A Brief History of the Universe: Crash Course Astronomy #44


Hey folks, Phil Plait here, and for the past
few episodes, I’ve been going over what we know about the structure, history, and
evolution of the Universe, and how we know it. Now it’s time to put that into action. We
can use this knowledge of physics, math, and astronomy to figure out what the Universe
was like in the past, going all the way back to literally the first moment after it was
born. So, here you go: a brief history of the Universe: In the beginning there was nothing. Then there
was everything. Oh, you want more? It may seem a little weird to suppose that
we can understand how the Universe got its start. But it’s much like any other field
of science: We have clues, observations, based on what we see going on now. Knowing the rules
of physics we can then run the clock backwards and see what things were like farther and
farther into the past. For example, as I’ve talked about in the
past couple of episodes, the Universe is expanding. That means in the past it was denser, more
crowded, and hotter. At some point it was hotter than the surface of a star, hotter
than the core of a star, hotter than the heart of a supernova. And as we push the timer back
even farther we find temperatures and densities that make a supernova look chilly and positively
rarefied. A lot of what we know about the early Universe
comes from experiments done in giant particle colliders. When the cosmos was very young
and very hot, particles were whizzing around at high speeds and slamming into each other,
creating other subatomic particles in the process. That’s exactly what colliders do!
The higher energy we can give our colliders, the faster we can whack particles together,
and the earlier phase of the Universe we can investigate. That’s one of the main reasons
why we keep making ‘em bigger and more powerful, to test our ideas of what the young cosmos
was like. So let’s wind the clock back. Looking around
us, peering into the Universe both near and far, what can we say about the beginning of
everything? When the Universe got its start, it was unfathomably
hot and dense. It was totally different then than it is today, because when you pump more
energy into something, the way it behaves, even its fundamental physical nature, changes. If you take a snowball and heat it up, it’ll
melt. We call that a phase change, or a change of state. Heat it more and it vaporizes, changing
into a gas. It’s still water, still composed of water molecules, but it looks and acts
pretty differently, right? When you heat something up what you’re doing
is giving it more energy. In a solid this means the atoms wiggle around more and more
until they break free of their restrictive bonds with each other, and the solid melts.
The atoms are still bound by other forces, but if you heat them more they break free
of those, too, and the liquid becomes a gas. Heat them more, give them more energy, and
the atoms whiz around faster and faster. Heat them to millions or billions of degrees, and
the atoms themselves fall apart. They collide so violently they can overcome the hugely
strong forces holding their nuclei together, and you get a soup of subatomic particles;
electrons, neutrons, and protons. Heat them more and even protons and neutrons
will collide hard enough to shatter into their constituent subatomic particles, which are
called quarks. And as far as we know, quarks and electrons are basic particles, so they
can’t be subdivided any more. Maybe you can see where I’m going here.
As we wind the clock backwards, the Universe gets denser and hotter. At some point in the
past it was so hot that atoms wouldn’t have been able to hold on to their electrons. A
little farther back and it was so hot that nuclei couldn’t stay together, and the Universe
was a small, ultra dense ball of energy mixed with neutrons, protons, and electrons. Go a wee bit farther back and even that changes.
Neutrons and protons couldn’t form, because the instant they did they’d whack into each
other hard enough to fall apart. The Universe was a sea of electrons and quarks. The cosmos was a bizarre, unfamiliar place
back then. Even the basic forces we see today — gravity, electromagnetism, and the two
nuclear forces responsible for holding atomic nuclei together as well as letting them disintegrate
in radioactive decay — were all squeezed together into one unified super force. Like the snowball melting and vaporizing,
each of these moments in the history of the Universe was like a phase change. The very
nature of reality was changing, its laws and behavior different.
At some point, we go so far back, so close to that first moment in time, that our laws
of physics… well, they don’t break down so much as say, “Here Be Dragons.” We
just don’t understand the rules well enough to be able to say anything about that first
razor thin slice of time. How far back are we talking here? If we call
the instant of the Big Bang “time zero,” then our physics cannot describe what happens
in the first 10-43 seconds. Now let me just say, only semi-sarcastically,
that that’s not so bad. The Universe is 13.82 billion years old, so being able to
go back to that very first one-ten-millionth of a trillionth of a trillionth of a trillionth
of a second is a massive triumph of physics! What happened after that fraction of a second
is better understood. The Universe expanded and cooled, the four forces went their separate
ways, and the first basic subatomic particles were able to hold themselves together. This all happened
in the very first second of the Universe’s existence. Three minutes later — yes, three minutes
— the Universe cooled enough that these subatomic particles could start to stick together.
For the next 17 minutes, the Universe did something remarkable: it made atoms. It was still ridiculously hot, like the core
of a star, but it’s at those temperatures that nuclear fusion can occur. For a few minutes
the particles smashed together, forming deuterium, an isotope of hydrogen, helium, and just a
smattering of lithium. A little bit of beryllium was made as well, but it was radioactive,
and rapidly decayed into lithium. Then, at T+20 minutes, the Universe cooled
enough that fusion stopped. When it did, there was three times as much hydrogen as helium
in the Universe. This primordial ratio is still pretty much true today. When we measure
the Sun’s elemental abundance, we see it’s roughly 75% hydrogen, 25% helium. At this point the Universe is still hotter
than a star’s surface, but it’s also still expanding and cooling. As it does, structures
