0:00:11 > 0:00:14The natural world is beautiful
0:00:14 > 0:00:15but complex.
0:00:18 > 0:00:21The skies dance with colour.
0:00:21 > 0:00:22CHEERING
0:00:26 > 0:00:30Shapes of great geometrical beauty
0:00:30 > 0:00:32form and disappear.
0:00:36 > 0:00:39And the planet itself is constantly transformed.
0:00:43 > 0:00:45But this seemingly infinite complexity
0:00:45 > 0:00:47is the shadow of something deeper.
0:00:53 > 0:00:55The underlying laws of nature.
0:00:57 > 0:01:01The world we live in is beautiful to look at.
0:01:01 > 0:01:03But it's even more beautiful to understand.
0:01:23 > 0:01:26Everything in the universe is in motion.
0:01:35 > 0:01:37And yet it feels as if we're standing still.
0:01:40 > 0:01:44This appears to be such a simple observation,
0:01:44 > 0:01:48but the study of motion lies at the very foundation of modern physics...
0:01:50 > 0:01:53and leads to the astonishing conclusion
0:01:53 > 0:01:55that the division of time into
0:01:55 > 0:01:59past, present and future
0:01:59 > 0:02:00is an illusion.
0:02:04 > 0:02:06Our intuition is wrong.
0:02:09 > 0:02:13Space and time are stranger than we could possibly have imagined.
0:02:30 > 0:02:35From our viewpoint here on Earth, the planet seems motionless,
0:02:35 > 0:02:37as the universe revolves around us.
0:02:42 > 0:02:45Every day for four-and-a-half-billion years,
0:02:45 > 0:02:47the sun has risen in the east,
0:02:47 > 0:02:51tracked across the sky and set below the western horizon.
0:03:02 > 0:03:06And as the years pass, so the seasons turn.
0:03:08 > 0:03:11Summer fades into autumn...
0:03:16 > 0:03:17..and autumn
0:03:17 > 0:03:19into winter.
0:03:23 > 0:03:28But these seemingly perpetual cycles are delicate,
0:03:28 > 0:03:32evocative hints that our planet is far from stationary.
0:03:40 > 0:03:43I've always loved the passing of the seasons.
0:03:43 > 0:03:46A gentle experience with a powerful resonance.
0:03:46 > 0:03:49I always remember the words of those hymns that I used to sing
0:03:49 > 0:03:51when I was six or seven that celebrate them.
0:03:51 > 0:03:54"Let me plough the fields and scatter",
0:03:54 > 0:03:58"In the bleak midwinter, the frosty winds made moan."
0:03:58 > 0:04:02The daily changes are almost imperceptible.
0:04:02 > 0:04:07The reddening of the leaves and the cooling of the streams is subtle.
0:04:07 > 0:04:11But those changes mask a jarring, celestial violence.
0:04:11 > 0:04:15So what is going on out there in space, in time,
0:04:15 > 0:04:19as the days pass, the seasons change?
0:04:27 > 0:04:32The most familiar aspect of our planet's motion is the day,
0:04:32 > 0:04:34caused by the Earth's rotation.
0:04:42 > 0:04:45You'd have to go back to the turn of the 17th century to find anyone who
0:04:45 > 0:04:47would argue that the Earth doesn't spin.
0:04:52 > 0:04:57But you need a piece of 21st century technology to experience just how
0:04:57 > 0:04:59fast it's moving.
0:04:59 > 0:05:02We're going to get ourselves airborne from Wharton, here,
0:05:02 > 0:05:05and then we're going to climb up to altitude and were going to try and
0:05:05 > 0:05:06beat the Earth's rotation.
0:05:16 > 0:05:20The Earth spins so fast that you can't beat it with any old crate.
0:05:21 > 0:05:23You need something a bit special.
0:05:33 > 0:05:36This is a Eurofighter Typhoon.
0:05:36 > 0:05:41It flies at least Mach 1.85 - twice the speed of sound.
0:05:41 > 0:05:43I can't tell you exactly how fast, because it's classified.
0:05:43 > 0:05:47They go to at least 55,000 feet, but again, I can't tell you -
0:05:47 > 0:05:51it's classified. And you can't film down those air intakes,
0:05:51 > 0:05:53because they're classified, as well.
0:05:53 > 0:05:55This one is BAE Systems' development aircraft -
0:05:55 > 0:05:57I'm going to get in it in
0:05:57 > 0:05:59a minute - and it's got all the test software in.
0:05:59 > 0:06:01The pilot told me that, you know,
0:06:01 > 0:06:04it's a bit ropey, so press control, alt,
0:06:04 > 0:06:07delete occasionally if it all goes funny and usually it comes back on.
0:06:08 > 0:06:10Which is good.
