Browse content similar to Wonders of the Universe. Check below for episodes and series from the same categories and more!
Line | From | To | |
---|---|---|---|
We all have an intuitive understanding of time. | 0:00:23 | 0:00:26 | |
It seems obvious to us that things change, | 0:00:26 | 0:00:29 | |
and the future will be different to the past. | 0:00:29 | 0:00:32 | |
But why are we compelled to travel into the future? | 0:00:36 | 0:00:39 | |
The answer to that question can be seen | 0:00:39 | 0:00:42 | |
in how the world around us is always changing. | 0:00:42 | 0:00:46 | |
This is Kolmanskop, | 0:00:49 | 0:00:50 | |
an abandoned diamond mining town in southern Namibia. | 0:00:50 | 0:00:55 | |
For half a century, | 0:01:00 | 0:01:02 | |
it's fallen into disrepair | 0:01:02 | 0:01:04 | |
as it's slowly reclaimed by the sands. | 0:01:04 | 0:01:06 | |
The process at play here at Kolmanskop | 0:01:15 | 0:01:17 | |
is happening everywhere in the universe - decay. | 0:01:17 | 0:01:21 | |
Or in the language of physics, an increase in entropy. | 0:01:21 | 0:01:28 | |
Entropy explains why, | 0:01:30 | 0:01:32 | |
left to the mercy of the elements, | 0:01:32 | 0:01:35 | |
mortar crumbles, glass shatters | 0:01:35 | 0:01:38 | |
and buildings collapse. | 0:01:38 | 0:01:39 | |
And a good way to understand how | 0:01:42 | 0:01:44 | |
is to think of objects not as single things, but as being made up | 0:01:44 | 0:01:48 | |
of many constituent parts, like the individual grains | 0:01:48 | 0:01:52 | |
that make up this pile of sand. | 0:01:52 | 0:01:55 | |
Now, entropy is a measure of how many ways | 0:01:58 | 0:02:00 | |
I can re-arrange those grains and still keep the sand piled the same, | 0:02:00 | 0:02:05 | |
and there are trillions and trillions and trillions | 0:02:05 | 0:02:09 | |
of ways of doing that. | 0:02:09 | 0:02:10 | |
I mean, pretty much anything I do to this sand pile, | 0:02:10 | 0:02:13 | |
if I mess the sand around and move it around, | 0:02:13 | 0:02:16 | |
then it doesn't change the shape or the structure at all. | 0:02:16 | 0:02:19 | |
So, in the language of entropy, this sand pile has high entropy, | 0:02:19 | 0:02:24 | |
because there are many, many ways | 0:02:24 | 0:02:26 | |
that I can re-arrange its constituents and not change it. | 0:02:26 | 0:02:30 | |
But now, let me create some order in the universe. | 0:02:30 | 0:02:35 | |
Now, there are approximately as many sand grains in this sandcastle | 0:02:42 | 0:02:46 | |
as there are in the sand pile. | 0:02:46 | 0:02:49 | |
But now, virtually anything I do to it will mess it up, | 0:02:49 | 0:02:53 | |
will remove the beautiful order from this structure | 0:02:53 | 0:02:56 | |
and because of that, the sandcastle has a low entropy. | 0:02:56 | 0:03:00 | |
It's a much more ordered state. | 0:03:00 | 0:03:03 | |
So, many ways of re-arranging the sand grains | 0:03:03 | 0:03:07 | |
without changing the structure - high entropy. | 0:03:07 | 0:03:10 | |
Very few ways of re-arranging the sand grains | 0:03:10 | 0:03:13 | |
without changing the structure, without disordering it - | 0:03:13 | 0:03:18 | |
low entropy. | 0:03:18 | 0:03:19 | |
Now, imagine I was to leave this castle in the desert all day, | 0:03:27 | 0:03:31 | |
the desert winds are going to blow the sand around | 0:03:31 | 0:03:34 | |
and this castle is going to disintegrate. | 0:03:34 | 0:03:37 | |
It's going to become less ordered. | 0:03:37 | 0:03:39 | |
But there's nothing fundamental | 0:03:39 | 0:03:43 | |
in the laws of physics that says | 0:03:43 | 0:03:45 | |
that the wind couldn't pick up some sand from over here, | 0:03:45 | 0:03:49 | |
deposit it here and deposit it in precisely the shape of a sandcastle. | 0:03:49 | 0:03:55 | |
You know, in principle, | 0:03:55 | 0:03:56 | |
the wind could spontaneously build a sandcastle out of a pile of sand. | 0:03:56 | 0:04:01 | |
There's no reason why that couldn't happen. | 0:04:10 | 0:04:14 | |
It's just extremely, extremely unlikely, | 0:04:14 | 0:04:17 | |
because there are very few ways of organising this sand | 0:04:17 | 0:04:21 | |
so that it looks like a castle. | 0:04:21 | 0:04:23 | |
It's overwhelmingly more likely | 0:04:27 | 0:04:30 | |
that when the wind blows the sand around, | 0:04:30 | 0:04:32 | |
it will take the low entropy structure, the castle, | 0:04:32 | 0:04:36 | |
and turn it into a high entropy structure, the sand pile. | 0:04:36 | 0:04:40 | |
So, entropy always increases. Why is that? | 0:04:48 | 0:04:52 | |
Because it's overwhelmingly more likely that it will. | 0:04:52 | 0:04:57 | |
So, everything tends from order to disorder. | 0:05:06 | 0:05:09 | |
That means that there is a difference between the future | 0:05:09 | 0:05:13 | |
and the past, and that's one reason why time travels in one direction. | 0:05:13 | 0:05:19 | |
Everything that we see on Earth, from the grandest mountain | 0:05:33 | 0:05:36 | |
to the most fleeting cloud, | 0:05:36 | 0:05:39 | |
is made from the same set of building blocks. | 0:05:39 | 0:05:42 | |
They're called the chemical elements. | 0:05:42 | 0:05:45 | |
We now know that the Earth is made of 92 chemical elements | 0:05:49 | 0:05:53 | |
and that's pretty amazing if you think of the complexity | 0:05:53 | 0:05:56 | |
that we see around us. We also know that everything beyond Earth, | 0:05:56 | 0:06:00 | |
everything we can see in the universe, | 0:06:00 | 0:06:02 | |
is made of those same 92 elements, | 0:06:02 | 0:06:05 | |
and notice I didn't say "we think" that's what they're made of. | 0:06:05 | 0:06:09 | |
I said "we know" that's what they're made of, because we can prove it. | 0:06:09 | 0:06:14 | |
The chemistry set we have on Earth extends far beyond the planet. | 0:06:20 | 0:06:24 | |
We have set foot on the moon | 0:06:28 | 0:06:30 | |
and know that it's rich in helium, silver and water. | 0:06:30 | 0:06:34 | |
And discovered that Mars is rich in iron. | 0:06:36 | 0:06:40 | |
And we know that Venus's thick atmosphere is full of sulphur. | 0:06:42 | 0:06:47 | |
But what of the rest of the universe? | 0:06:49 | 0:06:51 | |
