Wonders of the Universe s01e99 Episode Script
Learning Shorts
1 We all have an intuitive understanding of time.
It seems obvious to us that things change, and the future will be different to the past.
But why are we compelled to travel into the future? The answer to that question can be seen in how the world around us is always changing.
This is Kolmanskop, an abandoned diamond mining town in southern Namibia.
For half a century, it's fallen into disrepair as it's slowly reclaimed by the sands.
The process at play here at Kolmanskop is happening everywhere in the universe - decay.
Or in the language of physics, an increase in entropy.
Entropy explains why, left to the mercy of the elements, mortar crumbles, glass shatters and buildings collapse.
And a good way to understand how is to think of objects not as single things, but as being made up of many constituent parts, like the individual grains that make up this pile of sand.
Now, entropy is a measure of how many ways I can re-arrange those grains and still keep the sand piled the same, and there are trillions and trillions and trillions of ways of doing that.
I mean, pretty much anything I do to this sand pile, if I mess the sand around and move it around, then it doesn't change the shape or the structure at all.
So, in the language of entropy, this sand pile has high entropy, because there are many, many ways that I can re-arrange its constituents and not change it.
But now, let me create some order in the universe.
Now, there are approximately as many sand grains in this sandcastle as there are in the sand pile.
But now, virtually anything I do to it will mess it up, will remove the beautiful order from this structure and because of that, the sandcastle has a low entropy.
It's a much more ordered state.
So, many ways of re-arranging the sand grains without changing the structure - high entropy.
Very few ways of re-arranging the sand grains without changing the structure, without disordering it - low entropy.
Now, imagine I was to leave this castle in the desert all day, the desert winds are going to blow the sand around and this castle is going to disintegrate.
It's going to become less ordered.
But there's nothing fundamental in the laws of physics that says that the wind couldn't pick up some sand from over here, deposit it here and deposit it in precisely the shape of a sandcastle.
You know, in principle, the wind could spontaneously build a sandcastle out of a pile of sand.
There's no reason why that couldn't happen.
It's just extremely, extremely unlikely, because there are very few ways of organising this sand so that it looks like a castle.
It's overwhelmingly more likely that when the wind blows the sand around, it will take the low entropy structure, the castle, and turn it into a high entropy structure, the sand pile.
So, entropy always increases.
Why is that? Because it's overwhelmingly more likely that it will.
So, everything tends from order to disorder.
That means that there is a difference between the future and the past, and that's one reason why time travels in one direction.
Everything that we see on Earth, from the grandest mountain to the most fleeting cloud, is made from the same set of building blocks.
They're called the chemical elements.
We now know that the Earth is made of 92 chemical elements and that's pretty amazing if you think of the complexity that we see around us.
We also know that everything beyond Earth, everything we can see in the universe, is made of those same 92 elements, and notice I didn't say "we think" that's what they're made of.
I said "we know" that's what they're made of, because we can prove it.
The chemistry set we have on Earth extends far beyond the planet.
We have set foot on the moon and know that it's rich in helium, silver and water.
And discovered that Mars is rich in iron.
And we know that Venus's thick atmosphere is full of sulphur.
But what of the rest of the universe? It seems impossible that we could discover what the stars are made of, because they're so far away.
Even the nearest star, Proxima Centauri, is 10,000 times more distant than Neptune, 4.
2 light years from Earth.
Yet despite these vast distances, these alien worlds are constantly sending us signals, telling us exactly what they're made of.
Our only contact with the distant stars is their light that has journeyed across the universe to reach us, and encoded in that light is the key to understanding what the universe is made of, and it's all down to a particular property of the chemical elements.
You see, when you heat the elements, when you burn them, then they give off light and each element gives off its own unique set of colours.
So this is strontium and it burns with a beautiful red colour.
Sodium is yellow.
Potassium is lilac.
And copper is blue.
Each element has its own characteristic colour.
It's this property that tells us what the stars are made of.
But it's a little more complicated than simply looking at the colour of the light that each star emits.
You can see why by looking at the light from our nearest star - the sun.
This is a spectrum of the light taken from our sun, and at first glance, it looks very familiar.
It looks like a stretched-out rainbow.
But if you look a bit more closely, then you see that this spectrum is covered in black lines.
These are called absorption lines.
Each element within our sun not only emits light of a certain colour, it also absorbs light of the same colour.
By looking for these black lines in the sun's light, we can simply read off a list of its constituent elements, like a barcode.
For example, these two black lines in the yellow bit of the spectrum are sodium.
You can see iron.
Right down here, you can see hydrogen.
So, by looking at these lines in precise detail, you can work out exactly what elements are present in the sun, and it turns out that that's about 70% hydrogen, 28% helium, and 2% the rest.
And you can do this not only for the sun but for any of the stars you can see in the sky, and you can measure exactly what they're made of.
So, that star there is Polaris, the pole star, and you can see that because all the other stars in the night sky appear to rotate around it.
Now, it's 430 light years away.
But we know, just by looking at the light, that it's got about the same heavy element abundance as our sun, but it's got markedly less carbon and a lot more nitrogen.
And the same applies for other stars.
Sirius, the dog star, contains three times as much iron as the sun.
And Proxima Centauri is rich in magnesium.
But although the quantities of the elements may vary, wherever we look across space, we only ever find the same 92 elements that we find on Earth.
We are made of the same stuff as the stars and the galaxies.
Everything in the universe, from the most distant star or galaxy to our small planet, is made from just 92 chemical elements, and here on planet Earth, there's one element that defines it more than any other.
Life is completely dependent on carbon.
I mean, I'm made of about a billion, billion, billion carbon atoms, as is every human being out there, every living thing on the planet.
Imagine how many carbon atoms that is.
So where does all that carbon come from? Well, it comes from the only place in the universe where elements are made - stars.
But in order for us to live, a star must die.
Stars in the prime of their lives, like our sun, burn the element hydrogen, converting it into helium.
But forming the other elements requires much higher temperatures, temperatures that can only be reached at the end of a star's life.
Imagine this old prison in Rio is a dying star.
Out there is the bright surface, shining off into space.
As I descend deeper and deeper into the prison, the conditions would become hotter and hotter and denser and denser, until down there in the heart of the star is the core.
Deep in its core, the star is fighting a futile battle against its own gravity.
As it desperately tries to stop itself collapsing under its own weight, new elements are made in a sequence of separate stages.
Stage one - while the star burns hydrogen to helium in the core, vast amounts of energy are released and that energy escapes, literally creating an outward pressure which balances the force of gravity and, well, it holds the star up and keeps it stable.
