All language subtitles for BBC World Service - A simple guide to chaos theory - BBC World Service (720p).English

Imagine, the year is 1905.

One day, the clock on the
tower in Berne, Switzerland,

is a little late.

Two minutes late, to be more
precise.

For that reason, a man who
lives near the tower does not

wake up at the same time
that he usually wakes up to

go to work.

Realising the mistake, he
becomes a little nervous.

It takes him a little longer to

get dressed, drink some
coffee and leave the house.

He leaves five minutes later
than usual. He is about to

cross the street.

Meanwhile, a banker gets
into his new car without

knowing that it has a
problem with the brakes.

Our man crosses the street
and doesn't see the car.

The man is run over and dies.

This man is no less than
Albert Einstein.

That year Einstein should
have published four works

that would become the basis
of modern physics.

Innovations like GPS, TV
screens, the semiconductors

that allowed us to create
laptops, never happen.

The computer, the laptop, the
mobile you are watching this

video on never come into
existence.

And this video... doesn't exist
either.

This sequence of events is an
example of what is known as

the butterfly effect, a

manifestation of Chaos
Theory.

For many centuries, the world
was explained through the

laws of Isaac Newton and
classical physics.

According to these laws, if

the current state of an object
is known, its future behaviour

can be predicted with
relative ease.

Chaos Theory questions this
deterministic vision: not

everything is predictable
anymore, nor does it work

like clockwork.

Since the 1800s,

mathematicians have raised
the idea that not all

phenomena could be
predicted by Newtonian laws.

But a meteorologist named
Edward Lorenz made chaos

theory a visible phenomenon.

It all started in 1961 when he
was working on a

mathematical model to
forecast the weather.

Lorenz entered data such as
temperature, humidity,

pressure, and wind direction
into his computer.

His computer would draw a
graph modelling what the

weather would be like,

not always accurate, but very
close to reality.

One morning, Lorenz decided
to verify some results.

He stopped the computer, to
save time, entered the

numbers himself, and went to
grab a coffee.

When he returned, the chart
was incredibly different from

the original.

At the beginning it started

out pretty similar, but in the
middle it presented a

completely different
trajectory.

Surprised, he checked the
numbers.

He found that the number he
had entered was three tenths

less than the number used by
the computer.

That difference, which

altered the trajectory so
much, is equivalent to a

particle of dust on the Eiffel
Tower, or one less feather

in the weight of a duck.

Lorenz deduced that this
experiment was not a special case,

that there were other
systems in which tiny

differences produced, over
time, monumental changes,

making everything seem

unpredictable... that the
flapping of a butterfly in

Brazil could, in theory, cause

enough of a disturbance to
spark a tornado in Texas.

Even though we have a good
idea of how the universe

works, there are no

measurements that allow us
to determine the exact

position and speed of every
atom in the universe.

And this "inaccuracy" in our

calculations makes
predictions difficult,

one of the reasons why long-term

prediction is impossible.

But chaos is not the same as
disorder.

Although chaos makes
predictions difficult, the

universe is not random
and

effects still follow causes.

And no matter how chaotic it
may seem, a system always

follows a trajectory towards a
certain point.

For example, in the
calculations Lorenz used for

his model, the
trajectory

created a pattern that
resembled the wings of a

butterfly.

Understanding these patterns

of chaos has practical
applications.

In the stock market it
reminds us that a slight

fluctuation can cause a
crisis

in the market
-

and that is
why we cannot speak of

predictions but of
probabilities.

In the human body, it allows us to understand the chaotic behaviour

of a heart with cardiac arrhythmia.

Even in human behaviour, the
butterfly effect can be used

to analyse social phenomena.
For example, how trolling on

social networks can be triggered
by a single negative comment.

Our universe continues to
obey the laws of cause and effect.

The sun will continue to rise
every morning.

The planes we build will keep
flying.

Ultimately, chaos theory
introduces an element of

uncertainty into our reading
of the Universe.

It reveals the limit of our
knowledge.