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Imagine that our sun is the size of just a single grain of sand. | 0:00:07 | 0:00:13 | |
Now, our sun is just one of a multitude of stars. | 0:00:20 | 0:00:25 | |
It's surrounded by over 200 billion of them | 0:00:25 | 0:00:29 | |
in our own Milky Way galaxy alone. | 0:00:29 | 0:00:33 | |
Our sun is just a speck in the vast beach of stars. | 0:00:33 | 0:00:39 | |
But the Milky Way galaxy is in itself just one | 0:00:43 | 0:00:48 | |
of 100 billion galaxies, scattered throughout the cosmos. | 0:00:48 | 0:00:53 | |
It's been estimated that there are more stars in the universe | 0:01:01 | 0:01:05 | |
than there are grains of sand on all the beaches in all the world. | 0:01:05 | 0:01:11 | |
Just think about that for a moment. | 0:01:11 | 0:01:13 | |
The size and scale of the universe is awe-inspiring. | 0:01:15 | 0:01:20 | |
But, as a scientist, what I find so remarkable is that the human race | 0:01:20 | 0:01:25 | |
has managed to deduce so much about what it looks like. | 0:01:25 | 0:01:30 | |
Let me try and put this achievement into context. | 0:01:32 | 0:01:35 | |
From our vantage point, living on a minuscule speck orbiting around | 0:01:35 | 0:01:41 | |
this single grain of sand, we've managed to deduce the size and shape | 0:01:41 | 0:01:47 | |
of all those beaches. | 0:01:47 | 0:01:49 | |
To my mind, this is one of the human race's greatest accomplishments, | 0:01:49 | 0:01:55 | |
and I'd like to tell you the story of how we did it. | 0:01:55 | 0:01:59 | |
This film is the astonishing story of how we gazed upwards from our | 0:02:01 | 0:02:07 | |
isolated and unremarkable vantage point and began to deduce the shape, | 0:02:07 | 0:02:13 | |
size and origin of everything that there is. | 0:02:13 | 0:02:19 | |
It's the story of how we came to understand reality | 0:02:19 | 0:02:23 | |
at the largest scale. | 0:02:23 | 0:02:26 | |
It's the story of everything. | 0:02:26 | 0:02:29 | |
I want you to pause for a moment and think about this one basic question. | 0:02:51 | 0:02:57 | |
Here I am, sitting under the night sky. | 0:02:57 | 0:03:00 | |
Above me is the atmosphere and beyond that the moon, | 0:03:00 | 0:03:05 | |
and way beyond that the stars. | 0:03:05 | 0:03:07 | |
But then what? | 0:03:07 | 0:03:09 | |
What's the totality of everything there is? | 0:03:09 | 0:03:13 | |
It's a question we've all asked at one point or another. | 0:03:13 | 0:03:15 | |
I remember as a kid, growing up in Baghdad, | 0:03:15 | 0:03:18 | |
during the summer, we'd take the beds up onto the roof | 0:03:18 | 0:03:22 | |
and I remember lying awake at night, looking up at the stars | 0:03:22 | 0:03:25 | |
and wondering whether space went on forever | 0:03:25 | 0:03:29 | |
or whether the universe had an edge. | 0:03:29 | 0:03:32 | |
Today, we're beginning to understand | 0:03:32 | 0:03:35 | |
just how complex this question really is. | 0:03:35 | 0:03:39 | |
But 500 years ago, it seemed like there was a very simple answer. | 0:03:41 | 0:03:46 | |
You see, the prevailing belief was that the Earth was enclosed | 0:03:46 | 0:03:51 | |
in a vast but thin shell of rotating stars that were fixed in position. | 0:03:51 | 0:03:58 | |
When you look up on a starry night, | 0:03:58 | 0:04:01 | |
it's not difficult to see why people believed we lived within this shell. | 0:04:01 | 0:04:06 | |
But in the 16th century, | 0:04:09 | 0:04:11 | |
something happened which would shatter this view of the universe. | 0:04:11 | 0:04:16 | |
It was an event that would set the human race on a journey | 0:04:16 | 0:04:20 | |
to uncover the true size and shape of everything. | 0:04:20 | 0:04:26 | |
This is a Type Ia supernova. | 0:04:38 | 0:04:41 | |
An exploding star. | 0:04:41 | 0:04:44 | |
It's an event of almost unimaginable scale. | 0:04:44 | 0:04:48 | |
It shines five billion times more brightly than our own sun. | 0:04:48 | 0:04:53 | |
In 1572, a supernova like this would have become visible on Planet Earth. | 0:04:58 | 0:05:03 | |
At the time, it was known simply as "the phenomenon". | 0:05:05 | 0:05:09 | |
And to anyone who saw it, it must have been an extremely shocking | 0:05:09 | 0:05:13 | |
and mysterious sight. | 0:05:13 | 0:05:15 | |
This new light in the night sky | 0:05:15 | 0:05:17 | |
shone more brightly than Venus and even became visible during the day. | 0:05:17 | 0:05:23 | |
It's not surprising, then, that many sought a religious explanation | 0:05:23 | 0:05:28 | |
for this bizarre and troubling event. | 0:05:28 | 0:05:31 | |
One possible interpretation | 0:05:31 | 0:05:33 | |
of the new star of 1572, which was put forward by some intellectuals, | 0:05:33 | 0:05:40 | |
was that this is the star the wise men saw 1,570 years earlier. | 0:05:40 | 0:05:47 | |
It's the star that shone over Bethlehem, and it's now returned. | 0:05:47 | 0:05:54 | |
So something as cosmically important as the incarnation of God on Earth | 0:05:54 | 0:05:59 | |
might be being proclaimed by this new star. | 0:05:59 | 0:06:03 | |
The phenomenon fascinated and mystified many people across Europe. | 0:06:06 | 0:06:11 | |
In England, it fired the imagination | 0:06:11 | 0:06:14 | |
of the MP of the sleepy Oxfordshire town of Wallingford. | 0:06:14 | 0:06:18 | |
His name was Thomas Digges. | 0:06:18 | 0:06:21 | |
But just as Digges began to study this mysterious new star, | 0:06:25 | 0:06:30 | |
it started to grow dimmer. | 0:06:30 | 0:06:32 | |
Digges' friend, mentor and fellow astronomer, a man named John Dee, | 0:06:35 | 0:06:41 | |
reasoned with him that this phenomenon could be a moving star, | 0:06:41 | 0:06:45 | |
something previously thought to have been impossible. | 0:06:45 | 0:06:48 | |
Perhaps it had grown brighter | 0:06:48 | 0:06:52 | |
as it approached the Earth and faded as it had gone away. | 0:06:52 | 0:06:57 | |
Now, although this theory was wrong, it got Digges thinking about | 0:07:01 | 0:07:06 | |
the true nature of the stars that surround the Earth. | 0:07:06 | 0:07:09 | |
It began to seem very unlikely that they were all arranged | 0:07:09 | 0:07:13 | |
in a vast, thin shell. | 0:07:13 | 0:07:15 | |
Maybe this apparent shell was just an illusion? | 0:07:15 | 0:07:20 | |
It would take Thomas Digges another four years | 0:07:23 | 0:07:26 | |
before he published his strange idea. | 0:07:26 | 0:07:29 | |
And when he did, it was in the form of a simple diagram, | 0:07:29 | 0:07:33 | |
added to a translation of the works of Nicolaus Copernicus. | 0:07:33 | 0:07:39 | |
The man who'd first argued that the sun | 0:07:39 | 0:07:42 | |
was at the centre of the universe. | 0:07:42 | 0:07:45 | |
Have a look at this. | 0:07:45 | 0:07:47 | |
On this side is Copernicus' model. | 0:07:47 | 0:07:49 | |
Absolutely revolutionary. | 0:07:49 | 0:07:51 | |
He has the sun at the centre with the Earth in orbit around it, | 0:07:51 | 0:07:55 | |
