[MUSIC PLAYING]
[MUSIC PLAYING]

Hey, I'm Diana, and you're watching "Physics Girl."
Hey, I'm Diana, and you're watching "Physics Girl."

And explosions are--
And explosions are--

[EXPLOSION]
[EXPLOSION]

--crazy!
--crazy!

The bigger the better, right?
The bigger the better, right?

Especially if they're in space and nobody's getting hurt.
Especially if they're in space and nobody's getting hurt.

But if you are really, truly an evil mastermind,
But if you are really, truly an evil mastermind,

and you honest to goodness want to take over the universe,
and you honest to goodness want to take over the universe,

are explosives your best bet?
are explosives your best bet?

Let's talk physics.
Let's talk physics.

Every explosion follows the same basic formula.
Every explosion follows the same basic formula.

You pull some trigger followed by the rapid expansion
You pull some trigger followed by the rapid expansion

of some material, and that leads to the release
of some material, and that leads to the release

of some type of energy.
of some type of energy.

It could be radiation, could be heat,
It could be radiation, could be heat,

could be motion, sound, or all of the above at once.
could be motion, sound, or all of the above at once.

Phew.
Phew.

But an explosion isn't always destructive
But an explosion isn't always destructive

if it doesn't start out with enough energy
if it doesn't start out with enough energy

to, say, knock down a building.
to, say, knock down a building.

But even if you've got powerful explosives,
But even if you've got powerful explosives,

you have to be able to transfer your energy to the right thing.
you have to be able to transfer your energy to the right thing.

[EXPLOSION]
[EXPLOSION]

Now in space explosions, let's address
Now in space explosions, let's address

the obvious, which is that you can't
the obvious, which is that you can't

hear the explosions which is going to put
hear the explosions which is going to put

a damper on your destruction.
a damper on your destruction.

So when Kendra Shaw nuked the Cylon Basestar,
So when Kendra Shaw nuked the Cylon Basestar,

it didn't actually sound like--
it didn't actually sound like--

[EXPLOSION]
[EXPLOSION]

That's because our perception of sound
That's because our perception of sound

is the ear sensing tiny, rapid, pressure
is the ear sensing tiny, rapid, pressure

changes against the eardrum.
changes against the eardrum.

[MUSIC PLAYING]
[MUSIC PLAYING]

These ukulele strings are vibrating and bumping
These ukulele strings are vibrating and bumping

into the air molecules next to them,
into the air molecules next to them,

which are bumping into the molecules next to them
which are bumping into the molecules next to them

and sending a pressure wave through the air,
and sending a pressure wave through the air,

just like compression waves move through the rings of a slinky.
just like compression waves move through the rings of a slinky.

So the sound you hear--
So the sound you hear--

[MUSIC PLAYING]
[MUSIC PLAYING]

--is the compression and decompression
--is the compression and decompression

of air molecules over and over against your eardrum.
of air molecules over and over against your eardrum.

But outer space really doesn't have many particles in it.
But outer space really doesn't have many particles in it.

So this empty coffee mug would have about 300 particles in it
So this empty coffee mug would have about 300 particles in it

in outer space, whereas here on earth this empty mug
in outer space, whereas here on earth this empty mug

has about 10 to the 21 molecules in it,
has about 10 to the 21 molecules in it,

and that's just the air inside.
and that's just the air inside.

So that's a pretty big difference between outer space
So that's a pretty big difference between outer space

and our atmosphere.
and our atmosphere.

So that initial huge disturbance of the explosion
So that initial huge disturbance of the explosion

will never actually get transmitted to your ear,
will never actually get transmitted to your ear,

unless, of course, you're right next to the explosion,
unless, of course, you're right next to the explosion,

in which case, let's be honest.
in which case, let's be honest.

You're not going to survive to share the audio recording.
You're not going to survive to share the audio recording.

So space is pretty empty, which limits the destruction you can
So space is pretty empty, which limits the destruction you can

do with an explosive in space.
do with an explosive in space.

Because when you detonate TNT, it's
Because when you detonate TNT, it's

not the shrapnel-- that is, the fast moving stuff
not the shrapnel-- that is, the fast moving stuff

that flies away from the bomb-- or the hot gas
that flies away from the bomb-- or the hot gas

from the weapon itself that does the most destruction.
from the weapon itself that does the most destruction.

It's the shock wave.
It's the shock wave.

When an explosive explodes, it's expansion
When an explosive explodes, it's expansion

both heats up and pushes gas particles around it,
both heats up and pushes gas particles around it,

forming what's called a shock wave or a blast wave.
forming what's called a shock wave or a blast wave.