It seems impossible that we could discover what the stars are made of, | 0:06:53 | 0:06:57 | |
because they're so far away. | 0:06:57 | 0:07:00 | |
Even the nearest star, Proxima Centauri, is 10,000 times | 0:07:00 | 0:07:07 | |
more distant than Neptune, 4.2 light years from Earth. | 0:07:07 | 0:07:11 | |
Yet despite these vast distances, these alien worlds are constantly | 0:07:13 | 0:07:18 | |
sending us signals, telling us exactly what they're made of. | 0:07:18 | 0:07:23 | |
Our only contact with the distant stars is their light | 0:07:23 | 0:07:28 | |
that has journeyed across the universe to reach us, | 0:07:28 | 0:07:30 | |
and encoded in that light is the key to understanding | 0:07:30 | 0:07:34 | |
what the universe is made of, | 0:07:34 | 0:07:36 | |
and it's all down to a particular property of the chemical elements. | 0:07:36 | 0:07:40 | |
You see, when you heat the elements, when you burn them, | 0:07:40 | 0:07:43 | |
then they give off light | 0:07:43 | 0:07:44 | |
and each element gives off its own unique set of colours. | 0:07:44 | 0:07:49 | |
So this is strontium | 0:07:49 | 0:07:52 | |
and it burns with a beautiful red colour. | 0:07:52 | 0:07:57 | |
Sodium is yellow. | 0:08:02 | 0:08:04 | |
Potassium is lilac. | 0:08:06 | 0:08:08 | |
And copper is blue. | 0:08:10 | 0:08:12 | |
Each element has its own characteristic colour. | 0:08:16 | 0:08:19 | |
It's this property that tells us what the stars are made of. | 0:08:24 | 0:08:28 | |
But it's a little more complicated | 0:08:29 | 0:08:32 | |
than simply looking at the colour of the light that each star emits. | 0:08:32 | 0:08:37 | |
You can see why by looking at the light | 0:08:37 | 0:08:41 | |
from our nearest star - the sun. | 0:08:41 | 0:08:42 | |
This is a spectrum of the light taken from our sun, | 0:08:47 | 0:08:51 | |
and at first glance, it looks very familiar. | 0:08:51 | 0:08:53 | |
It looks like a stretched-out rainbow. | 0:08:53 | 0:08:56 | |
But if you look a bit more closely, | 0:08:56 | 0:08:57 | |
then you see that this spectrum is covered in black lines. | 0:08:57 | 0:09:01 | |
These are called absorption lines. | 0:09:01 | 0:09:05 | |
Each element within our sun not only emits light of a certain colour, | 0:09:05 | 0:09:10 | |
it also absorbs light of the same colour. | 0:09:10 | 0:09:13 | |
By looking for these black lines in the sun's light, | 0:09:13 | 0:09:17 | |
we can simply read off a list of its constituent elements, | 0:09:17 | 0:09:21 | |
like a barcode. | 0:09:21 | 0:09:23 | |
For example, these two black lines | 0:09:23 | 0:09:25 | |
in the yellow bit of the spectrum are sodium. | 0:09:25 | 0:09:28 | |
You can see iron. Right down here, you can see hydrogen. | 0:09:28 | 0:09:34 | |
So, by looking at these lines in precise detail, | 0:09:34 | 0:09:38 | |
you can work out exactly what elements are present in the sun, | 0:09:38 | 0:09:42 | |
and it turns out that that's about 70% hydrogen, | 0:09:42 | 0:09:46 | |
28% helium, and 2% the rest. | 0:09:46 | 0:09:48 | |
And you can do this not only for the sun but for any of the stars | 0:09:48 | 0:09:53 | |
you can see in the sky, and you can measure exactly what they're made of. | 0:09:53 | 0:09:59 | |
So, that star there is Polaris, the pole star, and you can see that | 0:10:03 | 0:10:08 | |
because all the other stars in the night sky appear to rotate around it. | 0:10:08 | 0:10:13 | |
Now, it's 430 light years away. | 0:10:13 | 0:10:17 | |
But we know, just by looking at the light, | 0:10:19 | 0:10:22 | |
that it's got about the same heavy element abundance as our sun, | 0:10:22 | 0:10:27 | |
but it's got markedly less carbon and a lot more nitrogen. | 0:10:27 | 0:10:34 | |
And the same applies for other stars. | 0:10:38 | 0:10:42 | |
Sirius, the dog star, contains three times as much iron as the sun. | 0:10:45 | 0:10:49 | |
And Proxima Centauri is rich in magnesium. | 0:10:52 | 0:10:56 | |
But although the quantities of the elements may vary, | 0:10:59 | 0:11:03 | |
wherever we look across space, | 0:11:03 | 0:11:05 | |
we only ever find the same 92 elements that we find on Earth. | 0:11:05 | 0:11:10 | |
We are made of the same stuff as the stars and the galaxies. | 0:11:13 | 0:11:18 | |
Everything in the universe, from the most distant star or galaxy | 0:11:35 | 0:11:39 | |
to our small planet, | 0:11:39 | 0:11:41 | |
is made from just 92 chemical elements, | 0:11:41 | 0:11:44 | |
and here on planet Earth, | 0:11:44 | 0:11:46 | |
there's one element that defines it more than any other. | 0:11:46 | 0:11:50 | |
Life is completely dependent on carbon. | 0:11:55 | 0:11:59 | |
I mean, I'm made of about a billion, billion, billion carbon atoms, | 0:11:59 | 0:12:04 | |
as is every human being out there, every living thing on the planet. | 0:12:04 | 0:12:10 | |
Imagine how many carbon atoms that is. | 0:12:10 | 0:12:13 | |
So where does all that carbon come from? | 0:12:13 | 0:12:15 | |
Well, it comes from the only place in the universe | 0:12:15 | 0:12:18 | |
where elements are made - stars. | 0:12:18 | 0:12:22 | |
But in order for us to live, a star must die. | 0:12:22 | 0:12:27 | |
Stars in the prime of their lives, like our sun, | 0:12:30 | 0:12:33 | |
burn the element hydrogen, converting it into helium. | 0:12:33 | 0:12:37 | |
But forming the other elements requires much higher temperatures, | 0:12:39 | 0:12:44 | |
temperatures that can only be reached | 0:12:44 | 0:12:46 | |
at the end of a star's life. | 0:12:46 | 0:12:49 | |
Imagine this old prison in Rio is a dying star. | 0:12:55 | 0:12:58 | |
Out there is the bright surface, shining off into space. | 0:12:58 | 0:13:03 | |
As I descend deeper and deeper into the prison, | 0:13:03 | 0:13:07 | |
the conditions would become hotter and hotter and denser and denser, | 0:13:07 | 0:13:12 | |
until down there in the heart of the star is the core. | 0:13:12 | 0:13:19 | |
Deep in its core, | 0:13:22 | 0:13:23 | |
the star is fighting a futile battle against its own gravity. | 0:13:23 | 0:13:28 | |
As it desperately tries | 0:13:29 | 0:13:31 | |
to stop itself collapsing under its own weight, | 0:13:31 | 0:13:34 | |
