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Hey, I'm Diana, and you're watching "Physics Girl."
And explosions are--
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--crazy!
The bigger the better, right?
Especially if they're in space and nobody's getting hurt.
But if you are really, truly an evil mastermind,
and you honest to goodness want to take over the universe,
are explosives your best bet?
Let's talk physics.
Every explosion follows the same basic formula.
You pull some trigger followed by the rapid expansion
of some material, and that leads to the release
of some type of energy.
It could be radiation, could be heat,
could be motion, sound, or all of the above at once.
Phew.
But an explosion isn't always destructive
if it doesn't start out with enough energy
to, say, knock down a building.
But even if you've got powerful explosives,
you have to be able to transfer your energy to the right thing.
[EXPLOSION]
Now in space explosions, let's address
the obvious, which is that you can't
hear the explosions which is going to put
a damper on your destruction.
So when Kendra Shaw nuked the Cylon Basestar,
it didn't actually sound like--
[EXPLOSION]
That's because our perception of sound
is the ear sensing tiny, rapid, pressure
changes against the eardrum.
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These ukulele strings are vibrating and bumping
into the air molecules next to them,
which are bumping into the molecules next to them
and sending a pressure wave through the air,
just like compression waves move through the rings of a slinky.
So the sound you hear--
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--is the compression and decompression
of air molecules over and over against your eardrum.
But outer space really doesn't have many 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
has about 10 to the 21 molecules in it,
and that's just the air inside.
So that's a pretty big difference between outer space
and our atmosphere.
So that initial huge disturbance of the explosion
will never actually get transmitted to your ear,
unless, of course, you're right next to the explosion,
in which case, let's be honest.
You're not going to survive to share the audio recording.
So space is pretty empty, which limits the destruction you can
do with an explosive in space.
Because when you detonate TNT, it's
not the shrapnel-- that is, the fast moving stuff
that flies away from the bomb-- or the hot gas
from the weapon itself that does the most destruction.
It's the shock wave.
When an explosive explodes, it's expansion
both heats up and pushes gas particles around it,
forming what's called a shock wave or a blast wave.
And it's energy moves outward similarly to a sound wave
where the molecules bump into each other,
and that moves outward through the particles.
But it can move faster than the speed of sound,
and the molecules also get pressed together,
which creates a huge difference of pressure
right next to each other.
What happens when you have a huge difference in pressure?
Violent wind.
We're talking many times more powerful than the most
destructive hurricanes and tornadoes on earth.
So whatever didn't get knocked over
with the shrapnel gets blown over by the wind.
So can a blast wave happen in space?
Well, the gravitational waves that were detected last year
are kind of like a blast wave, except for instead
of moving through air, they're moving
through space time itself.
But those needed two black holes to collide.
And while atomic weapons are powerful,
they're not the 10 to the 47 joules
released by that collision.
They're more like 10 to the 15 joules, 32 orders of magnitude
off.
And you didn't even feel the collision.
Granted, it happened really far away.
Anyways, we already said that space
doesn't have enough particles to transmit sound,
so it doesn't have enough particles to transmit the blast
wave either.
So your bomb would just release shrapnel and hot gas
and radiation.
Which don't get me wrong are still dangerous,
you just won't get the blanket destruction radially outward
from the explosion.
Most likely that shrapnel will just keep flying through space.
And note, things won't slow down in space,
because there's no friction or air drag to slow them down.
So they'll just keep going at the same high speed
until they hit something.
And that radiation?
Well, you get less of it per area as it spreads out.
So if you miss your target initially,
it's more of a crapshoot whether your explosion is
going to destroy what you want.
So you can't have the cool sound effects in space,
and you can't wreck blanket damage.
What's an evil overlord to do in this universe?
Not saying I've got any plans, but here are
some tips for more effective space weapons.
You probably want to use electromagnetic radiation,
also known as light, because it can transmit its energy
without using a medium.
It can travel through space.
I would also suggest using that light
to interfere with your enemies communications
rather than trying to burn their ship,
because even the most focused x-ray laser gun will spread out
over long distances so it might be
more effective to just go medieval and throw
blunt objects at their ship.
But of course, explosives that explode inside the ship
are always effective.
In the words of Google auto fill,
explosions are not enough.
If you want to learn a little bit more
about hypothetical space warfare, "It's OK to Be Smart"
has another video on space battles.
I'll put the link in the video description.
Thank you for watching, and happy, peaceful physicsing.
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