So the fine tuning argument has been used to argue for theism, or the multiverse. The argument as I understand it goes something like this:

  1. We live in a universe with life.

  2. The physical constants of the universe if even slightly different would give us a universe without life.

  3. The existing configuration of constants is extremely improbable.

  4. Universe is designed, or we live in a multiverse (where all configurations of constants are manifested in different universes).

An objection to this argument that comes to mind is with regards to 3. I see no reason to believe any other configuration of constants is possible. So there's an "illusion" of a space of possibilities where the laws of physics have the same equations but the constants can take on varying values. But we have no reason to think such a space of possibilities exists. We only knowledge of one universe with these specific numerical values for the constants. The probability of this configuration of constants may very well be 1. There's no way to know. So the question really boils down to, "why is the universe the way it is?".

What are the responses to this objection?

EDIT: Here's a video from a physicist that illustrates this objection:


  • 3
    Many physicists working on theories that try to "unify" the fundamental forces of physics think there will turn out to be multiple possible low-energy vacuum states with different values of various "constants", and where the vacuum was originally in a more symmetrical but unstable high-energy state (where all particles were massless, for example) and then dropped randomly to one of the low-energy 'metastable' states by spontaneous symmetry breaking. See quotes I posted here.
    – Hypnosifl
    Commented Apr 26, 2021 at 16:36
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    If this is true, then in eternal inflation models a natural consequence is that different regions far apart can drop randomly to different low-energy vacuum states with different constants. However, if you want to know more about arguments for why physicists think some constants of nature were determined by spontaneous symmetry breaking, and the arguments for eternal inflation models with different "bubble universes" that have settled to different vacuum states, this would be a question for physics.stackexchange.com/questions
    – Hypnosifl
    Commented Apr 26, 2021 at 16:39
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    We have methodological reasons to reject skeptical non-explanations like "there's no way to know" when an alternative is available. Other things being equal, a theory that provides a background to what we observe is preferable to a "theory" that it just happens this way. We have science because we generally prefer potential explanations to skepticism.
    – Conifold
    Commented Apr 26, 2021 at 17:41
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    The goal of unifying the strong, electromagnetic, and weak forces into a Grand Unified Theory with strong empirical support, let alone unifying all three with gravity into a Theory of Everything, has not been accomplished yet, so it's true there's no agreed-upon and empirically supported probability distribution. But most physicists think there are good reasons to believe such a theory is out there waiting to be found, and that it will likely feature spontaneous symmetry breaking.
    – Hypnosifl
    Commented Apr 26, 2021 at 20:32
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    The ID does not have to be God, simulation speculations are very popular these days and they are from a different context. Both ID and random generation are generic potential explanations for coincidences of any sort. They are neither myths nor completed theories, they are templates for more specific hypotheses that point to further exploration. Neither simulation nor multiverse are treated as more than that, and are better methodologically than a pessimistic discussion stopper like "there's no way to know".
    – Conifold
    Commented Apr 27, 2021 at 0:20

7 Answers 7


Your wish that there were no evidence to support the unlikelihood of the universe is unjustified wishful thinking.

The values of the constants of the universe, things like the Baryon number, and the relative strengths of the various forces, are not set by any physics-based constraints we know of in the Standard Model. Instead, we actually have good reason to think they change. The basic idea of the Big Bang Inflation theory is that our Cosmological Constant was very very high for a brief time, then dropped to something close to zero. We also think it may be growing slightly. In the Standard Model, a CC only changes when other constants change -- so we have good reason to think that these parameters are variable.

Additionally, all our "laws" appear to be mere regularities -- physicists believe that every one of them spontaneously breaks (IE fundamental properties reset), per gauge symmetry theory. https://www.pnas.org/content/93/25/14256

For a philosophic discussion of symmetry theory see: https://plato.stanford.edu/entries/symmetry-breaking/

The view that our universe is astonishingly unlikely per our current laws of physics is widely accepted among physicists. That is why multiverse speculations are so widely held among the non-theist physicists.