new elements are made in a sequence of separate stages. | 0:13:34 | 0:13:38 | |
Stage one - while the star burns hydrogen to helium in the core, | 0:13:43 | 0:13:50 | |
vast amounts of energy are released and that energy escapes, | 0:13:50 | 0:13:54 | |
literally creating an outward pressure | 0:13:54 | 0:13:57 | |
which balances the force of gravity | 0:13:57 | 0:13:59 | |
and, well, it holds the star up and keeps it stable. | 0:13:59 | 0:14:03 | |
But eventually, the hydrogen in the core will run out. | 0:14:05 | 0:14:10 | |
Now, at that point, | 0:14:10 | 0:14:11 | |
the core will start to collapse very rapidly, | 0:14:11 | 0:14:15 | |
leaving a shell... | 0:14:15 | 0:14:18 | |
of hydrogen and helium behind. | 0:14:18 | 0:14:23 | |
Beneath this shell, as the core collapses, | 0:14:27 | 0:14:30 | |
the temperature rises again, | 0:14:30 | 0:14:34 | |
until at a hundred million degrees, | 0:14:34 | 0:14:37 | |
stage two starts and helium nuclei begin to fuse together. | 0:14:37 | 0:14:43 | |
A helium fusion does two things. | 0:14:51 | 0:14:53 | |
Firstly, more energy is released and so, the collapse is halted. | 0:14:53 | 0:14:59 | |
But secondly, two more elements are produced in that process - | 0:14:59 | 0:15:06 | |
carbon... | 0:15:06 | 0:15:07 | |
..oxygen. Two elements vital for life. | 0:15:10 | 0:15:15 | |
So, this is where all the carbon in the universe comes from. | 0:15:15 | 0:15:20 | |
You know, every atom of carbon in my hand, | 0:15:20 | 0:15:23 | |
every atom of carbon in every living thing on the planet | 0:15:23 | 0:15:28 | |
was produced in the heart of a dying star. | 0:15:28 | 0:15:32 | |
But in only about a million years, | 0:15:34 | 0:15:37 | |
the supply of helium in the core is used up | 0:15:37 | 0:15:40 | |
and for stars as massive as the sun, that's where fusion stops, | 0:15:40 | 0:15:45 | |
because there isn't enough gravitational energy | 0:15:45 | 0:15:48 | |
to compress the core any further and restart fusion. | 0:15:48 | 0:15:52 | |
But for massive stars, the fusion process can continue. | 0:15:52 | 0:15:57 | |
Launching stage three, in which carbon fuses into magnesium, | 0:15:59 | 0:16:04 | |
neon, sodium and aluminium. | 0:16:04 | 0:16:09 | |
And so it goes on. Core collapse, | 0:16:09 | 0:16:12 | |
followed by the next stage of fusion | 0:16:12 | 0:16:14 | |
to create more elements, each stage hotter and shorter than the last. | 0:16:14 | 0:16:21 | |
And eventually, in a final stage that lasts only a couple of days, | 0:16:23 | 0:16:29 | |
the heart of the star is transformed into almost pure iron, | 0:16:29 | 0:16:35 | |
whose chemical symbol is Fe, | 0:16:35 | 0:16:40 | |
and this is where the fusion process stops. | 0:16:40 | 0:16:43 | |
In its millions of years of life, | 0:16:45 | 0:16:47 | |
the star has made all the common elements, | 0:16:47 | 0:16:51 | |
the stuff that makes up 99% of the Earth. | 0:16:51 | 0:16:54 | |
The core is now a solid ball of those elements, | 0:16:57 | 0:17:00 | |
stacked on top of each other in layers. | 0:17:00 | 0:17:03 | |
The star has only seconds left to live. | 0:17:06 | 0:17:09 | |
When a star runs out of fuel, | 0:17:11 | 0:17:13 | |
then it can no longer release energy through fusion reactions, | 0:17:13 | 0:17:17 | |
and then, there's only one thing that can happen. | 0:17:17 | 0:17:20 | |
LOUD EXPLOSIONS | 0:17:23 | 0:17:25 | |
In about the same amount of time it takes this prison block to crumble, | 0:17:36 | 0:17:40 | |
the entire star falls in on itself. | 0:17:40 | 0:17:43 | |
Yet even the implosion of the star only forges the first 26 elements. | 0:17:50 | 0:17:56 | |
For the remaining 66 elements, | 0:17:56 | 0:17:58 | |
we have to look to some of the rarest conditions in the universe, | 0:17:58 | 0:18:02 | |
the explosive death throes of the very largest stars, | 0:18:02 | 0:18:07 | |
stars at least nine times the mass of our sun. | 0:18:07 | 0:18:10 | |
It's called a supernova, | 0:18:10 | 0:18:12 | |
the biggest explosion in the universe. | 0:18:12 | 0:18:16 | |
Only these events can generate the enormous temperatures, | 0:18:34 | 0:18:38 | |
hundreds of millions of degrees, necessary to fuse large amounts | 0:18:38 | 0:18:44 | |
of the heaviest elements, elements like platinum, silver and gold. | 0:18:44 | 0:18:50 | |
So, the most precious elements are created | 0:18:55 | 0:18:58 | |
in the death throes of the most massive stars. | 0:18:58 | 0:19:01 | |
For centuries, people thought that light travelled instantly from one place to another, | 0:19:13 | 0:19:19 | |
but then, 350 years ago, | 0:19:19 | 0:19:23 | |
one man's study of the planets and moons of the solar system | 0:19:23 | 0:19:26 | |
revealed that it did in fact take time for light to travel. | 0:19:26 | 0:19:30 | |
Ever since Galileo discovered that Jupiter had moons, | 0:19:33 | 0:19:36 | |
astronomers realised that you could use Jupiter | 0:19:36 | 0:19:38 | |
and its moons as a very precise clock in the sky. | 0:19:38 | 0:19:42 | |
So here's the solar system, there's the sun, there's the Earth, | 0:19:42 | 0:19:45 | |
here's Jupiter, and here is Jupiter's innermost moon, Io. | 0:19:45 | 0:19:50 | |
Now it was known that Io takes precisely 42 and a half hours | 0:19:50 | 0:19:54 | |
to orbit around Jupiter, so if from the Earth, you see Io emerge | 0:19:54 | 0:20:00 | |
from behind Jupiter at say, midnight on a Tuesday, then you know | 0:20:00 | 0:20:05 | |
that it should re-emerge again at half-past six | 0:20:05 | 0:20:08 | |
on Thursday afternoon. Beautiful. | 0:20:08 | 0:20:11 | |
Now, one of the men charged with making precise tables | 0:20:11 | 0:20:15 | |
of exactly when Io should be seen to emerge from behind Jupiter | 0:20:15 | 0:20:20 | |
was the Danish astronomer Ole Romer, but he noticed something surprising. | 0:20:20 | 0:20:25 | |
You see, depending on the time of year, | 0:20:25 | 0:20:27 | |
Io emerged later than expected or earlier than expected. | 0:20:27 | 0:20:33 | |
Now, Romer's genius was to realise that had nothing to do at all | 0:20:33 | 0:20:37 | |
