Eli: From the smallest atoms to the most massive
stars, everything we can see is made up of
matter.
Black holes, the Earth, this pencil, the device
you're watching this video on, and you yourself
are all made up of the same stuff.
But all of this makes up less than five percent
of the universe.
The rest of it is part of the DARK UNIVERSE,
which in turn is made up of dark energy and
dark matter.
But how do we know that?
In order to find dark matter, you can't look
for something you /can/ see, but instead for
its effects on the matter around it.
This galaxy cluster should not work.
Of course, gravity is holding everything together,
and because of that, the bodies on the outside
of the cluster /should/ be moving with less
velocity than the ones closer to the center.
It's sort of like Earth and its atmosphere.
The further you get from the core of the Earth,
the weaker its pull becomes, meaning that
the velocity required for a satellite to stay
in motion is greater than that of the moon.
Swiss astronomer Fritz Zwicky thought so,
too, but upon further observation, he found
the opposite.
While recording the movement of the Coma Galaxy
Cluster, he found that the velocity of the
bodies at the edge of the cluster was far
greater than he expected.
There just wasn't enough matter in the galaxy
cluster for it to stay together.
It should have been flung apart by its own
velocity, but it wasn't.
There had to be /something/ causing the discrepancy,
and he hypothesized that there was some sort
of invisible, virtually undetectable matter
he dubbed 'dark matter' that was acting as
a sort of glue that held the whole universe
together.
About forty years later, American astronomer
Vera Rubin conducted similar experiments on
individual galaxies and found similar, but
much more accurate results.
Her calculations showed that galaxies could
contain up to ten times as much dark matter
as they did regular matter.
So, we know that dark matter is there, but
what /is/ it, exactly?
Its difficult to pin down something that we
can't detect with the scientific equipment
we have available today, but through process
of elimination, astronomers were able to identify
what dark matter /might/ be.
Scientists began by conducting every test
in the book, but to no avail.
Dark matter emitted no detectable waves, it
gave off no light, and it didn't appear to
have any physical effects on the matter around
it.
This crossed anything we knew as matter off
the list.
Anything made of regular atoms would have
been detectable in some way.
The only particles left were the subatomic
ones that we have no way of measuring.
This made a lot of sense, since many of the
particles shared the same properties as dark
matter.
They didn't give off light or any other waves,
and they didn't interact with normal matter,
but they did have mass, and therefore, gravity.
That would explain not only how they held
galaxy clusters together, but how they had
gone virtually undetected until very recently.
Keep in mind, however, that all of this is
just a theory.
We don't /know/ that dark matter is out there,
because we have no concrete way of proving
its existence.
Its existence is the most solid explanation
as to why galaxies and galaxy clusters appear
the way they do, and we don't have a better
working theory... yet.
And just think: everything I've been talking
about in the last three minutes has all been
about dark matter, which when combined with
regular matter, only makes up thirty percent
of the known universe.
I didn't even touch on dark energy, which
makes up the other seventy percent of the
universe.
This is fascinating, that after centuries
of scientific inquiry, discovery, and innovation,
we still know so little about our own universe.
It's a vast field of unknowns out there, and
that is equal parts breathtaking and terrifying.