start to form as the gravity of matter can overcome the tremendous heat. These will become
the galaxies we see today. This is important and a bit weird, so I’ll get back to it
in a minute. The next big event happened when the Universe
was at the ripe old age of about 380,000 years. Up to this point, electrons couldn’t bond
with the atomic nuclei zipping around; every time they did it was so hot that random photons
would blow them off again. The Universe was ionized. But then, after 380 millennia, it had cooled
enough that electrons could combine with protons and helium nuclei, becoming stable neutral
atoms for the very first time. We call this moment “recombination.” This was an important event! Free electrons
are really really good at absorbing photons, absorbing light. When the Universe was still
ionized, prior to recombination, it was opaque. A photon couldn’t get very far before an
electron sucked it up. But after recombination, the photons were
free to fly. The Universe became transparent! Why is this important? Because the light emitted at this time is
what we see as the cosmic microwave background today! Those neutral atoms emitted light;
they were as hot as a red dwarf star. Those photons have been traveling ever since, fighting
the expansion of the Universe, redshifting into the microwave part of the spectrum, and
seen today all over the sky. That background glow predicted by the Big Bang model has been
on its journey to Earth for almost 13.8 billion years! This light is incredibly important, because
it tells us what the Universe was like not long after it formed. For example, that light looks almost exactly
the same everywhere you look in the sky. It looks “smooth.” That tells us that matter
was very evenly distributed everywhere in the Universe at that time, and also that all
the matter had the same temperature. If there had been one spot that was denser, lumpier,
then it would have been hotter, and we’d see that in the background radiation as a
patch of bluer light. That’s pretty weird. When you look at the
background radiation from opposite sides of the sky, you’re seeing it coming from opposite
ends of the universe! Even back then, those regions of the Universe were separated by
vast distances, and had plenty of time to go their separate ways, change in different ways.
They should look pretty different. But they don’t. As telescopes got better, very tiny variations
in the light were found. But they were really teeny, only a factor of 1 in 100,000. In other
words, one part of the sky may look like it has a temperature of 2.72500 Kelvins, but
another spot is at 2.752501. The Universe had lumps, but they were far,
far smaller than expected. Something must have happened in the Universe to force it
to be this smooth even hundreds of thousands of years after the Big Bang. This led theoretical physicist Alan Guth to
propose a dramatic addition to the Big Bang model: At some point in the very early Universe,
the expansion suddenly accelerated vastly. For the tiniest fraction of a second, space
inflated hugely, far faster than the normal expansion, increasing in size by something
like a hundred trillion trillion times! We call this super-expansion “inflation.”
It sounds a little arbitrary, but it actually has quite a bit of physical foundation now;
in a sense it’s like one of the phase changes of the Universe that happened in that first
fraction of second dumped huge amounts of energy into the fabric of space-time, causing
it to swell enormously. Inflation explains why the Universe was so
smooth at the time of recombination: Space expanded so rapidly that any lumps in it were
smoothed out, like pulling on a bedsheet to flatten out the wrinkles. Inflation explains several other problems
in cosmology as well, and although the details are still being hammered out, the basic idea
is almost – pardon the expression – universally agreed upon by astronomers. The fluctuations we see in the background
glow now were actually incredibly small perturbations in the fabric of space at the time of inflation,
which got stretched by inflation to macroscopic size. These denser spots were seeds, eventually
growing even more, their gravity attracting flows of dark matter. Normal matter collected there too, condensing,
eventually forming the first stars about 400 million years after the Big Bang. Eventually,
those teeny little bumps from the beginning of the Universe became galaxies and clusters
of galaxies, now tens of billions of light years away. Our own galaxy, our own piece
of the Universe, started the same way, as a quantum fluctuation in space 13.8 billion
years ago. Now look at us. How’s that for an origin
story? There are still many unanswered questions
in our understanding of cosmology. What’s dark energy? What was the role of dark matter
in the early Universe? Where did the Universe come from in the first place? Are there more
universes out there? Hidden away where we can’t see them? If time and space started
in the Big Bang, does it even make sense to ask what came before it, or is that like asking
what’s north of the north pole? We don’t know the answers to these questions,
and trust me, there are thousands more just like them. But here’s the fun part: we might
yet be able to answer them! After all, even asking if the Universe had a beginning, let
alone what happened between then and now, was nuts just a century or two ago. Now we
have a decent handle on it, and our grip is getting better all the time. Science! Asking – and answering – the
biggest questions of them all. I love this stuff. Today you learned that the timeline of the
Universe’s history can be mapped using modern day physics and astronomical observations.
It started with a Big Bang, when the Universe was incredibly dense and hot. It expanded
and cooled, going through multiple stages where different kinds of matter could form.
It underwent a phenomenally rapid moment of expansion called inflation which smoothed
out much of the lumpiness in the matter. Normal matter formed atoms between 3 and 20 minutes
after the bang, and the lumps left over from inflation formed the galaxies and larger structures
we see today. Crash Course Astronomy is produced in association
with PBS Digital Studios. Head over to their YouTube channel to catch even more awesome
videos. This episode was written by me, Phil Plait. The script was edited by Blake de Pastino,
and our consultant is Dr. Michelle Thaller. It was directed by Nicholas Jenkins, edited
by Nicole Sweeney, the sound designer is Michael Aranda, and the graphics team is Thought Café.