with the orbit of Io around Jupiter. | 0:20:37 | 0:20:40 | |
It was to do with the orbit of the Earth around the sun. | 0:20:40 | 0:20:44 | |
You see, what Romer noticed was that | 0:20:44 | 0:20:47 | |
when the Earth was in a position in its orbit so that it was close to Jupiter, | 0:20:47 | 0:20:52 | |
then Io emerged earlier than it was expected to. | 0:20:52 | 0:20:56 | |
Then, as the year passed and Earth moved around the sun | 0:20:56 | 0:21:00 | |
and got further away from Jupiter, Romer noticed that Io | 0:21:00 | 0:21:04 | |
then emerged later than it was expected to. | 0:21:04 | 0:21:08 | |
Romer realised that it takes time for light to travel from Jupiter | 0:21:08 | 0:21:13 | |
to the Earth, so when the Earth is far away from Jupiter, | 0:21:13 | 0:21:17 | |
it takes longer for the light to travel and therefore you see | 0:21:17 | 0:21:21 | |
Io emerge from behind Jupiter later than you would expect. | 0:21:21 | 0:21:25 | |
Then, when the distance is small, | 0:21:25 | 0:21:27 | |
it takes less time for the light to travel | 0:21:27 | 0:21:30 | |
and you see Io emerge earlier than you might expect. | 0:21:30 | 0:21:35 | |
So Romer had discovered that light doesn't travel instantaneously. | 0:21:35 | 0:21:40 | |
It moves through space with a finite speed. | 0:21:40 | 0:21:44 | |
This remarkable insight led to a measurement of the speed of light. | 0:21:53 | 0:21:57 | |
We now know that light travels | 0:22:02 | 0:22:05 | |
at precisely 299,792,458 metres per second. | 0:22:05 | 0:22:10 | |
That means that in the time it takes for me to click my fingers, | 0:22:10 | 0:22:14 | |
light has travelled around the Earth seven times... | 0:22:14 | 0:22:17 | |
or that it travels ten million, million kilometres in one year. | 0:22:17 | 0:22:23 | |
And that's the yardstick we use to measure the universe, | 0:22:23 | 0:22:29 | |
because ten million, million kilometres is approximately one light year. | 0:22:29 | 0:22:34 | |
It's easy to think that the universe has always existed, | 0:22:56 | 0:22:59 | |
but our best scientific theory states that it emerged in one moment, | 0:22:59 | 0:23:04 | |
from an event known as the Big Bang. | 0:23:04 | 0:23:06 | |
And one of the most significant pieces of evidence for this theory | 0:23:13 | 0:23:17 | |
comes from our understanding of light and colour. | 0:23:17 | 0:23:21 | |
To reveal how colour can unlock the secrets of our universe's creation, | 0:23:24 | 0:23:29 | |
I've come to one of the most spectacular natural wonders on Earth. | 0:23:29 | 0:23:33 | |
This is Victoria Falls in Zambia. | 0:23:43 | 0:23:45 | |
But I'm not here to marvel at the scale of this wonder. | 0:24:00 | 0:24:03 | |
I've come to see a much more delicate feature that appears above the water. | 0:24:03 | 0:24:08 | |
These magnificent rainbows are a permanent feature | 0:24:10 | 0:24:14 | |
in the skies above Victoria Falls. | 0:24:14 | 0:24:17 | |
Now, rainbows are a beautiful phenomena, | 0:24:17 | 0:24:19 | |
but I think they're even more beautiful when you understand how they're made | 0:24:19 | 0:24:23 | |
because they are a visual representation | 0:24:23 | 0:24:26 | |
of the fact that light is made up of, well, all the colours of the rainbow. | 0:24:26 | 0:24:32 | |
Just like light shining through a prism, | 0:24:34 | 0:24:37 | |
rays of light from the sun are refracted as they enter the water droplets. | 0:24:37 | 0:24:42 | |
The light beams then reflect off the back of the droplets | 0:24:43 | 0:24:47 | |
and are bent for a second time as they leave. | 0:24:47 | 0:24:50 | |
This bending and reflecting splits the light, | 0:24:51 | 0:24:54 | |
and the colours hidden inside the white sunlight are revealed. | 0:24:54 | 0:24:58 | |
What we see as different colours are actually different wavelengths of light, | 0:25:02 | 0:25:06 | |
so blue light has a relatively short wavelength, | 0:25:06 | 0:25:11 | |
and then you go through green and yellow all the way to the red end of the spectrum, | 0:25:11 | 0:25:16 | |
which has a very large wavelength. | 0:25:16 | 0:25:19 | |
Starlight is made up of countless different wavelengths, | 0:25:30 | 0:25:33 | |
and when we look at the most distant stars | 0:25:33 | 0:25:36 | |
and galaxies in the universe, their light appears redder, | 0:25:36 | 0:25:39 | |
and it's this colouring that helps reveal that our universe had a beginning. | 0:25:39 | 0:25:46 | |
When light is emitted by a distant star or galaxy, | 0:25:47 | 0:25:51 | |
its wavelength doesn't have to stay fixed - | 0:25:51 | 0:25:54 | |
it can be squashed or stretched and when light's stretched, | 0:25:54 | 0:25:59 | |
its wavelength increases and it moves to the red end of the spectrum. | 0:25:59 | 0:26:05 | |
So the interpretation of the fact that the most distant galaxies appear red, | 0:26:05 | 0:26:09 | |
is that the space in-between them and us | 0:26:09 | 0:26:12 | |
has stretched during the time it's taken the light to journey over that vast distance. | 0:26:12 | 0:26:20 | |
That means that our entire universe is expanding. | 0:26:20 | 0:26:25 | |
Now just think about what an expanding universe implies, | 0:26:27 | 0:26:31 | |
because if the galaxies are all rushing away from each other, | 0:26:31 | 0:26:36 | |
that means that if you re-wind time, | 0:26:36 | 0:26:38 | |
then they must have been closer together in the past, and actually if you just keep re-winding, | 0:26:38 | 0:26:43 | |
then you find that at some point in the past, | 0:26:43 | 0:26:46 | |
all the galaxies we can see in the sky were quite literally on top of each other. | 0:26:46 | 0:26:51 | |
The universe was squashed down to a point. | 0:26:51 | 0:26:55 | |
That implies that the universe may have had a beginning | 0:26:55 | 0:27:00 | |
and that is the Big Bang Theory. | 0:27:00 | 0:27:04 | |
Life on Earth takes seemingly endless forms. | 0:27:19 | 0:27:24 | |
Yet all creatures, however different, | 0:27:24 | 0:27:27 | |
have evolved over billions of years from an ancient common ancestor. | 0:27:27 | 0:27:32 | |
This connection is explained by the theory of evolution by natural selection, | 0:27:41 | 0:27:46 | |
