# How long is a piece of string? (2009) BBC HorizonHow Long Is A Piece Of String? (One Part)

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### Documentary Description

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.

Chapters
1. Chapter 1
How Long is a Piece of String?: Introduction
Alan Davies discovers that answering that question is much harder than he originally thought.
2. Chapter 2
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.
3. Chapter 3
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.
4. Chapter 4
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.
5. Chapter 5
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.
6. Chapter 6
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.
7. Chapter 7
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.
8. Chapter 8
End of the World
If Alan was to find the most accurate way of measuring his string he could theoretically create a black hole.
9. Chapter 9
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.
Source: BBC

How long is a piece of string?
Alan Davies leaves behind his role in the TV quiz show QI to explore the world of quantum mechanics for the BBC science programme Horizon. The stand-up comic admits to deliberately failing at physics so he wouldn't have to take the O-level. But after making a TV documentary, he says he now understands aspects of quantum mechanics.

"There is no point in my making the programme if I don't," he says. "They have to explain it again and again until I do understand." "They" are the physicists he meets in the programme - "I was always getting into trouble for calling them physicians instead of physicists," says Alan. "They showed me the aspects of quantum mechanics that are explicable."

Horizon set Alan what appeared to be a simple challenge. All he had to do was measure a piece of string. But the catch was he had to do it with absolute precision. And that turned into a mind-bending journey though the worlds of maths and physics, using quantum mechanics to try to work out where the individual atoms and particles that make up the string actually are.

Laser experiment
Quantum mechanics allows matter to behave as both particles and waves and to be in different places at the same time. Alan describes how this was demonstrated in a simple experiment using a laser and a special camera. A single wave of light, a photon, passes through two slits at the same time and creates an interference pattern.

"A photon... can't be split," says Alan "but it's clearly in two places at the same time which is very exciting". "I didn't understand that whole side of physics," he says. "The principle that light can be in two places at the same time is absolutely extraordinary".

But even if he accepts the idea now, he still finds it uncomfortable, which puts him "firmly in the Einstein Camp". That's what he was told by MIT professor of quantum physics Seth Lloyd. "It's the only time in my life that I'll be compared to Einstein," says the comedian, "unless my hair goes white and I comb it backwards." Alan's exploration of the complexities of sub-atomic physics in the programme involves playing the role of layperson, repeatedly posing the question, "How Long is a Piece of String?" of some of the world's top scientists?

"Scientists love that sort of question," says Alan, who claims to "thoroughly enjoy being told stuff. "I'm quite a curious person. I don't mind being the one who doesn't know things," he says, "a role I often play in QI."

But he admits his understanding of quantum mechanics is somewhat superficial. "It's like showing someone a microphone and expecting them to be a stand-up comic." "In the intervals waiting for a camera or the director, when you overhear them (the scientists) talking, their conversation may as well be in a different language."

But he is capable of dropping a reference to quantum computers into conversation.

"If you ask what will the world look like in the next century? These are the computers that are going to be changing the world. Seth builds them. I don't understand them."

As for his understanding of theoretical physics, "I liked the idea of all of humanity fitting inside a sugar cube because more than 99.9% of matter is space," he says.

"It's not QI. It's VI, very interesting."

Have his attitudes to science changed? "I'm more inclined to linger in the science pages of The Week magazine," he says, "But my principle obsessions are still watching sitcoms and football."

Alan Davies presents Horizon: How Long is a Piece of String at 9pm on Tue 17 Nov on BBC Two

Source: BBC News