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Religion, spirituality, and other “pseudoscientific” theories are constantly seen as backwards and lacking of evidence. But if a lack of evidence before believing in something is considered irrational, why is so much of physics that is based on literally zero testable evidence taken seriously?

There is no direct evidence of a multiverse, certain interpretations of quantum mechanics, string theory, and many other things. Why are so many of these kinds of theories taken seriously?

There have been entire books written about some of these theories with people being fascinated about how intellectual they seemingly sound despite the fact that there is zero experimental evidence for any of these theories.

Should they be given the same treatment as other forms of pseudoscience?

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    The justification for them, such as it is, comes from the mathematical side of physics. We have, unfortunately or not, found that mathematics and modeling are both more malleable than we might have wished, but still, the idea that we can anticipate specific physical phenomena as "solutions to equations" has shown some measure of promise (e.g. black holes, or perhaps the structure of DNA). Since experience has to be interpreted partly a priori anyway, it's not like we could really get around possible speculation. Jul 12, 2023 at 18:51
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    Multiverse theories, at least the more profligate ones, do push the boundaries of admissible scientific hypotheses, because they trivialize the possible solutions to their equations (viz. all solutions are given, for all possible equations!). Still, the demarcation problem suggests that multiverse theories might not be pseudoscience strictly, perhaps occupying a vague zone between science and pseudoscience. Offhand, I favor a definition of pseudoscience as involving already-falsified premises, e.g. astrology "could" be true in the abstract but Jul 12, 2023 at 18:58
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    @DavidGudeman I just don't agree with the theory of probability behind statements about things being "astronomically unlikely" in that connection. Or even if I did, I would not agree with the meta-science about such probabilities (that calculating such probabilities gives us scientific justification in the intended manner). OTOH I also think that the intersection of higher set theory and deontic logic indicates a strong intentionality throughout our world, an intentionality that could "guide" the flow of events in the world. I wouldn't want to press my claims as science, though. Jul 12, 2023 at 20:02
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    As soon as I saw the subject in Hot Network Questions, I knew that you were the one who asked this question.
    – RonJohn
    Jul 13, 2023 at 5:22
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    I think this question could stand a lot of editing to remove loaded language, unsupported claims, and misuse of terminology, and may merit downvotes, but I don't think it merits closure. The core question, "if a lack of evidence before believing in something is considered irrational, why is [theoretical physics] taken seriously?" is answerable.
    – g s
    Jul 13, 2023 at 22:32

6 Answers 6

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Unlike pseudoscience, both types of speculation in physics begin with evidence, remain constrained by evidence, and have falsifiable empirical predictions as the end goal.

Which mathematical formalism we use to map successfully between accurate measurements of reality is arbitrary so long as they work, and what words we use to describe what the math means are arbitrary so long as the math works. However...

Interpretations: Within a model, words can sometimes be translated into math in ways we did not expect and are not remotely obvious. If so, they are no longer arbitrary, but constitute substantive predictions.

Example: In 1920, physicists didn't know that there could be empirical predictions made about the claim that quantum randomness could be explained in terms of human ignorance of some difficult or impossible to measure classically deterministic antecedent(s). By 1970, that claim had been expressed mathematically, described in terms of empirical predictions, measured, and falsified. If everyone had been content to shut up and calculate, this important discovery of 20th century physics might never have been made.

New models: New mathematical formalisms for established evidence may turn out to make empirical predictions that contradict the predictions of the old model within its domain, but in ways that we had not yet been able to test. Or they may make predictions outside the domain of relevance of the old model. Given the staggering complexity of the math used in the candidate models, these may also be extremely non-obvious. The great value of new models where old models work well is that the new models may suggest new predictions, which hopefully can suggest new experiments, which allows for their falsification or, hopefully, the ability to make successful predictions that we previously couldn't make. A side benefit is that it drives the discovery of new kinds of mathematics relevant to the structure of the physical world, which can itself lead to new predictions by old models, or the formulation of still other new models.

Example: String Theory hopes to eventually be able to make predictions related to the effects of gravity on the smallest scales. So far it remains an extremely cumbersome, but apparently viable, way of duplicating the results of well established quantum mechanics.

Pop science: The value of popular science books on speculative physics, besides book sales, is to build public interest and thereby attract scholars and grant money to projects for the extension of human knowledge.