0:06:15 > 0:06:18Get in. Feet-wise, comfy?
0:06:18 > 0:06:20Good.
0:06:20 > 0:06:23That's for if you need to control it at any point.
0:06:23 > 0:06:25- It's unlikely!- Unlikely.
0:06:27 > 0:06:30Sit back. Right.
0:06:32 > 0:06:35Worst comes to the worst, do it in your glove.
0:06:37 > 0:06:39'Time is 6-9, runway 0-7, clear takeoff.'
0:06:39 > 0:06:43Surface wind 350 degrees, seven knots. Over on cable.
0:06:51 > 0:06:53- Ready?- Yeah.- Go for it.
0:06:55 > 0:06:56And we're off.
0:06:57 > 0:06:59Oh, lovely and bright.
0:06:59 > 0:07:02MUSIC: Blue Orchid by The White Stripes
0:07:09 > 0:07:10Oh!
0:07:10 > 0:07:14# You got a reaction, didn't you?
0:07:14 > 0:07:17# You took a white orchid
0:07:17 > 0:07:20# You took a white orchid and turned it blue
0:07:20 > 0:07:23# Something better than nothing
0:07:23 > 0:07:27# Something better than nothing It's giving up... #
0:07:27 > 0:07:30- I have to say, that's the way to depart an airfield.- It is a bit.
0:07:34 > 0:07:36You see, on the east side,
0:07:36 > 0:07:38everything is darkening up quite nicely as the sun
0:07:38 > 0:07:41starts to set. And on the ground, it's already...
0:07:41 > 0:07:45It's dark on the ground now, as far as the sun is concerned.
0:07:45 > 0:07:48Accelerating.
0:07:48 > 0:07:50So that's 9.78.
0:07:50 > 0:07:54- Yeah.- And the G-suit is inflating. - Yeah.
0:07:56 > 0:07:59'Turning directly towards the setting sun,
0:07:59 > 0:08:03'the Typhoon accelerates to catch up with the Earth's spin.
0:08:12 > 0:08:16'Beneath us, a 6,000 billion, billion-tonne rock
0:08:16 > 0:08:19is spinning at 650 mph.
0:08:23 > 0:08:27'Match that speed and something interesting happens
0:08:27 > 0:08:29'to the sun's motion across the sky.'
0:08:32 > 0:08:36650 mph, so we are travelling at precisely
0:08:36 > 0:08:38the speed of the Earth's rotation.
0:08:38 > 0:08:44- That's right.- So if we stop the sun, it's about two thirds down.
0:08:44 > 0:08:45So it should just stay there now,
0:08:45 > 0:08:48because we're going at exactly the same speed as the Earth.
0:08:53 > 0:08:56'But travel faster than the planet's surface,
0:08:56 > 0:08:59'and the normal passage of the day is reversed.'
0:09:02 > 0:09:03Right, accelerating.
0:09:03 > 0:09:06Accelerating. Oh, there we go.
0:09:06 > 0:09:09- That's acceleration.- Mach 1.
0:09:11 > 0:09:12Through the sound barrier.
0:09:16 > 0:09:19'As the jet accelerates,
0:09:19 > 0:09:22'it starts to overtake the spin of the Earth...
0:09:27 > 0:09:31'..causing the setting sun to rise again.'
0:09:31 > 0:09:32Starting to grow a little.
0:09:32 > 0:09:35It is, I can see it.
0:09:35 > 0:09:36We are beating the Earth!
0:09:39 > 0:09:40Absolutely terrific.
0:09:43 > 0:09:46- Starting to climb again, you can see it.- Yes.
0:09:46 > 0:09:47That's Mach 1.4.
0:09:50 > 0:09:51So it's 1,000 miles an hour.
0:09:51 > 0:09:53We're doing almost 1,000 miles an hour.
0:09:57 > 0:10:00And now the sun, it's almost a full vista with the clouds.
0:10:03 > 0:10:05- The sunrise!- It is.
0:10:05 > 0:10:08Two sunrises in one day!
0:10:08 > 0:10:12And all you need is the world's most advanced fighter aircraft.
0:10:12 > 0:10:13There we go.
0:10:15 > 0:10:16Beautiful.
0:10:19 > 0:10:22We've done it, we've outrun the Earth!
0:10:22 > 0:10:23BRIAN LAUGHS
0:10:24 > 0:10:26- Goodbye, sun!- Yes, right.
0:10:26 > 0:10:29Let's get ourselves on our way home.
0:10:31 > 0:10:32Do me a favour.
0:10:32 > 0:10:36We've had a bit of a quarrel with Lambeth parking services.
0:10:36 > 0:10:38THEY LAUGH
0:10:38 > 0:10:40Just one last favour before we left.
