Wednesday, January 30, 2019

Just because it’s falsifiable doesn’t mean it’s good science.

Flying carrot. 
Title says it all, really, but it’s such a common misunderstanding I want to expand on this for a bit.

A major reason we see so many wrong predictions in the foundations of physics – and see those make headlines – is that both scientists and science writers take falsifiability to be a sufficient criterion for good science.

Now, a scientific prediction must be falsifiable, all right. But falsifiability alone is not sufficient to make a prediction scientific. (And, no, Popper never said so.) Example: Tomorrow it will rain carrots. Totally falsifiable. Totally not scientific.

Why is it not scientific? Well, because it doesn’t live up to the current quality standard in olericulture, that is the study of vegetables. According to the standard model of root crops, carrots don’t grow on clouds.

What do we learn from this? (Besides that the study of vegetables is called “olericulture,” who knew.) We learn that to judge a prediction you must know why scientists think it’s a good prediction.

Why does it matter?

The other day I got an email from a science writer asking me to clarify a statement he had gotten from another physicist. That other physicist had explained a next larger particle collider, if built, would be able to falsify the predictions of certain dark matter models.

That is correct of course. A next larger collider would be able to falsify a huge amount of predictions. Indeed, if you count precisely, it would falsify infinitely many predictions. That’s more than even particle physicists can write papers about.

You may think that’s a truly remarkable achievement. But the question you should ask is: What reason did the physicist have to think that any of those predictions are good predictions? And when it comes to the discovery of dark matter with particle colliders, the answer currently is: There is no reason.

I cannot stress this often enough. There is not currently any reason to think a larger particle collider would produce fundamentally new particles or see any other new effects. There are loads of predictions, but none of those have good motivations. They are little better than carrot rain.

People not familiar with particle physics tend to be baffled by this, and I do not blame them. You would expect if scientists make predictions they have reasons to think it’ll actually happen. But that’s not the case in theory-development for physics beyond the standard model. To illustrate this, let me tell you how these predictions for new particles come into being.

The standard model of particle physics is an extremely precisely tested theory. You cannot just add particles to it as you want, because doing so quickly gets you into conflict with experiment. Neither, for that matter, can you just change something about the existing particles like, eg, postulating they are made up of smaller particles or such. Yes, particle physics is complicated.

There are however a few common techniques you can use to amend the standard model so that the deviations from it are not in the regime that we have measured yet. The most common way to do this is to make the new particles heavy (so that it takes a lot of energy to create them) or very weakly interacting (so that you produce them very rarely). The former is more common in particle physics, the latter more common in astrophysics.

There are of course a lot of other quality criteria that you need to fulfil. You need to formulate your theory in the currently used mathematical language, that is that of quantum field theories. You must demonstrate that your new theory is not in conflict with experiment already. You must make sure that your theory has no internal contradictions. Most importantly though, you must have a motivation for why your extension of the standard model is interesting.

You need this motivation because any such theory-extension is strictly speaking unnecessary. You do not need it to explain existing data. No, you do not need it to explain the observations normally attributed to dark matter either. Because to explain those you only need to assume an unspecified “fluid” and it doesn’t matter what that fluid is made of. To explain the existing data, all you need is the standard model of particle physics and the concordance model of cosmology.

The major motivation for new particles at higher energies, therefore, has for the past 20 years been an idea called “naturalness”. The standard model of particle physics is not “natural”. If you add more particles to it, you can make it “natural” again. Problem is that now the data say that the standard model is just not natural, period. So that motivation just evaporated. With that motivation gone, particle physicists don’t know what to do. Hence all the talk about confusion and crisis and so on.

Of course physicists who come up with new models will always claim that they have a good motivation, and it can be hard to follow their explanations. But it never hurts to ask. So please do ask. And don’t take “it’s falsifiable” as an answer.

There is more to be said about what it means for a theory to be “falsifiable” and how necessary that criterion really is, but that’s a different story and shall be told another time. Thanks for listening.



