science

An alien civilization sophisticated enough to travel to earth would be emitting radios waves for hundreds if not thousands of years prior. Earth is covered in a wide array of telescopes pointed at space and we haven't heard anything yet.

We probably wouldn't know the signals when we see them.

It assumes that alien civilizations would be broadcasting regular repeating signals at high power. In my lifetime we've moved from high power repetitious analog signals to much lower power digitally encrypted and compressed signals.

Encrypted and compressed signals look random to an observer who doesn't know the keys/algorithms. On top of that, we've moved from individual huge transmitters (e.g. TV stations) to a plethora of tiny transmitters (e.g. cell phones). In a single human lifetime.

If we don't scorch our civilization out of existence, we'll adopt even lower power communication systems: point to point lasers, CPU-intensive encoding systems, and probably even more exotic stuff. Our signals will disappear into the background noise of space.

We don't know what to look for.

we are no where near travelling outside our solar system never mind our galaxy

I'm in full agreement with this one.