along with the other planets. | 0:07:55 | 0:07:57 | |
And in the outermost shell is that of the fixed stars - | 0:07:57 | 0:08:00 | |
the stellarum fixarum. | 0:08:00 | 0:08:03 | |
On this side is Digges' diagram, included in the English translation. | 0:08:03 | 0:08:08 | |
Exactly the same, but he's taken Copernicus' stars | 0:08:08 | 0:08:11 | |
out of their fixed shell | 0:08:11 | 0:08:14 | |
and scattered them out into endless space. | 0:08:14 | 0:08:16 | |
Digges' diagram was describing a radical new picture of the cosmos. | 0:08:19 | 0:08:24 | |
One where the stars in the night sky now existed in an infinite space. | 0:08:27 | 0:08:35 | |
Digges shows it, unlike Copernicus, as being infinite. | 0:08:40 | 0:08:46 | |
This is a sphere, he says, of the stars fixed infinitely up. | 0:08:46 | 0:08:51 | |
And that is a moment when perhaps Europeans start to think | 0:08:51 | 0:08:57 | |
of the world as unbounded, as infinite, as a world without end. | 0:08:57 | 0:09:04 | |
Digges' new picture of the universe was revolutionary. | 0:09:08 | 0:09:12 | |
Previously, we'd been contained within a small shell of stars. | 0:09:12 | 0:09:18 | |
Now we were suspended within an infinite static universe. | 0:09:18 | 0:09:23 | |
But this picture of everything produced a strange paradox. | 0:09:27 | 0:09:32 | |
If this infinite universe contained an infinite number of stars, | 0:09:32 | 0:09:38 | |
then why was it dark at night? | 0:09:38 | 0:09:42 | |
In the traditional old-fashioned view of the universe, | 0:09:45 | 0:09:48 | |
the universe was infinite and static. | 0:09:48 | 0:09:52 | |
It was very soon recognised that | 0:09:52 | 0:09:54 | |
a static infinite universe was ridiculous. | 0:09:54 | 0:09:58 | |
And that is because, in such a universe, | 0:09:58 | 0:10:02 | |
there would be an infinite number of stars and every line | 0:10:02 | 0:10:06 | |
of sight from us would intercept one of these stars. | 0:10:06 | 0:10:11 | |
The universe - static infinite universe - could not be dark. | 0:10:11 | 0:10:15 | |
It should be glowing as bright as the sun. | 0:10:15 | 0:10:18 | |
And we know that's not our universe. | 0:10:18 | 0:10:20 | |
In our universe, the night sky is dark. | 0:10:20 | 0:10:24 | |
Although Thomas Digges first raised this question, | 0:10:32 | 0:10:35 | |
the problem came to be known as Olbers' paradox. | 0:10:35 | 0:10:39 | |
As simple as the question sounds, | 0:10:39 | 0:10:42 | |
it would take until the 20th century to find a truly satisfactory answer | 0:10:42 | 0:10:48 | |
for why the night sky is not as bright as the day. | 0:10:48 | 0:10:52 | |
Solving Olbers' paradox would require many great scientists, | 0:10:58 | 0:11:02 | |
who weren't afraid to think differently. | 0:11:02 | 0:11:05 | |
Radically differently. | 0:11:05 | 0:11:06 | |
You see, solving the paradox is all about understanding the shape, size | 0:11:06 | 0:11:11 | |
and origin of everything there is. | 0:11:11 | 0:11:14 | |
Without this understanding, the puzzle would be impossible to solve. | 0:11:14 | 0:11:18 | |
You see, stuck here on Earth, | 0:11:18 | 0:11:19 | |
we don't have access to interstellar travel. | 0:11:19 | 0:11:22 | |
So we have to allow our minds to make that intellectual leap. | 0:11:22 | 0:11:26 | |
By simply looking up, | 0:11:32 | 0:11:34 | |
Digges and his contemporaries had begun a scientific journey | 0:11:34 | 0:11:40 | |
to understand what everything might actually look like. | 0:11:40 | 0:11:43 | |
But, for 200 years after Thomas Digges' insight, | 0:11:45 | 0:11:49 | |
little progress was made in understanding the most | 0:11:49 | 0:11:52 | |
distant reaches of the cosmos. | 0:11:52 | 0:11:54 | |
At the end of the 18th century, however, all that would change. | 0:11:55 | 0:12:01 | |
Until the end of the 1700s, everything that lies outside | 0:12:02 | 0:12:07 | |
the solar system is, for astronomers, pretty uninteresting. | 0:12:07 | 0:12:13 | |
Astronomy until then was the science of our system - | 0:12:13 | 0:12:18 | |
of the Earth and the planets, satellites and comets. | 0:12:18 | 0:12:22 | |
The stars were a kind of glorified and rather interesting backdrop. | 0:12:22 | 0:12:26 | |
This changes around 1800. | 0:12:26 | 0:12:30 | |
This small and unremarkable house in Bath was once home to the astronomer | 0:12:42 | 0:12:48 | |
William Herschel and his sister, and devoted assistant, Caroline. | 0:12:48 | 0:12:52 | |
Together, they would develop and build a new generation of telescopes | 0:12:52 | 0:12:57 | |
that would allow them to see further out into space | 0:12:57 | 0:13:00 | |
than any human had ever done before. | 0:13:00 | 0:13:03 | |
William Herschel was born in Hanover, but moved to England | 0:13:05 | 0:13:09 | |
in 1761 to pursue a career as a musician and composer. | 0:13:09 | 0:13:14 | |
But he soon developed a passion for astronomy | 0:13:14 | 0:13:18 | |
and began building telescopes in his spare time. | 0:13:18 | 0:13:22 | |
Herschel soon perfected a technique for producing telescopes | 0:13:23 | 0:13:28 | |
borrowed from Sir Isaac Newton. | 0:13:28 | 0:13:31 | |
The telescopes used metal mirrors | 0:13:31 | 0:13:34 | |
that were capable of capturing much more starlight | 0:13:34 | 0:13:37 | |
than the glass lenses that were popular among other astronomers. | 0:13:37 | 0:13:42 | |
This tiny room at the back of Herschel's house | 0:13:47 | 0:13:49 | |
used to be his workshop. | 0:13:49 | 0:13:51 | |
It was here that he'd smelt various metals together in the furnace | 0:13:51 | 0:13:55 | |
to make the reflecting mirrors for his telescopes. | 0:13:55 | 0:13:59 | |
And he would experiment with different metals, | 0:13:59 | 0:14:02 | |
different combinations, to get them as reflective as possible. | 0:14:02 | 0:14:07 | |
Then, with his sister Caroline to help him, | 0:14:07 | 0:14:09 | |
he'd spend literally hours on end | 0:14:09 | 0:14:12 | |
polishing the surface of the mirrors to achieve the precision required. | 0:14:12 | 0:14:18 | |
And you have to remember, this was quite | 0:14:18 | 0:14:20 | |
a dangerous, confined environment. | 0:14:20 | 0:14:22 | |
The floor still bears the scars of the molten metal | 0:14:22 | 0:14:27 | |
that they'd spilt, cracking the paving stones. | 0:14:27 | 0:14:29 | |
With his powerful telescopes, Herschel and his sister Caroline | 0:14:33 | 0:14:37 | |
would scour the heavens, night after night, cataloguing the stars. | 0:14:37 | 0:14:43 | |
The universe they were seeing was revealing itself | 0:14:44 | 0:14:48 | |
to be one of dynamic complexity, a universe of natural, organic motion, | 0:14:48 | 0:14:55 | |
a place of endless wonder. | 0:14:55 | 0:14:58 | |
Herschel's revolutionary telescope design made him famous. | 0:15:00 | 0:15:05 | |
With it, he'd discover a new planet, Uranus, | 0:15:05 | 0:15:09 | |
a discovery that would earn him the job of the King's astronomer. | 0:15:09 | 0:15:14 | |
