The Italian physicist Carlo Rovelli delves into the meaning of time. He tells Andrew Marr how we live in a timeless world but have evolved to perceive time's flow.

The astrophysicist Carole Mundell is interested in the extragalactic. Her studies of the universe beyond our Milky Way help expand knowledge of cosmic black holes and explain powerful explosions in space.

Space travel is the new frontier, but exactly 250 years ago the Endeavour set sail from Plymouth seeking to test the limits of scientific understanding. An exhibition at the British Library, curated by Laura Walker, tells the story of Captain Cook's world-changing voyages and their studies into the skies, seas and lands beyond our shores.

And the marine biologist Helen Scales is more interested in exploring the world beneath the oceans. Her latest book marvels at the wonders of fish, from centuries-old giants to tiny restless travellers moving in shoals across our globe.

Producer: Katy Hickman.