So, a question: traditional objections to galactic travel (e.g. 1G accel) is the requirement for huge amounts of propulsion mass. Even with a method of perfect

So, a question: traditional objections to galactic travel (e.g. 1G accel) is the requirement for huge amounts of propulsion mass. Even with a method of perfect E=mc^2 of some special fuel matter, you still need a whole load of propulsion mass to chuck in the opposite direction, which in turn requires more energy to accelerate. the question is, could we get around that by converting from mass-less forms of energy, and generating mass on-the-fly, skipping the need to accelerate tons of acceleration mass; or is there some restriction that would disallow this? If I fire 2 photons at each other on a ship travelling at 0.5c, and this creates 2 particles e+ and e-; would the particles also be travelling at 0.5c along with the ship; would their velocity/momentum be in random directions etc?