But eventually, the hydrogen in the core will run out.
Now, at that point, the core will start to collapse very rapidly, leaving a shell of hydrogen and helium behind.
Beneath this shell, as the core collapses, the temperature rises again, until at a hundred million degrees, stage two starts and helium nuclei begin to fuse together.
A helium fusion does two things.
Firstly, more energy is released and so, the collapse is halted.
But secondly, two more elements are produced in that process - carbon .
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oxygen.
Two elements vital for life.
So, this is where all the carbon in the universe comes from.
You know, every atom of carbon in my hand, every atom of carbon in every living thing on the planet was produced in the heart of a dying star.
But in only about a million years, the supply of helium in the core is used up and for stars as massive as the sun, that's where fusion stops, because there isn't enough gravitational energy to compress the core any further and restart fusion.
But for massive stars, the fusion process can continue.
Launching stage three, in which carbon fuses into magnesium, neon, sodium and aluminium.
And so it goes on.
Core collapse, followed by the next stage of fusion to create more elements, each stage hotter and shorter than the last.
And eventually, in a final stage that lasts only a couple of days, the heart of the star is transformed into almost pure iron, whose chemical symbol is Fe, and this is where the fusion process stops.
In its millions of years of life, the star has made all the common elements, the stuff that makes up 99% of the Earth.
The core is now a solid ball of those elements, stacked on top of each other in layers.
The star has only seconds left to live.
When a star runs out of fuel, then it can no longer release energy through fusion reactions, and then, there's only one thing that can happen.
LOUD EXPLOSIONS In about the same amount of time it takes this prison block to crumble, the entire star falls in on itself.
Yet even the implosion of the star only forges the first 26 elements.
For the remaining 66 elements, we have to look to some of the rarest conditions in the universe, the explosive death throes of the very largest stars, stars at least nine times the mass of our sun.
It's called a supernova, the biggest explosion in the universe.
Only these events can generate the enormous temperatures, hundreds of millions of degrees, necessary to fuse large amounts of the heaviest elements, elements like platinum, silver and gold.
So, the most precious elements are created in the death throes of the most massive stars.
For centuries, people thought that light travelled instantly from one place to another, but then, 350 years ago, one man's study of the planets and moons of the solar system revealed that it did in fact take time for light to travel.
Ever since Galileo discovered that Jupiter had moons, astronomers realised that you could use Jupiter and its moons as a very precise clock in the sky.
So here's the solar system, there's the sun, there's the Earth, here's Jupiter, and here is Jupiter's innermost moon, Io.
Now it was known that Io takes precisely 42 and a half hours to orbit around Jupiter, so if from the Earth, you see Io emerge from behind Jupiter at say, midnight on a Tuesday, then you know that it should re-emerge again at half-past six on Thursday afternoon.
Beautiful.
Now, one of the men charged with making precise tables of exactly when Io should be seen to emerge from behind Jupiter was the Danish astronomer Ole Romer, but he noticed something surprising.
You see, depending on the time of year, Io emerged later than expected or earlier than expected.
Now, Romer's genius was to realise that had nothing to do at all with the orbit of Io around Jupiter.
It was to do with the orbit of the Earth around the sun.
You see, what Romer noticed was that when the Earth was in a position in its orbit so that it was close to Jupiter, then Io emerged earlier than it was expected to.
Then, as the year passed and Earth moved around the sun and got further away from Jupiter, Romer noticed that Io then emerged later than it was expected to.
Romer realised that it takes time for light to travel from Jupiter to the Earth, so when the Earth is far away from Jupiter, it takes longer for the light to travel and therefore you see Io emerge from behind Jupiter later than you would expect.
Then, when the distance is small, it takes less time for the light to travel and you see Io emerge earlier than you might expect.
So Romer had discovered that light doesn't travel instantaneously.
It moves through space with a finite speed.
This remarkable insight led to a measurement of the speed of light.
We now know that light travels at precisely 299,792,458 metres per second.
That means that in the time it takes for me to click my fingers, light has travelled around the Earth seven times or that it travels ten million, million kilometres in one year.
And that's the yardstick we use to measure the universe, because ten million, million kilometres is approximately one light year.
It's easy to think that the universe has always existed, but our best scientific theory states that it emerged in one moment, from an event known as the Big Bang.
And one of the most significant pieces of evidence for this theory comes from our understanding of light and colour.
To reveal how colour can unlock the secrets of our universe's creation, I've come to one of the most spectacular natural wonders on Earth.
This is Victoria Falls in Zambia.
But I'm not here to marvel at the scale of this wonder.
I've come to see a much more delicate feature that appears above the water.
These magnificent rainbows are a permanent feature in the skies above Victoria Falls.
Now, rainbows are a beautiful phenomena, but I think they're even more beautiful when you understand how they're made because they are a visual representation of the fact that light is made up of, well, all the colours of the rainbow.
Just like light shining through a prism, rays of light from the sun are refracted as they enter the water droplets.
The light beams then reflect off the back of the droplets and are bent for a second time as they leave.
This bending and reflecting splits the light, and the colours hidden inside the white sunlight are revealed.
What we see as different colours are actually different wavelengths of light, so blue light has a relatively short wavelength, and then you go through green and yellow all the way to the red end of the spectrum, which has a very large wavelength.
Starlight is made up of countless different wavelengths, and when we look at the most distant stars and galaxies in the universe, their light appears redder, and it's this colouring that helps reveal that our universe had a beginning.
When light is emitted by a distant star or galaxy, its wavelength doesn't have to stay fixed - it can be squashed or stretched and when light's stretched, its wavelength increases and it moves to the red end of the spectrum.
So the interpretation of the fact that the most distant galaxies appear red, is that the space in-between them and us has stretched during the time it's taken the light to journey over that vast distance.
That means that our entire universe is expanding.
Now just think about what an expanding universe implies, because if the galaxies are all rushing away from each other, that means that if you re-wind time, then they must have been closer together in the past, and actually if you just keep re-winding, then you find that at some point in the past, all the galaxies we can see in the sky were quite literally on top of each other.
The universe was squashed down to a point.
That implies that the universe may have had a beginning and that is the Big Bang Theory.
Life on Earth takes seemingly endless forms.
Yet all creatures, however different, have evolved over billions of years from an ancient common ancestor.
This connection is explained by the theory of evolution by natural selection, and some of the best evidence for evolution are in the preserved remains of ancient creatures found in fossil beds.
This is one of them, the Burgess Shale in the Rocky Mountains of Canada.
Well, this is one of the most important fossil sites in the world, but actually it's one of the most important scientific sites of any kind, and it's not just because of the number and diversity of animals you find fossilised in these rocks, it's because of their age.
