Many of us follow the idea of "seeing is 
believing"
But we all know that there are a lot of times
where this isn't exactly true.
One of the most mysterious of which
could be key to understanding the universe 
around us
Dark matter is defined as particles that 
don't
absorb, reflect, or emit light
They don't really interact with normal matter,
and they can't be detected using electromagnetic 
radiation.
Essentially, with current technology as it 
is,
we have no way of really finding dark matter 
in space
But if we can't detect dark matter...
how do we know it's there?
To make it easier to visualize, let's look 
at
two bottles with coins in them
One of these bottles is full of water,
while the other has just air.
You really can't tell the difference between
the bottles just by looking at them. What 
you
can see however is that the water makes the 
coins
move differently than air
Let's abstract this thinking into how dark 
matter was discovered.
The first person to discover and coin the 
term
"dark matter" was an astronomer named Fritz 
Zwicky.
In the 1930s, he was observing the Coma galaxy 
cluster,
and he used a method called the "virial theorem"
to infer the gravitational mass of the cluster.
His results led him to argue that there was 
simply not enough
combined mass of visual matter in the cluster
to hold it together gravitationally
Zwicky didn't have enough evidence to prove 
the existence
of dark matter, but more evidence of this 
mysterious substance
has popped up over the years. Let's look 
at one more example.
When you look at the image of a galaxy, you 
can see
that there are more stars concentrated near 
the center
of the galaxy rather than the edges.
This leads astronomers to the logical conclusion 
that the
gravity must be stronger near the center 
and weaker
near the edges of the galaxy.
This means that the stars near the edges 
of the
galaxy have to orbit slower than the ones 
near the center.
Otherwise, they'd break the force of gravity 
and
move off into space
While observing the Andromeda galaxy, astronomer 
Vera Rubin
was testing out the new spectrometer of a 
colleague, Kent Ford Jr.
The wavelengths measured using the spectrometer
allowed them to calculate the speed of the 
stars in the galaxy.
What they found, however, was very unexpected.
All of the stars in the galaxy were orbiting 
at the same speed!
But there simply wasn't enough visible mass 
in the galaxy
to create gravity strong enough to keep those 
stars in orbit.
Unless there was something else, in between 
the stars - Dark matter.
But what is dark matter exactly?
Because of its properties, we currently have 
no
way to find out exactly what dark matter 
consists of.
There have been many candidates - WIMPs, 
axions, bosons,
and neutrinos being just a few, but with 
many of
these particles being theoretical or some 
of the most elusive known to
man, hopes have been constantly raised and 
dashed with no results.
Rise of new technology brings rise of new 
information,
and along with it comes ways of finding out 
how the universe
around us came to be. Dark matter may have
existed even before the Big Bang, which gives 
us insight
not only into the Big Bang and how matter 
came into the
arrangements that it's in today, but also 
about times
even before the big bang and the known universe.
And with that, I'll leave you to think about
what else lurks in the dark.
