Do Extraterrestrials Exist?

Possibly, the odds are we'll never know for sure, though.

We humans have only been sending out radio signals (for another civilisation to detect) for about 100 years.  So an extraterrestrial species, with our same level of development but living 200 light years away (the universe is said to be about 156 BILLION light years wide) would still have to wait another 100 years to get our signals.  And then they would need the technology to filter them out from all of the rest of the Universe's noise. And visa versa, we would have to wait another 100 years to pick up on their radio emissions.

What if these extraterrestrials turn out to be as self-destructive as humans sometimes are?  It turns out they were releasing signals 1000 years ago, but they blew themselves up 500 years ago.  We would never know they were there.

As long as living creatures, especially advanced life forms, are relatively rare in the Universe, then what with the distances, the time gaps (the Universe is almost 20 billion years old), the cosmological noise, the risks of species self-destruction or an asteroid collision destroying advanced life forms, we'd be very lucky to ever make contact with any extraterrestrials.