I'm coming at this from the POV of a physicist. Physics demonstrates that the universe does not feel any obligation to follow a humans naive idea of what makes sense. This idea of what "makes sense" was developed for surviving in a Newtonian world, and understanding the behaviour of an electron passing through two slits with dimensions proportional to their wavelength is not included in that kind of common sense. But if we allow for things to be unexpected, they do appear to be logical and internally consistent. Requiring that the universe be logical and internally consistent seems to be a requirement for doing physics.

I struggle to come up with an experiment that could detect evidence that this universe exhibits behaviour that is not internally consistent. Perhaps someone with more imagination than me could write one down. Having read stories that lacked internal consistency, I know that there are signs of it, so an experiment ought to be possible.

My question is less practical though. Is there an argument that our universe should be possible to describe with internally consistent rules?

I'm not asking about the possibility of actually deriving these rules. There are an abundance of ways that a reality can have rules that are not possible to obtain. Nor do I place any constraint on the structure of these rules. But does the reality itself have to behave in a way that does not require contradictions in those rules?

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Geoffrey Thomas
    Commented Jan 13, 2022 at 9:23
  • Consider Black Holes. Is their existence inconsistent or merely incomprehensible (to us at this stage of cosmology and physics understanding)? Commented Jan 13, 2022 at 16:09
  • why not "yes and no"? sorry, just complaining about that move
    – user57343
    Commented Jan 17, 2022 at 19:35

14 Answers 14


There is a nonzero epistemic chance that change in general is inconsistent; that article describes inconsistent change theory as "surprisingly robust." If laws of physics are laws governing physical changes, then if change itself is inconsistent, in some sense the laws must be, too; one could even argue that the compatibility question regarding quantum physics and relativistic physics might be an example of necessary inconsistency in known physical laws.

I also would suggest looking up the essay "A Paraconsistent Approach to Quantum Computing" (I would link the essay directly but my browser is acting up, so just search that quoted title). This reflects on earlier talk of "dialethic machines" (see the IEP article on paraconsistent logic); intuitively, a dialethic machine tolerating inconsistent inputs and yielding manageable inconsistent outputs resembles a quantum computer superpositioning information over both the 0 and 1 values (untrue and true together).

Lastly, Schrodinger IIRC proposed a logic for quantum objects in which the law of identity has been abrogated. Depending on how tightly-knit one thinks the LOI and the LNC are, this will affect one's picture of an option in inconsistent physics. I myself think that DNE (~~A = A) is more like the merger of the LOI and the negation concept, though it is often said that the LNC is expressive of "what negation means."

  • I'm interested in your answer and I will get back to it when I have read some of the sources you quote. Please could you unpack some of those acronyms? In particular LNC and DNE?
    – Clumsy cat
    Commented Jan 10, 2022 at 16:29
  • 2
    LNC = law of noncontradiction, DNE = double-negation elimination. There is an argument going back to Aristotle that the LNC "expresses what we mean by 'not'," or in other words is the law of identity applied to the concept of 'not.' However, it seems to me that it is more like the LNC is the law of identity applied to the conjunction and negation operators together, not the negation operator alone, which maps more to DNE/DNI (~~A = A or A = ~~A), or even to an inequality (A ~= ~A). Commented Jan 10, 2022 at 16:43
  • I would doubt change by itself is inconsistent. Rather it is studied by some approaches with inappropriate tools. That is tools that are fundamentally static. Like trying to capture motion through photography alone. It is certain to appear inconsistent.
    – Nikos M.
    Commented Jan 10, 2022 at 21:23
  • So I've only read the first essay so far. It's a lot to take in at once, but it's also a very satisfying comparison of many different takes. I certainly need to read it again. I'm lookign forward to reading the second one. Did you mention dialethic machines because you think that to some extent we are a dialethic machine?
    – Clumsy cat
    Commented Jan 11, 2022 at 9:01
  • @NikosM. I do see your objection to that "motion is inconsistent" argument. Though an objects whole momentum, phase and energy tie in with questions about self identity perhaps? There is a "motion paradox" that I like rather more, about rotation and centrifugal force in an empty universe; physics.stackexchange.com/questions/1372/…
    – Clumsy cat
    Commented Jan 11, 2022 at 11:07

If it's not consistent, you can't usefully make predictions. Since we so far are pretty good at predictions based on the physical laws we have discovered, it is a good working hypothesis that the universe is consistent, even if there is no way to prove it.

