The Cosmic Classroom - Solar Neutrino Problem

Uploaded by vmargoniner on 09.10.2009

Welcome back to the Cosmic Classroom.
We'll now talk about the Solar Neutrino problem,
which is hard to understand because after all you don't,
you're not really sure what the Neutrino is let alone
the Solar Neutrino problem. What's the problem?
So let me first explain what the problem is.
The problem is that when four protons fuse to become
an atom of Helium, as I mentioned before, they will
emit Gamma Rays, they will emit Positrons, but they
will also emit, as I mentioned before, two Electron Neutrinos.
Those are here,two Electron Neutrinos.
Those two Electron Neutrinos we can predict how many
of those should be around, should be arriving on Earth or
should be detecting on Earth. Because we know the
rate of fusion in the sun. And the reason why we
know the rates of fusion in the Sun is because all of
the energy that's being generated in the center of
the Sun eventually leaves the Sun on its surface.
So we eventually observed that then we can count up all that
energy and we know that that energy is coming from fusion.
Before we can predict the rate of fusion,how many
Protons are being combined into,into Helium?
How fast? There's a certain number of
predicted neutrons, number density of Neutrinos that are
then predicted to arrive here on Earth on our observatories.
Neutrinos are funny things because they have very
small masses it was actually believed that they didn't even
have masses for a while. We now know that they
have very small masses and it's small, I mean
much smaller than an Electron really really small masses.
So they travel very fast almost at the speed of light.
They don't have a charge, so they don't seem to
react electromagnetically with anything else.
They travel right through, they travel right through you and
me, they travel right to, to the sun, they travel right through.
And it's hard to detect them because they travel right
through most things, but it's every now and then
they interact with matter. So if we understand Neutrinos
and if we understand how they interact with matter we
should be able to count them on Earth, you know,take into
account that, the fact that we just detect a few of them.
And this number of detected Neutrinos should match with
what, with what we expect. Many experiments try to
detect those Neutrinos and different experiments
got the same results. Always getting just the
third of the expected number of Neutrinos.
As if two thirds got lost somewhere, or if we don't
know fusion,you know. Maybe it, maybe it's not
the Neutrinos that are formed, maybe it's less,
it's weird it doesn't match. So for a long time this
is the problem,this was the Neutrino problem.
If there are so many being created in the sun,
why is that we're detecting only a third of them.
The solution to the Neutrino problem came when people
started to realize that Neutrinos actually do have mass and
therefore there're different kinds of Neutrinos,slightly
different flavors of Neutrinos. What's created in the fusion
is in the Electron Neutrino, but there is also a Muon
Neutrino and a Tauon Neutrino. So there are three types
Electron Neutrino, and I'll put the Electron Neutrino here.
Muon, Tauon, and Electron Neutrino. And they change types,
they interfere with one another these particles,
they also behave as waves just like light does.
So they, they have some interference with one another.
And when they are traveling together, it's like they steel
energy from each other,the energy is conserved but
maybe one, one Neutrino will give a little bit of energy
from another Neutrino,and then it'll take some energy away.
So they can change types, Neutrinos can change types.
So the solution to the Neutrino problem is, was
to understand that the three Neutrinos that were emitted.
So three Neutrinos here, for example, that were
emitted from the sun. Let's say this is the sun,
right here, that's a terrible sun, but this is the sun.
It's emitting three,three Neutrinos that are then
traveling in our direction. Earth is there a way.
During this trip they exchange energy with
one another and maybe this Electron Neutrino
here will become a Muon Neutrino, and maybe this
one here will become a Tauon Neutrino, and maybe
this one here will continue to be an Electron Neutrino.
And a little bit later they change energy again so
maybe now this one becomes a Tauon Neutrino, and this
one here becomes an Electron Neutrino, and maybe this
one became a Muon Neutrino. They like changing energies
like, like kids playing together, changing the ball, changing energy.
In other words this start happening very soon after
they are created, they start interfering one another they
start playing ball with one another, by the time they
reach Earth there's only a third of Electron Neutrinos,
because the other third is Tauon Neutrinos and the
other is Muon Neutrinos. So they are all there, we
find them, but they have changed masses, they have
changed energies slightly. New detectors are able
to detect, not only the Electron Neutrino, but
the Muon and the Tauon Neutrino, and guess what,
they count them all. So now we understand
we can account for all the Neutrinos and we know that,
they are, they're not, and we know that there's more
than one kind of Neutrinos. That's the solution for
the Neutrino problem. Now I have three times as
many as we're detected before, and the problem is solved.
Neutrinos change type. They oscillate into different types.
And I hope this was helpful to you, and I'll see you in class.