All language subtitles for What is Dark Matter and Dark Energy

Matter, as we know it;

Atoms, stars and galaxies, planets and
trees, rocks and us.

This matter accounts for less than
5% of the known universe.

About 25% is dark matter;
and 70% is dark energy.

Both of which are invisible.

This is kind of strange because it
suggests that everything we experience is

really only a tiny fraction of reality.

But it gets worse.

We really have no clue what dark matter
and energy are, or how they work.

We are pretty sure they exist though.

So, what do we know?

Dark matter is the stuff that makes
it possible for galaxies to exist.

When we calculated why the universe
is structured the way it is,

it quickly became clear that there's just
not enough normal matter.

The gravity of the visible matter
is not strong enough to form

galaxies and complex structures.

The stars would more likely be scattered
all over the place and not form galaxies.

So, we know there is something else inside
and around them.

Something that doesn't
emit or reflect light.

Something dark...

but besides being able to calculate
the existence of dark matter,

we can see it... kind of.

Places with a high concentration of dark
matter bend light passing near by.

So we know there's something there that
interacts with gravity.

Right now, we have more ideas about
what dark energy is not, than what it is!

We know dark matter is not just clouds of
normal matter without stars,

because it would emit particles
we could detect.

Dark matter is not anti-matter,

because anti-matter produces unique gamma
rays when it reacts with normal matter.

Dark matter is also not
made up of black holes,

very compact objects that violently affect
their surroundings,

while dark matter seems to be
scattered all over the place.

Basically, we only know 3 things for sure;

1. Something is out there.

2. It interacts with gravity.

3. There is a lot of it.

Dark matter is probably made up of a
complicated exotic particle

that doesn't interact with
light and matter in a way we expect,

but right now, we just don't know.

Dark energy is even more
strange and mysterious.

We can't detect it, we can't measure it
and we can't taste it.

But we do see its effects very clearly.

In 1929, Edward Hubble examined how
the wavelength of light

emitted by distant galaxies, shifts
towards the red end

of the electromagnetic spectrum
as it travels through the space.

He found that fainter, more distant galaxies
showed a large degree of red shift;

closer galaxies, not so much.

Hubble determined that this was because
the universe itself is expanding.

The red shift occurs,
because the wavelengths of light

are stretched as the universe expands.

More recent discoveries have shown that,
the expansion of the universe is accelerating.

Before that, it was thougth that the pull
of gravity would cause the expansion to

either slow down or even retract and
collapse in on itself at some point.

Space doesn't change its properties
as it expands; there's just more of it.

New space is constantly
created everywhere,

galaxies are tight bound clusters of stuff
held together by gravity

so we don't experience this expansion
in our daily lives.

But we see it everywhere around us.

Wherever there is empty space in the
universe, more is forming every second.

So, dark energy seems to be some
kind of energy intrinsic to empty space.

Energy that is stronger than
anything else we know

and it keeps getting stronger
as time passes by.

Empty space has more energy than
everything else in the universe combined.

We have multiple ideas about
what dark energy might be.

One idea is, the dark energy is not
a thing, but just a property of space.

Empty space is not nothing, it has its own
energy.

It can generate more space and
is quite active.

So, as the universe expands,
it could be that just more and more space

appears to fill the gaps and this leads
to a faster expanding universe.

This idea is close to an idea that
Einstein had back in 1917,

of the concept of a cosmological constant,

a force that counteracted
the force of gravity.

The only problem is, that when we tried
to calculate the amount of this energy

the result was so wrong and weird,
that it only added to the confusion.

Another idea is, that empty space is
actually full of

temporary, virtual particles that
spontaneously and continually

form from nothing and then dissapear into
nothing again.

The energy form those particles
could be dark energy.

Or maybe dark energy is an unknown kind of
dynamic energy fluid or field

which permeates the entire universe,
but somehow has the opposite effect

on the universe than normal
energy and matter.

But if it exists, we don't know
how and where or how we could detect it.

So there are still a lot of questions to
answer.

Our theories about dark matter and
dark energy are still just that;

theories.

On one hand, this is kind of frustrating,
on the other hand this is frontier science

making it very exciting.

It shows us that no matter how much
we feel we're on top of things,

we are still very much
apes with smartphones, on a tiny

fragile island in space looking into
the sky wondering how our universe works

There is so much left to learn,
and that is awesome.

This video is supported by the
Australian Academy of Science,

which promotes and supports
excellence in science.

Learn more about this topic
and others like it at nova.org.au.

It was a blast of work with them
so go check out their site.

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Subtitles by the Amara.org community