The Expansion of the Universe

Nobel Prize–winning astronomer Adam Riess helped discover that the universe isn’t just expanding—it’s accelerating. The force behind this cosmic push was dubbed Dark Energy, one of the greatest mysteries in modern physics. But decades later, dark energy remains unseen and unexplained.

Now, the story has taken another turn. As Riess continues to refine measurements of the universe’s expansion rate, his results clash with other leading observations. This growing discrepancy, known as the Hubble Tension, is pushing cosmology toward a potential crisis. If it doesn’t resolve, our understanding of the universe’s past—and its fate—may need a radical rethink.

Janna Levin, Pioneer Works Founding Director of Sciences, sat down with Riess and cosmologist Licia Verde to explore one of the hottest questions in science today: What is really driving the expansion of the universe, and what will it mean if we’ve been wrong all along? ♦