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Crash Course: The Big Bang
Crash Course: The Big Bang
Crash Course is a fast, funny, irreverent look at history. In this episode, brothers John and Hank Green give us their take on what makes Big History so darn important.
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Key Ideas
As this video progresses, key ideas will be introduced to invoke discussion.
Think about the following questions as you watch the video
- Why is the Big Bang a good start date for history?
- What do different scales give you?
- How old is the Universe?
- How do we know that the Big Bang is the beginning?
- What are the two simplest elements that were formed after the Big Bang?
- What is cosmic background radiation (CBR)?
- What is redshift?
: Hi, I'm John Green, and this is Crash Course Big History
: in which we'll be looking at the history of, like, everything.
: I'm talking about 13.8 billion years--
: from the Big Bang to now.
: I mean, in this series, we are literally going to attempt
: to tell you the story of what Douglas Adams famously called:
: >> Mr. Green, Mr. Green!
: That's not history, that's science.
: And science is for nerds.
: Oh, me from the past, things would be so much easier
: for you if you would just accept that you are,
: in fact, a nerd and that's okay.
: I mean, look at this picture, dude.
: Anyway, academics often describe history
: as, like, all the stuff that's happened
: since we started writing things down,
: but they only start there
: because that's where we have the best information.
: And, yeah, I think that the advent
: of writing was a huge deal, obviously,
: but as a start date for history, it's totally arbitrary.
: It's just a line we drew in the sand and said,
: "Okay, history begins now!"
: In Big History, we're going to start history
: when it really starts-- at least, we think--
: at the creation of the universe.
: And we're going to end that story where it ends.
: Please let that be after I die.
: Well, I guess it will definitely be after I die,
: it's just, I want it to be a while after I die.
: So we're even going to terrify traditional historians
: by using physics to make some predictions about the future
: and we're going to end many trillions and trillions
: of years from now when the universe itself--
: spoiler alert-- dies, at least in a manner of speaking.
: Hey! I'm not John.
: If you're thinking we look a little bit the same,
: that's because we're brothers.
: I'm Hank.
: Anyway, if you want to learn the 13.8-billion-year history
: of the universe in the same amount of time
: that we usually cover the 238 years of American history,
: you're not going to get the same resolution.
: Of course, knowing the names and dates
: of American history is important,
: but we just can't do that in Big History.
: As you zoom out, you see a lot more of the picture.
: The details get a little fuzzy, but we quickly realize
: that history is everything-- cosmology, geology,
: biology, social sciences, literature, physics.
: Everything.
: You might think that such a scale would be filled
: with way too much detail,
: but the amount of detail an answer requires depends
: on the nature of the question.
: Some questions can only be explored by zooming out.
: That is what Big History does.
: Speaking of zoomed out, this is"Earthrise,"
: one of the most famous photographs of all time.
: William Anders, an Apollo astronaut,
: took it in 1968.
: From the surface of another world,
: we see our planet as a little ball in space.
: No borders, no people, no buildings,
: just oceans and clouds and continents
: being shined upon by the sun.
: That sheer expansion of scale gives me perspective.
: It lets me imagine all the complexity of life on Earth,
: from the gasoline engine that powered my trip
: to the studio, to political instability
: in Nepal as part of a thriving, living, teeming mass of life
: loading in the emptiness of space.
: So what that photograph does for physical space,
: Big History aims to do for everything.
: I mean, we want to contextualize all of existence.
: We want to outline the most powerful
: and important breakthroughs, the tremendous scale of existence,
: and how we know what we know, and why we're sure we know it.
: All right, let's go to the Thought Bubble.
: So, the universe is big-- like, really big--
: and it's also old-- like, 13.8 billion years old.
: Which is enough years that there is no way
: to actually comprehend it, so let's just compress
: that age to 13 years--
: small enough that our puny brains can handle it.
: On that time scale, the universe would have begun 13 years ago,
: in 2001.
: George W. Bush had just been sworn in as president.
