Time Travel in Superman - The Movie

[Jeff Root]

This has almost certainly been pointed out elsewhere, but it
occurred to me independently, so I'm writing it up.

At the very end of the first 'Superman' movie with Cristopher
Reeve, Superman apparently flies around the Earth so fast that
he makes a visible ionization trail, and keeps flying faster
and faster, until he is flying faster than the speed of light
relative to the Earth.

Superman's flying faster than the speed of light causes him to
go backward through time. Logically, the faster he flies, the
faster he goes back in time, and the longer he maintains that
speed, the farther back in time he goes. He goes far enough to
save his girlfriend. I'm not sure whether he also managed to
save the world-- it's been a while since I saw the movie.

The audience sees Earth's way exaggerated rotational motion
slow down, stop, and then reverse direction as Superman flies
around it. That isn't explained in the movie, but it has a
simple explanation: We are following Superman as he goes back
through time. We must be, or he would disappear from our view.

Superman does not cause the Earth to go back in time by flying
around it. The fact that he flies around Earth is incidental
to his flying at ludicrous speed relative to the Earth. He can
only go back in time himself, or carry something with him as he
goes back in time.

So, here comes the error I want to point out: When Superman
goes back in time and we follow him, and we see that we are
following him back in time by the fact that Earth's rotation
slows and reverses, the ionization trail he left behind remains
visible. Or actually, it continues to fade as it had been
before Superman reached light speed. The trail far behind him
continued to fade as we watched, even though we were seeing an
earlier time when the earlier part of the trail was brighter,
though the whole trail was shorter. We should have seen the
trail evolve backward in time, along with Earth's rotation.

-- Jeff, in Minneapolis

[Frog march]

if he went back in time, wouldn't he crash into himself? :D

[Jeff Root]

He wouldn't be any more likely to crash into himself than into an
orbiting satellite. But when he first started going back, he would
probably be super-posed on himself (pun not intended but greatly
appreciated) at first. He would be in two slightly different places
at the same time, which may be exactly what you meant. I hadn't
thought of that problem in this context.

I said "probably" because, at such ludicrous speed, he might fly
forward a whole relativistlcally-contracted body length in a single
quantum of spacetime -- if there is such a thing. So one instant
he would be in one place, and in the next/previous instant he
would be in two places.

Since Superman is changing the past, I assume that he (and we)
would not see himself or his own ion trail from the future. That is,
before he reached light speed, he would not see his future self up
ahead of him. However, once he does start going back in time, he
should see his past self when he passes it, and we would continue
to see it from our distant vantage point. I think this because we
see the Earth's rotation direction change. If we see the past Earth,
we should also see the past superman (or his ionization trail).

I kinda wish the guy in the apartment above me were doing what
it sounds like he's doing. He must have a Wii exercise program,
or the like. Pretty intense for about 15 minutes. The floor really
creaks good. He also must have his air conditioner going!

-- Jeff, in Minneapolis

[JustAFriend]

If I remember correctly from growing up on early 60's comic books, both Superman and the Flash used this gag to time-travel back then, too. (I seem to remember Flash even running faster-than-light on some sort of super running-conveyor belt.)

The movie was just copying it.

[Noclevername]

Technically that's bad physics, not bad astronomy.

[Swift]

As best as I can tell, comic book physics (whether in an actual comic book or in a comic book movie) has no basis in reality. To call it fantasy physics is an insult to both fantasy and physics. ;)

[ravens_cry]

There was a rather weird Flash story where the Flash went almost the speed of light because Death was chasing him. It was resolved because of time dilation. Eventually the Flash got far enough in the future that all life was gone. With nothing living Death had no reason to exist and so vanished.
So yeah, assuming the Flash could go that fast, it (basically) used (a portion of) real world physics as part of a pretty trippy superhero story.
But Supermans "travel around the Earth backwards to go back in time" felt painful, even to my pre-pubescent brain when I saw it the first time.

[mike alexander]

My own recollection is that Supes traveled in time by spinning very rapidly on his vertical axis. One way he went into the past, the other way into the future. I forget which was which.

[ravens_cry]

Like this (http://superdickery.com/index.php?option=com_content&view=category&layout=blog&id=33&Itemid=52&limitstart=10)?

[Jeff Root]

Yes, of the very few Superman comics I had as a kid, more
than one showed him spinning to time-travel. That was in
the early 1960's.

I think that's how Superman died. He choked when his cape
wrapped around his neck at super-speed.

-- Jeff, in Minneapolis

[ravens_cry]

Well, it was the Silver Age. Weirdness was basically mandatory.