For Ars Technica, science writer Jennifer Ouellette and theoretical physicist Sean Carroll review time travel used in 20 popular movies, ranging from The Terminator to Bill and Ted’s Excellent Adventure to Interstellar. Each movie is rated on scientific accuracy and how entertaining the use of time travel is. Here’s part of their review of Superman (1978).
Our standards are admittedly lax when it comes to the physical mechanism by which cinematic heroes journey through time, but “flying really fast around the Earth so that it reverses the direction of its rotation and sends it back to a previous moment” is such thoroughgoing lunacy that one must almost pause in admiration. Then we return to our senses and ask, “Why does Superman’s flight have any effect on the rotation of the Earth? And what does that rotation have to do with the direction of time? Do I get younger if I start twirling counterclockwise?” No, dear reader, you do not. Indeed, by the rules handed down by Einstein, Superman’s near-speed-of-light journey would actually send him into the future, not into the past.
To its dubious credit, Superman pioneers two different flaws that will frequently recur in movies to come. First, time travel is portrayed as a miraculous cure-all, which is then never used again. Superman essentially goes back in time to save his girlfriend. This is admirable, but aren’t there other, more historically significant global disasters that could be averted by the same strategy? This is a narrative problem, not a scientific or logical one, but it rankles.
Then, of course, there is the flaw that almost always accompanies stories in which the past gets changed by time-travelers: Where did those time-travelers come from? We, the viewers, see a sequence of events that seems to make sense if we don’t think too hard. Lois Lane dies, Superman gets upset, he travels back in time, stops the events that led to Lois dying, and we live happily ever after. But at the end of this sequence, Superman still has the memory of Lois dying the first time around. Yet because he changed history, that event he remembers never happened. Lois certainly doesn’t remember it. How does he?
After an unbelievably stressful and busy winter/spring, I am hoping to find some time to read this summer. One of the books on my short list is Sean Carroll’s The Big Picture, one of those “everything is connected” things I love. From a post by Carroll on what the book’s about:
This book is a culmination of things I’ve been thinking about for a long time. I’ve loved physics from a young age, but I’ve also been interested in all sorts of “big” questions, from philosophy to evolution and neuroscience. And what these separate fields have in common is that they all aim to capture certain aspects of the same underlying universe. Therefore, while they are indisputably separate fields of endeavor — you don’t need to understand particle physics to be a world-class biologist — they must nevertheless be compatible with each other — if your theory of biology relies on forces that are not part of the Standard Model, it’s probably a non-starter. That’s more of a constraint than you might imagine. For example, it implies that there is no such thing as life after death. Your memories and other pieces of mental information are encoded in the arrangement of atoms in your brain, and there’s no way for that information to escape your body when you die.
4. You live in the past. About 80 milliseconds in the past, to be precise. Use one hand to touch your nose, and the other to touch one of your feet, at exactly the same time. You will experience them as simultaneous acts. But that’s mysterious - clearly it takes more time for the signal to travel up your nerves from your feet to your brain than from your nose. The reconciliation is simple: our conscious experience takes time to assemble, and your brain waits for all the relevant input before it experiences the “now.” Experiments have shown that the lag between things happening and us experiencing them is about 80 milliseconds.
5. Your memory isn’t as good as you think. When you remember an event in the past, your brain uses a very similar technique to imagining the future. The process is less like “replaying a video” than “putting on a play from a script.” If the script is wrong for whatever reason, you can have a false memory that is just as vivid as a true one. Eyewitness testimony, it turns out, is one of the least reliable forms of evidence allowed into courtrooms.
1. Traveling into the future is easy. We travel into the future all the time, at a fixed rate: one second per second. Stick around, you’ll be in the future soon enough. You can even get there faster than usual, by decreasing the amount of time you experience elapsing with respect to the rest of the world — either by low-tech ways like freezing yourself, or by taking advantage of the laws of special relativity and zipping around near the speed of light. (Remember we’re talking about what is possible according to the laws of physics here, not what is plausible or technologically feasible.) It’s coming back that’s hard.
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