It sounds like a simple question. But as comedian Alan Davies discovers, finding the answer involves a journey through maths, physics and quantum mechanics via the fundamental nature of the universe.

Measurement is something we take for granted. But imagine a world without it. No distance, no time, no weight, no mass. It would be impossible to describe what something looks like, where it is or how it relates to anything. Creating a system of measurement has allowed us to understand how the Earth revolves around the Sun, how time advances.

In Alan's attempt to find out how long a piece of string is, he encounters both the history and current understanding of measurement – a journey that takes him from the maths used to measure the extent of the visible universe right down to the physics of the smallest particles of matter – the quantum world.

Helping Alan are three leading scientists. Massachusetts Institute of Technology physicist Seth Loyd guides Alan through the disturbing world of the sub-atomic; Oxford University maths professor Marcus du Sautoy gives Alan the mathematical tools to make his measurements; and high school physics teacher Dr Becky Parker opens Alan’s eyes to the bizarre and counter-intuitive world of the atom. At this atomic level Alan discovers that his piece of string is fractal – made up of endless chains of self repeating patterns – and is therefore infinitely long. He discovers that time travels forwards and backwards and that thanks to such things as the uncertainty principle, the very act of measuring affects the nature of reality.

In this mind-bending program, Alan discovers that ‘how long is a piece of string?’ can lead to some of the most fundamental questions of the universe.

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“It was a fine idea, putting this maths-phobic funnyman in the presenter’s role, and made it an amusing journey” Daily Express