13.8 billion years ago, something incredible occurred.
The Big Bang, the moment when space and time were born. The beginning of
the ever-expanding existence that we call the universe.
Everything we can touch, feel, sense, measure or detect is the universe, from the tiniest particles
to the largest galaxies, to the very existence of space, time, energy and life.
The beginning of the universe is the beginning of everything.
In a way, we are a small part of the universe attempting to understand itself
as we peer out into the unknown and observe the wonders that it has to offer.
We have been able to discover extraordinary things from Earth,
but now, we must leave our blue planet and explore the farthest reaches of the cosmos.
Our journey begins at home, the Earth,
a world unlike any other, the only place in the known universe confirmed to host
life. Millions upon millions of different species exist upon its dynamic surface,
but none have changed its landscape like human beings.
From this view, human activity is easy to see. Our buildings, roads,
and farming fields will likely be evidence of our existence for hundreds, if not thousands of years
to come. But as we drift ever higher, everything that we are, everything that we have created,
begins to blur. From up here, it would be difficult to see that we ever existed at all.
Our entire history can be traced back to this single blue marble. It is the place
where billions of people have lived and died and where many more billions will be born.
This is the world where it all started for us, the cradle of humanity.
But now we must leave all of this behind
and travel further than any human being has ever travelled before.
First, we will pass the moon, our closest
neighbour and the only other place we have walked apart from Earth.
Then we will cross the orbits of the planets
as we head towards the emptiness that is interstellar space, the area in between the stars.
Our magnificent star that warms our seas, stirs our atmosphere and gives energy to the growing
green plants that provide oxygen for life on Earth slowly becomes just one of billions.
Many of the stars so familiar to us in our night's sky can now be seen,
unaffected by the Earth's atmosphere, like colourful bright
pinpricks upon a black canvas. This is just a tiny corner of the Milky Way Galaxy.
Some of these stars have their own planets orbiting them,
known as exoplanets, some of which may have the right conditions for life
as we know it. But there is no time for us to stop and explore these alien worlds,
because we still have a long way to go, and the Milky Way is unimaginably vast.
Enormous clouds of gas and dust, along with hundreds of billions of stars, planets and moons,
span an area 100,000 light-years across, and hiding deep within that bright bulge,
at the very core of the galaxy is a monster, a supermassive black hole.
Now we can see the sheer scale of the galaxy that we call home,
and although it is unimaginably large to us, it is only a droplet
within an ocean of galaxies that exist throughout the observable universe.
Each of these bright points is another galaxy sprawling with clouds of gas
and dust and billions of stars and planets.
Like the Milky Way, which is now just a faint dot in the distance,
most of these galaxies conceal a supermassive black hole at their centre,
and some of them are even merging together in a dynamic cosmic dance of interacting gravity.
From this spectacular view, you will notice that the cosmos is not evenly populated
Instead, large empty voids can be seen in between dense clusters that are strung
together in a magnificent cosmic web. This is a small part of the observable universe,
a single page from a 13.8 billion-year-old story spread out in front of our eyes.
But where do we go from here? Will we find an edge to the universe? In order to answer that,
we must travel billions of light-years back to where our journey began.
The reason we have come home is because as far as astronomers can tell, there is no edge to the
universe. There is only an edge to the observable universe, which is everything we can see from
Earth, an unimaginably large area spanning 93 billion lights years of ever-expanding space.
What we have just explored can be seen using powerful telescopes from Earth because we are able
to see the light from those objects. But light has a cosmic speed limit, and so beyond the edge
of the observable universe is the place where light hasn't had enough time to reach us yet.
When a distant galaxy millions of light-years away is observed,
you are seeing it as it was millions of years ago, not as it is today.
So the farther away you look, the farther back in time you are able to see until eventually,
you find the earliest light that occurred just a few hundred thousand years after the Big Bang.
Although not a physical edge, this is the edge of our observable universe.
It is the afterglow of the Big Bang called the cosmic
microwave background. It is the farthest point in the cosmos we are able to see from Earth.
But what we don't know is how much of the entire universe is our
observable universe. It could be just a tiny speck of a much larger area.
You can imagine it like a spotlight centred on wherever you are standing
right now. You can see to the edge of your spotlight but not beyond.
It is impossible to know what is outside of our cosmic spotlight.
However, scientists assume that it is the same as what we can already see, running under the same
laws of physics and is dominated by trillions of other stars, galaxies and clusters. The
unobservable universe may continue infinitely in all directions for all we know. There are
many different theories. But the truth is, it is a mystery that we still are yet to solve.
I hope you enjoyed your journey to the edge of the observable universe. If you did, then please tap
the like button and consider subscribing if you haven't already, there are plenty more incredible
space adventures for us to go on. Thank you so much for watching, and I'll see you all next time.