Wisdom for the Modern Mind

Why Does the Universe Seem to Expand at Two Different Rates?

Imagine setting off on a long journey with two impeccably maintained navigation instruments showing different speeds. One insists that you are traveling at 67 kilometers per hour, while the other reads 73. You check the settings, replace the batteries, repeat the measurements, and discover that the disagreement refuses to disappear. In everyday life, you would look for a malfunction. In cosmology, a comparable discrepancy raises questions about how we describe the history of the entire universe. For decades, astronomers have measured how quickly space is expanding. Results obtained from the nearby and relatively late universe systematically differ from the value inferred from the light of…