There's an aspect of our lives that we all take for granted.
It's something so familiar, you usually don't give it a second thought.
One of the key elements of being a human being is that we can tell the time.
It allows us to make sense of the world -
past, present and the future.
But it's nowhere near as straightforward as you might think.
I'm Professor Brian Cox and I want to find out what makes time tick.
We have ways to measure the passing of time but we don't know what happens when time passes.
I can't even tell you at the moment what at the moment means.
Even momentarily.
Knowing the time is not easy.
I' damned sure that flow of time is ultimately an illusion.
There's no big clock in the sky which ticks away at the same rate
for everybody, no matter where they are or what they're doing.
Did time have a beginning?
Why does time tick?
And does our future already exist?
I'm going to try and answer one of the simplest questions you could ask -
"What time is it?"
So, what time is it now? It's 5:58. What time have we got to be there?
The sun rises at 6:11.
So we've got about 13 minutes.
"What time is it?" is a question that humanity has asked for millennia.
Many of our ancient civilisations went to great lengths
to try and answer this simple question.
None more so than the Maya.
I've come to the Yucatan Peninsula of Mexico to see the ancient Mayan temples at Chichen Itza.
You're not usually allowed to do this. But because it's 6am and there's nobody here,
we've got permission to walk up the pyramid.
It's just absolutely incredible.
The Maya had an obsession with time, working out intricate ways to track its passing.
The Maya didn't have clocks, they didn't know how to build timepieces.
But they used the world around them to keep time extremely precisely.
And they had interlocking cycles of time, incredibly complicated, that were based on the movement of
all the bright celestial objects you can see in the sky.
If you think our lives are ruled by time, the Maya took time worship to a whole new level.
They didn't just track its passing.
They believed they had to help time pass.
They thought that time actually created space
and they thought that they had to feed the sun, to help it go through the sky, in order to make the space,
you know, make their world.
And they fed the sun with blood, with human blood.
So they made blood sacrifices to the sun to kind of sustain it on its journey across the sky.
Such was their fixation with knowing the time,
that time itself is manifest in Mayan architecture.
Everything about this building is about time.
There are 91 steps on the way up and there are four sides to the building.
That's four 91s, 364, and then one step at the top to make 365.
So the building itself is
a visual representation of the passing of time.
This is the first stop on my journey
to try and answer what appears at first to be a very simple question.
Telling the time was something the Maya thought they'd mastered.
But it's not as easy as you might think.
I'd like to understand what time is.
And it's a very tall order.
Some of the best physicists in the world are working on that really simple question - what is time?
And the Maya thought they knew,
2,000 years ago.
Newton thought he knew 400 years ago.
Einstein kind of thought he knew for about six months in 1915 and then changed his mind in 1916.
And it's a problem that's confounded us to this day.
This is truly the unknown.
What time is it?
I don't know.
Do you know?
Since the dawn of civilisation, every culture has tracked the passing of time by looking up.
As the earth rotates, the sun, moon and stars move across the sky,
giving us a daily rhythm - an instinctive way to tell the time.
So if you want to know what time it is, you don't need a watch, you don't need a clock.
You just need to look up at the sun, that regular rising and setting, the clockwork of the passing of the day.
But actually, it turns out that that regularity, the length of the day,
isn't quite as precise as you might think.
For the last four billion years or so, the speed our planet spins has been gradually slowing down.
The length of a day has been steadily getting longer.
It's all down to the moon.
You see, the moon holds the water on the surface of the earth towards it so you get a tidal bulge.
And the earth spins underneath that bulge and that's what you see as the tide's coming in and out.
And there's friction between the surface of the earth and the water
which means that the spin, or the rate of spin of the earth, slows down.
And that causes the day to lengthen.
600 million years ago, the day was just under 22 hours long.
But the earth isn't just slowing down over millions of years.
The very thing that we relied on for telling the time,
the fact that the earth takes 24 hours to spin once on its axis,
is something we now realise we can't rely on even from day to day.
For the last 30 years, measuring the exact length of each day has been the job of scientists
at the Westford Observatory, just north of Boston, Massachusetts.
