Astronomy writer Stuart Clark tackles some of the biggest questions about our universe, including gravity and dark energy. His book The Big Questions: The Universe is out now.

We send Heather Christie to the Secret Garden Party in Cambridgeshire, where she encounters a giant colour-reading eyeball and has a session with a sex scientist.

Joining the podcast for the "show and tell" news section are environmentguardian.co.uk's James Randerson and science correspondent Ian Sample. We discuss zombie ants, the heartbreaking tale of starvation at a seed bank in Pavlov, how sponges point to life earlier than previously thought and why the moon is shrinking.

WARNING: contains explicit sexual language.

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