�鶹��ý

If there are advanced alien civilizations in the Milky Way, we ought to be thinking about how to say hello to our neighbours. The vast space between stars makes that difficult, but a fresh simulation suggests that using the sun as a lighthouse beacon could make a galactic community possible.

In the same way that plane and train operators use flashing lights as signals, we could one day manipulate the light shining from our sun, like waving a hand in front of a torch to shine out a message.

One way to do that is to lasso huge swathes of asteroids or mine a chunk out of Mercury to build a planet-sized sheet to orbit our sun. Another, more feasible, idea is to use powerful lasers to change how Earth’s transits look to other worlds, adding a message encoded in light to our planet’s shadow as it passes in front of the sun.

Yes, it would be tricky. But if other advanced aliens were also attempting to make contact, we could eventually create a galactic communications network. A new simulation by at the University of St Andrews, UK, finds that it could take at least 300,000 years to build a network around the Milky Way, assuming there are 500 technologically advanced civilizations who manage to manipulate their planet’s transit in a visible way.

To chat with them all, we’d have to build a kind of relay network around the galaxy to avoid celestial obstacles.

“If you want to communicate with someone on the other side of the galactic centre, there’s lots of stuff in the way – dust, stars, a big black hole – so you can take the long way around using the network,” says Forgan.

Orbit signals

When searching for potential extraterrestrial signals, you would have to look in just the right direction at just the right time to spot one. But planets pass between their stars and us regularly, so if the orbit of another world is aligned in such a way that we can see it passing in front of its sun, and its inhabitants were to alter the look of their planet’s transits as a signal, we could find them.

Constructing any kind of enormous orbiting object would take a lot of work, though, making it an unlikely eventuality, says at Harvard University.

“Once a civilization is advanced enough to have the technology to build megastructures, it’s much more likely to leave its planet,” he says.

“Each signal would take thousands of years to travel back and forth,” he adds. “In cosmic time that may not be that long, but you need patience.” That’s not to mention the interstellar politics involved in setting up a cooperative galactic network.

The upside of communication via transit is that we already have projects such as the Kepler space telescope watching for planets passing in front of their stars. If other planets are seeking to make contact in this way, we don’t have to do any extra work to see them.

Reference:

Read more: We still haven’t heard from aliens – here’s why we might never