Over half a billion years old, they are some of the earliest fossils of complex life.
I mean, it's as if at one instant in this time we call the Cambrian Era, complex multi-cellular life suddenly emerged almost intact on the planet.
It's called the Evolutionary Big Bang.
So the Burgess Shale tells us that complex life seemed to emerge suddenly and a new theory may also suggest what triggered this moment.
Well, this is one of the beautiful animals you find up here in the fossil beds.
It's called a trilobite.
It's a very complex organism.
It's got an external skeleton, it's got jointed limbs but perhaps most remarkably these, because these are compound eyes.
They were very sophisticated and this was one of the first predators to be able to detect shapes and see movement and it could successfully chase its prey.
These creatures were among the first to harness the light that filled the universe.
Before they emerged, the rise and fall of the sun and the stars in the night sky simply went unnoticed.
Now there is a speculative theory that the emergence of the eye actually triggered the Cambrian explosion, this Evolutionary Big Bang, because once one species got eyes, then other species had also to develop eyes to either chase them as predators or evade them as prey, and that led to an evolutionary arms race.
More and more complex life forms developed.
So the evolution of the eye may have played a fundamental role in the emergence of complex life on Earth .
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and could have led to the evolution of our species.
The light we can see is just a tiny fraction of the light in our universe.
Beyond the visible spectrum, our world is also bathed in the light we can't see.
X-rays, infrared, ultraviolet are all types of light, but although we can't see this light, we can still sense it.
This sand has been under the full glare of the sun all day and I can feel the heat radiating off it.
Well, heat is nothing more than a form of light, although we don't normally call it light.
It's actually infrared light and the only difference between infrared and visible light is the wavelength.
Infrared has a longer wavelength than visible light.
Infrared isn't the end of the story.
There are even longer wavelengths of light, and these can reveal something extraordinary about our universe.
To detect them, you don't need a billion-pound satellite or a telescope built into the side of a mountain.
You just need one of these, a radio, because when we tune a radio, we're tuning into a form of light - radio waves.
MUSIC PLAYS ON RADIO But detecting them and understanding them provides the key to understanding the origin of the universe.
When you de-tune the radio a bit, you can just hear static but about 1% of that static is music to the ears of a physicist because that is stretched light from the Big Bang.
Carry him home safely to me The reason we can't see this ancient light is because as the universe expanded, the light waves were stretched and transformed into radio waves and microwaves.
This first light is called the Cosmic Microwave Background or CMB.
The CMB fills every part of the universe.
If my eyes could only see it, then the sky would be ablaze with this primordial light both day and night.
Although we are not sensitive to this light, specialised cameras are, and when they are pointed towards the heavens, something beautiful emerges.
These scattered colours are the fading embers, the last remnants of light from the beginning of the universe.
Looking out into space, you might think that the cosmos is a constant unchanging place, that the stars will always be there.
But in fact, the stars are only a temporary feature in the sky, and though they may burn brightly for many millions or billions of years, they can only live for as long as they have a supply of hydrogen to burn.
And when a star like our sun runs out of hydrogen, it begins to die.
But it doesn't go quietly.
At the end of its life, the sun won't simply fade away to nothing.
As it begins to run out of fuel, its core will collapse and the extra heat this generates will cause its outer layers to expand.
In around a billion years' time, this will have a catastrophic effect on our fragile world.
Gradually, the Earth will become hotter and hotter, so there will be one last perfect day on Earth, but eventually, the existence of all life on this planet will become impossible.
Long after life has disappeared, the sun will have grown so much, it will fill the entire horizon.
It will have become a red giant, the last phase of its life.
Our planet might not survive to this point, but if it does, little more than a scorched and barren rock will remain to witness the final death throes of our star.
In six billion years, our sun will explode, throwing vast amounts of gas and dust out into space to form a gigantic nebula.
At its heart will be a faintly glowing ember, all that remains of our once-magnificent sun.
It will be smaller than the size of the Earth, less than a millionth of its current volume, and a fraction of its brightness.
Our sun will have become a white dwarf.
With no fuel left to burn, a white dwarf's faint glow comes from the last residual heat from its extinguished furnace.
The sun is now dead, its remains slowly cooling in the freezing temperatures of deep space.
Looking at it from where the Earth is now, it would only generate the same amount of light as the full moon on a clear night.
The fate of the sun is the same as for all stars.
One day they must all eventually die, and the cosmos will be plunged into eternal night, because this structured universe that we inhabit and all its wonders, the stars and the planets and the galaxies, cannot last forever.
The cosmos WILL eventually fade and die.
Black holes are the most destructive places in the universe, able to devour entire stars.
Yet we've never seen one.
It's because of their effects on the stars and galaxies, and the dust and gas around them, that we know that they exist.
But the reason why black holes are invisible can be demonstrated here on Earth.
Near a black hole, space and time do some very strange things because black holes are probably the most violent places we know of in the universe.
This river provides a beautiful analogy for what happens to space and time as you get closer and closer to the black hole.
Now, upstream, the water is flowing pretty slowly.
Let's imagine that it's flowing at three kilometres per hour and I can swim at four, so I can swim faster than the flow and can easily escape.
But as you go further and further downstream towards the waterfall in the distance, the river flows faster and faster.
Imagine I decide to jump into the river just there on the edge of the falls.
The water is flowing far faster than I could swim, so no matter what I did, no matter how hard I tried, I would not be able to swim back upstream.
I would be carried inexorably towards the edge and I would vanish over the falls.
Well, it's the same close to a black hole because space flows faster and faster and faster towards the black hole - literally this stuff, my space that I'm in, flowing over the edge into the black hole.
And at the very special point called the event horizon, space is flowing at the speed of light into the black hole.
Light itself, travelling at 300,000 kilometres per second, is not going fast enough to escape the flow, and light itself will plunge into the black hole.
So the fact that black holes can swallow light means that they will for ever remain invisible to our eyes.
Gravity is the force that keeps our feet firmly rooted to our planet.
Yet although it may appear constant and unchanging, this force varies on all the planets in the solar system and on the exo-planets we've discovered orbiting other suns.
To experience the gravity on these worlds, I need to go for a spin.
This is a centrifuge.
It was built in the 1950s to test whether fighter pilots had the right stuff, but it's going to allow me to feel what it would be like to stand on the surface of any of the planets in the solar system that are more massive than the Earth, and in fact, also what it would be like to stand on some of the planets that we've found around distant stars.
Threetwoone.
As the centrifuge rotates, it feels exactly as if gravity is increased.
