What must astronomers compare redshift-inferred distances against to test if the rate of expansion is accelerating?
Answer
Independent distance indicators like Type Ia supernovae.
By comparing the distance inferred from redshift against an independent distance indicator, such as Type Ia supernovae, astronomers can test whether the rate of expansion is constant, increasing, or decreasing over time.
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Why Do Galaxies have a Redshift Proportional to Distance? - YouTube
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