That hypothesis should be thoroughly tested within the next hundred years.
Our galaxy is a good testing ground for whether advanced civilizations are ubiquitous. There are 400 billion star systems in the Milky Way, and if we turn out to be the only civilization in this galaxy, there's no reason to be optimistic it will be found in abundance in other galaxies.
Firstly, if life is inevitable in the presence of liquid water and molecular chemistry we should find evidence of it in our own solar system, or at least in biosignatures of exoplanets
Any advanced technological civilization should leave a footprint in the radiowave frequencies of the EM spectrum. Radio and microwave energy is the only part of the electromagnetic spectrum that can realistically be used for communication and navigation. Radio astronomy programs like SETI should hopefully be able to make a detection if alien technology is out there.