0:10:40 > 0:10:42THEY LAUGH
0:10:42 > 0:10:44RADIO CHATTER
0:11:04 > 0:11:07So that worked beautifully well.
0:11:07 > 0:11:11What happens when you light those engines on full,
0:11:11 > 0:11:14accelerate up to 1.4 times the speed of sound,
0:11:14 > 0:11:17you can't tell you're going at that speed at all,
0:11:17 > 0:11:21apart from the fact that out in the front of the cockpit,
0:11:21 > 0:11:25the sun just gently rises up again
0:11:25 > 0:11:28in the West, over Ireland.
0:11:28 > 0:11:32And then you put the brakes on and your face goes funny.
0:11:32 > 0:11:34But it was terrific.
0:11:34 > 0:11:36Thank you. THEY LAUGH
0:11:36 > 0:11:38And for the tape, he wasn't ill.
0:11:38 > 0:11:39THEY LAUGH
0:11:47 > 0:11:51To turn on its axis once every 24 hours,
0:11:51 > 0:11:53the Earth is spinning at breakneck speed.
0:11:57 > 0:12:01At the equator, where the ground has furthest to travel each day,
0:12:01 > 0:12:04its speed exceeds 1,000 miles an hour.
0:12:11 > 0:12:14Which presents a deep paradox.
0:12:16 > 0:12:21Here, right now, on a lazy spring day in the south of England,
0:12:21 > 0:12:26this piece of ground is thundering along at 650mph, and yet,
0:12:26 > 0:12:28I can't feel it.
0:12:28 > 0:12:31And when you think about it, that's a very strange thing.
0:12:31 > 0:12:35I mean, what is motion if you can't perceive it?
0:12:35 > 0:12:38Well, the answer is a deep one.
0:12:38 > 0:12:40You can't perceive that you're moving
0:12:40 > 0:12:42if you're travelling in a straight
0:12:42 > 0:12:44line at a constant speed.
0:12:44 > 0:12:47And that's a fundamental property of nature.
0:12:47 > 0:12:50It's the way our universe is constructed.
0:12:50 > 0:12:53So I don't feel that I'm moving from minute to minute,
0:12:53 > 0:12:57because I'm almost moving in a straight line.
0:12:57 > 0:12:59I have to make it round in a circle,
0:12:59 > 0:13:04but it's 15,000 miles around and I have 24 hours to do it.
0:13:08 > 0:13:11Although we don't experience the sensation
0:13:11 > 0:13:13of moving around our planet's axis,
0:13:13 > 0:13:18we do experience events that are a direct consequence of living
0:13:18 > 0:13:19on a spinning globe.
0:13:36 > 0:13:37In the Philippines,
0:13:37 > 0:13:42the warmth of the tropical sun and the spin of the Earth conspire to
0:13:42 > 0:13:45produce some of the most extreme weather on the planet.
0:13:55 > 0:13:59And for the people who live here, it poses an ever-present threat.
0:14:39 > 0:14:43With the kids out of the way, Leanilla begins the work
0:14:43 > 0:14:46she hopes will allow them to leave Tacloban for ever.
0:15:22 > 0:15:27Every time it rains, darker memories rise to the surface.
0:15:40 > 0:15:46Three years ago, driven by heat rising from the tropical waters,
0:15:46 > 0:15:48a storm formed over the Pacific Ocean.
0:15:53 > 0:15:55As it tracked north,
0:15:55 > 0:16:00the Earth's rotation gave rise to a force known as the Coriolis force,
0:16:00 > 0:16:05which acted on the air falling into its low-pressure heart,
0:16:05 > 0:16:07causing the storm to spin,
0:16:07 > 0:16:09increasing its intensity.
0:16:16 > 0:16:22So what began as a tropical storm at sea hit Tacloban as a category five
0:16:22 > 0:16:23super-typhoon.
0:16:42 > 0:16:46Leanilla's family were caught directly in its path.
0:17:04 > 0:17:08Leanilla took the children and sought shelter in the local church -
0:17:08 > 0:17:11the only solid structure in the neighbourhood.
0:17:37 > 0:17:40But while the family were in the relative safety of the church,
0:17:40 > 0:17:44Leanilla's husband was caught up in the chaos raging outside.
0:18:10 > 0:18:15Boosted by the Coriolis force, winds approaching 200mph
0:18:15 > 0:18:16whipped up the ocean...
0:18:19 > 0:18:22..into a devastating storm surge.
0:18:33 > 0:18:36Over 90% of the city was destroyed...
0:18:39 > 0:18:43..leaving Leanilla with an anxious wait for news of her husband.
0:19:17 > 0:19:20Exposed to the full force of the storm,
0:19:20 > 0:19:23Juvie had been swept inland for more than a mile.
