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2-5 Birth of Elements V

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От Большого взрыва до тёмной энергии

Токийский университет

4.8 (оценок: 1,533) | Зарегистрировано учащихся: 40K

We have learned a lot recently about how the Universe evolved in 13.7 billion years since the Big Bang. More than 80% of matter in the Universe is mysterious Dark Matter, which made stars and galaxies to form. The newly discovered Higgs-boson became frozen into the Universe a trillionth of a second after the Big Bang and brought order to the Universe. Yet we still do not know how ordinary matter (atoms) survived against total annihilation by Anti-Matter. The expansion of the Universe started acceleration about 7 billion years ago and the Universe is being ripped apart. The culprit is Dark Energy, a mysterious energy multiplying in vacuum. I will present evidence behind these startling discoveries and discuss what we may learn in the near future. This course is offered in English.

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4.8 (оценок: 1,533)

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LF

Feb 29, 2016

This was an excellent course! It was very interesting, well-explained, and easy to follow (even for someone like me, who isn't necessarily up-to-date on mathematics). Can't recommend enough!

VK

Jan 02, 2017

Maybe the best course I have taken so far. Very interesting subject great professor and perfect distribution of content. Would like to see another course by professor Murayama in the future.

Из урока

Birth of Elements and Higgs Boson

We are made of chemical elements. So one of the fundamental questions “where do we come from?” leads to another question: “how were elements born?”. This is related to the Higgs Boson, an important particle in answering this question which remained elusive until its discovery was recently announced on July 4, 2012. In this module, we will learn recent research outcomes on these topics.

2-1 Birth of Elements I5:45

2-2 Birth of Elements II11:26

2-3 Birth of Elements III6:10

2-4 Birth of Elements IV9:37

2-5 Birth of Elements V14:10

Преподаватели

Hitoshi Murayama
MacAdams Professor of Physics, University of California, Berkeley

Текст видео

So to sum it up, what we have discussed so far, the

big bang produced only hydrogen, and helium, and no other heavy elements.

There was just a little bit of heavy ones, but

you can pretty much ignore them, so to a good

approximating just hydrogen, and helium, and that lead to the

formation of force stars, and inside the stars you form.

Bigger elements like carbon, oxygen, silicone, all the way up to iron, and

as long as these elements are stuck inside the stars, we still don't get

to use them to form a body, so it doesn't explain where we came from.

But fortunately, as you saw on a previous, few minutes,

these stars can actually explode at the end of their life.

And that would release a lot of stuff back into the outer space.

And then, what had been synthesized at the core

of these stars gets released like carbon, nitrogen, oxygen

and iron that eventually form a body.

So what is believed, is that our sun is probably the third generation star.

So we had the initial stage of the

star formation based on the hydrogen heating alone.

Some of it exploded, which leads to more stuff, you

accumulate them, form the stars once again, they also reach

the end of life exploded, and the sun use that

kind of material to form the initial core of the star.

And that led to our own existence.

So the explosion star, like this is very important

because that will be the origin of our own existence.

Origin of some Nobel, Nobel prize as well. And so we are literally stardust.

So we came from the star. That is what we are actually made of.

But of course you should still ask the question, is that really true?

Is there any evidence for that?

So this is the famous one called crab nebula and is believed to be a reminent of

the past supernova that happened actually very recently in year 10, 40, 54.

The reason we know the year.

Is that there is some historical record in old Japanese literature, by Teika

Fujiwara and in this old manuscript, you find a reference to a super nova.

What the literally says is guest star.

There is a star, he could see which wasn't there before, that's

why it's a guest star and that was a super nova explosion.

And these days you can study the object, in many different ways.

By using optical telescope, just the usual telescope, you can observe xrays.

You can use infrared light like when we talked about

seeing big the black hole at the center of the galaxy.

And radio, which we have

used also for the

[INAUDIBLE]

observed the big bang itself.