[I explain all this business with naturalness and inventing new particles that never show up in my book. I know you are sick of me mentioning this, but the reason I keep pointing it out is that I spent a lot of time making the statements in my book as useful and accurate as possible. I cannot make this effort with all my blogposts. So really I think you are better off reading the book.]

83 comments:

  1. Hi
    I think going beyond the SM is going in the wrong direction. It would then be even more complicated!

    The SM and GR should both reduce to something simpler, I think.

    A proper theory should be so clear that falsification should not even be a question. E.g., evolution.

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  2. Why don't dark matter and dark energy falsify GR?

    The universe is not accelerating.

    Don't forget to use common sense when doing science .

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  3. Isn’t saying “Dark Matter can be represented as a fluid” just make the hypothesis of Dark Matter formally unfalsifiable?

    You do say that a hypothesis needs to necessarily be falsifiable to be scientific. Doesn’t Dark Matter miss, as a hypothesis, that which a particular particle mass Dark Matter retains? Please enlighten me as to what criteria you are thinking for “fluid Dark Matter”

    Regards

    Marco Parigi

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  4. Gosh! A few hours back I published some notes/comments; may be I made a fool of myself. I was only wondering if there is a direct perception which circumvents all the math. May be I am totally wrong. Now I am keenly listening.

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  5. I just have one question, one question that is eating me. I learnt that gravitational waves keep the information they hold intact. Now what happens if I pass gravitational waves through the double slit in the double slit experiment? If they produce an interferences pattern in the presence of the observer, then the observer does to influence the gravitational wave data; the information must be intact even after passing through the slits. Also are there any other waves like gravitational waves which keep the information they hold intact and may be passed through the double slits in the presence of the observer? Please help me.

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  6. To be honest, there are other reasonable motivations for heavier-than-SM particles discoverable at LHC or FCC besides naturalness. E.g. in the context of dark matter models, you have the so called "dark matter miracle", that WIMPs of such mass naturally give you the observed dark matter abundance.

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  7. "You need to formulate your theory in the currently used mathematical language, that is that of quantum field theories." Do you mean by this the Wightman axioms (or, rather, some modification of the Wightman axioms that has interacting models, with non-trivial n-point connected VEVs), or do you mean the conventional ill-defined Lagrangian interaction terms, and the various regularization and renormalization schemes that are used to hack the ill-definedness, the end result of which is a system of non-trivial n-point connected VEVs that match experiment? Or do you mean something else?
    It's just possible that my prejudices come through in that (if it's not an incomprehensible word salad), but I'm always trying to refine my prejudices so that they're the same prejudices as other physicists have. When your book arrives in a few days, I'll perhaps find a more complete answer there.

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  8. Gokul,

    First, I do not answer random questions by visitors. Please pose your question in a forum that can address such queries, eg Physicsforums. Second, the brief answer is that interference itself is a wave-phenomenon and isn't necessarily related to quantum mechanics. You can pass a water wave through a double slit and will see interference. I don't really know what you mean by information, I am afraid, it's one of these topics one can discuss endless if one doesn't have a useful definition.

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  9. kkumer,

    Yes, that's right. The "WIMP miracle" is not an argument from technical naturalness and hence not of the same type as the argument from the mass of the Higgs-boson. The WIMP miracle is also a numerological argument though. I discussed this here and also in my book. Last time I looked the WIMP miracle wasn't in any better condition than the arguments for naturalness.

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  10. Peter,

    The usual ill-defined Lagrangian will do to get your stuff published. I think you know the answer full well so why do you waste my time?

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  11. Dear Sabine,
    Isn't all thinking about foundations a waste of time? But hey, I know *my* answer, and I know I telegraphed that I know my answer, but I'm always curious what other people's answers are, and yours here is an interesting variant, for which thanks. I'm practically certain you don't care only about being published.
    My 1709.06711 has been with Physica Scripta for three months, but it has no Lagrangian in it, so I guess it'll be rejected soon unless something stays their hand. Hey ho.