0:19:41 > 0:19:46The Hernandez family experienced a singular event that affected their
0:19:46 > 0:19:49lives dramatically and directly.
0:19:58 > 0:20:00The Coriolis force that caused it
0:20:00 > 0:20:04isn't a fundamental force of nature in its own right.
0:20:04 > 0:20:08It appears because of the Earth's rotation.
0:20:14 > 0:20:19So-called fictitious forces like this arise whenever anything spins
0:20:19 > 0:20:21or rotates.
0:20:22 > 0:20:26And because the Earth's orbital motion through space is complex -
0:20:26 > 0:20:31affected not only by the sun, but also the moon -
0:20:31 > 0:20:33there are other fictitious forces at work.
0:20:38 > 0:20:41One of these plays a subtle but important role
0:20:41 > 0:20:45in a twice daily phenomenon with which we are all familiar.
0:20:47 > 0:20:49The ebb and flow of the tides.
0:21:02 > 0:21:06We usually think of the moon in orbit around the Earth
0:21:06 > 0:21:10as the Earth stays still. But that's not quite right.
0:21:10 > 0:21:12Actually, they are both in orbit.
0:21:12 > 0:21:15They are in orbit around a point called the common centre of mass
0:21:15 > 0:21:17of the Earth-Moon system.
0:21:17 > 0:21:21Essentially, what's happening is something like that,
0:21:21 > 0:21:23although it's quite difficult to do.
0:21:23 > 0:21:27Now, when things rotate around in circles,
0:21:27 > 0:21:29other forces come into play.
0:21:29 > 0:21:32In this case a force called the centrifugal force.
0:21:32 > 0:21:35So that's the force you'd feel if you were hanging on to a roundabout,
0:21:35 > 0:21:38going faster and faster and you have to hang on tighter and tighter
0:21:38 > 0:21:40because of the force trying to throw you off.
0:21:40 > 0:21:42That's the centrifugal force.
0:21:43 > 0:21:47Now, let's bring the moon back.
0:21:47 > 0:21:50So now there are two forces at play in this system.
0:21:50 > 0:21:51There's a gravitational pull -
0:21:51 > 0:21:54the moon - which pulls everything towards it,
0:21:54 > 0:21:58and there's that centrifugal force, trying to throw everything off.
0:21:58 > 0:22:03And they are in perfect balance at the centre of the Earth.
0:22:03 > 0:22:05But think about the ocean, here.
0:22:05 > 0:22:08That's closer to the moon,
0:22:08 > 0:22:13and so the moon's gravitational pull wins and you get a tidal bulge.
0:22:13 > 0:22:16Now think about this point on this side of the Earth.
0:22:16 > 0:22:21That's farther away from the moon, so the centrifugal force wins,
0:22:21 > 0:22:25throwing the water off, and you get a tidal bulge.
0:22:25 > 0:22:30Now the Earth just rotates underneath those tides
0:22:30 > 0:22:35once a day and that's why you get two tides every day.
0:22:41 > 0:22:45On an English beach, the complex gravitational interaction
0:22:45 > 0:22:48between Earth and Moon is distilled
0:22:48 > 0:22:51into the gentle advance and retreat of the waves.
0:22:54 > 0:22:58But in some parts of the world, on a few days of the year,
0:22:58 > 0:23:01this mismatch of the forces across the Earth
0:23:01 > 0:23:04unleashes something far more destructive.
0:23:17 > 0:23:22For nearly 4,500 miles, the Amazon snakes through dense rainforest
0:23:22 > 0:23:27from its source high in the Andes to the shores of the Atlantic Ocean.
0:23:36 > 0:23:39And here, close to the mouth of the river,
0:23:39 > 0:23:43its banks are home to the Rivieros.
0:24:05 > 0:24:07In this remote part of the jungle,
0:24:07 > 0:24:10Joao's family are completely dependent on the river.
0:24:31 > 0:24:34The Amazon is the centre of their world...
0:24:36 > 0:24:38..the place where they work and play.
0:24:48 > 0:24:51But today is different.
0:24:51 > 0:24:54Today, they must get away from the water.
0:24:54 > 0:24:57Because this part of the river
0:24:57 > 0:24:59is home to a monster.
0:25:27 > 0:25:32In the ancient Tupi language, Pororoca means "great roar".
0:25:32 > 0:25:36A sound so loud, it can be heard ten miles away.
0:25:49 > 0:25:50Pororoca...
0:26:01 > 0:26:04When the moon and sun fall into alignment with the Earth...
0:26:07 > 0:26:09..their gravitational pull is combined...
0:26:12 > 0:26:15..causing the Pororoca to emerge from the ocean.
0:26:30 > 0:26:33The Pororoca is one of the biggest
0:26:33 > 0:26:36and most powerful tidal waves on the planet.
