Why is space so dark?

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Whether you look up at the night sky or marvel at the picture of the universe online,

the question remains the same.

Why is space dark?

Why isn't it colorful, like Earth's blue daytime sky?

The answer is certainly not a lack of light.

But first, let's figure out why it's light on our planet.

And why our sky is so beautifully blue.

Unlike in the vacuum of space on Earth,

we've got an atmosphere filled with different kinds of gas molecules.

Also, since Earth is relatively close to the Sun,

a lot of light reaches the surface of our planet.

When these light waves hit the molecules in Earth's atmosphere,

blue and violet ones are just the right length to scatter.

As a result, we've got a blue sky.

During the day, the Sun's light completely covers the side of Earth facing it.

Then, the Sun sets at the end of the day.

And since light waves move in a straight line,

until they make contact with something,

they can't reach very far into the side of Earth that no longer faces the Sun.

Without the Sun, all we have is the darkness of space again.

You might object.

But the Moon is just as close to the Sun as our planet.

Then why is its sky always black?

Unlike Earth, the Moon doesn't have a strong atmosphere.

And even though the Sun's light does reach its surface,

there are no gaseous molecules for it to bounce off of.

That's why the whole spectrum of visible light

makes its way down to the surface of our natural satellite.

Okay.

But there are billions of stars in our galaxy alone.

There are billions of galaxies in the Universe.

Plus, you can find other space objects that reflect light,

like planets or large moons.

Then why don't all these light sources make our night sky super bright?

This contradiction is known in astronomy and physics circles,

as old versus paradox.

And it can be explained by the theory of space-time expansion.

This idea claims that the Universe expands faster than the speed of light.

That's why the light coming from distant galaxies

is likely to be stretching and turning into infrared light,

as well as microwaves and radio waves.

They are not detectable by human eyes.

That's why they appear black.

Human perception plays its role here too.

Our eyes are well adapted to the conditions on our home planet.

And how we perceive light is influenced by our visual system.

If there are no familiar cues, like an atmosphere or objects reflecting light,

it's likely to be difficult for people to perceive light in space.

Interestingly, stars do give off.

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Light in all colors, including those not visible to the human eye,

like infrared or ultraviolet.

If we could see microwaves, space would seem glowing to us.

That's because the cosmic microwave background,

which is energy leftovers from the big bang scattered around the early universe,

still fills the cosmos.

One more reason why interstellar and interplanetary space seems to be dark

is that space is an almost complete vacuum.

So there's virtually nothing between stars and planets

to help light scatter to reach our eyes.

And with no light, all our eyes see is black.

At the same time, space might not be as black as astronomers initially thought

and as your eyes tell you.

At least that's what a 2021 study suggests.

With the help of NASA's New Horizons mission to Pluto and the Kuiper Belt,

scientists have managed to see space without any light interference

from Earth or the Sun.

The research team looked through the images taken by the probe

and subtracted all light from the Milky Way,

known stars and possible galaxies.

They also removed the light that might have leaked in from camera quirks.

And guess what?

The background light of the universe was still twice as bright as predicted.

The reasons for this extra brightness are still unknown.

Astronomers will keep studying this topic.

But until they find the answer, one thing we should probably agree on,

space seems to be more charcoal than pitch black.

Hey Mythbusters, today we're debunking some classic space myths.

Pop on the next space shuttle and let's get to the bottom of these tails once and for all.

Picture this, you're floating weightlessly in space,

sipping on a cup of delicious hot chocolate.

When a peculiar thought pops into your head,

can you scream in outer space?

And if yes, would anyone hear that scream?

If you've watched the movie Alien, then you know the answer to this one.

You can't hear sounds in outer space.

It's not that sounds don't exist.

It's just that you can't hear them.

There's no one better to clarify this myth than Chris Hadfield.

He's been on a couple of spacewalks during his life as an astronaut.

And once you're out there in the darkness of space,

you can't hear anything.

All you hear is sound, complete silence.

But hey, just around the corner is a massive ball of explosion,

aka the Sun.