This new role gave him the time and resources to start a much | 0:15:14 | 0:15:18 | |
grander task, to try and map all the stars in the universe, in an attempt | 0:15:18 | 0:15:24 | |
to draw a picture of everything. | 0:15:24 | 0:15:27 | |
In 1785, Herschel published this remarkable image. | 0:15:31 | 0:15:36 | |
It shows an approximation of the Milky Way, | 0:15:36 | 0:15:40 | |
with our sun residing at the centre. | 0:15:40 | 0:15:44 | |
Herschel had seen that we are part of a vast disc of stars, | 0:15:44 | 0:15:49 | |
a huge galaxy of suns that seemed to have a clear boundary. | 0:15:49 | 0:15:54 | |
It appeared as though Herschel's craftsmanship | 0:15:59 | 0:16:02 | |
had actually allowed him to see to the edge of everything. | 0:16:02 | 0:16:06 | |
But soon a nagging problem began to emerge. | 0:16:12 | 0:16:16 | |
Dotted around the sky, Herschel and others | 0:16:16 | 0:16:19 | |
had been observing strange, cloud-like objects, | 0:16:19 | 0:16:23 | |
known as nebulae. | 0:16:23 | 0:16:25 | |
Some of these nebulae seemed to have distinctive form | 0:16:29 | 0:16:33 | |
and complex structure. | 0:16:33 | 0:16:35 | |
Some astronomers began to suggest a radical idea. | 0:16:37 | 0:16:40 | |
Perhaps the Milky Way was not everything that there was. | 0:16:41 | 0:16:46 | |
Perhaps some of these nebulae were in fact themselves gigantic | 0:16:46 | 0:16:51 | |
galaxies of stars, just like ours, that actually existed in deep space. | 0:16:51 | 0:16:57 | |
Unfortunately, there was no way to answer this question satisfactorily. | 0:16:59 | 0:17:03 | |
The problem was that, | 0:17:05 | 0:17:07 | |
for all Herschel's great technological achievements, | 0:17:07 | 0:17:10 | |
and for all of those long, cold nights that he spent with Caroline | 0:17:10 | 0:17:14 | |
outside, gazing painstakingly at the heavens, there was one problem | 0:17:14 | 0:17:19 | |
they couldn't solve. | 0:17:19 | 0:17:20 | |
They had no way of accurately measuring distances in outer space. | 0:17:20 | 0:17:26 | |
It would not be until after Herschel's death | 0:17:28 | 0:17:31 | |
that a cunning method was developed | 0:17:31 | 0:17:33 | |
to measure the distances to objects deep into space. | 0:17:33 | 0:17:36 | |
The technique was known as stellar parallax. | 0:17:38 | 0:17:41 | |
If you look at an object like your finger from two vantage points, | 0:17:44 | 0:17:48 | |
it will shift in your frame of reference. | 0:17:48 | 0:17:51 | |
By observing how much it shifts, you can calculate | 0:17:51 | 0:17:56 | |
how far away it is. | 0:17:56 | 0:17:58 | |
My finger is moving a lot more between each frame | 0:17:58 | 0:18:02 | |
than the building that is behind it. | 0:18:02 | 0:18:05 | |
Now, an astronomer called Friedrich Bessel worked out that if you took | 0:18:09 | 0:18:13 | |
images of stars when the Earth was at either side of its orbit around | 0:18:13 | 0:18:18 | |
the sun, it would be possible to actually see the stars shifting. | 0:18:18 | 0:18:24 | |
By observing how much they shifted, | 0:18:24 | 0:18:26 | |
you could then work out their distance from us. | 0:18:26 | 0:18:29 | |
Bessel calculated that the relatively close star, | 0:18:34 | 0:18:37 | |
61 Cygni, must be some 100 trillion kilometres away. | 0:18:37 | 0:18:44 | |
But amazing though this technique was, | 0:18:44 | 0:18:46 | |
it was still very severely limited. | 0:18:46 | 0:18:49 | |
The diameter of the Earth's orbit is 300 million kilometres. | 0:18:51 | 0:18:56 | |
This means the parallax method can only measure objects | 0:18:56 | 0:19:00 | |
out to about 300 trillion kilometres, | 0:19:00 | 0:19:04 | |
only a tiny fraction of the size of the Milky Way. | 0:19:04 | 0:19:07 | |
It soon became clear that there was plenty in the heavens | 0:19:13 | 0:19:16 | |
that was practically impossible to measure, | 0:19:16 | 0:19:19 | |
particularly those mysterious nebulae. | 0:19:19 | 0:19:22 | |
They would remain an enigma until the beginning of the 20th century, | 0:19:25 | 0:19:29 | |
when they ignited a great debate. | 0:19:29 | 0:19:33 | |
One group of astronomers agrees that there is only one galaxy, ours, | 0:19:33 | 0:19:39 | |
the Milky Way and everything else we see, | 0:19:39 | 0:19:41 | |
the globular clusters, the nebulae, are all somehow inside that galaxy. | 0:19:41 | 0:19:49 | |
Then there are other astronomers who argue no, many of these nebulae are | 0:19:49 | 0:19:54 | |
themselves giant island universes, unimaginably far away from us. | 0:19:54 | 0:20:00 | |
There was evidence on both sides. | 0:20:00 | 0:20:02 | |
This mystery remained a source of bitter debate | 0:20:06 | 0:20:09 | |
until the beginning of the 1920s. | 0:20:09 | 0:20:13 | |
The woman who would help solve the problem is one of the great | 0:20:14 | 0:20:18 | |
unsung heroes of science. | 0:20:18 | 0:20:21 | |
She worked at the Harvard College Observatory | 0:20:21 | 0:20:24 | |
and her name was Henrietta Leavitt. | 0:20:24 | 0:20:27 | |
Leavitt's job was to count and catalogue the stars | 0:20:28 | 0:20:32 | |
producing images from observatories around the world. | 0:20:32 | 0:20:36 | |
She was a brilliant scientist who loved her work. | 0:20:36 | 0:20:39 | |
This is one of the photographic plates of space | 0:20:42 | 0:20:45 | |
that Leavitt worked with. | 0:20:45 | 0:20:47 | |
You can see her bright marks highlighting | 0:20:47 | 0:20:50 | |
tiny details within the image. | 0:20:50 | 0:20:53 | |
With meticulous care, | 0:20:53 | 0:20:55 | |
hundreds of subtle features of stars have been noted. | 0:20:55 | 0:20:59 | |
It was this ability that would help her come up with an ingenious idea, | 0:21:05 | 0:21:10 | |
one that would help unravel the true size of the universe. | 0:21:10 | 0:21:15 | |
The idea rested on finding an objective way of defining | 0:21:15 | 0:21:20 | |
the true brightness of a star. | 0:21:20 | 0:21:22 | |
Leavitt became fascinated by a type of star known as a Cepheid variable, | 0:21:26 | 0:21:32 | |
which pulses in the night sky. | 0:21:32 | 0:21:35 | |
Her breakthrough was discovering | 0:21:35 | 0:21:36 | |
that their brightness was precisely related to the speed they blinked. | 0:21:36 | 0:21:42 | |
Let me explain. | 0:21:42 | 0:21:44 | |
These two stars are blinking at the same rate, which means they should | 0:21:46 | 0:21:50 | |
be exactly the same brightness. | 0:21:50 | 0:21:53 | |
If one star appears dimmer, you can then calculate how much further away | 0:21:53 | 0:21:58 | |
it is than the brighter one. | 0:21:58 | 0:22:01 | |
Leavitt's method meant that she knew | 0:22:01 | 0:22:05 | |
the true brightness of the Cepheid variables. | 0:22:05 | 0:22:08 | |
She had found a method to measure the distance to stars that lay | 0:22:08 | 0:22:12 | |
far beyond the reaches of parallax. | 0:22:12 | 0:22:15 | |
But without access to a telescope, | 0:22:17 | 0:22:19 | |
she could go no further with her work. | 0:22:19 | 0:22:22 | |
