I think I'd rather deal with the aliens who just have really good rockets. At least we could potentially comprehend the rulebook they play by. Who even knows what the hell the Walkers of Sigma 957 are about?
Perhaps they figured out AI or have made space-adapted biological life forms that can survive constant acceleration at 25Gs and are sending them out to scout the universe for other life, and once they find it they would signal back to the home planet.
25G of constant acceleration would kill any human, especially if it were maintained for the time it would take to approach light speed, but for an AI or a creature specifically developed to survive that it would make a trip to the Solar System from Alpha Centauri take 5-8 years.
Then again, if they could do 1G of constant acceleration that would only add like 2 years to the total trip. Long enough to be one-way for most people but short enough to be survivable under ideal circumstances.
Assuming they stopped outside of Neptune's or Pluto's orbit they would still have a few years of travel to make it to Earth but they would have started detecting our broadcasts long before arriving.
I'm not saying this happened, rather that it becomes plausible when you take some liberties with the starting conditions.
>Then again, if they could do 1G of constant acceleration that would only add like 2 years to the total trip. Long enough to be one-way for most people but short enough to be survivable under ideal circumstances.
It would take ~2 weeks to to approach light speed while continuously accelerating at 25G. It would only take ~1 year to do so at 1G continuous acceleration.
On cosmic time and distance scales, those are essentially the same, especially since once we approach the speed of light, there's no going faster.
As such, tolerance for G forces seems pretty irrelevant for interstellar travel.
Doing so within the confines of a solar system is another matter altogether, I'd expect.
I picked 25G as it would be an insane but reasonable acceleration, and time is always a factor. Trimming 2 years off of a voyage might seem worthless on an intergalactic scale, since once you are more than a few solar systems away you're on the scale of AI scouts and generation ships, but for a close star like Alpha Centauri, 2 years (each way) might be the difference between a one way death march and the possibility of a heroic return home.
Now add in the mass to slow down once you begin to approach your destination.
Which doesn't sound like a lot but its probably as much or more antimatter than exists in the entire solar system, so if it were the fuel then whoever was using it would need to have figured out a method to create and store antimatter in bulk along with the ability to react antimatter as rocket fuel without destroying the rocket its fueling.
