The absence of receiving meaningful radio waves from outer galaxies does not necessarily mean that there are no intelligent alien species in the universe. There are several factors that could contribute to why we have not detected such signals:
Distance: The universe is vast, and the distances between galaxies are immense. Even with radio waves traveling at the speed of light, it takes a significant amount of time for signals to travel across such distances. The signals from potential extraterrestrial civilizations would have to traverse vast cosmic distances to reach us, and vice versa.
Directionality: Radio signals emitted by intelligent civilizations would be highly directional, meaning they are focused in a specific direction. Detecting these signals requires our planet to be in the path of the directed signals, which is a rare occurrence given the vastness of space.
Signal Strength: By the time radio signals from other galaxies reach us, they may have weakened significantly due to distance and other cosmic phenomena. Detecting these faint signals against the background noise of the universe can be challenging, even with advanced radio telescopes.
Technological Factors: It's also possible that other civilizations may be using communication technologies or methods that are different from or more advanced than radio waves. There could be other forms of communication that we are currently unaware of or unable to detect.
Timing: Even if there are other intelligent civilizations in the universe, the chances of their existence overlapping with our own at the same time in cosmic history are uncertain. Intelligent civilizations could have existed in the past or may emerge in the future, making it difficult for us to coincide in time.
It is important to note that the search for extraterrestrial intelligence (SETI) is an ongoing field of scientific research. Scientists are actively conducting searches for signs of intelligent life using various methods, including radio telescopes, optical telescopes, and more advanced techniques. While we have not yet detected any conclusive evidence of intelligent alien civilizations, the possibility of their existence still remains an open question.