How the Universe Works

What is our universe made of?

It's the biggest unanswered question in science.

Despite the name, space is not an empty space at all.

Space itself is something.

There's a hidden structure and a force that exists within space itself.

Spacetime is something absolutely real.

It's absolutely fundamental.

It's really part of the fundamental architecture.

A force that connects everything in our universe.

It's an active player in the game of life.

It underpins our reality, tying together all of space and time since the very beginning.

We call it space time.

It's everything.

Spacetime is what the universe really is.

Spacetime is how our universe works.

But what exactly is it?

And how does it control our past, present, and future?

We can't see it.

We can't touch it.

But without space time, we wouldn't be here.

Spacetime is the fabric of our reality.

It shapes and governs our lives.

If we want to understand the story of the universe, it's absolutely crucial we understand how space time behaves.

Spacetime has been active since the beginning of everything and is the key to the evolution of everything.

We have to understand space time in order to understand the history of the universe,

to understand how the universe began, how it evolved, and what's going to happen in the future.

The story of space time is the story of our universe.

To know how the universe, to know how the story evolves and how it will end,

we need to go back to the very beginning, to a time when there was nothing,

no stars, no space, a time before there was time, then all of a sudden…

Our entire universe was born in the Big Bang.

It started in an instantaneous moment where from nothing our universe was created.

The very definition of the moment of the Big Bang is that space and time were created at that instant.

It is, as far as we currently know, the coming into existence of space and time itself.

The infant universe, a tiny speck of energy and space time materialized from nowhere.

Then, the universe suddenly expanded.

The idea of inflation is that a very tiny

time, far shorter than a second, grew by many, many, many orders of magnitude.

So imagine myself suddenly becoming the size of a galaxy.

In a fraction of a second, the universe grew from smaller than the size of an atom to the size of a cricket ball.

In cosmic terms, it's similar to a grain of sand growing almost to the size of the observable universe.

The universe at the instant of inflation actually expanded faster than the speed of light.

It seems to be a violation of everything you've heard in physics.

You may be thinking, hey, hey, hey, Mr. Astronomy Guy.

Nothing can move faster than the speed of light.

And it turns out that's kind of true.

But the rule is, nothing can move through the Universe faster than the speed of light.

In inflation, it's space itself that is expanding.

So there is no violation.

There is no paradox.

Inflating fast, the Universe went through a phenomenal growth spurt.

At the moment of the Big Bang, space time was this entity that was flying out in all directions.

It was space itself that was expanding.

However, the Universe didn't expand evenly.

One spot in the Universe was ever so slightly more dense than a spot right next to it.

And we're talking about a tiny, tiny fraction of a percent.

One part in a hundred thousand.

But that was enough.

Fluctuations in expanding space time created areas with higher density.

Inflation made these high density regions larger.

Which enabled our Universe to take shape.

When parts of the Universe didn't inflate quite the same way as others, all of a

sudden things could start to come together.

As the Universe cooled, energy turned into matter.

In the denser regions that matter started to clump together and crucially,

these regions had more mass than others.

Mass bends space time.

So anything that is made of matter bends space time.

And the more matter you have in one place, the more you bend it.

In fact, I'm bending space time right now.

When I flex, I bend it even more because of my incredibly high bustle density.

I don't bend at the maximum.

I don't want to destroy the Earth and the solar system.

But, you know, it's an effect.

It's a real thing.

Space isn't constant.

It's not something that is always the same everywhere.

It actually bends constantly.

It curves.

It warps depending on the matter inside of it.

We'd see the curving grid of space time moving and reacting to objects within it.

And we'd feel the curving of space time as the force we call gravity.

Gravity is different from all the other forces.

It is intimately connected with the curvature of space time.

Something that can bend space and time has gravity.

That's what gravity is, the bending of space and time itself.

It's hard to visualize this, but a good analogy is a trapeze artist and their safety net.

You can imagine a trapeze artist falling into a net on purpose.

That net is flat and looks like a nice, orderly, evenly spaced grid.

But when they fall into it, they distort that grid.

Well, that's a lot like space.

If you have matter in space, it warps the framework.

When the trapeze artist is resting in the net, they're bending that space time grid a little bit.

If you had two trapeze artists in there, double the mass in roughly the same volume, you would get a bigger dip.

You have a bigger distortion.

And that's how space time works.

More mass equals a bigger curve in space time, which equals more gravity.

But understanding the nature of gravity and space time is no easy thing.

It's an idea developed by one of the greatest minds ever.

Einstein had the idea that space itself is something, something that can be bent,

something that can be stretched, that we are all bound together by space time.

Einstein says that space and time have a geometry.

They have a life of their own.

They have dynamics.

These dynamics are what we call gravity.

