The big question for this segment is, how did our universe get more

complex as a result of the first three thresholds of increasing complexity?

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Okay.

Now we're ready to go back to the beginning and

start telling the story of big history.

What I'm going to do in this lecture is to tell the story of the first

three thresholds of increasing complexity.

But I'm going to tell that story in a very simple way.

The first three thresholds of increasing complexity are.

One, the appearance of the universe itself almost 14 billion years ago

in the big bang.

Two, the appearance of the first stars,

beginning perhaps 200 million years after the big bang.

Three, the creation of new chemical elements inside dying stars.

A process that began a as soon as the first stars died and

continues to the present day.

As you study these first three thresholds of increasing complexity, look for

how woven through them all are the core concepts

of increasing complexity, new energy flows,

the Goldilocks conditions that made them possible, and new emergent properties.

The new qualities that make these thresholds different.

Okay, let's review the first three thresholds.

Threshold one is the creation of the universe.

This is a fantastic question.

How did everything come to be?

It's the biggest question we can ask.

What was there, before the big bang?

Well the truth is we don't know.

Now cosmologists love to guess of course, but

the truth is that right now we really don't know the answer to that question.

It could be that there was absolutely nothing, zilch, not even time or space.

Or it's possible that there was what cosmologists call a multiverse.

A vast, kind of, multidimensional space, out of which new universes kept appearing.

Each beginning with its own private big bang.

So what happened at the beginning of our universe?

But here's a very, very simple account of what happened.

According to big bang theory, something appeared.

We don't know what it appeared out of.

That thing was tinier than an atom.

It was staggeringly hot.

We're talking trillions of degrees here.

And it was expanding incredibly fast.

And it contained everything that's in today's universe.

A lot happened in the first second.

The rate of expansion slowed.

Different forms of energy appeared out of this chaos.

They include gravity, the force that pulls everything together.

Electromagnetism.

And the strong and weak force.

Those hold atomic nuclei together, and they won't play a huge role in our story.

Matter also appeared in several forms, including dark matter,

which we don't really understand.

And atomic matter made of quarks and electrons, and

we are made out of atomic matter.

The first important date after the big bang comes about 400,000 years later,

that's almost half a million years later.

The universe has been expanding and cooling, and

it's now cool enough for electrons, which have negative charges,

to hitch up with protons that have positive charges.

And, they form atoms, which are electrically neutral.

That, before that, photons of light couldn't travel freely

through the universe because they kept getting tangled up in charged particles.

But now they can move freely.

So this is a vast release of energy.

It's known to astronomers as the cosmic background radiation, the CBR.

Or sometimes the cosmic microwave background, the CMB.

Now, how do we know all of this?

After all, it's a very, very strange story, and

it's a very strange claim to make that you know what happened 14 billion years ago.

Well there are several very powerful forms of evidence.

Perhaps the most powerful of all was the discovery in the 1920s by Edwin Hubble.

And you're gonna learn a lot about this later in the course.

That the universe seemed to be expanding.

No one expected that.

But that seemed to mean that at some point in the past,

it must have been infinitely small.

But most astronomers remained skeptical for several decades, and

many continue to argue that the universe was basically as Newton had argued.

Infinite and unchanging.

What clinched the theory of the big bang, for most scientists,

was the discovery in the 1960's of cosmic background radiation.

This was energy coming from everywhere on the universe.

Now, that was strange.

It was not just coming from galaxies or stars.

It was even coming from dark areas of the universe.

The big band theory predicted something like this, as we've seen.

It predicted that when atoms first formed, there'd be this huge release of energy.

And that's what scientist picked up in the 1960's.

The rival steady state theory could not explain this energy.

So that's when the big band cosmology story became the standard story of

the origins of the universe, and accepted by most astronomers and cosmologists.

So let's review what's happened as we've crossed this

first threshold of increasing complexity.

In the new universe, there are huge energy flows.

We don't know where they came from.

What were the Goldilocks conditions that created this universe?

We don't know.

We really don't know this.

It's possible that in the next 10 or 20 years we'll figure this out, but

at the moment we don't know.

And what emerged?

Well, what emerged was a universe, an entire universe.

And the rest of this course is gonna tell you the history of that universe.

The early universe, in the first few million years after the big bang,

was very, very simple.

There were hydrogen and helium atoms.

There were tiny differences in temperature,

differences of just a tiny fraction of a degree.

The distribution of atoms was very, very smooth so

the universe was very homogenous.

There was energy, there was dark matter, and there was dark energy.

That was it.

No stars, no planets, no living organisms.

With such a simple universe, how can you make more complex things?

This is actually a huge problem.

The Second Law of Thermodynamics, as we've seen,

says that though the total amount of energy in the universe stays the same,

it changes its form so it can do less and less work over time.

But it takes work to make complex things or to create complex structures.

