WEBVTT

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Time.

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Time does not exist.

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I have 15 minutes to convince you of it.

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Take two watches.

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

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A bit more precise, okay?

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Make sure that they show the same time.

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They show the same time, the same as here,

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around 2:45.

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

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Keep them like that for a while:

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one, two, three.

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Then bring them back together

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and see what they show.

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If the watches are a little more
precise than these,

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they no longer show the same time.

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The watch held higher reads faster,

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and the watch held lower reads slower.

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This is a fact.

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

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They're not precise enough.

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However, today there exist
extremely precise watches.

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That's one of them.

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It's the Boulder atomic clock in Colorado,

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

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

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There are also smaller versions,
more commercial versions,

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that are good enough
to observe this effect with.

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They are in small boxes.

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If you take one and put it low down,

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and put another high up,

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

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Time goes faster higher up,

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and slower lower down.

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It's a fact.

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For instance,

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imagine you have a twin brother,

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you are the same age,
you grew up together.

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Imagine that your brother
goes to live in the mountains,

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and you go to live by the sea.

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If much later you meet up again,

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

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It's not just watches that are influenced

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by the strength
of the gravitational field,

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but all phenomena connected with time.

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

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Everything.

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A swinging pendulum.

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Time goes faster higher up,
and slower lower down.

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

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the first satellites for GPS
were sent into orbit,

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for the sat nav devices
we have in our cars

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to tell us where we are,

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physicists told engineers,

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

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

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On satellites, there's a clock.

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

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so they'd need to take that into account.

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The engineers said, "Oh, okay."

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

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GPS is operated by the US military.

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So, heading up the project
were American generals.

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The American generals were army generals.

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

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

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

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

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

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The GPS would not work

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

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

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that time went faster up there.

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What does this mean?

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

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

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Somehow, we need to think

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

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for who moves more slowly,
for who moves faster,

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time goes at different speeds.

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We need to change how we see the world,

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from a single clock beating the time,

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to many clocks, each with its own time.

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

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Strange and difficult.

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But if you think about it,

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

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Is the Earth flat or round?

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This room, is it stationary
or is it moving?

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Stationary.

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

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(Hesitation)

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A swallow comes from another swallow,

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

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swallow, swallow, swallow.

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

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from another human being.

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

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Not the case.

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We and the swallows
have the same, common ancestors.

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So, what's this all about?

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We tend to develop simple,
natural ideas about the world

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that are wrong.

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Not because they are
not adaptable to our lives.

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

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they refer to, are good on, our scale.

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They are no longer good
when we look at life,

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

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or when we think about
what happens very far away,

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

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

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that about high and low, right?

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Things fall from high to low.

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That is high, and this is low.

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

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

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

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

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This isn't entirely true.

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What's high here is low in Sydney.

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

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

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

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it's a notion appropriate only here to us.

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

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

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and go to the moon, as our astronauts did.

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

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and things are a little more complicated.

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

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I'm coming back to time -

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

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

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

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on their way to the moon.

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The Earth is round.

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But we knew that before.

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

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

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The Earth is moving.

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Now we've seen it from beyond it,

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

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

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How did they deduce these things?

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Simply by starting
with what we know about the world,

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observing, and putting
together known facts,

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and noticing that the known facts
can be better understood

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if we change our conception
of the structure of,

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our way of looking at, the world.

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

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something crucial.

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

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that we nowadays observe:

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we just need to buy
those very precise clocks,

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and anyone can see it's the case.

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It was understood before it was observed,

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by Einstein,

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

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

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

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on the other, he had electromagnetism.

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Endeavouring to combine these two things

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in order to have
a coherent picture of the world,

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

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

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This was 100 years ago.

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The same thing is happening today.

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

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

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

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We have confirmed them,

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we've seen there are black holes, etc.

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

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

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

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

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with general relativity.

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So science tried once again
with endeavors

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

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In 1963, two brilliant America scientists,

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

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and Bryce DeWitt, the man
in the color photo,

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simply took Einstein's
general relativity equation,

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Einstein's theories,

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and quantum mechanics,

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and put them together
and wrote an equation

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

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

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

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An equation that to start with
was very confusing.

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

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Today, the theory has been developed,

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and we can write it more precisely,

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and we can better understand
its significance.

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That's what I work at.

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

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and left everyone open-mouthed.

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

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from one end to the other.

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It has the characteristic as follows.

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All equations, if you remember
something of school physics,

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all the important fundamental
equations of physics

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

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they say how things change with time -

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back to time again -

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

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

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This equation here
doesn't have time in it,

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

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

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time is no longer there.

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What does this mean?

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

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If you listen to me carefully,

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

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

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Let's go back to simpler physics.

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The first thing that those
who enroll in physics study

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

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We need to describe
how its position changes with time.

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

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We look at the position
and what the clock reads,

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make a chart,

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

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But, here, we are not observing time;

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

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The hand is moving,

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and this is moving.

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We're just describing
how this position shifts

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when the hand's position shifts.

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

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We always describe something
as a function of something else.

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Clocks are just things
among others that move,

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

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more or less all together.

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What does this mean?

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It means that we can do without time

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and just talk in terms of
how the pendulum moves

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as a function of the position of the hand.

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

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

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that I started talking
the moment the lights went off,

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and so on and so forth,

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with no reference to time at all.

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

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

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

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I could say this is towards
that bright light there,

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and this is towards
the red circle underneath me.

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If I'm on Earth, I complicate life.

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

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

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

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

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

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

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Well, the notion of time
becomes meaningless, disappears,

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as soon as I leave normal space

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

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And where is this space?

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Where things are extremely big
or extremely small:

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

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If we observe the extremely small,

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observe on an extremely small scale,

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space, space itself fluctuates, spikes,

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it's like a stormy sea,

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

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as if time jumps.

