Re: a mere 4.3 light years away
It's impossible with current physics. Have a bit of fun. Assume that you have a reaction mass which converts to energy with 100% efficiency. Assume that the energy is then converted to thrust with 100% efficiency. Next calculate how long it would take to decelerate at 1g from 0.25c back to 0. Don't forget relativity. (You don't want to be that guy.) I'm giving you the magic lasers & the power of the sun to get up to 0.25c. (And I DO mean magic. Do the math on creating lasers to drive the final mass calculated below at 1g.) Finally, use the rocket equation to compute how much reaction mass is required to drive a final payload of 500kg at 1g for that much time. Again, don't forget relativity.
Not possible.
Of course, we don't have to accelerate at 1g for the trip. A generation ship is almost certainly within current technology & probably engineering, just really freakingly expensive.
New physics, however, is new. Specifically, the idea of slipping past spacetime in some fashion rather than going through would conceivably eliminate the c barrier, but unless the tech to actually do so allows us to either bypass the rocket equation or throw a truly amazing constant at it, it won't do us any practical good.
Biting the hand that feeds IT
