Three Recent Time Loop Episodes That Are Instant Classics

I’m not really a fan of time loop stories, both because the repetition annoys me and because the physics make no damn sense (which is true of most time travel stories in general). But in recent years, people writing time-loop stories seem to understand that the audience is used to the trope, so they don’t waste time on the first few repetitions but just jump right into the meat of the story where somebody’s already in on the loop, and they make sure each loop is quite distinct from the others, so I’m finding them less annoying than I used to. Syfy’s Dark Matter did this effectively in “All the Time in the World,” episode 4 of season 3.

Also, it seems we’re getting more episodes lately where the so-called “time” loop turns out to be a simulation or a dream rather than an actual time-travel event. It was openly a coma patient’s repeating nightmare in the Cloak and Dagger episode, and I can think of two recent examples where it was a computer simulation (in one case a VR game where the viewpoint character was simply respawning when he died), though naming them would be a spoiler.

I’m not a fan of “Magic to Make the Sanest Man Go Mad,” because turning Harry Mudd into a cold-blooded mass murderer does not make any damn sense and makes it impossible to continue seeing him as a harmless, comic nuisance like he is in TOS and TAS. Sure, I’ve seen it argued that he knew the killings would be undone by the time loop so nobody would really be hurt, but that ignores the particularly cruel and sadistic murder he committed at a point where he believed he was already out of the loop, and which was only undone because he was manipulated into looping one more time. So he intended that murder to stick, and it was by far the most horrific murder in the episode. I just can’t reconcile that with Stephen Kandel & Roger C. Carmel’s Harry Mudd.

@20/Keleborn: It’s more a case of a relatively harmless comic nuisance being retroactively portrayed as a cold-blooded murderer a decade earlier in his life.

@26/Ian: “So, you’re just dandy with the physics of FTL and transporters, but time travel is beyond the pale? That’s rather…selective. ;-)”

No, because it’s based on the specifics of each case. It’s not arbitrary. I have no problem with a time travel story that takes care with the physics and logic of the idea, e.g. Robert L. Forward’s novel Timemaster. The problem is that there are so very few of those. Any SF concept can be handled with greater or lesser degrees of plausibility, but the reason I don’t care for time travel stories is that they’re almost never done plausibly. Most of them are wish-fulfillment fantasies that completely fall apart if you really dig into their underlying logic. Especially any story based on the premise that a new timeline would “erase” or “overwrite” the original, which is a fundamental contradiction in terms. Change or erasure requires a before and an after — one version follows the other. But a single moment in time cannot come after itself. The perception that it does is an illusion created by the time traveler’s revisitation of that moment, like rewinding a tape. If there are two versions of a single moment, then by definition they are simultaneous, not consecutive. So a new timeline doesn’t “replace” the original; it exists alongside it in parallel. So any story that shows a timeline being rewritten or altered — especially in the ludicrous Back to the Future way where the characters can actually see the change happening — is utter fantasy. But “changing history” is more dramatic than parallel timelines, because the stakes are higher if the world you know is in danger of being erased, so that’s the approach that’s usually favored in time-travel fiction, even though it’s an utter impossibility.

And Groundhog Day-style time loop stories — which, yet again, are their own distinct category from other flavors of time travel story — are even more of a logical muddle, because they require the absurd premise of a single moment in time coming after itself, not just once but multiple times. The idea of time somehow looping back on itself for every character save one who manages to keep moving forward in their perceptions is easy enough to imagine as a narrative, but there’s no way to make physical sense of it. Well, I barely managed to find a way in my novel Star Trek: Department of Temporal Investigations — Watching the Clock to rationalize the physics of the time loops in the first-season TNG episode “We’ll Always Have Paris,” but it required delving into some incredibly abstruse temporal theory involving multiple dimensions of time, and it still wasn’t very convincing.

@30/Jana: No. The time traveler’s perception that the same event happens twice is an illusion created by the time travel, like rewinding a tape. If you rewatch a sporting event on your DVR, it doesn’t mean the outcome can be any different. As far as the universe is concerned, it only happens once, and the time traveler is simultaneously present in two incarnations.