There are lots of different ways of measuring the spin of the earth
but strangely, one of the best is to look for light
that began its journey a long time ago,
from a galaxy far, far away.
Unlike the Maya, the scientists here don't rely on the sun to track the spin of the earth.
To make these measurements, you need something that's as steady as possible, as far away as possible.
So, as bright as possible. And the brightest things
we know of in the universe are these things called quasars.
They're, we think, the nuclei of galaxies.
So, a big, huge black hole, sucking loads of dust and stars into them, throwing out radio waves.
And it's those radio waves that we actually use, remarkably, to tell the time on the earth.
Thanks.
Arthur Niell is the man who keeps track of time.
Oh yeah! Mind your ears, probably pops just now.
This is like an airlock. It is an airlock.
How do you make this measurement?
What we actually use are two radio telescopes,
actually two or more, but with two radio telescopes, we can do this.
And what we measure is this radio wave coming in from space.
As it comes in, we look to see the instant of time when this radio wave
arrives at the same time at two different telescopes.
When a quasar is directly overhead, the radio waves arrive at the two
separate telescopes in synch and the stopwatch is set running.
As the earth spins, the radio waves drift out of synch,
taking different times to reach each telescope.
But after one full rotation,
the two telescopes are back in synch and the clock is stopped.
This gives you the exact time for one rotation of our planet -
one day.
But it's never quite the same.
Sometimes, you get there a little early and sometimes you get there
a little bit late relative to the clock we have on earth that's beating out very regular seconds.
So, 24 hours...
You come round 24 hours and you think,
"Uh-oh, we're not quite there yet. "
And so, the earth rotates a little bit more.
Sometimes, it speeds up a little and gets there a earlier
compared to the time that you expect it to.
So the day is, in a sense, the length of day is wobbling?
Yes, the length of the day is not 24 hours exactly.
Surprisingly, earth's daily erratic speed changes
are mostly caused by wind.
As the winds speed up or slow down, by the way they push on the mountains
or the friction on the surface of the earth, they then slow down or speed up the solid part of the earth.
Down in the control room, Arthur has the most recent timing for a day.
The latest measurement that came back was from just two days ago,
and the length of day was about 1.9 milliseconds more than 24 hours.
So, 24 hours, 1.9 milliseconds?
Right. Makes a difference, it all adds up.
Because the earth doesn't spin at a steady rate, using the movement
of the sun or other nearby celestial bodies to tell you what time it is,
is not going to be very reliable.
The earth's spin's erratic.
It changes from day to day,
so you can't use that age-old way of telling the time.
To know what time it is, you have to stop looking into the sky
and looking at the stars and the planets, and you have to look down into the world of the small.
You have to look into the world of the atom to tell the time.
The tree's in the way!
If there's one place on earth where you can come to find the time,
it's here in Washington DC.
This is the home of the US Naval Observatory,
one of a select bunch of time lords
dotted across the planet who are the keepers of time on earth...
Universal Time, 19 hours, 54 minutes exactly.
.. a time now derived from atomic clocks.
Dennis McCarthy, director of time.
We defined a time in the 1950s based on the position of the moon with respect to the stars.
We needed a more accurate kind of time.
Not only does it have to be more accurate
but it has to be more accessible.
That accessible kind of time is provided by atomic clocks.
What we need to tell time is something which repeats with great regularity, that you can count on.
How well we can tell time depends on which atom you're using.
So we choose certain ones to use for keeping atomic time.
So, how can atoms give us the time?
What you can do...
An atom is
very crudely...
The atomic nucleus sits there and electrons sit in orbit around the nucleus.
But they only sit in specific places, so you can't have them anywhere.
You can have them here and here and here.
And when they jump up to there,
and then back down to there again, they emit light.
And that light has a particular frequency.
And it's this light that allows us to tell the time so precisely.
Inside the clocks are the atoms of a rare metal called caesium.
The electrons in the caesium atoms are made to jump up.
Then, as they fall back down, they give out light.
These light waves peak over nine billion times every second.
And it's this light that drives the clock,
effectively producing nine billion ticks for each atomic second.
