Interstellar, Causal Loops, and Saving Humanity

Spoiler alert: I will be revealing plot points of the movie Interstellar. In fact, I’ll be assuming the reader has already seen it.

Given my deconstruction of Christopher Nolan’s movie Inception at Google in promotion of my book Inception and Philosophy: Because it’s Never Just a Dream, a few people have asked for my take on Nolan’s latest cinematic endeavor: Interstellar. But I’m not sure how useful I can be for making sense of the whole movie; if Inception was a philosophic thriller, Interstellar is a scientific one – and I’m only a philosopher. Although my study of the philosophy of science has made me very familiar with a number of scientific theories referenced in Interstellar – quantum mechanics, relativity, etc. – much more informed minds have already spoken on the topic. For example, the famous physicist Kip Thorne served as the scientific advisor to the film and wrote the book “The Science of Interstellar.” If you’re interested in understanding the science behind the film, I highly recommend it.

However, I have to admit that what I saw as scientific inadequacies in the film initially detracted from my enjoyment of the film. Many of the same “flaws” bothered astronomer Phil Plait as well. But it turns out, like me, many of the “problem areas” he identified weren’t problems all. For example, he failed to take into account that Gargantua – the black hole that sits at the center of the new solar system – is not an ordinary black hole, but a supermassive rotating black hole even larger than the one sitting at the center of our galaxy. So, for example, it turns out there can be a one hour/seven-year time dilation outside the event horizon of such a black hole. (Notice the similiarity to the 1 hour/10 year dream-time dialtion in Inception) Plait had to offer a retraction correcting most of his scientific complaints.

Plait had other complaints about the movie that weren’t grounded in scientific inaccuracies. For example, the notion that love is somehow an extra dimensional force yet to be explained is not only unscientific – but is just downright silly. I would agree – and the movie could have done without it. Thankfully, that makes me able to ignore it. But another complaint I’ve heard centers around an essential plot point in the movie: the salvific actions of the five-dimensional beings. And if it sticks, it doesn’t seem to be something I could ignore.

Why Make It So Difficult?

Early in the film we learn that five-dimensional beings have taken action to try to ensure the survival of the human race. Earth is dying and will soon be incapable of supporting life, but the five dimensional beings place a wormhole next to Saturn that leads to a planetary system that could potentially support human life. By the end of the film, we learn that these five dimensional beings are us. In other words, the human race does survive and eventually evolves into beings capable of ascending beyond our four dimensional universe, and existing in the “bulk” – a realm that contains multiple universes, including ours. The power this affords them makes them able to create things like the wormhole; they may even be responsible for the creation of the planetary system as well.

But this raises a perplexing problem for the film. If these five-dimensional beings are so powerful, and their intent on ensuring the survival of the human race, why did they make it so hard? Why did they put the wormhole by Saturn, where it would take 2 years to reach? Why not a little bit closer? Why didn’t they just put one obviously habitable planet around Gargantua, instead of giving the humans 12 planets to choose from? Or why didn’t they just tell the humans which one was habitable? Why did they rely on Cooper being able to convey information about the interior of black holes back in time to his daughter via Morse code? Why not just give them the information?

But in the same way that a better understanding of science can help circumvent scientific problems with the film, I believe a better understanding of philosophy can help us circumvent this criticism as well. Specifically, what philosophers have said about time travel and “causal loops” is particularly helpful.

The Trials of a Time Lord

If time travel is possible, it seems that backwards causation is possible. For example, if time travel is possible then my pushing of the go button on my Time Machine now can cause the past event of me appearing in 1950. But since it is generally held that causes precede their effects, many philosophers suggest, time travel is impossible.

The reason that causes are thought to always precede their effects is because effects can’t exist without their causes. If X causes Y, then X brings Y into existence. But X can’t do that unless it exists before Y; how can X bring Y into existence unless it already exists? How could my pressing go on my Time Machine cause the event of my appearance in 1950 unless my pressing of the button existed before my appearance occurred? Since clearly it did not, it can’t—and time travel is impossible.

