In 1998, it was announced that very distant type Ia supernovae were dimmer than expected based on their redshifts. What did this imply about the state of the universe?

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The discovery that distant type Ia supernovae were dimmer than expected suggested that the expansion of the universe is accelerating. This was contrary to the then-prevailing idea that the universe's expansion was slowing down due to gravitational attraction. The implication of an accelerating universe led to the conclusion that there must be some form of unknown energy, later termed "dark energy," driving this acceleration.

In 1998, It Was Announced That Very Distant Type Ia