This number never changes, never alters, and that's why it's so accurate.
So, the atomic clock is actually putting out an electronic signal
which is essentially analogous to the ticking of a pendulum clock,
you know, a pendulum clock which might tick once every second or once every couple of seconds.
This thing is providing us something which is going nine billion times per second.
So it provides us with a very fine definition of time.
We actually have a number of clocks at the Naval Observatory located all over the grounds.
Here's one of them.
This is the Master Clock System One.
This is the Master Clock System Two.
So if I want an answer to the question, "What time is it?",
there it is? That's it.
'Universal time, 20 hours, 0 minutes exactly. '
Atomic time is the heartbeat driving modern life.
It acts as a single global time frame, a way to synchronise
the world with a time stamp accurate to a billionth of a second.
It plays a key role in everything from navigation and scheduling to global communication.
It is THE definition of time on earth.
Problem solved!
Well, not quite.
Knowing atomic time is actually somewhat irrelevant to answering the question, "What time is it?"
The labels you give to time 2008, May the 21st - it's...
What day is it today?
12th. 12th, right.
To us, this is the year 2008 because a Pope defined it to be so about 500 years ago.
In the Islamic calendar, it's 1429.
In the Jewish calendar, it's 5768.
And in 2012, in the Mayan calendar, it'll be the end of the long count - 130000.
All different, all arbitrary.
So, if you really want to know what time it is, then we're going to have to go a little deeper.
The time that ticks on your watch is the time now, the time of the present.
But the feeling we experience as the present time is something we shouldn't take for granted.
Much of what we believe is in the present is drawn from the past.
What we feel is happening now happened a little while ago.
We feel that we experience a now around us -
everything we see happen now.
But actually, the light coming from distant things into your eye takes time to get there.
So, you look at the sun.
The sun is 93 million miles away.
That means light takes over eight minutes to get from it into my eyes.
So I'm seeing the sun as it was eight minutes in the past.
It could explode and I wouldn't notice for eight minutes.
I'd just see that beautiful image of the setting sun.
To answer the question what time is it, we need to know when time began.
The fact that light travels at a finite speed offers us a unique opportunity.
It allows us to look back, not just eight minutes, but millions, even billions of years.
I've come to Baltimore to look back in time.
Former director of the Hubble space telescope Steve Beckwith
was responsible for taking an extraordinary photograph.
As a director, I had at my discretion
10% of the telescope time per year that I could use for anything.
One year, I took all of my time, in fact I took a little bit more
than all of my time and decided that we would devote it to the deepest picture ever taken of the universe.
In 2004, Steve pointed the Hubble telescope at a tiny piece of the night sky
and took a picture called the Ultra-Deep Field.
It took a million seconds of exposure on the Hubble space telescope,
the world's most powerful telescope.
And in this image, we can look back in time 13 billion years.
It's a difficult picture almost to comprehend, isn't it?
Because in some sense, it's...
3D is the wrong word, but it's some sense...
Oh, no, it IS the right word. It IS 3D. We are looking back in time.
Every single galaxy in this image can be dated.
This galaxy emitted its light when the universe was 8.8 billion years old.
Then, as you go back in time, this is a galaxy that emitted its light
when the universe was 3.3 billion years old.
You can see it looks completely different. It's really very chaotic.
And this is one billion years after the Big Bang, very red, a little tail, very small.
The most distant galaxy in the Ultra-Deep Field is a red one that's right over here. This one here?
The light from that was emitted when the universe was 700 to 800 million years old.
So, really,
this is one of the first structures that formed in the universe?
One of the first formed and one of the first we've been able to see.
In a sense, you see this almost...
I was going to say paradoxical,
but strange behaviour of the universe as revealed by astronomy.
Because I'm trying to say, "Well, what does that look like now?"
"What would that look like now?"
In a sense, it's the wrong language to use, isn't it? That's what it looks like now.
That's right.
Steve has turned his photo into a movie to journey back in time.
You see these little pieces coming at us?
We're going back in time. You can see the three-dimensional effect.
Some of these others are a little farther back,
but here we're going back,
we're probably back now about three billion years from the present.
