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Crash Course: Stars & Galaxies
Crash Course: Stars & Galaxies
The guys at Crash Course explain the process by which stars are formed and explode, in their own unique style.
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- Download English Transcript
Key Ideas
As this video progresses, key ideas will be introduced to invoke discussion.
Think about the following questions as you watch the video
- What pulled together the hydrogen and helium atoms found in space not long after the Big Bang? What was the result?
- Will Earth be affected by the collision of the Milky Way and Andromeda galaxies?
- At what temperature do hydrogen and helium atoms fuse together?
- Do bigger stars live longer or do smaller stars?
- Where do the metals heavier than iron come from?
- Where did the metal in the ring on John’s finger come from?
: Hi, I'm John Green, and this is Crash Course Big History.
: Today, we're going to be exploring what happened
: to the universe after the Big Bang, particularly,
: how you and I and everyone you know emerged from stars.
: And we'll also be investigating the burning question
: of why anyone who studies history
: has to care about chemistry.
: Mr. Green, Mr. Green!
: I'm sorry, but I hate chemistry.
: Why can't we just learn about like English kings
: stabbing each other?
: Sorry, me from the past, the thing is if you look far back
: enough in your family tree, you're going to find not just
: like farmers, and foragers, and fish, and microbes,
: you're going to find stars.
: And I don't mean stars like Kim Kardashian,
: who is actually not a star, she is a person.
: I mean actual stars, me from the past.
: And to understand how we got from stars to people,
: you're going to need some chemistry.
: So last episode we went from the very beginning of everything
: to the release of cosmic background radiation.
: And CBR is a major piece of evidence
: that the Big Bang happened.
: Studying it closely also tells us the age of the universe
: and it allows us to see the minute variations in temperature
: and density of the early universe.
: And it turns out that those tiny differences
: are a really big deal.
: So when the universe inflated from much, much smaller
: than an atom to the size of a grapefruit in a split second,
: there were quantum fluctuations, tiny little blips
: on the unpredictable quantum scale.
: And they created those little variations that we see
: in cosmic background radiation.
: And as the universe continued to expand--
: I mean it is currently larger than a grapefruit--
: those variations in density were inflated to such a scale
: that gravity was able to take hold and start clumping together
: clouds of hydrogen and helium gas.
: So 380,000 years after the Big Bang,
: the universe was becoming an increasingly cold
: and increasingly boring place.
: Like temperatures were no longer high enough
: to forge new elements, and if hydrogen and helium
: hadn't clumped together,
: nothing would have ever happened ever again.
: Our universe would just be a dull, homogeneous place
: with some clouds of hydrogen and helium gas floating around.
: Dull and gassy, just like North Dakota.
: I'm just kidding, North Dakota.
: You do have a lot of natural gas,
: but you're very interesting.
: I mean you have Mount Rushmore.
: What's that?
: Oh, oh I see.
: Sorry, yeah, then...
: But what happened is that while the universe on the whole
: continued to cool, thanks to those tiny variations
: that emerged during inflation, certain pockets of the universe
: were about to get very hot.
: Indeed, a liberal dose of hot sauce was yet to come.
: Hydrogen and helium though are light gases;
: they are the lightest two elements.
: So light that they require very little encouragement
: to escape the earth's atmosphere.
: But while the explosive force of the Big Bang flings matter
: and energy apart, gravity has the ability to pull
: tiny pockets of the cosmos back together,
: provided it has some wrinkles in the universe to work with.
: As gravity sucked hydrogen and helium atoms together,
: enormous, thick clouds began to form.
: While the expansion of the universe continued to increase
: the gaps between these clouds,
: the density of these pockets also increased.
: The vastness of empty space began to be filled
: with tiny islands where atoms of hydrogen and helium
: were increasingly squished together.
: Despite being the lightest of all the elements,
: the immense amount of all that gas built pressure
: up in the center.
: Increasing pressure meant increasing temperatures,
: just like after your 2:00 a.m. taco run,
: suddenly these gassy pockets were burning inside.
