[TomBombadildoze]

> The nearest galaxy is 25k light years away so even at the maximum speed it would take 25 thousand years to travel here.

Given your arithmetic, I assume by "maximum speed" you mean the speed of light, in which case travel wouldn't take 25k years. It would in fact be instantaneous. At relativistic speeds, distances contract and time dilates.

Now, this is all moot because this:

> The idea that aliens would use these to propel ships is rather ludicrous, and highly unlikely.

... is absolutely correct. No amount of energy will propel a massive object to the speed of light.

edit: I realized I may have misinterpreted. From the perspective of someone watching their own kind travel that expanse, it would indeed appear to the outside observer to take 25k years to travel.

[marcusverus]

As long as we're being pedantic, the trip is only instantaneous if you're able to instantly accelerate to c. Otherwise, it would take around two years for the occupant (one year to accelerate to c upon departure and another to decelerate on arrival), assuming acceleration at 1G.

[AnimalMuppet]

Ahem. To add yet more pedantry, one year of acceleration at 1G doesn't get you to c, but only fairly close. (I worked that problem nearly 40 years ago, so my memory of "how close" is a bit obscure.)

[umvi]

Plus reaching the speed of light requires infinite energy, literally. You have to settle on some small fraction of the speed of light, depending on how much mass and energy you have.

[dvh]

It's pointless to travel at speed of light to get instantaneous travel when you spend half an hour boarding rocket and 2h in traffic from the city to starport.

[gibolt]

And you have to stow your laptop for the duration of the instantaneous flight

[umvi]

It's only instantaneous for you. Anyone not on the light speed rocket will be dead by the time you deboard on the other side.