and some of the best evidence for evolution | 0:27:46 | 0:27:49 | |
are in the preserved remains of ancient creatures found in fossil beds. | 0:27:49 | 0:27:54 | |
This is one of them, | 0:27:56 | 0:27:57 | |
the Burgess Shale in the Rocky Mountains of Canada. | 0:27:57 | 0:28:00 | |
Well, this is one of the most important fossil sites in the world, | 0:28:03 | 0:28:08 | |
but actually it's one of the most important scientific sites of any kind, | 0:28:08 | 0:28:13 | |
and it's not just because of the number and diversity of animals | 0:28:13 | 0:28:17 | |
you find fossilised in these rocks, it's because of their age. | 0:28:17 | 0:28:21 | |
Over half a billion years old, | 0:28:23 | 0:28:25 | |
they are some of the earliest fossils of complex life. | 0:28:25 | 0:28:29 | |
I mean, it's as if at one instant in this time we call the Cambrian Era, | 0:28:34 | 0:28:40 | |
complex multi-cellular life suddenly emerged almost intact on the planet. | 0:28:40 | 0:28:47 | |
It's called the Evolutionary Big Bang. | 0:28:47 | 0:28:50 | |
So the Burgess Shale tells us that complex life seemed to emerge suddenly | 0:28:53 | 0:28:58 | |
and a new theory may also suggest what triggered this moment. | 0:28:58 | 0:29:02 | |
Well, this is one of the beautiful animals | 0:29:08 | 0:29:10 | |
you find up here in the fossil beds. | 0:29:10 | 0:29:12 | |
It's called a trilobite. It's a very complex organism. | 0:29:12 | 0:29:16 | |
It's got an external skeleton, it's got jointed limbs | 0:29:16 | 0:29:19 | |
but perhaps most remarkably these, because these are compound eyes. | 0:29:19 | 0:29:26 | |
They were very sophisticated | 0:29:26 | 0:29:28 | |
and this was one of the first predators to be able to detect shapes | 0:29:28 | 0:29:31 | |
and see movement and it could successfully chase its prey. | 0:29:31 | 0:29:35 | |
These creatures were among the first to harness the light that filled the universe. | 0:29:37 | 0:29:43 | |
Before they emerged, the rise and fall of the sun and the stars in the night sky simply went unnoticed. | 0:29:43 | 0:29:51 | |
Now there is a speculative theory that the emergence of the eye | 0:29:51 | 0:29:55 | |
actually triggered the Cambrian explosion, | 0:29:55 | 0:29:58 | |
this Evolutionary Big Bang, because once one species got eyes, | 0:29:58 | 0:30:04 | |
then other species had also to develop eyes to either chase them as predators | 0:30:04 | 0:30:10 | |
or evade them as prey, and that led to an evolutionary arms race. | 0:30:10 | 0:30:16 | |
More and more complex life forms developed. | 0:30:16 | 0:30:20 | |
So the evolution of the eye may have played a fundamental role | 0:30:24 | 0:30:27 | |
in the emergence of complex life on Earth... | 0:30:27 | 0:30:30 | |
..and could have led to the evolution of our species. | 0:30:32 | 0:30:37 | |
The light we can see is just a tiny fraction of the light in our universe. | 0:30:48 | 0:30:53 | |
Beyond the visible spectrum, | 0:30:54 | 0:30:57 | |
our world is also bathed in the light we can't see. | 0:30:57 | 0:31:01 | |
X-rays, infrared, ultraviolet are all types of light, | 0:31:01 | 0:31:07 | |
but although we can't see this light, we can still sense it. | 0:31:07 | 0:31:11 | |
This sand has been under the full glare of the sun all day | 0:31:14 | 0:31:17 | |
and I can feel the heat radiating off it. | 0:31:17 | 0:31:21 | |
Well, heat is nothing more than a form of light, | 0:31:21 | 0:31:25 | |
although we don't normally call it light. | 0:31:25 | 0:31:28 | |
It's actually infrared light and the only difference between infrared | 0:31:28 | 0:31:33 | |
and visible light is the wavelength. | 0:31:33 | 0:31:35 | |
Infrared has a longer wavelength than visible light. | 0:31:35 | 0:31:39 | |
Infrared isn't the end of the story. | 0:31:41 | 0:31:43 | |
There are even longer wavelengths of light, | 0:31:43 | 0:31:48 | |
and these can reveal something extraordinary about our universe. | 0:31:48 | 0:31:54 | |
To detect them, you don't need a billion-pound satellite | 0:31:54 | 0:31:57 | |
or a telescope built into the side of a mountain. | 0:31:57 | 0:32:01 | |
You just need one of these, a radio, | 0:32:01 | 0:32:05 | |
because when we tune a radio, | 0:32:05 | 0:32:09 | |
we're tuning into a form of light - radio waves. | 0:32:09 | 0:32:14 | |
MUSIC PLAYS ON RADIO | 0:32:14 | 0:32:18 | |
But detecting them and understanding them | 0:32:20 | 0:32:23 | |
provides the key to understanding the origin of the universe. | 0:32:23 | 0:32:28 | |
When you de-tune the radio a bit, you can just hear static | 0:32:31 | 0:32:33 | |
but about 1% of that static is music to the ears of a physicist | 0:32:33 | 0:32:40 | |
because that is stretched light from the Big Bang. | 0:32:40 | 0:32:45 | |
# Carry him home safely to me... # | 0:32:45 | 0:32:50 | |
The reason we can't see this ancient light | 0:32:52 | 0:32:54 | |
is because as the universe expanded, the light waves were stretched | 0:32:54 | 0:32:59 | |
and transformed into radio waves and microwaves. | 0:32:59 | 0:33:04 | |
This first light is called the Cosmic Microwave Background or CMB. | 0:33:04 | 0:33:10 | |
The CMB fills every part of the universe. | 0:33:12 | 0:33:16 | |
If my eyes could only see it, then the sky would be ablaze | 0:33:17 | 0:33:22 | |
with this primordial light both day and night. | 0:33:22 | 0:33:26 | |
Although we are not sensitive to this light, specialised cameras are, | 0:33:33 | 0:33:38 | |
and when they are pointed towards the heavens, something beautiful emerges. | 0:33:38 | 0:33:43 | |
These scattered colours are the fading embers, | 0:33:54 | 0:33:57 | |
the last remnants of light from the beginning of the universe. | 0:33:57 | 0:34:03 | |
Looking out into space, you might think that the cosmos | 0:34:13 | 0:34:16 | |
is a constant unchanging place, that the stars will always be there. | 0:34:16 | 0:34:23 | |
But in fact, the stars are only a temporary feature in the sky, | 0:34:23 | 0:34:28 | |
and though they may burn brightly for many millions or billions of years, | 0:34:28 | 0:34:32 | |