We just can't hear the explosions happening because there's no medium for sound to travel through.

It would be quite uncomfortable for an astronaut, though,

if they could hear all the noises going on in outer space.

Now, imagine your zipping through space,

feeling like a futuristic superhero.

When a shooting star passes by your side,

but wait, is it really a star?

Unfortunately, shooting stars are not stars at all.

They are small space rocks known as meteorites,

entering Earth's atmosphere and creating a stunning light show.

Oh, and since we're debunking myths,

let's head straight for another one.

You've probably heard that meteors only crash into Earth on extremely rare occasions,

like once every dinosaur extinguishing apocalypse.

That's not true.

Scientists estimate that about 48 tons

of meteoritic material fall on Earth each day.

But almost all of this material is vaporized in Earth's atmosphere.

The bright trail we see in the night sky

is what we popularly call a shooting star.

Next time you make a wish upon a shooting star,

remember, you're actually hoping on a tiny piece of space debris.

It's not so romantic, after all.

Can we or can we not fly into the stratosphere on air balloons?

Apparently, we can.

The Earth's stratosphere starts relatively close to the ground,

about seven or eight miles up from the Earth's surface.

But it continues a long way up.

If you were to fly yourself all the way into the stratosphere

with some type of air balloon,

just make sure you have really good equipment at hand.

You'll need a special suit and some breathing devices.

Because air starts to get pretty thin the higher you get.

Of course, if you do go all the way up,

you need to get a picture of the Earth's curvature.

So take a chest harness with you

where you can put a special camera or something like that.

And how about you livestream the whole thing?

That would be a first.

Imagine it's been 102 days since you left Earth.

You've adapted well to life in outer space,

but something weird is happening to your body.

You're getting taller.

How is that even possible?

Don't stress about it. It's completely normal.

The truth of the matter is, you're not getting taller.

This is what happens to your body when it's not under the effect of gravity.

Our body has natural space between vertebrae.

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And joint. On Earth, this space is almost completely squeezed

due to the force of gravity.

But in space, your body gets some time off of the pushing force of gravity

and begins to stretch more and more.

So yes, astronauts can grow up to 3% taller when they're on long missions.

And here's a curiosity.

NASA has that all covered when they're tailor-making space suits, of course.

This way, astronauts will always have extra space in their suits.

Once astronauts are back on Earth, the anti-gravity effect will wear off.

So maybe they'll spend a few days wearing capri pants

before it fits perfectly on their bodies again.

Never have I ever pictured an airplane door bursting open mid-flight

and a bunch of passengers being sucked into the atmosphere like flying feathers.

Well, I'm betting most of you have had similar thoughts when getting inside a plane.

Now imagine if this were to happen in outer space.

Common knowledge says that if an astronaut is sucked out of an airlock,

this person would be burned to a crisp.

Brace yourselves, because this is not only true,

but the reality of it is way worse.

According to astronaut Chris Hadfield, this is what would happen.

The part of your body in the shade of the sun

would experience temperatures of negative 418 degrees Fahrenheit,

while the part of you getting sunlight would burn at around 480 degrees Fahrenheit.

Your lungs would collapse, and your blood would start to boil like tea water.

So you would burn, freeze, lose your ability to breathe, and boil.

Yikes!

How many times have you heard that astronauts have to work out every second of every day,

otherwise they'll pass up?

This is a complete myth.

Remember we talked about gravity earlier?

Due to the lack of gravity in outer space,

our bodies don't have to do any heavy work.

Our torsos don't have to sustain the weight of our heads,

and we don't have to make any effort to move our legs,

because essentially, there's no walking in outer space.

Now, imagine living like that for six months,

or even a year of your life.

Your muscles could turn into jello.

That's why astronauts work out.

They'll strap themselves and run on a treadmill,

or they'll do some weightlifting in a special machine.

This way, their muscles won't feel the lack of gravity too much.

They do need to keep hydrated, though.

You know what?

If I was an astronaut, I'd ask NASA if I could take my super soft water flask up into space with me.

