This is the universe.
And this tiny little bit here, this is what the trees, the rocks, the planets, stars, galaxies...
...sausages, eagles, Donald Trump, and human beings are made of.
Matter. But what is the rest of it?
Well...
...its love!
*inhales* Not really.
Some of it–around 27 percent–is dark matter.
Ordinary matter makes up less than 5 percent of the universe
and the rest is made of something else called dark energy.
But we'll come back to that in a bit.
So what is dark matter?
Well, its an elusive substance that doesn't emit or reflect light, or any radiation from the electromagnetic force.
That's why we call it dark...
Duh.
In fact, the only thing that we know that it interacts with is gravity,
and it's also why we know it exists at all.
In the 1960s and 70s, an American astronomer called Vera Rubin was studying how fast spiral galaxies spin.
Most of the mass of stars are concentrated in the middle of the galaxy
and the huge mass of all these stars keep everything orbiting within the galaxy.
In theory, the stars nearer the center should be orbiting faster than those nearer the edge.
So as the distance for the center increases, the speed of the orbit decreases.
Just like the planets in our own solar system.
But what she found was shocking.
The graph looked more like this:
As the distanced increased, the speed stayed more or less constant.
This meant that there must be something else there.
Something that was adding to the mass of the galaxy and making gravity more uniform throughout.
If you looked through a telescope and saw a galaxy, that would be pretty cool.
But if you pointed it in a different direction and saw the same galaxy, now that would just be preposterous.
Well, believe it or not, that's exactly what astronomers saw.
But how could the same galaxy appear in two different places at the same time?
Well, it makes sense if there's something massive and invisible between you and it.
Something much like dark matter.
You see, Einstein proved that huge amounts of mass can bend light.
So if light were coming off a galaxy in this direction,
it would bend toward you and hit you right in the telescope.
But you would see the light coming from here. So it would look like the galaxy was here.
And if you take light coming off the galaxy in this direction,
it would also bend towards you, and you'll think the galaxy is here as well.
Light would bend like this in every direction.
And in three dimensions, to us, that would look like a galaxy stretched out into a ring.
And it's exactly what astronomers saw.
It's called an Einstein Ring and it can't be explained without the extra mass from dark matter to bend the light.
You can even do this at home. All you need is a wine glass.
Although, just the base. You don't need the top bit.
*glass shattering*
And if you're under 18, please,
for the love of science and to try and keep all of your blood inside your body,
get an adult to help with this.
So, now we have our dark matter lense. We need a galaxy.
Just like a huge cloud of dark matter, the glass bends the light of the galaxy into an Einstein ring.
Push it to the side and it creates arcs too. Just like in the deep space images taken from the Hubble telescope.
So what might dark matter be?
Well, here's what we know so far.
It's invisible. It has mass.
It doesn't interact with regular matter or even seem to interact with itself.
Needless to say, this makes it very difficult to study.
But that doesn't mean scientists don't have a few ideas.
The most popular theory is that dark matter is made up of a new kind of particle
which interacts very differently to anything else we know.
Scientists call it a "weakly interacting massive particle"
or WIMP for short.
That seriously is the name they gave it.
It means it's a particle with a mass that interacts very weakly with regular matter, but only through gravity and the weak force.
There are experiments going on at the moment to prove the existence of this particle.
But so far, none of them have been sensitive enough to detect them.
Another idea was that dark matter is really just huge blobs of normal matter roughly the size of Jupiter.
These gigantic invisible objects are called "massive astrophysical compact halo objects"
In other words... MACHOs
These objects including neutron stars, and brown and white dwarfs, are composed of ordinary matter
but they only emit very little to no light. So again, they are incredibly hard to detect.
You can probably see a theme occurring.
But my personal favorite theory is that dark matter could be an invisible parallel universe hovering directly above our own.
According to world-famous physicist, Michio Kaku, who suggests that this may be the case,
The reason we can't see it is because light only travels in the plane of our universe.
However, we can still feel its mass because gravity is essentially the bending of space,
and so maybe able to travel between universes.
Whatever it is, it is clearly integral to the structure of our universe, and maybe even life itself.
Without dark matter's extra mass, the universe couldn't have formed into the complex web that we see today.
There just isn't enough of the ordinary matter that we see out there to coalesce into galaxies,
and it would just be spread out randomly throughout the cosmos.
No galaxies, no solar systems. And no solar systems, no us.
...and no me.
So dark matter really... matters.
But, if it only accounts for 27 percent of the universe and ordinary matter 5 percent,
what about the other 68 percent? What's the story there?
Well to find out, here's Jade from Up and Atom to tell us.
Jade, you can borrow my pie chart.
*laughs*
Thanks, Dom!
So dark energy makes up the biggest chunk of our universe.
And besides the fact that it has a really cool name, we don't really know much else about it.
It makes dark matter look like the extroverted cousin.
Sorry, Dom.
Although it likes to remain mysterious, scientists have their theories as to where it might come from.
Some think that it comes from the energy of empty space.
Yeah, you did hear that correctly.
Or that it's a new force or even a field that changes with time.
However, as you'll find out, the real mystery is why there's not more of it.
Thank you, Jade!
So head over to Jade's channel right now and watch her video about dark energy.
Do it! Do it now!
I've been Dom and you've been watching Every Think.