The faster it spins, the greater the effect and we measure this in multiples of the strength of Earth's gravity, known as 1G.
The first planet I'm travelling to is Neptune.
Its gravity is just fractionally stronger than here on Earth.
So this is the gravitational field on Neptune and you feel, "You know what? I could probably get used to this.
"I could probably live on the surface of Neptune.
" Can you lift your hands a little? There we go.
Yeah, and down.
And it is actually quite an effort.
It is noticeably heavier.
It's like having a reasonably heavy weight in your hand.
To go to 2.
5G? Yes, so now we'll move, move from Neptune to Jupiter.
Let's go there.
Jupiter is over 1,300 times more massive than the Earth, but because it's mostly gas, it's not very dense so its gravity is just over twice as strong at its surface.
Well, now actually it is quite difficult to lift my hand.
And that's 2.
5G.
I wouldn't want to sit here for half an hour.
Can you lift both of your hands above your head? See what happens there.
Let's see, so actually just about, but actually it's an immense amount of hard work.
So it would be hard work living on Jupiter.
Let's go to 4G.
Actually, this is heading to a planet around A planet called Ogle 2TRL9B which is around a star in the constellation of Carina.
It's one of the exo-planets we've discovered.
Oh, and there we go.
Now, that is actuallybeginning to feel quite unpleasant.
Can you describe what you're feeling? Very heavy face.
My head is extremely heavy.
How about your lungs, inhaling, exhaling, breathing? It's much harder work.
I can't lift my hand off my leg.
OK.
And that's at 4G? Yeah.
Well, my head and my face feel very, very heavy.
It's quite an unpleasant feeling.
We'll go to 5 and let me know if you have any visual disturbances.
I am now en-route to a newly discovered exo-planet, Wasp 8b.
4.
4.
This world sits in the small and faint constellation of Sculptor.
Quite hard to speak.
It has a gravitational force nearly five times that of the Earth.
Right, we'll go to 5G.
Very foggy.
OK.
Very foggy.
Very foggy? Still foggy? Yeah.
Right.
Take it down.
OK, we'll take you down.
Very interesting.
It was, wasn't it? My face felt a bit saggy, though.
Well, you looked a little different.
That was, um, quite unpleasant that time, actually.
So you realise that we're, obviously, very finely tuned to live on a planet that has a gravitational, an acceleration due to gravity of 1G.
When you go to 2G, it's difficult.
When you go to 3G and 4G it becomes unpleasant, and 5G, anyway, for me, was on the border of being so unpleasant that you pass out.
So although gravity feels weak here on Earth, it certainly isn't weak everywhere across the universe.
And that's because gravity is an additive force.
It scales with mass, so the more massive the planet or star, the stronger its gravity.
Every moment of our lives, we experience a force that we can't see or touch.
Yet this force is able to keep us firmly rooted to the ground.
It is, of course, gravity.
But despite its intangible nature, we always know it's with us.
Now if I was to ask you, "How do you know that there's gravity around here?" Then you might say, "Well, it's obvious.
"You know, I can just do an experiment, I can drop something.
" Well, yes, but actually gravity is a little bit more subtle than that but to really experience it, to understand it, you have to do something pretty extreme.
And this plane has been modified to help me do it.
Thanks to its flight plan, it's known as the Vomit Comet.
Once we've climbed to 15,000 metres, this plane does something no ordinary flight would do - its engines are throttled back and the jet falls to Earth.
And then, something quite amazing happens.
THEY SQUEAL AND CHEER Push to me, push to me! I'm now plummeting towards the ground just like someone's cut the cable in a lift, and you see, we're all just floating.
By simply falling at the same rate as the plane, for a few fleeting moments, we are all free of gravity's grip.
But this isn't just a joy ride.
Now, look, there's something very profound here because although I'm falling towards the ground, as you see, gravity has completely gone away.
Gravity is not here any more.
'Because the aircraft is accelerating towards the ground at 1G, 'the effects of the Earth's gravity are completely cancelled out.
' So it is possible by the simple act of falling to get a very different experience of gravity.
Nothing can travel faster than the speed at which light travels, but although light travels fast, it's not infinitely fast so the further away an object is, the further back in time we see it.
The sun is 150 million kilometres away.
Now that's very close by cosmic standards, but light travels at only 300,000 kilometres per second, so that means that we're seeing the sun as it was in the past, actually eight minutes in the past.
But when we look beyond our sun, to far more distant stars, we reach further back in time.
As the sun dips below the horizon and night falls .
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the universe just fades into view.
And then, as it gets darker and darker, the Milky Way appears - a vast swathe of billions and billions of suns as you look out towards the centre of our Milky Way galaxy.
But I think for me, the most magical thing you can see in the sky with the naked eye, is just below the constellation of Cassiopeia, the W of stars in the sky.
There, look at that.
Actually, I've got to say, that's amazing.
You see, that misty patch of light is not a cloud in the sky, it's not even gas and dust in our galaxy.
Thatis another galaxy.
It's the Andromeda galaxy, which is roughly the same size as our own - an island of hundreds of billions of stars, 25 million, million, million kilometres in that direction.
The light that I've just captured in my camera began its journey two and a half million years ago.
At that time on Earth, there were no humans.
Homo habilis, our distant ancestors, were roaming the plains of Africa and as those light rays travelled through the vastness of space, our species evolved and thousands and thousands and thousands of generations of humans lived and died.
And then, two and a half million years after their journey began, these messengers from the depths of space, and from way back in our past, arrived here on Earth, and I just captured them and took that picture.
But by peering further than the naked eye will allow, we can journey to a time way before human history.
In the last 20 years, powerful space telescopes have carried us ever deeper into space and we have become virtual time travellers.
This is NGC 520 and it's the product of a cosmic collision, but this galaxy is a hundred million light years away.
That means that the light began its journey from this galaxy to my eye when the dinosaurs roamed the Earth.
But these spectacular galaxies are not the end of our journey into the past.
In 2004, we peered further back in time than ever before and captured the light from the most distant galaxies in the universe.
The image is called the Hubble Ultra Deep Field.
It's a picture taken by the Hubble Space Telescope over a period of 11 days, and it focused its camera on the tiniest piece of sky, just below the constellation of Orion.
Now, it's a piece of sky that you would cover if you took your thumb, held it in front of your face and then moved it 20 times further away.
But the Hubble captured the faintest lights from the most distant regions of the universe and it took this photograph.
Now, almost every point of light in that image is not a star, but a galaxy of over a hundred billion stars.
The most distant galaxies in that image are over 13 billion light years away.
That means that the faint light from those galaxies began its journey to Earth 13 billion years ago.