Comments 100

  • What's north of the north pole? Polaris.

  • in the beginning there was something and now there are many things according to me….

  • science can not answer this question…..what is the first thing to ever exist and how did it get there. answer that one please

  • please make a video about general relativity

  • 0:26 to 0:29

    OH WOW SLOW IT DOWN PHIL,TOO MUCH INFORMATION

  • Does anybody know what quarks are made of? Are they made out of photons? Is CBR made out of photons? If matter won over antimatter why is a meson made out of a quark and antiquark?

  • Wtf you said gravity isnt a force, but why includes it in 4 forces?

  • Expanding into what? It's hard to wrap one's brain around the expansion into expansion, limitless space. As the word "expand" implies boundaries / limits.

  • The cosmic background radiation started on its journey through space long before the earth was formed. How come the light from the early universe didn't pass us by before we ever got a chance to look at it?

  • Kan ( THE UNIVERSE) Kuff ?

  • Phil Plait has a lot on his plate

  • People like you makes the my world better

  • Particle accelerater😂😂

  • Crash course a car transmission please Good Sir?

  • Love ya guys

  • My fav is Dark Matter

  • This is the future of learning. It’s fascinating how fast and efficient he is while he explains.

  • Yep! Somewhere in the far reaches of the Universe, there was a planet called the Seed Planet. Millions of years after the earth cooled, the seed from the Seed Planet, were blasted trillions of miles through space. Our little insignificant Earth is the only planet in which the conditions were just right, for the seed to take root. There are millions of different plant life on our planet, that could not have survived the hot, hostile environment, BELIEVED to have existed in the beginning. The beliefs of SCIENTISTS, requires more magic than God. I can more easily believe in magic, with a magician than without. The main difference is that God is a CREATOR, not a magician. Now go ahead and insult me. Just so you know, beforehand, stupid people don't get to me.

  • Make a video on Large hadron collider

  • Is time also expanding with space?

  • I have no idea what he's talking about, but this is really cool.

  • You talk about heating gas but don't talk about plasma what is this ._.

  • Anyone notice that those hands do not stay still

  • Ehm if the universe started 13 billion years ago then why is our year the year 2018 and not 13 000 002 018?

  • If you guys want to watch him more watch how the universe works, love that show

  • Young Universe: It's not a phase moooooom!

  • Extremely clear presentation. I'm going to recommend this one for my young nephew.

  • PHIL YOU ARE AMAZING AND THIS SERIES IS AMAZING

  • "In the beginning, there was nothing". This is incorrect. we have no data to indicate if there was nothing, or something before our universe was born.

