Why is dark energy making the universe expand faster?

In 1998, two teams studying distant Type Ia supernovae found that the universe’s expansion was accelerating. The simplest explanation is dark energy, a mysterious component that acts like a repulsive effect on cosmic scales. It appears to make up about 68 percent of the universe’s total energy content. One possibility is that it is a cosmological constant, a term Einstein introduced in 1917. Although its true nature remains unknown, dark energy strongly affects the future of the cosmos.