Question

When is it estimated humans will be capable of intergalactic space travel?

Answer 1

My guess would be about `4` billion years, when the Andromeda Galaxy is due to collide with ours, but I'm not sure that counts.

Explanation:

The distances involved in intergalactic space travel would require some mechanism of Faster Than Light (FTL) travel to be accomplished in practical, useful time frames. Such mechanisms would tend to violate the principle of causality, so are unlikely to exist according to our current models.

Actually if a ship could achieve a sustained acceleration of `1`g for `14` years followed by a sustained deceleration of `1`g for `14` years, then the passengers could cross the current `2` million or so light year distance to Andromeda in a mere `28` years.

However, external observers in either galaxy would perceive the elapsed time as more than `2` million years. So it's not very useful to anyone apart from the passengers.

Of course we could be less ambitious and travel to one of the much closer satellite galaxies of the Milky Way, a mere `25000` or `70000` light years or so according to whether the disputed concentration of stars at `25000` light years counts as a galaxy.