: It was in this rather uncomfortable state of heartburn
: that the first stars flared into life,
: roughly 100 million years after the Big Bang.
: By a billion years after the Big Bang, the universe
: was starting to look like what we think of as a universe.
: An immense vastness littered with hundreds of billions
: of galactic islands containing hundreds of billions of stars.
: And as recent work with Kepler space telescope has revealed,
: a mind-numbing number of planets.
: So the universe is big, it's really big.
: But it's not so big that it's impossible
: for the average person to get a mental picture
: of like our neighborhood.
: Our galaxy, the Milky Way, formed from these
: galactic mergers with other galaxies that stopped
: like around ten billion years ago.
: Our galaxy is about 100,000 light years across,
: which means that it takes,
: you know, 100,000 years for light to get across it.
: And even if humans become like technologically capable
: of colonizing the galaxy in the next millions of years,
: our little galactic island is probably where
: we're going to stay just peeping out on the rest of the universe.
: So there are between 200 and 400 billion stars in the Milky Way
: with huge distances between them.
: There hasn't been a merger between our galaxy and another
: for a long time, but our neighbor Andromeda,
: which has closer to a trillion stars, is actually set
: to collide with us in 3.75 billion years.
: But don't worry, this isn't going to be like a car crash
: because the vast distances between stars make it
: very unlikely that stars will actually hit each other
: in such an event.
: Although many new stars will form.
: Instead of a car crash,
: think of like a three-billion-year-long tango
: of two graceful galactic dancers.
: This is going to totally mess up the constellations
: that we're familiar with now, but the good news is that
: by that time, the sun will have wiped out life on earth
: regardless, so we won't have to worry about it.
: And the even better news is that let's face it, there's no way
: our species is making it until the sun wipes us out.
: As far as these galactic islands go, ours is a modest size.
: Like Malin 1 is a spiral galaxy like ours, but it's a whopping
: 680,000 light years across.
: And the giant elliptical galaxy excitingly named M87--
: because astronomers are so good at naming things--
: is 980,000 light years across.
: And with its radio jets, the elliptical galaxy Hercules A--
: that's a slightly better name-- is a whopping 1.5 million
: light years across from end to end.
: Galactic islands are separated
: by millions and millions of light years.
: And the Virgo super cluster of galaxies to which
: the Milky Way belongs is roughly 110 million light years
: in diameter, and that's only one of many likely infinite
: super clusters in the universe.
: Wait, literally infinite?
: Wow.
: Unfortunately, we can't know whether the universe
: truly is infinite or not because of a little thing
: called the cosmic horizon.
: We can only see the light that has reached us
: from the start of the universe 13.8 billion years ago.
: Simply looking into the sky is an act of investigating history,
: and the farther we look back we begin to see
: more primitive things.
: The first stars in galaxies.
: Mind you, the light we observe billions of years after it
: first shown and the continued expansion of the universe
: means that the cosmic horizon is approximately 46 billion
: light years away by now.
: Roughly double that and you know that our little cosmic bubble
: is about 92 billion light years across.
: I mean compare that to our already huge
: 100,000 light year galaxy.
: Just for a little bit of context...
: But beyond our little cosmic bubble there is more universe,
: eternally inflating.
: And where our universe is sort of one hole in a block
: of Swiss cheese, other holes might exist
: in that block of cheese, multiple universes with laws
: of physics completely different from ours.
: I know, right, it's nuts!
: It's actually more like cheese, but it's nuts!
: But our cosmic bubble, while it's very large,
: is not such an intimidating place.
: Like it's pretty easy just to get a mental picture of it.
: A vast bubble with a lot of empty space
: and a light dusting of galaxies.
: To further this point, and don't take this too seriously,
: but in 2002, Karl Glazebrook and Ivan Baldry
: added up the light from 200,000 galaxies and determined
: that if you were able to stand outside our cosmic bubble
: and look at it with human eyes, the color of our universe
: would be-- wait for it: beige.
: That's a bit of a anticlimax, so they tried to dress it up
: by calling it cosmic latte.