Pseudoscience vs falsified real science: the scientific method is the slaughterhouse of good ideas. The flat Earth hypothesis is a good idea. It makes great predictions. I use its mathematical formalism whenever I give or interpret directions. It's much better than the slanted Earth hypothesis or the bumpy Earth hypothesis, and arguably better predictions than the dome-shaped Earth hypothesis or the spherical Earth with fixed direction gravity hypothesis (in which the upside down Australians all fall skyward to their doom). What makes it pseudoscience is that to believe it now in the context of abundant evidence for a more successful model, one has to come up with reasons why it doesn't comport with evidence, and those reasons themselves do not comport well with evidence, necessitating still other reasons, and so on.

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    Things like the multiverse and certain interpretations of quantum mechanics are not based on evidence and have no hope for empirical verification. Others, like much of string theory, are motivated, not by any empirical evidence, but by esthetic judgments that certain symmetries are needed. Jul 12, 2023 at 22:07
  • @DavidGudeman The argument goes that with enough development of the hypotheses, one can then arrive at an empirically testable prediction. Or so I assume.
    – Passer By
    Jul 13, 2023 at 8:41
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    About flat earth: If we model the Earth as a smooth manifold, then it is locally flat, which is at least compatible with the flat earth hypothesis :-)
    – j4nd3r53n
    Jul 13, 2023 at 9:51
  • @DavidGudeman The many-worlds interpretation has credibly hoped for empirical (dis)confirmation since 1984. See: D. Deutsch's paper from 1984/85. I find that my own limited training is not sufficient to fully follow his argument, but IJOTP is a respected peer-reviewed publication.
    – g s
    Jul 13, 2023 at 15:28
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    One must distinguish between expressions of interpretations of quantum mechanics made by people who know what they're interpreting and interpretations of quantum mechanics made by Marvel Comics scriptwriters and mystics with prestigious but irrelevant degrees in unrelated fields; these are, of course, pseudoscience. And one must distinguish between an in-principle-testable "interpretation basis" and the common-language interpretation and any implications that one might intuit from unclear definitions therein.
    – g s
    Jul 13, 2023 at 16:07
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[... ]why is so much of physics that is based on literally zero testable evidence taken seriously?

There is no direct evidence of a multiverse, certain interpretations of quantum mechanics, string theory, and many other things. Why are so many of these kinds of theories taken seriously?

(emphasis is mine)

Multiverse, interpretations of quantum mechanics and string theory are far from much of physics - these are in fact marginal subjects, whose scientific merits are disputed by the physics community, and which at best have status of hypotheses - to be confirmed by experimental proof before they are accepted as theories.

Interpretations of quantuim mechanics
Interpretations are by definition not theories - different physicists obtain the same results using the quantum mechanics apparatus, regarding of the interpretation that believe in. Interpreting QM is usually acknowledged as a philosophical rather than scientific endeavor and occasionally frowned upon, as testified by the famous adagio Shut up, and calculate! supposedly addressed by Feynmann and Landau to their students, who were too concerned with the interpretation.

Multiverse and string theory
Multiverse and string theory are widely regarded as runaway mathematical efforts to combine various disjoint physical theories in one coherent mathematical structure. Runaway precisely because they are unlikely to be ever verified. It is for this reason that some mainstream scientific journals refuse to accept manuscripts on these subjects, forcing them to perpetuate in non-peer-reviewed online publications (e.g., in principle anyone can post their manuscript on arXive.) Taking such a subject for a PhD thesis is regarded as a suicidal in terms of a future academic career.

To summarize: the question is based on misrepresentation (even perhaps not quite deliberate.)

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Actually, there was a fairly interesting argument for string theory that went like so (I'm citing this by memory, but it was occurrent in the literature at some point):

  1. General relativity is in formal logical tension with quantum mechanics.
  2. String theory is a unique and nontrivial solution to that tension.
  3. So all evidence for GR and QM is evidence for string theory.

Be that as it may, concerns about the viability of string theory as a scientific research program were acknowledged widely, and dissenters could publish books like Not Even Wrong without destroying their careers. In fact, theoretical physicists have proposed a number of alternative solutions to the GR-QM tension, proposals which are at worst labeled "fringe science" and not pseudoscience (the following list is not assumed to be completely exhaustive; it is a reflection of the alternatives that I am familiar with at this time):

  1. Loop quantum gravity
  2. Causal-dynamical triangulation
  3. Crystallographic cosmology
  4. Causal sets

One can also consider Max Tegmark and Stephen Wolfram's meta-theories about the mathematized universe (or multiverse). Now keep in mind, pseudoscientists will often use their theories to try to manipulate the scientific laity in various ways: astrologers for the sake of psychological and economic predation/parasitism, creationists for the sake of cognitive-religious predation. The star-seers try to scare people into making decisions, including life choices, based on the supposed imminent dangers posed by various celestial alignments; the false prophets issue warnings of moral corruption in this life and eternal torment in a future state.