She was forbidden from working | 0:22:22 | 0:22:24 | |
in the supremely male-dominated world of the observatory. | 0:22:24 | 0:22:28 | |
But her discovery now gave astronomers a tool | 0:22:29 | 0:22:32 | |
to measure the distances to the mysterious nebulae. | 0:22:32 | 0:22:36 | |
The idea that our Milky Way might contain everything that existed | 0:22:38 | 0:22:42 | |
was about to crumble. | 0:22:42 | 0:22:45 | |
The scale of the universe is really only understood | 0:22:45 | 0:22:50 | |
amazingly recently. | 0:22:50 | 0:22:52 | |
In the 1920s, it was absolutely plausible | 0:22:52 | 0:22:56 | |
that the universe consists of one galaxy, | 0:22:56 | 0:23:00 | |
and some of the best astronomers in the world, in the US for example, | 0:23:00 | 0:23:06 | |
seriously held that view, and had good evidence that it was true. | 0:23:06 | 0:23:10 | |
And they were wrong. | 0:23:10 | 0:23:11 | |
The evidence to finally settle the great debate would be found | 0:23:13 | 0:23:17 | |
thanks to the powerful new Hooker telescope | 0:23:17 | 0:23:20 | |
being built at the Mount Wilson Observatory | 0:23:20 | 0:23:23 | |
just outside Los Angeles. | 0:23:23 | 0:23:26 | |
Using this incredible piece of technology, | 0:23:26 | 0:23:29 | |
and Henrietta Leavitt's ingenious method for calculating distance, | 0:23:29 | 0:23:33 | |
a young astronomer would make a discovery that would change | 0:23:33 | 0:23:37 | |
our view of the universe and for ever immortalise his name. | 0:23:37 | 0:23:42 | |
The astronomer was called Edwin Hubble. | 0:23:42 | 0:23:46 | |
Hubble was a very different kind of scientist to Leavitt. | 0:23:46 | 0:23:51 | |
He was a larger-than-life character, extrovert, with a huge ego. | 0:23:51 | 0:23:56 | |
But he was still a hugely-talented and visionary scientist. | 0:23:56 | 0:24:00 | |
He was born and grew up in America but spent some time in England, | 0:24:00 | 0:24:03 | |
and this seems to have had a lasting impression | 0:24:03 | 0:24:06 | |
because he would be heard walking around the observatory | 0:24:06 | 0:24:09 | |
shouting things like, "By Jove!" | 0:24:09 | 0:24:11 | |
and "What-ho!" in a completely over-the-top British accent. | 0:24:11 | 0:24:15 | |
The talented, passionate and eccentric Hubble | 0:24:17 | 0:24:20 | |
rapidly gained a name for himself in the world of astronomy. | 0:24:20 | 0:24:24 | |
But it wouldn't be until 1923, | 0:24:24 | 0:24:26 | |
that he would discover something in what was then known | 0:24:26 | 0:24:29 | |
as the Andromeda Nebula | 0:24:29 | 0:24:31 | |
that would reveal the true scale of our universe. | 0:24:31 | 0:24:34 | |
I've come to the University College London Observatory | 0:24:35 | 0:24:38 | |
to meet astronomer Dr Steve Fossey, | 0:24:38 | 0:24:40 | |
to see for myself just what Hubble's revelation was. | 0:24:40 | 0:24:46 | |
We're going to key in the co-ordinates | 0:24:46 | 0:24:48 | |
of Andromeda to the console here. | 0:24:48 | 0:24:50 | |
So zero hours 43 minutes... | 0:24:50 | 0:24:53 | |
'For Hubble and his assistant, Milton Humason, | 0:24:53 | 0:24:57 | |
'studying Andromeda was a long and painstaking process. | 0:24:57 | 0:25:01 | |
'But today, we can quickly locate and photograph it in great detail.' | 0:25:01 | 0:25:07 | |
-This is an image that we took a couple of weeks ago. -Right. | 0:25:07 | 0:25:11 | |
If I zoom in, you'll see just there | 0:25:11 | 0:25:14 | |
is the Hubble Cepheid, the first Cepheid that he found | 0:25:14 | 0:25:18 | |
that unlocked the whole problem. | 0:25:18 | 0:25:22 | |
Because presumably that is when he could use Leavitt's method | 0:25:22 | 0:25:27 | |
of working out how far away it is. | 0:25:27 | 0:25:28 | |
Exactly. Once he had seen this and identified it as a variable, | 0:25:28 | 0:25:32 | |
he then had the key to determining just how bright that object was. | 0:25:32 | 0:25:36 | |
And worked out that it couldn't have been in our own galaxy. | 0:25:36 | 0:25:39 | |
It had to be millions of light years away. | 0:25:39 | 0:25:41 | |
Absolutely, that is exactly it. You see the nuclear region, | 0:25:41 | 0:25:44 | |
but as we adjust the contrast here, I can stretch the contrast | 0:25:44 | 0:25:48 | |
-just to bring out some of the detail in the galaxy. -Oh, wow! | 0:25:48 | 0:25:52 | |
Spiral arms. You see the dust lanes in silhouette | 0:25:52 | 0:25:55 | |
against the billions of stars that are within Andromeda. | 0:25:55 | 0:26:00 | |
By finding one of the variable stars in Andromeda, | 0:26:02 | 0:26:06 | |
and measuring exactly how long it took to pulse, | 0:26:06 | 0:26:10 | |
Hubble was able to use Leavitt's work | 0:26:10 | 0:26:13 | |
to calculate exactly how far away it was. | 0:26:13 | 0:26:16 | |
This is the photographic plate | 0:26:19 | 0:26:21 | |
where Hubble marked his new Cepheid variable star. | 0:26:21 | 0:26:26 | |
Using it, he calculated that Andromeda was many, many times | 0:26:26 | 0:26:31 | |
more distant than the furthest reaches of the Milky Way. | 0:26:31 | 0:26:35 | |
Andromeda was indeed an island universe, | 0:26:38 | 0:26:42 | |
a vast galaxy of stars. | 0:26:42 | 0:26:46 | |
We now know that Andromeda is over 2.5 million light years away. | 0:26:48 | 0:26:54 | |
This means that the light that reaches us from Andromeda today, | 0:26:54 | 0:26:59 | |
left on its journey before modern humans had evolved. | 0:26:59 | 0:27:04 | |
-That's our neighbour. -That's our neighbour, | 0:27:04 | 0:27:07 | |
our nearest large, galactic neighbour. | 0:27:07 | 0:27:09 | |
I have to remember that what I am looking at here is the real thing. | 0:27:09 | 0:27:13 | |
These are photons that have travelled millions of years | 0:27:13 | 0:27:18 | |
-to reach my eye. -Exactly. | 0:27:18 | 0:27:21 | |
These are photons directly from Andromeda | 0:27:21 | 0:27:23 | |
that are arriving in my eye. | 0:27:23 | 0:27:25 | |
Today, we have the power to see Andromeda | 0:27:33 | 0:27:36 | |
as Hubble had only dreamed of. | 0:27:36 | 0:27:39 | |
We now estimate that Andromeda | 0:27:45 | 0:27:47 | |
contains over a trillion stars. | 0:27:47 | 0:27:51 | |
And it is just one of a vast multitude of galaxies | 0:27:53 | 0:27:57 | |
scattered throughout our universe. | 0:27:57 | 0:28:01 | |
In 1923, the universe had been the size of the Milky Way. | 0:28:23 | 0:28:30 | |
By 1924, the space that surrounds us | 0:28:30 | 0:28:34 | |
had been revealed to be billions of times bigger | 0:28:34 | 0:28:38 | |
and home to almost unimaginable cosmic complexity. | 0:28:38 | 0:28:43 | |
Hubble had shown that there are a multitude of galaxies outside | 0:28:46 | 0:28:50 | |
of our own and had pushed back the boundaries of the universe. | 0:28:50 | 0:28:56 | |
But he had not seen an edge of space. | 0:28:56 | 0:28:58 | |
He had not seen everything. | 0:28:58 | 0:29:02 | |
There was still no clue | 0:29:02 | 0:29:03 | |