Once you encounter something that is in contradiction to current models, either you improve the models (by formulating rules that capture what you have observed) and continue to be able to predict. Or you hypothesize that the universe isn't consistent, throw up your hands in confusion, and stop being able to make useful predictions. One is clearly more useful than the other, and has been more successfull in the past.

  • You first sentence seems like a good argument for making the assumption that it should be internally consistent, but not much of an argument that it is internally consistent. I would not be able to agree with the rest of your first paragraph, we have constructed some beautiful theories (e.g. MSSM) which were ultimately not found in reality, and out best theories have some pretty big holes in (gravity, dark matter, etc.). We have some good predictions and some bad ones, there is no general rule.
    – Clumsy cat
    Commented Jan 10, 2022 at 11:47
  • 3
    @Clumsycat The answer explicitly states “there is no way to prove it,” because there isn’t. The only evidence for the universe’s internal consistency is the success of hypotheses that build off of that axiom. That evidence is, necessarily, circumstantial, not proof—as an axiom, it can’t be proven. That’s the answer to this question.
    – KRyan
    Commented Jan 10, 2022 at 20:15
  • "If it's not consistent, you can't usefully make predictions." Until you define what it means for the universe to be "consistent", this is a meaningless sentence. There is no standard sense of the word "consistent" that applies to the universe. I don't even know of any non-standard sense of the word that applies to the universe. Commented Jan 10, 2022 at 23:03
  • @DavidGudeman For example, there are domains where Special Relativity, which is a well-tested theory, and Quantum Mechanics, which is also a well-tested theory, clash and are inconsistent. That means in these domains we can't properly predict what happens due to singularities in the equations. The general assumption here would be it's our theories that are incomplete. If both theories were already the Truth and it was actually the Universe that is inconsistent, then you can just give up, you have reached the boundaries of knowledge and a place where you can only confusedly give up. Not useful.
    – kutschkem
    Commented Jan 11, 2022 at 7:53
  • @KRyan That seems like a sound conclusion. And thanks, I understand this answer better now.
    – Clumsy cat
    Commented Jan 11, 2022 at 8:45

You state a form of Hume's 'problem of induction': do we have any reason except the regularity of regularities in the past, to think the future will resemble the past?

Then you frame a version of Hilbert's 6th problem, can physics be axiomatised? That is, a set of rules given with a minimum of assumptions, and those self-evident, or compelling. Godel Incompleteness & Turing's Halting Problem basically ended thus project. And I would relate that to the nature of the universe being that rules emerge, and are not 'foundational' - except maybe the uncertainty principle.

The universe in a very real sense is unpredictable, random, chaotic. The quantum foam of virtual particles. Sensitivity to initial conditions. Stochastic processes. Limits imposed by the uncertainty principle.

What seems to happen is that large scale order emerges from this disorder. Continuous symmetries, conservation laws, emergent regularities and consistencies.

Time seems to emerge in two ways. As an asymmetrical dimension, where travel is only possible in one direction (Relativity). And as the thermodynamic arrow of time, the tendency of ordered systems to become disordered. We have good reasons from the search for quantum-gravity, to think the dimensions, including time, emerge from something else, eg a spin lattice network. I would say this points to the idea all laws are emergent, and to say a law is 'inviolable' is only to say, what we've seen so far strongly obeys a given symmetry. CPT violation shows how even strong patterns can have exceptions based on higher symmetries.

The expectation of consistency is deeply related to everything in the universe having once been in the same place at the same time, or very, very close to it, at the Big Bang. Which the asymmetry in the time dimension seems to have started from, beginning causality.

Dark matter shows we don't have the full picture, but we know it's there because it's part of the story, part of explaining the structure we see. All kinds of other universes and materials and behaviours of things could be out there, but if they don't interact with our universe we can't evidence them. The order and consistency relates to telling the story of what was 'one thing'. New rules can always emerge, because they are only the observation of patterns.

