Physics errors in the movie "Arrival"

Question

After seeing the movie Arrival, though I enjoyed it, I nevertheless kept feeling that there were some serious violations of physics occurring. However, I'm not sure what the precise problems are (I am not a physicist).

Question: what, if any, are the physical laws broken in Arrival ?

Spoiler alert

In particular, I felt that the main character's seeming ability to not only see into the future, but also influence it, must have violated laws regarding the light-speed limit on information transfer.

But, maybe more importantly, doesn't it violate some kind of energy conservation? i.e. the movement of information and other influences over vast spans of spacetime, seemingly instantaneously, powered by...

her brain(?). Perhaps the movie implied that she was simply "remembering" the future, not influencing it, but I suppose that's a violation of relativity (future events influencing the past). And makes her future actions look inane.

Incidentally, I think that issues relating to the alien's technology are valid, but perhaps easier to explain away by e.g. "sufficiently advanced technology being indistinguishable from magic" arguments.

Also, I am aware that there are some media articles on this, but I do not find them to be very scientific (I always appreciate equations accompanying words).

Answer 1

The movie is not in particular conflict with special relativity. It does have some substantial paradoxes, as all time-'travel' stories do, but those do not interact with special relativity.

The connection you're thinking of actually runs as follows:

Under special relativity, the ability to travel faster than light grants you the ability to see, and interact with, events in your past and future light cones.

This is why faster-than-light travel is problematic, because it immediately makes you liable to all the paradoxes of causality under time-travel conditions (i.e. the grandfather paradox and its derivatives). The problem comes from the causality structure, not from the faster-than-light side.

In the movie, on the other hand, you start off right at the problems with causality, and with or without SR, if you want to analyze the plot you're going to have to resolve those loops somehow. If people can remember their future, what happens to those memories if they do things that will change those outcomes? (That said, I think that the loop as presented in the movie is self-consistent, i.e. it's a loop in which the Louise's actions implement the future she sees, instead of contradicting it. The problem with those loops, of course, is how you get into them, but that's the fundamental paradox of the movie.)

If you add SR into the mix, then yes, Louise could talk to Alice at event $E_A$, remember it at an event $E_{A'}$ in the far causal past of $E_A$, and then send a subluminal message to Bob, who receives it at an event $E_B$ that's spatially separated from $E_A$ (so, simultaneous in some frames of reference), resulting in superluminal communication. Is this a problem? Well, not particularly: you could use it to transfer information back in time, but you could already do that, and that was already a causal problem to begin with, so SR doesn't tell you anything new.

Answer 2

There's actually a deep philosophical question about time at issue here: the A-theory of time and the B-theory of time.

Roughly, the A theory of time says that our everyday experience of time--that only now exists, the past is gone, and the future is not yet existent--is actually how the universe and time operate. At each moment, the present moment--now--transforms via the laws of physics into the next moment. We remember the past because the present moment was created from the past state, leaving evidence of itself in the present moment. The future has never existed, so we can't remember it because it can't have had an effect on now yet.

The B-theory of time states that time is much more like space than we can imagine. All of space already exists. When you look at the night sky and your gaze drifts from north to south, the different parts of the sky that become visible aren't coming into existence just in time to meet your gaze. The scene changes merely because you can't see everything all at once. The idea of the B-theory of time is that all time--past, present, and future--already exist. We are merely limited to the time that we can see as we involuntarily turn our gaze into the awaiting future, like a person standing on a train looking out through a narrow tube. The scene changes not because the future comes into being at the expense of the present, but because our vision and interaction with the universe is narrowed to a small slice of the total reality, which we give the name "the present."

One may interpret the aliens teaching humanity their language as rewiring their brains to be able to see time through the B-theory (remember that the linguist Louise Banks starts dreaming differently as she learns more of the language). The language itself is timeless, being written forwards and backwards simultaneously. It reminds me of the Tralfamadorians of Kurt Vonnegut's Slaughterhouse Five.

The most important thing I learned on Tralfamadore was that when a person dies he only appears to die. He is still very much alive in the past, so it is very silly for people to cry at his funeral. All moments, past, present and future, always have existed, always will exist. The Tralfamadorians can look at all the different moments just that way we can look at a stretch of the Rocky Mountains, for instance. They can see how permanent all the moments are, and they can look at any moment that interests them. It is just an illusion we have here on Earth that one moment follows another one, like beads on a string, and that once a moment is gone it is gone forever.

When a Tralfamadorian sees a corpse, all he thinks is that the dead person is in bad condition in that particular moment, but that the same person is just fine in plenty of other moments. Now, when I myself hear that somebody is dead, I simply shrug and say what the Tralfamadorians say about dead people, which is "So it goes."

In a sense, we are always traveling into the future at the speed of light (one second per second) in the future direction. We can turn a bit this way or that in order to travel through space instead. We just haven't yet figured out how to turn around and enjoy the view.