Theoretical Virtues of Major Theories of Time
In this paper, I have two main goals. The first of which is to develop an account of why people believe or choose to believe certain scientific and/or metaphysical theories, with an focus on theories of time. In particular, I will argue that people choose to believe intuition-preserving theories of time (intuition-preservation as a theoretical virtue). Additionally, I consider if this is a good thing or not, and whether people should evaluate theories on the basis of intuition-preservation. The second goal is to use the developed account to examine the theoretical virtues of some of the most popular competing metaphysical theories of time, namely: Presentism, Growing Block Theory, and Eternalism.
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This article was published 2021-12-15 00:00:00 -0500, which makes this post and me old when I published it.
In this paper, I have two main goals. The first of which is to develop an account of why people believe or choose to believe certain scientific and/or metaphysical theories, with an emphasis on theories of time. In particular, I will argue that people choose to believe intuition-preserving theories of time (intuition-preservation as a theoretical virtue). Additionally, I consider if this is a good thing or not, and whether people should evaluate theories on the basis of intuition-preservation. The second goal is to use the developed account to examine the theoretical virtues of some of the most popular competing metaphysical theories of time, namely: Presentism, Growing Block Theory, and Eternalism.
There are a number of extra-explanatory attributes of scientific and/or metaphysical theories which are called theoretical virtues. On one inventory, there are ~12 theoretical virtues: evidential accuracy, causal adequacy, explanatory depth, internal consistency, internal coherence, universal coherence, beauty, simplicity, unification, durability, fruitfulness, and applicability. Keas acknowledges that the epistemic status of theoretical virtues are tenuous at best and still under debate by philosophers, that it is widely accepted that these virtues help us to infer which rival theory is the best explanation (Keas 2016). This is important because when there are rival theories explaining more or less the same thing, there comes a point where you cannot make a point strictly empirically on the observations that they explain, or the predictions that they make, something else must be appealed to.
While I think that this systematization of virtues is quite robust, I think that it misses two virtues that I think are very important for metaphysical theories, which is why they were probably not considered by Keas. I think that Testability is a theoretical virtue that flies under the radar because it is so baked into the idea of science itself. In some way, it even is integrated into the definition of what a scientific theory is, like Popper’s Falsification Principle. The other theoretical virtue that I think is missed is the idea of intuition-preservation. What I mean by this is that we have certain intuitions, things that seem a certain way to us that are not wholly rationally formed. If two theories, all else equal, explain the same things, but one has a counter-intuitive premise and the other does not, I think that most people would choose the one that most matches their intuitions. In the next section, I will explain why I think that these two theoretical virtues are important for understanding the discourse in the metaphysics of time.
Intuitions in Philosophy and Theory Selection
For choosing metaphysical theories of time to believe, I think that people first and foremost value theories that match with their intuitions of time. A big reason why this is probably the case is because of the reduction of cognitive dissonance. The main idea is that you would not want to accept a non-intuitive theory if you have to, because that means you have to restructure a lot of the things that you think or think that you know. Another big reason that I think this is the case because a lot of the metaphysical problems of time are undecidable or empirically undetectable, so intuitions are the only evidence that theories are allowed to trade on. A good example of this is the distinction of endurance and perdurance. Endurantism is the view that objects only have spatial parts and perdurance is when objects have both spatial and temporal parts. This results in a 3D and a 4D approach, respectively, which is what makes this debate a rather puzzling one to look at, since there is no way of empirically deciding it. There is no real way to test this, so we have to rely on our intuitions to get us to choose a theory to believe. Maybe sometimes it just fits into our web of beliefs better than other theories.
The idea of intuitions being used while engaging in philosophy is not a new idea. Climenhaga argues that philosophers use intuitions as evidence, and that this is in fact the best way to understand how philosophy is done. He offers three reasons why he thinks that this is the case: the fact that philosophers tend to believe intuitive claims, philosophers offer error theories to explain when intuitions go “awry”, and philosophers are more confident in rejecting theories that have intuitive counterexamples (Climenhaga 2018). Climenhaga makes an important point which I think is worth repeating as well, that just because this is how philosophy is or seems to be done does not mean it is how it should be done. None of this is to say that our intuitions cannot be wrong, or perhaps something more concerning, be abused.