Likewise, philosophers have suggested that time travel makes paradox possible – like the grandfather paradox. If time travel is possible, I can travel back in time and kill my grandfather before he sires my father. This would prevent my own existence and thus prevent the very action I just took to prevent it. Paradox. Paradoxes are impossible, so too must time travel be impossible…or so the argument goes.

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Time Travel Made Possible

To resolve these problems, philosophers have tried to describe time travel in a logically consistent way. For example, some suggest that, to travel into the past is not actually to travel into one’s own past; my time machine would simply send me to a different universe (timeline) that has a similar past---one that is the same up to the past moment to which I traveled. So, if I traveled back in time to kill my grandfather, it’s not my grandfather I would kill – but the grandfather of some other version of me that would have existed in some alternate timeline. Paradox averted. This was the theory of time travel used by J.J. Abrams when he rebooted Star Trek.

Other solutions however are more faithful to the traditional conception of time travel – to the idea that, by traveling to the past, I will be traveling into the past of my own universe (i.e., into my own past).

For example, to avoid objections based in backwards causation and the grandfather paradox, some suggest that our universe is a four dimensional object. “Block world” it’s often called. Normally we think of our universe as a progressive series of events. The past existed, the pressent exists, and the future will exist. And we observe this progression as time passes. On the block world theory, this is inaccurate. Our perception of the passage of time is an illusion; in reality, all moments in time exist, past present and future. We think we are moving in time and the future does not yet exist. But in reality, it exists just as much of the present moment – and so does the past. When the universe came into existence, it was not a disorganized agglomeration of matter that over billions of years eventually coalesced into stars and galaxies that would eventually culminate in a heat death. Its past, present and future came into existence as a whole – as a unit – a “block” in which that entire progression takes place. On one end of the block, so to speak, is the big bang and on the other is the heat death. But it’s not like the latter happened and the former will happen – they’re all just there.

This isn’t just philosophical theory. This view regarding the name of time and the universe is entailed by Einsteinian relativity. And if it is true, backwards causation is not problematic at all. Recall, it seemed problematic because it would suggest that effects could exist before their causes. But if the block world theory is correct, nothing exists before or after anything else. There is a temporal order to events, for course—or, more specifically, everything has space-time coordinates—but all those events simply exist in the block. My appearance in 1950 in my Time Machine does have an existing cause: the event of my pressing the start button in my Time Machine in 2014. And that event exists in the block just as much as my appearance in 1950. If the whole universe exists as a block, there seems to be no reason in principle that the causal arrow can’t point both directions within that block.

Likewise, the block world theory solves the grandfather paradox by making such paradoxes impossible. If I set out to try to kill my grandfather before he sires my father, I will necessarily fail; since my existence is “already” a fact of the block, so too is my father’s existence a fact on the block. Indeed, since the entire universe came into existence as a whole, whatever action I will take while in the past was “already” a part of the past “before” I traveled there. In fact, if I indeed attempt to kill my grandfather but fail, it never was the case that I could’ve done anything but that – for those events came into existence with the entire rest of the universe (i.e., with the block). So, while the block world theory does make time travel possible, it does entail that changing the past is impossible. Whatever did occur, must occur. And, whatever will occur, must occur.

(As I have argued elsewhere, this view is not very friendly to the idea of libertarian free will. If the entire universe exists as one whole complete block, the future cannot be any different than it is. There are no alternate possibilities. But free will is already on shaky ground; many lines of evidence stand contrary to its existence. So this really isn’t an objection to the Block World theory.)

‘Round and ‘Round She Goes—Where She Stops….

Interestingly, this theory also makes “causal loops” possible. A causal loop is when something brings about its own existence – it has no definite origin spot in the timeline. For example, suppose you come across a Time Machine in an old abandoned mine. You then use the Time Machine to travel back to the past where you give it to someone and leave instructions for burying it in the mine – right where you found it in the future. Question: who invented the Time Machine? Where did the idea come from – who figured it out? It seems no one – and yet time travel would seem to make such a thing possible. This fact in itself is used by some as an objection to the possibility of time travel.