That's over three times the age of the Earth.
It seems obvious to us that things change, and the future will be different to the past.
But why are we compelled to travel into the future? The answer to that question can be seen in how the world around us is always changing.
This is Kolmanskop, an abandoned diamond mining town in southern Namibia.
For half a century, it's fallen into disrepair as it's slowly reclaimed by the sands.
The process at play here at Kolmanskop is happening everywhere in the universe - decay.
Or in the language of physics, an increase in entropy.
Entropy explains why, left to the mercy of the elements, mortar crumbles, glass shatters and buildings collapse.
And a good way to understand how is to think of objects not as single things, but as being made up of many constituent parts, like the individual grains that make up this pile of sand.
Now, entropy is a measure of how many ways I can re-arrange those grains and still keep the sand piled the same, and there are trillions and trillions and trillions of ways of doing that.
I mean, pretty much anything I do to this sand pile, if I mess the sand around and move it around, then it doesn't change the shape or the structure at all.
So, in the language of entropy, this sand pile has high entropy, because there are many, many ways that I can re-arrange its constituents and not change it.
But now, let me create some order in the universe.
Now, there are approximately as many sand grains in this sandcastle as there are in the sand pile.
But now, virtually anything I do to it will mess it up, will remove the beautiful order from this structure and because of that, the sandcastle has a low entropy.
It's a much more ordered state.
So, many ways of re-arranging the sand grains without changing the structure - high entropy.
Very few ways of re-arranging the sand grains without changing the structure, without disordering it - low entropy.
Now, imagine I was to leave this castle in the desert all day, the desert winds are going to blow the sand around and this castle is going to disintegrate.
It's going to become less ordered.
But there's nothing fundamental in the laws of physics that says that the wind couldn't pick up some sand from over here, deposit it here and deposit it in precisely the shape of a sandcastle.
You know, in principle, the wind could spontaneously build a sandcastle out of a pile of sand.
There's no reason why that couldn't happen.
It's just extremely, extremely unlikely, because there are very few ways of organising this sand so that it looks like a castle.
It's overwhelmingly more likely that when the wind blows the sand around, it will take the low entropy structure, the castle, and turn it into a high entropy structure, the sand pile.
So, entropy always increases.
Why is that? Because it's overwhelmingly more likely that it will.
So, everything tends from order to disorder.
That means that there is a difference between the future and the past, and that's one reason why time travels in one direction.
Everything that we see on Earth, from the grandest mountain to the most fleeting cloud, is made from the same set of building blocks.
They're called the chemical elements.
We now know that the Earth is made of 92 chemical elements and that's pretty amazing if you think of the complexity that we see around us.
We also know that everything beyond Earth, everything we can see in the universe, is made of those same 92 elements, and notice I didn't say "we think" that's what they're made of.
I said "we know" that's what they're made of, because we can prove it.
The chemistry set we have on Earth extends far beyond the planet.
We have set foot on the moon and know that it's rich in helium, silver and water.
And discovered that Mars is rich in iron.
And we know that Venus's thick atmosphere is full of sulphur.
But what of the rest of the universe? It seems impossible that we could discover what the stars are made of, because they're so far away.
Even the nearest star, Proxima Centauri, is 10,000 times more distant than Neptune, 4.
2 light years from Earth.
Yet despite these vast distances, these alien worlds are constantly sending us signals, telling us exactly what they're made of.
Our only contact with the distant stars is their light that has journeyed across the universe to reach us, and encoded in that light is the key to understanding what the universe is made of, and it's all down to a particular property of the chemical elements.
You see, when you heat the elements, when you burn them, then they give off light and each element gives off its own unique set of colours.
So this is strontium and it burns with a beautiful red colour.
Sodium is yellow.
Potassium is lilac.
And copper is blue.
Each element has its own characteristic colour.
It's this property that tells us what the stars are made of.
But it's a little more complicated than simply looking at the colour of the light that each star emits.
You can see why by looking at the light from our nearest star - the sun.
This is a spectrum of the light taken from our sun, and at first glance, it looks very familiar.
It looks like a stretched-out rainbow.
But if you look a bit more closely, then you see that this spectrum is covered in black lines.
These are called absorption lines.
Each element within our sun not only emits light of a certain colour, it also absorbs light of the same colour.
By looking for these black lines in the sun's light, we can simply read off a list of its constituent elements, like a barcode.
For example, these two black lines in the yellow bit of the spectrum are sodium.
You can see iron.
Right down here, you can see hydrogen.
So, by looking at these lines in precise detail, you can work out exactly what elements are present in the sun, and it turns out that that's about 70% hydrogen, 28% helium, and 2% the rest.
And you can do this not only for the sun but for any of the stars you can see in the sky, and you can measure exactly what they're made of.
So, that star there is Polaris, the pole star, and you can see that because all the other stars in the night sky appear to rotate around it.
Now, it's 430 light years away.
But we know, just by looking at the light, that it's got about the same heavy element abundance as our sun, but it's got markedly less carbon and a lot more nitrogen.
And the same applies for other stars.
Sirius, the dog star, contains three times as much iron as the sun.
And Proxima Centauri is rich in magnesium.
But although the quantities of the elements may vary, wherever we look across space, we only ever find the same 92 elements that we find on Earth.
We are made of the same stuff as the stars and the galaxies.
Everything in the universe, from the most distant star or galaxy to our small planet, is made from just 92 chemical elements, and here on planet Earth, there's one element that defines it more than any other.
Life is completely dependent on carbon.
I mean, I'm made of about a billion, billion, billion carbon atoms, as is every human being out there, every living thing on the planet.
Imagine how many carbon atoms that is.
So where does all that carbon come from? Well, it comes from the only place in the universe where elements are made - stars.
But in order for us to live, a star must die.
Stars in the prime of their lives, like our sun, burn the element hydrogen, converting it into helium.
But forming the other elements requires much higher temperatures, temperatures that can only be reached at the end of a star's life.
Imagine this old prison in Rio is a dying star.
Out there is the bright surface, shining off into space.
As I descend deeper and deeper into the prison, the conditions would become hotter and hotter and denser and denser, until down there in the heart of the star is the core.
Deep in its core, the star is fighting a futile battle against its own gravity.
As it desperately tries to stop itself collapsing under its own weight, new elements are made in a sequence of separate stages.
Stage one - while the star burns hydrogen to helium in the core, vast amounts of energy are released and that energy escapes, literally creating an outward pressure which balances the force of gravity and, well, it holds the star up and keeps it stable.
But eventually, the hydrogen in the core will run out.