  • Let there be light!
    sound familiar?

  • my kind sir plz dont end the series

  • so why did it cool in the beginning, i mean things only cool if the have something colder next to them to pass the energy on to. where did the energy get passed to for the stuff to cool?

  • this should be required viewing for anyone trying to vote

  • SCREEEEEEEEAM OMG ASTRONOMY ISSSS SO BIGGGGGGGGG WHYYYYYYY

  • So i have a question about time counting: didn't you sad that time and gravity are the same thing? So just after the big bang, every think were so dense , shouldn't be the clock ticking really fast??

  • Gods made some dope stuff.

  • I've always thought the model predicts the universe's expansion to approach 0 as time approaches infinity; is this not current anymore?

  • Hey Phil, how would you like a chom-chom?

  • These scientists are weird. "Recombination" is actually "Combination". Neutral atoms could not exist before that cooling point, as explained in the narrative.

  • I've watched it more then once..lol

  • It should be called light matter rather than normal matter.

  • I like how he explain the timeline of the Universe. I was very amazed how Universe begin. From nothing to Everything. Ugh!! There's a lot of question in my mind but thanks to your video. 😁

  • Had I encountered such an enthusiastic teacher as Phil Plait way back, I would've gone and studied one of the fields in hard science even though I'm not such a smart guy. My curiosity grows more as I'm learning something new.

  • Again, in order to be a good teacher, one of the most important things to have is enthusiasm and belief in what you're teaching!

  • 7:20 – Maybe it's just an optical illusion, but doesn't that look a bit like Earth?
    (Oceans in red/orange, continents in blue)
    I almost can see Africa and South America there…

  • It's bizarre to me that the universe is only a dozen or so billion years old. How can that be? What was there before the universe? I always thought it was infinitely old, I think perhaps the the universe AS WE KNOW IT, is so young, but the universe itself is infinite. Maybe the universe used to be like it is now, then collapsed in on itself, then expanded again. Maybe it's an endless cycle. I don't know.

  • Is his name Feel Played ?

  • Light bulbs: Upside down Cassiopeia??

  • ❤️❤️

  • How can I thank you sir for this wonderful videos and rich knowledge, Thanks a lot 🙏

  • Please please please if it's just a soup I will give everything I own every dime I make if you create life. Please I beg you create a dog cat
    And a human. Never gonna happen if you think rocks in a cave and some soup created us then your in denial

  • The universe is not expanding. The universe is infinite. You are confusing the "universe" with the "observable universe". Two totally different things. Since the universe was created about 4.323 298 86 × 10^16 s ago, thus we can only see 4.323 298 86 × 10^16 s times 299 792 458 m/s or about 13 x 10^24 m or 13 Ym. Anything beyond this distance would be invisible as the light leaving this region at the time of creation would not have reached the earth yet. The obserable universe is constantly increasing at a rate of 299 792 458 m for every second that passes.

    Creation was an explosion OF space, NOT an explosion IN space. All of the objects in space are in motion so when we look back towards the edge of the observable universe what we see the way it was when the photons first left that point and not how it is now do to the movement of all of the spacial bodies.

    I'm surprised you don't understand this.

  • How is the Big Bang true if that much matter in one spot would collapae into a black hole?

  • Can you do a video of how the stars became galaxies?

  • Quirks and stuff!

  • Once the universe ends… Everything will go back to atoms which it would go back to time zero until the cycle will repeat.

  • Is it 2.752501k or 2.72501k!? I can’t sleep not knowing. You said one thing your pop up video said something different! The agony

  • Love watching these videos while I play Elite: Dangerous. A bit of educational stuff while I pretend to be a space trucker

  • The Universe is timeless

  • just like we can look at cosmic microwave background radiation, shouldn't it also be possible to look at wavelengths that are not as redshifted, and look at the universe with the first stars being born?

  • Not even science can explain how God created the universe. We’re not just here from an explosion that happened from nothing. God is the creator of the universe, the ocean and the earth.

  • hey can you create crash course for Christians like me.

  • Excellent video, Phil. You’re the best.

  • Damn girl, are you the beginning of the universe? 'Cause you're hotter than the heart of a supernova

  • this video made me feel unfathomably hot and dense

  • The universe is a giant loaf of cosmic bread.

  • It has been said that there cannot be "nothing". That even a cubic meter of anything is "something" at least in terms of space/time.