: Most Americans on the Internet were connecting
: to it with dial-up modems.
: Right, so the first stars and galaxies
: would have formed 12 years ago, but seven and a half more years
: would pass until the earth formed, about 4.5 years ago.
: Move a little bit up to four years ago--
: that's when the first single-celled life formed
: on Earth.
: Then leap forward nearly three and a half more years
: before the first multicellular organisms
: and the Cambrian explosion...
: What I'm trying to explain is that all complex life
: on Earth is a fairly recent development.
: Like, on this scale, the dinosaurs went extinct
: about three weeks ago-- roughly the last time
: I changed my Facebook status.
: Humans and chimpanzees split
: from their last shared ancestor about three days ago.
: The first homo sapiens emerged 50 minutes ago,
: roughly the last time I checked my email.
: We left Africa 26 minutes ago.
: The American Indians reached the Americas six minutes ago--
: roughly the last time I check my Twitter.
: We invented agriculture five minutes ago,
: Ancient Egypt three minutes ago, the Black Death 24 seconds ago,
: The Industrial Revolution, six seconds,
: World War I, two seconds.
: The Cold War, the first man on the moon, your birth,
: the internet, the Big Mac, all within the last second.
: But in many other ways, complex life
: and humanityareexceptional.
: >> Thanks, Thought Bubble.
: Also exceptional, by the way, the Mongols.
: Okay, let's begin at the beginning-- the Big Bang.
: Hank, wait a second... whoa, whoa, whoa.
: I don't understand how we know that the Big Bang
: is really the beginning.
: Like, what happened before the Big Bang?
: Well, okay, theoretical physicists say
: that space and time are not two different things.
: They are two expressions of one thing: spacetime.
: And spacetime was created by the Big Bang,
: thus, time didn't exist before the Big Bang,
: so it doesn't make much sense to ask what happened before it.
: There was no "then" then.
: Of course, this, like many ideas in cosmology,
: doesn't really make any sense to our puny human brains.
: It's largely beyond our comprehension
: rather like explaining color to a blind person.
: We know that it's true because the math works
: and it explains our observations so elegantly,
: but it's so far outside of how we directly perceive the world
: that I don't think it's something
: even the most genius physicists are able to imagine.
: But, yeah, if you're going to do a chronological study
: of the universe, the creation of time
: is probably a pretty good place to start the story.
: So the Big Bang wasn't something that happened
: inside the universe, nor did it expand into some kind of void.
: It was literally the moment when both time
: and space were created.
: The thing that was banging was the universe itself.
: It was expanding from an unimaginably tiny point
: to an unimaginably large universe unimaginably quickly.
: "Unimaginable" is basically the subtitle to the story
: of the Big Bang, but then again, it's also kind of the subtitle
: to everything else in Big History.
: I mean, I can only do this occasionally,
: but sometimes you look outside and you're like,
: "Oh, my goodness, this is nuts!
: How did we get trees?"
: Needless to say, we will be talking about that.
: Anyway, the universe is a hard worker
: and it got most of the heavy lifting done
: in those first few seconds.
: For comparison, it takes me about 20 minutes
: after I wake up for me to even get myself
: into a standing position.
: But the universe is somewhat more efficient.
: In the barest fraction of the first second,
: the universe inflated
: from something many, many, many times smaller than an atom
: to about the size of a grapefruit.
: Like, think of it this way.
: In much less than a blink of an eye,
: if it had originally been the size of a tennis ball,
: it would have inflated to over 90 billion light-years across.
: This inflation theory has been well backed up
: by mathematics for a long time now,
: but it has recently received some staggering new support
: from the BICEP Project of the South Pole
: which sadly has nothing to do with my guns.
: Ten seconds after the Big Bang, the universe had expanded enough
: that the normal rules of the universe
: with atomic forces and gravity and electromagnetism
: that we know and love today were already in charge.
