Parallel universes and quantum revolution | Christophe Galfard | TEDxParis

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From Louis de Broglie, Nobel Prize in physics in 1929, to Serge Haroche, Nobel Prize in physics in 2012, join Christophe Galfard in a scientific journey of a whole century to discover the theory behind Schrödinger's cat, the quantum world and parallel universes.

Have you ever asked yourself
about the actual nature of the universe?

I'm not talking about
any abstract universe but our universe,

the one in which we all live,
the one where you are now.

Have you ever thought about
what you body was really made of?

Or the air you breathe
or even the very chair you are sitting on?

If the answer is yes,

then you might have noticed
that around you

you can find clues
that can help you decode all that.

For example, if I grab my glass,
you see there is water in it,

and I throw it at you, here,

some of you would move aside a little.

Nobody in this room,
or anywhere else on Earth

ever thought that once
you throw the water,

it would stop halfway in the air
turn around and go back into my glass.

And why is that?

We all have this feeling
that some laws of Nature actually exist,

and that those very laws cannot be broken.

The aim of theoretical physics
is to figure out what those laws are.

One have to admit that, as humans,
we are rather good at that.

Just to give you an idea: since Newton,

we can all describe every single thing
that is happening around us,

including the state of objects.

That, we know how to do.

But since Newton,
we went a little further than that.

We even entered a world
that goes beyond our senses.

A world in which our intuition
no longer applies.

It is a wonderful world,
and I'll tell you why.

In 1905, Albert Einstein taught us

that light is made of
tiny pieces of energy.

In Latin, "tiny pieces"
would be translated as "quanta."

What Einstein and other fellows did,
was to open us up on a new world,

the world of quantum mechanics
and quantum physics,

a tiny world that is the world of
luminous rays.

I'll ask you to imagine that, for a
moment, you are in 1942 in Paris,

where a young scientist
just got his thesis published

He is 32, and his name
is Louis de Broglie,

and he states something extraordinary.

In support of his calculations,
he states the light that is around us,

and this matter
that your bodies are made of

are not that different from one another.

The matter would actually
be made of those tiny pieces of energy.

That would mean that matter itself
would follow the laws of quantum science.

And for this,

De Broglie achieved the dream
of every PhD student on earth

when receiving a Nobel Prize
for his thesis, 7 years later.

And that's not so bad after all.

On the founding fathers of quantum physics

immediately got his hands on this idea

and started to work on trying to find out

how the whole world
of the infinitely small works.

And guess what?

He succeeded in finding an equation

that he named the Schrödinger's equation.

It describes the way particles behave
within our universe.

In a few words, he did
for the world of the infinitely small

what Newton did for the world around.

If you shoot an arrow,
Newton would tell you where it will land.

If you throw a particle,

well, Schrödinger would tell you
what it will become.

Unfortunately, in the world
of the infinitely small,

particles are no arrows.

They are not even like small balls.

Instead, you have to imagine a kind
of cloud filled with small balls

that are either present or missing,
that exist or don't exist

and that are overlaid
and that are almost everywhere.

Schrödinger's equation describes
how this cloud will evolve through time.

what he eventually found was very strange.

Just to give you an idea

of what it could mean
from our world's perspective,

he came up with a thought experiment

he named the Schrödinger's cat experiment.

Here it goes: in this box, there is a cat.

(Mioawing)

It might have been sleeping.
Anyhow, there is a cat.

But there is more than a cat.

It didn't sound very happy,
because on its side

Schrödinger placed, and so did I,
a radioactive substance.

What is a radioactive substance?
It is a substance we can split into two.

That's why the first row had to sign
the legal discharge earlier,

it's radioactive in there.

So, we have a substance
that can be split into two

without us knowing in advance
whether or not it will happen.

So, there is this little substance inside

and with the one I place here,
there is a 50/50 chance it will break,

or be blown apart between now
and the end of the experiment.

But Schrödinger did not only did that.

With this little substance,
he added a device, as smart as sadistic,

that would release a poison
and eventually kill the cat

in case the substance blows away.

If on the contrary the substance
stays as is, the cat is safe.

The laws of quantum physics tell us
as long as no-one has looked inside,

as long as no-one opened the box,

the radioactive substance has blown away
but at the same time, hasn't.

It means the poison has
and hasn't been released.

Consequently, the cat inside
is not dead or alive, but dead and alive.

It sounds completely insane, I agree.

But after all, that's what maths
tells us, and they are positive.