as to how big our universe was, or even what shape it might be. | 0:29:03 | 0:29:08 | |
To understand the strange truth about everything would require | 0:29:11 | 0:29:15 | |
more than just observations. | 0:29:15 | 0:29:18 | |
It would require mathematics - | 0:29:18 | 0:29:21 | |
a powerful new type of mathematics that would be able to describe | 0:29:21 | 0:29:25 | |
the bizarre properties of space itself. | 0:29:25 | 0:29:29 | |
When you're trying to understand the universe, it's easy to think, | 0:29:30 | 0:29:33 | |
what you do is you make lots and lots of observations, see what's there, | 0:29:33 | 0:29:36 | |
and you fit it all together into your grand picture. | 0:29:36 | 0:29:39 | |
But the problem is, unless you have some sort of idea | 0:29:39 | 0:29:42 | |
what the picture should be, you don't know what observations to make, | 0:29:42 | 0:29:46 | |
you don't know what's significant. | 0:29:46 | 0:29:47 | |
And throughout the history of science, | 0:29:47 | 0:29:50 | |
every so often someone has to come up with a new mathematical idea. | 0:29:50 | 0:29:53 | |
The new mathematical ideas about space were so weird, | 0:29:55 | 0:30:00 | |
so far removed from common sense, that it would take over 2,000 years | 0:30:00 | 0:30:05 | |
and the genius of Albert Einstein to formulate them. | 0:30:05 | 0:30:09 | |
But when they were ready, these strange new types | 0:30:11 | 0:30:15 | |
of mathematics would lead to a revolution | 0:30:15 | 0:30:17 | |
in our understanding of the space that surrounds us. | 0:30:17 | 0:30:21 | |
OK. So what is space? | 0:30:25 | 0:30:31 | |
We think we know the answer. I can talk about this room being spacious. | 0:30:35 | 0:30:40 | |
There's a lot of space in here. | 0:30:40 | 0:30:42 | |
Or a confined space. There's not enough volume, not enough space. | 0:30:42 | 0:30:46 | |
But does space only exist when there's stuff in it? | 0:30:46 | 0:30:50 | |
Does space only have a meaning when it's enclosed by walls? | 0:30:50 | 0:30:54 | |
Think of the distance between two objects. | 0:31:00 | 0:31:05 | |
Does that gap still exist if you take the objects away? | 0:31:05 | 0:31:11 | |
What meaning can we give to distance | 0:31:12 | 0:31:16 | |
if it doesn't have a start and end point? | 0:31:16 | 0:31:19 | |
Ultimately, the question is this - | 0:31:21 | 0:31:23 | |
does space in itself have form? | 0:31:23 | 0:31:27 | |
Does it have structure or shape? | 0:31:27 | 0:31:30 | |
Or is it just the place where things happen? | 0:31:32 | 0:31:35 | |
The properties of space were first described by the mathematician | 0:31:37 | 0:31:41 | |
Euclid over 2,000 years ago, in his legendary text, The Elements. | 0:31:41 | 0:31:48 | |
In it, he laid down a set of simple, logical rules about space, | 0:31:48 | 0:31:52 | |
in what today, we call Euclidian geometry. | 0:31:52 | 0:31:57 | |
Euclidian geometry is the geometry we see around us every day. | 0:31:57 | 0:32:01 | |
If you're sitting in a room and it's the usual rectangular room, | 0:32:01 | 0:32:04 | |
what you see is lots of straight lines, right-angles, you see | 0:32:04 | 0:32:08 | |
parallel lines, the window, the two sides of the window are parallel. | 0:32:08 | 0:32:12 | |
If you extended them, they'd stay exactly the same distance apart, | 0:32:12 | 0:32:16 | |
they would never meet. | 0:32:16 | 0:32:18 | |
And the other thing you would see if you look a little closer | 0:32:18 | 0:32:21 | |
is that any triangle you draw, the angles in the triangle | 0:32:21 | 0:32:25 | |
always add up to 180 degrees. | 0:32:25 | 0:32:27 | |
That's characteristic of Euclidian geometry. | 0:32:27 | 0:32:30 | |
And people used to think that this was how geometry was, | 0:32:30 | 0:32:33 | |
that nothing else was possible. | 0:32:33 | 0:32:35 | |
For Euclid himself, and for almost all mathematicians | 0:32:44 | 0:32:48 | |
for the next 2,000 years, | 0:32:48 | 0:32:50 | |
these rules weren't just true mathematically, | 0:32:50 | 0:32:54 | |
they were also true statements about physical reality itself. | 0:32:54 | 0:32:59 | |
So they thought that two parallel lines | 0:32:59 | 0:33:02 | |
would remain parallel for ever. | 0:33:02 | 0:33:04 | |
That a triangle in real space would always have | 0:33:04 | 0:33:08 | |
angles adding up to 180 degrees. | 0:33:08 | 0:33:11 | |
But weird as though this might sound, | 0:33:11 | 0:33:13 | |
it's not actually always true. | 0:33:13 | 0:33:15 | |
Almost 250 years ago, in a small town in northern Germany, | 0:33:17 | 0:33:22 | |
a mathematician was born who had the ability and originality to start | 0:33:22 | 0:33:28 | |
to unravel Euclid's geometry | 0:33:28 | 0:33:30 | |
and begin to change our ideas about space. | 0:33:30 | 0:33:33 | |
His name was Carl Friedrich Gauss. | 0:33:33 | 0:33:38 | |
Gauss tackled many great problems in his career, but from a young age, | 0:33:38 | 0:33:43 | |
he began to speculate that the rules of Euclid may not be as absolute | 0:33:43 | 0:33:48 | |
as everyone had assumed. | 0:33:48 | 0:33:50 | |
Specifically, Gauss began to see that in curved spaces, | 0:33:52 | 0:33:57 | |
other types of geometry could exist, with different rules to Euclid's. | 0:33:57 | 0:34:03 | |
For example, on the surface of a sphere, the angles of a triangle | 0:34:04 | 0:34:09 | |
can add up to more than 180 degrees. | 0:34:09 | 0:34:12 | |
Many others would refine and develop Gauss's ideas. | 0:34:17 | 0:34:23 | |
But one of his greatest achievements would be to give us a cunning method | 0:34:23 | 0:34:27 | |
of accurately measuring curvature. | 0:34:27 | 0:34:30 | |
It would become known simply as the Remarkable Theorem. | 0:34:30 | 0:34:35 | |
Let me explain with this globe. | 0:34:38 | 0:34:41 | |
We can see that it's three-dimensional, | 0:34:41 | 0:34:43 | |
because we can stand back and look at it. | 0:34:43 | 0:34:45 | |
But what if you were an ant, stuck on the surface? | 0:34:45 | 0:34:49 | |
How would it know that that surface is curved? | 0:34:49 | 0:34:52 | |
So, imagine you're the ant, and you start off at the North Pole. | 0:34:52 | 0:34:56 | |
And facing south, you move down towards the equator. | 0:34:56 | 0:35:04 | |
At the equator, you still face south, and you shuffle sideways, | 0:35:04 | 0:35:09 | |
along the equator. | 0:35:09 | 0:35:11 | |
Then, you reach a certain point, and then you start walking backwards | 0:35:12 | 0:35:17 | |
so you're still facing the same direction, and head back | 0:35:17 | 0:35:21 | |
to the North Pole. | 0:35:21 | 0:35:22 | |
Now, look what's happened here. | 0:35:24 | 0:35:26 | |
You've been pointing south all the way round, and yet when you arrive | 0:35:26 | 0:35:30 | |
back at your starting point, you're facing in a different direction. | 0:35:30 | 0:35:35 | |
Understanding this gives us a way of calculating the curvature | 0:35:35 | 0:35:39 | |
of a surface without ever leaving it. | 0:35:39 | 0:35:42 | |
