Life on Earth arose about as soon as it was possible for life to arise

[jeff47]

18. How well would a person from 1000 AD hear us?

Today, we do long-range communication via radio waves.

Someone from 1000 AD could not "hear" our technology at all - they lacked the equipment to detect our communication. Similarly, we may lack the technology to "hear" more advanced species. RF is totally unsuitable for communication over interstellar distances, so an interstellar species is going to have to use something else.

Additionally, our radio waves are only strong enough to be detectable in our local neighborhood. If there is a clone of our species 250 light-years away, that was broadcasting 250 years ago, we can't hear them. The signal is too weak by the time it reaches Earth.

And to make that problem even worse, our RF is getting weaker. We peaked in about the 1960s. Since then, we have been using lower and lower power RF signals. We are using lots more RF from cell phones, wifi and the like. But the signals are about only 200mW to 2W. "Wolfman Jack" broadcasted from a 250,000W radio station.

It is extremely likely that other species went through the same RF pattern - nothing for millennia, then a very short high-powered window, followed by weaker and weaker signals. And that high-powered window only reaches a couple dozen stars before it is overwhelmed by background static.

The distances involved are so mind-bogglingly vast that it is utterly different from our Earth-bound experience.

Finally, Kepler data indicates there's roughly 40 billion planets in the habitable zones around the stars in the Milky Way alone. Even if advanced life is a 1-in-a-billion chance, that means there's about 40 advanced species in just our galaxy. But those 40 are spread out over hundreds of billions of light years. When a signal only goes about 200 light years, it's very, very unlikely that it's going to stumble across another one of the 40.