: But I don't mind beige.
: I mean look, this stuff is gigantic and somewhat scary,
: but you can't be scared of beige.
: And a lot of cosmologists infuse their lessons with a sense
: of awe at this vast expanse.
: And that awe is certainly justified.
: I mean the universe is literally awesome.
: Though let me ask you this, if you lived in New York City
: would you feel bashful or depressed about the size
: of your city compared to, say, the miles and miles
: of the plains of Saskatchewan?
: So yeah, there are millions and millions of light years
: of empty space, but it's empty space.
: One thing we find out about the rising complexity in Big History
: is just how unique some of these tiny areas
: of the universe can be.
: This is where the action is.
: Enough of the pontification, let's get back to those
: gassy, heartburn-suffering stars.
: As core regions of the gas clouds heat up,
: the atoms get jumpy, move faster and faster and collide
: with ever-increasing ferocity.
: Eventually it's ferocious enough to overcome
: the electric repulsion between the atoms,
: they fuse and the cloud officially becomes a star.
: Hydrogen atoms fuse into helium atoms at about
: ten million degrees, releasing yet more energy.
: The sun is a massive hydrogen bomb in the sky.
: And the release of energy in just the right amounts
: is very good for us, provided we don't mess up the ozone layer
: too bad or spend too much time tanning on the beach.
: When it comes to stars, size matters.
: If an initial cloud is smaller than 8% of the size of our sun,
: it'll never form a star.
: Maybe only a brown dwarf.
: If the initial cloud is 60 to 100 times our sun
: it will probably split into two or more regions
: of stellar formation.
: If the cloud is between 8% and eight times the size of our sun
: it has a longer lifespan.
: Our sun is middle-aged and will last for about
: another five billion years.
: Much smaller stars may have lifespans of hundreds
: of billions of years.
: Large stars sometimes only live for a few hundred million years.
: As all stars run out of hydrogen and helium as fuel,
: the outer edges of the star swells up.
: Fusion of heavier elements occurs,
: requiring higher and higher temperatures,
: creating heavier and heavier elements,
: all the way up to iron.
: But elements heavier than iron can't be created in the stars.
: There simply isn't enough energy
: to fuse those heavier nuclei together.
: So how is the rest of the periodic table formed?
: When giant stars, eight to 60 times the size of our sun
: exhaust their fuel, they collapse.
: This may last no longer than a second,
: but it will be followed by a huge explosion.
: These explosions shine with the energy of billions of stars
: and combine with proton and neutron capture,
: supernova are responsible for creating the heavier elements
: of the periodic table.
: Flinging out these elements, the rest of the cosmos
: is fertilized and nourished by the ashes of dead stars.
: Carl Sagan said it best, "We are made of star-stuff,"
: and he really meant that.
: I mean you see this globe?
: It was made in the belly of a star.
: You see your computer?
: Made in the belly of a star.
: Your dog, made in the belly of a star.
: Your right hand, made in the belly of a star.
: Your left hand, potentially made in the belly
: of a different star.
: Stellar evolution bridges the gap between the mindboggling
: origin of our universe and the tangible material stuff
: that you see around you,
: and, in fact, the tangible material stuff that you are.
: Humans haven't just appeared out of nowhere.
: We've changed form.
: We used to be much hotter, of course--
: I mean temperature-wise.
: This is why chemistry is important to understanding
: the grand narrative of 13.8 billion years.
: And it's also why we look at the big history
: of individual objects, something we call little big histories.
: Like see this ring on my finger?
: I bought it in a jewelry store.
: A nice person sold it to me.
: A jeweler crafted it and miners dug it out of the ground.
: But it got there by being flung out of a huge star
: in a massive explosion billions of years ago.
: It wound up in our solar system, was part of the tiny
: .1% of matter that didn't get sucked into the sun,
: accreted from the dusty debris in the one sliver
: of the solar system where the earth was.
: And because gold is an iron-loving element,
: it was more prone to sink to the center of the earth,
: making it even more unlikely that it should be found
: on the earth's crust.