By contrast, string or causal set theorists, say, do not tend to insist on people agreeing with them to such an extent, and might not be much of true believers in their very own ideas anyway: they are mainly, for lack of a better word, "nerds" who just enjoy the intellectual exercise involved in working through the mathematics of their models.


We should also consider that the boundary between a testable empirical hypothesis, and the abstract production of a mathematical concept, might be vague. In his work on the theory of "Ultimate-L" (I will leave the definition of that phrase for the reader to find), Hugh Woodin has framed an empirical prediction that an important component of his theory (see slide 11) will not be proven inconsistent within the next one thousand years. And so are predictions of (in)consistency a way to "empiricize" even the most esoteric mathematics? I don't know how string theory contributed to pure mathematics, but it is said to have done so in some interesting way, but then we can imagine that there are seemingly pure theories of mathematics with applications to physics that we can make predictions about the (in)consistency of in turn. (One might think that the deeper background for string-theoretic mathematics (topology, I assume) is immune to the flexibility and fluctuation of set theory, but note that Saharon Shelah has been dreaming of a way to force over arithmetical propositions that we might have believed (or hoped) were barricaded against forcing dynamics and so if we ever found a way to alter relatively basic arithmetic in this vein, who knows how we might alter the premises of empirically-applicable geometry/topology as well?)


ADDENDUM: The history of QFT in brief

I think getting at why modern theoretical physics is continuous with scientific empiricism as a historical program requires understanding how the Standard Model arose, how that evoked the question of supersymmetry, and how abstract models of symmetry conditions justified speculation about string theory even though no substantively unique evidence for string theory was forthcoming.

So, just to give a thematic overview of the history: in the late 1800s and early 1900s, scientists made great empirical discoveries about uranium (which had been known beforehand as e.g. "pitchblend," and used as paperweights for having a relatively boring metallic appearance (it is a metal, not glowing green gel, after all)), radiation, and stellar dynamics, that converged in the realization that uranium could be subjected to a process that might unleash a huge amount of energy, a process not entirely difficult to figure out. And all things considered, the even more ominous ability to use a random kind of metal (uranium again, also plutonium of course) to cause nuclear fusion in a random kind of water (heavy water, that is), which was gleaned from analysis of the physics "situation," was an even greater testament to the embyro of the Standard Model back then.

Correct me if I'm wrong, but I think I've read that one impetus for string theory was the practice of Feynman diagrams, since there is a not-mysterious lookalike aspect to the stringy things there and the general hypothesis of string theory (which is sort of intermediary between pure particle physics on the one hand, and unparticle physics on another). At any rate, the conceptual transition from point particles to strings was not an obscure, alien conjecture, but even the doctrine of point particles was itself already conjectural, for there is no absolute proof a priori that the units of empirical substance must be zero-dimensional rather than higher-dimensional, even within the dimensionality that humans can experience thoroughly from the inside.

Now, appeals to symmetry can be motivated by the weight of the prior evidence, which is that the mathematics of the experimentally (or: technologically) supported physics organized various factors according to discernible symmetry and symmetry-breaking parameters. There is an induction from that, if not to a further theory outright, yet to the string hypothesis (or, indeed, to any such hypothesis, i.e. any not-pseudoscientific extensions proposed for the Standard Model). More precisely, empirical information coming from astrophysics/cosmology is used to calibrate recognized deficits in the Standard Model.

Now that model is heavily grounded in particle-accelerator experiments, and we have strong operational knowledge about how to look for new particle information in those experiments. Thus far, we can justify a specific tabulation of particle types (elementary and combined). But the information we have about those types leaves out of view the evident cumulative impact of types that we have inferred can't be as readily detected by current accelerator technology. So balancing the microphysical and macrophysical evidence, we have an erotetic scheme encoded into the Standard Model, i.e. we can discern slots and metaslots in the particle table that need to be filled in (or else our theories about the known types will have to be seriously altered to accommodate the higher-level data).