they can only live for as long as they have a supply of hydrogen to burn. | 0:34:32 | 0:34:37 | |
And when a star like our sun runs out of hydrogen, it begins to die. | 0:34:40 | 0:34:44 | |
But it doesn't go quietly. | 0:34:47 | 0:34:48 | |
At the end of its life, the sun won't simply fade away to nothing. | 0:34:52 | 0:34:56 | |
As it begins to run out of fuel, its core will collapse | 0:34:59 | 0:35:03 | |
and the extra heat this generates will cause its outer layers to expand. | 0:35:03 | 0:35:08 | |
In around a billion years' time, | 0:35:15 | 0:35:17 | |
this will have a catastrophic effect on our fragile world. | 0:35:17 | 0:35:21 | |
Gradually, the Earth will become hotter and hotter, | 0:35:28 | 0:35:31 | |
so there will be one last perfect day on Earth, but eventually, | 0:35:31 | 0:35:37 | |
the existence of all life on this planet will become impossible. | 0:35:37 | 0:35:42 | |
Long after life has disappeared, the sun will have grown so much, | 0:35:46 | 0:35:49 | |
it will fill the entire horizon. | 0:35:49 | 0:35:53 | |
It will have become a red giant, the last phase of its life. | 0:35:59 | 0:36:05 | |
Our planet might not survive to this point, but if it does, | 0:36:14 | 0:36:17 | |
little more than a scorched and barren rock will remain | 0:36:17 | 0:36:21 | |
to witness the final death throes of our star. | 0:36:21 | 0:36:26 | |
In six billion years, our sun will explode, | 0:36:37 | 0:36:41 | |
throwing vast amounts of gas and dust out into space to form a gigantic nebula. | 0:36:41 | 0:36:46 | |
At its heart will be a faintly glowing ember, | 0:36:54 | 0:36:58 | |
all that remains of our once-magnificent sun. | 0:36:58 | 0:37:02 | |
It will be smaller than the size of the Earth, | 0:37:02 | 0:37:05 | |
less than a millionth of its current volume, and a fraction of its brightness. | 0:37:05 | 0:37:10 | |
Our sun will have become a white dwarf. | 0:37:10 | 0:37:13 | |
With no fuel left to burn, a white dwarf's faint glow | 0:37:23 | 0:37:27 | |
comes from the last residual heat from its extinguished furnace. | 0:37:27 | 0:37:31 | |
The sun is now dead, | 0:37:34 | 0:37:37 | |
its remains slowly cooling in the freezing temperatures of deep space. | 0:37:37 | 0:37:42 | |
Looking at it from where the Earth is now, | 0:37:46 | 0:37:48 | |
it would only generate the same amount of light as the full moon on a clear night. | 0:37:48 | 0:37:55 | |
The fate of the sun is the same as for all stars. | 0:37:59 | 0:38:03 | |
One day they must all eventually die, | 0:38:03 | 0:38:07 | |
and the cosmos will be plunged into eternal night, | 0:38:07 | 0:38:11 | |
because this structured universe that we inhabit and all its wonders, | 0:38:11 | 0:38:15 | |
the stars and the planets and the galaxies, cannot last forever. | 0:38:15 | 0:38:21 | |
The cosmos WILL eventually fade and die. | 0:38:21 | 0:38:26 | |
Black holes are the most destructive places in the universe, | 0:38:52 | 0:38:55 | |
able to devour entire stars. | 0:38:55 | 0:38:59 | |
Yet we've never seen one. | 0:39:00 | 0:39:03 | |
It's because of their effects on the stars and galaxies, | 0:39:03 | 0:39:06 | |
and the dust and gas around them, that we know that they exist. | 0:39:06 | 0:39:10 | |
But the reason why black holes are invisible | 0:39:15 | 0:39:18 | |
can be demonstrated here on Earth. | 0:39:18 | 0:39:20 | |
Near a black hole, space and time do some very strange things | 0:39:43 | 0:39:48 | |
because black holes are probably the most violent places | 0:39:48 | 0:39:51 | |
we know of in the universe. | 0:39:51 | 0:39:54 | |
This river provides a beautiful analogy for what happens to space and time | 0:39:54 | 0:39:59 | |
as you get closer and closer to the black hole. | 0:39:59 | 0:40:02 | |
Now, upstream, the water is flowing pretty slowly. | 0:40:05 | 0:40:09 | |
Let's imagine that it's flowing at three kilometres per hour | 0:40:09 | 0:40:12 | |
and I can swim at four, so I can swim faster than the flow and can easily escape. | 0:40:12 | 0:40:19 | |
But as you go further and further downstream towards the waterfall in the distance, | 0:40:27 | 0:40:33 | |
the river flows faster and faster. | 0:40:33 | 0:40:36 | |
Imagine I decide to jump into the river just there on the edge of the falls. | 0:40:55 | 0:41:00 | |
The water is flowing far faster than I could swim, so no matter what I did, | 0:41:00 | 0:41:05 | |
no matter how hard I tried, I would not be able to swim back upstream. | 0:41:05 | 0:41:10 | |
I would be carried inexorably towards the edge | 0:41:10 | 0:41:13 | |
and I would vanish over the falls. | 0:41:13 | 0:41:16 | |
Well, it's the same close to a black hole | 0:41:22 | 0:41:26 | |
because space flows faster and faster and faster | 0:41:26 | 0:41:29 | |
towards the black hole - | 0:41:29 | 0:41:31 | |
literally this stuff, | 0:41:31 | 0:41:34 | |
my space that I'm in, flowing over the edge into the black hole. | 0:41:34 | 0:41:37 | |
And at the very special point called the event horizon, | 0:41:37 | 0:41:42 | |
space is flowing at the speed of light into the black hole. | 0:41:42 | 0:41:47 | |
Light itself, travelling at 300,000 kilometres per second, | 0:41:52 | 0:41:56 | |
is not going fast enough to escape the flow, | 0:41:56 | 0:41:59 | |
and light itself will plunge into the black hole. | 0:41:59 | 0:42:03 | |
So the fact that black holes can swallow light | 0:42:10 | 0:42:13 | |
means that they will for ever remain invisible to our eyes. | 0:42:13 | 0:42:18 | |
Gravity is the force that keeps our feet firmly rooted to our planet. | 0:42:32 | 0:42:37 | |
Yet although it may appear constant and unchanging, | 0:42:37 | 0:42:40 | |
this force varies on all the planets in the solar system | 0:42:40 | 0:42:44 | |
and on the exo-planets we've discovered orbiting other suns. | 0:42:44 | 0:42:50 | |
To experience the gravity on these worlds, I need to go for a spin. | 0:42:50 | 0:42:54 | |
This is a centrifuge. | 0:43:03 | 0:43:05 | |
It was built in the 1950s to test whether fighter pilots had the right stuff, | 0:43:05 | 0:43:10 | |
but it's going to allow me to feel what it would be like | 0:43:10 | 0:43:13 | |