You've probably heard that space smells like burnt steak, or barbecue sauce.

Now, as much as this sounds absurd, this myth is more true than it is false.

Astronauts obviously can't smell space when they're in it,

because they can't take off their helmets.

They usually smell it once a space vehicle docks and they open up a hatch.

Apparently, what causes this smell is the presence of hydrocarbons that float around in space.

Who would have thought, huh?

Hey smart people, let me ask you a question.

Do you really think that if astronauts fly at the speed of light,

they won't age a single second?

I knew you'd say no.

Let's get a few things straight.

First of all, we haven't figured out how to operate vehicles at the speed of light.

This would require an immense amount of energy, and we don't have the technology to do that.

Second, even if we manage to send a human inside a spacecraft that traveled at the speed of light,

this person would still age.

They would age differently than the people who remained on Earth.

That's a fact, but they would still age.

Do you really think there's such a thing as immortality? Nah.

If you've seen the first avatar, then you certainly remember that humans only managed to get to Pandora

because they traveled in cryosleep.

In other words, they froze their bodies, put them in a cryo bed, and traveled for years without ages.

Yes, this sounds amazing, but we still don't have the technology to do that.

Our bodies are mainly made out of water, right?

And when you freeze water, it expands.

That's why you should never leave soda cans unattended in your freezer.

Right now, if we froze a person's body, the water inside of it would expand,

harming tissues and organs.

So no, we can't cryosleep our way into interstellar travel.

Not yet, at least.

The universe is not static.

It evolves all the time and grows in all directions.

It's expanding, and scientists found this out almost a century ago.

And it's not at a stable rate.

The more time goes by, the faster the universe expands.

As this happens, stars, planets, and galaxies move farther and farther apart,

which leaves more space between them.

If that's the case, the universe is supposed to become colder as it expands.

Right?

After all, it was a lot denser when the big bang happened, and a lot hotter.

As it was expanding, space was cooling down, which created conditions for planets, stars, and other space objects to form.

Yeah, that's not exactly the case now.

Scientists were surprised to hear it too, but our universe is actually getting hotter.

They observed the temperature of cosmic gas farther away from our home planet,

compared to young gases closer to the Earth.

Since we measure distance in space by light years, farther areas are like going back to the past,

and regions closer to us are like observing the present day.

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They found out the temperature of a gas in space

has gone up more than 10 times in the last 10 billion years.

Now, the temperature of the cosmic gas that's spread all across the universe

can get to around 4 million degrees Fahrenheit.

Wow!

As the universe expands, gravitational force does its part

and pulls gas and dark matter together.

It's doing some pretty hard work there.

It creates galaxies and clusters of galaxies out of them.

And this process is totally chaotic.

It's so messy that more and more gas heats up

as all of this is happening.

Space was extremely hot when it was just forming

13.7 billion years ago.

What if it gets warm like that once again?

Scientists are observing the situation.

They found out the temperature in space increased

by measuring cosmic gases using something called redshift.

They generally use this method when they want to see

how far away some space objects are.

Those that are closer to us have shorter light wavelengths.

The farther some object is, the longer its light wavelengths are.

And they can now determine the temperature of a certain object from its light.

On average, space is a pretty cold place.

The glow that's left from the Big Bang is called the CMB,

which is short for the cosmic microwave background.

It's so powerful and intense, it bades the entire universe in light.

It's the only thing that significantly heats up matter.

But there are many smaller mechanisms that help to heat up matter in the universe.

And they could go crazy if space warms up.

Like stars, they emit radiation that affects nearby dust and gas.

They radiate throughout the far infrared too.

When a star is at its early stage, the radiation coming from it

forms protoplanetary structures that look like disks.

They primarily form in a single plane.

And a bright central star produces spectacularly illuminated gas.

And there are blue reflections of this gas.

It was like that with our planetary system too.

Strong energy and gravitational forces cause collisions, dust, and gas

in an uncontrolled vortex that's forming planets.

That's why most planets in our solar system orbit in the same direction.

