The Dynamic and Dangerous Galaxy#

Nothing in the universe ever stays still. In our home, the Milky Way galaxy, there are billions of stars. They all orbit the central part of the galaxy.

Some stars, like our own Sun, are pretty steady. They usually stay about 30,000 light years away from the galactic center and take around 230 million years to complete one trip around.

But the way everything moves isn’t like a calm ballet. It’s more like a skating rink full of drunk toddlers! This chaotic movement makes the galaxy a bit dangerous for us.

• Our local area in space is always changing.
• Stars are zooming around at hundreds of kilometers every second.
• We’re usually safe because the distances between objects are huge.

But we might not always be so lucky in the far future. Sometime down the line, we could run into trouble:

• A star going supernova (a giant explosion).
• A huge object passing close by and showering Earth with asteroids.

If something big like this were heading our way, we’d likely know about it thousands, maybe even millions of years beforehand. The problem is, with our current technology, we couldn’t really do much about it. Unless… we could somehow move our entire solar system out of the way!

(Imagine some snazzy intro music here, like in the video)

What is a Stellar Engine?#

To move the solar system, we’d need something called a stellar engine. Think of it as a massive machine, a “megastructure,” specifically built to steer a star through the galaxy. This is the kind of project an extremely advanced civilization might build – one with technology like a Dyson sphere (a structure built around a star to capture its energy) and thinking millions of years into the future.

But how could you possibly move the hundreds of thousands of objects orbiting the Sun? Good news: you don’t have to! All that other stuff is held by the Sun’s gravity, like it’s glued on. If the Sun moves, everything else will follow along. So, we only need to figure out how to move the Sun.

People have come up with lots of ideas for what a stellar engine could look like and how it would work. We’re going to look at two main ideas that scientists think could actually work, based on what we know about physics today.

Idea 1: The Shkadov Thruster#

This is the simplest type of stellar engine suggested.

• What it is: Basically, a giant mirror.
• How it works: It uses the same idea as a rocket engine. Rockets push fuel one way to move the other. The Shkadov thruster uses light (photons) released by the Sun as its “fuel.” Photons carry a tiny bit of push, or momentum.
  • Example: If an astronaut in space turned on a flashlight, the light shooting out would push them backwards, just very, very slowly.
  • The Sun makes way more photons than a flashlight, so it creates a lot more push.
• The Goal: To reflect up to half of the Sun’s light radiation in one direction. This creates a constant, albeit small, push to slowly steer the Sun where we want it to go.
• Staying in Place: For the Shkadov thruster to work right, it can’t orbit the Sun. It has to stay put relative to the Sun. The Sun’s gravity will try to pull it in, but the pressure from the sunlight hitting the mirror would balance that pull, holding the mirror up in the right spot.
• Materials: This balancing act means the mirror needs to be extremely light. It would likely be made of super-thin reflective material, like micron-thin foil from aluminium alloys.
• The Right Shape: The shape of the mirror matters a lot.
  • Wrapping the Sun in a giant ball (a spherical shell) wouldn’t work. That would bounce light back onto the Sun, heating it up and causing all sorts of bad problems.
  • Instead, you’d use a shape like a parabola. This shape is great because it sends most of the photons around the Sun and makes them all go in the same direction. This gives you the biggest possible push.
• Avoiding Disaster on Earth: We need to be careful not to accidentally make Earth too hot or too cold by blocking or focusing sunlight onto us. The only safe place to build a Shkadov thruster is right over the Sun’s poles (north or south pole).
• Movement Limitations: Building it over the poles means we can only push the Sun in one direction in the plane of our solar system (up or down, compared to the planets’ orbits). This limits which direction we can move the Sun in the Milky Way galaxy a bit.
• Complexity: For a civilization advanced enough to build a Dyson sphere, building this thruster is relatively simple in concept. It’s not complicated, just incredibly difficult to actually build.
• How Fast Can it Move Us?
  • At full power, this engine could probably move the solar system about a hundred light years over 230 million years.
  • Over a few billion years, this gives us almost complete control over where the Sun goes in the galaxy.
  • But, in the shorter term, this might not be fast enough if we needed to quickly get out of the way of a deadly supernova.

That’s why some people thought, maybe we can come up with something faster?

