In our best scientific theories, is there a difference between "the universe" and "reality"?

Are all scientific realists committed to the idea that there is a mind independent universe that our theories are true of, or can some realists talk about them referring to a part of the universe only, such that the universe as a whole may not exist? I recall that

many philosophers think that many utterances which include no explicit ceteris-paribus clause implicitly do include such a clause.

For the most part, philosophers have thought that if scientists have discovered any exceptionless regularities that are laws, they have done so at the level of fundamental physics. A few philosophers, however, are doubtful that there are exceptionless regularities at even this basic level. For example, Cartwright has argued that the descriptive and the explanatory aspects of laws conflict. “Rendered as descriptions of fact, they are false; amended to be true, they lose their fundamental explanatory force”

But I'm unclear whether e.g. Cartwright can claim that there is no whole of reality. After-all, ceteris paribus claims might - I'm thinking - presuppose that "exceptionless regularities" could hold, it just so happens that we cannot establish knowledge of them. I'm extremely unclear on this, whether 'exceptionless regularities' need to be metaphysically impossible, let alone which philosophers can or do claim it.

  • In buddhism e.g. I'm fairly sure there everyone is a nominalist about wholes but claims there are collections of things. Would that - taken alone - allow realism, just not knowledge about everything that is real?
    – user62233
    Dec 1, 2021 at 8:11
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    Possible example: numbers are real but we do not usually say that they are part of the "universe". Dec 1, 2021 at 11:44
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    In a sense the question might be whether "real" does play any role at all in our best theories, or if it's just a metatheoretically convenient construct. We do, it seems, want on occasion to quantify over all of space-time, but it might be extraneous within science for us to be able to quantify over "all things" with absolute generality, even if in discussing our theories that is a useful tool to have.
    – Paul Ross
    Dec 1, 2021 at 12:21
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    @anon Mahayana Buddhists (i.e. Zen, Vayrajana) are pretty much antirealists. Whereas Scientific realism would say that the fundamental physical reality is what is real, Buddhists reject entities like quarks or bosons as lacking inherent Self-existence. To perceive such entities as fundamentally real in the Scientific realist sense is to be committing Self-grasping of these phenomena. Dogen Zenji encompasses this in his claim of UNNAMABLE and UNSPEAKABLE nature of the universe of all things (jap. Immo, eng. Thusness). What follows is also a form of neutral monism but its too much for comments Dec 2, 2021 at 20:39

5 Answers 5


This question jumbles a few things, which I think can be untangled.

A) It is possible to do science as a nominalist, rather than as a realist. But every scientist I have ever interacted with, is very much of an indirect realist. There may be a few exceptions, but for almost all scientists scientist == scientific realist.

B) Indirect realism presumes there is a reality which we infer by successful models and predictions. Again, every scientist I have interacted with presumes their theories are valid. That is what is proposed when they propose a theory. But when they find exceptions, this causes no massive worldview problems for them. It is the nature of science that it is fault-tolerant -- science does not REQUIRE "exceptionless regularities".

You asked about the "best" science. The best current science holds that all our laws are regularities, based on symmetries, and that all these symmetries spontaneously break. IE those "laws" break too. Here is a description of this thinking, in the form of gauge symmetry theory: https://www.pnas.org/content/93/25/14256

Gauge Symmetry postulates some more fundamental rules that drive the gauge behavior, hence some more fundamental symmetries, and assumes these are "exceptionless", but once more, the theory could tolerate exceptions, without any major problem.

C) Cartwright has a major challenge to accomplish if he thinks that "exceptionless regularities" is logically impossible. It is a burden on claimants of logical impossibility to support their claim, and for the claim to be valid, the majority of reasonable readers would have to agree with the logic argument. I don't think Cartwright has met this bar for demonstrating the impossibility of exceptionless regularities. A discussion of the claim and the validity of his argument would make for a good separate question.

D) Getting to the "universe" vs. "reality". The claim that everything that is "real" or can be "known" about our universe is in the purview of science, is the philosophical position of "scientism". Scientism is a worldview derivable from reductive physicalism. However, the near-consensus of philosophers of science, is that reductionism has failed as a project (See SEP's Scientific Reductionism, section 5) https://plato.stanford.edu/entries/scientific-reduction/.

So SCIENCE itself is "pluralist" rather than reductive. Once one accepts pluralism, then there are multiple fields of knowledge, such as History, mathematics, Logic, etc which are non-scientific, but appear to give us knowledge about the "real universe". Additionally, as science DEPENDS on many of these other fields (math, logic, plus the philosophy of science to justify the scientific claim to epistemological validity) -- the basic premise of scientism is inconsistent with the actuality of science's dependence on outside knowledge.

The majority of philosophers, and the majority of scientists, now identify as "non-reductive physicalists". The meaning of non-reductive physicalism is a bit self-contradictory. If everything is physics (per the name), that IS reductionism! The basic coherence of non-reductive physicalism is, I believe, highly suspect. The meaning, in practice, seems to be a belief that physics is "really real" while other fields, such as math and literary criticism are "real" to perhaps a lesser or derivative degree. There is no "scientific evidence" for this view, it is a purely philosophic position. And the philosophy is self-contradictory, because the epistemology of indirect realism premises that equally pragmatically valid models are equally "real".

But one does not need to be a physicalist of any kind to do science, or accept scientific realism. All one must do, is accept METHODOLOGICAL naturalism. The greatest articulator of how to DO methodological naturalism, Karl Popper, considered physicalism to require reductionism, and reductionism to be falsified, hence physicalism was falsified. Popper's ontological view was there were three worlds -- that of matter, that of experience, and that of ideas. https://tannerlectures.utah.edu/_resources/documents/a-to-z/p/popper80.pdf

So, per Popperian methodological naturalism, math, logic, aesthetics, and literary criticism all reveal aspects of "reality", not just science.

