If one is going to bring real world physics into discussions about Superman, then it's impossible for Superman to fly in the first place. An insistence that real world physics be followed means no Superman, period.
No Superman movie has ever been realistic when it comes to showing Superman fly. Even if it were possible to fly without the aid of machinery, there would have to be both conservation of momentum and energy, which has never been shown. To be realistic, when Superman changes trajectory during flight, he must pull or push some other masses outside himself, and such an effect could plausibly be harmful or even fatal to people around him.
The 1978 film suggested that Superman's powers arose because the galaxy he was from, not our own, had a different law of space and time. Each galaxy he passed through on his way to Earth had a different law of space and time, as was heard in one of Jor-El's lectures to the baby Kal-El (at the two minute mark of this video
), right before he forbids him to interfere in human history.
That Superman's body, originating in another galaxy where the laws of physics are different, might produce effects contrary to our
laws of nature, when accelerated to near or beyond the speed of light, would seem as plausible as any of the other things we routinely accept in science fiction, such as warp drives and transporters.
Anyway, it's rather amusing to read the claim that time travel doesn't work right in a movie about a virtually invulnerable man with X-ray vision who can fly, when all the other multiple and independent powers are accepted without objection.