There may be other ways for communication which we still don't know. Back in the year of 1492 Lorenzo de' Medici has died in Florence. Sending that urgent message from Florence to Venice (259 km) by horse would have taken several days. Sending that message by a signal pigeon would have taken several hours (if that pigeon wasn't catched by a bird of prey ;)

Today that message is travelling that same distance over the Interent in way under 1 second. This fact would have been incredible for that medieval person.

Imagine how science has been progressing during these 500 years. How much more do we know today than was known in 1492? If you had shown WhatsApp to a person in Florence in the year of 1492, you would have been burnt for witchcraft right away. ;)

Now imagine that there may be ways of communication we still don't know. But in the year of 2500, there may be transmitters available which let us communicate with intelligent, advanced civilizations many 1000 light years far out...