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  12. "You need to formulate your theory in the currently used mathematical language, that is that of quantum field theories" Quantum field theory (QM plus finite lightspeed) and thermodynamics can conflict. Transitions through Schrödinger's box (e.g., tunneling) have thermodynamic and kinetic constraints versus temperature.

    … 1) Hund's paradox
    … 2) Matter interference through a multi-slit grating
    … 3) Optically resolved, robust, polycyclic, small (under 250 amu) chiral molecules. Gloves turn inside-out, shoes don't. 2-Trifluoromethyl-D_3-trishomocubane is insubordinate.
    … 4) What pattern emerges, if any?

    Elliptic, plane, and hyperbolic geometries each exclude the other two. Asking "which two are wrong?" is “more studies are needed.”

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  13. VYT,

    I am not approving your comment because you have asked this question like two dozen times on this blog already and it's clear you did not understand the replies you were given. Please consult a forum if you want to further pursue the matter. Thanks,

    B.

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  14. All the WIMP searches are based on particles the use the weak force. This is the preferred model for Dark Matter. However, what is never cited is that a dark matte particle might not interact by the weak force and only by gravity. What this means is that there is no way to find it with our current capabilities. We can only see its affects, if it exists, on the scale of the cosmos. Now, it could be we could see its affects appear as missing energy in an FCC. At best we can do is figure out its properties indirectly. There are string models that predict massive neutral particle without the weak interaction, but no one ever talks about detecting them because it would be very hard, indirect, or impossible to detect them.

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  15. Thank you for another interesting blog post. Point taken. 😁

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  16. Hi,

    Right after reading the post, I thought, „yes, agreed“. Then I felt a „yes, but...“ in my belly.

    You state: „Why is it not scientific? Well, because it doesn’t live up to the current quality standard in olericulture [...]. According to the standard model of root crops, carrots don’t grow on clouds.“

    What about the past history of fundamental physics? Would we have arrived at the SM and GR when physicists in those days would have abandoned all predictions that were clearly apart from or contradicting to the „standard models“ of their time?

    I am not advocating for „falsifyable is sufficient“. I am just wondering about what really could be a set of criteria to judge whether or not a prediction is a „good prediction“ and worth an invest into experimental checks. Even if that prediction really confronts established models.

    Best, Pascal

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  17. "Why don't dark matter and dark energy falsify GR?

    The universe is not accelerating.

    Don't forget to use common sense when doing science ."


    This is not a competition to compress the most nonsense into the shortest soundbite.

    I'll address each in turn.

    First, GR says that matter tells space-time how to curve, and space-time tells matter how to move. It says nothing at all about the composition of such matter. Dark energy, the cosmological constant, has been part of GR for more than 100 years. I find it hard to even figure out how someone could even formulate the thought that dark matter and dark energy falsify GR.

    Why do you think that the universe is not accelerating?

    What does your common sense tell you which conflicts with standard cosmology. How does it do so?

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    Replies
    1. Hello Phillip
      I do not believe in the big bang so I do not believe in expansion or acceleration.
      I have not believed since I first heard about it in middle school.
      Common sense tells me space is Newtonian.
      PS Some of us are restricted to soundbites.
      Greg

      Delete
  18. Isn’t saying “Dark Matter can be represented as a fluid” just make the hypothesis of Dark Matter formally unfalsifiable?

    How? Why do you believe this?

    You do say that a hypothesis needs to necessarily be falsifiable to be scientific. Doesn’t Dark Matter miss, as a hypothesis, that which a particular particle mass Dark Matter retains? Please enlighten me as to what criteria you are thinking for “fluid Dark Matter”

    This means that it is pressureless and has the same equation of state as ordinary matter. What it is composed of is another question.

    If I am a detective, and I see a person who has obviously been murdered, then my hypothesis "this person has been murdered" does not depend on my stating the identity of the murderer.

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  19. Sabine, If you give away all your material on the blog then no one will have to buy your book!

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  20. "A major reason we see so many wrong predictions in the foundations of physics"

    maybe its just statistical. If there is only one correct answer to a problem, then there are a million+ incorrect guesses.

