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.
4-2 Inflation and Uncertainty Principle II (Uncertainty Principle I )
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来自 The University of Tokyo 的课程
从大爆炸到暗能量
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从本节课中
Inflation and Dark Energy
At the very beginning, the Universe exponentially expanded during a period known as the cosmic inflation. Recent studies suggested that the Universe has entered into another stage of expansion, considered to be caused by 'mysterious' dark energy. In this module, we will learn about inflation, dark energy, and the possible fates of our Universe.
与讲师见面
Hitoshi MurayamaMacAdams Professor of Physics, University of California, Berkeley
Professor, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), Todai Institutes for Advanced Study (TODIAS)
So we talked abut Inflation almost like an ultimate free lunch, but the free
lunch comes with a catch as I said and, and that catch is uncertain principle.
It turns out that this uncertain principle is
a catch but is actually a positive catch.
It actually helps us understand the structure of the universe today.
So, it's based on this idea that physics is not always certain.
There is uncertainty
to it.
So this is actually an experiment people could do by firing electrons on a screen.
Just imagine that electrons have been fired by these guns, but you
don't know how to aim it really, so it's a random shot.
So you hold your gun.
You keep firing it, you know, wherever you can,
and you don't know exactly where you're aiming it.
So it's totally random.
And,
and suppose that there's a screen you would like to hit.
But there's another wall between the screen and you, which has two holes in it.
And if you keep doing it, you know, you would think okay.
When I fire a shot here, if I fire a gun here then that would hit the wall.
It wouldn't make it all the way to the screen.
Only when, when I fire a shot right in front
of this hole and then the bullet goes through the hole and hits the screen.
So, there will be many shots around here.
And if I do the same also down here.
If I shoot the gun right in front of the, of the
hole in the wall, then the bullets end up reaching the screen.
Which means again, we see lots of shots on here, but nothing in between.
Nothing up here, nothing down there.
And that's what you would expect.
Right?
And that's why we thought in, among
physics, physcists too for some four centuries.
So when physics was believed to be certain, when
you fire shot you know exactly where it's going to land.
But if you actually do this experiment with tiny object like electrons.
So if you look at the microscopic world,
that actually doesn't turn out to be the case.
So let's watch this video here.
Now, we are looking at the detector planes on the monitor.
Bright spots appear here and there.
These spots indicate individual electrons. Electrons are sent out only occasionally.
Therefore, the chance of finding one electron in the microscope is very small.
Not to mention, the chance of finding two. since electrons are
one by one as particles, we have to conclude that each electron must
have passed through at either side of the biprism, thus creating a
uniform distribution without any interference when accumulated.
Under such conditions do electrons form a uniform distribution.
But look! We begin
to see some fringes in the
perpendicular direction that looks like interference fringes.
Since this experiment lasted for more than 30 minutes, I have sped the movie up.
Interference fringes are now clearly visible.
Isn't that incredible? So each time you fire shot, you don't
know where it's going to land at all. It looks totally random to you, I believe.
But after a while, you see a pattern emerging.
And that pattern is something we physicists can predict.
So it's not totally random, there is certain regularity to it.
But each time you can predict.
So in that sense, physics is indeed uncertain.
You don't know exactly what's going to happen for one experiment.
But if you keep doing millions of experiments,
you can predict the pattern of the outcome.
So that's what a microscopic world actually does.
And to describe this kind of strange
situation we need something called quantum mechanics.
And that is the laws of physics that govern the microscopic world.
So, even though each electron is a particle, when you shoot
it, it lands at a very particular place because it's a point.
But when you see this pattern that emerged towards the end of the day,
it looks like actually waves, and this is an experiment that you can do.
So, if you have a hose, you shot water into the pond,
it lands here and there's another guy doing the same thing over there.
And each water shot into the pond will creat a ripple of waves.
It does it from here. It does it from over there.
But when the two waves overlap with each other,
and this is where you see these fringe pattern.
And this is called interference of waves.
And the word interference doesn't sound very positive, but what you
see is the regular variation in the depth of the wave.
And that is the effect of interference.
So what we, we saw in the case of the experiment on a previous slide
is that well, we think electron is a particle.
But by doing this experiment, we saw a pattern
emerging that shows the electron is actually a wave.
On the other hand, we always use the thing that the
light is a wave, but it also behaves like a particle too.
So a particle is a wave, a wave is
a particle, and that's what quantum mechanics is telling us.
And strangely
enough, when you remember the previous slide, then electron can
actually go through two different holes at the same time.
If there were only one hole, then electron knows which hole to
go through, then there was no possibility of this interesting fringe pattern.