Idea 2: The Caplan Thruster#

Because the Shkadov thruster might not be fast enough for urgent situations, we thought we could design a better, faster engine. We even asked an astrophysicist friend if he could help figure it out for this video. He did! He designed one and wrote a paper about it that got published in a scientific journal (you can find it in the sources document if you’re curious). We’re going to call his design the Caplan thruster.

• How it works: This engine works much more like a regular rocket – you shoot stuff out one way to push yourself the other way.
• What it is: It’s a massive platform in space.
  • It’s powered by a Dyson sphere collecting energy from the Sun.
  • It collects material directly from the Sun to use as fuel.
  • It uses nuclear fusion to power itself and create a super-fast jet of particles.
• Propulsion:
  • It blasts a jet of particles away from the solar system at nearly 1 percent the speed of light. This is the main engine push.
  • There’s also a second jet that acts a bit like a tugboat, helping to push the Sun along.
• Fuel Source: This thing needs a lot of fuel – millions of tons every second!
  • It uses huge electromagnetic fields to suck up hydrogen and helium from the Sun’s solar wind.
  • But the solar wind isn’t enough. This is where the Dyson sphere helps again. Using its collected power, the sunlight can be focused onto small areas of the Sun’s surface.
  • This focusing heats those spots to incredibly high temperatures, lifting billions of tons of material right off the Sun.
  • This lifted material is collected and separated into hydrogen and helium.
• The Main Jet: The collected helium is burned in powerful thermonuclear fusion reactors (like miniature stars!). This creates the main exhaust jet.
  • The jet is made of radioactive oxygen.
  • It’s unbelievably hot, nearly a billion degrees!
  • This jet is what gives the engine its primary push.
• Balancing Act: With a powerful engine sitting so close to the Sun, you need to make sure it doesn’t just crash into it. The Caplan thruster has a way to balance itself.
  • It uses the collected hydrogen.
  • It accelerates this hydrogen using electromagnetic fields (like in particle accelerators).
  • It shoots a jet of this accelerated hydrogen back at the Sun.
  • This second jet balances the whole thruster and also transfers the main push of the engine back onto the Sun itself, moving it.
• How Fast Can it Move Us? This engine is much faster.
  • In as little as ** a million years**, it could move the Sun by 50 light years. That’s more than enough distance to get out of the way of a dangerous supernova.
  • At full power, this engine could completely change the Sun’s path in its galactic orbit in just 10 million years.
• Using Up the Sun? You might worry that taking millions of tons of material every second would use up the Sun. But luckily, the Sun is so incredibly massive that even billions of tons being taken off barely makes a difference over the timescales we’re talking about.
• Extending the Sun’s Life: In fact, this megastructure could actually help the Sun! By slowly removing mass, the Sun becomes a lower-mass star. Lower-mass stars burn their fuel slower. This means the Caplan thruster could actually keep the solar system habitable for many more billions of years than it would be otherwise!

Our Future Among the Stars#

With a Caplan thruster, we could truly turn our entire solar system into a spaceship, a vehicle capable of interstellar travel.

• We could steer the solar system to travel backwards through the galaxy, for example.
• As we move, we could pass by and potentially colonize hundreds or even thousands of other star systems.
• It might even be possible to steer the solar system right out of the Milky Way galaxy entirely and explore beyond it!

Stellar engines are the ultimate machines built by civilizations who don’t just think years ahead, or even decades, but think in terms of eons – millions and billions of years.

We know for sure that one day our Sun will run out of fuel and die. A stellar engine could be the key that allows the very distant future descendants of humans to travel safely to other stars without having to build individual tiny ships to cross the terrifying, dark, empty space between star systems.

Until we build a stellar engine, we’re kind of just floating along in the galaxy, completely at the mercy of whatever happens out there. We might not like where the galactic currents take us. But maybe, just maybe, our descendants will set sail and become an interstellar species for millions of years into the future.

A Look Back and Forward (Year 12,019)#

This video was our last one for the year 12,019 according to the human era calendar. And wow, what a year it was! So many things happened everywhere, affecting so many different people.

Calendars and holidays are really just made-up ideas, but they’re helpful. They let us cut our lives into smaller chunks that our brains can handle and make sense of.

We’re leaving year 12,019 behind with a strange mix of feeling disappointed by how things are, but also hopeful for the future. The world can feel messed up, but the important thing is, we can work to fix it.

In just a few days now, this year will be over, and we’ll get a fresh chance to try again.

Thank you so much for watching our videos and for sticking around for so many years. We really appreciate you.

See you all in 12,020!