The search for intelligent life outside of our solar system is a difficult one. We tend to think that if we expand the scope of our search to include more galaxies, this is sufficient. But we must accept that even if we had the technology to examine every galaxy exhaustively in perfect detail, we are only covering a minuscule part of the search space, which is almost entirely inaccessible to us by the laws of physics.
We can only see something in the current snapshot in time. Let’s try to imagine a search for human radio signals on Earth from the perspective of a distant alien civilization. The Earth is 4.4 billion years old. Humans started producing radio signals in 1894, so these radio signals have been transmitting for the past 121 years. These signals have only had the opportunity to propagate 121 light years away from Earth in that time. Beyond that distance, no alien civilization would be able to detect these signals. Moreover, an alien civilization would have to coincidentally have developed at a pace in which their technology was at least as advanced at exactly the right time to detect such signals during this tiny window in time upon their arrival. This is a 121 year window out of the 13.82 billion years in which the universe has existed.