: All of the antimatter created in the Big Bang had combined
: with matter and annihilated itself leaving
: behind only one-billionth of the matter created in the Big Bang.
: And that billionth is everything.
: And I mean everything-- every grain of sand,
: every blueberry you will ever eat,
: every star that you will ever see.
: Everything.
: We're already tried to understand how big a billion is,
: but just pause to think about that.
: Everything--everything-- is one-billionth of the matter
: created in the Big Bang.
: (imitates explosion)
: The First Law of Thermodynamics is that
: matter and energy cannot be created or destroyed.
: Everything we have now, we had then.
: The matter that makes up your body right now has been around
: since those moments 13.8 billion years ago.
: It's simply changed form.
: After just three minutes, the universe was cool enough
: that the nuclei of atoms started forming--
: just hydrogen and helium back then, the two simplest elements.
: Keep those two in mind, however, because it turns out
: if you take a bunch of hydrogen and you wait, like,
: several billion years, you might just grow yourself some humans.
: Let's remember, at this time,
: the universe was still very, very hot.
: I don't want to use the world "unimaginable" too often.
: But it was unimaginably hot.
: The universe remained, like, an uber hot sea dominated
: by radiation, but then luckily it simmered down
: to a balmy 5,000 degrees Fahrenheit
: about 380,000 years after the Big Bang,
: allowing matter and radiation to separate.
: And remember:
: I mean, you are a somewhat firm bag of energy.
: In my case, I'm not that firm.
: So anyway, at 5,000 degrees Fahrenheit,
: radiation was finally able to move freely
: through the universe, and we see that radiation today
: as the end of the dark ages that followed the Big Bang
: and the beginning of a brilliant flash that we call:
: Which is a great name for a band.
: Physicists call it "The fingerprint of the universe"
: and it's one of the most important pieces
: of historical evidence we have for the Big Bang
: because CBR is everywhere.
: Tune your radio to a frequency that doesn't have a station,
: a portion of the static you hear is actually
: that cosmic background radiation being picked up by your radio.
: So you can literally hear the universe in its infancy.
: Sometimes it can be tricky to know what's true,
: especially when we're talking about stuff
: that happened so far in the distant past.
: That is why we created science:
: So just using your limited human senses, you might come
: to the same conclusion as 19th century scientists--
: that the universe is static, eternal, and infinite.
: Then, using our minds, if the universe is infinite--
: it contains infinite stars and it has always existed--
: then the night sky and the daytime sky for that matter
: would literally be filled with stars,
: so much that day and night would be indistinguishable.
: This is clearly not the case, so something must be amiss.
: The universe must either be not static,
: not infinite, or not eternal.
: So which is it?
: You know how when an ambulance drives towards you,
: the sound waves are compressed
: and the siren sounds higher pitched,
: and as it speeds away the waves are stretched out
: and the pitch is lower?
: It's the Doppler effect.
: Well, here's another name you've heard:
: Edwin Hubble.
: He realized that light does the same thing.
: Galaxies in stars moving away
: from us have their lights stretch out,
: making it more red, and stars moving toward us
: have their light compressed, making it more blue.
: Combined with the work of Henrietta Leavitt,
: which allowed us to accurately estimate how far away stars are,
: Hubble was able to determine that stars
: on the whole are flying away from each other.
: He discovered that the most remote objects
: in the sky were all red-shifted and were actually
: other galaxies beyond the Milky Way moving away from us.
: From here, he built upon the work
: of Belgian Catholic priest Georges Lemaitre
: who hypothesized that the universe began
: at a single point.
: Big Bang cosmologists wanted proof, though.
: They knew that the amount of radiation released
: by the Big Bang would be massive and they wanted to see it.
: It wasn't until the 1960s that it was found-- accidentally--
: by two guys working on an antenna
: at Bell Laboratories in New Jersey.
: They were trying to eliminate all the background noise
: from an extremely sensitive radio antenna,
: but they found this faint hum coming from every direction.