As we keep going and you get to the smaller ones,
you get back to about eight or nine billion years.
And then, when we get to the very tiny, most distant ones,
we'll be back probably 10 or 11 billion years in time.
We're deep into the universe, looking at the smallest structures,
back in time to about 13 billion years.
And, suddenly, we run out.
Steve's amazing photo allows us
to travel back through almost the entire history of the universe.
But if we want to know what time it is right now,
we have to go back a little further than Steve's picture allows.
We need to get back to the point when time itself started ticking,
back to the moment the universe began.
The Big Bang, so the theory goes, was the beginning of everything - including time.
If you think about it, that's a remarkable thing to say.
It means that the first day of the universe didn't have a yesterday.
If time began at the Big Bang, then there was no yesterday.
There was nothing, no time at all.
And then the Big Bang happened and...
all this appeared.
To know the time, we need to know precisely, how old is the universe?
Since the moment of the Big Bang, the universe has been expanding.
If we could work out exactly how fast the universe is stretching,
then we could imagine rewinding this expansion
all the way back to the beginning.
I've come to Berkeley, just east of San Francisco,
to meet Saul Perlmutter.
A few years ago, he worked out a clever way to calculate when it all began.
So, could you describe to the nuts and bolts of the measurement?
The tool that we started to work with is a...
kind of exploding star, a supernova.
And there's one kind of supernova, we call it the type 1A,
which, when they explode, they always seem to reach the exact same brightness and then fade away.
Saul uses these special supernovae
to measure how fast the universe is expanding.
These particular stellar phenomena always explode the same way,
giving out light with a particular blue colour.
But it takes time for this light to reach us and, in that time,
the universe continues to expand.
As the universe expands, the wave length of the light gets stretched.
This turns the original blue colour into red.
In an expanding universe, the amount that the universe stretches is exactly the same amount
that the light from the supernova has its wavelength stretched while it's travelling to us.
Ah, so we look back and we see that the nearby ones are pretty much the colour that they were.
That's right, they look blue, right? And then further away... Redder and redder.
They go redder and redder as the light is stretched. Exactly.
And now you can start asking, "Let me now map out the history
"of all those different stretches, all those different
"times in history, how much the universe has expanded. "
And back calculate when was everything right on top of each other?
When were all the distances at zero?
And that's what we call the beginning of the universe.
Using Saul's observations, we can reverse the expansion
of the universe to arrive at the point it all began.
We now know this time was roughly 13.7 billion years ago,
the start of space and the start of time.
So the answer to the question, "What time is it?"
is not 2008 or any other arbitrary number on a calendar.
It's 13.7 billion years.
Or is it?
You get these very precise sounding numbers
like 13.7 plus or minus a percent. And that sounds very impressive.
But that doesn't have to be the beginning of everything.
That's just the beginning of this period that we can learn about
by watching the expansion of the universe.
The idea that everything began at the Big Bang
leads to one of the most profound questions in science -
what exactly triggered the beginning of the universe?
If there was something before the Big Bang,
might that something include time?
The orthodox view today is that there was no time.
Time began at the Big Bang, time zero.
But there are theories that suggest that maybe the universe existed before then in some sense.
Maybe time has existed for ever, and what we see as the Big Bang
is just the creation of our little bits of space and time.
I've come to Cambridge to find out what happened before the Big Bang.
Neil Turok is one of the world's leading cosmologists and he believes
the accepted view that time began at the Big Bang is completely wrong.
I would say the standard hypothesis,
that the universe sprang into existence 13.7 billion years ago,
doesn't make any sense.
Something mysterious happened 13.7 billion years ago
and we do not yet know what that was.
'Neil has a theory for what caused the Big Bang.
'If he's right, it would mean that time has been around a lot longer than originally thought. '
If you want to explain the Big Bang, the simplest option is that something caused it.
And, if something caused it, there was a time before the Big Bang.
So, if you look at the... the universe,
and if we try to draw a graph of time and space,
and we follow the particles emerging from the Big Bang,
then they come out of this event 13.7 billion years ago.
