Name: ダークマターの発見まであと少し？ (How Close Are We to Finding Dark Matter?)
Uploaded: 2021-01-14T08:13:09.000Z
Duration: 10 min 59 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

様態の副詞

When we think about what our universe is made up of, we automatically think of stars, planets, galaxies!

But the reality is that is less than five percent of the mass of the universe.

Well that's one of the biggest questions in science today, and what some of the greatest minds in astrophysics are trying to decipher.

The hunt for dark matter has spanned decades and though we can't see it, smell it, feel

it, taste it, or hear it, we can see its gravity impacting other things.

So if we only really know five percent of the story, discovering this elusive dark matter

would unlock an entirely new understanding of everything and everyone in our known universe.

So how close are we to finding dark matter?

If you're not really familiar with dark matter, let me get you up to speed on what we know so far.

But there are a few things we are at least confident about:

Dark matter is this really mysterious, strange substance.

It's amazing in some sense because it's all around us.

Right now, as I'm sitting here, a wind of dark matter is going through me.

It doesn't interact with me, which, at least, it doesn't interact with me much so my body

doesn't realize it's there, the Earth doesn't realize it's there.

If it were not a new particle, if there's something totally crazy, then science would

be revolutionized overnight in a way that it has never been in the history of mankind.

And then finally we know a lot about what dark matter isn't.

So there have been lots of different kinds of experiments that have looked and tried to discover what dark matter is and haven't found it yet.

And so we've excluded a lot of possibilities.

But why is this missing piece of our universe so important to find and understand?

It could be that someday if we could manipulate this stuff, we could actually use it as a source of energy or something.

In the far future, there might even be a huge payoff for us if we could manage to do that.

In the late 1900s when JJ Thompson discovered the electron in cathode ray tubes nobody knew what the electron was good for.

He just thought this was an interesting thing to study.

And now when we think about how we live our lives, we all go around all the time with

our heads in our phones, which are packed full of devices that rely on the quantum mechanical properties of the electron.

And so although we haven't found dark matter yet, there's a huge amount of it out there.

And understanding its quantum mechanical properties, who knows how it's going to change our lives?

This is a puzzle that is being put forward by the universe to us.

I cannot think of anything else better to do with my time than to try to answer that puzzle.

Even though we haven't seen it yet, there's a few key pieces of evidence we have found so far in the search for dark matter that tell us we're on the right track:

We are certain that dark matter exists because the evidence for additional mass in the galaxy is all over the place in astronomical observations.

You can see the gravitational pull on stars and on galaxies, to even a lot more subtle

things like you can see the relativistic effect of invisible clumps of dark matter causing light rays to bend.

Most recently there have been beautiful observations using optical data and X-ray data looking

at gravitational lensing to infer the distribution of matter in colliding clusters of galaxies.

But by far the smoking gun for dark matter is the Cosmic Microwave Background.

This is the earliest thing that we can see through our telescopes through light.

It's basically a photograph of a moment in history after the Big Bang, when the universe was only three hundred and eighty thousand years old.

It also shows temperature data, and when we measure the fluctuations in temperature, the position of the peaks can determine the ingredients of our universe.

It shows that less than five percent of the total mass of the universe is made up of what we call “normal matter,” like visible stars, planets, and galaxies.

Then twenty six point eight percent of the mass of the universe is dark matter and the rest is made up of dark energy.

If you asked me what dark matter was I'd say I have no idea.

If you ask me what dark energy is, you wouldn't be able to show that because it would be I have no bleep bleep bleep bleep idea.

Which means we should just leave dark energy for another day.

Now, the reason the CMB was so significant in proving dark matter exists is because when

we compare theoretical models with these peaks, there's an extremely compelling match, practically ruling out a universe without dark matter.

So basically putting it all together, dark matter is the simplest explanation we have

that explains all of the data that we have from different types of observations.

To match these discoveries and observations, scientists came up with a theory for what dark matter could be: WIMPs.

WIMPs — which stands for weakly interacting massive particles, but of course, the name

WIMP is so cute that everybody likes to use it instead — are particles that are heavy,

and that's where the “massive” comes from and “weakly interacting” means that they

have an interaction strength that's maybe around the electroweak force.

WIMPs started being discussed sometime in the 1980s.

They've really been dominating the conversation, I would say, until about the last five or 10 years.

WIMPs are beautiful because they solve a lot of problems kind of for free.

You don't add too much, you just get a lot of explanations for mysteries that we want to know.

If we can find WIMPs, it's possible that that would then mean we have found dark matter.

So scientists began planning and building a lot of different experiments to look for WIMPs, dispersed all over the world.

Experiments look for dark matter in three ways.

So the experiments that make it try to produce dark matter particles in ultra high energy collisions of proton beams and accelerators like in the Large Hadron Collider.

And those experiments look for some evidence that dark matter particles were produced and flew out of the detector.

The Large Hadron Collider is pushing particles together at such high speeds that when they

slam into each other, the kinetic energy that breaks off can be frozen into matter to be studied.

It's possible that these tests could generate something that matches the properties of dark matter.

The second search method is called indirect detection — the “break it” method.

This is when we observe dark matter in space, and since it is so far away from us, we are

only seeing what is produced when dark matter particles are annihilating each other — which

could happen if there's a high enough density of them.

And finally, the “shake it” method is actually called direct detection —

because scientists theorize that dark matter may set off extremely sensitive detectors.

And we use a detector which has three and a half tons of argon and is located a mile underground in Sudbury Ontario, Canada.

And what we're looking for is some evidence that a dark matter particle struck an argon atom and then that argon atom deposited the energy in the detector.

It takes months or even years to get the experiments going and they often run for month or years

just collecting the data that they need in order to see if the dark matter is there where they think it might be.

So with all of these different searches, and all these different methods, have we found anything close to WIMPs?

That means that WIMPS are still allowed to be the answer. On the other hand,

when you don't find something for a few years, then you start to think, "All right, well, maybe I'd to look in other places too."

I think what we're seeing now is a push in that direction.

In fact, the search for dark matter is experiencing a major, exciting shift right now for the first time in decades.

The search for WIMPs will continue, but scientists are clamoring onto the scene with new ideas for what dark matter could be, bringing the hunt to new corners of the universe.

Once you go beyond the idea of WIMPs and start thinking about other ideas for what dark matter could be, you find actually there's a lot of great possibilities.

There are very light-mass particles like sterile neutrinos, which is kind of a cousin of the

neutrinos that are part of the standard model, or axions, this is kind of a very, very, light particle that explains certain mysteries for the strong nuclear force.

One thing I'm actually really excited about is looking for dark matter through new forces.

I think this is an avenue that is a relatively modest mathematical change to the theory,

that opens up a whole new range of different experimental handles.

You could imagine that it's actually something to do with extra dimensions of space where