0:26:42 > 0:26:46A seething wall of water that engulfs everything in its path
0:26:46 > 0:26:49as it surges up the river for nearly 200 miles.
0:27:10 > 0:27:15But as the Pororoca strikes, not everyone is trying to escape.
0:27:47 > 0:27:49# My veins are blue and connected
0:27:49 > 0:27:52# And every single bone in my brain is electric
0:27:52 > 0:27:55# But I dig ditches like the best of 'em
0:27:55 > 0:27:58# Yo trabajo duro Como en madera y yeso... #
0:27:59 > 0:28:04Serginho Laus has devoted his life to surfing the Pororoca.
0:28:06 > 0:28:08Waiting for the few times a year
0:28:08 > 0:28:11when the Earth's orbit around the sun and the centre of mass
0:28:11 > 0:28:12of the Earth-Moon system
0:28:12 > 0:28:15provides the ultimate ride through the jungle.
0:28:56 > 0:29:00Then, as suddenly it appears, the Pororoca passes...
0:29:02 > 0:29:05..leaving nothing but stories in its wake.
0:29:53 > 0:29:55The tides are a familiar,
0:29:55 > 0:30:00everyday result of the details of the Earth's complex spinning
0:30:00 > 0:30:05and rotational motion, and its gravitational dance with the moon.
0:30:05 > 0:30:08We experience them almost from moment to moment,
0:30:08 > 0:30:13certainly over the length of one lazy summer's afternoon.
0:30:13 > 0:30:15But the very existence of the moon
0:30:15 > 0:30:20has its origins in a series of chance events way back in deep time
0:30:20 > 0:30:25that created this stage on which we live out our lives.
0:30:32 > 0:30:344.6 billion years ago,
0:30:34 > 0:30:38the solar system formed from a cloud of gas and dust,
0:30:38 > 0:30:40collapsing under its own gravity.
0:30:44 > 0:30:48As the cloud fell inwards,
0:30:48 > 0:30:49it began to spin.
0:30:53 > 0:30:58And it was out of this maelstrom that our planet was forged,
0:30:58 > 0:31:00from colliding rock and ice.
0:31:12 > 0:31:16The Earth's spin was taken from the primordial cloud
0:31:16 > 0:31:18out of which it formed.
0:31:22 > 0:31:27With every impact, the Earth grew, until eventually...
0:31:30 > 0:31:33..the sun rose over the newly formed planet...
0:31:35 > 0:31:36..for the first time.
0:31:43 > 0:31:47The first sunrise and the first day.
0:32:00 > 0:32:06For around 100 million years, the young Earth circled the sun alone
0:32:06 > 0:32:12until, it's thought, a catastrophic impact resulted in the creation
0:32:12 > 0:32:15of our planet's constant companion.
0:32:18 > 0:32:20It's not long after the Earth formed,
0:32:20 > 0:32:25a planet the size of Mars crashed into it in a glancing collision,
0:32:25 > 0:32:30throwing rocks and debris thousands of miles out into space.
0:32:30 > 0:32:35And over time, those rocks coalesced together to form the moon.
0:32:41 > 0:32:46The moon formed 15 times closer to the Earth than it is today,
0:32:46 > 0:32:49so it wasn't 250,000 miles away,
0:32:49 > 0:32:53it was ten or 15,000 miles away.
0:32:53 > 0:32:55It would have been a smooth object
0:32:55 > 0:32:59with volcanoes just seething with lava.
0:33:00 > 0:33:02An incredible sight.
0:33:07 > 0:33:11The collision that formed the moon also had a dramatic
0:33:11 > 0:33:14and lasting effect on the Earth.
0:33:17 > 0:33:20You might expect that when the planets formed
0:33:20 > 0:33:23out of that rotating disc of gas and dust, then they
0:33:23 > 0:33:25would all spin along with it.
0:33:25 > 0:33:28So their spin axis would be at right angles
0:33:28 > 0:33:31to the disc of the solar system.
0:33:31 > 0:33:34But that collision that formed the moon knocked
0:33:34 > 0:33:40the Earth over, so now it's at an angle of 23.5 degrees.
0:33:40 > 0:33:43And that means, as it orbits around the sun,
0:33:43 > 0:33:47then at some points, the northern hemisphere points towards the sun,
0:33:47 > 0:33:51and at other points, the northern hemisphere points away from the sun.
0:33:54 > 0:34:00A random event that happened so long ago has shaped the character of our
0:34:00 > 0:34:04planet ever since, and we experience its legacy every day.
0:34:08 > 0:34:13But these spins and orbits have had a deeper effect because they are an
0:34:13 > 0:34:17essential part of the stage upon which life evolved,
0:34:17 > 0:34:22and over billions of years natural selection has shaped the animals
0:34:22 > 0:34:24and plants that live on Earth
0:34:24 > 0:34:27in response to this celestial clockwork.