00:13:49.285 --> 00:13:53.975
These two clocks, each weaving
its own path at a different speed,

00:13:53.975 --> 00:13:57.421
in the smallest of places, they go
forward and backward, they move, etc.

00:13:57.537 --> 00:13:59.631
On this extremely small scale,

00:13:59.631 --> 00:14:04.112
our notion of time is no longer good,
no longer useful, no longer works well.

00:14:04.587 --> 00:14:11.167
So we have to re-describe
the world in terms of those variables,

00:14:11.447 --> 00:14:14.446
one by one, without reference to time,

00:14:14.446 --> 00:14:17.155
as if we had a lot of clocks
that had lost their hands,

00:14:17.155 --> 00:14:21.135
and we could only see
how one moves in respect to the other.

00:14:21.485 --> 00:14:25.217
Imagine, to give you an idea,

00:14:25.217 --> 00:14:28.378
how we think about the world
as a combination of things that move,

00:14:28.378 --> 00:14:31.084
that change, that dance, all together,

00:14:31.084 --> 00:14:32.904
in time to a conductor of an orchestra

00:14:32.910 --> 00:14:36.924
who gives the beat:
1, 2, 1, 2 ... all together ... 1, 2.

00:14:37.653 --> 00:14:39.855
This picture no longer works
for the small.

00:14:39.855 --> 00:14:44.156
In the extremely small,
there's no unique beat for all,

00:14:44.156 --> 00:14:49.545
and the world is as if it were a dance
of every microelement with its neighbor,

00:14:49.545 --> 00:14:51.285
but not all together.

00:14:53.475 --> 00:14:56.224
What's the moral of this whole story?

00:14:56.224 --> 00:14:58.756
Time is a useful concept,

00:14:58.756 --> 00:15:00.907
it organizes our daily experiences,

00:15:00.907 --> 00:15:02.860
but it is not a fundamental concept.

00:15:02.860 --> 00:15:05.534
Just as "high" and "low"
are very useful concepts,

00:15:05.534 --> 00:15:09.834
but don't work anymore
when we leave our everyday surroundings.

00:15:10.974 --> 00:15:12.716
This is true of a lot of things.

00:15:12.716 --> 00:15:15.256
It's this that I love about science.

00:15:15.256 --> 00:15:18.856
What science teaches us
is that our image of the world,

00:15:18.856 --> 00:15:21.058
our perception of the world,

00:15:21.058 --> 00:15:23.541
is very often wrong, limited,

00:15:23.541 --> 00:15:26.036
working only in our usual surroundings.

00:15:26.676 --> 00:15:30.607
The human race is like
someone born in a small town

00:15:30.607 --> 00:15:32.468
where everyone behaves in the same way,

00:15:32.468 --> 00:15:34.760
until they leave and say,
"Oh, but there's more.

00:15:34.760 --> 00:15:37.245
We can eat different things,
say different things,

00:15:37.245 --> 00:15:39.559
speak different languages,
have different ideas."

00:15:39.559 --> 00:15:44.060
Humanity leaves behind
the smallness of its thoughts

00:15:44.319 --> 00:15:46.710
and discovers that everything's different:

00:15:46.710 --> 00:15:48.784
species transform from one to another,

00:15:48.784 --> 00:15:50.305
"high" and "low" are not real,

00:15:50.305 --> 00:15:51.937
time is not what it seems.

00:15:51.937 --> 00:15:57.287
The world is bigger, more beautiful,
more diverse, and more thought-provoking

00:15:57.287 --> 00:15:59.831
than what it seems at first sight,

00:15:59.831 --> 00:16:02.214
this thing, a little banal,
with "high" and "low,"

00:16:02.214 --> 00:16:04.266
with people that move,
and rocks that fall.

00:16:04.266 --> 00:16:05.516
It's much richer.

00:16:05.516 --> 00:16:09.262
And to understand that,
we have little need of ancient knowledge.

00:16:09.262 --> 00:16:11.909
Ancient knowledge, all ancient knowledge,

00:16:11.909 --> 00:16:13.414
what our forefathers taught us,

00:16:13.414 --> 00:16:14.864
really only applies here.

00:16:14.974 --> 00:16:17.443
If we look a little further,
it's no longer valid.

00:16:17.443 --> 00:16:20.721
As was said in the first video today,
the universe is endless.

00:16:20.721 --> 00:16:24.015
We were born in a tiny,
little corner of it,

00:16:24.015 --> 00:16:26.682
have ideas that apply
only to this tiny, little corner,

00:16:26.682 --> 00:16:29.136
when we then start
to look a little further afield.

00:16:29.136 --> 00:16:32.117
I think what we discover at each step -

00:16:32.117 --> 00:16:33.647
and I'm concluding -

00:16:33.647 --> 00:16:36.834
is far more extensive,
more beautiful, more complex,

00:16:36.834 --> 00:16:39.417
than any of the ideas
our forefathers told us about,

00:16:39.417 --> 00:16:41.351
or our moms and dads taught us.

00:16:41.351 --> 00:16:43.208
And this beauty that overwhelms us,

00:16:43.208 --> 00:16:45.446
this mystery that always lies before us

00:16:45.446 --> 00:16:48.351
to which we gain access,
step by step, little by little,

00:16:48.351 --> 00:16:50.950
but which forever remains boundless,

00:16:50.950 --> 00:16:53.526
draws us, fascinates us,
and we want to get to see it.

00:16:53.526 --> 00:16:54.889
This, for me, is science.

00:16:54.889 --> 00:16:56.019
Thank you.

00:16:56.019 --> 00:16:58.438
(Applause)