I took an astronomy class a few years ago and in that class we learned about the drake equation. This mathematical formula is a theoretical formula that predicts the number of intelligent (communication-able) life forms in our universe based some known and unknown variables (that require estimations).
The equation is as follows:
R + Fp + Ne + Fl + Fi + Fc + L = N
R is the number of stars in our galaxy that form (like our sun) per year.
Scientists figured out that in infant galaxies stars form rather quickly...about 50 per year. Meaning the number here must be smaller than 50 for our older galaxy...(lets use 50)
Fp is the fraction of these stars that develop planets.
Scientists have found about 500 planets around other stars. knowing we don't have the technology to find them all, and knowing that there are between 200 - 400 billion stars in the milky way, a guess of 1/1000 or .001 stars would be more than a conservative guess (that's 200 million to 600 million stars with planetary systems...)
Ne is the number of Earth like planets in these planetary systems.
Your guess is as good as any astronomers. Lets say that like our system, only 1-2 planet will be Earth like.
Fl is the fraction where life develops on these Earth like planets?
Who knows? Lets say .2
Fi is the fraction of these planets where intelligent life develops.
Well the only life we know of is on Earth, and we developed intelligent life. but that doesn't mean anything so lets say .25
Fc is the fraction of these planets where communication develops.
Again, using Earth as a baseline, lets go with 1.
L is the lifespan of these communicative civilizations.
There are two points to add here. first, Humans have only known about radio waves since 1865. That is about 150 years ago. With that said, we have only been listening and transmitting for a shorter amount of time. Lets say we have been transmitting for 100 years.
Second, if you ignore technological improvements that make past means of communications useless, imagine where humans were 1000 years ago. Now imagine 1000 years from now. Lets say we communicate for the same way for about 1000 years (a very very conservative estimate).
Ok, lets plug in the numbers. If my math is correct, that 500 planets with intelligent life. Now while that is completely speculative, there are more things to consider.
Forget language barriers
Forget technology barriers
Think about the size of our galaxy (100,000 light years). using simple probability, that means that in our hypothetical universe each life form is an average of 200 light years away. Meaning, if we send them a message, now, we will receive a response in 400 years (there and back)...that means we can talk to them twice in our 1000 year communication capable lifetime.
Many hypothetical possibilities and assumption, but you get the gist. Here is a handy site for your calculations:
I'm skeptical about finding this life if it exists. And if it does, I probably (hypothetically) won't know about it in my life time..