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    Is there evidence that these constants change? Commented Apr 26, 2021 at 19:09
  • So I've posted this video in my original post from a physicst: youtube.com/watch?v=c6DP5lgzmTA She basically says there's no empirically supported probability distribution. Is she missing some evidence to the contrary? Commented Apr 26, 2021 at 19:32
  • You Tube videos, and videos in general, are not good references for anything other than being told something, they lack the content and evidence needed to support a claim. Your citing one physicist posting a video - is a classic case of cherry picking data to provide confirmation bias, and doing so using weak/invalid references. Your speaker makes false claims about science -- she does not understand the scientific process. Multiple tests are not needed to "establish a probability distribution". Science is not based on replication, but on hypothesis and test.
    – Dcleve
    Commented Apr 27, 2021 at 6:56
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    @DikranMarsupial Empirical reasoning can never satisfy logical absolutism. Rejecting empirical reasoning as invalid because the logical justifications don’t close can be selectively applied against any specific empirical point. Unless she rejects all of science though, this is just cherry picking rationalizations. A pragmatist replies that the range of distribution functions that lead to Fine Tuning is immensely broad, and recasting the Fine Tuning argument in favor of an infinitesimally small slice of distro functions that could then support life is still unjustified Fine Tuning.
    – Dcleve
    Commented Sep 6, 2023 at 16:09
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    @DikranMarsupial Quines argument that theory is always underdetermined by facts, when applied to a demand for falsification of THIS theory vs any other, will lead to rejecting all theories as unjustified. Applying this argument selectively is rationalizing. Accepting pragmatic truth rather than absolute truth is a precondition for doing science at all.
    – Dcleve
    Commented Sep 6, 2023 at 16:45

The first thing to say is that if you want to read a more detailed treatment of fine-tuning, a good start would be the SEP article on it.

In regard to fine-tuning arguments based on fundamental physical constants, it is not unnatural for scientists to ask why the constants have the values they do. Einstein expressed the hope that we would discover a fundamental theory of everything that would explain all the different constants and show how they fit together, but at present no such plausible theory exists. Merely to assume that the constants must be the way they are and that this requires no explanation is rather obscurantist. Having an explanation, even a weak and tentative one, is better than having none.

There have been a number of responses to fine tuning arguments.

  • Maybe our understanding of what constitutes life is too narrow and so life is possible under a wider range of possibilities than we suppose.

  • We have no grasp of the range of antecedent possible values for the fundamental constants or how likely they are. In Bayesian terms, we have no way to find uninformative priors for the range of values.

  • The universe actually seems to be rather poorly fine-tuned for life. Most of it is empty and uninhabitable. So maybe this speaks against a designer who is interested in creating living things.

  • We have no basis on which to reason about what a super-powerful super-intelligent being might or might not do, and extrapolating from our own abilities and intellligence is not an adequate basis for speculation.

A common claim is that the mere fact that we exist as living observers of the universe is somehow evidence that the universe must be the way it is. This is a kind of anthropic or observer bias objection. It doesn't really work as it confuses the knowledge we actually possess of our own existence with the antecedent probability of our existence. This issue is related to what is commonly discussed within Bayesian theory as the problem of old evidence. It is concerned with what we would know counterfactually if the evidence had turned out otherwise.

In the case of hypotheses that are related to our existence, this counterfactual possibility is one in which we do not exist to observe it, so it is problematic to handle. (Incidentally, this problem lies at the heart of the Sleeping Beauty paradox as well.) But this does not preclude us from making plausible inferences. As John Leslie points out, if I am facing a firing squad of expert marksmen and they fire and I observe that I am still alive afterwards, it is reasonable for me to infer that they missed intentionally, since it is highly unlikely they would all attempt to shoot me and fail. Merely saying, "They must have missed since I am here to observe the result" explains nothing. This example has also been discussed quite extensively in various papers on the subject.