That's the direction this giant whirlpool was spinning a long time ago too.

Active stars, colliding galaxies, stellar cataclysms, black holes, neutron stars.

The universe has so many sources of energy.

And when you surround normal matter in space with such an energetic environment,

it heats up drastically.

When you heat something up, it radiates that energy away in a certain way.

In most cases, galaxies have just a couple of areas where stars are forming

at regions where gas is collapsing.

A bubble that surrounds that area contains ionized hydrogen.

Three-quarters of our sun is hydrogen.

Thanks to that hydrogen, the sun keeps us warm.

In its core, hydrogen transforms into helium and causes atomic fusion.

Yep, that's how our sun releases its energy.

Radiation heats all that gas to thousands and thousands of degrees.

At the same time, it ionizes a large number of atoms and molecules,

which basically means it turns them into ions.

Atoms are neutral particles, and ions are either negatively or positively charged particles.

If the universe heats up, our sun might too.

If its temperature hits 30,000 degrees Kelvin,

it could become hot enough to ionize all those materials it had previously ejected,

and it could create a real planetary nebula.

This would be a nebula in the shape of a ring that forms because of an expanding gas

that surrounds an aging star.

As the temperature goes up all the time, hydrogen ionizes.

At a few thousand degrees, this could turn the nebula in our solar system pink with emission lines.

Our sun could come to its end if it reaches the temperature of 50,000 degrees Kelvin.

If you could float in space and come closer, you'd see it glow in eerie green tones

because of doubly ionized oxygen.

Higher energy phenomena make more galaxies collide.

This heats gas even more and eventually results in x-ray emissions.

What about black holes and radiating neutron stars?

When they go crazy, they can shape whole galaxies and who knows what more?

Maybe we'd have more mazers too.

Those are natural lasers our universe produces.

They arise when big populations of molecules receive large amounts of energy.

By now, scientists have found the strongest yet the most distant mazer.

So powerful, it's more luminous than the light 6000 suns would produce and in just one emission line.

Maybe then we'd discover even stronger mazers.

That's in the case that we're even going to be here at all.

Because as the universe is getting hotter, cosmic radiation is getting stronger.

Not so good for life on Earth.

Increased cosmic radiation could harm us.

Who knows if life would even be possible on Earth in that case.

Or if the powerful gravitational force would pull our home planet too and crash it into another one.

But maybe life as we know it wouldn't completely disappear.

Or if that happened, it could possibly somehow find its way once again, maybe in the distant future.

There's a possibility our universe could support life at its early stages.

It doesn't look like that when you think of the chaos the big bang caused, right?

But that was only in its mere beginnings.

After things had settled down a bit, the drags of enormous, earliest stars formed rocky planets.

In our solar system, those are Earth, Mars, Mercury and Venus.

You can't set your foot on the rest of them since they're gas giants.

Back in that time, radiation was quite intense, so rocky planets had an adequate environment to form.

Since it takes a lot of energy to whirlpool dust and particles and bake a planet in the end.

This period of time coincides roughly with that when the first stars formed in our universe.

Ancient stars were way bigger than our Sun.

They lived shorter though, they would have just exploded as supernovas on their end.

And they would leave heavy metals across the space around them.

Those are the particles rocky planets formed from.

Radiations spread around the whole universe back then.

It has changed over time.

Today, it's almost an absolute zero.

400,000 years after the Big Bang, when hydrogen atoms were forming,

CMB was almost as hot as the surface of our Sun.

And about 15 million years after the Big Bang, its temperature was close to room temperature,

which is around 80 degrees Fahrenheit.

These things were happening across the universe, so there were many planets that could potentially hold life.

If we were one of those ancient worlds, we wouldn't need a star to keep us warm.

CMB would be enough to do it.

So, it's possible that life in space is way older than we think it is.

There could have been ancient worlds with liquid water on their surface.

What if there were some primitive forms of organisms like on our home planet a long time ago?

Or even more developed ones?

Perhaps we'll find out one day.

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