Now, at that point, the core will start to collapse very rapidly, leaving a shell of hydrogen and helium behind.
Beneath this shell, as the core collapses, the temperature rises again, until at a hundred million degrees, stage two starts and helium nuclei begin to fuse together.
A helium fusion does two things.
Firstly, more energy is released and so, the collapse is halted.
But secondly, two more elements are produced in that process - carbon .
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oxygen.
Two elements vital for life.
So, this is where all the carbon in the universe comes from.
You know, every atom of carbon in my hand, every atom of carbon in every living thing on the planet was produced in the heart of a dying star.
But in only about a million years, the supply of helium in the core is used up and for stars as massive as the sun, that's where fusion stops, because there isn't enough gravitational energy to compress the core any further and restart fusion.
But for massive stars, the fusion process can continue.
Launching stage three, in which carbon fuses into magnesium, neon, sodium and aluminium.
And so it goes on.
Core collapse, followed by the next stage of fusion to create more elements, each stage hotter and shorter than the last.
And eventually, in a final stage that lasts only a couple of days, the heart of the star is transformed into almost pure iron, whose chemical symbol is Fe, and this is where the fusion process stops.
In its millions of years of life, the star has made all the common elements, the stuff that makes up 99% of the Earth.
The core is now a solid ball of those elements, stacked on top of each other in layers.
The star has only seconds left to live.
When a star runs out of fuel, then it can no longer release energy through fusion reactions, and then, there's only one thing that can happen.
LOUD EXPLOSIONS In about the same amount of time it takes this prison block to crumble, the entire star falls in on itself.
Yet even the implosion of the star only forges the first 26 elements.
For the remaining 66 elements, we have to look to some of the rarest conditions in the universe, the explosive death throes of the very largest stars, stars at least nine times the mass of our sun.
It's called a supernova, the biggest explosion in the universe.
Only these events can generate the enormous temperatures, hundreds of millions of degrees, necessary to fuse large amounts of the heaviest elements, elements like platinum, silver and gold.
So, the most precious elements are created in the death throes of the most massive stars.
For centuries, people thought that light travelled instantly from one place to another, but then, 350 years ago, one man's study of the planets and moons of the solar system revealed that it did in fact take time for light to travel.
Ever since Galileo discovered that Jupiter had moons, astronomers realised that you could use Jupiter and its moons as a very precise clock in the sky.
So here's the solar system, there's the sun, there's the Earth, here's Jupiter, and here is Jupiter's innermost moon, Io.
Now it was known that Io takes precisely 42 and a half hours to orbit around Jupiter, so if from the Earth, you see Io emerge from behind Jupiter at say, midnight on a Tuesday, then you know that it should re-emerge again at half-past six on Thursday afternoon.
Beautiful.
Now, one of the men charged with making precise tables of exactly when Io should be seen to emerge from behind Jupiter was the Danish astronomer Ole Romer, but he noticed something surprising.
You see, depending on the time of year, Io emerged later than expected or earlier than expected.
Now, Romer's genius was to realise that had nothing to do at all with the orbit of Io around Jupiter.
It was to do with the orbit of the Earth around the sun.
You see, what Romer noticed was that when the Earth was in a position in its orbit so that it was close to Jupiter, then Io emerged earlier than it was expected to.
Then, as the year passed and Earth moved around the sun and got further away from Jupiter, Romer noticed that Io then emerged later than it was expected to.
Romer realised that it takes time for light to travel from Jupiter to the Earth, so when the Earth is far away from Jupiter, it takes longer for the light to travel and therefore you see Io emerge from behind Jupiter later than you would expect.
Then, when the distance is small, it takes less time for the light to travel and you see Io emerge earlier than you might expect.
So Romer had discovered that light doesn't travel instantaneously.
It moves through space with a finite speed.
This remarkable insight led to a measurement of the speed of light.
We now know that light travels at precisely 299,792,458 metres per second.
That means that in the time it takes for me to click my fingers, light has travelled around the Earth seven times or that it travels ten million, million kilometres in one year.
And that's the yardstick we use to measure the universe, because ten million, million kilometres is approximately one light year.
It's easy to think that the universe has always existed, but our best scientific theory states that it emerged in one moment, from an event known as the Big Bang.
And one of the most significant pieces of evidence for this theory comes from our understanding of light and colour.
To reveal how colour can unlock the secrets of our universe's creation, I've come to one of the most spectacular natural wonders on Earth.
This is Victoria Falls in Zambia.
But I'm not here to marvel at the scale of this wonder.
I've come to see a much more delicate feature that appears above the water.
These magnificent rainbows are a permanent feature in the skies above Victoria Falls.
Now, rainbows are a beautiful phenomena, but I think they're even more beautiful when you understand how they're made because they are a visual representation of the fact that light is made up of, well, all the colours of the rainbow.
Just like light shining through a prism, rays of light from the sun are refracted as they enter the water droplets.
The light beams then reflect off the back of the droplets and are bent for a second time as they leave.
This bending and reflecting splits the light, and the colours hidden inside the white sunlight are revealed.
What we see as different colours are actually different wavelengths of light, so blue light has a relatively short wavelength, and then you go through green and yellow all the way to the red end of the spectrum, which has a very large wavelength.
Starlight is made up of countless different wavelengths, and when we look at the most distant stars and galaxies in the universe, their light appears redder, and it's this colouring that helps reveal that our universe had a beginning.
When light is emitted by a distant star or galaxy, its wavelength doesn't have to stay fixed - it can be squashed or stretched and when light's stretched, its wavelength increases and it moves to the red end of the spectrum.
So the interpretation of the fact that the most distant galaxies appear red, is that the space in-between them and us has stretched during the time it's taken the light to journey over that vast distance.
That means that our entire universe is expanding.
Now just think about what an expanding universe implies, because if the galaxies are all rushing away from each other, that means that if you re-wind time, then they must have been closer together in the past, and actually if you just keep re-winding, then you find that at some point in the past, all the galaxies we can see in the sky were quite literally on top of each other.
The universe was squashed down to a point.
That implies that the universe may have had a beginning and that is the Big Bang Theory.
Life on Earth takes seemingly endless forms.
Yet all creatures, however different, have evolved over billions of years from an ancient common ancestor.
This connection is explained by the theory of evolution by natural selection, and some of the best evidence for evolution are in the preserved remains of ancient creatures found in fossil beds.
This is one of them, the Burgess Shale in the Rocky Mountains of Canada.
Well, this is one of the most important fossil sites in the world, but actually it's one of the most important scientific sites of any kind, and it's not just because of the number and diversity of animals you find fossilised in these rocks, it's because of their age.
