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.
De la lección
From Daily Life to the Big Bang
Understanding the Universe in which we live and how to probe it can begin with simple daily life experiences such as night and day and the four seasons. Starting from these observations, we will take a journey from our local Earth at the present time all the way to the edge of the universe and back to its birth, learning the techniques and findings in modern physics that provide us this understanding.
Director, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), Todai Institutes for Advanced Study (TODIAS) MacAdams Professor of Physics, University of California, Berkeley
So this is the image of Andromeda galaxy that
is a 2.5 million light years away from us.
But it's our closest neighbor so they as big as our own galaxy and we can
observe the stars, individual stars in this Andromeda
galaxy because it's actually pretty close to us.
2.5 million light years away is pretty close to us in the universe.
And you can again study how quickly these stars move about.
In the Andromeda galaxy you'll find that they're moving very fast.
So even if you put the entire mass of all the stars combined, you can observe in
your telescope together, that wouldn't provide enough force of
gravity to keep these individual stars inside Andromeda galaxy.
So there must be some mass that's providing extra force
of gravity beyond the stars you can observe in your telescopes.
So what could that be?
So here is actually data that shows that you do
need more mass than that meets your eye in the telescopes.
So the data points here shows how quickly the stars are moving
as a function of the distance from the center of Andromeda galaxy.
You really see that something is wrong with this, right?
So, as we saw in the solar planet the solar system, the farther away you are,
the speed has to go down.
But, it looks, you know, it's more or less the same, no
matter how far you away, you move out from the center of Andromeda.
And if the stars are the only source of
gravity, you can, you know, count them up using telescope.
You see that the curve has to fall down like
this, just like what it was in our solar system.
So there's the big difference between the speed the
star's actually moving with, and the speed, the stars can actually be
supported by the force of gravity due to other stars inside the galaxy
This difference has to be explained by something else.
And we call that the dark matter.
There must be other form of mass or matter in a given galaxy
that provides even stronger force of gravity, but we don't see it, so we call that dark.
And as far as Andromeda goes, it's part
of this system we call the local group, which consists of more than 40 galaxies.
Most of them are very small, or dwarf galaxies.
And Andromeda and our Milky Way galaxy are the biggest, twins in this local group.
And because Andromeda at the 2 and a half
million light years away is just a neighbor from
us, we're actually pulling with each other with also a gravity and we're
going to actually probably collide in 4 and ahalf billion years from now.
And that sounds like a really scary thing but it turns out if
you look out into space, you see many galaxies actually colliding and merging.
So this is a picture of two galaxies getting pretty
close to each other, by the mutual pull of gravity.
This is different pair of galaxies, which have started to merge.
And this another picture that shows the
two galaxies have pretty much merged already.
One center, the other center, and they are now merging into a single galaxy.
So this kind of collision and merger of
galaxies actually happen all the time in the Universe.
And, and it does, it sounds scary, but it's actually a good thing.
So in this picture you
see this blue, twinkling lights all over in this picture.
And that's the way the new stars are born.
So if you let the galaxy live on it's own, then eventually it would age.
And then, just fades away.
But if the two galaxies collide and merge, then gets rejuvenated.
It gets young again.
And new stars are born.
So that's actually a very interesting lesson we
may draw about a human life as well.
But anyway, back to the discussion of
how quickly revolve around the center of galaxies.
You can actually measure these things fairly precisely these days.
So this is yet another galaxy which you can
look, you know, fairly, fairly out there, edge on.
And you can map out the velocity of individual
stars again as a function of distance from the center.
And just like in the solar system, you would expect that it would
fall down like 1 over square root r, but it stays fairly flat.
So this kind of plot is called rotation curve of galaxies and,
and all the rotation curves we have measured today, basically they look flat.
That means there's extra mass than beyond we can see.
Yet another galaxy, same
deal. Flat rotation curve.
It doesn't go down like one of a square at all.
So putting all this, this, data together, we
came to understand, the real nature of galaxies.
What you can see in telescopes, is only this disk,
which is, sort of at the center of this whole thing.
That this is the only thing you can see.
But around it, you have this blob, or sea, of dark matter, you don't
get to see.
And, thanks to the gravity of the sea of dark matter, so you live in this
ocean of dark matter, you are trapped inside,
and that's how you can happily move about.
Without this dark matter, the galaxies would just fly apart, and
should have disappeared many billions of light, billions of years ago.
And the galaxy may extend over, like, you know,
a hundred thousand light years, but the, the dark
matter will just keep going over millions of light
years and, and that's the real nature of our galaxies.
So now is the question to you, how do we know if this is
a right picture, and what goes beyond
this, this distance of millions of light years?
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Hitoshi MurayamaDirector, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), Todai Institutes for Advanced Study (TODIAS)
