Observations of distant supernovae in the late 1990s showed the expansion of the universe is accelerating rather than slowing under gravity, implying roughly 68 percent of the universe's total energy content is an unseen component dubbed dark energy. No experiment has yet detected it directly or explained its physical nature, whether a constant property of space itself or a dynamic field.
What would resolve this Direct physical detection or a theoretical account of dark energy that makes testable predictions distinguishing it from a simple cosmological constant, confirmed by independent observational surveys of cosmic expansion.
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