Time doesn't exist | Carlo Rovelli | TEDxLakeComo

Carlo Rovelli is a theoretical physicist known for his work on quantum gravity. He has worked at the Sapienza University of Rome, Imperial College in London, and at the University of Pittsburgh and at Yale University in the United States. He is a professor at the Theoretical Physics Center at Aix-Marseille University, a senior member of the Institut Universitaire de France (IUF) and of the International Academy for Philosophy of Science (IAPS), and professor at the Beijing Normal University. He has devoted himself particularly to the philosophy and history of ancient science and has recently published a text on the Greek philosopher Anaximander, "The First Scientist," (Mondadori, 2011). He collaborates with "Il sole 24 ore" and "La Repubblica."

This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Learn more at http://ted.com/tedx

Time.

Time does not exist.

I have 15 minutes to convince you of it.

Take two watches.

Hopefully better than these old-fashioned
pocket watches of my grandfather.

A bit more precise, okay?

Make sure that they show the same time.

They show the same time, the same as here,

around 2:45.

Now, try raising one of them
and lowering the other.

Keep them like that for a while:

one, two, three.

Then bring them back together

and see what they show.

If the watches are a little more
precise than these,

they no longer show the same time.

The watch held higher reads faster,

and the watch held lower reads slower.

This is a fact.

Obviously, with watches like these,
it's not very easy to see that.

They're not precise enough.

However, today there exist
extremely precise watches.

That's one of them.

It's the Boulder atomic clock in Colorado,

one of those that are used to fix
the official time in the United States.

We have similar ones
in Italy, in Florence, lots.

There are also smaller versions,
more commercial versions,

that are good enough
to observe this effect with.

They are in small boxes.

If you take one and put it low down,

and put another high up,

when you bring them back together again,
they no longer show the same time.

Time goes faster higher up,

and slower lower down.

It's a fact.

For instance,

imagine you have a twin brother,

you are the same age,
you grew up together.

Imagine that your brother
goes to live in the mountains,

and you go to live by the sea.

If much later you meet up again,

your brother will be older,
and you will be younger than he.

It's not just watches that are influenced

by the strength
of the gravitational field,

but all phenomena connected with time.

Aging, the speed of our thoughts,
a flower coming into bloom.

Everything.

A swinging pendulum.

Time goes faster higher up,
and slower lower down.

You see, when at the beginning of the 90s,

the first satellites for GPS
were sent into orbit,

for the sat nav devices
we have in our cars

to tell us where we are,

physicists told engineers,

"Be careful, up there,
on the satellites, time goes faster."

To work, the device needs to receive
messages from a satellite.

On satellites, there's a clock.

The clock goes faster than
what we would expect down here,

so they'd need to take that into account.

The engineers said, "Oh, okay."

However, the entire project was, and is,
a project of the American military.

GPS is operated by the US military.

So, heading up the project
were American generals.

The American generals were army generals.

When told time goes slower,
faster, etc., their response was:

"Time goes slower? Faster?
I don't believe it."

So, the first satellites were sent up
with a double system

that could work taking or not taking
into account this effect.

The version that didn't take
this effect into account didn't work.

The GPS would not work

if it didn't take into account
the fact that up there time went faster.

So, even the American generals
could not be other than convinced

that time went faster up there.

What does this mean?

It means time is not
what we imagine it to be.

We cannot think of a unique time
that flows the same everywhere.

Somehow, we need to think

that higher up, lower down,
more to the right, more to the left,

for who moves more slowly,
for who moves faster,

time goes at different speeds.

We need to change how we see the world,

from a single clock beating the time,

to many clocks, each with its own time.

The world is a choir of these clocks
that go at different speeds.

Strange and difficult.

But if you think about it,

it's not the first time we've changed
how we see the world, is it?

Is the Earth flat or round?

This room, is it stationary
or is it moving?

Stationary.

No, we know it's moving,
travelling very fast around the sun.

(Hesitation)

A swallow comes from another swallow,

its mother was a swallow,
its grandmother, and so on,

swallow, swallow, swallow.

I was born from a human being,
who was born from another human being,

from another human being.

So it's impossible I and a swallow
share the same ancestors.

Not the case.

We and the swallows
have the same, common ancestors.

So, what's this all about?

We tend to develop simple,
natural ideas about the world

that are wrong.

Not because they are
not adaptable to our lives.

They are adaptable to our lives,
indeed that's the case;

they refer to, are good on, our scale.