Of course, all observers’ perceptions of the flow of time are relative to their frames of reference, which is how time travel can theoretically exist at all. But causality has to remain consistent. There’s nothing in the laws of physics that precludes an effect coming before its cause, since it is all relative. But the chain of cause and effect has to happen in a mathematically unitary way — that is, any interaction must have a single, knowable result, or the laws of physics break down. If something happens, then it happens, period. It’s part of the universe, part of the overall chain of cause and effect regardless of the order it happens in, and thus it can’t be “erased” from reality. The only way a single event can happen two or more ways is if they all happen in parallel timelines. Even if it looks to the time traveler as if one has “replaced” the other, that’s a subjective perception arising from the time traveler’s movement from one timeline to the other, and that one person’s perception does not outweigh the rest of reality. Step back and look at the universe as a whole, and you see both timelines existing side by side all along. That’s the only way it can actually happen, physically, mathematically, and logically.

@32/Jana: “I don’t think that it can actually happen at all. It just seems possible to us because we’re so used to conceptualising time as space.”

You’ve got this backward. The reason we’ve learned to conceptualize time and space as facets of the same thing is because Einstein figured out that they actually are, that what we think of as time is in fact one of the four dimensions of spacetime. That’s not a belief or a metaphor, it’s an outgrowth of the mathematics devised to explain real scientific observations and make predictions which have been extensively confirmed by countless experiments over the past century. The reality of the Einsteinian model of spacetime has been proven by the discrepancies in the orbit of Mercury, by the time-dilation corrections necessary to make GPS/satnav calculations work, by countless other observational and experimental confirmations. General Relativity is a correct (though incomplete) description of the universe. And the equations of General Relativity predict that in certain extreme conditions, such as those found within the ergosphere or singularity of a rotating black hole, spacetime would distort in such a way that “spacelike” and “timelike” axes would be inverted — in essence, time would behave like space, allowing motion through it both directions.

But what I’m saying isn’t even about that. The point is about whether a story even makes any logical sense within itself. Even a fantasy story should be self-consistent according to its own internal rules. But if you dig down into most time travel stories, really analyze their internal logic in detail, you usually run into a self-contradiction, an irresolvable paradox or absurdity that makes the logic of the story fall apart and that you have to ignore if the story is to work. In real physics, time travel would require a black hole or a wormhole; but in fiction, it almost always requires a plot hole.

“If the timeline is immutable, everything is predestined, and choice is an illusion. “

I see it the other way around: That the lack of free will is an illusion created by time travel. Go back to my “rewind the tape” metaphor. If you watch a replay of a sporting event, you know that the outcome will be exactly the same as it was last time, and that creates the illusion that the outcome is predestined. But it wasn’t. It’s just that it already happened. Time travel can make it look as though an event has a second chance to happen, but that’s an illusion. We do have freedom of choice, but we only get to make each choice once.

Another way of looking at it is that our freedom of choice depends on our circumstances, on the degrees of freedom permitted by our environment and situation. If you’re standing in an open field, you have the freedom to choose any direction in which to move, albeit only in two dimensions. But if you then fall off a cliff, your freedom to choose your direction of motion becomes enormously more constrained. By the same token, in an immutable timeline, a time traveler’s freedom to influence events around them would be far more constrained than that of someone moving through time normally. The restrictions on the time traveler’s freedom to act are not generalizable to everyone else, because the time traveler exists within conditions radically different than those of a normal person.

“If there’s a multitude of timelines, everything happens anyway, and choice is meaningless.”

This isn’t actually true either. Quantum multiverse theory doesn’t require every possible outcome to occur; it merely says that the total wave equation of the universe is a sum over multiple distinct states. It also applies to changes in quantum particle states and thus has nothing to do with human choice, despite the way fiction tends to interpret it. Since the mechanisms in the brain that we use to make decisions are on a macroscopic scale and thus follow classical physics, they shouldn’t be affected by quantum multiplicity. No matter what timeline you’re in, you’ll make the decisions that arise logically from your circumstances and needs. If you have a reason to turn right, all the quantum fluctuations in the universe won’t make you randomly turn left. Maybe those quantum divergences would create the opportunity for humans to make different choices if they’re on the fence and could go either way, but most decisions aren’t just coin flips; we make them for specific reasons that wouldn’t randomly change. So the number of different paths that people’s lives could follow would still be finite and would tend toward the most likely outcomes.

