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This question has to do with scientific claims about the universe and could be asked in a number of ways.

To my own very imperfect understanding, claims about "the universe" cannot be scientific claims in any proper sense. As claims about a single entity they do not and could not submit to standard principles of verification. (They might even be subject to Hume's arguments about miracles.) As claims about a totality that presumably includes the claimants, they fall prey to paradoxes of self-reference, such as sets of all sets, and so forth.

Yet scientists and philosophers of science regularly do make highly considered claims about "the universe." They also make claims about the possibility of a "unified physical theory" that would seem to involve some of the same sorts of problems.

Is this just a manner of speaking on the part of scientific pragmatists? Or do physicists understand themselves to be making perfectly valid claims about the physical universe, implying that such claims can be made from "outside" the physical totality, so to speak? Which suggests dualism of a nearly Cartesian order.

Perhaps I am misunderstanding something obvious here. How do philosophers of physics deal with such issues? Is this a well understood problem? Do the potential fallacies here in any way relate to the emergence of "other universe" theories as an attempt to provide some apparatus of comparison for "this universe"?

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  • So the claim the Earth is round is not scientific because there is only one Earth? No, because it can be verified by multiple paths, and none of them reach an edge. The same way, we can test most propositions about the Universe because they would have multiple effects, each testable.
    – user9166
    Feb 22, 2016 at 21:26
  • Perhaps I'm not stating this correctly. In one sense there is only "one" of any particular thing, but they must nonetheless fall under some concept of what they are "like." The "universe" seems to have very different status as a completely singular totality, a totality that includes whatever can be said about it. But I guess I'm not expressing this clearly, because I don't have my terminology clear. It isn't an original idea. but I'll have to find how it is stated by others.
    – Nelson Alexander
    Feb 22, 2016 at 22:01
  • This ignores the fact that the roundness of the Earth can be confirmed by multiple paths. Every general-enough fact, e.g. geodesic following in General Relativity, is in some sense a fact about the whole universe, that can be tested at various points and considered true if it does not seem to vary. The universe is not a non-repeatable event, like a miracle or a single case of a disease remission, it is a large collection of events that are statistically related. So the whole notion of uniqueness leading to non-repeatability does not really apply.
    – user9166
    Feb 22, 2016 at 22:11
  • If I discovered something so unique there was nothing like it elsewhere at all, say a lost alien spacecraft inside which the laws of physics were different, I could still make a whole science out of studying it, if it were large or complex enough to consider all the various parts important.
    – user9166
    Feb 22, 2016 at 22:18

2 Answers 2

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There is no problem studying unique systems in science (the earth or the sun are examples). As for the problem of totality: cosmology is not about the totality of facts but about the global structure of the universe.

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  • Thanks, but our "sun" can be compared to other "suns" and placed in a range of measurements under the concept "sun." There is no logical problem saying "the sun" is X years old. But to say "the universe" is X years old is quite different. All, any statement about the universe would seemingly be, in some sense, about the statement as well. As in Russell's paradox of set of all sets. Perhaps I am not getting my idea across, because I don't have a clear grasp of it.
    – Nelson Alexander
    Feb 22, 2016 at 1:42
  • @NelsonAlexander there could be a problem if we thought that cosmological models include ourselves but it's not really the case. Cosmological models don't even include galaxies since they take the universe to be homogeneous (just like the model of a gas in statistical mechanics needs not assign precise states to every single particle to make predictions). The global structure of the universe does not predict life, consciousness and what we think about the universe.
    – Quentin Ruyant
    Feb 22, 2016 at 14:01
  • @NelsonAlexander about unique systems: take the theory of continent formation. We don't have other planets with continents and oceans to compare yet we model the earth...
    – Quentin Ruyant
    Feb 22, 2016 at 14:02
  • Right, theories about the whole have multiple consequences, each separately open to having alternate states due to different causes if the theory did not hold. Each falsifying alternate explanation is usually separately testable.
    – user9166
    Feb 22, 2016 at 21:29
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Abduction is the key word for understanding the approach they take.

Scientists have gotten in the habit of speaking about their discoveries as ontological truths, such as "The Higgs Boson exists." In actuality, their data merely suggests that they have observed data which fits well with their model in a region of the state-space which could have potentially falsified their theory. However, science has received enough trust from the people that they are permitted to make such ontological truths. They are not the only ones. For example, the Christians are permitted to say "He is risen" when one might have required them to say "I believe he is risen."

Abduction is the inference to the best hypothesis. It is saying "out of all the possibilities I can think of, hypothesis A fits the data so much better than any other hypothesis that I am going to presume A is actually true." Making this assumption is very tricky, and many are not even aware they are making it!

Physical Cosmologists are proposing models for how our universe works. If one of them shows great promise, they may change their wording to start suggesting it as an ontological truth. This is perhaps justified by the fact that English is a messy language, and one may use syntax associated with ontology to express semantics which are empirical in nature. If at some point they truly believe their model is correct, then they have engaged in abduction.

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  • Thanks, but this seems more about the bracketed status of all scientific claims. I am not asking about truth claims. I am wondered about the specific problems of scientific claims about a "totality" or "single case" such as "the universe," not "parts of the universe," where there is no possible comparison, repetitions of events, or "external stance." I'm not sure your answer addresses that.
    – Nelson Alexander
    Feb 21, 2016 at 22:33
  • @NelsonAlexander One can develop a theory of everything which makes claims about what happens in the "single case," which are naturally unverifiable by scientific means, and also makes a plethora of "parts of the universe" cases which can be verified. Typically the goal of physical cosmology is to try to identify the "simplest" explanation for all that is.
    – Cort Ammon
    Feb 21, 2016 at 22:35
  • I think one might draw an analogy to how, in cryptography, we say "breaking this by brute force woudl require 3/4 of the energy in the known galaxy," when all we have are some scribbles on the paper to suggest that's hwo much energy it would take. Nobody can test it. However, it is effective to make such a claim (btw, thats how much energy it takes to simply advance the 256 bit counter needed as part of cracking AES by brute force... 3/4 of the known energy in the galaxy!)
    – Cort Ammon
    Feb 21, 2016 at 22:37
  • Okay, then it does seem "universe" is not really an object of science per se, but a pragmatic term with various definitions. But it still seems to necessarily consist in observations about a totality that by definition includes the observer and the observations. Which is a logical problem unlike estimating energy in the galaxy, which is just a practical problem.
    – Nelson Alexander
    Feb 21, 2016 at 23:32
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    @NelsonAlexander I find science always removes the observer from their model, unless something forces them to include it. Science's fundamental assumptions of independent identically distributed variables does not work unless one can show that the effect of the observer can approach zero. I don't think they like to admit that one, though. The cosmologists are only concerned with values which are theoretically too large for the observe to influence, but you are correct. Inclusion of the observer an the observations (and the observe's actions) is a major limitation of science.
    – Cort Ammon
    Feb 22, 2016 at 0:00

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