Acceleration to near-C, at a constant 1G, takes about 1 year

how much fuel will that acceleration cost?

what happens when you encounter a grain of sand traveling at
near c.

how much energy would it cost to detect that grain of sand
at a distance far enought to allow for a course change.

and we dont yet know if there is anything in the void between the solar systems that would allow for a course change.

how do you know that there are even enought ions in the void?
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.