  • In the case of the firing range, we have a crucial piece of information that allows us to make the conclusion that the squad intentionally missed: we know they exist. And we know this before the firing takes place. We do not know if god exists apriori so the analogy fails.
    – user62907
    Commented Sep 6, 2023 at 6:38
  • That is not the real point of the example. The point is that we cannot simply appeal to observer bias to conclude that something is probable just because we know it happened and we wouldn't be in a position to know anything if it didn't. There are some objections to Leslie, e.g. by Elliot Sober. There has been quite a bit of discussion of the example, e.g. Jonathan Weisberg, 2005, “Firing squads and fine-tuning: Sober on the design argument”, Brit. J. Phil. Sci, 56(4): 809–821. Matthew Kotzen, 2012, “Selection biases in likelihood arguments”, Brit. J. Phil. Sci, 63(4): 825–839.
    – Bumble
    Commented Sep 6, 2023 at 7:42
  • I agree with Leslie’s objection in that sense. I’ve read Sober’s work and his main contention with design is that there’s no way of knowing what a designer would want to do if he even exists. I think the problem is deeper. The deepest problem is addressing the probability of the designer’s very existence. And there is no way to justify that that probability is non zero. Hence, no matter how improbable an event is, fine tuning or not, one is not justified to conclude that a designer did it. For one, the designer may be metaphysically impossible.
    – user62907
    Commented Sep 6, 2023 at 7:53
  • See IETP on this subject here: iep.utm.edu/design-arguments-for-existence-of-god
    – user62907
    Commented Sep 6, 2023 at 7:58

The simplest argument is (simply) that if the constants of nature were slightly different, we wouldn't be here to register that fact. So however improbable our universe may be, we are nonetheless and indeed here.

Regarding your assertions "I see no reason to believe any other configuration of constants is possible" and "but we have no reason to think such a space of possibilities exists": have you looked for a reason, who is "we", and are you trained as an astrophysicist?

In the field of cosmology, discussions like these arise in the context of the anthropic argument, about which lots has been written. I suggest you do a search on the physics stack exchange and possibly post your question there.

  • I'm not a physicist. But here's a physicist making the same argument : youtube.com/watch?v=c6DP5lgzmTA Does that make the argument any better? Commented Apr 26, 2021 at 19:30
  • I am, in a loose sense, but not an expert on this topic. Commented Apr 27, 2021 at 0:38

This is an interesting question, and there have already been some good answers (especially those by @Dcleve and @bumble), so I thought I would just give a brief review/Fisking of the video that is linked at the end of the question (which is well worth watching).

The video is by Sabine Hossenfelder†, who is a working theoretical physicist (Google scholar profile) and science communicator. Her YouTube channel is well worth subscribing to - it is very good and I'd also recommend reading her book "Lost in Math - How beauty leads physics astray". However, when watching the video there is an important piece of background information, which is that Hossenfelder is a fundamentalist Popperian who appears to believe that falsification is the absolute demarcation between science and non-science, which is not something I would agree on. I would view science as a search for the best naturalistic explanation for reality (including the bits we can't observe). I would argue that a falsifiable naturalistic explanation was a better explanation than one that wasn't, but I don't see it as a reliable means demarcation. I see research on multiverses as being obviously scientific, Hossenfelder does not. However, just because an argument is not a scientific one, doesn't mean it is wrong.

"According to this idea [fine tuning] it is extremely unlikely our universe would just happen to be the way it is by chance, and the fact that we nevertheless exist requires an explanation"

I would disagree that this requires an explanation. It is possible that there is no reason that the universe is the way it is. However an explanation for the universe that also explains why the constants have the values that they have is arguably a better explanation than one that doesn't... unless, of course, you happen to be a fundamentalist Popperian and require the explanation of the constant values to be falsifiable.

While Hossenfelder mentions religion, I am going to steer clear of that and stick to multiverses as the example as religion is likely to trigger cognitive biases that just get in the way of discussion of the validity of the argument.

"the same argument is used by physicists to pass of unscientific ideas like the multiverse or naturalness as science"

Note "pass off" is a rather loaded wording, and the "unscientific ideas" is predicated on a strict Popperian view of what science is, which is not necessarily correct.

