If you were hunting for alien intelligence, looking for a surefire signature from across the Universe of their activity, you’d have a few options. You could look for an intelligent radio broadcast, like the type humans began emitting in the 20th century. You could look for examples of planet-wide modifications, like human civilization displays when you view Earth at a high-enough resolution. You could look for artificial illumination at night, like our cities, towns, and fisheries display, visible from space.
Or, you might look for a technological achievement, like the creation of particles like antineutrinos in a nuclear reactor. After all, that’s how we first detected neutrinos (or antineutrinos) on Earth. But if we took that last option, we might fool ourselves. Earth created a nuclear reactor, naturally, long before humans ever existed. Read more.