They are no longer good
when we look at life,

not on a scale of 10, 100 or 1,000 years,
but on a scale of millions of years,

or when we think about
what happens very far away,

with very fast, very small,
or very big objects.

There's an example I really like
and think useful in understanding time,

that about high and low, right?

Things fall from high to low.

That is high, and this is low.

It's one of the basic structures
of the world as we see it.

We organize our world
in terms of high and low, right?

So in the universe, there's high and low.

Okay? A universal direction,
which is higher or lower.

This isn't entirely true.

What's high here is low in Sydney.

What's more, if we leave the Earth,
there's not really high and low.

Astronauts, we saw the pictures,
they move in any direction.

The notion of high and low
doesn't exist out there in the universe;

it's a notion appropriate only here to us.

It's convenient and useful
to organize phenomena around us,

but it becomes useless and meaningless
the moment we leave our planet

and go to the moon, as our astronauts did.

In all these cases, we find our simple way
of looking at the world is wrong,

and things are a little more complicated.

The nice thing is that
in all these cases, including time -

I'm coming back to time -

Nowadays, it's easy to think
that the Earth is round,

and that outside of it
there's no high or low.

We've seen the pictures taken
by the astronauts of Apollo 11

on their way to the moon.

The Earth is round.

But we knew that before.

Some of us already knew
that the Earth was round, right?

Aristotle knew, Anaximander knew
that the Earth was round and flew.

The Earth is moving.

Now we've seen it from beyond it,

but Galileo and Copernicus deduced it
without needing to see it.

Darwin didn't see
species change; he deduced it.

How did they deduce these things?

Simply by starting
with what we know about the world,

observing, and putting
together known facts,

and noticing that the known facts
can be better understood

if we change our conception
of the structure of,

our way of looking at, the world.

In this way, all these people came
to understand something new,

something crucial.

The fact that time goes
slower lower down and faster higher up,

that we nowadays observe:

we just need to buy
those very precise clocks,

and anyone can see it's the case.

It was understood before it was observed,

by Einstein,

almost 100 years ago,
97 years ago, in 1915,

who was simply trying to clarify the ideas
of the physics of the world of his day.

On one hand, Einstein had Newton's theory,
the great theories of mechanics;

on the other, he had electromagnetism.

Endeavouring to combine these two things

in order to have
a coherent picture of the world,

he realized that time doesn't go
at the same rate for everyone,

that there are many different times,
that time goes at different rates.

This was 100 years ago.

The same thing is happening today.

Because, today, we are again
in the same situation.

Today, we have the great inheritance
of Einstein's very beautiful theories,

which, for a century,
we have discovered work perfectly.

We have confirmed them,

we've seen there are black holes, etc.

Alongside it, throughout the 20th century,
quantum mechanics was advancing.

This morning we heard Marco telling us
about the world of particle physics,

all in terms of quantum mechanics,
an outstanding theory of motion,

but which doesn't work well
with Einstein's theories,

with general relativity.

So science tried once again
with endeavors

to use what we know
to try to gain greater insight.

In 1963, two brilliant America scientists,

Joe Wheeler, the man
in the black and while photo,

and Bryce DeWitt, the man
in the color photo,

simply took Einstein's
general relativity equation,

Einstein's theories,

and quantum mechanics,

and put them together
and wrote an equation

that Wheeler called "DeWitt's Equation,"
and Dewitt "Wheeler's Equation,"

and everyone else, a bit fed up,
"Wheeler-DeWitt's Equation."

It's that one there,
but I won't go into details.

An equation that to start with
was very confusing.

It was studied a lot,
and today we continue to study it.

Today, the theory has been developed,

and we can write it more precisely,

and we can better understand
its significance.

That's what I work at.

This equation has a characteristic
that was stunning at the time,

and left everyone open-mouthed.

This equation was created putting together
all that we know about the world

from one end to the other.

It has the characteristic as follows.

All equations, if you remember
something of school physics,

all the important fundamental
equations of physics

from Galileo to Newton,
Maxwell, Einstein, and so on,

they say how things change with time -

back to time again -

and so they all have "t," time, in them,
whether it's velocity or acceleration,

changes in time, there's always
time in the equations.

This equation here
doesn't have time in it,

the variable "time" has been left out,
it's vanished, it's not there.

It's as if trying to write
all we know about the world,

time is no longer there.

What does this mean?

That is what I'll try to explain
in the remaining four minutes.

If you listen to me carefully,

I hope I'll be able to make clear to you

what it means to write an equation
to describe the world without time.

