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  • 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 "life, the universe, and everything".

  • 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 gonna start history when it really starts - at least, we think

  • - at the creation of the universe, and we're gonna end that story where it ends - please

  • let that be after I die! Well, I guess it will definitely be after I die, just - I want

  • it to be a while after I die!

  • So we're even gonna terrify traditional historians by using physics to make some predictions

  • about the future, and we're gonna 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 wanna 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 gonna 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.

  • There are much broader historical questions in the story of the universe that can only

  • be explored by zooming out to the ultimate scale. 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 floating in the emptiness of space.

  • So what that photograph does for physical space, Big History aims to do for everything.

  • I mean, we wanna contextualize all of existence. We wanna 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.

  • Alright, 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 timescale, 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 multi-cellular

  • organisms in 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 fifty minutes ago, roughly the last time I checked my email.

  • We left Africa 26 minutes ago. The American-Indians reached the Americas 6 minutes ago - roughly

  • the last time I checked my Twitter.

  • We invented agriculture 5 minutes ago. Ancient Egypt? 3 minutes ago! The Black Death? 24

  • seconds ago. The Industrial Revolution - 6 seconds. World War One, 2 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 humanity are exceptional. Thanks, Thought Bubble! Also

  • exceptional, by the way, the Mongols!

  • Okay, let's begin at the beginning! The big bang!

  • Hank, wait a second! Woah, woah, woah, woah, woah. I- I don't understand how we know that

  • the big bang is really the beginning. Like, what happened before the big bang?

  • Well. Okay. Uh... Theoretical physicists say that space and time are not two different

  • things. They are two expressions of one thing - space-time. And space-time 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 gonna 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 twenty 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'd originally been the size of a

  • tennis ball, it would have inflated to over ninety 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 at 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 anti-matter 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've 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.

  • 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 wanna use

  • the word 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 thousand years after

  • the big bang, allowing matter and radiation to separate.

  • And remember, matter is just a more congealed form of energy. I mean, you are a somewhat

  • firm bag of energy. In my case, 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 Cosmic Background Radiation,

  • 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, that

  • elegant system for sorting out the facts from the fertilizer.

  • 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... But then, using our

  • minds, if the universe is infinite and contains infinite stars and it has always existed,

  • then the night sky, and the day-time 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 and stars moving away from us have their light stretched 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 - kinda 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 lead 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 periodic table

  • had to wait for the fiery furnaces and 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 twenty 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 Two 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 Two textbook

  • with the big bang, but it would be about a hundred 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.

  • See you next time!

Hi. I'm John Green and this is Crash Course Big History, in which we'll be looking at

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ビッグバンクラッシュコース ビッグヒストリー #1 (The Big Bang: Crash Course Big History #1)

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    稲葉白兎 に公開 2021 年 01 月 14 日
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