  • I'm glad that you have given me proper names for Hume's problem of induction and Hilbert's 6th problem. Possibly Hume's problem is closer to the crux of the question, if we decide there is no fundamental requirement for consistency. Your comments on the distinction between behaviour at different scales also nicely illustrates why fundamental truth doesn't come out of observation. We only get probabilistic comparisons by observing things. In the end, you sort of dodge the question, but the impression is that you feel that consistency is a necessary assumption, and not possible to determine?
    – Clumsy cat
    Commented Jan 11, 2022 at 13:28
  • Popper claimed the idea science is based on induction is a myth, that it's about falsifying incorrect or incomplete models. If you look at Bayesian reasoning, which closely follows how we do things intuitively, guessing reasoning and experience all go into generating our prior probabilities. I don't think consistency is a necessary assumption, I think everything can be generated via uncertainty principle +Anthropic principle
    – CriglCragl
    Commented Jan 11, 2022 at 13:59
  • yes, I think most people would agree that even falsification is not perfectly achievable from observations. We get confidence intervals, and we pick a level to call "proof". So no absolute conclusion can stem from observation (pardon the pun). The remaining question is; do we know anything about our universes internal consistency without making observations?
    – Clumsy cat
    Commented Jan 11, 2022 at 14:07

I suspect you won't like this answer — physicists tend to like concepts that are neat and contained while philosophers deal with scruffy, unruly ideas — but it's worth considering a quote from Wittgenstein:

1.1 The world is the totality of facts, not of things.

Facts are things that we have use for (or have to overcome); they are mental constructs, not physical. It's a 'fact' that an object has mass because 'mass' is something we can use (or have to overcome as a problem). If we want to hurt an enemy, we throw a heavy stone, then we systematically improve — impose order on — our use of mass so that we can hurt enemies more. But through all of this, we have no real idea what 'mass' is; we just know how we can use it.

What the world is, the world of things... [shrug].

The functional regularity of physics tends to infer that there is ontological regularity in the universe. But that itself is just another mental conception: something we humans find useful in or lives and work. Many mystical traditions hold the intuition that there is a higher-order regularity in the universe — karma, dao, the will of God, etc. — but again, that is nothing more than a useful human conception. Humans like order and regularity. We find order where we can, and ignore (or fear) what cannot be organized and structured. We are ineluctably biased towards consistency, so that the 'facts' which constitute our world are only those things that we can find order, structure, and use for. The more we dig for the essence of the universe, the more we find reflections of ourselves.

  • Can we not come upon a fact we did not wish to learn? For example the muon was broadly perceived as inconvenient and messy; "Who ordered that?" - I.I.Rabi. This would indicate that the facts of our universe may be more than just the nice neat symmetric ones we would like to find.
    – Clumsy cat
    Commented Jan 10, 2022 at 16:00
  • @Clumsycat: The only reason we have the conception of muons is that the (nice, orderly) standard model needed something with those characteristics to make it complete. If muons are considered inconvenient and messy, then eventually someone will revise the standard model to make them more convenient and orderly. And let's be clear: we still have little idea what muons are; they are a label that defines a particular effect from which we infer the existence of some ostensible 'thing'. It's all a bit crazy-making, really... Commented Jan 10, 2022 at 16:16
  • " If muons are considered inconvenient and messy, then eventually someone will revise the standard model to make them more convenient and orderly." this is exactly what physics aspires to do, and operates on the assumption that it can, and with the muon we succeeded. But I don't follow your argument for why we should always succeed? And actually, this is a stronger requirement than what I ask. I'm asking if there must exist a consistent set of rules, not if we will be able to keep finding them.
    – Clumsy cat
    Commented Jan 10, 2022 at 16:23
  • Also, I would note that the muon was observed before it was predicted.
    – Clumsy cat
    Commented Jan 10, 2022 at 16:25
  • 3
    this is the point that's soooo hard to get across. Rules are a product of human cognition. The universe doesn't have 'rules'; the universe merely is what it is. Humans formulate rules based on what they can see and know. It's like asking whether ducks have bills. Humans think ducks have bills; ducks (and the rest of the universe) don't make the distinction. Commented Jan 10, 2022 at 17:22

Reality cannot be inconsistent with itself because there is no two properties that are the negation of each other. Black is not non-white, rich is not non-poor. The only pair of truly contradictory predicates is the pair existence/non-existence, but of course, our own notion of reality limits it by definition to what is existent. Thus, the fact that the Eiffel Tower exists cannot be contradicted by the fact that the Eiffel Tower doesn't exist because any Eiffel Tower that wouldn't exist wouldn't be part of reality.