Then we embark upon the quest for possible symmetry, sometimes "supersymmetry" is how they put it. This means doing a lot of peculiar, but extremely relevant and historically grounded, mathematics, hence we end up generating speculation about strings or world-crystals or stranger things besides (I myself am often struck by the peculiarity of the anyon/plekton hypothesis, which has been partly, but nontrivially, corroborated by now, as far as I know).

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    Revenge of the Nerds!
    – Scott Rowe
    Jul 13, 2023 at 2:25
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I don't think you understand the domain of theoretical physics. It is the domain of mathematical modelling, in contrast to experimental physics. It is basically math, but distinguished from pure math by working towards experimentally dustinguishing between sets of assumptions different math is based on. It exactly is speculation based on assumptions at the cutting edge, but then a great deal of work does get tested, people just talk about that less. Consider the Lambda-CDM model of the cosmos, or the Standard Model of particle mechanics, these show exemplary convergence between models and testing, to form complex models with high predictive accuracy formed from generations of work. These parts of just accepted physics don't draw discussion and attention, like the wildly speculative fringes that make the news.

Intetpretations of the measurement problem in quantum mechanics are, as far as we understand, not falsifiable. So can reasonably argued to not be part of science, but be philosophy, albeit part that you need a grounding in physics to get to grips with. My experience is that the overwhelming vast majority of working physicists only care about making accurate predictions, and pay basically zero attention to this area, which is of great popular concern. We may not have an answer to the measurement problem, but look at how the Von Neuman-Wigner Interpretation never gained widespread acceptance, and is now considered a footnote describing misguided thinking, despite being proposed by some of the smartest and highest profile physicists in history. That is successful resistance to authority alone, and good science practice in action.

Many Worlds can be understood not as a true multiverse, there is substantial debate whether the other worlds are real among adherents. A better term than multiverse is wavefunction of the universe, which basically just says, the universe is a quantum system and Many Worlds just treats it as such.

There are many critics of String Theory, and how much time and energy was invested in developing it, without any hope of experimental results. For why, you'd have to understand how it held up the potential of reconciling a wide range of outstanding problems at once. In it's defence, the Holographic Principle and AdS-CFT correspondence came out of it, and hold up great potential of future developments. The deep power of octonion mathematics, still as I understand it holds up promise for understanding particle physics, for understanding rotations in multiple orthogonal interacting fields, too. It's the same like Knot Theory mathematics seems to have some potential bearing on particle families and interactions. This debate I was lucky enough to be at gave a pretty balanced picture of the positives and negatives: Is String Theory A Failing Model?

"Why are so many of these kinds of theories taken seriously?"

It is up to physicists what to take seriously, and what to spend their all-to-brief lives in research hoping to contribute new insights to. Not, armchair critics. Fortunately.

Scientists work on what they are curious about and can get funded to do, as discussed here: Is the SETI project built on false premises?

Science is what scientists do: Can one speak unambiguously of "the" scientific method?

Focusing only on short term concrete results, including experimental tests, is not part of a balanced distribution of money and resources for best results: What are the values of science research without immediate applications?

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    That is one of the worst ad hominem arguments I've seen on this site. I encourage you to delete it. Jul 12, 2023 at 23:45
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    @RonJohn In this video she argues that Quantum entanglement is just predetermined with a hidden variable (we just don't know the outcome yet), I think this goes against Bell's Theorem. To be fair my understanding of quantum physics is essentially based on youtube.com/@LookingGlassUniverse. But Sabines dismissiveness towards other physicists raises my alarm bells. So while I can not actually evaluate her statements due to a lack of my own knowledge I am very reserved w.r.t. anything she says.
    – Felix B.
    Jul 13, 2023 at 14:08
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    @RonJohn, yes, an ad hominem argument is any argument directed against a person instead of against the person's argument. It is not always a fallacy. In fact, in this case, ad hominem itself is not a fallacy. Since my argument was based on the credibility of Hossenfelder, an ad hominem argument questioning her credibility is appropriate. However, you have to offer an argument. Just calling her names is not an argument, and it is not appropriate for this site. Jul 13, 2023 at 17:18
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    @FelixB., in the video she isn't arguing that there are hidden variables; she is explaining why Bell's Theorem doesn't rule out hidden variables; namely that it is possible to have hidden variables if you are willing to give up measurement independence. She makes a total of one comment that could be considered dismissive of other physicists, and the point of the comment is that they ignore this alternative. Jul 13, 2023 at 17:48
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    @FelixB., there isn't at least one comment per video. And the purpose of the analogy is to illustrate local variables, so I don't see your complaint. And she not only does not pretend other physicists didn't think of it, she spends considerable time explaining their argument against it. Jul 14, 2023 at 14:46
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No.