And it's energy moves outward similarly to a sound wave
And it's energy moves outward similarly to a sound wave

where the molecules bump into each other,
where the molecules bump into each other,

and that moves outward through the particles.
and that moves outward through the particles.

But it can move faster than the speed of sound,
But it can move faster than the speed of sound,

and the molecules also get pressed together,
and the molecules also get pressed together,

which creates a huge difference of pressure
which creates a huge difference of pressure

right next to each other.
right next to each other.

What happens when you have a huge difference in pressure?
What happens when you have a huge difference in pressure?

Violent wind.
Violent wind.

We're talking many times more powerful than the most
We're talking many times more powerful than the most

destructive hurricanes and tornadoes on earth.
destructive hurricanes and tornadoes on earth.

So whatever didn't get knocked over
So whatever didn't get knocked over

with the shrapnel gets blown over by the wind.
with the shrapnel gets blown over by the wind.

So can a blast wave happen in space?
So can a blast wave happen in space?

Well, the gravitational waves that were detected last year
Well, the gravitational waves that were detected last year

are kind of like a blast wave, except for instead
are kind of like a blast wave, except for instead

of moving through air, they're moving
of moving through air, they're moving

through space time itself.
through space time itself.

But those needed two black holes to collide.
But those needed two black holes to collide.

And while atomic weapons are powerful,
And while atomic weapons are powerful,

they're not the 10 to the 47 joules
they're not the 10 to the 47 joules

released by that collision.
released by that collision.

They're more like 10 to the 15 joules, 32 orders of magnitude
They're more like 10 to the 15 joules, 32 orders of magnitude

off.
off.

And you didn't even feel the collision.
And you didn't even feel the collision.

Granted, it happened really far away.
Granted, it happened really far away.

Anyways, we already said that space
Anyways, we already said that space

doesn't have enough particles to transmit sound,
doesn't have enough particles to transmit sound,

so it doesn't have enough particles to transmit the blast
so it doesn't have enough particles to transmit the blast

wave either.
wave either.

So your bomb would just release shrapnel and hot gas
So your bomb would just release shrapnel and hot gas

and radiation.
and radiation.

Which don't get me wrong are still dangerous,
Which don't get me wrong are still dangerous,

you just won't get the blanket destruction radially outward
you just won't get the blanket destruction radially outward

from the explosion.
from the explosion.

Most likely that shrapnel will just keep flying through space.
Most likely that shrapnel will just keep flying through space.

And note, things won't slow down in space,
And note, things won't slow down in space,

because there's no friction or air drag to slow them down.
because there's no friction or air drag to slow them down.

So they'll just keep going at the same high speed
So they'll just keep going at the same high speed

until they hit something.
until they hit something.

And that radiation?
And that radiation?

Well, you get less of it per area as it spreads out.
Well, you get less of it per area as it spreads out.

So if you miss your target initially,
So if you miss your target initially,

it's more of a crapshoot whether your explosion is
it's more of a crapshoot whether your explosion is

going to destroy what you want.
going to destroy what you want.

So you can't have the cool sound effects in space,
So you can't have the cool sound effects in space,

and you can't wreck blanket damage.
and you can't wreck blanket damage.

What's an evil overlord to do in this universe?
What's an evil overlord to do in this universe?

Not saying I've got any plans, but here are
Not saying I've got any plans, but here are

some tips for more effective space weapons.
some tips for more effective space weapons.

You probably want to use electromagnetic radiation,
You probably want to use electromagnetic radiation,

also known as light, because it can transmit its energy
also known as light, because it can transmit its energy

without using a medium.
without using a medium.

It can travel through space.
It can travel through space.

I would also suggest using that light
I would also suggest using that light

to interfere with your enemies communications
to interfere with your enemies communications

rather than trying to burn their ship,
rather than trying to burn their ship,

because even the most focused x-ray laser gun will spread out
because even the most focused x-ray laser gun will spread out

over long distances so it might be
over long distances so it might be

more effective to just go medieval and throw
more effective to just go medieval and throw

blunt objects at their ship.
blunt objects at their ship.

But of course, explosives that explode inside the ship
But of course, explosives that explode inside the ship

are always effective.
are always effective.

In the words of Google auto fill,
In the words of Google auto fill,

explosions are not enough.
explosions are not enough.

If you want to learn a little bit more
If you want to learn a little bit more

about hypothetical space warfare, "It's OK to Be Smart"
about hypothetical space warfare, "It's OK to Be Smart"

has another video on space battles.
has another video on space battles.

I'll put the link in the video description.
I'll put the link in the video description.

Thank you for watching, and happy, peaceful physicsing.
Thank you for watching, and happy, peaceful physicsing.

[MUSIC PLAYING]
[MUSIC PLAYING]