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  21. You do not need it to explain existing data. No, you do not need it to explain the observations normally attributed to dark matter either. Because to explain those you only need to assume an unspecified “fluid” and it doesn’t matter what that fluid is made of. To explain the existing data, all you need is the standard model of particle physics and the concordance model of cosmology."

    but to unify standard model of particle physics and the concordance model of cosmology, don't you need to propose a specific dark matter particle as an extension of the standard model that fits the bill? whether its sterile neutrinos, neutralinos, axions or something else

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  22. Pascal,

    You are reading too much into this analogy. It's there simply to say that quality criteria do matter.

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  23. Matt,

    That falsifiability isn't sufficient for a good prediction is a point that, in hindsight, I wish I had stressed more in my book. I kind of do say it, but not very clearly.

    As to naturalness. If anyone had the patience, they could browse through 10 years of this blog's archive and find that I have explained this issue multiple times before and after writing the book. But it's a rather complex topic (as with its history and the arguments for and against it and the different types of naturalness and the way it enters predictions), so if someone really wants to understand it, my blogposts won't do.

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  24. Adam,

    Yes, right. In fact there are infinitely many wrong guesses. What do you learn from that? Guessing is not a particularly promising method.

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  25. neo,

    As I said, you don't need it to explain existing data, so you need a different motivation. Maybe you want to say that the need to eventually unify general relativity with the standard model requires that you bring the two together. That is right. Alas, that is no reason why dark matter particles must be in the energy range of a next larger collider (or exist to begin with). Best,

    B.

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  26. I have found something wrong in every philosophy of science I have read, including ones of those I am closest to - Bas van Fraassen (too antirealist), Paul Feyerabend (too anarchist) - so I am creating my own.

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  27. Saw a video where Arkani-Hamed argued that the new collider is necessary to understand the Higgs properly, e.g. to test for substructure and measure self-energy. He made the claim that the first spin-zero particle observed deserved the same degree of examination as earlier-observed particles that were less unusual. Would you take your "nothing to see here, move along" argument about the adequacy of the SM far enough to disagree with these claims?

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  28. Bee,

    thanks. i recall there are physicists who state that naturalness is still possible, since LHC 14 TEV is not enough energy to fully exhaust the parameter space. (and hence need to build a larger collider)

    that your arguments against naturalness is only valid up to LHC energies, where it has been tested. there could be particles produced at the proposed FCC which satisfy naturalness criteria.

    reference

    arXiv:1901.09966 [pdf, other] hep-ex hep-ph physics.ins-det

    Physics Beyond Colliders at CERN: Beyond the Standard Model Working Group Report

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  29. Sabine,

    Physics has solutions looking for problems ie:
    All of the "falsifiable Theories" That you have been railing against in this blog for as long as I have read it (please do keep up the good work)

    And Physics has problems looking for solutions ie:
    Everything in your post from a few weeks back
    http://backreaction.blogspot.com/2019/01/good-problems-in-foundations-of-physics.html


    What is the criteria you are using to gate "good problems"? I am asking because there are currently a few things that float around the internet and seem to get played with by various lets call them skunkworks-type-organizations from time to time. These things while "looking" like engineering kind of "smell" like physics here in descending order of credibility:

    "Hi Temp" Superconductors, how do they work?
    http://www.superconductors.org/news.htm
    This seams like a thing us dumb engineers want to know, that could come from Physics people. (Splain Me Sumthin PHYSICS, please)

    "Mach Effect" This looks like BS and smells like BS but then, NASA 'Whisky-Tango-Foxtrot' I thought NASA was trust-worthy do I need to Put them in the Trash pile too now or perhaps there is a good reason why: Spinning-Frame == Accelerated-Frame, WHY???
    https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Mach_Effects_for_In_Space_Propulsion_Interstellar_Mission

    "Low Energy Nuclear Reactions" NASA again, I'm calling it can't trust them anymore...
    https://nari.arc.nasa.gov/node/259
    https://nari.arc.nasa.gov/sites/default/files/SeedlingWELLS.pdf


    TLDR: Explaining the first of the three things I mention ("Hi Temp" Superconductors) feels to me (the "lay-man") to be Exactly the sort of thing "Physics Can Do For You" The other too seem like pathological science.
    It's just a gut thing for me. But you have articulated a list of the avenues you (An expert? I think so anyway.) think are profitable to peruse. How did you make that list and why didn't "Hi Temp" superconductivity make the list?