So, when you throw an electron into that wall, one electron
actually passes through two wall, two holes at the same time.
Very counter-intuitive,
that, but that's exactly what this experiment has demonstrated.
So, if you actually measure the electron along a particular
location this way, you do see the fringe pattern emerging.
So that's what quantum mechanics does.
The laws of physics at subatomic scales has this uncertainty principal built in.
You cant predict what happens each time when you do the experiment.
But over time you find
a regular pattern.
And the only way we can make sense out of this experiment is that
you have to accept the fact, a particle, like electron behaves like a wave.
Well, a wave like a photon behaves like a particle.
And once you know this, you also learn something else.
Namely, that if electron is a wave, then a wave when squeezed into narrow space.
The wave gets amplified.
For example, this is why tsunami equals such a disaster after an earthquake.
When a wave comes into narrow valley, or narrow bay, it's confined to small space
and the waves amplify and cause devast, devastation
in, in, in some parts of the world.
So, when you're thinking about small space,
wave tends to get bigger, and that's exactly
what inflation does.
When you're in, during the inflation, and suppose
you're looking at an object just next to you.
But because the universe is getting stretched out so rapidly, what you
thought was your neighbor is now gone all the way beyond some distance.
So you feel like you are being near-sighted at the moment.
You can only see some things that are very, very close to you.
So you're kind of confined in a very narrow space.
And this constant H we talked about before,
that tells you how quickly the universe expands exponentially.
And that tells you what, how big this size of a space is.
So during the inflation, you're really narrow, near-sighted.
You, you, the only things that you can see are things around you.
And because you're confined in a small space, now the wave is amplified.
Namely, there's a big uncertainty.
And that's how,
during inflation, these quantum effects show big
uncertainties, and therefore, big wakes of waves.
And you can simulate this on a computer So, when you think
of the vacuum, you think it's a totally empty nothing in there.
Right?
But when you do the computer simulation using this
quantum uncertainty principle, vacuum is not empty, but it's active.
It's like this.
So energy is bubbling in and out all the time.
So if you're here, you may borrow energy for
some time, but you have to gree, give it back.
Or maybe you lend some energy to others, you need to give it, take it back again.
But as long as everything works out in the end by conserving energy, it's okay.
You can lend energy.
You can borrow energy, and vacuum, what we think
is empty is doing this actually all the time.
So if you put these things together, what would happen?
So you have this vacuum, which is lending and borrowing energy all the time.
And then you also have this inflation that is stretching out the universe so quickly.
Now, if you put these things together, you find something really interesting.
So universe we think was born incredibly tiny.
Entire visible universe was smaller than 10 to the
minus 26 centimeters, much much smaller than the size
of an atomic nucleus.
So in that small confines of space, there was big uncertainty principle
at action, and you keep borrowing and lending energies all the time.
But, suppose you Lend energy to somebody else.
But then the universe gets stretched so quickly, the person you've lent your, your
energy to is now so far away, you're not going to get it back now.
Suppose you borrowed
energy from somebody else, then the person you need
to give energy back to is now gone forever.
Again, you're stuck with energy you borrowed.
So, combining uncertainty principle and this rapid
expansion of space, you are in the
end stuck with small variation of slightly
more energy here, slightly less energy here.
And you're not going to actually put them back
into a smooth space again because you cannot.
They're just so far away separated from each other.
So that's the way that you get stuck with the ripples of energies.
Here you have a little more, here you have a little less.
Only by a little though, we are talking about 1 mm, 1
mm ripple on 100 meter deep ocean, that's a 10 to minus 5.
It's very tiny.
And these ripples keep getting stretched by the microscopic size because
the universe expands so quickly in an exponential way.
And that is how we believe that these tiny variation in temperature had been created.
So inflation produced this uncertain principles and
little ripples of energies from here to there.
And that got printed on the temperature map of the cosmic micro background.
And this small temperature variations have the
[UNKNOWN]
the density variation in dark matter.
And dense part accumulates more stuff, and the difference keeps multiplying.
At the end of the day, you see these wrinkles in space-time.
So there's the dense part of the universe, there's a sparse part of the
universe, and that's how we believe that
the structure of the universe was formed today.
Namely, the fact that we have stars in galaxies today.
We owe
that back to this quantum noise, from uncertain principle during the inflation.
So that's a very mind boggling idea.
While the structure we see today,
over millions of light-years actually originated
from the fluctuation of the vacuum at 10 to the minus 26 centimeters.
And that's indeed what inflation does. But how do we know that this is true?
So if this is
true, is there any test we can do that indeed these
structures we see today recently came from this microscopic quantum noise?
So think about that.
