Galactism

It begins close to home

Humanity is the first life we know of to send itself and its tools beyond its world. Already, panels in orbit catch the Sun’s light to power everything we keep in space. The Moon holds the mass to build far more. Three days away and easy to lift from, it can make more and more of space a part of our home.

Blue shows what could be built. Watch it spread from the Earth and the Moon, here and at every scale that follows.

The blue lights are an illustration, scattered at random over the places where such things could be built; they are not measurements. The small disc is the Earth you have just left, drawn as it is at this moment, and the ring is the path of the Moon, a little over one light-second out. From here on every frame looks straight down on the disk of the Galaxy. The opening view is turned toward the Earth’s sunlit side when that direction would show mostly night, and its clouds are those of a typical day, not today’s.

Mars is the first step

Mars is the first world where people can build a home that stands on its own, from its own ice and rock. A people who make Mars live will know how to make a home around another star, and this project expects the first starships to come from there.

The orbits are to scale and the planets are where they are today. They are tipped sixty degrees to the Galaxy’s disk, so they appear as ovals. From the Earth, blue lines reach Mars and collectors close to the Sun, which would catch light that now streams past the planets unused. From Mars they go on to the asteroid belt.

Explore the Solar System

Everything we have built is in this frame

Voyager 1, launched in 1977, is the most distant thing people have made, about one light-day out. Inside its path lie the asteroids, the moons of the giant planets and the ice beyond Neptune: material enough to build living room many times the land area of the Earth, around a star that can power all of it.

The ovals at the center are the orbits of the giant planets; sunlight takes four hours to reach Neptune. Voyager appears inside the one-light-day ring because it has also climbed far above the plane of this map.

Four light-years of almost nothing

Then the map empties. The nearest star is about nine thousand times farther away than Neptune, and everything so far has shrunk to the point of light at the center. This is the gap a starship has to cross.

The rings mark distance from the Sun by the time light takes to cover it.

The nearest stars

Alpha Centauri is three stars, a little over four light-years away, and nuclear fusion puts it within reach. An engine driven by small fusion explosions would throw its exhaust out at about three percent of the speed of light, and a ship can cruise at about the speed of its exhaust and still stop at the far end. At that pace the crossing takes a century and a half.

Each blue line is a ship, and the clock counts the years since they left together. Three percent is our middle estimate; the range, and what it rests on, is in the findings.

Ninety-five neighbors

These are all the known systems within twenty light-years. In fuel, a far star costs no more than a near one: at a given speed a longer crossing burns only more time. What the longer crossing asks is that the ship last. Suppose it lasts five centuries, enough for fifteen light-years. The Sun’s ships then reach forty-one systems themselves, the settlements they found send ships on to the rest, and all ninety-five are reached within a thousand years.

Most of these are red dwarfs, small dim stars, or brown dwarfs, bodies too small to shine as stars at all. A settlement is taken to launch its own ships two centuries after it is founded. If ships last longer, more of the lines start at the Sun. If they last less, the chains grow longer and wait on the slow drift of the stars. Stars above or below the Galaxy’s plane are drawn where they would fall on it.

Send the ships yourself

Every settlement sends ships

So the edge of settled space keeps moving: about a light-year every fifty years, in every direction. After fifteen thousand years it is nearly three hundred light-years from the Sun and has passed half a million stars.

From here the faint neighbors drop off the map. Only stars that give off more than about fifty times the light of the Sun are drawn; stars like the Sun are far too many to plot.

We live in a hollow

The amber glow is interstellar dust, measured in three dimensions out to 1,600 light-years. The dark gap around the Sun is real: a cavity about a thousand light-years across, cleared by exploding stars. The wave crosses it in under thirty thousand years and reaches the edge of this map in eighty-five thousand, with thirty-five million stars behind it.

The streaks pointing away from the Sun come from the way the dust is measured. They are not real.

Explore the Kiloparsec

The whole of it

Everything so far fits inside the small ring around the Sun. The Milky Way holds some two hundred billion stars in a disk a hundred thousand light-years across. After three hundred thousand years, about as long as our species has existed, the wave is the blue patch around the Sun.

Nobody has seen the Galaxy from outside. This is a reconstruction from measurements, and most of the far side is inferred.

Explore the Galaxy

A million years

The wave is twenty thousand light-years from where it began and has reached one star in nine.

Two and a half million years

Nine stars in ten are behind the wave. Most of the Galaxy’s stars crowd toward its center. What is still dark is the thin outer disk, where stars lie farther apart and the wave slows. This is a simple model and every one of its assumptions can be changed, but its lesson survives large errors: at three percent of the speed of light, nearly all the Galaxy’s stars are reached in a few million years.

Run the simulation yourself

Now suppose we wait

The blue wave asks little of a star: rock, ice and light, which nearly every system has. That is how machines travel, and how people travel who go with them and build their homes from what they find. Suppose instead that people set out only for worlds like the Earth. About one system in forty has one, and on average fewer than one lies within a ship’s reach, so they must wait for the drift of the stars to bring the next one near. Look back at the Sun. In the same two and a half million years they have gone six hundred light-years.

The amber disc is their wave. Its edge moves at about 75 kilometers a second, the pace at which stars pass one another.

Sixty million years

Those who wait cross the Galaxy too. It takes them about sixty million years to reach nine stars in ten: twenty-five times as long.

Forty to eighty million years, depending on how common worlds like the Earth are. Each region is colored where its stars are today; over this long the turning of the Galaxy would carry them around it.

See this case in the simulation