Over half a billion years old, they are some of the earliest fossils of complex life.
I mean, it's as if at one instant in this time we call the Cambrian Era, complex multi-cellular life suddenly emerged almost intact on the planet.
It's called the Evolutionary Big Bang.
So the Burgess Shale tells us that complex life seemed to emerge suddenly and a new theory may also suggest what triggered this moment.
Well, this is one of the beautiful animals you find up here in the fossil beds.
It's called a trilobite.
It's a very complex organism.
It's got an external skeleton, it's got jointed limbs but perhaps most remarkably these, because these are compound eyes.
They were very sophisticated and this was one of the first predators to be able to detect shapes and see movement and it could successfully chase its prey.
These creatures were among the first to harness the light that filled the universe.
Before they emerged, the rise and fall of the sun and the stars in the night sky simply went unnoticed.
Now there is a speculative theory that the emergence of the eye actually triggered the Cambrian explosion, this Evolutionary Big Bang, because once one species got eyes, then other species had also to develop eyes to either chase them as predators or evade them as prey, and that led to an evolutionary arms race.
More and more complex life forms developed.
So the evolution of the eye may have played a fundamental role in the emergence of complex life on Earth .
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and could have led to the evolution of our species.
The light we can see is just a tiny fraction of the light in our universe.
Beyond the visible spectrum, our world is also bathed in the light we can't see.
X-rays, infrared, ultraviolet are all types of light, but although we can't see this light, we can still sense it.
This sand has been under the full glare of the sun all day and I can feel the heat radiating off it.
Well, heat is nothing more than a form of light, although we don't normally call it light.
It's actually infrared light and the only difference between infrared and visible light is the wavelength.
Infrared has a longer wavelength than visible light.
Infrared isn't the end of the story.
There are even longer wavelengths of light, and these can reveal something extraordinary about our universe.
To detect them, you don't need a billion-pound satellite or a telescope built into the side of a mountain.
You just need one of these, a radio, because when we tune a radio, we're tuning into a form of light - radio waves.
MUSIC PLAYS ON RADIO But detecting them and understanding them provides the key to understanding the origin of the universe.
When you de-tune the radio a bit, you can just hear static but about 1% of that static is music to the ears of a physicist because that is stretched light from the Big Bang.
Carry him home safely to me The reason we can't see this ancient light is because as the universe expanded, the light waves were stretched and transformed into radio waves and microwaves.
This first light is called the Cosmic Microwave Background or CMB.
The CMB fills every part of the universe.
If my eyes could only see it, then the sky would be ablaze with this primordial light both day and night.
Although we are not sensitive to this light, specialised cameras are, and when they are pointed towards the heavens, something beautiful emerges.
These scattered colours are the fading embers, the last remnants of light from the beginning of the universe.
Looking out into space, you might think that the cosmos is a constant unchanging place, that the stars will always be there.
But in fact, the stars are only a temporary feature in the sky, and though they may burn brightly for many millions or billions of years, they can only live for as long as they have a supply of hydrogen to burn.
And when a star like our sun runs out of hydrogen, it begins to die.
But it doesn't go quietly.
At the end of its life, the sun won't simply fade away to nothing.
As it begins to run out of fuel, its core will collapse and the extra heat this generates will cause its outer layers to expand.
In around a billion years' time, this will have a catastrophic effect on our fragile world.
Gradually, the Earth will become hotter and hotter, so there will be one last perfect day on Earth, but eventually, the existence of all life on this planet will become impossible.
Long after life has disappeared, the sun will have grown so much, it will fill the entire horizon.
It will have become a red giant, the last phase of its life.
Our planet might not survive to this point, but if it does, little more than a scorched and barren rock will remain to witness the final death throes of our star.
In six billion years, our sun will explode, throwing vast amounts of gas and dust out into space to form a gigantic nebula.
At its heart will be a faintly glowing ember, all that remains of our once-magnificent sun.
It will be smaller than the size of the Earth, less than a millionth of its current volume, and a fraction of its brightness.
Our sun will have become a white dwarf.
With no fuel left to burn, a white dwarf's faint glow comes from the last residual heat from its extinguished furnace.
The sun is now dead, its remains slowly cooling in the freezing temperatures of deep space.
Looking at it from where the Earth is now, it would only generate the same amount of light as the full moon on a clear night.
The fate of the sun is the same as for all stars.
One day they must all eventually die, and the cosmos will be plunged into eternal night, because this structured universe that we inhabit and all its wonders, the stars and the planets and the galaxies, cannot last forever.
The cosmos WILL eventually fade and die.
Black holes are the most destructive places in the universe, able to devour entire stars.
Yet we've never seen one.
It's because of their effects on the stars and galaxies, and the dust and gas around them, that we know that they exist.
But the reason why black holes are invisible can be demonstrated here on Earth.
Near a black hole, space and time do some very strange things because black holes are probably the most violent places we know of in the universe.
This river provides a beautiful analogy for what happens to space and time as you get closer and closer to the black hole.
Now, upstream, the water is flowing pretty slowly.
Let's imagine that it's flowing at three kilometres per hour and I can swim at four, so I can swim faster than the flow and can easily escape.
But as you go further and further downstream towards the waterfall in the distance, the river flows faster and faster.
Imagine I decide to jump into the river just there on the edge of the falls.
The water is flowing far faster than I could swim, so no matter what I did, no matter how hard I tried, I would not be able to swim back upstream.
I would be carried inexorably towards the edge and I would vanish over the falls.
Well, it's the same close to a black hole because space flows faster and faster and faster towards the black hole - literally this stuff, my space that I'm in, flowing over the edge into the black hole.
And at the very special point called the event horizon, space is flowing at the speed of light into the black hole.
Light itself, travelling at 300,000 kilometres per second, is not going fast enough to escape the flow, and light itself will plunge into the black hole.
So the fact that black holes can swallow light means that they will for ever remain invisible to our eyes.
Gravity is the force that keeps our feet firmly rooted to our planet.
Yet although it may appear constant and unchanging, this force varies on all the planets in the solar system and on the exo-planets we've discovered orbiting other suns.
To experience the gravity on these worlds, I need to go for a spin.
This is a centrifuge.
It was built in the 1950s to test whether fighter pilots had the right stuff, but it's going to allow me to feel what it would be like to stand on the surface of any of the planets in the solar system that are more massive than the Earth, and in fact, also what it would be like to stand on some of the planets that we've found around distant stars.
Threetwoone.
As the centrifuge rotates, it feels exactly as if gravity is increased.
The faster it spins, the greater the effect and we measure this in multiples of the strength of Earth's gravity, known as 1G.