Logical consistency is a cognitive property of our mental representations, not any property of whatever it is that we are trying to represent, whether in the real world or outside of it. We can make inconsistent statements, but we cannot even imagine or conceive what such could possibly represent.

One example of an inconsistent notion is omnipotence when conceived maximally as the power to perform any action whatever. Anyone can say that some being is omnipotent, but no one can really make sense of such a statement precisely because omnipotence in this sense is illogical and therefore nonsensical.

There is nothing we know of in the real world that would make an omnipotent being impossible, but the idea itself is nonsensical to us. That an idea is nonsensical does not say anything about whether there is or not something in the real world satisfying this idea, but it does prevent us from making sense of the idea itself.

So for all we know the universe might be somehow incompatible with itself, but it is very unlikely that anyone will ever be able to find out.

  • This is a very good understanding of what I was attempting (somewhat ineffectively) to ask. When you say "Reality" in the first paragraph do you refer to the world as we perceive it? When you say "the universe" in the last paragraph do you mean a possible external reality? I ask because you have different conclusions for them.
    – Clumsy cat
    Commented Jan 11, 2022 at 17:34
  • @Clumsycat Reality is the whole of what exist. The world, or misleadingly, "the real world", is what we tend to call now the physical or material world. It is what we believe exists outside our own mind. We normally take it to be a part of reality. The universe has now a scientific description. The universe is either a part or the totality of the world. We think of it therefore as obviously a part of reality. Nature is whatever we can perceive. We also experience the contents of our own mind and so we see that as a part of reality, and indeed the only part we really know. Commented Jan 12, 2022 at 18:14

I would take kutschkem's answer one step further and assert that if our universe were internally inconsistent on large physical scales then we wouldn't be here to ponder that fact- because such a universe would not support the formation of galaxies, stars, planets, or the evolution of life.

  • Why not? Naively I would say that many fictional universes exist that lack internal consistency and support the existence of things like stars? My understanding of kutschkem's answer at present is that our universe may be either way and that cannot be proven.
    – Clumsy cat
    Commented Jan 11, 2022 at 8:49
  • How are you planning to prove that an "inconsistent universe" is incapable of formation of galaxies, stars, planet or life? This feels like just someone's opinion
    – Tvde1
    Commented Jan 11, 2022 at 16:37
  • @Tvde1, this is the opinion of a physicist whose business it is to know what's required to create those formations. An inconsistent universe is one in which different portions of it possess different physical laws, and those laws change from time to time. In the simplest case, if gravity doesn't always work at all times with a 1/(distance)^2 dependency, then you don't get galaxies. Commented Jan 11, 2022 at 22:52

So, maybe a more pragmatic answer:

  • In is entirely possible that the universe is not gouverned by coherent rules. Most of it might not even exist it's all in your head; it may be a simulation; it may be governed by some whimsical demon that decides the results of any process ore experiment for teh lulz. All of these ideas have been seriously argued for by educated poeple.
  • On the other hand, the main answer to the question in the title is that it seems to be like that. That is, we have been able to find laws that describe the behvaiour of nature. In some fields, these laws are more explicit and/or more succesful than in others. In many cases, the laws are not quite what people initially thought, because our intuition doesn't cover more exotic circumstances. Furthermore, the laws or theories change every now and then in more or less radical ways.
  • Thus, I guess there won't be an experiment that refutes a law-based universe: Assume some experiment contradicts our best theories, or even seems to give totally unpredictable results. Essentially, you could now conclude that the universe is incoherent and lawless, or that the true laws are more complicated than you thought, and there are some more factors you have to take into account. The second choice has proved to be successfull in the past, so that's what most people (including most physicicists) would choose.

I think of this problem as a computer scientist. The universe is a giant state machine. Time is what separates one state from another. The laws of physics are a compact description of the state transition table. When we talk about "consistency", we are really asking: "How small is the transition table?" Because the most general answer is: any state can transition to any other state, stochastically. Such a universe, on average, would be utterly incomprehensible and would just look like noise if we could observe it from without. On the other end, the smallest transition table is the identity function: every state transitions only to itself. Such a universe is static, frozen solid for all time, no matter which configuration it starts in.

