It seems the best shot for humans to visit other stars is a relativistic rocket, such as the hypothetical 1g rocket, which would dilate time in order for the mission to be completed in the crew's lifespan. Unfortunately, even travelling to the nearest star (Proxima Centauri, 4.26 LY), according to 1g rocket calculator tools online, would take 3.5 years ship time. I have also heard that 1g rockets can reach 0.99999999996 C, but only after 12 years ship time, and would take another 12 years ship time to decelerate.
My question is, can a relativistic rocket ever dilate time enough to be practical? Like say, travelling 500 lightyears in only 12 days ship time?
I have heard that rockets can't accelerate much faster than 1g without killing the crew, and that an equal amount of time is needed to decelerate at 1 g. But couldn't the rocket accelerate at 1g as close as possible to C, and then decelerate at freefall speed, keeping the crew closer to C as long as possible, and increasing the time dilation experienced? I'm sure someone who knows better can tell me why I'm wrong.
I'm also assuming this is a laser sail, and have read of hypothetical laser sail methods to accelerate small payloads to 0.26 C in ten minutes. I highly suspect that would kill the crew. Intuitively, I feel using beams to accelerate the ship would be more subtle, and not cause the ship to experience high G forces, but once again, I'm sure somebody who knows more about it can tell me why I'm wrong.
So, that's the question, is there anyway to accelerate a human crew, without killing them, close enough to C and fast enough that the time dilation shortens interstellar trips to weeks or months ship time, thus making it a more practical mode of travel.
What's the absolute most we could shorten, say, a 500 lightyear trip for them?