Could aliens destroy us
from light years away? Mh, another day at the Kurzgesagt Labs, where we answer the most important
questions with science. Today: how might civilizations wage war
across light years? What kind of devastating weapons
could they use, and what would they look like? Meet our two players. A yellow dwarf star system
home to a species of primates. "Humans," as they call themselves, recently became
a technological civilization. They have rockets,
nuclear reactors and memes. How cute! The Smorpians disagree. They reside on a planet around
the orange dwarf star HD 40307, 42 light years away. Smorpian civilization
developed earlier than humans and they have much better technology. They've recently built
a Dyson swarm around their star which gives them near limitless energy. And they noticed humanity, which is unfortunate as the Smorpians
are planning a hyperspace bypass through our solar system, so they decided that humanity has to go. Interstellar war is hard though. Front lines, tactics, and logistics
are meaningless at these scales. It's also fought across time. Decades will pass
between firing a weapon and learning whether it hit or not. Sending an invasion fleet is futile. Even if the Smorpians travel
in a large fraction of the speed of light, the journey to Earth would take
decades or even centuries, and humans would have
plenty of time to prepare. If you want to learn more
about the mind numbing problem of war between alien civilizations, we made a video about it. Today we'll help the Smorpians
construct a weapon that is not only extremely long range
and as fast as physically possible, but that will totally destroy
everything on Earth, so no human survivors will come to an act
of vengeance on swap in the future. In interstellar war,
you want to win with one shot. Our bird scientists have found
three Smorpian designs: the Star Laser, the Relativistic Missile, and the Ultra-Relativistic Electron Beam. All based on real technologies that humans are using
in some form already. Let's see how they work. [The Star Laser] As an advanced technological civilization, the Smorpians harness
the energy of their star by surrounding it with billions
of solar power satellites. This Dyson swarm collects 1%
of the star's energy output, a million billion billion watts, 50 billion times more
than all humanity generates. What if all the power
of the Dyson swarm, all those satellites were used
to create a star laser? Like any laser, the bigger it is,
the longer its range. Human-built lasers
use small mirrors to focus, so they have short ranges. The Smorpians could turn
their entire Dyson swarm into a collective focusing element
a million kilometers wide. The star laser has an insane
range as a result, enough to focus on target Earth from a distance of over
2 million light years. OK, let's shoot it. Countless tiny beams combine
into a single huge beam. Laser beams are normally
invisible in space, but the star laser is so powerful that light scattering off bits
of dust and gas in its path makes it clearly visible in the sky. A gigantic column of green light. The laser travels at the speed of light, which, oddly enough,
is still pretty slow on a galactic level. It takes a whole day until the laser
has left the Smorpian system, shooting into the emptiness between stars. It will travel for decades, occasionally melting the odd bit
of interstellar dust or asteroid. 42 years after being fired,
it arrives without warning. Humans only notice
a weird green glow in the sky, and then they're gone. 1% of the energy of a star, concentrated into a beam
the diameter of Earth, traveling 42 light years. It burns the exposed half of the planet with the intensity of 3 million Suns. The seas boil and evaporate,
fires scour the land, and within minutes Earth's crust
begins to melt into a sea of lava. As the planet rotates, it turns into a red hot hell
with no trace of life. After a day, it's all over
and the laser dies down. In another 42 years, the Smorpians will know
if they've been successful. That's another thing
about interstellar war. When you attack, your grandchildren
will be the ones to find out if you won. It's like all the bombs from World War II
exploding in the 80s and us only seeing the effect today. OK, the star laser's extreme range,
speed of light attack, and ability to melt down any target make it a premier interstellar weapon. But is there something else? [The Relativistic Missile] What if instead of converting the energy
of their Dyson swarm into a laser, the Smorpians used it
to shoot a super bullet? A relativistic missile going as close
to the speed of light as possible. This sort of weapon is at the limits of what the Smorpian
technology can handle, as it requires loads of a highly
dangerous material: antimatter. The evil twin of regular matter. Humans have only managed to produce
a few nanograms of antimatter. With their unlimited energy, Smorpians can manufacture it
at an industrial scale to build antimatter rockets. When antimatter and matter are mixed,