: Rare and shiny things are valued by a lot of human social orders,
: and during the agrarian era, gold became a sign
: of social standing and wealth.
: And in marriage tradition, giving someone an expensive gift
: can be a sign of esteem.
: Hence Sara and I spent $450 on this,
: which we could have spent on an Xbox.
: Tiny wrinkles in the early universe had a major impact
: on one of the unifying themes of 13.8 billion years:
: rise in complexity.
: Wrinkles created stars, stars created elements,
: and some of those elements came together to form life,
: and, of course, us.
: Gradually, we see an increase in the number of connections
: and building blocks present in the universe.
: For instance, a star's comprised primarily of two elements:
: hydrogen and helium.
: But here's the thing, if there had been no wrinkles
: in the early universe, energy would have been
: evenly distributed across the cosmos.
: Without flow of energy, like say that through a star,
: no complexity could arise.
: None whatsoever.
: This state of existence
: is called thermodynamic disequilibrium,
: which means that energy is not evenly distributed.
: A simple structure like a star is big, but it's just
: a large pile of the lightest elements and doesn't score
: very high in energy flow density.
: Your brain is 75,000 times more complex than a similar size
: chunk of the sun.
: Its building blocks and nodes are way more intricate.
: Your brain has way more connections than there are stars
: in the galaxy.
: You wouldn't think a story that spans cosmology, geology,
: biology, and human history would have a unifying theme,
: but rise in complexity is something that stretches
: across all 13.8 billion years.
: And it began with those tiny wrinkles in the early cosmos.
: So now moving fast, I hope you see why
: a basic understanding of chemistry is important
: to understanding our ancestry.
: I mean stars are pretty much
: your great-great-great-et cetera grandparents.
: And you wouldn't ignore your grandparents, would you?
: >> Mr. Green, Mr. Green, no, no way, I mean
: they're a big part of my plan to get a car for my 16th birthday.
: That's really touching, me from the past.
: Also I've got bad news for you.
: So in today's episode, we've learned that everything
: around us, everything that we can touch, and feel, and see,
: even us, is debris floating around enormous stars
: in the vacuum of space.
: We clump into specks, we change form, but we owe
: our entire existence to these burning, gassy balls that we see
: in the night sky.
: We may just be the ashes of dead stars, but those ashes hold
: the potential to arrange themselves in increasingly
: complex ways from which the earth and all it contains
: Today, we're going to be exploring what happened
: to the universe after the Big Bang, particularly,
: how you and I and everyone you know emerged from stars.
: And we'll also be investigating the burning question
: of why anyone who studies history
: has to care about chemistry.
: Mr. Green, Mr. Green!
: I'm sorry, but I hate chemistry.
: Why can't we just learn about like English kings
: stabbing each other?
: Sorry, me from the past, the thing is if you look far back
: enough in your family tree, you're going to find not just
: like farmers, and foragers, and fish, and microbes,
: you're going to find stars.
: And I don't mean stars like Kim Kardashian,
: who is actually not a star, she is a person.
: I mean actual stars, me from the past.
: And to understand how we got from stars to people,
: you're going to need some chemistry.
: So last episode we went from the very beginning of everything
: to the release of cosmic background radiation.
: And CBR is a major piece of evidence
: that the Big Bang happened.
: Studying it closely also tells us the age of the universe
: and it allows us to see the minute variations in temperature
: and density of the early universe.
: And it turns out that those tiny differences
: are a really big deal.
: So when the universe inflated from much, much smaller
: than an atom to the size of a grapefruit in a split second,
: there were quantum fluctuations, tiny little blips
: on the unpredictable quantum scale.
: And they created those little variations that we see
: in cosmic background radiation.
: And as the universe continued to expand--
: I mean it is currently larger than a grapefruit--
: those variations in density were inflated to such a scale
: that gravity was able to take hold and start clumping together
: clouds of hydrogen and helium gas.
: So 380,000 years after the Big Bang,
: the universe was becoming an increasingly cold
: and increasingly boring place.
