Known physics permits creating matter from energy: https://en.wikipedia.org/wiki/Pair_production https://en.wikipedia.org/wiki/Pair_production If you have a s

Known physics permits creating matter from energy: https://en.wikipedia.org/wiki/Pair_production https://en.wikipedia.org/wiki/Pair_production If you have a source of energy on the spacecraft, like a solar panel, you could theoretically convert some of that energy to particle pairs with mass. But this is such an inefficient process (and so inherently low-mass with any practical energy source) that I doubt the claimed thruster could work this way.