So you might think that the universe ought to be getting simpler and

simpler, rather than more complex.

Here's one possible solution, and it involves gravity.

Gravity seems to have been the first driver of increasing complexity.

Now, the thing about gravity is that it likes to clump things together.

It likes to pull things together.

And the early universe we've seen was distributed very evenly.

So it's as if gravity needed to take everything in the universe and

rearrange it and make it clumpier.

So think of this early universe, think of all these huge clouds of hydrogen and

helium atoms.

Gravity got to work on them and

it starts to clumping them together where they are slightly denser.

It makes them even denser.

And as they get denser, gravity gets more, and more powerful.

So it compresses these clouds, and as the clouds get denser, they got hotter,

while the rest of the universe was cooling.

So suddenly we have a mechanism that's heating up parts of the universe.

Now eventually these clouds, and you should think of billions and billions of

them, got so hot that at the center, atoms started breaking apart once more,

and then protons began to fuse together to form helium nuclei.

Now this is exactly what happens in an H-bomb.

When you do that you release huge amounts of energy and

it's that energy that created the first stars.

Because at the center of each of these clouds you now have a sort of furnace

that's pushing back against gravity and the balance between gravity and

fusion is what forms a star.

So we can think of stars as the products of these two opposite forces.

Fusion at the center pushing back against gravity,

which is trying to smush the star together.

And once they get in balance, the star can exist for billions of years.

So now, there are billions of stars.

And the universe as a whole is more complex and more varied.

It's no longer homogenous.

We have now huge differences in density.

Stars are very, very dense indeed.

In temperature.

Stars are very hot.

And also in gravitational energy.

The gravitational forces around stars are very powerful indeed.

Let's review where we are after threshold two.

Stars, we've seen, represent a new level of complexity.

They also generate new energy flows by fusion at the heart of stars.

So with stars we have new flows of energy through the universe and

those flows of energies are gonna power life on our planet.

What were the Goldilocks conditions for forming stars?

Well that seems to be fairly clear.

First is the existence of gravity.

That is to say a force that can't wait to clump everything together.

Doesn't like a homogenous universe.

So there were tiny unevenesses in the early universe and

gravity seized on those to clump matter together to eventually form stars.

And, finally, what emerged that's new?

Well it's very clear what emerged.

Stars emerged and galaxies.

We have new differences in gravity and energy and density.

We have new structures.

Stars have structures.

They have fusion at their center.

They have stores of material outside.

And they form gravity.

And they form galaxies and galaxies, too, have structure.

As you can see, if you ever look at some of the most beautiful astronomical

photographs that we have available today.

Once stars formed,

the universe still consisted mostly of hydrogen and helium atoms.

Other elements formed inside dying large stars.

Here's how it worked, if a star had lived for

long enough,eventually it's burnt out.

It's fused all the protons in it's center to create helium nuclei.

Now at that point the furnace at the center stops working.

The center collapses, gravity takes over.

It crushes the star very, very fast.

And as it does so, it creates extreme temperatures at the center.

Much higher than the temperatures that had existed before that.

Now, the temperatures are so high at the center that helium nuclei can start

fusing to form other elements, such as carbon, and nitrogen, and oxygen.

If the star is big enough,

this process can be repeated until the center of the star fills up with iron.

It collapses, it expands, it collapses

building new elements up to iron which is element 26 on the Periodic Table.

Then if the star is really huge, it will blow apart in a supernova,

a vast explosion, creating temperatures so

hot that they forge all the other elements in the periodic table.

So, once a few large stars have died and super novae, now we have a universe

with more than 90 elements, instead of just the two in the early universe.

And those elements can combine to form a colossal diversity

of different types of materials.

So, where are we after threshold three?

Well, the universe is clearly more complex and now it's more complex chemically.

That is to say we now have over 90 different chemical elements.

And it's not just that there's a lot more elements.

Those are the ones can all combine in new ways to form a vast range of new material.

What about the energy flows.

Well, the energy flows that created chemical complexity,

all occurred inside dying stars.

But chemical complexity also generates new forms of energy.

We can call it chemical energy.

The energy that's locked up and

then released, as atoms and molecules combine and break apart.

And that energy is gonna be crucial for the existence of life on earth.

What were the Goldilocks conditions for the formation of new elements?

Well, that's fairly simple.

It was the colossal temperatures generated inside dying, large stars.

Now it was important that there were large, because the larger the stars,

the more powerful gravity is.

And that could generate larger temperatures, higher temperatures.

And of course super novae generated the highest temperatures of all.

Those were the Goldilocks conditions.

And finally, what emerged?

Well, what emerged was a universe that was chemically

more complex in which you now have diverse form of matter

with which you can make a whole range of complex new things.

And that will lead us to our next thresholds of increasing complexity.

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BIG HISTORY FRAMEWORK: David Christian - How did our Universe get more complex?

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