So if someone goes back in time and thereby creates a parallel timeline where events happen differently (alongside the original timeline where they happened the original way), then that change is specifically because of the time traveler’s actions and their macroscopic influences on people and events. It doesn’t mean that every decision in the universe is made in every possible way.

@35/Jana: “I was talking about the fact that humans think about time in spatial terms.”

And you said that was the only reason people believed in time travel. My point is that it isn’t — the possibility of time travel emerges from the equations of General Relativity. That’s not human belief or bias or metaphor, that’s the actual laws of nature as discovered through observation and experiment. There are actual equations and theoretical models that allow for the possibility of time travel, emerging both from GR and from quantum physics. Of course it’s prohibitively impractical, since it would require extreme conditions like black holes and would most likely destroy any macroscopic object that attempted to pass through a time warp, but we have a fairly solid theoretical understanding of how time travel would work if the practical obstacles could be surmounted.

“Concerning free will and predetermination, the crucial point is that in order to have free will, the future must be open (another spatial metaphor). If I can visit the future or the past, I can make choices, but seen from the outside, everything is fixed.”

From your perspective; not from another’s. The whole reason relativity is called that is because it established that there is no single, universal, absolute description of the universe — the universe you perceive is relative to how and from where you observe it, and the perceptions of observers in two different frames of reference can contradict each other yet both be equally correct descriptions of reality. So if one observer sees a fixed reality and a different observer sees a reality that they can choose and shape, neither one is wrong, and neither one’s perception can or should be assumed to apply to the other. Both of them are right, relative to their particular frames of reference.

Besides, free will is always limited. Nobody ever has absolute freedom of choice. We only have the freedom to choose among the viable options available to us in a given situation, and some situations offer more options than others (as in my “fall off a cliff” example). So to speak of “free will” as a single, universal constant, as something that either exists absolutely or doesn’t exist at all, is ridiculous. It varies from case to case, from person to person. So one person’s lack of freedom does not prove that nobody has freedom. It’s a basic logical fallacy to mistake a specific case for a general case.

Anyway, quantum physics basically says that the future is already defined in the wave equation of the universe, that past, present, and future all already exist, but knowing that equation would require exact measurements of every particle in the universe, and there are physical limits on our ability to gain that much knowledge (e.g. the Uncertainty Principle, among other things). So in that sense, our free will resides in the gaps in our knowledge — we can’t know what the outcomes to all our choices will be, and that’s what gives us the freedom to choose them. That very act of choice may be woven into the fabric of the universe along with everything else, but that’s exactly why I think the choice does matter. Maybe there’s only one way we can end up making it, but that doesn’t mean we have no say in it; on the contrary, it means our say in our decisions is an integral part of what shapes the universe. Our choice in a given moment is the end result of every prior choice in our lives and every prior circumstance shaping that moment. So it’s not arbitrary; it’s the logical outcome of everything that led up to it, including our prior life experiences and choices. And what we choose in that moment is part of what leads to the next outcome, and the next.

@36/Keleborn: “If in a rotating black hole, the spacelike and timelike axes become inverted, does that mean that under those conditions space has only one direction?”

Well, that part always confused me a bit, since there are of course three dimensions of space, not just one. It might only be in one of those three dimensions that you’d be required to move in a single direction. But you’re probably right to say it’s “down,” if “down” is defined as the direction toward which the gravitational field draws you. The geometry of spacetime would be so severely warped by the intense gravity that there would be directions you couldn’t possibly move in without exceeding the speed of light.

@38/Ian: “While the things you are saying about time and causality are true, I fail to see how they establish time travel as particularly more impossible than the other sorts of impossible physics found routinely in SFF.”

