Main content
Sorry, this episode is not currently available

How Long is a Piece of String?

Horizon 2009-2010

Alan Davies tries to answer the proverbial question: how long is a piece of string? But the task soon turns into a mind-bending voyage of discovery where nothing is as it seems.

Alan Davies attempts to answer the proverbial question: how long is a piece of string? But what appears to be a simple task soon turns into a mind-bending voyage of discovery where nothing is as it seems.

An encounter with leading mathematician Marcus du Sautoy reveals that Alan's short length of string may in fact be infinitely long. When Alan attempts to measure his string at the atomic scale, events take an even stranger turn. Not only do objects appear in many places at once, but reality itself seems to be an illusion.

Ultimately, Alan finds that measuring his piece of string could - in theory at least - create a black hole, bringing about the end of the world.

1 hour

Last on

Mon 1 Oct 2012 22:30
Βι¶ΉΤΌΕΔ HD

More episodes

Previous

Why Do We Talk?2009-2010

Next

How Many People Can Live on Planet Earth?2009-2010

See all episodes from Horizon

Clips

See all clips from How Long is a Piece of String? (4)

Chapters

Timings (where shown) are from the start of the programme in hours and minutes

  • How Long is a Piece of String?: Introduction

    Alan Davies discovers that answering that question is much harder than he originally thought.

    Duration: 01:36

  • Different Types of Measurement

    Alan visits mathematician Marcus du Sautoy to help him find an answer. However, this creates more questions, which requires a trip to a place dedicated to measurement, the National Physics Laboratory.

    Duration: 10:15

  • Infinitely Long String

    Finding out the exact length of the string proves even more troublesome when Marcus proposes the string could be infinitely long, thanks to the theory of fractals.

    Duration: 08:34

  • A Physics Approach

    After leaving Marcus, Alan visits a physics teacher to see if measuring the string in atoms can help him find an answer. However, this means exploring Quantum Mechanics.

    Duration: 07:47

  • Two Places at Once

    Alan goes to a lab to explore the theory of Quantum Mechanics in more detail to see if his string can be in two places at once, confusing him even further.

    Duration: 08:40

  • Dead or Alive?

    Still no closer to an answer Alan is introduced to the theory that his string may have multiples lengths at the same time, all with the help of a stuffed cat.

    Duration: 06:48

  • Proving Quantum Mechanics Works

    Alan doesn’t believe Quantum Mechanics is important on a basic scale, but photosynthesis and the ability to smell might just change his mind.

    Duration: 08:26

  • End of the World

    If Alan was to find the most accurate way of measuring his string he could theoretically create a black hole.

    Duration: 03:45

  • Final Summary

    Trying to find the solution to this question has been a philosophical journey for Alan, but he still visits Marcus du Sautoy to tell him his personal answer.

    Duration: 03:09

Credits

Presenter Alan Davies
Participant Marcus du Sautoy
Participant Becky Parker
Participant Seth Lloyd
Producer Rob Liddell
Executive Producer Andrew Cohen

Broadcasts