Let's go back to simpler physics.

The first thing that those
who enroll in physics study

is how a pendulum moves, for example,
or something else that moves.

We need to describe
how its position changes with time.

So we need to measure the position
and the time with a clock, right?

We look at the position
and what the clock reads,

make a chart,

and write an equation that describes
how the position changes with time.

But, here, we are not observing time;

here, we are looking at
the hand's position, right?

The hand is moving,

and this is moving.

We're just describing
how this position shifts

when the hand's position shifts.

And if you think about it,
it's what we always do.

We always describe something
as a function of something else.

Clocks are just things
among others that move,

but that have the characteristic
of all moving together ...

more or less all together.

What does this mean?

It means that we can do without time

and just talk in terms of
how the pendulum moves

as a function of the position of the hand.

Instead of saying,
"I woke up at 8 this morning,"

I could say that I woke up
when the sun was in a given position,

that I started talking
the moment the lights went off,

and so on and so forth,

with no reference to time at all.

Let's take "high" and "low," for example.

I could say this is high, and this is low,

or I could avoid mentioning
"high" or "low."

I could say this is towards
that bright light there,

and this is towards
the red circle underneath me.

If I'm on Earth, I complicate life.

But if I'm an astronaut in a capsule
and say to my friend,

"Hey, Anderson, could you pass me
that clock up there?"

he'll reply, "Where's up there?"

But if I say "the one towards
the red mat" instead,

he'll be, "Oh, the one
towards the red mat."

So the notion of high or low
is meaningless when we leave the Earth.

Well, the notion of time
becomes meaningless, disappears,

as soon as I leave normal space

and enter one where I have to use
quantum gravity, this equation here.

And where is this space?

Where things are extremely big
or extremely small:

there where we're still without
clear ideas on the world.

If we observe the extremely small,

observe on an extremely small scale,

space, space itself fluctuates, spikes,

it's like a stormy sea,

but what it is, is space-time
in the extremely small,

as if time jumps.

These two clocks, each weaving
its own path at a different speed,

in the smallest of places, they go
forward and backward, they move, etc.

On this extremely small scale,

our notion of time is no longer good,
no longer useful, no longer works well.

So we have to re-describe
the world in terms of those variables,

one by one, without reference to time,

as if we had a lot of clocks
that had lost their hands,

and we could only see
how one moves in respect to the other.

Imagine, to give you an idea,

how we think about the world
as a combination of things that move,

that change, that dance, all together,

in time to a conductor of an orchestra

who gives the beat:
1, 2, 1, 2 ... all together ... 1, 2.

This picture no longer works
for the small.

In the extremely small,
there's no unique beat for all,

and the world is as if it were a dance
of every microelement with its neighbor,

but not all together.

What's the moral of this whole story?

Time is a useful concept,

it organizes our daily experiences,

but it is not a fundamental concept.

Just as "high" and "low"
are very useful concepts,

but don't work anymore
when we leave our everyday surroundings.

This is true of a lot of things.

It's this that I love about science.

What science teaches us
is that our image of the world,

our perception of the world,

is very often wrong, limited,

working only in our usual surroundings.

The human race is like
someone born in a small town

where everyone behaves in the same way,

until they leave and say,
"Oh, but there's more.

We can eat different things,
say different things,

speak different languages,
have different ideas."

Humanity leaves behind
the smallness of its thoughts

and discovers that everything's different:

species transform from one to another,

"high" and "low" are not real,

time is not what it seems.

The world is bigger, more beautiful,
more diverse, and more thought-provoking

than what it seems at first sight,

this thing, a little banal,
with "high" and "low,"

with people that move,
and rocks that fall.

It's much richer.

And to understand that,
we have little need of ancient knowledge.

Ancient knowledge, all ancient knowledge,

what our forefathers taught us,

really only applies here.

If we look a little further,
it's no longer valid.

As was said in the first video today,
the universe is endless.

We were born in a tiny,
little corner of it,

have ideas that apply
only to this tiny, little corner,

when we then start
to look a little further afield.

I think what we discover at each step -

and I'm concluding -

is far more extensive,
more beautiful, more complex,

than any of the ideas
our forefathers told us about,

or our moms and dads taught us.

And this beauty that overwhelms us,

this mystery that always lies before us

to which we gain access,
step by step, little by little,

but which forever remains boundless,

draws us, fascinates us,
and we want to get to see it.

This, for me, is science.

Thank you.

(Applause)