The first planet I'm travelling to is Neptune.
Its gravity is just fractionally stronger than here on Earth.
So this is the gravitational field on Neptune and you feel, "You know what? I could probably get used to this.
"I could probably live on the surface of Neptune.
" Can you lift your hands a little? There we go.
Yeah, and down.
And it is actually quite an effort.
It is noticeably heavier.
It's like having a reasonably heavy weight in your hand.
To go to 2.
5G? Yes, so now we'll move, move from Neptune to Jupiter.
Let's go there.
Jupiter is over 1,300 times more massive than the Earth, but because it's mostly gas, it's not very dense so its gravity is just over twice as strong at its surface.
Well, now actually it is quite difficult to lift my hand.
And that's 2.
5G.
I wouldn't want to sit here for half an hour.
Can you lift both of your hands above your head? See what happens there.
Let's see, so actually just about, but actually it's an immense amount of hard work.
So it would be hard work living on Jupiter.
Let's go to 4G.
Actually, this is heading to a planet around A planet called Ogle 2TRL9B which is around a star in the constellation of Carina.
It's one of the exo-planets we've discovered.
Oh, and there we go.
Now, that is actuallybeginning to feel quite unpleasant.
Can you describe what you're feeling? Very heavy face.
My head is extremely heavy.
How about your lungs, inhaling, exhaling, breathing? It's much harder work.
I can't lift my hand off my leg.
OK.
And that's at 4G? Yeah.
Well, my head and my face feel very, very heavy.
It's quite an unpleasant feeling.
We'll go to 5 and let me know if you have any visual disturbances.
I am now en-route to a newly discovered exo-planet, Wasp 8b.
4.
4.
This world sits in the small and faint constellation of Sculptor.
Quite hard to speak.
It has a gravitational force nearly five times that of the Earth.
Right, we'll go to 5G.
Very foggy.
OK.
Very foggy.
Very foggy? Still foggy? Yeah.
Right.
Take it down.
OK, we'll take you down.
Very interesting.
It was, wasn't it? My face felt a bit saggy, though.
Well, you looked a little different.
That was, um, quite unpleasant that time, actually.
So you realise that we're, obviously, very finely tuned to live on a planet that has a gravitational, an acceleration due to gravity of 1G.
When you go to 2G, it's difficult.
When you go to 3G and 4G it becomes unpleasant, and 5G, anyway, for me, was on the border of being so unpleasant that you pass out.
So although gravity feels weak here on Earth, it certainly isn't weak everywhere across the universe.
And that's because gravity is an additive force.
It scales with mass, so the more massive the planet or star, the stronger its gravity.
Every moment of our lives, we experience a force that we can't see or touch.
Yet this force is able to keep us firmly rooted to the ground.
It is, of course, gravity.
But despite its intangible nature, we always know it's with us.
Now if I was to ask you, "How do you know that there's gravity around here?" Then you might say, "Well, it's obvious.
"You know, I can just do an experiment, I can drop something.
" Well, yes, but actually gravity is a little bit more subtle than that but to really experience it, to understand it, you have to do something pretty extreme.
And this plane has been modified to help me do it.
Thanks to its flight plan, it's known as the Vomit Comet.
Once we've climbed to 15,000 metres, this plane does something no ordinary flight would do - its engines are throttled back and the jet falls to Earth.
And then, something quite amazing happens.
THEY SQUEAL AND CHEER Push to me, push to me! I'm now plummeting towards the ground just like someone's cut the cable in a lift, and you see, we're all just floating.
By simply falling at the same rate as the plane, for a few fleeting moments, we are all free of gravity's grip.
But this isn't just a joy ride.
Now, look, there's something very profound here because although I'm falling towards the ground, as you see, gravity has completely gone away.
Gravity is not here any more.
'Because the aircraft is accelerating towards the ground at 1G, 'the effects of the Earth's gravity are completely cancelled out.
' So it is possible by the simple act of falling to get a very different experience of gravity.
Nothing can travel faster than the speed at which light travels, but although light travels fast, it's not infinitely fast so the further away an object is, the further back in time we see it.
The sun is 150 million kilometres away.
Now that's very close by cosmic standards, but light travels at only 300,000 kilometres per second, so that means that we're seeing the sun as it was in the past, actually eight minutes in the past.
But when we look beyond our sun, to far more distant stars, we reach further back in time.
As the sun dips below the horizon and night falls .
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the universe just fades into view.
And then, as it gets darker and darker, the Milky Way appears - a vast swathe of billions and billions of suns as you look out towards the centre of our Milky Way galaxy.
But I think for me, the most magical thing you can see in the sky with the naked eye, is just below the constellation of Cassiopeia, the W of stars in the sky.
There, look at that.
Actually, I've got to say, that's amazing.
You see, that misty patch of light is not a cloud in the sky, it's not even gas and dust in our galaxy.
Thatis another galaxy.
It's the Andromeda galaxy, which is roughly the same size as our own - an island of hundreds of billions of stars, 25 million, million, million kilometres in that direction.
The light that I've just captured in my camera began its journey two and a half million years ago.
At that time on Earth, there were no humans.
Homo habilis, our distant ancestors, were roaming the plains of Africa and as those light rays travelled through the vastness of space, our species evolved and thousands and thousands and thousands of generations of humans lived and died.
And then, two and a half million years after their journey began, these messengers from the depths of space, and from way back in our past, arrived here on Earth, and I just captured them and took that picture.
But by peering further than the naked eye will allow, we can journey to a time way before human history.
In the last 20 years, powerful space telescopes have carried us ever deeper into space and we have become virtual time travellers.
This is NGC 520 and it's the product of a cosmic collision, but this galaxy is a hundred million light years away.
That means that the light began its journey from this galaxy to my eye when the dinosaurs roamed the Earth.
But these spectacular galaxies are not the end of our journey into the past.
In 2004, we peered further back in time than ever before and captured the light from the most distant galaxies in the universe.
The image is called the Hubble Ultra Deep Field.
It's a picture taken by the Hubble Space Telescope over a period of 11 days, and it focused its camera on the tiniest piece of sky, just below the constellation of Orion.
Now, it's a piece of sky that you would cover if you took your thumb, held it in front of your face and then moved it 20 times further away.
But the Hubble captured the faintest lights from the most distant regions of the universe and it took this photograph.
Now, almost every point of light in that image is not a star, but a galaxy of over a hundred billion stars.
The most distant galaxies in that image are over 13 billion light years away.
That means that the faint light from those galaxies began its journey to Earth 13 billion years ago.
That's over three times the age of the Earth.