By combining information from these different techniques you

can bet a better understanding of what is

going on inside this object And this time

sequence of the X-ray textures coming from Chandra satellite.

By putting that into a movie file, you

can see that there's still a throbbing going on.

So, this happened like thousand years ago when it exploded, but is still

releasing material.

That you can see in this throbbing dissolute movie and we can see that

the supernova does release material into space and that's how we can do exist.

We believe that something like that is

going to happen soon, actually very nearby.

Do you know which star is Beetlejuice in this picture?

You probably can identify Orion constolation, Orion.

So

Betelgeuse is on the left top corner of this Orion constellation.

And it weighs as much as 20 times the mass of the sun.

And it's fairly nearby.

It's only 640 light-years away.

So by now, listening to my lectures you would immediately notice that

this is actually a very close distance on the scale of the universe.

And if the star is disclosed, you can even measure how big it is

just by looking at it using telescope. This is the data that shows that the

apparent size of Betelgeuse has shrunk by 15%, in a mere 15 years.

Something is really happening with this star.

So you can even observe the surface of the star, when the star is so close.

And what you see in this picture here, is that the surface

is also really throbbing now.

You'll see parts that are swelling up, you see parts that's sinking in.

So you see that surface is very dynamical at this moment.

So that really show us that's somethings going to

happen to this star pretty soon Pretty soon

the case may mean next 10000 years, but

you know explosion may happen tomorrow as well.

We don't really know we can predict, but it's clear that this going to happen

sometimes soon into a big supernova. So putting thing in perspective

the way we can tell, how old a star is? And what it is the stars made of?

Well we can do, again going back to this sort of prism, by measuring the

spectrum of colors coming from star, you see

these lines, which shows some colors are missing.

And this is called spectroscopy,

which is very important technique in studying the astronomical objects.

This particular star, which is actually our sun, has a lot

of these lines which shows that is has many heavy elements.

These stars are called population one, a

lot of metals, elements heavier than helium.

This is clearly contaminated by the past super nova explosions.

If you look hard enough, sometimes you find stars which seems much cleaner.

Less contamination of these heavy elements.

So they are called population two stars.

If you go way back into the beginning of the

universe, there must have been what is called population three stars.

Which are made of Hydrogen and Helium alone,

without any contamination from the previous generation of stars.

We haven't

found those, but people still looking. So, now we comes to this

question, how do we know that big bang produced hydrogen, helium, but not more?

We need a different tool, as we talked about.

What we can look back to the point when universe was only 380,000 years

old, by using radio telescopes, because we can detect the cosmic micro background.

Which is the start light coming from the big bang itself we talked about it.

But there's a wall, right, you can't go beyond

that using telescopes, we can't see through that wall,

we need some different technique to understand what's

going on on the earlier moments of the universe.

So you, we use a different tool, called particle accelerator.

The idea is very simple, universe is so dense and hot, we'd like to understand

what happened back then, so there's something we

can try to do in our own laboratory.

We try to create an environment

where similar reactions can be created artificially.

Which must have happened early on, at the beginning of the universe.

So that way, we can go back to the

moment, when the universe was only three minutes old.

What we do is bring in literally, neutrons

and protons together, smash them against each other, And see if they can form

something heavier, like helium. So we can try to redo this

kind of reaction that happened right after big bang, in our own laboratory, and

that's the way we try to go beyond this wall of 300,000 years old universe.

So, by studying these reactions in the laboratory, you can

measure the probability for a reaction like this to happen.

And once you've measured that you can make a prediction, on how much

of the helium must have been synthesized at the beginning of the universe, and

that process is called Big Bang Nuclear Synthesis.

And that would give you a prediction, that the ration

of hydrogen to helium in our universe must be roughly 3:1.

Indeed you can measure the ration of

hydrogen, helium by looking at, again, the spectrum

of light coming from the far away objects, and this 3:1 ratio agrees very well.

With observation. So that's how we can compare,

what you would predict based on what you learn from particle

accelerators versus what we can actually go back, and see using telescopes.