: Like temperatures were no longer high enough
: to forge new elements, and if hydrogen and helium
: hadn't clumped together,
: nothing would have ever happened ever again.
: Our universe would just be a dull, homogeneous place
: with some clouds of hydrogen and helium gas floating around.
: Dull and gassy, just like North Dakota.
: I'm just kidding, North Dakota.
: You do have a lot of natural gas,
: but you're very interesting.
: I mean you have Mount Rushmore.
: What's that?
: Oh, oh I see.
: Sorry, yeah, then...
: But what happened is that while the universe on the whole
: continued to cool, thanks to those tiny variations
: that emerged during inflation, certain pockets of the universe
: were about to get very hot.
: Indeed, a liberal dose of hot sauce was yet to come.
: Hydrogen and helium though are light gases;
: they are the lightest two elements.
: So light that they require very little encouragement
: to escape the earth's atmosphere.
: But while the explosive force of the Big Bang flings matter
: and energy apart, gravity has the ability to pull
: tiny pockets of the cosmos back together,
: provided it has some wrinkles in the universe to work with.
: As gravity sucked hydrogen and helium atoms together,
: enormous, thick clouds began to form.
: While the expansion of the universe continued to increase
: the gaps between these clouds,
: the density of these pockets also increased.
: The vastness of empty space began to be filled
: with tiny islands where atoms of hydrogen and helium
: were increasingly squished together.
: Despite being the lightest of all the elements,
: the immense amount of all that gas built pressure
: up in the center.
: Increasing pressure meant increasing temperatures,
: just like after your 2:00 a.m. taco run,
: suddenly these gassy pockets were burning inside.
: It was in this rather uncomfortable state of heartburn
: that the first stars flared into life,
: roughly 100 million years after the Big Bang.
: By a billion years after the Big Bang, the universe
: was starting to look like what we think of as a universe.
: An immense vastness littered with hundreds of billions
: of galactic islands containing hundreds of billions of stars.
: And as recent work with Kepler space telescope has revealed,
: a mind-numbing number of planets.
: So the universe is big, it's really big.
: But it's not so big that it's impossible
: for the average person to get a mental picture
: of like our neighborhood.
: Our galaxy, the Milky Way, formed from these
: galactic mergers with other galaxies that stopped
: like around ten billion years ago.
: Our galaxy is about 100,000 light years across,
: which means that it takes,
: you know, 100,000 years for light to get across it.
: And even if humans become like technologically capable
: of colonizing the galaxy in the next millions of years,
: our little galactic island is probably where
: we're going to stay just peeping out on the rest of the universe.
: So there are between 200 and 400 billion stars in the Milky Way
: with huge distances between them.
: There hasn't been a merger between our galaxy and another
: for a long time, but our neighbor Andromeda,
: which has closer to a trillion stars, is actually set
: to collide with us in 3.75 billion years.
: But don't worry, this isn't going to be like a car crash
: because the vast distances between stars make it
: very unlikely that stars will actually hit each other
: in such an event.
: Although many new stars will form.
: Instead of a car crash,
: think of like a three-billion-year-long tango
: of two graceful galactic dancers.
: This is going to totally mess up the constellations
: that we're familiar with now, but the good news is that
: by that time, the sun will have wiped out life on earth
: regardless, so we won't have to worry about it.
: And the even better news is that let's face it, there's no way
: our species is making it until the sun wipes us out.
: As far as these galactic islands go, ours is a modest size.
: Like Malin 1 is a spiral galaxy like ours, but it's a whopping
: 680,000 light years across.
: And the giant elliptical galaxy excitingly named M87--
: because astronomers are so good at naming things--
: is 980,000 light years across.
: And with its radio jets, the elliptical galaxy Hercules A--
: that's a slightly better name-- is a whopping 1.5 million
: light years across from end to end.
: Galactic islands are separated
: by millions and millions of light years.
: And the Virgo super cluster of galaxies to which
: the Milky Way belongs is roughly 110 million light years
: in diameter, and that's only one of many likely infinite
: super clusters in the universe.