: They tried everything they could to get rid of it,
: including murdering the pigeons
: that kept pooping on the antenna.
: Kind of sad, but those pigeons, they gave their lives
: for one of the most profound discoveries in modern science.
: A conversation with a local radio astronomer led them
: to show their findings to an astronomer
: at Princeton who confirmed the existence
: of what had been predicted for years.
: The final piece of that Big Bang puzzle is that we can see it.
: Light has a speed.
: When we look at the sun, we're seeing the light
: that left it eight minutes ago.
: But if we look at something
: that's 13.8 billion light-years away,
: we're seeing the stuff that happened 13.8 billion years ago.
: That radiation has been traveling
: since the very beginning of the universe.
: Not only can we tell very clearly
: that there was just nothing there before that,
: we can now study that radiation to learn the sequence
: of events of the Big Bang.
: We can also see that the chemical composition
: of the early universe is what we'd expect to see.
: A lot of hydrogen, a lot of helium,
: and a tiny pinch of lithium.
: The rest of the period table had to wait
: for the fiery furnaces in the bellies of stars to be created.
: But more on that next episode.
: As far as we've come in the past century
: in crafting a history of the universe,
: there are still many things
: cosmologists have yet to discover.
: For instance, the universe behaves
: as if there's a bunch of matter in it
: that we can't see or detect.
: Galaxies' gravitation is affected by this matter,
: but it's otherwise completely invisible to us.
: Physicists call it "dark matter"
: but we have no idea what it is.
: But as in any historical endeavor,
: new discoveries will alter the story in future years,
: so expect the Big Histories of ten or 20 years from now
: to look very different from today's.
: But this isn't discouraging because, like,
: knowing everything would be boring.
: There's a lot left to discover and at the current pace
: of scientific inquiry, many of those amazing discoveries
: will await us in our lifetime-- or at least in your lifetime.
: - Whether it be World War II or the life of Abe Lincoln,
: all histories ultimately start with the Big Bang.
: Yeah, it would be silly to start
: your typical World War II textbook with the Big Bang,
: but it would be about 100 trillion trillion times
: more ridiculous to say the Big Bang,
: the mother of all historical events, was not history.
: And that's why Big History reaches
: into the lives of every person on this tiny speck of dust
: we call home regardless of nation, class, or creed,
: and forms our common story.
: in which we'll be looking at the history of, like, everything.
: I'm talking about 13.8 billion years--
: from the Big Bang to now.
: I mean, in this series, we are literally going to attempt
: to tell you the story of what Douglas Adams famously called:
: >> Mr. Green, Mr. Green!
: That's not history, that's science.
: And science is for nerds.
: Oh, me from the past, things would be so much easier
: for you if you would just accept that you are,
: in fact, a nerd and that's okay.
: I mean, look at this picture, dude.
: Anyway, academics often describe history
: as, like, all the stuff that's happened
: since we started writing things down,
: but they only start there
: because that's where we have the best information.
: And, yeah, I think that the advent
: of writing was a huge deal, obviously,
: but as a start date for history, it's totally arbitrary.
: It's just a line we drew in the sand and said,
: "Okay, history begins now!"
: In Big History, we're going to start history
: when it really starts-- at least, we think--
: at the creation of the universe.
: And we're going to end that story where it ends.
: Please let that be after I die.
: Well, I guess it will definitely be after I die,
: it's just, I want it to be a while after I die.
: So we're even going to terrify traditional historians
: by using physics to make some predictions about the future
: and we're going to end many trillions and trillions
: of years from now when the universe itself--
: spoiler alert-- dies, at least in a manner of speaking.
: Hey! I'm not John.
: If you're thinking we look a little bit the same,
: that's because we're brothers.
: I'm Hank.
: Anyway, if you want to learn the 13.8-billion-year history
: of the universe in the same amount of time
: that we usually cover the 238 years of American history,
: you're not going to get the same resolution.
: Of course, knowing the names and dates
: of American history is important,
: but we just can't do that in Big History.