Like I said, it’s about the internal logic of the stories and the self-contradictions that you almost invariably run into if you really try to dig into the cause and effect. Time travel stories tend to be more centrally about logic and causality than most other kinds of story — if I do X, it leads to Y result, and if I don’t do X, it leads to Z result. So they invite more attention to the causal logic of their events, yet I’ve rarely encountered a time travel story where that causal logic didn’t have a big handwavey leap in the middle of it somewhere.

It’s different from a story with, say, FTL travel, since the FTL is usually just a means to get the characters to the story, rather than a key component of the story logic itself. There are some stories where the actual mechanics and operation of the FTL is important, and if such a story centered on a major logic hole or contradiction, that would be a problem for me. But that would only be the case in a small subset of the stories that used the idea. Time travel stories are different because they usually have that kind of hole in them somewhere, when they aren’t just pure fantasy.

@42/Keleborn: But the spacetime metric I’m talking about isn’t just falling straight into the singularity. On the contrary, it’s a topology that exists around the edges of a rotating black hole (or a massive rotating cylinder in the original Frank Tipler paper). Basically the dense, rapidly rotating mass “drags” spacetime around it, a phenomenon called frame-dragging or gravitomagnetism (because it’s basically to gravity what magnetism is to electricity, arising in the same way and following essentially the same math). This frame-dragging is what inverts the spacelike and timelike axes, because it drags your light cone (the range of paths you can follow in spacetime without exceeding the speed of light) sideways until it overlaps the time axis. This all creates a sort of oblate “shell” of inverted spacetime around the black hole, and it’s by following the right path through that region (the ergosphere) that you can end up on a closed timelike curve (i.e. go back in time).

It is true, though, that the singularity inside a rotating black hole would take on the shape of a ring/torus (a Kerr ring singularity) rather than a point, and if the BH were large enough or your ship magically indestructible enough that you could pass through the center of the Kerr ring, it would basically be like a wormhole, sending you to a different part of spacetime, which could be another place, another time, or another universe altogether. (This was referenced in ST:TNG’s “Yesterday’s Enterprise,” with the time vortex described as “a Kerr loop of superstring material,” though they should’ve said “cosmic string.”)

“Addendum: is there a “layman’s explanation” for why the black hole has to be rotating?”

I think the frame-dragging/gravitomagnetism I discussed above is the explanation. No rotation means no dragging of spacetime axes.

“And does this mean that Newton was wrong, that one really can define absolute rotation?”

I don’t recall Newton saying that you couldn’t. But per Einstein, an accelerated reference frame is distinct from an unaccelerated one, and rotation is an acceleration.

@48/Jana: Sure, and that’s actually part of the reason I’m not crazy about parallel-timeline stories myself, at least the kind that presume all alternatives happen instead of just some. There’s a difference between my story preferences in fiction and my views of what time travel or multiverse theory would actually say about free will in reality. After all, the main reason I’m not crazy about time travel as a genre is because it usually doesn’t obey anything remotely similar to realistic physics, or even hold together logically by its own internal rules.

As for free will, yes, it’s a relevant question if it exists, but my point is, you can’t take the restrictions on a time traveler’s free will as proof that nobody has free will, because a time traveler is operating under a radically different set of conditions and constraints from an ordinary person, so their situation can’t be generalized to others.

@50/Ian: Good grief, there’s no call to attack me. I’m not asserting any kind of factual claim, and I’m not saying that you can’t like the genre. I’m just answering the question of why I personally don’t love time travel as a genre, and I’m entitled to that opinion. I never claimed it was anything but personal taste. So lay the hell off. You’re totally out of line here.

@55/Sunspear: The tendency of time-travel stories to ignore the motion of the Earth is one of those recurring logic holes that annoy me about the genre. And it’s one that goes all the way back to H.G. Wells, although at least Wells portrayed his Time Machine as passing through all the intervening moments at an accelerated rate — although people around the machine were unaware of its presence, a paradox that never quite made sense (yet another logic hole!). I mean, if it were just sitting in place the whole time, people would see it there and perceive the guy inside as slowed down to the same degree that he saw them as sped up.