: Wait, literally infinite?
: Wow.
: Unfortunately, we can't know whether the universe
: truly is infinite or not because of a little thing
: called the cosmic horizon.
: We can only see the light that has reached us
: from the start of the universe 13.8 billion years ago.
: Simply looking into the sky is an act of investigating history,
: and the farther we look back we begin to see
: more primitive things.
: The first stars in galaxies.
: Mind you, the light we observe billions of years after it
: first shown and the continued expansion of the universe
: means that the cosmic horizon is approximately 46 billion
: light years away by now.
: Roughly double that and you know that our little cosmic bubble
: is about 92 billion light years across.
: I mean compare that to our already huge
: 100,000 light year galaxy.
: Just for a little bit of context...
: But beyond our little cosmic bubble there is more universe,
: eternally inflating.
: And where our universe is sort of one hole in a block
: of Swiss cheese, other holes might exist
: in that block of cheese, multiple universes with laws
: of physics completely different from ours.
: I know, right, it's nuts!
: It's actually more like cheese, but it's nuts!
: But our cosmic bubble, while it's very large,
: is not such an intimidating place.
: Like it's pretty easy just to get a mental picture of it.
: A vast bubble with a lot of empty space
: and a light dusting of galaxies.
: To further this point, and don't take this too seriously,
: but in 2002, Karl Glazebrook and Ivan Baldry
: added up the light from 200,000 galaxies and determined
: that if you were able to stand outside our cosmic bubble
: and look at it with human eyes, the color of our universe
: would be-- wait for it: beige.
: That's a bit of a anticlimax, so they tried to dress it up
: by calling it cosmic latte.
: But I don't mind beige.
: I mean look, this stuff is gigantic and somewhat scary,
: but you can't be scared of beige.
: And a lot of cosmologists infuse their lessons with a sense
: of awe at this vast expanse.
: And that awe is certainly justified.
: I mean the universe is literally awesome.
: Though let me ask you this, if you lived in New York City
: would you feel bashful or depressed about the size
: of your city compared to, say, the miles and miles
: of the plains of Saskatchewan?
: So yeah, there are millions and millions of light years
: of empty space, but it's empty space.
: One thing we find out about the rising complexity in Big History
: is just how unique some of these tiny areas
: of the universe can be.
: This is where the action is.
: Enough of the pontification, let's get back to those
: gassy, heartburn-suffering stars.
: As core regions of the gas clouds heat up,
: the atoms get jumpy, move faster and faster and collide
: with ever-increasing ferocity.
: Eventually it's ferocious enough to overcome
: the electric repulsion between the atoms,
: they fuse and the cloud officially becomes a star.
: Hydrogen atoms fuse into helium atoms at about
: ten million degrees, releasing yet more energy.
: The sun is a massive hydrogen bomb in the sky.
: And the release of energy in just the right amounts
: is very good for us, provided we don't mess up the ozone layer
: too bad or spend too much time tanning on the beach.
: When it comes to stars, size matters.
: If an initial cloud is smaller than 8% of the size of our sun,
: it'll never form a star.
: Maybe only a brown dwarf.
: If the initial cloud is 60 to 100 times our sun
: it will probably split into two or more regions
: of stellar formation.
: If the cloud is between 8% and eight times the size of our sun
: it has a longer lifespan.
: Our sun is middle-aged and will last for about
: another five billion years.
: Much smaller stars may have lifespans of hundreds
: of billions of years.
: Large stars sometimes only live for a few hundred million years.
: As all stars run out of hydrogen and helium as fuel,
: the outer edges of the star swells up.
: Fusion of heavier elements occurs,
: requiring higher and higher temperatures,
: creating heavier and heavier elements,
: all the way up to iron.
: But elements heavier than iron can't be created in the stars.
: There simply isn't enough energy
: to fuse those heavier nuclei together.
: So how is the rest of the periodic table formed?
: When giant stars, eight to 60 times the size of our sun
: exhaust their fuel, they collapse.