And, at that event, all the particles were
on top of each other and space had shrunk to no size at all.
So the density was infinity, there is no space to talk about.
So, that's the point at which time began?
No! Not at all.
'Neil has come up with a clever, if mind-boggling, solution.
'With maths drawn from the almost unintelligible realm of string theory,
'he believes the solution lies in additional dimensions of space
'and the existence of parallel worlds that he calls membranes,
'or branes for short. '
How, then, can we picture this, the beginning of our bit of space
if time has gone on for ever?
The first concrete model we could come up with, coming out of
string theory, was a particular set-up called brane worlds.
And what happens in a brane world is that the three dimensions of space we live in,
which I'll draw as a two-dimensional sheet, just so that I can draw a picture of it.
You're to imagine that this is our three-dimensional world
and we're made out of particles which can travel within that world.
Literally, well, you and me and everything? Our universe.
Yes, is within this world.
So, what string theory says is that there's not just this
three-dimensional world or sheet in my picture of it.
There's another one, separated from ours by a very tiny gap
and that tiny gap is a fourth dimension of space.
So what can happen is that these two brane worlds can move towards each other and hit.
So as they move towards each other, they become one.
In Neil's model, everything we see around us exists entirely on one of his branes.
But there are other branes in the universe,
separated from us by an additional unseen dimension of space.
If we go back in time 13.7 billion years,
it was the collision of two branes that created the event
we know as the Big Bang,
and it was this that brought the universe we see today
into existence.
And so the radiation and matter of the Big Bang was the energy of the collision.
Um...
And as they separated again, the two branes were now filled...
or replenished... with matter and radiation.
So literally in this picture, the universe, which is all these branes, exists for ever? Yes.
There's no beginning of time? Yes, that's right.
I think time probably has always been there and always will be there,
and all we can really say is that something dramatic happened 13.7 billion years ago.
'Neil's theory is controversial.
'Rooted in string theory and requiring additional
'unseen dimensions of space, it's challenging stuff.
'But if it's true, time has always existed. '
Whether time began at the Big Bang or time is eternal,
I want to know what time actually is.
From decades to centuries, we feel the need to divide time.
But if we start to break it down to hours and minutes and seconds,
is there a point where we can't divide it any further?
Is there a smallest unit of time?
When you look out into the universe,
you see things happening on time scales of millions or even billions of years.
Here on earth, we're used to thinking of things in days or minutes, or even seconds.
But actually, a lot of things can happen in a second.
Just as we need a microscope to see small things,
we need specialist kit to see smaller times.
I've come to use the very latest high-speed video camera.
And... action!
By filming very short time intervals,
this camera can then play back action in super-slow motion.
I'm hoping for when I'm about 60, I can go...
it's an absolute outrage!
With the camera capturing the world in milliseconds,
this is life 40 times slower than we're used to seeing it.
He looks like some sort of fish!
Action!
What does that make you think about your face?
It's rather more elastic than I had hitherto suspected.
Print that one and let's get another one.
As we continue to divide time,
we start to see previously hidden details.
With the action 80 times slower,
each millisecond reveals the world in a new light.
Oh! Oh!
Cut!
The world looks completely different
when we start to see time divided into smaller chunks,
but just how far can we keep on dividing time?
There's nothing special about a second.
You can break it down, you can break it down into milliseconds
or microseconds, nanoseconds, picoseconds, attoseconds.
These tiny fractions of time, million billionths of a second
are impossible for our eyes to perceive.
But within an atom, a second is an eternity
filled with billions and billions of interactions.
This is a world where it seems that time can be divided again and again,
but can it?
The smallest unit of time that has any sort of significance in
the universe as we understand it is called the plank time,
which is ten to the -43 seconds.
That's a million million million million million million millionth
and a little bit more of a second.
This is the time it takes light to travel the shortest
possible distance that our current theories can handle.
Beyond this point, our understanding of time...
.. stops.
To tell the time, we used to look up at the sun and stars but the earth doesn't keep good time.
With the advent of atomic clocks,
we can now track time with far greater accuracy and by looking back in time,
we can work out the moment when time itself began, at least in the universe we see around us.
