[goatlover]

If humans can expand inter-galactically, then it likely it would have happened already by some other species, given the size and age of our galaxy. But since we're not part of some prior alien galactic empire, it's probably not feasible. And we would also be able to see the energy output from other galactic civilizations nearby. But we see nothing. Not from Andromeda, not from anywhere in our local cluster.

[logicchains]

>If humans can expand inter-galactically, then it likely it would have happened already by some other species, given the size and age of our galaxy.

That's only true if we assume the chance of life arising is relatively high. It could actually be incredibly massively low, and we wouldn't notice, because we're observing from a position of extreme selection bias. I.e. probability(intelligentLifeInUniverse given weAreObservingIt) = 1.0.

[chii]

> And we would also be able to see the energy output from other galactic civilizations nearby

or they are utilizing an energy source so efficient that no leaks happen (that we can observe).