: This may last no longer than a second,
: but it will be followed by a huge explosion.
: These explosions shine with the energy of billions of stars
: and combine with proton and neutron capture,
: supernova are responsible for creating the heavier elements
: of the periodic table.
: Flinging out these elements, the rest of the cosmos
: is fertilized and nourished by the ashes of dead stars.
: Carl Sagan said it best, "We are made of star-stuff,"
: and he really meant that.
: I mean you see this globe?
: It was made in the belly of a star.
: You see your computer?
: Made in the belly of a star.
: Your dog, made in the belly of a star.
: Your right hand, made in the belly of a star.
: Your left hand, potentially made in the belly
: of a different star.
: Stellar evolution bridges the gap between the mindboggling
: origin of our universe and the tangible material stuff
: that you see around you,
: and, in fact, the tangible material stuff that you are.
: Humans haven't just appeared out of nowhere.
: We've changed form.
: We used to be much hotter, of course--
: I mean temperature-wise.
: This is why chemistry is important to understanding
: the grand narrative of 13.8 billion years.
: And it's also why we look at the big history
: of individual objects, something we call little big histories.
: Like see this ring on my finger?
: I bought it in a jewelry store.
: A nice person sold it to me.
: A jeweler crafted it and miners dug it out of the ground.
: But it got there by being flung out of a huge star
: in a massive explosion billions of years ago.
: It wound up in our solar system, was part of the tiny
: .1% of matter that didn't get sucked into the sun,
: accreted from the dusty debris in the one sliver
: of the solar system where the earth was.
: And because gold is an iron-loving element,
: it was more prone to sink to the center of the earth,
: making it even more unlikely that it should be found
: on the earth's crust.
: Rare and shiny things are valued by a lot of human social orders,
: and during the agrarian era, gold became a sign
: of social standing and wealth.
: And in marriage tradition, giving someone an expensive gift
: can be a sign of esteem.
: Hence Sara and I spent $450 on this,
: which we could have spent on an Xbox.
: Tiny wrinkles in the early universe had a major impact
: on one of the unifying themes of 13.8 billion years:
: rise in complexity.
: Wrinkles created stars, stars created elements,
: and some of those elements came together to form life,
: and, of course, us.
: Gradually, we see an increase in the number of connections
: and building blocks present in the universe.
: For instance, a star's comprised primarily of two elements:
: hydrogen and helium.
: But here's the thing, if there had been no wrinkles
: in the early universe, energy would have been
: evenly distributed across the cosmos.
: Without flow of energy, like say that through a star,
: no complexity could arise.
: None whatsoever.
: This state of existence
: is called thermodynamic disequilibrium,
: which means that energy is not evenly distributed.
: A simple structure like a star is big, but it's just
: a large pile of the lightest elements and doesn't score
: very high in energy flow density.
: Your brain is 75,000 times more complex than a similar size
: chunk of the sun.
: Its building blocks and nodes are way more intricate.
: Your brain has way more connections than there are stars
: in the galaxy.
: You wouldn't think a story that spans cosmology, geology,
: biology, and human history would have a unifying theme,
: but rise in complexity is something that stretches
: across all 13.8 billion years.
: And it began with those tiny wrinkles in the early cosmos.
: So now moving fast, I hope you see why
: a basic understanding of chemistry is important
: to understanding our ancestry.
: I mean stars are pretty much
: your great-great-great-et cetera grandparents.
: And you wouldn't ignore your grandparents, would you?
: >> Mr. Green, Mr. Green, no, no way, I mean
: they're a big part of my plan to get a car for my 16th birthday.
: That's really touching, me from the past.
: Also I've got bad news for you.
: So in today's episode, we've learned that everything
: around us, everything that we can touch, and feel, and see,
: even us, is debris floating around enormous stars
: in the vacuum of space.
: We clump into specks, we change form, but we owe
: our entire existence to these burning, gassy balls that we see
: in the night sky.
: We may just be the ashes of dead stars, but those ashes hold
: the potential to arrange themselves in increasingly
: complex ways from which the earth and all it contains