In summary -- science reveals a set of laws that so far all break, but there is no logical necessity for this, it is just a contingent discovery. And science CANNOT encompass all of realty, based on the logical contraction of science relying upon non-science fields. But one can be a scientific realist while accepting both of these truths.


Our best theories are the ones which 1) accurately account for experimental data collected before they were written, and 2) accurately predict the outcomes of experiments not yet performed, including 3) predicting the existence of entirely new phenomena not described or hinted at by previous theories.

If those new predictions are borne out by new experiments, then you get a Nobel prize.

The object of such model-making activity on the part of mathematical physicists is to yield theories which represent as accurately as possible the functioning of the real world, defined here as the observable universe we inhabit.

This means physicists do not draw distinctions between "reality" and "the universe".


I understand that you ask what ontological claims about reality scientific realism makes.

Scientific realism is committed to the claim that reality is described by our best scientific theories. Let's assume that it is physics that best describes what fundamental reality really is.

Take colours as an example. Herein, a typical claim is that the colours are not real, and are made up by the brain because the real things are only certain photon frequencies. Another claim is that solid objects don't really exist because things are really just field excitations.

Scientific realists such as Sean Carroll are reductionists who reject the existence of large scale concepts like liquidity, or solidity and propose that quarks, fields, and so forth are the "real stuff".

  • Not all scientific realists are reductionists. What you are describing in your fourth paragraph is often criticized by scientific realists as greedy reductionism. Dec 4, 2021 at 21:03
  • @JustSomeOldMan Are then those scientific realists not committed, ontologically, to the claim that reality is described by our best scientific theories? Do you mean non-reductive materialists? I thought that this was made untenable, by multitude of essays such as say, J. Kim "The Myth of Nonreductive Materialism" (or the whole Supervenience disciussion), if reality is to be considered equally real on multiple layers of different theories. Dec 4, 2021 at 21:50
  • Like much of metaphysics, in some cases it comes down to how you want to use the adjective “real”. Indeed, it would seem strange for a chemist to reject the reality of the differences between the solid, liquid, and gaseous form of the same substance. It the context I remember, the argument made was essentially, “so the ocean is made up of, and reducible to, a bunch of particles we agree are real; why does this imply the ocean isn’t real?” There’s nothing keeping one from applying the character sequence “r-e-a-l” as an adjective describing conglomerations of things we agree to be real. Dec 4, 2021 at 22:33
  • @JustSomeOldMan It then has to work with a notion of weak or strong emergence. While weak emergence is trivial, it is reducible to bottom down physics. (In fact, all reductionists are weak emergentists.). But, if strong emergence is the case, which is irreducible, then we need to use the notion of downward causation, and 1) the claim is typically controversial in science or deemed plain unscientific (i.e. Sabine Hossenfelder and many many others) and 2) there were no successful / convincing examples of downward causation for science to accept it. Dec 4, 2021 at 22:45
  • How does that imply, or even pertain to, using the character-sequence r-e-a-l as an adjective describing conglomerates? The point is, people have widely different criteria for the use of the word “real”, which contributes to why metaphysics is denigrated. Just because conglomerates reduce to particles does not mean a sequence of characters used to describe the latter cannot be used to describe to former. No oceanographer will deny the reality of the ocean simply because it is a conglomerate, nor will you deny the reality of your mother because she is a conglomerate. Dec 4, 2021 at 23:02

Specifically regarding scientific theories, what's "real" is typically what's "measurable", i.e., detectable by some reproducible experimental apparatus (or maybe just your five senses).

But the universe as a whole contains mostly spacetime regions outside our light cone (e.g., https://en.wikipedia.org/wiki/Light_cone) with which we can never interact or know anything about. So they're maybe real in one sense, but not necessarily in another.

Or, even more esoterically, consider dark matter and energy. Their existence is very difficult to detect because their interactions via the known forces, except gravity, are non-existent. Now, suppose or imagine some even-darker thing that also has no gravitational interaction. If such a thing exists, then it's part of the universe, even though we'll never detect it, period, whereby it's not real in that sense.

So you've really got to very carefully and concretely nail down what you want to mean by "universe", "reality", "exist" before the question is well-posed.


Short Answer

In our best scientific theories, is there a difference between "the universe" and "reality"?

That depends. While most philosophers will accede that the universe is essentially what is described in WP's article 'universe', the question of what constitutes 'reality' is far more controversial. If you consider the difference in positions between scientific realism and instrumentalism, a range of positions probably can be described from a firm no-difference to absolutely depending on to what extent one subscribes to realism and instrumentalism, material and mental.

Long Answer

Let's consider two positions. First, that of the scientific realist who embraces eliminative materialism. In this broad category, there is only the material, so universe and reality must be the same. What constitutes reality is at best an illusion of mental state that doesn't actually exist. Clearly in this case, they are the same.

But, not all scientists are realists who accept eliminativism. In a more moderate position, a philosophy can accept a duality, such as Cartesian duality, thereby accepting that what is 'reality' is actually a worldview of an individual that is subjective, and that only through intersubjective agreement, perhaps as Dennett has characterized heterphenomenological discourse, is something like a "shared-reality" created. For instance, consider the Kantian notion of Das Ding an Sich, which concedes an object has an existence independence of observation, but is ultimately unknowable. In this philosophical characterization, the universe is not truly knowable, and our understanding is largely phenomenological.

So, the coincidence of 'university' and 'reality' is ultimately one of that degree that unfolds from one's first principles. Since metaphysical presuppositions often built on intuition play a large role in defining a theory, without taking this into account, one cannot draw an inference about the ultimate nature of their realtion.

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