If we want to know, "What time is it?", we're certainly making progress.
But there's one last profound question I want to answer.
It really encapsulates our experience of life.
It cuts to the very heart of what it feels like to be human.
It's how we define the time line of our lives.
Why does time seem to tick along in the way that it does?
Have you ever wondered
why you have to go into the future at the rate that you do,
at the speed that you do?
Do you get up and look at yourself in the mirror and say,
"Why am I getting older?"
"Why do I have to move into the future?"
"Why am I not allowed to go back into the past?"
"Why am I not allowed to stand still in time?"
And so if you want to understand why, you know, why existence
feels like this, then you need to know what time is and why it passes in the way that it does.
A hundred years ago, it was Albert Einstein
who started tackling these profound questions.
As part of his radical new theory of nature,
he fundamentally altered the way we understand time.
Einstein's picture is that time is a dimension like space,
and you move through it and so that's how you feel it's passing.
Really what you're doing is you're moving through it just in the same way that you can move through space.
Einstein was the first to link space and time in this unique way.
In Einstein's universe, when you sit still in space,
you travel through time, you travel into the future,
and you travel through time at a fixed speed.
It sounds really weird, how you travel at a speed, but you do and that speed is the speed of light.
That just doesn't sound right.
It does sound strange because it's one of the laws of the universe
that you can't travel at the speed of light, right?
Actually, you can't travel through space at the speed of light, that's what you can't do.
You can and do travel through time at the speed of light.
And it's this that creates our sense of moving into the future.
So it's a "one, two, three", the time ticking on your watch, that is,
in Einstein's theory, you flying through the time dimension, into the future, at the speed of light.
It's quite, it's quite a...
.. counter-intuitive picture.
You're not kidding.
We experience time passing because we are all travelling along the time dimension.
But strangely, Einstein also said we don't all experience the same time.
For Einstein, space and time are not the separate things that we feel them to be.
They're in many ways the same,
and in fact, they're merged together
into a single entity called space time.
Space time can be pictured as a sort of fabric
where time and space are inextricably woven together.
As a result, the dimensions of space and time can get mixed up.
Although we are all travelling through space time at the speed of light,
it's the mixing of time and space
that Einstein said causes time to tick differently for each of us.
For Einstein,
time wasn't like a...
a metronome that just ticks the same for everybody.
It's different for you and me,
and everywhere in the universe, the metronomes tick at different rates.
Einstein said that two people will only ever agree on
the speed time ticks if they're standing next to each other.
If I were to fly past you incredibly fast, I would see your time tick much slower than mine.
This idea lies at the heart of Einstein's theory of relativity.
No-one has a right to claim that their time is the time,
the absolute time.
It just depends on who's moving relative to who.
Because of the mixing of space and time,
time ticks differently for you relative to other people,
depending on how fast everyone is moving.
When someone moves relative to me,
they use some of their speed of light through space time to move through space.
So they haven't got as much left to move through time,
and that means that their speed through time is a bit slower.
They've sort of, in a very real sense, used a bit of it up.
It's a really profound way of understanding Einstein's theory of space time.
And the strange nature of time doesn't stop there.
It's not just how fast you're moving but what you're next to that also affects time.
According to Einstein,
you should see the time tick slower at my feet than at the top of my head.
This is because the nearer you are to a big object like the earth,
the more bent and warped is the space time,
and the slower time ticks.
On our planet, the effect is miniscule but out there in the universe,
the vast mass of the stars and galaxies
bend and warp the space time so much
that time ticks all over the place.
In the 1960s, Einstein's strange notion of time was put to the test.
Using the large Haystack radio antenna just north of Boston,
an experiment was devised to see if the sun causes time to tick differently
to how it ticks here on earth.
Astronomer Irwin Shapiro was at the helm.
What we wanted to see was how long it would take a light signal
to get from the earth to Mercury,
and its echo to get back to the earth,
and that's what we were looking for,
a measurement of time to very high accuracy.
But even using one of the most powerful radio antennas in the world, this wasn't going to be easy.
Any echo coming back from Mercury would be incredibly weak.