'This was an amazing insight.' | 0:35:44 | 0:35:47 | |
But it only applies to curved surfaces, which are two-dimensional. | 0:35:47 | 0:35:52 | |
It would take a brilliant student of Gauss's, Bernhard Riemann, | 0:35:52 | 0:35:57 | |
to develop these ideas in a way that could be applied | 0:35:57 | 0:36:01 | |
to the three-dimensional space that surrounds us. | 0:36:01 | 0:36:05 | |
It would be a daring, outlandish, | 0:36:05 | 0:36:08 | |
and to non-mathematicians, absurd-sounding concept. | 0:36:08 | 0:36:12 | |
Aged just 26, Riemann encapsulated his strange new ideas about geometry | 0:36:13 | 0:36:19 | |
in a lecture that was to become legendary among mathematicians. | 0:36:19 | 0:36:24 | |
In June 1854, Riemann delivered his lectures to an enraptured audience. | 0:36:24 | 0:36:31 | |
In them, he detailed how he'd taken Gauss's ideas on curved surfaces, | 0:36:31 | 0:36:37 | |
and generalised them, so that they applied not only to curved | 0:36:37 | 0:36:41 | |
two-dimensional surfaces, but the curvature of space in any dimension. | 0:36:41 | 0:36:46 | |
OK, so I'm sure this all sounds rather complicated. | 0:36:57 | 0:37:00 | |
What exactly do we mean by curved space in any dimension? | 0:37:00 | 0:37:05 | |
So let me try and explain. | 0:37:05 | 0:37:07 | |
Here's the thing, Gauss talked about curved two-dimensional surfaces. | 0:37:07 | 0:37:12 | |
Well, here we have a sheet of paper, and it's two-dimensional. | 0:37:12 | 0:37:16 | |
So if I curve it, we can visualise and see this curvature. | 0:37:16 | 0:37:21 | |
But only because it's embedded in three dimensions. | 0:37:21 | 0:37:24 | |
Now, what if we curved three dimensions? | 0:37:24 | 0:37:27 | |
Presumably, we'd need a fourth dimension. | 0:37:27 | 0:37:30 | |
But how do you get to this four-dimensional space? | 0:37:31 | 0:37:36 | |
It's impossible to step outside of our three-dimensional world. | 0:37:36 | 0:37:41 | |
Wherever you travel in the universe, | 0:37:41 | 0:37:43 | |
no matter how far you go, you're always stuck in three dimensions. | 0:37:43 | 0:37:48 | |
The genius of Riemann was to show that you didn't | 0:37:48 | 0:37:52 | |
need to stand in a fourth dimension to tell if space was curved. | 0:37:52 | 0:37:57 | |
You could actually do it from the inside. | 0:37:57 | 0:38:01 | |
But for Riemann, this would always remain a purely mathematical idea. | 0:38:01 | 0:38:07 | |
It would take Albert Einstein to tie these mathematical ideas together, | 0:38:07 | 0:38:12 | |
and apply bendy, curved, non-Euclidian geometries | 0:38:12 | 0:38:17 | |
to the real space that surrounds us. | 0:38:17 | 0:38:21 | |
I think the most important point about the whole story | 0:38:21 | 0:38:24 | |
of non-Euclidian geometry is it shows | 0:38:24 | 0:38:26 | |
how mathematics and the real world relate. | 0:38:26 | 0:38:29 | |
And it starts out with mathematicians pottering around, asking, | 0:38:29 | 0:38:34 | |
"Could there be a geometry different from Euclid's?" | 0:38:34 | 0:38:37 | |
and if anyone said, "Why are you studying that?" | 0:38:37 | 0:38:40 | |
They'd say, "Haven't got a clue." "What's it useful for?" | 0:38:40 | 0:38:43 | |
"No idea. It's just interesting." | 0:38:43 | 0:38:45 | |
But they pottered around and they found a surprising answer - | 0:38:45 | 0:38:50 | |
that different geometries were possible. | 0:38:50 | 0:38:52 | |
And even at that point, nobody had any real applications for this idea. | 0:38:52 | 0:38:57 | |
And then when the moment is ripe, Einstein comes along and says, | 0:38:57 | 0:39:02 | |
"That's what I need, that's real physics." | 0:39:02 | 0:39:05 | |
And suddenly this piece of esoteric mathematics | 0:39:05 | 0:39:08 | |
becomes vital to the scientific enterprise. | 0:39:08 | 0:39:12 | |
Einstein would reveal that we live not in the flat world of Euclid, | 0:39:13 | 0:39:19 | |
but in the strange, curved worlds of Gauss and Riemann. | 0:39:19 | 0:39:24 | |
In the space of a few, short years, | 0:39:24 | 0:39:28 | |
Einstein went from wrestling with some of the most difficult | 0:39:28 | 0:39:31 | |
and abstract mathematical ideas to dinner dates with Charlie Chaplin. | 0:39:31 | 0:39:37 | |
And it was all thanks to the pinnacle of his life's work - | 0:39:37 | 0:39:41 | |
the general theory of relativity. | 0:39:41 | 0:39:45 | |
In the general theory of relativity, Einstein took the mathematics | 0:39:45 | 0:39:50 | |
of Gauss and Riemann | 0:39:50 | 0:39:51 | |
and used it to paint a revolutionary picture of the physical world. | 0:39:51 | 0:39:56 | |
He showed that just as Gauss had suspected, the geometry of the space | 0:39:56 | 0:40:01 | |
around us isn't always of the regular, flat, Euclidian kind. | 0:40:01 | 0:40:07 | |
'But if space is bent, and warped all around us, | 0:40:16 | 0:40:19 | |
'surely we must be able to observe that this is the case? | 0:40:19 | 0:40:24 | |
'Well, we do - just not in the way you might expect. | 0:40:24 | 0:40:28 | |
'This was Einstein's major insight. | 0:40:28 | 0:40:31 | |
'He showed that it was the ability for space to bend and warp, | 0:40:31 | 0:40:34 | |
'for it to be flexible, and change its geometry, | 0:40:34 | 0:40:37 | |
'that gives rise to the force we call gravity.' | 0:40:37 | 0:40:41 | |
Right. | 0:40:45 | 0:40:47 | |
Now, since Newton's time, | 0:40:47 | 0:40:49 | |
gravity was thought to be a force that pulls all objects together. | 0:40:49 | 0:40:53 | |
So if I drop this apple, | 0:40:53 | 0:40:55 | |
it's as though there's an invisible rubber band that's pulling it | 0:40:55 | 0:40:59 | |
down towards the earth. | 0:40:59 | 0:41:00 | |
But Einstein's general theory of relativity gives us a completely | 0:41:00 | 0:41:04 | |
different picture, and a totally new perspective. | 0:41:04 | 0:41:07 | |
So although gravity appears to be a force, | 0:41:09 | 0:41:13 | |
it's nothing more than the curvature of space itself. | 0:41:13 | 0:41:17 | |
When an object falls, it's not being pulled by gravity at all, | 0:41:17 | 0:41:21 | |
it's just following the simplest path through bent space. | 0:41:21 | 0:41:25 | |
But the equations of general relativity didn't end there. | 0:41:28 | 0:41:33 | |
They revealed that it was the presence of mass | 0:41:33 | 0:41:35 | |
that caused space to curve and distort. | 0:41:35 | 0:41:39 | |
The reason we have gravity on Earth is because the Earth is actually | 0:41:39 | 0:41:44 | |
bending the space around it. | 0:41:44 | 0:41:49 | |
In Einsteinian theory of the universe, | 0:41:49 | 0:41:53 | |
space becomes a dynamic entity that reacts to its contents. | 0:41:53 | 0:41:59 | |
Space knows about the presence of gravitating bodies, and responds | 0:41:59 | 0:42:04 | |
to the presence by changing its geometry in really interesting ways. | 0:42:04 | 0:42:10 | |
So what was in the 16th, 17th, 18th, 19th century, a very boring, | 0:42:10 | 0:42:15 | |