"There is a long list of calculations of this type [that allow constants that do or don't support life], but they are not the relevant part of the argument"

I think this is actually quite an important point. We have theory/calculations to support the plausibility of other sets of values of constants, but no evidence, so this is part of our prior beliefs. We can state our premises, but whether the conclusion is correct depends on whether the premises (theory/calculations) are correct. Any argument constructed from priors, can only really tell you whether is is reasonable to believe the conclusion if you accept the premises (but then again that is no different to predicate logic).

"particle physicists use the same argument when the ask for the next particle collider"

To some extent that is true, but it is also implying that particle physicists are using an argument for financial reasons rather than scientific ones. This seems a bit of an ad-hominem attack that doesn't really work for me.

"they claim it requires explanation why the mass of the Higgs boson happens to be what it is"

So again, this seems to boil down to what you think science is about, if you think that science is a search for the best explanation, then of course it requires explanation, because everything requires better explanation, especially if we don't have an explanation at all.

"what is wrong is the claim that the constants of nature that we observe are unlikely. There is no way to quantify this probability because we will never measure a constant of nature that has a value other than the one it does have. If you want to quantify a probability you have to collect a quantity of data."

This is incorrect. You do need data to empirically estimate a probability, but that is not the only means of quantifying a probability. Another way to quantify a probability is to calculate it using a model.

"You could do that, for example, if you were throwing dice. Throw them often enough and you get an empirically supported probability distribution."

The problem here is insertion of "empirically supported" as if you couldn't have a probability distribution without empirical support. But this isn't the case, most often when people say "this is unlikely to happen by random chance", they are talking about a probability quantified by a model, not by an empirically determined distribution. This seems to me to be an expression of Hossenfelder's rather extreme position on what science is - it is all about empirical evidence.

"but we do not have an empirically supported distribution for the constants of nature"

yes, but we do have theoretical/model based distributions on which the argument could be based.

"And why is that, ... , because they are constant. Saying that the only value we have ever observer is unlikely is a scientifically meaningless statement"

This is again dependent on whether you share Hossenfelder's extreme falsificationist view of what science is. Others have no problem with the use of models in science to determine likelihood, it is what is usually meant by "caused by random chance" (not that random chance is an explanation for anything).

"we have no data and will never have data which allow us to quantify the probability of something we cannot observe. There is nothing quantifiably unlikely therefore there's nothing in need of explanation"

Again, this is entirely contingent on Hossenfelders position on what science is (search for explanation - verses falsifiability) and whether probabilities can only be quantified by empirical estimation rather than by statistical models.

"If you look at the published literature on the supposed fine-tuning of the constants of nature, the mistake is always the same. They just postulate a particular probability distribution". It is this postulate that leads to their conclusion"

This is not a mistake, depending on what you are trying to argue. If you are arguing that it is reasonable to believe the theory on which the distribution is postulated, then it is reasonable to conclude that it is likely we live in a multiverse. If you state it as an unconditional conclusion about the nature of reality directly, then it is a mistake.

I think most usages of "fine tuning" arguments are the former, Hossenfelder seems to treat them as the latter, perhaps because that is more in accord with her view of what science is about?

"logical fallacies... begging the question"

Absolutely, if this was interpreted as evidence of what is real, rather than what we should believe. Note the theory used to postulate the distribution will have some evidence in the form of consilience - what other observations we can make that do not have a good explanation in the absence of that theory.

"they pick a particular distribution that makes it unlikely"

That seems a little unfair. The particular distribution is based on a theory that is explicitly stated and open to criticism. Suggesting they chose their theory to fit in this argument is an insinuation, they formulated a theory that explains other evidence as well.

"they could as well pick a distribution that make the observed values likely"

but would it explain anything else? Consilience is part of what makes an explanation a good explanation. Who cares if you can pick a distribution that makes the observed values likely if it depends on a theory that can't explain any other theory?

"not all arguments are unscientific, the best known is [balancing a pen on its tip] if you saw that you'd be surprised ... you'd look for an explanation, a hidden mechanism ... but the balanced pen is a different situation. The claim that the balanced pen is unlikely is based on data"

Yes, we would intuitively see this as unusual as it doesn't fit with our experience (data) of how physical objects behave in the Earth's gravitational field.

