Our Universe is big, and it’s been around for a long time. So why don’t we see any evidence of aliens? If they are out there, why haven’t they contacted us, and how do we contact them? What methods might they use to try and contact us?
Where do we look for signs of alien civilizations?
The search for extraterrestrial intelligence, otherwise known as SETI, are the methods that scientists have proposed to discover evidence of aliens in the Universe.
Perhaps the most famous method is listening for their signals. Here on Earth, we have exploited the radio spectrum to send signals through the air. We even use it to communicate with spacecraft in the Solar System.
So, since it works so well for us, it makes sense that aliens might use radio waves to communicate from star to star. If there’s an alien civilization out there beaming a signal directly at the Sun, our largest radio telescopes should be able to pick up their signal.
The problem is that the galaxy is huge, with hundreds of billions of stars. Any one of which could be the world where the aliens live. Furthermore, we don’t know which frequency the aliens might use to communicate with us.
Even though the search for ET has been going for many years, we’ve only explored a fraction of the millions of available stars and frequencies on the radio spectrum.
So far, no definitive signal has been discovered.
Gieren et al. used the 8.2-m Very Large Telescope (Yepun) to image M33, and deduce the distance to that galaxy (image credit: ESO).
Another possibility is that aliens are using lasers to communicate with us. An alien could target an incredibly powerful laser at our star, and it would be detectable with our large optical telescopes. There have been a few dedicated searches for laser communication, and scientists have proposed we could search for these alien signals at the same time we’re searching for extrasolar planets.
Again, so far nothing has turned up.
View from inside the Borexino neutrino detector. Image Credit: Borexino Collaboration
It’s possible that aliens use a more exotic method of communication, like neutrinos.
Neutrinos are generated in high energy collisions, and can pass right through planets with ease. They would be incredibly difficult to detect with our current technology, but maybe advances in the future will make that a possible communication method.
But maybe Instead of searching for signals, we could look for their artifacts.
If the energy of transmitting signals across the vast reaches of space is too much, it might make more sense for aliens to construct self-replicating probes and let them journey from star to star.
These probes could leave behind an obvious alien-made structure which we could discover once we become a true spacefaring species.
We could also detect aliens by their impact on their home planets. With a large enough space telescope, we should be able to study the atmosphere of planets orbiting nearby stars. An industrialized civilization would probably be polluting its atmosphere with various gases — just like we have — which would be detectable.
Finally, we could search for evidence of aliens through their structures.
If a civilization starts building megastructures which block off a large portion of their star’s light, we should be able to detect evidence through our search for extrasolar planets.
A Star Trek-inspired space station.
A gigantic space station would give off a much different light signature than a nice spherical planet as it passes in front of its star.
There have been a few attempts to reach out to other worlds directly, transmitting signals out into space. It’s unlikely that these signals will actually reach any other civilization, and some scientists are concerned about the wisdom of this kind of communication.
Do we really want to alert potentially hostile aliens to our location in the Milky Way?
It’s exciting to think that there are other alien civilizations around us in the Milky Way, and with a little more work, we could discover their location and maybe even communicate with them.
Let’s hope they’re peaceful.
Source: Universe Today, story by Fraser Cain