still object, suddenly in Einsteinian theory, | 0:42:15 | 0:42:18 | |
it becomes a dynamic, almost alive body. | 0:42:18 | 0:42:22 | |
Einstein's theory revealed that space itself, | 0:42:26 | 0:42:30 | |
the entire universe, everything, | 0:42:30 | 0:42:34 | |
wasn't just unimaginably large, it also had a shape, and structure. | 0:42:34 | 0:42:41 | |
It was malleable. | 0:42:43 | 0:42:45 | |
Everything could be bent and warped. | 0:42:45 | 0:42:49 | |
Gauss, Riemann and Einstein, had between them come up with | 0:43:00 | 0:43:04 | |
a description of how the space and time we exist in can be warped. | 0:43:04 | 0:43:10 | |
They showed that space and time are not the fixed, unchanging | 0:43:10 | 0:43:15 | |
stage on which the actions of the universe are played out. | 0:43:15 | 0:43:18 | |
They are actually part of the performance. | 0:43:18 | 0:43:22 | |
It was soon realised that because the general theory of relativity | 0:43:27 | 0:43:32 | |
applied to everything, it gave physicists a way of being | 0:43:32 | 0:43:36 | |
able to step outside the universe, and imagine how it might be behaving | 0:43:36 | 0:43:41 | |
in its entirety. | 0:43:41 | 0:43:44 | |
And when they did this, they saw something | 0:43:44 | 0:43:47 | |
that was extremely disturbing. | 0:43:47 | 0:43:49 | |
The equations were giving a description of the universe | 0:43:53 | 0:43:57 | |
that seemed ridiculous. | 0:43:57 | 0:44:00 | |
They were describing something that was actually expanding. | 0:44:00 | 0:44:04 | |
It seemed preposterous that the entire universe | 0:44:09 | 0:44:13 | |
could be some sort of moving, organic, expanding entity. | 0:44:13 | 0:44:18 | |
It was such a strange prediction | 0:44:20 | 0:44:23 | |
that even Einstein refused to believe it. | 0:44:23 | 0:44:26 | |
Einstein had overturned common sense notions of space and time held by | 0:44:33 | 0:44:38 | |
humans over thousands of years. | 0:44:38 | 0:44:41 | |
But he still couldn't accept | 0:44:41 | 0:44:43 | |
that the whole universe might be dynamic and changing. | 0:44:43 | 0:44:47 | |
In fact, he was so convinced that it was static, the he was prepared | 0:44:47 | 0:44:51 | |
to modify his original equations by adding an extra term | 0:44:51 | 0:44:56 | |
called the cosmological constant that would stabilise the universe. | 0:44:56 | 0:45:02 | |
But Einstein was trying to fix something that wasn't broken. | 0:45:02 | 0:45:05 | |
It's at this point that our story returns to Edwin Hubble. | 0:45:07 | 0:45:12 | |
Armed with the Hooker telescope, Hubble would reveal the truth that | 0:45:12 | 0:45:17 | |
Einstein had refused to believe. | 0:45:17 | 0:45:20 | |
After discovering that our galaxy was just one of many, Hubble began | 0:45:21 | 0:45:26 | |
to study the ways in which these other galaxies were moving. | 0:45:26 | 0:45:31 | |
Hubble knew that, as a light source approaches us, the light wave would | 0:45:36 | 0:45:41 | |
become compressed and appear blue. | 0:45:41 | 0:45:45 | |
If an object was receding, the light waves would become stretched out | 0:45:46 | 0:45:51 | |
and appear red. | 0:45:51 | 0:45:53 | |
What he saw was astounding. | 0:45:58 | 0:46:00 | |
All distant galaxies were being red shifted. | 0:46:00 | 0:46:04 | |
They were all moving away from us. | 0:46:04 | 0:46:07 | |
Not only that, but the further away a galaxy was, | 0:46:07 | 0:46:11 | |
the faster it was moving away. | 0:46:11 | 0:46:14 | |
Hubble's observations and Einstein's general theory of relativity | 0:46:20 | 0:46:25 | |
were in agreement. | 0:46:25 | 0:46:27 | |
But, and this is the crucial point here, it's not that the galaxies | 0:46:27 | 0:46:32 | |
are flying away from each other through space. | 0:46:32 | 0:46:36 | |
But rather that the fabric of space itself | 0:46:36 | 0:46:39 | |
in between the galaxies is expanding. | 0:46:39 | 0:46:43 | |
So the universe in its entirety is getting bigger. | 0:46:43 | 0:46:48 | |
This is what Hubble and Einstein's work revealed. | 0:46:48 | 0:46:52 | |
Einstein soon visited Hubble to see the data for himself. | 0:47:00 | 0:47:05 | |
He would go on to admit that changing his equations had been | 0:47:05 | 0:47:10 | |
his biggest scientific blunder. | 0:47:10 | 0:47:13 | |
So, why was space expanding in this way? | 0:47:13 | 0:47:17 | |
Both Hubble and Einstein soon came to agree. | 0:47:20 | 0:47:24 | |
If the fabric of space was expanding | 0:47:25 | 0:47:28 | |
it meant, previously, the universe was smaller. | 0:47:28 | 0:47:32 | |
Rewind the clock far enough back... | 0:47:34 | 0:47:37 | |
..and it appeared as if there was a point | 0:47:38 | 0:47:41 | |
when our entire universe began. | 0:47:41 | 0:47:46 | |
The data were pointing towards a moment of creation. | 0:48:00 | 0:48:04 | |
But many scientists were not convinced by this apparent Big Bang. | 0:48:13 | 0:48:18 | |
It seemed like a leap too far. | 0:48:18 | 0:48:22 | |
But there was one piece of evidence | 0:48:22 | 0:48:24 | |
that had the power to convince everyone. | 0:48:24 | 0:48:28 | |
It seemed that if the Big Bang had happened, then some time after | 0:48:36 | 0:48:41 | |
the instance of creation, | 0:48:41 | 0:48:42 | |
a flash of light should have been emitted throughout the universe. | 0:48:42 | 0:48:47 | |
Every part of the cosmos should now be filled with this light. | 0:48:47 | 0:48:52 | |
And it turned out it was. | 0:48:55 | 0:48:58 | |
It just happened to be in a rather unusual form. | 0:48:58 | 0:49:02 | |
As unlikely as it sounds, the relic of the Big Bang fireball | 0:49:04 | 0:49:09 | |
was actually visible on television. | 0:49:09 | 0:49:12 | |
Let me explain how this is possible. | 0:49:16 | 0:49:19 | |
Imagine this balloon is our universe. | 0:49:19 | 0:49:21 | |
Here it is just a few hundred thousand years old. | 0:49:24 | 0:49:27 | |
At this point, something very strange happens, | 0:49:27 | 0:49:30 | |
because the universe suddenly becomes transparent | 0:49:30 | 0:49:32 | |
to visible light as atoms form. | 0:49:32 | 0:49:35 | |
It's as though a fog has lifted and light is suddenly able | 0:49:35 | 0:49:40 | |
to travel freely through the universe. | 0:49:40 | 0:49:42 | |
At every point in space, photons began to travel | 0:49:47 | 0:49:52 | |
unimpeded and the entire universe is filled with a blinding light. | 0:49:52 | 0:49:58 | |
But this light, released in the hot turmoil of the early universe, | 0:49:58 | 0:50:02 | |
didn't stay bright for ever. | 0:50:02 | 0:50:05 | |
As space expanded, it stretched through the spectrum | 0:50:05 | 0:50:09 | |
from visible light down into microwaves. | 0:50:09 | 0:50:13 | |
And it's these microwaves that get picked up by television aerials. | 0:50:17 | 0:50:22 | |
Incredibly, | 0:50:22 | 0:50:24 | |
almost one per cent of this static is the afterglow of creation itself. | 0:50:24 | 0:50:29 | |
It's the stretched out remnants | 0:50:29 | 0:50:32 | |