The more dense the region of matter, the greater the gravity, the deeper the curve.

This connection is the foundation of our physical reality.

It's the interaction between matter and energy and space time that created the Universe that we see around us today.

However, that doesn't mean we fully understand it.

There's much more that we don't know, and that's frustrating.

With the laws of physics I can talk about how space time behaves, but it does appear

to be something that stretches, that contracts, and that gravity is the embodiment of space time.

Born in the Big Bang, space, time and energy combine to create our infant Universe.

These basic materials were the foundations.

But how did we get to the incredible complex structures we see today?

How did space time build our majestic Universe?

Our entire Universe was created in the Big Bang 13.8 billion years ago.

Everything came from nothing.

Yet the modern Universe is a complex mosaic of matter.

When we marvel through our telescopes and the fantastic structure of our Universe

and its galaxies, you gotta ask, where did that come from?

Matter in the Universe arranges itself on a vast cosmic web.

Galaxies and galaxies' clusters are strung out on sheets and filaments.

It seems this intricate web is organized by a cosmic architect.

Spacetime.

It shaped everything from planets to galaxies, atoms to cities.

The Universe is made of space time.

It's everything.

Spacetime is what the Universe really is.

It's a hard concept to grasp, and even harder to visualize.

Scientists observe the Universe in different wavelengths of light.

This is the Sun, invisible light, X-ray, and ultraviolet.

Now, imagine if we could see it in the space time spectrum.

We would see space time distorting as objects move through it.

Spacetime can warp and push things around, it can expand and pull things apart.

But it's the shape of space time that dictates how we experience it.

Imagine you're in your car.

You go up hills and you go down hills.

So the shape of Earth's surface determines how you travel across Earth's surface.

In the same way, the geometry of space time determines how light and matter move through space time.

The rules are simple.

Any object with mass tells space time how to curve.

The curvature of space time tells matter how to move.

Because the shape of space time tells matter how to move, we call gravity,

this means that gravity and the shape of space time tells matter how to clump together and form larger structures.

But at the beginning, the space time landscape was very different to today's.

So the very first matter started to change the shape of space time.

So this space right here has a tiny bit more matter in it than this over here.

Wherever there was a little bit of extra mass, that would bend space a little bit more.

Well, if you're bending space a little bit more, then more mass would collect there.

In the early Universe, these denser regions of matter created deeper curves in space time.

And as the mass gets bigger, as stuff falls into that well,

it gets deeper and deeper and deeper and attracts more stuff.

And it's just a runaway process.

Gravity increased, pulling in more and more matter.

Got more dens, got more dens, got more dens.

And then before you know it, you've got a star.

And you've got a bunch of stars.

And you start to make a galaxy.

And these stars evolved and began forming large structures.

They sort of burned through all their nuclear fuel and exploded.

And they made all the heavier elements.

And with time, we got down to having things like planets, atmospheres,

people, all the things that we care about today.

All of this started out as energy fluctuations in expanding space time.

These at first very tiny fluctuations became these gigantic structures that we actually see today.

And over billions of years, that material began to coalesce into individual galaxies, stars, planets.

And you.

Fluctuations in the expansion of space time laid out the pattern of the Universe.

The curvature of space time controlled the evolution of everything we see today.

If space time didn't have that property of bringing mass together, then all we would be is a thin haze of hydrogen gas.

Not a very interesting universe at all.

If space time didn't curve because of matter inside of it, the universe would be a really weird place.

I mean, there'd be no gravity.

There'd be nothing to make things stick together.

No force of gravity means no stars, no planets, and no people.

We owe our existence to space time.

But even scientists struggle to understand it.

I wish I knew what space time is.

We know things about space time.

But at the same time, we feel like we know almost nothing about space time.

But sometimes, scientists get a glimpse of this elusive puppet master in action.

In 2016, astronomers witnessed a strange optical phenomenon.

A weird circle of light, similar to a cosmic halo.

This is actually what you would see in the sky if your eyes were as sensitive as a telescope.

They're real.

This is not some artifact of how we adjust the images.

Something is actually bending space and time itself into a lens.

That something is a red galaxy, which is over 7 billion light years away from Earth.

It's bending the light from a blue galaxy, which should be hidden behind it.

It's called gravitational lensing.

Gravitational lenses are caused by objects with huge masses, say clusters of

galaxies, that distort space and time so much that when light comes from farther

objects and has to pass around the galaxy clusters, the light bends.

It really is a true warp in space time.

Mass from the foreground galaxy creates curves in space time, which we know as gravity.

Light follows those curves and is warped.

So it bends around the galaxy.

Massive objects like clusters of galaxies can bend the path of light through space time.

A lot like a piece of glass can bend the path of light.