Many scientists would say that the "frozen" universe is extremely consistent, but boring. And they would say that the "maximally free" universe is chaotic and incomprehensible. But would they say it is inconsistent? I suspect not. But that is simply because this level of freedom hardly exists anywhere in our universe. If the freedom were dialed down to our universe + a few notable and observable exceptions, then there would be strong talk of "consistency".

For instance, if we found that the mass of the electron varied depending on which research group and machine was measuring it, but all our large-scale observations depend on it having a static, universal value, then some folks might tend to declare an inconsistency in the laws of physics. However, it should be clear that other folks would simply say there is deeper physics afoot and we just need to discover it (c.f. muon mass).

"Consistency" is basically presumed by scientists, and science is fundamentally built upon this presumption as an unstated axiom. If we admitted that physical law need not be consistent, then there would be effectively no way to discriminate between one theory and another. Take the Hubble constant, for instance. We have multiple values estimated by multiple teams. Astronomers generally believe that the Hubble constant has one value, and that there are deep, underlying reasons that different teams get different values. But in a world where inconsistency is accepted as possible and legitimate, there would be no reason to try to resolve the contradiction. The Hubble constant may take on different values depending on how it is measured, even if each of those methods were arbitrarily precise. Obviously, this kind of relaxation would make a hash of science.

Going back to the state machine, science is predicated on the notion that the "state machine" for the universe is indeed small. Small enough to write on a single sheet of paper at a size that the average human could read it. That's a pretty bold and remarkable idea, if we think about it! Instead of believing that the Standard Model is a fairly accurate description of the universe, we could instead accept thousands of competing, mutually incompatible models which each explain a small set of observations extremely well, while failing miserably on others (e.g., MOND). We would explain away the failures as "natural inconsistencies". After all, how could you possibly tell the natural ones from the unnatural ones?

So in this sense, science must assume that the universe operates according to consistent rules, because you simply cannot have objective science without this assumption. If you allow inconsistency, then every scientist can have their own theory, and you have no strong basis on which to object to it. Even a theory which predicts no observations could be correct, because it might explain something which will happen in the future but which has eluded our notice up until now.

Non-science has no such compulsion to believe in consistency, and indeed, religion practically demands that certain "inconsistent" events occur (i.e. "miracles"). At the same time, human nature (and indeed, all intelligence) must presume some level of consistency, because we need it just to operate in a hostile environment (predict food sources, threats, mating opportunities, etc.).

  • Please could the downvoter talk a bit about why they don't find this answer satisfying?
    – Clumsy cat
    Commented Jan 11, 2022 at 11:03
  • 1
    Doesn't chaos theory falsify your argument?
    – CriglCragl
    Commented Jan 11, 2022 at 13:08
  • @CriglCragl please spell it out. Commented Jan 11, 2022 at 22:28

Before asking about consistency you probably should agree upon the logic you are using. For example, quantum logic is far from being well understood. For another example, there are paraconsistent logics in which you might encounter assertions A such that you might be unable to establish that "A and not A" is false: the only thing you might hope for is to know that if A happens to hold then "A and not (A and not A)" holds as well.

PS Could the downvoter please explain what's wrong with this answer? I would probably benefit from knowing that.

  • Is quantum logic poorly understood? en.wikipedia.org/wiki/Quantum_logic I'd argue, it's just weird, & that isn't the same thing. The en.wikipedia.org/wiki/Quantum_Turing_machine shows there is not a fundamental discontinuity between the quantum & classical worlds.
    – CriglCragl
    Commented Jan 11, 2022 at 13:04
  • @CriglCragl I meant that a logic that would be adequate for arguing about quantum physics is poorly understood, as can be in particular seen from the limitations and criticism sections in the Wikipedia article about existing versions of it that you linked to. As for your second statement, could you explain better what do you mean by it? I never addressed any fundamental discontinuity, nor do I understand what that article about Quantum Turing machines says about its absence. Commented Jan 11, 2022 at 15:56

In fact, basic laws of physics can be derived purely via math from the assumption that these laws must be consistent with respect to certain aspects:

  • Consistency of movement regarding mirroring in space leads to conservation of momentum.
  • Consistency of movement regarding rotation leads to conversation of angular momentum.
  • Consistency over time leads to conversation of mass and energy.
  • Consistency of the vacuum speed of light being the maximum speed leads to ¿general? relativity theory.