of the very earliest light in the universe. | 0:50:32 | 0:50:35 | |
Today, with satellites, it's become possible to make an incredibly | 0:50:43 | 0:50:48 | |
precise map of the universe at the moment it became light. | 0:50:48 | 0:50:54 | |
This is the fossilised light of the first dawn. | 0:51:00 | 0:51:05 | |
Convincing evidence that the universe had a beginning. | 0:51:08 | 0:51:12 | |
Using the microwave radiation, cosmologists could even date it. | 0:51:16 | 0:51:22 | |
Our entire universe is 13.7 billion years old. | 0:51:22 | 0:51:28 | |
This beginning of everything would be the final piece of information | 0:51:32 | 0:51:36 | |
needed to answer the question Thomas Digges had first posed | 0:51:36 | 0:51:41 | |
over 400 years ago. | 0:51:41 | 0:51:44 | |
It would finally give us a satisfactory explanation | 0:51:44 | 0:51:48 | |
for why it gets dark at night. | 0:51:48 | 0:51:51 | |
OK, so here it is, here's where I hope this all makes sense. | 0:51:53 | 0:51:58 | |
The further away a star is, the longer it would take | 0:51:58 | 0:52:02 | |
for its light to reach the Earth. | 0:52:02 | 0:52:05 | |
So, if the universe has been around forever, | 0:52:05 | 0:52:08 | |
then all the light that's out there will have had time to reach us | 0:52:08 | 0:52:13 | |
and the night sky would be ablaze with starlight. But it's not. | 0:52:13 | 0:52:18 | |
And here's why. | 0:52:20 | 0:52:23 | |
Imagine when the universe was much younger | 0:52:23 | 0:52:25 | |
and smaller than it is today. | 0:52:25 | 0:52:29 | |
A beam of light on the other side of the universe begins a journey | 0:52:29 | 0:52:33 | |
towards our vantage point. | 0:52:33 | 0:52:36 | |
But, as space expands, | 0:52:36 | 0:52:39 | |
the distance the light has to cross keeps getting bigger and bigger. | 0:52:39 | 0:52:46 | |
Fast forward to today, and this light still hasn't reached us. | 0:52:46 | 0:52:51 | |
So, no matter how hard we look into the sky, | 0:52:51 | 0:52:54 | |
we simply won't be able to see it. | 0:52:54 | 0:52:58 | |
We can only see the stars whose light has had time to reach us | 0:52:58 | 0:53:02 | |
in the 13.7 billion years since the Big Bang. | 0:53:02 | 0:53:07 | |
This region is known as the observable universe. | 0:53:07 | 0:53:11 | |
And there are not enough stars here to light up the night sky. | 0:53:11 | 0:53:17 | |
So, we only ever see the stars and galaxies whose light | 0:53:17 | 0:53:22 | |
has had a chance to reach us, and that's why it gets dark at night. | 0:53:22 | 0:53:29 | |
The simplest fact that we take for granted, | 0:53:40 | 0:53:43 | |
that the sky at night is dark, | 0:53:43 | 0:53:45 | |
is in fact incredibly profound. | 0:53:45 | 0:53:48 | |
It took 200 years of theorising, of thinking, it took the development | 0:53:48 | 0:53:54 | |
of general relativity, before we could understand | 0:53:54 | 0:53:57 | |
why the sky at night is dark. | 0:53:57 | 0:54:00 | |
By reasoning and observing and imagining, we've found | 0:54:11 | 0:54:16 | |
ever better ways to project outside of the confines of our small rock | 0:54:16 | 0:54:22 | |
tumbling through space. | 0:54:22 | 0:54:24 | |
We've become ever more skilled at creating pictures | 0:54:24 | 0:54:30 | |
of everything. | 0:54:30 | 0:54:31 | |
This is a computer simulation of the universe in its infancy. | 0:54:37 | 0:54:42 | |
Using it, we can see how the force of gravity has shaped the universe | 0:54:42 | 0:54:47 | |
over billions of years. | 0:54:47 | 0:54:50 | |
The brightest white and yellow regions in this image | 0:54:50 | 0:54:53 | |
show where galaxies and clusters of galaxies form. | 0:54:53 | 0:54:58 | |
You can see how, as the universe evolves, | 0:54:58 | 0:55:01 | |
a strange and hidden structure begins to emerge. | 0:55:01 | 0:55:06 | |
This is the cosmic web. | 0:55:13 | 0:55:16 | |
It's our best picture yet of what everything might look like | 0:55:16 | 0:55:20 | |
at the largest scales. | 0:55:20 | 0:55:23 | |
It shows massive clusters of galaxies linked together | 0:55:26 | 0:55:31 | |
in vast filaments, each one containing trillions of stars. | 0:55:31 | 0:55:37 | |
Its scale is sometimes difficult to appreciate. | 0:55:44 | 0:55:48 | |
But it would take light almost 10 billion years | 0:55:48 | 0:55:52 | |
to cross the distance in this image. | 0:55:52 | 0:55:56 | |
But this incredible picture of everything is destined to change. | 0:56:05 | 0:56:11 | |
We are starting to understand that, in the distant future, the universe | 0:56:11 | 0:56:15 | |
will become a terrifyingly bleak and desolate place. | 0:56:15 | 0:56:20 | |
In 1998, a team of astronomers published a paper | 0:56:23 | 0:56:27 | |
in which they looked at supernova explosions in distant galaxies. | 0:56:27 | 0:56:31 | |
They were hoping to measure very accurately | 0:56:31 | 0:56:34 | |
how fast the universe was expanding. | 0:56:34 | 0:56:37 | |
Now, they expected to find that the rate of expansion was slowing down, | 0:56:37 | 0:56:41 | |
just because of the pull of gravity of all the matter in the universe. | 0:56:41 | 0:56:46 | |
But they were in for a big surprise. | 0:56:46 | 0:56:49 | |
The universe was getting bigger, faster. | 0:56:49 | 0:56:53 | |
The rate of expansion was accelerating. | 0:56:56 | 0:57:00 | |
There seemed to be some mysterious force pushing everything apart. | 0:57:00 | 0:57:05 | |
We still don't understand its origin, | 0:57:05 | 0:57:08 | |
but it's been dubbed dark energy. | 0:57:08 | 0:57:11 | |
There's one fascinating yet disturbing consequence of this. | 0:57:17 | 0:57:22 | |
If the expansion of the universe continues to accelerate | 0:57:22 | 0:57:27 | |
then our visible universe will begin to empty. | 0:57:27 | 0:57:32 | |
Let me explain. Imagine that I'm in a distant | 0:57:32 | 0:57:35 | |
galaxy that you can see from Earth. | 0:57:35 | 0:57:37 | |
As the space between us stretches, there will come a time in the future | 0:57:37 | 0:57:43 | |
when it is expanding so rapidly that light can't outrun it, | 0:57:43 | 0:57:48 | |
and the galaxy will disappear from view. | 0:57:48 | 0:57:52 | |
What this means | 0:57:54 | 0:57:56 | |
is that, far into the future, some 100 billion years from now, | 0:57:56 | 0:58:02 | |
if intelligent life forms still exist in our galaxy, | 0:58:02 | 0:58:06 | |
they'll look out into space and see only the stars in our own Milky Way. | 0:58:06 | 0:58:12 | |
All the other galaxies will have disappeared. | 0:58:12 | 0:58:16 | |
And they will be alone in a vast, dark, empty expanse. | 0:58:16 | 0:58:23 | |
I have here a box. What would happen if I were to remove everything | 0:58:32 | 0:58:37 | |
I possibly could from inside it? | 0:58:37 | 0:58:39 | |
What then exists inside the space in the box? | 0:58:39 | 0:58:44 | |
Is it really nothing? | 0:58:44 | 0:58:46 | |
Subtitles by Red Bee Media Ltd | 0:58:59 | 0:59:01 | |
E-mail [email protected] | 0:59:01 | 0:59:03 |