Beyond the Observable Universe
Do we exist in a MultiVerse?
Horizon - How BIG is the Universe?
The Universe
The entire observable universe is saturated in dark energy. But there is one final set of clues to be found on its furthest edge. And it may
contain the secrets to the universe beyond.
We're heading off the map into impossible territory. The edge of the observable universe is the farthest horizon our telescopes can see. But
for cosmologists like Sean Carroll, that's not enough. He wants to know the size of the whole universe.
Dr Sean Carroll "I definitely think it's okay to think about parts of the universe that we can't observe and can never observe. We've done a
very good job at understanding what the universe looks like in that visible portion. So now when our imaginations roam, we often sneak outside
the visible portion to ask what might the universe look like beyond our visible horizon. The universe that we can't see that's a playground
for theorists now."
But, if we can't see the rest of universe, how can we figure out how big it is? For Janna Levin, its a similar task to working out the shape
and size of the Earth. But there's a catch.
Janna Levin "We know if we could step far from the Earth, as an astronaut has. We can look down on it and see from the outside that it was
a sphere and it was curved. You can't step outside of universe. You have to do everything from inside of space."
Spherical Earth
Janna Levin
Without leaving the Earth, how do you know it's round, and therefore has finite size? It could be completely flat, and stretched to infinity in all
directions. One way is to use a simple piece of mathematics. All you have to do is draw a triangle.
Janna Levin "If you're drawing a small enough triangle on the beach, you won't notice the curvature of the Earth. It will look like a normal
triangle, you'll be able to draw the lines pretty straight and the interior angles will look like they add up to 180°, it will look
like the triangle you draw on a flat sheet of paper."
Beach Triangle
But this isn't a normal triangle, because the Earth's surface is curved. It's just so subtle, that the sides of the triangle still look straight.
Janna Levin "It would probably be a challenge on the beach to draw it big enough so that you would be able to notice the curvature of the Earth."
The key is to make the curvature more obvious by drawing the biggest triangle you can.
Globe Triangle
Janna Levin "If I draw a triangle big enough that it comes from the North Pole and wraps all the way around North America, now it's very obvious
that those angles are bigger than 180° and that the sides of the Triangle are not straight lines."
So, we can show the Earth is curved and therefore has finite size without leaving it. And we can find out the shape and size of the universe
in exactly the same way by looking for triangles of light.
Janna Levin "Light will travel in a straight line if the space is flat, and light itself will travel in an arc if space is curved. These
curves are going to be so subtle, more subtle than the curvature of the Earth. We really have to look back as far as we possibly can. And
that means the oldest relic we have in the universe. So that means looking at things like the light left over from the Big Bang."
The early universe was a hot, dense fireball. When it cooled, a pattern of light emerged at what is now the edge of the observable universe.
This is the Cosmic Microwave Background ir CMB. The CMB was discovered in the 1960s. But throughout his career, Dr Sean Carroll has been able
to explore it in greater and greater detail waiting for triangles to emerge.
Dr Sean Carroll
Sean Carroll "It takes good technology, you need better and better receivers, less and less noise in your detector, and ultimately you need
satellites to get a really good 360° view of the whole cosmic microwave background."
It was NASA's WMAP mission in 2003 that brought the most vital contours into sharp focus.
Sean Carroll "WMAP for the first time had that resolution so when WMAP came out, we could really use those features to make a big triangle
and to measure the geometry of space. Continents begin to appear, smaller islands, you get the finer resolution of the coastlines and so forth."
The islands are miniscule temperature variations in the early universe less than 100,000th of a degree
A distinctive feature for making triangles.
Sean Carroll "These splotches we see in the microwave background appear at all different sizes but there is a best size for them to be,
there is a size at which the fluctuations are the strongest. We know how big they are, we know how far away they are, so between us and
the size of a feature in the CMB, we can measure a triangle and use that to infer the geometry of space."
Sean's Triangles
The Earth, plus the opposite sides of island, form the three points of the very long, thin triangle key to measuring whether the
universe is flat or curved.
Sean Carroll "If the universe were positively curved, if the angles inside the triangle added up to greater than 180°, then it would be finite
in size. If the spatial geometry is flat, if the angles inside the triangle add up to 180, then it could go on for ever."
The result is one of the greatest triumphs of modern cosmology. A miracle of precision map making that measures the angles of the triangle to
the third decimal place. And it says that the universe is infinite.
Sean Carroll "The answer is that Euclid was right, space seems to us to be FLAT as far as we can measure it."
Prof. Saul Perlmutter
Saul Perlmutter "That means that the simplest picture of the universe, is a universe that is infinite. We really could live in a universe
where, there's Galaxy after a galaxy after Galaxy, every direction. Up, down, sideways. And, it never stops."
Cosmologists have found a way to picture the universe in its entirety confirmation of the tremendous power of making maps.
Sean Carroll "It will never cease to amaze me, we human beings here on this tiny little rock are able to reach out with our instruments and
our brains to understand the whole shebang."
And if an infinite universe isn't big enough for you then Saul Perlmutter has proved it's still growing.
Saul Perlmutter "All the distances are getting bigger, every day. So, its still infinite, all the same galaxies are there, its just that
we have pumped more space between every point in this infinite universe. That's really is mind-boggling."
But even this isn't the end of the story.