    So that, "in the beginning there was nothing" may be off.

    In terms of the hypothesis of the multiverse, could that be "in the beginning before our something there was something else, not our something." ????

  • Do the high speeds of subatomic particles (brownian motion?) exceed the speed of causation ("C" which is also the so-called speed of light)???

  • May I add that the Big Bang was silent? There was nothing for sound waves to bounce off of, therefore, no sound

  • Nothing was never nowhere…

  • Could someone please explain to me in other words the information presented in the video from minute 7 to 8?

  • Just maybe paralel universes do exist and maybe one reached the end of it’s life by forming such a massive black hole that engulfed all matter and acting like a compresser it squized it so tight and eventualy ejected it into a nearby univers that was us

  • i love this show. and i love how Phil delivers it every episode. thanks to this all of my question about the universe has multiplied to even more hahaha.

  • Pace of most of Phil's episodes is very fast, but this one is pretty incomprehensible.

  • We know what gravity does, but what IS gravity and can it be manipulated??

  • Let's say the Big Crunch Theory (One way the universe will end) is real, and the smaller it gets, the more the heat of stars and everything is put into a smaller spacez which ultimately gets so dense, it creates a singularity like the one that started the big bang. But it's SO GOSH DARN DENSE that it blows up to create another universe. I may have just figures out the Universe. And maybe the heat to make this possible is 42 quadrillion degrees Celsius! OH MY GO-

  • how is the universe 13.82 Billion years old and we can see light of galaxies 45 Billion light years away?

  • Lets say we figured out, all these questions, can't help to 🤔 what will be next for us..are we gonna live "Happily Ever After"?

  • What are antimatter?

  • Oh, is this a coincidence? I made a similar video (this one, it's 1500x better, mine is not) but such big coincidence!

  • So if we go a million years further can we observe our right-now- universe in Cosmic microwave background? (Assuming that universe is not expanding)

  • Ancient civilization and societies have their own tales of creation and universe like Mayans for e.g. many else can also be noted, are they lies and have no truthful base or modern science is not referring it

  • Something I was taught back in high school, but am not sure is true now:
    If you were able to travel to the edge of the universe, and go beyond, you would reappear on the exact opposite end of the universe, like Pac Man screen wraps.

    Is this true?

  • I love Phil more anyone here on crash course

  • Before watching any further. Yes, i want more.

  • 3% observation, 97% blind hubris

  • Here's a question I've always been wondering
    How can the universe be 14 billion years old and yet be 90 billion light years across???
    And how can the big bang even be initiated to start off our universe???? So many questions to so many science theories…

  • 6:15 to 7:30 is literally what the entire Christian Bible is about if we used the creation of light as a parable. If you know bible history, you’ll know what I’m talking about.

    Typology is a wonderful thing.

    “In the beginning was the Word (universe) and the Word was with God (outside of universe), and the Word was God. He was with God in the beginning. Through him all things were made; without him nothing was made that has been made. In him was life, and that life was the light of all mankind. The light shines in the darkness, and the darkness has not overcome it.

    The true light that gives light to everyone was coming into the world. He was in the world, and though the world was made through him, the world did not recognize him. He came to that which was his own, but his own did not receive him. Yet to all who did receive him, to those who believed in his name, he gave the right to become children of God— children born not of natural descent, nor of human decision or a husband’s will, but born of God.”
    ‭‭John‬ ‭1:1-5, 9-13‬ ‭NIV‬‬

    This is why the Son is bound by time (doesn’t know the day or hour the universe will end, just knows it’s near, and only knows what His Father tells him) and the Father is outside of time.

    His people have grown from the size of a mustard seed and expanded incredibly fast to many nations, just like the universe.

    As fast as the light entered the universe for the first time will be as fast as we are to leave as well. That’s why all Jesus knows is that it is near.

  • Anyone who thinks all of these countries, and billions of dollars are being invested into a particle collider so scientists can learn more about the early subatomic universe, well that person is about as dense as a black hole. There is clearly a weapon being searched for at the end of the subatomic rainbow.

  • Perhaps reality in that sense truly is a projection: from a tiny spot to everything at this moment… and therefore an illusion 🙂

  • this is literally way too big for my tiny human mind to understand, but that's why i like Astronomy!

  • Why u dislike

  • I call shenanigans

  • If Walter white was a astronomer

  • I don't buy this garbage

  • As per usual, great vid Well done for simplifying it to the point that I can follow. Thank you

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