According to Drake Equation estimates, the closest aliens in our own galaxy are likely to be about 21,000 light-years away. That means it will take 21 thousand years for our signals to reach them, and 21 thousand years to wait for a response. By the time we get a response, they may be all dead, or we may be all dead. That is some serious PING time!
Aliens may very well exist, in fact their existence may be a probabilistic certainty. But in all likelihood, one civilization won’t know about the other(s) unless it has existed for over 42 thousand years, and the foreign one has existed for at least 21 thousand years.
That is all assuming that both civilizations are actively trying to contact each other, and listen for any possible transmissions, and can decipher such transmissions meaningfully and concoct and transmit a logical response.
Assuming a civilization broadcasts messages for an average of 10,000 years, there may be about 22 currently broadcasting civilizations in our galaxy. Assuming 500 years (which may be much more realistic, since we’ve only been broadcasting for less than 100 years), there may be just 1.2 civilizations – Ours.