For details (e.g. the math involved) on the first points, look up the Noether theorem.

So there's not only reason to believe that the rules of the universe are consistent. There's also reason to reject the opposite proposition: Inconsistent rules would be inconsistent with the empirical verification of models mathematically derived from the assumption that the rules are consistent.


There are an abundance of ways that a reality can have rules that are not possible to obtain. Nor do I place any constraint on the structure of these rules. But does the reality itself have to behave in a way that does not require contradictions in those rules?

there's really not so much of "an abundance of ways that a reality can have rules that are not possible to obtain". The only way that "observing, formulating hypothesis and verification" (aka the scientific method) couldn't obtain some laws of physics is, if there would be an omniscient, omnipotent force that actively changes rules whenever those rules are being investigated:

  • A non-omniscient force could miss out on a scientist, who investigates in this field.
  • A non-omnipotent force could be unable to change a rule being investigated.
  • A non-active force wouldn't act to change the rules, exactly when they are investigated.

Even if the rules were changing based on time (instead of as a reaction to investigation), there could be scientists that investigate the current rules fast enough to formulate laws and then start investigating the time-based rules of change in rules.

Completely inconsistent rules would quickly lead to total chaos. For illustration, just watch a physics simulation that allows a gain of energy: Worlds simulated this way tend to explode violently rather quickly. Again an omniscient, omnipotent and active force could be an arbiter resolving conflicting rules on a case-by-case basis while keeping a potential energy gain "manageable". However such a force has long died by Occam's razor: There's simply no need to assume such a force exists considering repeatability of observations in our universe.

In reality, the closest you get to "inconsistent" rules is quantum mechanics, in which rules of Newtonian Physics and even Relativity Theory and the intuitions that follow break down. This is in part due to the effect that an observer has in quantum mechanics (Heisenberg's uncertainty and Schrödinger's cat comes to mind). However the effects can still be observed, replicated and put to use, e.g. in quantum computing. This is simply because the rules of quantum mechanics are although complex, confusing and dependent on the observation still consistent. It's just very hard to wrap your head around them.

  • So regarding your first part, we run into problems with things that would be consistent with all existing rules, but we don't find them. For example, a moderate supersymmetry model would carry all sorts of benefits, in terms of fitting together other parts of the standard model, but it has been excluded by experiment. So it's a pretty perfect theory, which doesn't actually exist. Noethers rules are amazing, and about as close as any physics gets to truth, but quantising them is fraught. They are the backbone of physics, but they cannot give you everything you need.
    – Clumsy cat
    Commented Jan 11, 2022 at 11:31
  • As for the second part, I offer you two (hypothetical) universes in which the rules of the universe cannot be enumerated; in universe 1 the universe does not last for sufficient time to complete the required observations, in universe 2 the complexity of the rules of the universe exceed the complexity of the universe, making some dynamic attribute appear either random or static.
    – Clumsy cat
    Commented Jan 11, 2022 at 11:34
  • Your comments seem to indicate that I didn't (fully) understand your question. Where in your question, did you ask about the rules being possible to determine (in full)? Also Universe 1 is clearly not ours while your question specifies "our universe". Plus, it is irrelevant, because it's already gone. Universe 2 is a paradox, how can the universe be simpler than itself? The rules are part of the universe, aren't they?
    – NoAnswer
    Commented Jan 11, 2022 at 11:40
  • ah, that comment was intended to illustrate ways there could be rules that we cannot obtain, but that are not due to any omnipresent being. As for universe 1, in our universe we cannot yet put an upper bound on the lifetime of a proton, having never seen one decay. Maybe one day we will quantify this upper limit, but we are not guaranteed that opportunity. It may be that protons last so long we never see a decay.
    – Clumsy cat
    Commented Jan 11, 2022 at 11:46
  • Well, I thought about leaving out the whole part of omniscient, omnipotent and active force, because it was very hypothetical. However I get the feeling that you want hypotheticals like that. If that's the case, you should ask a separate question, possibly linking back to this one and specifying that you're not asking about our universe.
    – NoAnswer
    Commented Jan 11, 2022 at 11:50

This has been brought up in the comments, but deserves an answer of its own:

It makes no sense to ask whether a) the universe is consistent or b) obeys consistent rules; doing so is a category error.