to stand on the surface of any of the planets in the solar system | 0:43:13 | 0:43:17 | |
that are more massive than the Earth, | 0:43:17 | 0:43:19 | |
and in fact, also what it would be like | 0:43:19 | 0:43:22 | |
to stand on some of the planets that we've found around distant stars. | 0:43:22 | 0:43:26 | |
Three...two...one. | 0:43:28 | 0:43:30 | |
As the centrifuge rotates, it feels exactly as if gravity is increased. | 0:43:33 | 0:43:39 | |
The faster it spins, the greater the effect | 0:43:39 | 0:43:42 | |
and we measure this in multiples of the strength | 0:43:42 | 0:43:47 | |
of Earth's gravity, known as 1G. | 0:43:47 | 0:43:50 | |
The first planet I'm travelling to is Neptune. | 0:43:52 | 0:43:56 | |
Its gravity is just fractionally stronger than here on Earth. | 0:43:56 | 0:44:00 | |
So this is the gravitational field on Neptune | 0:44:00 | 0:44:03 | |
and you feel, "You know what? I could probably get used to this. | 0:44:03 | 0:44:06 | |
"I could probably live on the surface of Neptune." | 0:44:06 | 0:44:09 | |
-Can you lift your hands a little? -There we go. -Yeah, and down. | 0:44:09 | 0:44:12 | |
And it is actually quite an effort. It is noticeably heavier. | 0:44:12 | 0:44:17 | |
It's like having a reasonably heavy weight in your hand. | 0:44:17 | 0:44:21 | |
To go to 2.5G? | 0:44:21 | 0:44:23 | |
-Yes, so now we'll move, move from Neptune to Jupiter. -Let's go there. | 0:44:23 | 0:44:27 | |
Jupiter is over 1,300 times more massive than the Earth, | 0:44:30 | 0:44:33 | |
but because it's mostly gas, it's not very dense | 0:44:33 | 0:44:36 | |
so its gravity is just over twice as strong at its surface. | 0:44:36 | 0:44:39 | |
Well, now actually it is quite difficult to lift my hand. | 0:44:39 | 0:44:44 | |
And that's 2.5G. I wouldn't want to sit here for half an hour. | 0:44:45 | 0:44:49 | |
Can you lift both of your hands above your head? | 0:44:49 | 0:44:53 | |
-See what happens there. -Let's see, so actually... | 0:44:53 | 0:44:56 | |
just about, but actually it's an immense amount of hard work. | 0:44:56 | 0:45:02 | |
-So it would be hard work living on Jupiter. -Let's go to 4G. | 0:45:02 | 0:45:06 | |
Actually, this is heading to a planet around... | 0:45:13 | 0:45:16 | |
A planet called Ogle 2TRL9B | 0:45:16 | 0:45:19 | |
which is around a star in the constellation of Carina. | 0:45:19 | 0:45:23 | |
It's one of the exo-planets we've discovered. | 0:45:23 | 0:45:26 | |
Oh, and there we go. | 0:45:27 | 0:45:29 | |
Now, that is actually...beginning to feel quite unpleasant. | 0:45:33 | 0:45:39 | |
-Can you describe what you're feeling? -Very heavy face. | 0:45:39 | 0:45:43 | |
My head is extremely heavy. | 0:45:43 | 0:45:45 | |
How about your lungs, inhaling, exhaling, breathing? | 0:45:45 | 0:45:47 | |
-It's much harder work. I can't lift my hand off my leg. -OK. | 0:45:47 | 0:45:53 | |
-And that's at 4G? -Yeah. | 0:45:53 | 0:45:55 | |
Well, my head and my face feel very, very heavy. | 0:45:55 | 0:46:00 | |
It's quite an unpleasant feeling. | 0:46:00 | 0:46:02 | |
We'll go to 5 and let me know if you have any visual disturbances. | 0:46:02 | 0:46:08 | |
I am now en-route to a newly discovered exo-planet, Wasp 8b. | 0:46:09 | 0:46:13 | |
4.4. | 0:46:15 | 0:46:17 | |
This world sits in the small and faint constellation of Sculptor. | 0:46:17 | 0:46:22 | |
Quite hard to speak. | 0:46:26 | 0:46:27 | |
It has a gravitational force nearly five times that of the Earth. | 0:46:31 | 0:46:35 | |
Right, we'll go to 5G. | 0:46:35 | 0:46:40 | |
-Very foggy. -OK. | 0:46:40 | 0:46:41 | |
-Very foggy. -Very foggy? | 0:46:45 | 0:46:47 | |
-Still foggy? -Yeah. -Right. | 0:46:55 | 0:46:57 | |
-Take it down. -OK, we'll take you down. | 0:46:58 | 0:47:00 | |
Very interesting. | 0:47:15 | 0:47:17 | |
-It was, wasn't it? -My face felt a bit saggy, though. | 0:47:18 | 0:47:22 | |
Well, you looked a little different. | 0:47:22 | 0:47:26 | |
That was, um, quite unpleasant that time, actually. | 0:47:40 | 0:47:45 | |
So you realise that we're, obviously, very finely tuned | 0:47:45 | 0:47:50 | |
to live on a planet that has a gravitational, | 0:47:50 | 0:47:54 | |
an acceleration due to gravity of 1G. | 0:47:54 | 0:47:57 | |
When you go to 2G, it's difficult. | 0:47:57 | 0:48:00 | |
When you go to 3G and 4G it becomes unpleasant, and 5G, anyway, | 0:48:00 | 0:48:05 | |
for me, was on the border of being so unpleasant that you pass out. | 0:48:05 | 0:48:11 | |
So although gravity feels weak here on Earth, | 0:48:18 | 0:48:21 | |
it certainly isn't weak everywhere across the universe. | 0:48:21 | 0:48:25 | |
And that's because gravity is an additive force. | 0:48:26 | 0:48:29 | |
It scales with mass, | 0:48:29 | 0:48:32 | |
so the more massive the planet or star, | 0:48:32 | 0:48:37 | |
the stronger its gravity. | 0:48:37 | 0:48:41 | |
Every moment of our lives, | 0:48:56 | 0:48:57 | |
we experience a force that we can't see or touch. | 0:48:57 | 0:49:01 | |
Yet this force is able to keep us firmly rooted to the ground. | 0:49:04 | 0:49:08 | |
It is, of course, gravity. | 0:49:08 | 0:49:12 | |
But despite its intangible nature, we always know it's with us. | 0:49:16 | 0:49:20 | |
Now if I was to ask you, "How do you know that there's gravity around here?" | 0:49:22 | 0:49:26 | |
Then you might say, "Well, it's obvious. | 0:49:26 | 0:49:28 | |
"You know, I can just do an experiment, I can drop something." | 0:49:28 | 0:49:31 | |
Well, yes, but actually gravity is a little bit more subtle than that | 0:49:33 | 0:49:39 | |
but to really experience it, to understand it, | 0:49:39 | 0:49:43 | |
you have to do something pretty extreme. | 0:49:43 | 0:49:46 | |
And this plane has been modified to help me do it. | 0:49:53 | 0:49:57 | |
Thanks to its flight plan, it's known as the Vomit Comet. | 0:49:57 | 0:50:02 | |
Once we've climbed to 15,000 metres, | 0:50:15 | 0:50:18 | |
this plane does something no ordinary flight would do - | 0:50:18 | 0:50:23 | |
its engines are throttled back and the jet falls to Earth. | 0:50:23 | 0:50:28 | |
