Name: 私たちが知っている宇宙は存在してはいけない｜物質・反物質問題 (The Universe As We Know It Shouldn't Exist | The Matter-Antimatter Problem)
Uploaded: 2021-01-14T10:42:38.000Z
Duration: 10 min 54 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：

the stuff that makes up you and me and basically everything you see around you —

should have been destroyed not long after it formed.

that's actually one of the biggest unsolved mysteries in science.

It's something we're very slowly starting to unravel,

and every year, scientists are uncovering new leads

that could help us figure out how and why we're all even here.

The reason we're so confident we shouldn't be here

is based on our understanding of antimatter.

When you hear that word, it might conjure up visions of this hypothetical,

mysterious substance, but that's because the name like stinks.

Antimatter definitely isn't hypothetical.

And despite what it's called, it isn't the opposite of matter, either.

In reality, antimatter is just like normal matter,

For instance, if an electron has charge of minus one,

then an anti-electron — which is called a positron —

We can study antimatter in radioactive decays and particle accelerators,

so we've been able to learn a decent amount about it.

And as far as we can tell, every kind of matter particle has an antimatter counterpart.

But when most people think of this stuff,

they're not thinking about cataloging particles and misleading names.

If there's one thing antimatter is known for, it's that when a particle of it touches

like, say, an electron hitting a positron —

It happens in a process called annihilation, and when it's over,

the original matter and antimatter particles are gone.

are some photons of extremely energetic gamma-ray light.

And that's where the problems start to come in.

the Big Bang should have created equal amounts of matter and antimatter.

It was all bunched up close together in a sort of “soup” made of hot, dense plasma,

and these particles were running into each other constantly.

matter and antimatter were also forming during these early days.

It happened during something called pair production

and it happens when a photon with enough energy turns into two particles:

one made of matter, and one made of antimatter.

Pair production occasionally happens now,

but it's nowhere near as common as it was billions of years ago.

Still, because it always produces equal amounts of matter and antimatter,

it shouldn't have upset that fifty/fifty balance.

So when the universe cooled and expanded, and pair production dramatically slowed,

Annihilation should have continued to rage until there was nothing left but photons.

But obviously that is not what happened, which is great.

Instead, we have good reason to believe that essentially all of the particles left over

from the beginning of the universe are made of matter,

and that almost none of them are antimatter.

It's not like there are secretly huge pockets of antimatter out there, either.

If there were, there would be a constant stream of annihilation reactions

And we'd be able to see a huge number of gamma rays as a result.

The only antimatter we actually see is the occasional stray particle from space,

the short-lived particles made in radioactive decays on Earth,

and the handful of particles made in accelerators.

Technically, it isn't a hundred percent impossible,

but it would be really hard for big chunks of antimatter to fit in with our current evidence

for the structure and evolution of the universe.

So the more likely explanation is that the modern universe contains essentially no antimatter.

The best explanation we have right now is that,

for some reason, more matter survived those early days of chaos.

Evidence suggests that for every billion antimatter particles made in the early universe,

about a billion and one matter particles were made.

So for every billion annihilations that made photons, one extra matter particle survived.

Based on what we've seen, matter and antimatter should be identical.

They should form the same way, and should decay into other particles at the same rates.

They should also be treated the same by what we consider the three fundamental forces in

the strong nuclear force that holds together atoms,

the weak nuclear force that governs atomic decay, and electromagnetism.

So basically, if you imagine swapping every matter particle with an antimatter one and

your experiment should behave identically.

Which means there should be no reason for the imbalance that we see.

Except, obviously, something had to have happened.

Otherwise, everything would just be made of photons,

and we wouldn't be having this discussion.

The challenge physicists have now is figuring out what caused that imbalance.

And there are a few things they could look for.

For example, this mystery could be caused by some reaction that produces more matter

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私たちが知っている宇宙は存在してはいけない｜物質・反物質問題 (The Universe As We Know It Shouldn't Exist | The Matter-Antimatter Problem)

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