The echo has very little power.
I can describe it as the power put out
by an ordinary housefly crawling up a wall
at the rate of a millimetre per millennium,
that's per thousand years.
That's how little comes back.
By knowing the distance to Mercury and the speed that light travels,
Irwin knew exactly how long it should take
for a signal to go out and come back again.
But applying Einstein's theory,
the presence of the sun would have an effect on the result.
We see something strange.
It's like a spike appears in the orbit
whenever the planet goes behind the sun as seen from the earth.
So it looks like it's drifted a bit further away as it goes round the back of the sun.
Right, it looks like it deviated from its orbit.
Instead of going in a nice smooth orbit,
it had a spike in the orbit... Which of course it doesn't have.
It's just a manifestation of the fact that light took longer
to get to the planet and back when the light went near the sun.
The apparent blip in Mercury's orbit is all down to the bending of time.
The huge mass of the sun bends and curves the space time,
the fabric of the universe.
As Irwin's radar beam passed by the sun,
the warping of space time meant that time for the radar pulse
got stretched relative to time on earth.
Time was slowed down by the mass of the sun.
This effect came to be known as the Shapiro time delay.
There are very few physicists actually that have an effect or anything named after them.
Well, it's sort of embarrassing,
but on the other hand I must say I take a secret pleasure in it!
Maybe not so secret!
Irwin's measurement agreed perfectly with Einstein's prediction.
We really do see time slow down near the biggest objects in the universe.
But this observation leads to an unsettling conclusion.
If time can get slowed down,
near the sun, for example, relative to me,
is there somewhere you can go in the universe where time would slow down so much that it would stop?
There are objects out there in the cosmos
that bend and warp space time so much
that something very peculiar happens to the passing of time.
These fearsome phenomena are black holes.
Black holes have fascinated MIT cosmologist Max Tegmark for some time.
So, the further down I get in the gravitational field,
the slo-o-ower and slo-o-ower time goes.
And if I were to then be orbiting around there and picking up
radio signals from earth, it would look like life back here was going in fast forward...
.. We'll notice that it's going too fast.
So the voices would literally do that.
Yeah, because time is running at different paces, right?
They're going to sound like Donald Duck.
Closer still to a black hole, and the passing of time
relative to someone out in space does something very weird.
If I were to throw you into a black hole and watch what
happened to the time ticking along on your wristwatch, I'd see it tick slower and slower and slower.
Arghhhhhhhhhh!
And it would look to you like my time had slowed down and I eventually got frozen on the horizon.
I would look very red in the face, not just because my blood pressure
had gone up but because actually, even the frequency of the light waves had slowed down.
At some point, I would actually see your watch stop.
As far as I was concerned, time for you would have stopped.
Whether you're standing on the edge of a black hole or standing on earth,
Einstein showed that your time is unique to you.
So the answer to the question "What time is it?"
is that it depends what you're doing.
Two people with identical atomic clocks,
moving around in different ways or sitting closer
or further away from a planet will give you different answers,
and they're both right.
There's no single answer to the question "What time is it?"
Time is something we all have a very close affinity with.
We celebrate special moments in time,
yet often despair at its passing.
If you want to know what's special about time,
you just have to look at our language.
The whole language that describes the human condition
is a language... it's a temporal language.
I had a great time yesterday. I'm looking forward to tomorrow.
It's the thing by which we label regrets and aspirations
and hopes and fears.
They're all labelled in terms of time.
And it's quite...
unbelievable almost that it's probably the thing we know least about, even now.
Our intuition about time is that the past has happened
and only exists in our memories, and the future is yet to come.
But if Einstein is taken at face value,
that time is just like the dimensions of space,
then we're hit with something completely counter-intuitive...
.. all of time has always existed.
Think about it. Space is here, and there are three dimensions.
I could walk down over there to the ocean and you wouldn't say that the ocean hadn't happened yet.
It's there and I can walk to it.
Well, there's no difference really between time and space in Einstein's theory.
So you decide time's a dimension,
then it's there in the same way that the ocean's over there.
So all moments in time already exist.
It's like moving along this road.