Daniel Dennett has coined a term called “intuition pump” which he first used to criticize Searle’s Chinese Room Argument, which he accused of eliciting intuitive, but ultimately incorrect answers in his framing of the thought experiment (Dennett 2010). I don’t think this is necessarily a salient concern in this case, because the metaphysics of time doesn’t really employ thought experiments a lot as compared to other fields of philosophy. But it is nonetheless something to keep track of and be aware of when evaluating various theories of time. Dickson also argues against the usage of intuition in philosophy, particularly metaphysics, and additionally questions the possibility of rational intuitions, that is if you have an intuition that A, it seems to you that A. Dickson questions the possibility of this type of intuition mostly on the grounds that such intuitions are private and is questionable at best whether these intuitions are universal and/or generalizable (Dickson 2007). I ultimately think that these concerns are not worth worrying about because people process information and organize justifications differently, so we should not expect uniformity of intuitions. Additionally, I do think that his argument and my counterargument applies to all types of intuitions, not just rational ones. In this way, I think that it is perfectly fine to use intuitions as evidence, or at the very least, have intuition-preservation be a salient theoretical virtue that is considered when comparing metaphysical theories of time.
In the following sections, I will analyze the major competing metaphysical theories of time in terms of two things: their core intuitions (and counter-intuitions) and how well they mesh with our current best science. I examine each theory’s relation to science, specifically Special Relativity (SR) and/or General Relativity (GR) because if a theory does not at least do that, it should not even be examined. SR and GR are among the most empirically tested scientific theories and as such their explanatory power is not something that can just be swept to the side. I think that a substantial amount of philosophical work is put into cohering theories with SR/GR. After this is done, I believe that this leads to the more or less equally plausible metaphysical theories of time. This is why I also examine the core intuitions of the theories in tension with their counter-intuitions because I think that intuition-preservation is the virtue that decides what theory of time a person ultimately chooses to believe.
An argument that could be levied against my identification of core intuitions of theories is that they seem more like propositions. While I present the intuitions in the form of propositions, I mean to show that, following van Inwagen, they should really be thought of as dispositions to believe that proposition (van Inwagen 1997). I think this way because I interpret intuitions not as full-blown beliefs, but more akin to sympathy to a proposition, still a propositional attitude, just a different attitude. I think that people could definitely hold the intuitions I identify as beliefs, and I do think that is probably the case many times, but the point is that these propositions do not have to be fully held as beliefs, they are not born out of entirely rational processes. In fact, many of these intuitions are not responsive to rationality and do not update with new information. As long as a theory can be updated to save face in front of science, if the intuitions are left untouched, that theory will certainly keep the same defenders.
Presentism is the thesis that only the present moment exists, there is no past or future. Once the current moment passes, it no longer exists, and time is just the succession of current moments. I think that the core intuitions of Presentism are:
Naïve anti-realism about past and future time
The present moment as privileged
What I mean by naïve anti-realism is that it seems hard to speak about something that we don’t really experience. While we have experienced the past moments, that is only when they were present moments, because we can only ever experience the present moment. Similarly, the future is moments that have not happened, so it seems odd to talk about them as if they exist. I think that the Presentist stretches this intuition and the second intuition about the present moment as privileged is hidden within it.
I think this is a very natural position to start at, but I think that there are some strong countervailing intuitions that may prevent people from becoming full-blown Presentists even if they possess Intuitions 1 and 2. One such counter-intuition would be the idea that it seems unlikely that time would just poof out of existence, it seems odd to think that the present moment just poofs in and out of existence for a brief moment. Additionally, one might be led to question where the present moments come from/how they come about, and not least of which how long is the present moment exactly?
