there are many answers possible. none of them is definitive.
- first: the theory of relativity has been proven but this doesnt mean that it is perfect. the laws of physics have proven themselves surprising quite
a few times.
- second: the MHD that is described by a poster here I am not sure it would work in space. using super conductor materials to convey the energy
generated by an antimatter battery to magnets powerful enough in order to lift the vessel is an interesting theory that has proven right . we
currently dont know how to use superconducters at ambient temperature though and we are a long way from being able to use it in our everyday life
(maybe some government agency has perfected the process though)
- now in order to travel a few million light years in space you can either try the straight line (it's really old school physics here

). and try
to go as afast as you can
2 problems:
- your mass will increase and reaching light speed will require more and more energy (thus adding more mass...)
- given your speed you will age slower than the people you are visiting in another galaxy...
an interesting way would be:
- twin universes composed of antimatter and there is no life: you basically enter this universe where the speed limit on the highway is far greater
than the speed of light in our universe
- space/time warp: you have mastered gravity (and the law of relativity

) and you can generate enough mass around you to create a wrap in space
that will bend space and time. instead of travelling a straight line you will create a shortcut in the universe.
problem with the first scenario: we are discovering quantum physics. twin universe pohysics may be the next step
problem with the 2nd: I let you imagine the energy required to bend space and time (basically creating your own worm hole....)
both have great advantages: you travel in space/time great distances WITHOUT experiencing the time problem (when time passes more slowly for you than
for the person you are visiting a few million light years away)
add to that you need to cancel inertia as you are traveling at speed where no human body can withstand the speed without being ripped off... imagine
you are in a car, at max speed and all of a sudden you need to avoid an obstacle. high chances your airbag will go off, and you will bounce on the
wheel... even worse at speed of light or greater