0:34:29 > 0:34:33The lowly dung beetle is a beautiful example.
0:34:42 > 0:34:45Their lives revolve around dung.
0:34:46 > 0:34:47Eating it...
0:34:49 > 0:34:50..fighting over it...
0:34:53 > 0:34:55..before rolling it away to safety.
0:34:58 > 0:35:00To aid their getaway,
0:35:00 > 0:35:04the beetles have evolved a trick that's intimately linked to the
0:35:04 > 0:35:06mechanics of the heavens.
0:35:10 > 0:35:14Using specialised photoreceptors on the tops of their eyes,
0:35:14 > 0:35:17they track the sun as it sweeps across the sky,
0:35:17 > 0:35:21using it to guide them on the quickest straight-line path
0:35:21 > 0:35:23away from the other beetles.
0:35:28 > 0:35:33But as night falls, the sun dips below the western horizon
0:35:33 > 0:35:37to be followed across the sky by the moon.
0:35:41 > 0:35:45So, by night, nocturnal beetles navigate by moonlight.
0:35:50 > 0:35:55And after the moon itself has set in the dead of night,
0:35:55 > 0:35:58they navigate by the light of the Milky Way.
0:36:01 > 0:36:04It's as if the beetles carry an imprint
0:36:04 > 0:36:08of events that happened billions of years in the past.
0:36:14 > 0:36:16Their unique behaviour can be traced back
0:36:16 > 0:36:19to the origin of the solar system.
0:36:23 > 0:36:26The collisions that set our world spinning,
0:36:26 > 0:36:30and the catastrophic impact that created the moon.
0:36:33 > 0:36:37We are separated from the violence of our planet's history
0:36:37 > 0:36:38by the passage of time.
0:36:41 > 0:36:45Although, almost paradoxically, it's in our experience of time,
0:36:45 > 0:36:48the setting of the sun,
0:36:48 > 0:36:53the rise and fall of the tides, and the passing of the seasons...
0:36:54 > 0:37:00..that we glimpse the reality of our voyage through space and time.
0:37:18 > 0:37:21It's July 10th and the northern hemisphere
0:37:21 > 0:37:22is tilted towards the sun.
0:37:22 > 0:37:26That means the sun rises high across the sky,
0:37:26 > 0:37:28and that increases the amount of sunlight falling
0:37:28 > 0:37:33on the ground in this little part of Oxfordshire, and that heats it up.
0:37:33 > 0:37:36The English summer is in full swing.
0:37:53 > 0:37:55But the Earth is on the move.
0:37:55 > 0:37:58A planet continuing to thunder around the sun
0:37:58 > 0:38:00because of the principle of inertia,
0:38:00 > 0:38:03its straight-line path curved into an orbit
0:38:03 > 0:38:06by the force of gravity.
0:38:06 > 0:38:09And as the Earth moves on that orbit,
0:38:09 > 0:38:13the North Pole tilts away from the sun and the violence of all that
0:38:13 > 0:38:18celestial mechanics is distilled into the gentle sensation of a lazy
0:38:18 > 0:38:21summer's day, giving way
0:38:21 > 0:38:24to the crisp chill of autumn.
0:38:24 > 0:38:29The sun rides lower in the sky and the nights draw in.
0:38:29 > 0:38:32As the Earth continues a yearly voyage,
0:38:32 > 0:38:37the North Pole tilts still further from the warmth of the sun.
0:38:37 > 0:38:39Autumn...
0:38:41 > 0:38:42..becomes winter.
0:38:42 > 0:38:46The sun barely rises above the tops of the trees,
0:38:46 > 0:38:49and Britain is plunged into a deep freeze.
0:38:53 > 0:38:56In the temperate latitudes of Oxfordshire,
0:38:56 > 0:38:59the passing of the seasons is relatively gentle.
0:39:03 > 0:39:05But if you head north,
0:39:05 > 0:39:10Earth's 23-degree tilt delivers a much more powerful challenge to the
0:39:10 > 0:39:12people that live in these lands of
0:39:12 > 0:39:16midnight sun and perpetual winter night.
0:39:23 > 0:39:27Sitting on the Arctic Circle, Tasiilaq experiences
0:39:27 > 0:39:31one of the largest seasonal temperature swings on the planet.
0:39:36 > 0:39:39In summer, days are long and mild,
0:39:39 > 0:39:42with nearly 23 hours of daylight to enjoy.
0:40:49 > 0:40:51Mmm!
0:40:54 > 0:40:58The dramatic seasonal shifts present elemental
0:40:58 > 0:41:01challenges to families like the Christiansens.
