and she wants to share it.

There are so many ways to share an idea.

She could draw a picture,

make an engraving, write a song,

send a telegraph,

or an email.

But how are these things different?

And more importantly,

why are they the same?

This story is about the fundamental particle

of all forms of communication.

It begins with a special skill

you likely take for granted --

language.

All language allows you to take a thought --

or mental object --

and break it down in a series of conceptual chunks.

These chunks are externalized

using a series of signals -- or 'symbols.'

Humans express themselves

using a variation in sound and physical action --

as do chirping birds --

and dancing bees --

and man-made machines,

exchanging a dancing stream of eletrical vibrations.

Even our bodies are built according to instructions

stored inside microscopic books -- known as 'DNA.'

All are different forms of one thing -- 'information.'

In simplest terms,

information is what allows one mind to influence another.

It`s based on the idea of communication as selection.

Information -- no matter the form --

can be measured using a fundamental unit --

in the same way we can measure

the mass of different objects -- using a standard measure --

such as kilograms or pounds.

This allows us to precisely measure and compare

the weight of, say, rocks, water, or wheat --

using a scale.

Information, too, can be measured and compared

using a measurement called 'entropy.'

Think of it as an information scale.

We intuitively know that a single page

from some unknown book

has less information than the entire book.

We can describe exactly how much

using a unit called the 'bit' --

a measure of surprise.

So, no matter how Alice wants to communicate

a specific message --

hieroglyphics, music, computer code --

each would contain the same number of bits,

though in different densities.

And a bit is linked to a very simple idea --

the answer to a yes-or-no question.

Think of it as the 'language of coins.'

So how is information actually measured?

Does information have a speed limit?

A maximum density?

Information theory holds the exciting answer to these questions.

It`s an idea over 3000 years in the making.

But before we can understand this,

we must step back --

and explore, perhaps, the most powerful invention

in human history --

the alphabet.

And for this, we return to the cave.