Comment by mrguyorama

>If you can figure out a way to apply thrust that doesn't require you to lug mass with you and throw it out the back of your spacecraft you will open up the stars to exploration

This is also called "Everything we know about physics is so radically wrong that it shouldn't be possible for us to make the predictions we do"

Reactionless drives are not physical, or if they are physically possible, will have such unique quirks and constraints as to be meaningless outside of some insane laboratory setup.

For example, making very high weight new atoms that have never existed in the universe before is physically possible, but the realities of making those atoms and their nuclear instability means it doesn't matter even if a super heavy element has some crazy properties that we would like to exploit, because there will never be enough of that element to make anything out of. The "rules" of atoms should still work well above 180 protons, but other physics makes that meaningless.

Without reactionless drives, interstellar travel is so physically difficult to be essentially impossible, and no amount of engineering or cleverness can change that.