Horizon investigates the cosmic dawn, the moment one hundred million years after the big bang when the first stars were born.

Particle physicist Professor Brian Cox asks, 'What time is it?' It's a simple question and it sounds like it has a simple answer. But do we really know what it is that we're asking?

From submariners who live on an 18-hour day to the railway clerk who fought to standardise time zones, and the cobbler who invented the first cheap watch, innovation expert Steven Johnson discovers the surprising journey of time in our lives. He locates the unsung heroes whose ideas transformed our world of time from the sundial to clocks accurate to billionths of a second.

Professor Brian Cox reveals how the fundamental scientific principles and laws explain not only the story of the universe but also answer mankind's greatest questions.

Professor Brian Cox seeks to understand the nature of time.