The past - we've experienced it but it's still there, and we're moving forward into the future,
but the future's there just in the same way that this road is there.
According to Einstein,
the past, present and future all exist.
So, the feeling we have of our future unfolding is misleading.
All of space and all of time are there,
and your life would be just a line,
like a piece of string, a route through space time.
So your birth would be here and your death would be there, and there's your life, and it just sits there.
So at face value, that means that time doesn't pass.
There's no such thing as the passing of time.
There's just a line, a path through space time that you took.
This is an astounding proposal.
According to Einstein, my birth...
my first day at school...
my graduation - all these events still exist somewhere in space time.
But there's more than that.
If you take Einstein at face value, the future is as real as the past.
A week next Tuesday, my 70th birthday, even my death -
all these future moments in time already exist.
This picture that Einstein has of time being this dimension
and the future being all mapped out and you just career headlong into it
is not very satisfactory, it doesn't feel right.
And actually, in physics it's not right, because Einstein's theory is what's called a classical theory.
It ignores the quantum world, the world of the small.
Quantum mechanics is what I do for a living.
In the quantum world, the world of sub-atomic particles, nothing is certain.
It's a world of probabilities,
one in which the future is certainly not predetermined.
The test we have now at the cutting edge of physics is to
find a way of getting Einstein's space time to work with our modern picture of quantum mechanics.
This challenge is what theoretical physicist Fay Dowker has been working on.
She's not throwing Einstein away but trying to bring him into the 21st century.
Our understanding of space time that we get from Einstein's theory
is not the final answer, it's not the final story.
It's not compatible with our other best theory, physical theory, that we have, which is quantum mechanics.
Fay's theory assumes that at small scales, at the quantum level,
space time isn't the smooth structure that Einstein suggested
but is made up of tiny bits.
Space time is in fact bitty, or granular, and if that's correct,
then what we experience as, say, the interval of a second
would in fact not be continuous
but it would be made up of individual... individual events,
grains of time, if you like, that accumulate one after the other.
It's almost like there are grains of time,
like grains of sand, right?
So it's like every event is a grain.
As one event happens, one grain of sand, then another one can happen
on top of it, and another one on top of it and another one on top of it,
and you build up the future, if you want.
You build up the universe as layers and layers of these grains.
How does that help us then understand what time actually is?
One thing that space time could do if it was grainy would be to grow
grain by grain.
And that's a possibility that a continuous space time doesn't have.
It can't...
can't... come into being in that way,
piece by piece, because there are no pieces because it's a continuum.
The past and the future just there?
Yes, so a grainy reality could... It could grow.
So it could come into being,
element by element, grain by grain,
and that growth itself could be the passage of time.
In Fay's universe, our reality is built up by tiny grains of space time.
This means that the future isn't set in stone.
It grows out of the past.
This picture of space and time is still pretty strange,
but at least it feels more intuitive -
you know, the future's not yet happened.
So I think, in this attempt to merge Einstein with quantum mechanics,
we're improving on Einstein.
We're getting a better picture of what time is and why time flows.
"What time is it?" is a profound question,
because it needs you to think about where time began.
It needs you to think about how much time has passed since time began.
It needs you to think about how you chop time up, how you count it.
How do you count moments?
From the journey of the sun to atomic clocks, we can accurately track the passing of time.
But what is time?
Did time have a beginning? Or has it always been?
Do we create our own future? Or is it already written?
Time has confounded us for millennia.
Irwin, what time is it? Well, that depends.
Are you talking about universal time or eastern time?
It's 13.7 billion years.
That's what time it is. I would say it's 4:45:54 but I'm 12 seconds off.
It's not an easy question to answer.
A great time to be a physicist.
Time to go home and have dinner.
It's a great question, although some great questions
actually turn out to be trick ones, right?
The time today...
is something we have no idea about.
We might not be in a position at this moment in time,
with our current understanding of nature,
to even understand what it is that we're asking.
MUSIC: "Just In Time" by Frank Sinatra
# Just in time
# I found you just in time
# Before you came, my time was runnin' low... #
Subtitles by Red Bee Media Ltd
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