The universe is about 13,750 million years old. The Fermi argument suggests that—if there were intelligent aliens in this galaxy, they should probably have filled it by now—unless they originated very close to us in time—which seems unlikely. The argument applies much more weakly to galaxies, because they are much further away, and they are separated from each other by huge regions of empty space. Also, the Andromeda Galaxy is just one galaxy. Say only one galaxy in 100 has intelligent life—and the Andromeda Galaxy isn’t among them. That bumps the required distance to be travelled up to 10 million light years or so.
Even within this galaxy, the Fermi argument is not that strong. Maybe intelligent aliens formed in the last billion years, and haven’t made it here yet—because space travel is tricky, and 0.1c is about the limit. The universe is only about 14 billion years old. For some of of that there were not too many second generations stars. The odds are against there being aliens nearby—but they are not that heavily stacked. For other galaxies, the argument is much, much less compelling.
The universe is about 13,750 million years old. The Fermi argument suggests that—if there were intelligent aliens in this galaxy, they should probably have filled it by now—unless they originated very close to us in time—which seems unlikely. The argument applies much more weakly to galaxies, because they are much further away, and they are separated from each other by huge regions of empty space. Also, the Andromeda Galaxy is just one galaxy. Say only one galaxy in 100 has intelligent life—and the Andromeda Galaxy isn’t among them. That bumps the required distance to be travelled up to 10 million light years or so.
Even within this galaxy, the Fermi argument is not that strong. Maybe intelligent aliens formed in the last billion years, and haven’t made it here yet—because space travel is tricky, and 0.1c is about the limit. The universe is only about 14 billion years old. For some of of that there were not too many second generations stars. The odds are against there being aliens nearby—but they are not that heavily stacked. For other galaxies, the argument is much, much less compelling.