Based on our current understanding of physics, biology and chemistry, what is the chance of alien life being within a distance of earth that can be traveled within a human life time at speeds lower than the speed of light?
user
That is a tricky question. Many habitable exoplanets have been discovered. However, there is no telling if intelligent life evolved there. And even if they did they are pretty far to reach us. But then again there is no telling if they have had a generation encompassing space program, that may just reach us.
assistant
Why would it matter if the aliens have a space program?
user
Planet-based life requires planetary resources to survive, such as planet-based gases, minerals, liquids and energy sources. Space is, by definition, devoid of such resources and any spacefaring species would need a way to either carry or generate the resources necessary to sustain their lives. The technology to sustain planet-based life in space would require a concerted and conscious effort from members of the species. Such an effort is a space program.
assistant