The immediate worry when evaluating Presentism is the idea that there is no definite present moment. One way this is true is experientially, there is time required for neural impulses to travel but also be processed, so in what way can we actually say that we are experiencing the present moment? However, the more pressing concern comes from Special Relativity, where we get the relativity of simultaneity. Depending on the frame of reference, we can have different ordering of events, so if we wanted to define our present moment in some kind of absolute simultaneity sheet, this would simply not be possible. This is a problem for the hardcore Presentist, but not so much for the Extended Presentist, which is a theory that maintains that all that exists is a present moment, but that it is more like a slab than a slice of time. Brading argues that we could ground this extended present as a slice of spacetime that is sufficiently large enough to sustain dynamical laws of matter (Brading 2013). This is not enough to make me sympathetic to the Presentist position, but I think that it is enough to make Presentism compatible with Special Relativity.
Growing Block Theory
Growing Block Theory is the view that past and present events exist, but future ones do not. I think that the core intuitions of this view amend well to Presentism:
- The present moment doesn’t/can’t just disappear after passage
- The present moment as privileged
Intuition 1 directly takes one of the counter-intuitions of Presentism and takes it into its own core. Indeed the intuition about the destruction of events is strong because Growing Block Theory could just as easily be formulated backwards, the Shrinking Block Theory where the future and present exists, but the past events get destroyed. This, of course, offends the intuitions of many, and that is why there are no proponents of the Shrinking Block Theory.
The countervailing intuitions to the Growing Block Theory have less force than Presentism, but I think they are enough to turn away at least some people from the theory. One such intuition would be wariness at the idea that the present and past are equally real. How we should understand the growth of the block and the status of the past compared to the present varies from account to account. The following is not a counter-intuition, but an argument by Merricks that is meant to produce a counter-intuitive result. Merricks says that in an unmotivated version of the Growing Block Theory which he calls UGH (Unmotivated Growing Hunk), a discrete amount of the future is also included in the block, meaning that the block still grows, but the growing edge is no longer the objective present (Merricks 2006). There would be importantly no way to know if the present we experience is the objective present, if there is even a notion in UGH, additionally it would seem that UGH is otherwise equivalent with the Growing Block Theory. There are ways out of this, but this is definitely an unintuitive result.
As far as science is concerned, Growing Block Theory is widely held by physicists and other scientists. It does not suffer the same problem of the relativity of simultaneity that Presentism faced. There is a small issue in regards to Closed Time-like Curves (CTCs), but in many solutions to the equations of General Relativity, such entities cannot exist. A Closed Time-like Curve is a worldline where light cones are set up to loop back on themselves, so it would be possible for an object to move around this loop and return to its original spacetime position. This opens up a can of worms of paradoxes, but forbidding CTCs in a solution of GR is certainly plausible. Additionally, many people believe that a theory of quantum gravity will be able to replace GR as our best explanation so we will be able to avoid CTCs (Besnard 2012).
Eternalism is the view that the past, present, and future are equally real. I think that the core intuitions of Eternalism are:
- Space exists, so time must exist as well (spacetime realism)
- There is no objective flow to time
What I mean by spacetime realism is that if we take seriously the idea of a spacetime manifold, we get a four-dimensional picture of what spacetime is. If space exists, then it would make sense that time exists as a dimension as well, with different times being as real as different places. As for Intuition 2, this is for people who think that there is no objective arrow of time. From a scientific perspective, there does not seem to be anything that grounds the direction of time that we experience. There are a number of philosophical explanations for this, but most are circular, so if a person is one who does not believe in a direction of time, or in intuitive terms, is disposed to believe that there is no arrow of time, Eternalism is an attractive option.
Eternalism is the one out of the three that meshes the most with our current best science. Besnard goes so far as to say that it also agrees with quantum mechanics (QM), or at the very least, the possibility of truly random events from QM. From this, Besnard further argues that through SR, both Presentists and Growing Block Theorists are forced to endorse an observer-dependent view of reality, which means that they are not compatible with the idea of random events occurring in the spacetime (Besnard 2012).