    Cause us engineers are greedy and want more tools and ya'know:
    Magnets How do They Work?
    https://www.youtube.com/watch?v=_-agl0pOQfs
    Seems like Physics's like... department-n-stuff

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  30. Sabine,
    My impression from the recent (non-)findings and discussions is, that theorists currently cannot provide meaningfull guidance to for experimental particle physics beyond the SM.
    You seem to assume on the othere hand, that (expensive) experiments should only be done,if there is some well motivated theory justifying it by providing definitive expectations. So much this would surely be welcome, perhaps the experimentalists have to take the risky lead and try to find something allowing theorists to narrow the infinity of conceivable theories to test (or falsify) to some outstanding, promising candidates.
    If I see it right, in the past some findings have been well beyond what was imagined before.

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  31. I don't quite see why a new theory of particles has too be in the language of quantum field theory. As I understand it, and I am not a specialist in this, QFT has predicted a cosmological constant that is in error by 120 orders of magnitude, and some might say that should be sufficient to falsify it. Even if that is not the case, why could not a new approach be valid, PROVIDED that it did not contradict any experimental observation. That may well be a barrier to high to climb, but I don't see per se why it is wrong to try.

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  32. Philip Helbig asks:

    How? Why do you believe this? (that Dark Matter is unfalsifiable)


    I believe this because every paper and discussion around Dark Matter starts with the premise that it exists. It is inferred by balancing Einstein's equations which are presumed to be proven correct in the context which infers DM.

    No falsifiability criterion has ever been divulged in any literature, so I believe it to be unfalsifiable. You would have easily changed my mind by listing (even hedged) criteria rather than probing my logic.

    To answer that question: No falsifiability criteria exists for unspecified, fluid Dark Matter.

    If you are a detective, we would give you the benefit of the doubt if you believe that a person has been murdered. If you are a forensic scientist, then falsifiability criteria apply for the hypothesis of murder.

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  33. SRP,

    I believe Nima has been fully aware that naturalness arguments are not to be trusted long ago (see his split susy stuff - also, the interview in my book) and consequently knows the best case for the next larger collider is measuring the properties of the Higgs. What he says is of course entirely correct. I have no problem with this whatsoever. The question is of course, is this sufficient motivation to spend such a large amount of money?

    The reason I came out on the side of "no" is that I don't see the potential in doing this. What would we do with knowledge about the Higgs self-coupling? There are other areas in physics right now where better knowledge has a larger potential to move us forward. Dark matter, for example. We know there is something there, but the data isn't good enough to tell us anything about the microscopic details, so we cannot make good predictions for Earth-bound experiments. We do not know where to look. So, I say, let's figure out first what's going on in the galaxies and if we can make better predictions for particle physics experiments, then let's look at this.

    Also, as I said elsewhere, quantum gravity and quantum foundations are areas where we both have good reason to think there is something new to find, and those new insights have a large potential to lead to further theoretical breakthroughs. Again, I think that's a more promising direction to invest in, especially since all those experiments come at a lower price tag than large particle colliders. Best,

    B.

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  34. neo,

    Naturalness arguments are subjective arguments. They are aesthetic arguments. As such they are hard to quantify and they can easily be amended. A decade ago, they said (in a nutshell) new particles should appear immediately and it should be an impossible-to-miss signal. Now that this hasn't happened, they're like "Oh, well, maybe it isn't that easy after all." Question to you: Why should we trust those "predictions"?

    Of course it is possible that there are more particles to find at higher energies, and that the standard model is natural in a more complicated way than expected or maybe it's just a little unnatural but not too badly unnatural, etc. All of this is possible. Maybe tomorrow they find a new particle and all of this discussion is redundant immediately.