But the block world theory avoids any such objections; on it, the Time Machine causal loop is not problematic. Sure, there is no moment in time in which the Time Machine comes into existence; but on the block world theory, there is no moment in time in which anything comes into existence. Everything comes into existence “at once,” as the block comes into existence as a whole. If the block contains a causal loop, like the non-invented Time Machine, then it came into existence with everything else. The block came into existence with the loop “already” intact; the block’s existence is the explanation for the loop’s existence.

The possibility of causal loops has been successfully defended by Richard Hanley. In his fascinating article “No End in Sight: Causal Loops in Philosophy, Physics and Fiction,” he identifies many different kinds of causal loops – such as object loops and information loops. Some loops are “easier” to account for than others – physical objects that exist in a loop will require some way to ensure that their matter is replenished. But at worst, causal loops only require grand coincidences. They are not logically incoherent. It’s even possible to be one’s own father and mother. What’s more, since the actions of conscious agents can easily make grand coincidences occur, causal loops are much more likely in a universe like ours – one that has conscious agents in it.

Solving Interstellar: It Had To Happen

Which brings us back to Interstellar; it involves a causal loop caused by conscious beings. The five dimensional beings are only around to save humanity because humanity was saved; they exist only because of the very actions they are taking to save humanity—their own race—from extinction. So why didn’t they do it differently? Why didn’t they make it easier? Why didn’t they place the wormhole closer to earth and make it a gateway to a new yellow star with multiple habitable planets—instead of one with a massive black hole and one barely habitable one?

Because they couldn’t do anything different than they did. Not only do they already know how the human race was saved, but they know that its salvation cannot happen any other way. As five dimensional beings, that exist outside our timeline, they view it—the entire block—as a whole. They can see its events, including (for example) the existence of the wormhole, where it leads, and the fact that they caused it, as determined properties of the block. Its events can’t be any other way. Even if they are responsible for the entire block—and thus humanity itself is responsible for its own existence—they could not have created it any other way. In fact, since their actions are a part of the block, we might even think of the five dimensional beings existing in a six-dimensional block in which their actions regarding the block—including the creation of the wormhole and everything else they did to save humanity—are determined properties.

One of the conceptual difficulties with causal loops – that make them seem impossible – is people thinking of them as happening over and over again in a repeating loop. Five dimensional beings save humanity, and then humanity grows up to be the five dimensional being, and then those beings save humanity again – and on and on. With that kind of understanding we might ask questions like, “Who put the wormhole there the first time? Where did it come from? If it wasn’t there to begin with, the loop couldn’t get started; but unless it’s started, the wormhole couldn’t be there.” But on the block world view, this question doesn’t make any sense. There was no first time. Causal loops don’t repeat; they’re just there. In the case of Interstellar, when the block came into existence, the wormhole was “already” there—as one fact among many, “already” written on the timeline.

There are still some other problems with the movie; it’s not perfect. When they said they had found planets orbiting a black hole, I immediately wondered where the light and heat necessary to make the planet habitable was going to come from. Black holes don’t emit light – that’s why they’re black. Now, the accretion disk surrounding the black hole generates x-rays and heat, and some visible light – I don’t think it would be enough to make an orbiting planet habitable. But, if that was the intended explanation, I’d be happy to overlook this and just enjoy the movie – but it would’ve been good to at least hear this hand waving explanation. Or at least see Gargantua in the sky of the habitable planet at the end, providing light – instead of the somewhat confusing voice over suggestion that the heroine of the story was “under the light of her new sun.”

(Update: It turns out that, apparently in the original 2008 screenplay, there is a neutron star orbiting Gargantuan called Pantagruel. This is never mentioned in the movie, but could have been the intended solution to the light and heat problem.)

Regardless, I hope I have shown that the causal loop that involves the five-dimensional beings saves the movie from reasonable, but erroneous, objections rooted in questions regarding why the five-dimensional beings didn’t make the salvation of the human race easier to accomplish.

Copyright 2014, David Kyle Johnson

Teaser Image: A screenshot from the new "Interstellar" trailer. PARAMOUNT