0:41:05 > 0:41:08As the Earth journeys around the sun,
0:41:08 > 0:41:11the whole of Greenland is tilted outwards
0:41:11 > 0:41:14towards the cold blackness of space.
0:41:25 > 0:41:29Human beings evolved in the equatorial valleys of Africa,
0:41:29 > 0:41:32and they're not well suited to the Arctic winter,
0:41:32 > 0:41:36where wind speeds exceed 100mph and temperatures plummet
0:41:36 > 0:41:40towards -30 Celsius.
0:41:48 > 0:41:52We require all the ingenuity and skills passed down from generation
0:41:52 > 0:41:56to generation to survive until the sun rides high again.
0:42:17 > 0:42:21To search for food, Michael, Malik and their friend Enoch
0:42:21 > 0:42:25must head out onto the treacherous frozen ocean.
0:42:33 > 0:42:36HE SHOUTS ORDERS
0:43:08 > 0:43:10HE SPEAKS IN OWN LANGUAGE
0:43:24 > 0:43:26HE SHOUTS ORDERS
0:43:30 > 0:43:33They've come here because, beneath the ice,
0:43:33 > 0:43:35the ocean waters teem with life.
0:43:49 > 0:43:51Despite appearances,
0:43:51 > 0:43:56the frozen depths of winter are in fact the best time to fish.
0:44:13 > 0:44:18For just a few months, ice provides a platform over the ocean,
0:44:18 > 0:44:22giving easy access to the fish below.
0:44:22 > 0:44:25A brief window in which they must catch enough
0:44:25 > 0:44:27to last the entire year.
0:44:49 > 0:44:52Lessons learned this winter will stay with Malik
0:44:52 > 0:44:53for the rest of his life.
0:44:57 > 0:44:59Until he becomes a hunter himself.
0:46:05 > 0:46:07HE LAUGHS
0:46:10 > 0:46:13Our planet's motion leads to something beyond the shifts
0:46:13 > 0:46:17in the thickness of the ice and the lengths of the days.
0:46:17 > 0:46:21It's reflected in the ever deepening relationship between father and son.
0:46:41 > 0:46:45The seasonal shifts in the colours and sounds of the wood are life's
0:46:45 > 0:46:48response to the clockwork of the solar system.
0:46:48 > 0:46:53Spring will follow winter as long as the Earth orbits the sun.
0:46:53 > 0:46:57The cycle of the seasons is effectively eternal,
0:46:57 > 0:47:01with the Earth returning to the same place every year.
0:47:01 > 0:47:07Except it doesn't return to the same place, because we don't only travel
0:47:07 > 0:47:11through space, we also travel through time.
0:47:18 > 0:47:21We live on a spinning ball of rock,
0:47:21 > 0:47:23hurtling through the universe.
0:47:28 > 0:47:30And yet in only a few moments
0:47:30 > 0:47:35does the violence of our world's motion break through.
0:47:43 > 0:47:44For the most part,
0:47:44 > 0:47:48our planet's movement is completely imperceptible to us.
0:47:53 > 0:47:58But there is a consequence of motion that affects us all more deeply than
0:47:58 > 0:48:02any other - our journey into the future.
0:48:25 > 0:48:28Once every year, Antonio Carter
0:48:28 > 0:48:33comes to the Church of St Constantine to pray for his life.
0:48:35 > 0:48:38In just a few hours, he will risk everything
0:48:38 > 0:48:39taking part in the Ardia...
0:48:44 > 0:48:46..the town's annual horse race.
0:48:47 > 0:48:51A tradition that has been part of his life since childhood.
0:49:10 > 0:49:15As the Earth has circled the sun, the Ardia has remained constant.
0:49:15 > 0:49:18The highlight of each passing year.
0:49:36 > 0:49:38GUNSHOT
0:50:03 > 0:50:06The race itself is a perilous cat-and-mouse chase
0:50:06 > 0:50:09through the village's most treacherous streets,
0:50:09 > 0:50:14that's taken place on the same two days in July for hundreds of years.
0:50:47 > 0:50:50Every year, the riders appear to take
0:50:50 > 0:50:55the same circuit around the same Sardinian town, at the precise
0:50:55 > 0:50:59moment the Earth returns to the same place in its orbit.
0:51:06 > 0:51:09But the reality is different.
0:51:09 > 0:51:11With every passing moment,
0:51:11 > 0:51:15we move to a different place in the universe.
0:51:15 > 0:51:19Not just in space, but also in time.
0:51:21 > 0:51:25We are hurtling into the future at the speed of light,
0:51:25 > 0:51:30and it's that motion we experience as the passing of time.
0:51:41 > 0:51:43It's only in the last century
0:51:43 > 0:51:47that we've discovered just how deeply motion
0:51:47 > 0:51:49and time are intertwined.