And if they match up, that would give us enough,

confidence that we understand what happened in the Big Bang itself.

So by putting this information together, I you can put them

in computer, and simulate how the first stars had been born.

And we will come back to this later,

but at the initial stage you don't have that much concentration

of gas, you have sort of a big blob of dark matter.

We briefly talked about it in the first lecture.

Once we have this blob of dark matter, gravity

force the ordinary gas in and it starts to

form this cloud of gas, or the molecular cloud,

and the core of the molecular cloud further collapses and

start producing something rather dense. And that would eventually become a star.

You can reproduce this process in a computer disc days.

And if you go further with this computer simulation, then this initial form of

star would start to accumulate more stuff from outside, by a gravitational pull.

But once they start accumulate so densley, then it starts to actually eject

it off.

It was sort of blowing out, by the

reaction, so that's something you can see in

this computer simulation, so for a while dust

just settles on the surface of this protostar.

It's not quite a star yet, but as it keeps accumulating on

the surface, you see this ejection of material, in the polar direction.

So it stops growing at

that stage, because whatever settles in further gets

blown out, so the stars wouldn't grow anymore.

So what do you learn is that, the first

stars can grow only up to like forty solar masses.

But that is big enough to synthesize the elements all the way up to Iron at

this stage, and that's how I believe that

initial elements have been synthesized inside the stars.

So, going back to the discussion

we had on the very beginning, we start with only hyrdogen and helium.

So we ask the question, where we could have

possibly come from because we need carbon, oxygen and son.

And the answer turns out to be that they

were built in stars, and we are the star dust.

But, you might have been listen carefully to me and ask the

question, Well you told me that we can only go up to an

iron, can't go beyond that because you

can't release energy by shedding mass beyond iron.

That's at the bottom of this curve.

How can you further climb up the hill?

And we, we of course know that there are elements that are

heavier than iron, like what you might buy in a jewelery store.

So we need a mechanism, to produce those elements as well.

And indeed, if you look at the so

called abundance of these elements in a universe and that you do see all

these heavier elements, like silver, gold, platinum,

lead, they must have been produced somewhere.

And, you know, it is the nature of the

science, that you don't have answers to every question, yet.

So you have to be studied.

We don't quite know where they came from. Many of us

think, that these heavier elements have been formed when the star is exploding.

We talked about element synthesized that are core, explosion releases.

But explosion itself may be bring the reaction even further.

And explosion is such a dynamic process, that you

can even put energy in to let the reaction happen.

So presumably

that's the way these heavier elements have been formed.

But we don't know for sure yet, so that's clear you

might be able to provide further studies to prove this idea.

This is yet another curious fact if you

think about this, lot of important things have

been explaining, explained by the property of these

individual particles coming in together, like protons and nuetrons.

What we know, is that proton neutron have

very similar masses within only like 2 per mole.

Basically they are exactly the same mass to good approximation.

But if you think of possible universe, where

the proton may be say 20% heavier than neutron.

Heavier. E=mc squared means more energy.

So proton can then release energy by turning into a, a neutron

in that case.

So all the protons end up decaying, in neutron if it is heavier by 20 percent.

So if that's the case, even if you manage to synthesize

like helium nucleus, protons in the nucleus would decay into neutrons.

They're all electrically neutral.

So you don't end up with anything, that can

become the atomic nucleus at the end of the day.

So no atoms were possible at all.

So the very existence of chemical elements, actually hinges on the fact

that proton, and neutron are pretty much the same in their mass.

[INAUDIBLE].

So that's one, another mystery we don't quite understand.

Why are the masses of particles, designed in such a way, that

somehow all this important things that

would sustain our life would become possible.

And another question of course is that even if you do manage to form this atomic

nuclei, you still need electrons to go around them to form atoms.

So how were

the atoms possible, why was that possible?

And that's the next question, about the Higgs boson.

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