>> Yes, I do.

>> Why is that?

>> Scientifically been proven?

>> Are we alone?

Or is there life elsewhere in the universe?

This is a question humans have wondered about for millennia and one that people still have

pretty strong opinions about even though there isn't definitive evidence to answer the

question one way or the other.

>> Do you think that aliens have ever come to earth?

>> People say that there is like... there has been aliens and they implant...

I forget what it is called, but they have like made these fields and they have like

produced something on earth.

>> I think Area 51 could be possible and could be real.

>> You know how there is area 51 and all that kind of stuff.

I reckon they have got technology that they won't bring it out yet, you know.

>> Do you think it is technology that came from aliens?

>> Well, possibly.

They could have.

They could be sharing information and gaining technology from aliens.

>> On YouTube there seems to be some pretty good evidence about it, but I don't know.

>> You have seen some videos of aliens.

>> Yeah.

>> That looked convincing.

>> Kind of, yeah.

>> So {?} apparently were beings that came down from heaven according to the old Sumerian

texts.

>> The oil paintings and stuff and Sumeria.

>> I think people believe that aliens have visited us just because they are not aware

of how vast the universe really is.

I mean, what is an exoplanet?

How far is a light year?

These are the things you need to understand if you are to judge the probability that alien

life could come and visit us.

What is a galaxy?

>> Specifically I wouldn't know.

>> Is a galaxy something totally different, like another universe maybe?

>> A galaxy is a sun and a moon, isn't it?>>

So a galaxy is bigger than that.

>> Galaxies, hundreds of stars, blah, blah, blah.

>> In fact, hundreds of billions of stars.

>> Billions of stars.

>> Yeah, hundreds of billions.

>> Yeah, yeah.

>> What is a galaxy?

It is a collection of stars and gas that are held together in a gravitationally bound system.

Every point of light that you see here is a star.

When we say 200 billion stars, it is probably at least 200 billion stars.

The galaxy is 100,000 light years across.

So, you know, it is just... the distances are unimaginable.

One light year, don't forget, is 10 trillion kilometers.

>> What is a light year?

You are an engineer.

>> A light year is a thousand years, isn't it?>>

A light year is a thousand years?

>> Isn't it?

>> Oh, about 150 million years...

>> Would be a light year.

>> Would be a light year.

That is what I believe it would be.

>> It is a distance.

>> Is it a distance?

A light year?

>> Have you heard the term exoplanet?

>> No.

>> No.

Never.

>> Exoplanet.

No.

>> Like a planet that we are not aware?

>> Well, exo should be... could be short for something.

>> Extraterrestrial planet or extraterrestrial life, maybe.

>> Something outside our planet.

>> So an exoplanet is simply a planet that orbits a star other than the sun.

Exo just means external, outside, so outside our solar system.

So it is just a planet.

You know, you can...

>> How many have you found?>>

Me personally?

I have found six.

But overall we now know of over 800 planets that have been confirmed and another probably

2000 planets that are waiting for information, but are pretty strong candidates.

So we don't see the planet directly, we see its impact on the start that it orbits.

We do it from the ground with a angle Australian telescope and we look for the wobble of the

star as the planet orbits it.

The planet goes around and the start moves backwards and forwards.

So if you can imagine seeing that from sort of along the line of sight a little bit more,

say like in this cartoon here, then you would see the star moving towards you and moving

away from you.

And so what we see here is the light from the star becoming ever so slightly bluer as

it moves towards us and ever so slightly redder as it moves away.

The big problem is that the main kind of planet you end up finding with this wobble technique,

because it is really reliant on the mass of the planet, basically like Jupiter, Saturn

and then we have started to get down to Neptune and Uranus.

>> To find smaller planets NASA launched Kepler, a one meter telescope with a 95 megapixel

camera.

Its mission is to observe 130,000 stars in our galaxy and look for dips in brightness

caused by planets passing in front of them.

>> So Kepler-62 is a solar system with five planets and the planets are very similar in

size to the terrestrial planets, the rocky planets in our own solar system.

They have a star in the middle and then you have three inner planets.

There is a green band which is this habitable zone, the goldilocks zone where you can expect

liquid water to exist on the surface of the planet.

And, in fact, there are two planets inside the habitable zone around Kepler-62.

If you are going to start looking for life around nearby stars, this is probably the

best one to start with.

>> Is there life beyond the earth?>>

Well we don't know for sure.

We can't say yes definitely.

But the probability is very high.

There are at least 200 billion stars in our galaxy.

We now know that on average there is at least one planet per star in our galaxy alone and

there are another 100 plus billion galaxies in the universe.

We also now know, thanks to the Kepler spacecraft, that at least one in six of those is earth

sized.

And so that is 33 billion potential earth sized planets.

Not all of them are going to be able to have life.

But the probability is getting pretty high already at this stage.

>> So there is no definitive evidence that alien life exists, but the sheer size of the

numbers suggest that they must be out there somewhere.

But with the vast distances across the universe, chances are it is going to be a long time

before we know for certain that we are not alone.

This video was created as part of a collaboration addressing 10 unanswered science questions.

So subscribe to Veritasium and then check out the other nine questions by clicking the

link.

>> Ok.

>> Is there more than one galaxy out there?

>> Yeah, probably.

>> How many would you say?

>> Oh, I couldn't tell you.

There is probably more than on my 10 fingers, I guess.

>> It is more than 100 billion.

>> A hundred billion?

Probably.

>> It is crazy.

>> Yeah.