Regarding the first part of that statement: Consistency is defined to be a property of a theory. A theory is a "set of sentences in a formal language." The universe clearly is not a set of sentences in a formal language. So asking whether the universe is consistent makes no sense whatsoever.

Regarding the second part: we have no indication whatsoever that the universe and its set of rules are two separate entities. This would be a worldview where the universe is some kind of (actual) computer which follows some algorithm (which we could approximate with our physical theories) in something vaguely like a von-Neumann architecture. Our theories can of course, being "sentences in a formal language", be consistent or not. They can also fit experiment or not.

But nowhere do we have any indication that there are real rules governing anything out there, for a definition of "real" which is comparable with the realness of the physical objects we see or describe. So it makes no sense to ask anything about the rules of the universe, beyond our formal systems, which obviously are just a description of the universe, not mandating its behaviour, because by all evidence we have so far (which is none, i.e. Occam's Razor), there are no rules.

Of course, as the plethora of other answers saying "yes" or "no" tell you, people have come up with interesting concepts surrounding this; but you'd have to define the concept of "consistency" (and possibly of "universe" and "rules" and "internally" and so on) very carefully to make any meaningful statement possible.


I think that very little can actually be proved about the universe.

For instance, it's possible that we're actually in a Matrix-like universe inside a computer, and nothing in our experience is actually "real". The programmers of this computer could change the rules any time they wish.

Another possibility is that there's no actual change in the universe. We're actually at a frozen moment in a static existence, and what we experience as memories is just the state of all our neurons in that frozen moment. This is similar to the argument that Creationists make regarding fossils -- the dinosaurs didn't actually live billions of years ago, God created these buried bones after creation thousands of years ago.

We only have our senses to go by, but since they're a part of the universe they're studying, they can be fooled by it.

If you believe any of these kinds of ideas, then you can conclude that nothing matters. But since it feels like things are actually happening, and that includes noticing that the universe seems to follow rules that we're able to discover, we've adopted this as an axiom.

Physicists and philosophers do wonder and debate why mathematics seems to be so good at describing physics. But it's hard to deny that empirically, it does. Assuming that the past is prologue tends to be useful.

Another way to look at this is that the question itself is vacuous. What does it mean for the universe's rules to be "consistent"? Consistent with what? As another answer says, the universe is what it is, and the rules are whatever actually happens. If something appears inconsistent to us, that's just our own ignorance of all the rules. This can be related to related to Goodman's riddle of induction.


A single belief can also be said to be consistent (if it is possible for it to be true) or inconsistent (if it is not possible)... A single belief which could not be false is said to express a necessary truth.


So, an inconsistent belief is about something impossible, expresses something that is necessarily not true: necessity is being violated.

Inconsistent with which "rules"?

  1. Nomological necessity (most agree "God" can break these rules)
  2. Metaphysical necessity
  3. Logical necessity: even if you don't assume classical logic makes for laws of thought (the basis of all rationality), paraconsistent logic need not entail there are true contradictions, dialetheism, inconsistencies.

In general

if consistency turns out not to be an essential requirement for all theories, then the way is open for the rational exploration of areas in philosophy and the sciences that have traditionally been closed off.

However, I'd probably think that inconsistencies in the law of physics cannot be explained by science, as they are like miracles, and will never be subsumed by any scientific theory. Whether or not that argument is acceptable for those sufficiently hard nosed.

  • I'm a bit confused if you only mean logical contradiction. obviously, explanations of contingent events can include some form of contradiction broadly thought, because they allow that it could be otherwise (it could be raining in Paris)
    – user57343
    Commented Jan 17, 2022 at 21:25

The universe simply is what it is. It does not answer to anything. Like God it is. Our understanding of it evolves but the universe is today exactly like it will be tomorrow regardless of what we learn about it.

The universe posits nothing. It makes no claim, it simply is. What does it mean for a non corporal entity to be consistent internally or externally? What sort of epistemology does the universe have that can be said it is inconsistent? I'm assaulted by an illogical universe every time I climb out of bed.

Why do good people suffer and bad people flourish? How could the shower scene from Schindlers list have actually happened? Maybe if you subscribe to many worlds interpretation of quantum mechanics you could find a universe that has logic to it, but it ain't this one.

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