However, given Newton's laws etc. we could have determined from first principles that a pen is unlikely to be in a balanced position in gravitational field without ever having observed any similar situations. We could work out for ourselves that fine-tuning was necessary. This is very much like having a theory of how constants are determined and using that as a basis for a probability distribution.

Again, this seems more a statement about Hossenfelders heavily empirical position on what science is.

Ironically ISTR pen balancing was the example Alan Guth used in his "popular science" book on his work on inflationary cosmology. It is very unlikely that we would see a universe that was so close to exactly flat as the one we observe, given what theory we had on the subject, so it "required" an explanation. Inflation gives a plausible explanation for why it is flat, but it also explains quite a lot of other things as well. This is how science works if you view it as a search for the best naturalistic explanation. The more a theory explains with reasonable plausibility, the better the explanation (all things being otherwise equal).

"You can alternatively [rather than frequentist] intepret the term "unlikely" using the Bayesian interpretation of probability. In the Bayesian sense, saying that something you observe is unlikely means you didn't expect it to happen. But with the Bayesian interpretation, the argument is that the universe was especially made for us doesn't work. That is because in that case it is easy enough to find reasons for why your probability assessment was wrong and nothing is in need of explanation"

This is missing the point. Under the Bayesian interpretation, those arguing for the multiverse have set out exactly what their arguments and assumptions are. If you want to disagree, then you provide a better theory that explains all of the observations that their theory explains (not just the fine-tuning) and use that instead. If you cherry pick an counter-theory simply to refute the fine-tuning conclusion, then you are the one begging the question.

If you view science as a search for the best naturalistic explanation, then it is about comparing and relative evaluation of explanations. If you are a hard-line falsificationist it is all about whether something can be falsified and trying to falsify. Hard-line falisficationism is more strongly skeptical of everything, but I think it can be taken too far. For example

"[the multiverse is an assumption that is an unnecessary addition to our theory of the universe]"

Again, whether it is necessary depends on what you think science is about. I'd say it was more a hypothesis that is suggested by our existing theory of the universe and worthy of consideration.

"but this does not mean the ... multiverse does not exist, it just means evidence cannot tell us whether they do or do not exist [which means it is not a scientific idea]"

Completely agree with the first bit. However, all of our knowledge will be a mixture of experience and theory (Kant?), this is a spectrum from purely experience (we exist to observe the constants) to completely theory (multiverse). The last bit is again more an assertion of what science is, which is not universally agreed to be hard-line Popperianism.

So there is some value in Hossenfelder's video, but there is also a fair amount that can be reasonably questioned. I find her YouTube channel very thought provoking, which I think is what it is for, even if you don't agree with what she presents.

† I am not sure what Hossenfelder's title is, so I will just refer to her as "Hossenfelder" rather than "Prof. Hossenfelder" or "Dr. Hossenfelder", but this is not done out of disrespect for her qualifications or experience.

  • She's a doctor and assistant professor — wikipedia
    – Rushi
    Commented Mar 19 at 6:25
  • @Rushi titles are culturally dependent. In the U.K. an assistant professor is not entitled to use the title "professor" (at least not at my institution) - so calling someone a Dr or a prof might both be a faux-pas. Female academics are often treated with disrespect, so I wanted to make it clear that was not what I was doing. Commented Mar 19 at 8:42
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    This is well worded. I hope for the love of God that it changes someone's mind, but my model of humanity suggests that it won't.
    – Scott Rowe
    Commented Mar 20 at 18:26
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    given Newton's laws etc. we could have determined from first principles that a pen is unlikely to be in a balanced position in gravitational field without ever having observed any similar situations. We could work out for ourselves that fine-tuning was necessary THIS. Very good answer to the video and the Popperian view.
    – Guilherme
    Commented Mar 28 at 7:38

That is correct. There is no evidence that it is possible for those constants to have been different. But let’s entertain the notion that they could. And let’s entertain the notion that it is very improbable for the constants that support life to emerge.

That is to say, let us suppose as if there were billions of different combinations of constants in a hat, and only one that allowed life was picked from that hat. The probability of that would be insurmountably low. This may be seen, very intuitively, to provide evidence for the existence of a designer that wanted life to happen.