0:51:54 > 0:51:59We feel as if we move through space as time ticks by,
0:51:59 > 0:52:01but that's an illusion.
0:52:01 > 0:52:04The separation of space and time is false.
0:52:04 > 0:52:07The first person to realise that was Albert Einstein.
0:52:07 > 0:52:10He thought deeply about motion,
0:52:10 > 0:52:14the idea that we can't tell whether we're moving or not, and he tried to
0:52:14 > 0:52:19reconcile that with our picture of the universal laws of nature.
0:52:19 > 0:52:22And he found that he could do,
0:52:22 > 0:52:26but at the expense of jettisoning space and time
0:52:26 > 0:52:32as separate entities and merging them together into a unified whole,
0:52:32 > 0:52:36a fabric of the universe called spacetime.
0:52:43 > 0:52:48In spacetime, the central idea is that of an event,
0:52:48 > 0:52:52a moment that has a location in space and time.
0:52:52 > 0:52:56So, although I've come back to this same place, this wood,
0:52:56 > 0:53:00over the course of the year in summer, autumn, winter
0:53:00 > 0:53:03and now spring, each one of those visits
0:53:03 > 0:53:07is a different moment with a different location in spacetime.
0:53:14 > 0:53:17As the Earth moves through spacetime,
0:53:17 > 0:53:21its orbit traces out a spiral as it circles the sun
0:53:21 > 0:53:24and races into the future.
0:53:27 > 0:53:30It never returns to the same place
0:53:30 > 0:53:34because each moment is a different location
0:53:34 > 0:53:36in the fabric of the universe.
0:53:40 > 0:53:42And just as the Earth travels
0:53:42 > 0:53:45relentlessly onwards on its path through space time...
0:53:46 > 0:53:48..so must we.
0:54:03 > 0:54:08So this is how Einstein asks us to picture the sweep of our lives -
0:54:08 > 0:54:10the experience of living.
0:54:10 > 0:54:13Our lives are series of moments
0:54:13 > 0:54:18and they're laid out like places on a map.
0:54:18 > 0:54:21There is me as a little baby
0:54:21 > 0:54:24with my dad and with my grandad.
0:54:26 > 0:54:28That idyllic summer,
0:54:28 > 0:54:31some time in the early '70s in a paddling pool with my sister.
0:54:34 > 0:54:36I was about four years old.
0:54:37 > 0:54:39And the perfect Christmas,
0:54:39 > 0:54:42with my grandparents some time back in the 1970s.
0:54:43 > 0:54:46There is me when I was 20 years old
0:54:46 > 0:54:50with a ridiculous haircut. I was playing a gig somewhere
0:54:50 > 0:54:52in the middle of Europe - in Budapest, I think.
0:54:56 > 0:54:57Wedding day.
0:55:00 > 0:55:02And me in Oldham where I grew up...
0:55:04 > 0:55:06..with my little boy, George.
0:55:16 > 0:55:18This isn't exactly like a map.
0:55:18 > 0:55:22See, I can return to these places in space -
0:55:22 > 0:55:24to Oldham, to central Europe,
0:55:24 > 0:55:28to Duluth, Minnesota - where I got married - back to Oldham again.
0:55:30 > 0:55:34But I can't return to these moments, to these events in spacetime.
0:55:34 > 0:55:38Because of the geometry of spacetime itself,
0:55:38 > 0:55:43we are compelled to move inexorably into the future.
0:56:17 > 0:56:20As we all journey through spacetime,
0:56:20 > 0:56:23it's only in our memories that we can revisit the past.
0:56:42 > 0:56:45But just because we can't go back in time...
0:56:46 > 0:56:49..doesn't mean that the past isn't out there.
0:56:59 > 0:57:02If you take Einstein's universe at face value -
0:57:02 > 0:57:04and there's no reason why you shouldn't -
0:57:04 > 0:57:07it's our best theory of space and time,
0:57:07 > 0:57:12and this picture of spacetime with events placed within it suggests
0:57:12 > 0:57:16something wonderful and, I think, quite magical.
0:57:16 > 0:57:20See, if I leave a place in space,
0:57:20 > 0:57:24then it doesn't cease to exist when I've left it,
0:57:24 > 0:57:29and in spacetime, if I leave an event,
0:57:29 > 0:57:33it doesn't cease to exist when I've left it.
0:57:33 > 0:57:37So, that suggests that all those summers you spent
0:57:37 > 0:57:38with your mum and dad,
0:57:38 > 0:57:42or that first Christmas with your grandparents long ago,
0:57:42 > 0:57:46all those most precious memories of people and places,
0:57:46 > 0:57:52all those summers and winters passed and seasons yet to come
0:57:52 > 0:57:54are out there,
0:57:54 > 0:57:55somewhere in spacetime.