they annihilate, which in more practical terms
means there's a big big boom releasing gamma rays and plasma. The physics is complicated, but basically, if you have
a really strong magnetic field you can deflect the plasma
through a nozzle just like in the chemical rockets
humans use. But it would be much, much faster. The fastest rocket possibly basically. Our relativistic missile
is much bigger than a skyscraper. At the bottom is the bell shaped
magnetic nozzle 100 meters wide. On top of it are 250 floors
filled with antimatter and matter ready to annihilate each other. On the top floor
is a 300 kilogram projectile looking quite small,
about the size of a person. To stop them getting damaged on the way, the missiles have dozens
of sacrificial layers that form a Whipple Shield. To make sure they do their job, the Smorpians build 1000 missiles. Let's fire them. Launching all the relativistic missiles
is a spectacular event. For a moment, the antimatter engines
lighting up outshine their star. Their exhaust is a long trail
of brilliant white, and as they accelerate away, they appear redder and redder
until they turn invisible. With the extreme amount of energy released
by the matter-antimatter reactions, the missiles are accelerated to 99.9999996%
of the speed of light. They have effectively infinite range, as there's nothing really
to slow them down. They arrive shortly
after you can see them. The light from their launch
will take 42 years to reach Earth, so human astronomers might see
the flash of the missile's launch, and then a few days later they'll hit. Not enough time to prepare. Each relativistic missile
packs the kinetic energy of a dinosaur killer asteroid, so only one needs to hit. They never reach the ground, disintegrating instead
at the edge of Earth's atmosphere. Intense blue flashes
set everything on fire. Then continent-sized fireballs
slam down on the surface to smash everything into dust, repeatedly, until nothing is left
but rubble and smoke. So interstellar missiles
with unlimited range, minimal warning, and delivering complete
destruction of a planet's surface. Nice. But they are a hassle to build. Is there something else maybe? [The Ultra-Relativistic Electron Beam] Humans do funny things to their food to rid it of bacteria
and make it safe to eat, like shooting electron beams
at strawberries. Small particle accelerators
send electrons into the food with an energy similar to the radiation
from nuclear reactions. Not enough to burn the food,
but deadly to bacteria. Smorpians had the same idea,
but bigger. The main challenge
with an electron beam is range. Electrons are negatively
charged particles, so they don't want to stay
near each other. A regular electron beam
will quickly spread out, making it harmless. Smorpians needed to cover distances
of dozens of light years, so they've used the rules
of the universe to trick the electrons by building an Ultra-Relativistic
Electron Beam, or UREB. What it does is accelerate the electrons to 99.99999… …99999… …99999… …99999… …9999998% of the speed of light. Phew! Faster than even
the most powerful cosmic rays. The closer something travels
to the speed of light, the slower time moves for it
relative to the rest of the universe. And since these electrons
are moving so incredibly fast, for every second of spreading
their experience, over 5 million years pass in real time. A physics trick that lets the beam
cross interstellar distances while remaining
tightly focused on its target. The biggest particle accelerator on Earth
is 27 kilometers long. The Smorpians need one
that's over 100,000 kilometers long. A megastructure 8 times longer
than Earth is wide. It's mostly a tube of magnets holding
the beam together until the exit. Like a long trumpet of doom
surrounded by an aura of deadly radiation. When it's fired, it produces a ruler
straight lightning bolt pointed at Earth. Its effects on arrival are less visible
than the other weapons. No flashes of light,
no massive firestorms, no explosions. It doesn't destroy rocks,
it destroys DNA. People get dizzy, then fall sick
as their cells are pierced by radiation. You might think that a deep bunker
could save a few humans, but no. The UREB is so penetrating that its effects accumulate
to lethal doses even underground, over days or weeks. In the end, just like our strawberries, Earth becomes sterile. [Simulation results] Hm, another elaborate animated
science explainer by Kurzgesagt where we've learned a lot,
not sure exactly what. Luckily, the Smorpians don't really exist, but others… might. One major downside of all our weapons is that others around the Milky Way
could see you firing them, which is not ideal because you don't want to present
yourself as a dangerous species and tell everybody where exactly you are. So maybe instead of shouting
or shooting out into the universe, the best course of action seems to be
to stay relatively quiet for now, and observe. Maybe one day we'll witness
distant stars shooting at each other and be glad we stayed out of it.