But this would be mistaken. For starter’s any combination of constants from that hat would be just as improbable (assuming each is equally unlikely). So, a particular “life-less” combination of constants being picked would have also been evidence for a God that wanted those constants to arise as well.

Yet no one argues that. There is a hidden apriori assumption that a God who wanted life creating constants is more likely to exist than a God who wanted a particular combination of life less constants. But there is no reason to suggest this. We don’t know the probabilities of different kinds of Gods existing.

Lastly, we also don’t know if their probability is more or less probable than the improbability of getting the right constants needed to fine tune life. Observing an improbable event doesn’t mean it is impossible for it to occur without design. One must show that the probability of a designer existing and choosing to design those constants is higher. Without this, one cannot appeal to God.

  • " For starter’s any combination of constants from that hat would be just as improbable (assuming each is equally unlikely). " this is incorrect reasoning. The relevant probability is the probability of a combination of constants supporting life. Even if all combinations are equiprobable, there may be vastly more combinations where life is impossible than combinations where it is. In that case you can't conclude that our non-existence would be equally likely. The "fine tuning" argument isn't quite as naive as you suggest (which is not to say I agree with it). Commented Sep 6, 2023 at 5:50
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    Why is the relevant probability the combination of constants supporting life? Also, no one said that our non existence would be equally unlikely. Please read the answer again
    – user62907
    Commented Sep 6, 2023 at 6:09
  • the argument is that our existance to observe the constants requires constants where life is possible, it doesn't require them to be the constants we actually observe. If the constants were different but still permitted life, something might be present to observe the constants. So it is a compound even and you need to sum the proabilities of constant combinations that support life. The exact form of life is irrelevant to the argument, and so are the precise values of the constants. Commented Sep 6, 2023 at 6:14
  • "Also, no one said that our non existence would be equally unlikely." the point I am making is that even if you assume all combinations of constants are equiprobable, that doesn't mean observing constants supporting life are equally probable as those not supporting life. The "you" didn't refer to you in general, but to a generalised "you", i.e. anybody. This is normal colloquial English usage in the U.K. The equiprobability of constant combinations is a naive representation of the argument. Commented Sep 6, 2023 at 6:22
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    Theory is always underdetermined by evidence, because the range of possible theories is infinite. For a rationalist, who demands logical closure before accepting anything as true, this means a rationalist must reject ALL empirical claims or conclusions, because there are infinite other options which have not been closed out. Selectively arguing against DESIGN inferences, by falsely claiming they have this as a unique fault, is not intellectually consistent. Your objection is no more true of design inferences than any other kind of inference.
    – Dcleve
    Commented Sep 6, 2023 at 16:53

What is the response to this criticism of the fine-tuning argument?

Universe is designed, or we live in a multiverse (where all configurations of constants are manifested in different universes).

Just show me God's blueprints for this "designed" universe. As an engineer using science to develop technology, the fine-tuning argument does not provide any science that can be applied to any discipline other than theology.

The intelligent design argument does not contain a single tool that allows humans to use "intelligent design" to create anything. The only discipline that benefits is theology.

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    I guess it is a giant exercise in question-begging, or "assuming the consequent" or whatever. Should let people know that... Even if what one argues for is true, a bad argument is still a bad argument.
    – Scott Rowe
    Commented Mar 20 at 18:09
  • @ScottRowe. Whether true or not, the burden of science to "reverse engineer" the universe remains unchanged. Commented Mar 20 at 18:26
  • I'm ok with knowing I am here, and not knowing God is here. Many people can't leave it at that though. Not sure why.
    – Scott Rowe
    Commented Mar 20 at 18:34

You are bang on here and the top answer here and comments are simply incorrect.

Repeat after me: there is no evidence that the universe could have been in such a way where the laws stayed the same but the constants didn’t.

Again, there is zero evidence for this. Until there is, there is zero evidence anything else could have been possible. Thus, there is zero evidence that these constants are improbable in any sense.

Just because one can imagine different constants doesn’t mean anything. I can imagine a coin turning into a bird when I flip it too. Does that mean it’s possible?

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