And then, something quite amazing happens. | 0:50:29 | 0:50:33 | |
THEY SQUEAL AND CHEER | 0:50:35 | 0:50:37 | |
Push to me, push to me! | 0:50:38 | 0:50:40 | |
I'm now plummeting towards the ground just like someone's cut the cable in a lift, | 0:50:43 | 0:50:49 | |
and you see, we're all just floating. | 0:50:49 | 0:50:52 | |
By simply falling at the same rate as the plane, | 0:51:09 | 0:51:11 | |
for a few fleeting moments, we are all free of gravity's grip. | 0:51:11 | 0:51:18 | |
But this isn't just a joy ride. | 0:51:30 | 0:51:32 | |
Now, look, there's something very profound here | 0:51:39 | 0:51:42 | |
because although I'm falling towards the ground, | 0:51:42 | 0:51:47 | |
as you see, gravity has completely gone away. | 0:51:47 | 0:51:50 | |
Gravity is not here any more. | 0:51:50 | 0:51:54 | |
'Because the aircraft is accelerating towards the ground at 1G, | 0:51:58 | 0:52:02 | |
'the effects of the Earth's gravity are completely cancelled out.' | 0:52:02 | 0:52:08 | |
So it is possible by the simple act of falling to get a very different experience of gravity. | 0:52:14 | 0:52:22 | |
Nothing can travel faster than the speed at which light travels, | 0:52:32 | 0:52:39 | |
but although light travels fast, it's not infinitely fast | 0:52:39 | 0:52:42 | |
so the further away an object is, the further back in time we see it. | 0:52:42 | 0:52:46 | |
The sun is 150 million kilometres away. | 0:52:52 | 0:52:55 | |
Now that's very close by cosmic standards, | 0:52:58 | 0:53:01 | |
but light travels at only 300,000 kilometres per second, | 0:53:01 | 0:53:06 | |
so that means that we're seeing the sun | 0:53:06 | 0:53:09 | |
as it was in the past, actually eight minutes in the past. | 0:53:09 | 0:53:15 | |
But when we look beyond our sun, to far more distant stars, | 0:53:21 | 0:53:25 | |
we reach further back in time. | 0:53:25 | 0:53:27 | |
As the sun dips below the horizon and night falls... | 0:53:35 | 0:53:39 | |
..the universe just fades into view. | 0:53:41 | 0:53:45 | |
And then, as it gets darker and darker, the Milky Way appears - | 0:53:49 | 0:53:53 | |
a vast swathe of billions and billions of suns as you look out | 0:53:53 | 0:53:59 | |
towards the centre of our Milky Way galaxy. | 0:53:59 | 0:54:02 | |
But I think for me, the most magical thing | 0:54:06 | 0:54:09 | |
you can see in the sky with the naked eye, is just below | 0:54:09 | 0:54:13 | |
the constellation of Cassiopeia, the W of stars in the sky. | 0:54:13 | 0:54:18 | |
There, look at that. | 0:54:30 | 0:54:34 | |
Actually, I've got to say, that's amazing. | 0:54:35 | 0:54:38 | |
You see, that misty patch of light is not a cloud in the sky, | 0:54:40 | 0:54:44 | |
it's not even gas and dust in our galaxy. | 0:54:44 | 0:54:47 | |
That...is another galaxy. | 0:54:47 | 0:54:50 | |
It's the Andromeda galaxy, which is roughly the same size as our own - | 0:54:50 | 0:54:54 | |
an island of hundreds of billions of stars, | 0:54:54 | 0:54:57 | |
25 million, million, million kilometres in that direction. | 0:54:57 | 0:55:03 | |
The light that I've just captured in my camera began its journey two and a half million years ago. | 0:55:08 | 0:55:14 | |
At that time on Earth, there were no humans. | 0:55:14 | 0:55:17 | |
Homo habilis, our distant ancestors, | 0:55:17 | 0:55:20 | |
were roaming the plains of Africa and as those light rays travelled | 0:55:20 | 0:55:24 | |
through the vastness of space, our species evolved | 0:55:24 | 0:55:29 | |
and thousands and thousands and thousands of generations of humans lived and died. | 0:55:29 | 0:55:35 | |
And then, two and a half million years after their journey began, | 0:55:35 | 0:55:39 | |
these messengers from the depths of space, and from way back in our past, | 0:55:39 | 0:55:47 | |
arrived here on Earth, and I just captured them and took that picture. | 0:55:47 | 0:55:52 | |
But by peering further than the naked eye will allow, | 0:55:57 | 0:55:59 | |
we can journey to a time way before human history. | 0:55:59 | 0:56:04 | |
In the last 20 years, powerful space telescopes have carried us | 0:56:04 | 0:56:08 | |
ever deeper into space and we have become virtual time travellers. | 0:56:08 | 0:56:13 | |
This is NGC 520 and it's the product of a cosmic collision, | 0:56:17 | 0:56:22 | |
but this galaxy is a hundred million light years away. | 0:56:22 | 0:56:27 | |
That means that the light began its journey from this galaxy | 0:56:27 | 0:56:30 | |
to my eye when the dinosaurs roamed the Earth. | 0:56:30 | 0:56:33 | |
But these spectacular galaxies | 0:56:44 | 0:56:46 | |
are not the end of our journey into the past. | 0:56:46 | 0:56:49 | |
In 2004, we peered further back in time than ever before | 0:56:49 | 0:56:54 | |
and captured the light from the most distant galaxies in the universe. | 0:56:54 | 0:57:00 | |
The image is called the Hubble Ultra Deep Field. | 0:57:02 | 0:57:06 | |
It's a picture taken by the Hubble Space Telescope | 0:57:06 | 0:57:09 | |
over a period of 11 days, and it focused its camera | 0:57:09 | 0:57:13 | |
on the tiniest piece of sky, just below the constellation of Orion. | 0:57:13 | 0:57:19 | |
Now, it's a piece of sky that you would cover | 0:57:19 | 0:57:21 | |
if you took your thumb, held it in front of your face | 0:57:21 | 0:57:26 | |
and then moved it 20 times further away. | 0:57:26 | 0:57:29 | |
But the Hubble captured the faintest lights from the most distant regions | 0:57:32 | 0:57:37 | |
of the universe and it took this photograph. | 0:57:37 | 0:57:40 | |
Now, almost every point of light in that image is not a star, | 0:57:44 | 0:57:49 | |
but a galaxy of over a hundred billion stars. | 0:57:49 | 0:57:55 | |
The most distant galaxies in that image are over 13 billion light years away. | 0:57:55 | 0:58:01 | |
That means that the faint light from those galaxies | 0:58:01 | 0:58:05 | |
began its journey to Earth 13 billion years ago. | 0:58:05 | 0:58:10 | |
That's over three times the age of the Earth. | 0:58:10 | 0:58:15 | |
Subtitles by Red Bee Media Ltd | 0:58:33 | 0:58:36 | |
E-mail [email protected] | 0:58:36 | 0:58:39 |