How did Superman turn back time in the first movie?

Question

In this what-if xkcd there is this question and answer about Superman:

In the first Superman movie, Superman flies around Earth so fast that it begins turning in the opposite direction. This somehow turns back time [... ] How much energy would someone flying around the Earth have to exert in order to reverse the Earth's rotation?

—Aidan Blake

Someone recently blew my mind by telling me I’d been misinterpreting that scene all my life. I like their take on it way better:

Superman wasn't exerting a force on the Earth. He was just flying fast enough to go back in time. (Faster than light, I guess? Comic book physics.) The Earth changed direction because we were watching time run backward as he traveled. It didn't actually have anything to do with the direction he was flying.

Is there any other source, (writer interview, script note, etc. ) to back this assertion?

Answer 1

tl;dr: No, there's no evidence that this is what Richard Donner or anyone involved with the movie intended us to believe. Moreover, that explanation does no better job than any other of explaining what we see on-screen, as the on-screen events cannot be from Superman's perspective and still fit with actual physics.

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What Happens

Superman flies into orbit and begins flying around the Earth counter-rotationally, reaching his maximum speed in about 8 seconds. During this period, the Earth continues to rotate at its normal speed and direction. Once Supes reaches his maximum speed (as evidenced by the "whoosing" noise he makes), the Earth comes to a complete stop for a few seconds, then begins rotating in the opposite direction. This goes on for ~30 seconds as we see events on Earth "un-happen".

Once he's finished, Supes comes to a complete stop, then begins flying in the direction of normal rotation. During that time, the Earth continues to rotate backwards, until Supes acheives the same rotational speed as he did originally, at which point the Earth then begins to rotate in its correct speed and direction again.

Why it Fails

Lets assume Supes can fly faster than light and assume that doing so would actually allow him to move backwards in time. This is a ridiculously simplified way of looking at general relativity, and almost completely ignores the effects of accelerating and decelerating at relativistic speeds, but it's a movie so lets just pretend.

In that case, as he approached light speed he should see the Earth gradually slow down as time dilation kicks in for him, then as he breaks the speed of light he should see the Earth begin rotating backward, increasingly fast as he moves backwards faster through time. This contradicts what we see on-screen:

• The Earth does not begin to slow down at all until Supes reaches his maximum speed. It should have already achieved its maximum counter-rotation by then.

• The Earth is completely stationary for several seconds. It should have appeared stationary only for the precise moment that Supes was moving at exactly the speed of light, and thus time was fixed. Once he kept accelerating, the backwards motion should begin immediately.

Even worse, the fact that time is going backwards is a function of Superman's speed, not his direction. The instant he slowed down from supra-light speed, time should have started going forward for him again. Instead:

• The Earth continues to rotate backwards even as Superman slows down. It should have slowed down, stopped, and began rotating normally as Supes decelerated.

• The Earth's reverse rotation slows down and corrects itself as Superman flies up to maximum speed in the opposite direction. It should have done the exact same thing that it did the first time: as he approaches light speed in the rotational direction, the Earth should have again slowed down and rotated backwards.

Conclusion

I think it's clear that no one involved with the movie was worried in the slightest about making a scientifically accurate portrayal of time reversal. The Earth rotating backwards was almost certainly meant as an easy-to-depict symbolic representation of time going backwards. We're meant to just hand-wave away the mechanics of how it actually worked because, after all, it's a flying immortal humanoid alien we're talking about.

Answer 2

In the Blu-ray commentary on the Extended Edition of Superman: The Movie, Richard Donner states during that scene:

And he stops the world. And now it's actually going backwards. Which means, none of this actually happens.

So the intention was that he's reversing the rotation of the Earth, which then reverses time. Must be some advanced Kryptonian science or something.

Answer 3

This theory of 'flying fast enough' seems to be backed up by the ST Enterprises' slingshot effect maneuver in IV: The Voyage Home and other episodes, and also backed up by some science:

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Wikipedia: In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense. Gravity assistance can be used to accelerate (both positively and negatively) and/or re-direct the path of a spacecraft.

The "assist" is provided by the motion of the gravitating body as it pulls on the spacecraft.1 The technique was first proposed as a mid-course manoeuvre in 1961, and used by interplanetary probes from Mariner 10 onwards, including the two Voyager probes' notable fly-bys of Jupiter and Saturn.

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Answer 4

As a kid who watched this in the theatre, I can tell you my eight year old brain that knew from reading comic books that Superman travelled in time by flying faster than light, that we are watching the Earth from Superman's perspective.

That's what I saw. I didn't see the earth's rotation reversed. The final moments when Superman appears to change direction makes sense, as he had achieved the speed to travel back in time, made sense to my kid brain, as he now he had to fly back the other way into normal time ie change direction from going back to forward, like I would a video recorder.

What we see is the film reversed. Literally. The SFX scenes played backwards, for a kid coming from seeing the original Time Machine movie, it was exactly the same way time travel was shown in that oscar winning sequence ie the Time Traveller sees the events around change in time lapse film fashion. Same here but in reverse.

Answer 5

Special Relativity's misinterpretation

According to Special Relativity's Theory, the faster you go, slower your proper time is, and if you reach v=c, then dt=0.

One could think that if you go faster than c, then you go back in time, however if you go faster than c, your proper time is not negative, but imaginary -- t * square root of (1 - v^2/c^2).

Answer 6

If you travel faster than light then it affects causality. For example, if you run faster than light you will reach the finishing line before the race even started. So that COULD explain it IF that was the intention at the time, of course, it wasn't. And you can't fly faster than light anyway, at least not in a cape.