, dark energy remains one of the greatest unsolved mysteries in physics, and scientists still do not know what it actually is. Discovering its nature could reshape our understanding of the cosmos.