If the laws of quantum physics
as we know them are correct

then Schrödinger and his equation
will tell you that in this box,

the cat is both dead an alive.

Let's have look.

(Miaowing)

Well, at least it's not dead,
which is good.

But you see, there was only one cat

as you might have expected
and you might be a bit relieved

that the cat is alive and not dead.

As for me, it disturbs a lot
that there is only one cat inside.

I believe in maths
and all the physics that's behind it,

and if maths says
that there should be two cats inside

the questions is:
where is the dead cat now?

It should then be there but is not.
So where is it?

As crazy as it sounds,

scientists are actually paid
to try and answer this very question.

(Laughter)

They were even paid for years.

Schrödinger published
this thought experiment in 1935.

For a decade after that, maybe even two,

almost all the scientist on earth
have been looking for the dead cat.

Up until a young American
named Hugh Everett III

came up with an incredible solution.

He thought to himself that if Einstein
and De Broglie were really right,

which seemed to be the case,

then light and matter are quantum

since our whole universe
is made of light and matter,

then, there is no reason at all
that the universe itself

would not be quantum.

And consequently, a superposition
within its different states,

where there are many possibles.

What he means is
that when I opened the box,

two cats were inside

and when I opened it,
our whole universe split into two:

one where we live now
and where the cat is alive,

and the other where it was dead.

This very universe
would be universe parallel to ours

that would remain forever.

At the end of one his lessons
on quantum physics,

Einstein told his students,

"If you understood what I said,
it means I wasn't clear enough."

(Laughter)

Hugh Everett III
didn't get the Nobel Prize

because he published
this paper with his thesis

on the contrary, he abandoned physics,
thinking it was rubbish.

(Laughter)

He might have been right though.

But at the time, to check his theory

would mean we would need to see
every single atom.

See them in their overlapping state,

to try them out
and actually observe them.

Then again, at this time,
it was experimentally out of the question.

But not now anymore.

At the end of 1990s,

in the Teacher Training College's
laboratories in Paris

Pr. Serge Haroche's team
succeeded in creating

an experiment categorized
as "Schrödinger's cat-like."

It wasn't with a cat,
but with big atoms and light.

And from this experiment,
he could see that atoms

were in overlapping states.

The same kind as a cat
both dead and alive.

He even saw those two states vanish
to leave space for only one,

and, in a certain way, to give birth
to the world we got used to living in.

This very experiment got him
the Nobel Prize in Physics 3 years ago.

We started in 1924
with Louis de Broglie's Nobel Prize

and arrived in 2012 with Serge Haroche's,

following an idea where we traveled
different times and lands.

Why did I tell you all this?

Why did we follow the hare-brain ideas
of all those loony scientists

talking about cats dead-alive cats
and parallel universe all over the place?

Is it of any use?

I could honestly understand
that you wouldn't get

why we actually fund research.

But, it turns out you'd be wrong.

From Broglie's discoveries
to Schrödinger's equation

many everyday life objects
have seen the light of day:

computers, mobile phones, lasers

and almost all medical equipment
you can find in a hospital.

But some of you will ask,
"What about Haroche's discovery?"

Well, it turns out that it allows for

a new industrial
and technology revolution.

By succeeding in considering
the cat as both dead and alive

he opened the way
to computers of the future

that they call quantum computers.

A quantum computer is a machine

that uses the overlay
of atoms state within its heart.

Does that makes sense?

Thanks to this system,
those small atoms and those machines

are capable of calculating
as if they were

in billions of different
parallel universes at the same time.

This means a single one of these computers
would make all of the computers

we have nowadays, look like abaci.

That's just that simple.

Fundamental research
is a rather understated discipline,

that can sometimes be completely secret.

Yet, it is the origin of many revolutions

and the genies behind them

can emerge anytime and anywhere.

Here is an example, Serge Haroche,
the same man we talked about earlier,

who was born in Casablanca, Morocco
and arrived in France when he was 12.

As a small digression,
I'd like to pinpoint the fact

if we had closed our borders back then,
France would have lost a Nobel Prize

and its hypothetical
and amazing applications.

(Applause)

Scientific knowledge
belong to every single person,

you, me, newborns here,
or somewhere else on Earth.

It is our duty to share and pass it on.

It is for everyone's sake
that I tell you this.

Besides, it is very likely
that, in the future,

a child from another country
will hold the keys of our future here

and not of a parallel universe.

Thank you very much.

(Applause)