: As you zoom out, you see a lot more of the picture.
: The details get a little fuzzy, but we quickly realize
: that history is everything-- cosmology, geology,
: biology, social sciences, literature, physics.
: Everything.
: You might think that such a scale would be filled
: with way too much detail,
: but the amount of detail an answer requires depends
: on the nature of the question.
: Some questions can only be explored by zooming out.
: That is what Big History does.
: Speaking of zoomed out, this is"Earthrise,"
: one of the most famous photographs of all time.
: William Anders, an Apollo astronaut,
: took it in 1968.
: From the surface of another world,
: we see our planet as a little ball in space.
: No borders, no people, no buildings,
: just oceans and clouds and continents
: being shined upon by the sun.
: That sheer expansion of scale gives me perspective.
: It lets me imagine all the complexity of life on Earth,
: from the gasoline engine that powered my trip
: to the studio, to political instability
: in Nepal as part of a thriving, living, teeming mass of life
: loading in the emptiness of space.
: So what that photograph does for physical space,
: Big History aims to do for everything.
: I mean, we want to contextualize all of existence.
: We want to outline the most powerful
: and important breakthroughs, the tremendous scale of existence,
: and how we know what we know, and why we're sure we know it.
: All right, let's go to the Thought Bubble.
: So, the universe is big-- like, really big--
: and it's also old-- like, 13.8 billion years old.
: Which is enough years that there is no way
: to actually comprehend it, so let's just compress
: that age to 13 years--
: small enough that our puny brains can handle it.
: On that time scale, the universe would have begun 13 years ago,
: in 2001.
: George W. Bush had just been sworn in as president.
: Most Americans on the Internet were connecting
: to it with dial-up modems.
: Right, so the first stars and galaxies
: would have formed 12 years ago, but seven and a half more years
: would pass until the earth formed, about 4.5 years ago.
: Move a little bit up to four years ago--
: that's when the first single-celled life formed
: on Earth.
: Then leap forward nearly three and a half more years
: before the first multicellular organisms
: and the Cambrian explosion...
: What I'm trying to explain is that all complex life
: on Earth is a fairly recent development.
: Like, on this scale, the dinosaurs went extinct
: about three weeks ago-- roughly the last time
: I changed my Facebook status.
: Humans and chimpanzees split
: from their last shared ancestor about three days ago.
: The first homo sapiens emerged 50 minutes ago,
: roughly the last time I checked my email.
: We left Africa 26 minutes ago.
: The American Indians reached the Americas six minutes ago--
: roughly the last time I check my Twitter.
: We invented agriculture five minutes ago,
: Ancient Egypt three minutes ago, the Black Death 24 seconds ago,
: The Industrial Revolution, six seconds,
: World War I, two seconds.
: The Cold War, the first man on the moon, your birth,
: the internet, the Big Mac, all within the last second.
: But in many other ways, complex life
: and humanityareexceptional.
: >> Thanks, Thought Bubble.
: Also exceptional, by the way, the Mongols.
: Okay, let's begin at the beginning-- the Big Bang.
: Hank, wait a second... whoa, whoa, whoa.
: I don't understand how we know that the Big Bang
: is really the beginning.
: Like, what happened before the Big Bang?
: Well, okay, theoretical physicists say
: that space and time are not two different things.
: They are two expressions of one thing: spacetime.
: And spacetime was created by the Big Bang,
: thus, time didn't exist before the Big Bang,
: so it doesn't make much sense to ask what happened before it.
: There was no "then" then.
: Of course, this, like many ideas in cosmology,
: doesn't really make any sense to our puny human brains.
: It's largely beyond our comprehension
: rather like explaining color to a blind person.
: We know that it's true because the math works
: and it explains our observations so elegantly,
: but it's so far outside of how we directly perceive the world
: that I don't think it's something
: even the most genius physicists are able to imagine.
