The conversation between human and AI assistant.
Why is the rate of the expansion of the universe accelerating?
How was dark energy discovered?
Dark energy was first inferred in the late 1990s through observations of distant supernovae that revealed they were moving away at a rate faster than expected, indicating the universe was expanding at an accelerating rate. Further observations of the cosmic microwave background radiation and large-scale structures of the universe also support the presence of dark energy.