The time shuffling machine and fatalism

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My aim here is to defend a toy argument for metaphysical fatalism. This post has two parts. First, I explain a couple of assumptions I make about the nature of time. These assumptions are plausible and widely held—or, at the very least, they are reasonable positions to hold. Second, In I outline and explain a thought experiment designed to bring our fatalist-friendly intuitions to the fore.

Before I get too far into the details, I want to briefly explain the claim at the center of my project. This claim is called metaphysical fatalism—or just fatalism, for short. Crudely sketched, fatalism is the idea that everything that happens had to happen just the way it did. In other words, there’s some kind of necessity to how the world is configured across time and space—such that it couldn’t have been arranged, in either dimension, any other way. Put differently: to say things could have turned out otherwise (e.g., that I could have worn a green shirt today instead of a red one) is to say something false. What follows is my attempt to construct and defend an argument for fatalism.

§1.

There are a few highly plausible, common sense claims about the nature of time that most of us accept—rightly so, I think—without thinking twice. Consider this:

The events, individuals, and so forth that reside in the past are unchangeable. Call this Past.

We have all sorts of strong intuitions that reinforce this. We take it, for instance, that there’s little reason to be upset over past mistakes in the sense that, well, there’s nothing we can do to change them. Even if we can learn from them, there’s little point in dwelling on them—events can’t be altered once they recede into the past. People often regret poor past choices partly because of their consequences in the present and future, but also because those choices are unchangeable. Once in the past, they can’t be undone.

It might be tempting to invoke time machines as a way—at least in principle—to change the past. So it might be argued that a time machine, if it could exist, would let us go back and change the past. Maybe I could go back and do a better job in school, thereby earning admission to a better graduate program. Let’s call this temptation the Time Machine Worry—or just Machine, for short.

But Machine isn’t much of a worry. Why? Because we don’t really think we can go back and change the past. Even if our intuitions are a bit foggy, they still support the idea that, even granting time travel to the past, the past remains unchangeable. Consider a familiar example: suppose you try to go back in time to kill your grandfather. Presumably, since he was a necessary condition of your existence, your existence implies his. If you exist, your grandfather must have existed. But if he didn’t, then how are you around to try to kill him? So, you can’t alter the past—at least not where your grandfather is concerned.

You may think these grandfather paradoxes are just edge cases. Maybe time travel could still change other parts of the past. But I’m going to argue, against Machine, that either (a) the past already includes the future visitor, or (b) the change makes the moment different from its earlier temporal counterpart. To draw out the relevant intuitions, consider this:

Suppose Stewie travels back in time to warn his younger self about doing poorly in school. Maybe Stewie’s stuck working lousy jobs because he flunked out, and he wants to change that. He has a long, serious conversation with younger-Stewie, who promises to do better. Satisfied, Stewie returns to the present—but everything is exactly the same. Call this case Grades.

Why didn’t Stewie’s intervention work? The answer: if older-Stewie succeeded in convincing younger-Stewie to finish school, then older-Stewie wouldn’t need to go back in time in the first place. But if the reason younger-Stewie did better is because older-Stewie went back in time, then older-Stewie has to exist in a timeline where younger-Stewie didn’t succeed. That’s the paradox. You can’t both succeed and fail at changing the past. We can avoid the paradox by adopting this simple rule:

If fact A in the past explains your traveling back in time to change A, then you can’t go back and change A.

Maybe that seems too strong. Let’s say you get into a time machine, squish a butterfly, and return to the present. Nothing about squishing that butterfly seems to violate our rule. But here’s the worry: either (Alpha) the past already includes you squishing that butterfly—so nothing was changed—or (Beta) your action creates a different moment entirely, and the original one vanishes. But where does that old timeline go?

Think of it like this: if the past is what already happened, and you travel back to squish a butterfly, then squishing that butterfly must already be part of the past. That’s Alpha: no real change. Beta faces a locating-the-change problem: if your timeline always had you squishing the butterfly, what happened to the timeline where you didn’t? Does it just disappear? If so, from your future vantage point, the past always had a squished butterfly. There’s no moment where it wasn’t squished. So either way, the past is fixed. That’s why Past is plausible. Time machines don’t give us a real way to change the past.

Let’s add another common sense idea about time. Time itself doesn’t do anything. It doesn’t increase or diminish causal powers. The passage of time just allows other processes (like entropy or aging) to unfold—it doesn’t cause them directly. Call this Toothless.

Here’s a comparison: I leave a program running overnight that wipes the company’s financial records. It’s not time that erases them—it’s the program. If I’d turned the program off before leaving, nothing would’ve been wiped. Time passes either way, but only the program’s activity has causal force.

So, if I’ve done my job right, you’ve got some intuitions supporting Past and Toothless. Now for the argument for fatalism.

§2.

Suppose that Bob the physicist builds a time-shuffling machine. It works like a card shuffler: it takes time segments and reorders them randomly. Call this machine Shuffle. It follows a couple of rules: (1) Shuffle can’t reside in the moments it shuffles, and (2) it only changes the order of the slices—not their contents.

Shuffle’s not a time machine. It doesn’t let you visit the past or future. It just reorders time segments. Now, some might worry this amounts to changing the past, especially if it rearranges events so effects precede causes. But I’m not concerned about that.

Here’s the real issue: if Shuffle can change the sequence of moments, then it seems it can change relational facts about the past—e.g., what came before what. But if Past is true, then the past can’t be altered—not even relationally. So maybe there can’t be a Shuffle. Call this the No-Shuffle Worry.

There are a few ways to respond.

One is to say Shuffle doesn’t really change the past because it doesn’t change the content of the moments. Call this response Denial.

Another option is to say, sure, Shuffle can’t really exist, but we can pretend it does for the sake of argument. Call this Pretend. That works fine for clarifying the argument, but I want something stronger.

So I propose a third approach. Call it Single. Suppose there’s just one future moment—call it Temporal—and Shuffle moves it into the past (from the safety of a past moment). If Past is right, then once Temporal is in the past, it is fixed. But also Toothless tells us that nothing about moving the moment, Temporal, changes anything within the moment itself. So, if it is unalterable in the past, then it was always unalterable. The shift in timeline position didn’t add or remove any properties.

So: if it’s unchangeable in the past, and timeline location isn’t causally efficacious, then it was always unchangeable.

That generalizes. If Temporal was fixed just by becoming past, and nothing else changed it, then every moment—past, present, or future—has that fixedness. So, nothing can ever be other than it is. That’s fatalism. Call this the Time Shuffle Argument.

Before concluding, here’s an aside. You’ll notice Time Shuffle doesn’t appeal to any fancy physical laws. It just draws on a few plausible principles that many of us already accept. My goal isn’t to prove fatalism, but to show there are good reasons to take it seriously, at least within the confines of the philosophy classroom.