: But, yeah, if you're going to do a chronological study
: of the universe, the creation of time
: is probably a pretty good place to start the story.
: So the Big Bang wasn't something that happened
: inside the universe, nor did it expand into some kind of void.
: It was literally the moment when both time
: and space were created.
: The thing that was banging was the universe itself.
: It was expanding from an unimaginably tiny point
: to an unimaginably large universe unimaginably quickly.
: "Unimaginable" is basically the subtitle to the story
: of the Big Bang, but then again, it's also kind of the subtitle
: to everything else in Big History.
: I mean, I can only do this occasionally,
: but sometimes you look outside and you're like,
: "Oh, my goodness, this is nuts!
: How did we get trees?"
: Needless to say, we will be talking about that.
: Anyway, the universe is a hard worker
: and it got most of the heavy lifting done
: in those first few seconds.
: For comparison, it takes me about 20 minutes
: after I wake up for me to even get myself
: into a standing position.
: But the universe is somewhat more efficient.
: In the barest fraction of the first second,
: the universe inflated
: from something many, many, many times smaller than an atom
: to about the size of a grapefruit.
: Like, think of it this way.
: In much less than a blink of an eye,
: if it had originally been the size of a tennis ball,
: it would have inflated to over 90 billion light-years across.
: This inflation theory has been well backed up
: by mathematics for a long time now,
: but it has recently received some staggering new support
: from the BICEP Project of the South Pole
: which sadly has nothing to do with my guns.
: Ten seconds after the Big Bang, the universe had expanded enough
: that the normal rules of the universe
: with atomic forces and gravity and electromagnetism
: that we know and love today were already in charge.
: All of the antimatter created in the Big Bang had combined
: with matter and annihilated itself leaving
: behind only one-billionth of the matter created in the Big Bang.
: And that billionth is everything.
: And I mean everything-- every grain of sand,
: every blueberry you will ever eat,
: every star that you will ever see.
: Everything.
: We're already tried to understand how big a billion is,
: but just pause to think about that.
: Everything--everything-- is one-billionth of the matter
: created in the Big Bang.
: (imitates explosion)
: The First Law of Thermodynamics is that
: matter and energy cannot be created or destroyed.
: Everything we have now, we had then.
: The matter that makes up your body right now has been around
: since those moments 13.8 billion years ago.
: It's simply changed form.
: After just three minutes, the universe was cool enough
: that the nuclei of atoms started forming--
: just hydrogen and helium back then, the two simplest elements.
: Keep those two in mind, however, because it turns out
: if you take a bunch of hydrogen and you wait, like,
: several billion years, you might just grow yourself some humans.
: Let's remember, at this time,
: the universe was still very, very hot.
: I don't want to use the world "unimaginable" too often.
: But it was unimaginably hot.
: The universe remained, like, an uber hot sea dominated
: by radiation, but then luckily it simmered down
: to a balmy 5,000 degrees Fahrenheit
: about 380,000 years after the Big Bang,
: allowing matter and radiation to separate.
: And remember:
: I mean, you are a somewhat firm bag of energy.
: In my case, I'm not that firm.
: So anyway, at 5,000 degrees Fahrenheit,
: radiation was finally able to move freely
: through the universe, and we see that radiation today
: as the end of the dark ages that followed the Big Bang
: and the beginning of a brilliant flash that we call:
: Which is a great name for a band.
: Physicists call it "The fingerprint of the universe"
: and it's one of the most important pieces
: of historical evidence we have for the Big Bang
: because CBR is everywhere.
: Tune your radio to a frequency that doesn't have a station,
: a portion of the static you hear is actually
: that cosmic background radiation being picked up by your radio.
: So you can literally hear the universe in its infancy.
: Sometimes it can be tricky to know what's true,
: especially when we're talking about stuff
: that happened so far in the distant past.
: That is why we created science:
: So just using your limited human senses, you might come
: to the same conclusion as 19th century scientists--
: that the universe is static, eternal, and infinite.