Speculation and assumptions are different things. A speculation is something that you think might be true. An assumption is something that you act as though it is true.

What a "speculative assumption" is supposed to mean, I have no idea.

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    On the basis of your definitions: speculative assumption = you act as though you think it is true.
    – Roger V.
    Jul 13, 2023 at 14:10
  • "Speculative" in English means a guess or hypothesis that is grounded more in imagination than in any real evidence or experience. Jul 14, 2023 at 14:47
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Your question:

Religion, spirituality, and other “pseudoscientific” theories are constantly seen as backwards and lacking of evidence. But if a lack of evidence before believing in something is considered irrational, why is so much of physics that is based on literally zero testable evidence taken seriously?

There is no direct evidence of a multiverse, certain interpretations of quantum mechanics, string theory, and many other things. Why are so many of these kinds of theories taken seriously?

There have been entire books written about some of these theories with people being fascinated about how intellectual they seemingly sound despite the fact that there is zero experimental evidence for any of these theories.

Should they be given the same treatment as other forms of pseudoscience?

You haven't stated directly what theories you're talking about. Nor have you given any examples of the kinds of books you're talking about.

But I will discuss scientific testing and related issues and consider a couple of theories that may or may not be an example of what you're thinking about.

You seem to think there is such a thing as evidence for a theory, but you're wrong. You can observe experimental results consistent with a theory every day for 200 years and the theory can still be wrong. This actually happened to Newtonian mechanics. In addition, a scientific theory isn't a digest of observations, it's an account of what's happening in reality and includes unobserved parts of reality. So there is no way to derive a theory from experimental evidence, or to show it is true with experimental evidence.

If we excluded all unobservable explanations, then the whole of science would have to be thrown out. For example, we can't observe the core of the sun or any other star. So all of astrophysics has to go by that standard. We also can't observe DNA of animals in the past, so evolution has to go too.

However, if you observe events that are incompatible with a theory, then there is a problem with that theory and it should be discarded or a new variant should be invented that fixes that problem. There are longer explanations of this sort of issue by Karl Popper, see the readings here:

https://fallibleideas.com/books#popper

So let's consider a couple of multiverse theories you might be talking about. Some versions of string theory claim there are lots of universes. None of these universes can be observed. In addition, directly observing many quantum gravity effects is difficult because the energy scales at which those effects would happen can't be generated with current technology. This leaves us with some indirect tests or various ideas about quantum gravity:

https://arxiv.org/abs/2002.02907

https://arxiv.org/abs/2004.01189

You have to be willing to work with this kind of problem or give up on having a quantum theory of gravity. It might be the case that there should be far fewer people working on this kind of thing, but to say that nobody should take it seriously is a bit harsh.

As far as interpretations of quantum mechanics, some of those can arguably be ruled out without doing any experiments. For example, the Copenhagen and statistical interpretations don't give an account of what's happening in reality to produce quantum mechanical effects. Since they don't give such an account they don't give any criteria for judging whether an experiment has been set up properly and they aren't testable. A theory that does give an account of what's happening in reality as described by quantum theory is the many worlds interpretation (MWI), which claims that reality consists of a structure that on the scale of everyday life looks a bit like a collection of parallel universes, but that this approximation breaks down in experiments that can and have been done, such as single particle interference experiments and entanglement experiments. For example, in single photon interference experiments photons are sent towards a pair of slits one at a time, so if you measure the number of photons in the experiment the probability of seeing more than one is negligible. If you let enough of them go through you see a pattern of light and dark bars on the other side. But if you block one of the slits you get a different pattern of light and dark bars. If a location on the screen goes dark as a result of slit being opened, then something is coming through the slit to deflect the particle from getting there and that thing acts exactly like the photon, e.g. it is deflected by mirrors, lenses etc. But we can't see such a particle using detectors so it is invisible, but it is affected by lenses and mirrors and even blocked by detectors so it must be interacting with something that acts just like those devices: so there are invisible mirrors, lenses and detectors too and invisible experimentalists who places those devices and invisible computers recording results from them and so on - there are whole invisible universes. For more on this see "The Fabric of Reality" by David Deutsch and the following papers:

https://arxiv.org/abs/1508.02048

https://arxiv.org/abs/2205.00568

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