Quantum theory – our best understanding of the world at the smallest level – is famously weird and notoriously confusing. It’s a theory that seems to say particles can be in two places at once, or somehow “know” if you’re looking at them. Or at least, that’s what you might have heard. But is that really what quantum theory tells us about reality?

To find out, presenter Marnie Chesterton travels to the birthplace of quantum theory: the remote, windswept island of Helgoland. Here, a century ago, a young scientist called Werner Heisenberg made a leap of understanding that laid the foundations of quantum mechanics, and changed the world.

To mark a century of quantum, leading physicists from across the globe have gathered on Helgoland for a conference, and Marnie joins them with an unconventional plan. She’s allowed to ask them JUST ONE QUESTION, in the hope it can get to the heart of what this strange and difficult subject is really about: “What IS quantum?”

Presenter: Marnie Chesterton Producer: Anand Jagatia Editor: Martin Smith Production Co-ordinator: Jazz George