[MUSIC PLAYING] ---Hey, I'm Diana, and you're watching "Physics Girl."

And explosions are-- [EXPLOSION] 7 00:00:16,120 --> 00:00:17,230 - -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] 28 00:01:01,290 --> 00:01:03,280 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] 36 00:01:15,700 --> 00:01:17,890 That's because our perception of sound is the ear sensing tiny, rapid, pressure changes against the eardrum.

[MUSIC PLAYING] 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-- [MUSIC PLAYING] - -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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