As the clocks go back, theoretical physicist Fay Dowker, philosopher Nikk Effingham and science fiction writer Una McCormack join Matthew Sweet get to grips with the weirdness of time travel.

Fay Dowker is Professor of Theoretical Physics at Imperial College London.Una McCormack's latest book is The Autobiography of Mr Spock.Nikk Effingham is Reader of Philosophy at the University of Birmingham and author of Time Travel: Possibility and Improbability

Producer: Torquil MacLeod

Radio 3 is broadcasting a series of programmes Capturing Twilight including a Free Thinking episode and an edition of Words and Music. On Sunday October 31st you can hear Music for the Hours - a day punctuated by moments of musical reflection. This is inspired by the daily rituals of the Liturgy of the Hours, also known as the Divine Office, which formed the basis of the earliest Christian services particularly in the monastic tradition. The music centres on medieval chant and the Renaissance vocal polyphony that arose from this tradition, with complementary choral works from contemporary composers, recorded specially for Radio 3 by the Tallis Scholars, directed by Peter Phillips. You can find details of the broadcasts on the BBC Radio 3 website.