While Eternalism agrees the most with science, I think that it is the easiest to intuitively understand, but the hardest to intuitively accept, because of the strength of the counter-intuitions. Since Eternalism entails that future events are real and we cannot do anything from our current position in time, it seems that Eternalism implies Fatalism. Fatalism is the thesis that future events are completely out of our control, most likely because they are wholly determined (Agler 2020). Arguments from Fatalism are purely intuitive arguments, an explicit premise would have to be something like, “But who wants to accept Fatalism” or “Fatalism is deeply unnerving”. To a determinist, this is a very easy pill to swallow, and probably a reason to accept Eternalism in the first place. Another counter-intuition that has less force, but is still somewhat pressing is the fact that it doesn’t seem like Eternalism matches our experience. In Eternalism, there is no passage and there is also no privileged present moment of time. This leaves much to be desired because of course it seems to us like both that time passes and that we have a present moment. Most often Eternalists would just offer an error theory for this and argue that ultimately this is mistaken or an illusory experience better understood in terms of other things.
Conclusion and Future Research
I believe that philosophical discourse, especially the metaphysics of time, would benefit from the increased awareness of the role of intuitions in theory selection. I say this not for the strategic benefits of persuasiveness that would be derived from targeting intuitions rather than rationality, but instead for increased awareness. I think that philosophers in the practice of philosophy think that they are doing one thing, but really are doing or getting at another thing. A lot of work is done in the philosophy of time to make sure that the theories do not conflict with SR and GR, but once that is out of the way, it is mostly intuition mongering. I think that once a theory of quantum gravity is more fully worked out this will lead to a flurry of literature to modify our existing theories or create new ones, but they will capitalize on more or less the same intuitions, unless quantum gravity radically undermines the way we conceive of time.
As for the work of identifying core intuitions, while I think that the ones I chose are pretty safe choices, they are of course up for debate. I think that there are most likely ones that I missed, but I tried to identify just the core intuitions, there are surely some intuitions that are non-central that still have persuasive force, same with counter-intuitions as well. Further research into this area could aim to analyze more theories in terms of the intuitions that they play on, or better yet, analyze particular accounts of the theories in terms of intuitions. This kind of work would be metaphilosophically valuable because one could find out what kind of extra-logical things that a philosopher is appealing to while arguing, but ultimately I think that the main benefit of this would be pedagogical. If a professor would talk about the intuitions that a theory aims to capture, and what intuitive premises a philosopher may be relying on when arguing for a stance, then I think students would be in a better position to fully understand what is being argued for and how it is being argued.
A particularly interesting blooming area of philosophy is experimental philosophy, which I think would mesh quite well with testing the idea of intuitions in theories of time. Norton has done work and found that ordinary thought about time is far less metaphysically demanding than philosophers have assumed (Norton 2021). Now this does not surprise me, for I think people necessarily have to be drawing from their phenomenology to develop their concept of time. Not many people are exposed to McTaggart or SR/GR in school, so they develop some internal model of time from what they have experienced. I think interesting further research would be if we could prime people with intuitions by trying to elicit them toward particular key propositions of a theory, and then presenting them with a list of theories of time with brief descriptions to see what they would pick.
Agler, David. 2020. Eternalism [PowerPoint slides]. Davidagler.com. http://www.davidagler.com/teaching/metaphysics/L4_Eternalism.pdf.
Besnard, Fabien. 2012. “Is there a philosophy of time compatible with relativity and quantum mechanics?”, AIP Conference Proceedings 1446, 437-447 https://doi.org/10.1063/1.4728010.
Brading, Katherine. 2013. Presentism as an Empirical Hypothesis. Philosophy of Science, 80(5), 1101–1111. https://doi.org/10.1086/673897.
Dennett, Daniel. 1980. The milk of human intentionality. Behavioral and Brain Sciences, 3(3), 428-430.
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Merricks, Trenton. 2006. Good-Bye Growing Block. Oxford Studies in Metaphysics 2:103-110.
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van Inwagen, Peter. 1997. “Materialism and the Psychological-Continuity Account of Personal Identity”, Philosophical Perspectives, 11: 305–319.