It’s one of the biggest puzzles in cosmology. Why two different methods used to calculate the rate at which the universe is expanding don’t produce the same result. Known as the Hubble tension, the enigma suggests that there could be something wrong with the standard model of cosmology used to explain the forces in the universe. Now, recent observations using the new James Webb Space Telescope are shaking up the debate on how close the mystery is to being resolved.

In this episode, Vicent J. Martínez, professor of astronomy and astrophysics at the University of Valencia in Spain, and his former teacher, Bernard J.T. Jones, emeritus professor of astronomy at the University of Groningen in the Netherlands, explain why the Hubble tension matters so much for our understanding of the universe. Also featuring Lorena Sánchez, science editor at The Conversation in Spain.

This episode was written and produced by Katie Flood with assistance from Mend Mariwany. Eloise Stevens does our sound design, and our theme music is by Neeta Sarl. Gemma Ware is the executive editor. Full credits available here. A transcript will be available shortly. Subscribe to a free daily newsletter from The Conversation.

• Tensión sobre la tensión de Hubble (in Spanish)
• Great Mysteries of Physics: a mind-blowing podcast from The Conversation 
• The universe is expanding faster than theory predicts – physicists are searching for new ideas that might explain the mismatch
• Cosmological models are built on a simple, century-old idea – but new observations demand a radical rethink