: Then, using our minds, if the universe is infinite--
: it contains infinite stars and it has always existed--
: then the night sky and the daytime sky for that matter
: would literally be filled with stars,
: so much that day and night would be indistinguishable.
: This is clearly not the case, so something must be amiss.
: The universe must either be not static,
: not infinite, or not eternal.
: So which is it?
: You know how when an ambulance drives towards you,
: the sound waves are compressed
: and the siren sounds higher pitched,
: and as it speeds away the waves are stretched out
: and the pitch is lower?
: It's the Doppler effect.
: Well, here's another name you've heard:
: Edwin Hubble.
: He realized that light does the same thing.
: Galaxies in stars moving away
: from us have their lights stretch out,
: making it more red, and stars moving toward us
: have their light compressed, making it more blue.
: Combined with the work of Henrietta Leavitt,
: which allowed us to accurately estimate how far away stars are,
: Hubble was able to determine that stars
: on the whole are flying away from each other.
: He discovered that the most remote objects
: in the sky were all red-shifted and were actually
: other galaxies beyond the Milky Way moving away from us.
: From here, he built upon the work
: of Belgian Catholic priest Georges Lemaitre
: who hypothesized that the universe began
: at a single point.
: Big Bang cosmologists wanted proof, though.
: They knew that the amount of radiation released
: by the Big Bang would be massive and they wanted to see it.
: It wasn't until the 1960s that it was found-- accidentally--
: by two guys working on an antenna
: at Bell Laboratories in New Jersey.
: They were trying to eliminate all the background noise
: from an extremely sensitive radio antenna,
: but they found this faint hum coming from every direction.
: They tried everything they could to get rid of it,
: including murdering the pigeons
: that kept pooping on the antenna.
: Kind of sad, but those pigeons, they gave their lives
: for one of the most profound discoveries in modern science.
: A conversation with a local radio astronomer led them
: to show their findings to an astronomer
: at Princeton who confirmed the existence
: of what had been predicted for years.
: The final piece of that Big Bang puzzle is that we can see it.
: Light has a speed.
: When we look at the sun, we're seeing the light
: that left it eight minutes ago.
: But if we look at something
: that's 13.8 billion light-years away,
: we're seeing the stuff that happened 13.8 billion years ago.
: That radiation has been traveling
: since the very beginning of the universe.
: Not only can we tell very clearly
: that there was just nothing there before that,
: we can now study that radiation to learn the sequence
: of events of the Big Bang.
: We can also see that the chemical composition
: of the early universe is what we'd expect to see.
: A lot of hydrogen, a lot of helium,
: and a tiny pinch of lithium.
: The rest of the period table had to wait
: for the fiery furnaces in the bellies of stars to be created.
: But more on that next episode.
: As far as we've come in the past century
: in crafting a history of the universe,
: there are still many things
: cosmologists have yet to discover.
: For instance, the universe behaves
: as if there's a bunch of matter in it
: that we can't see or detect.
: Galaxies' gravitation is affected by this matter,
: but it's otherwise completely invisible to us.
: Physicists call it "dark matter"
: but we have no idea what it is.
: But as in any historical endeavor,
: new discoveries will alter the story in future years,
: so expect the Big Histories of ten or 20 years from now
: to look very different from today's.
: But this isn't discouraging because, like,
: knowing everything would be boring.
: There's a lot left to discover and at the current pace
: of scientific inquiry, many of those amazing discoveries
: will await us in our lifetime-- or at least in your lifetime.
: - Whether it be World War II or the life of Abe Lincoln,
: all histories ultimately start with the Big Bang.
: Yeah, it would be silly to start
: your typical World War II textbook with the Big Bang,
: but it would be about 100 trillion trillion times
: more ridiculous to say the Big Bang,
: the mother of all historical events, was not history.
: And that's why Big History reaches
: into the lives of every person on this tiny speck of dust
: we call home regardless of nation, class, or creed,
: and forms our common story.