    But even so, naturalness will still not be a mathematically sound criterion. My argument against naturalness has nothing to do with the energy scale. I am simply saying that's not a criterion you can trust. Hence there is no reason to expect anything new.

    (And the last thing we need is physicists who amend their naturalness criteria.) Best,

    B.

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  35. Jonathan,

    My list of "good problems" was specifically referring to the foundations of physics. There are many other good problems in physics, I am sure.

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  36. M_Malenfant,

    Well, experiments have been in the lead for the past 40 years because theorists did not come up with useful predictions, and look where it got us: Nowhere. I think it's about time physicists sit down and think about what is going wrong here.

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  37. Ian,

    The reason that the supposedly so terrible prediction of the cosmological constant didn't rule out qft is that it's not a prediction. I explained this here.

    As to your issue with me stating the language in which such theories must be put forward is QFT, you seem to think that I say that this should be the case. I don't. I am merely pointing out that that is the current quality standard. If you want to publish a paper about a newly invented particle, that's how it works.

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  38. Blogger Marco Parigi said...

    ...because every paper and discussion around Dark Matter starts with the premise that it exists. It is inferred by balancing Einstein's equations which are presumed to be proven correct in the context which infers DM.

    No falsifiability criterion has ever been divulged in any literature, so I believe it to be unfalsifiable. You would have easily changed my mind by listing (even hedged) criteria rather than probing my logic.


    Showing that GR is incomplete and requires modification at large scales could falsify Dark Matter. As I understand it, that is what "Modified Gravity" hypotheses are all about.

    Alternatively, finding Dark Matter could falsify "Modified Gravity".

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  39. "I believe this because every paper and discussion around Dark Matter starts with the premise that it exists. It is inferred by balancing Einstein's equations which are presumed to be proven correct in the context which infers DM.

    No falsifiability criterion has ever been divulged in any literature, so I believe it to be unfalsifiable. You would have easily changed my mind by listing (even hedged) criteria rather than probing my logic.

    To answer that question: No falsifiability criteria exists for unspecified, fluid Dark Matter."


    I think that you are misunderstanding the literature. Of course, a paper discussing a dark-matter candidate assumes that it exists and explores the consequences. Many, many, many dark-matter candidates have been ruled out.

    Yes, it is more difficult to rule out dark matter completely, since the evidence doesn't say whether it is in a very light particle or in primordial black holes (much smaller or much larger than a solar mass). This does not mean that it cannot be ruled out, merely that is is more difficult to do so.

    More observations will narrow down the properties of potential dark-matter candidates, making them easier to rule out.

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  40. Greg,

    No one cares what you believe or not believe in. I will not approve the rest of your comments. Also, if you continue to submit such large amount of nonsense comments, I will just send all of them straight to junk.

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  41. Greg Field wrote
    "Common sense tells me space is Newtonian."

    I share your intuition, but I don't see how we could square that with the fact that, for example, particles decay more slowly in an accelerator because of time dilation, and also the fact that those particles never reach or exceed the speed of light however much energy is pushed into them.

    I do sometimes wonder if special relativity could be reformulated in a way that kept Newtonian space and time, at the expense of some other weirdness.

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  42. Ian Miller,

    A final theory does not have to be a QFT. Rather, it has to reduce to GR and QFT in the appropriate limits (hbar = 0 and G = 0, respectively), where they have been extensively tested. It is correct that QFT predicts, in the opinion of many if not most physicists (Sabine clearly thinks differently), a cosmological constant that is 120 orders of magnitude too large (30 orders on a linear scale). This could be construed as an reason not to trust GR+QFT in domains where the CC matters, i.e. in connection with dark energy.

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  43. Don't dismiss flying carrots so easily. I have observed these in my kitchen when I messed up my chopping.

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  44. "The reason that the supposedly so terrible prediction of the cosmological constant didn't rule out qft is that it's not a prediction"
    In this blog post:
    http://backreaction.blogspot.com/2016/02/much-ado-around-nothing-cosmological.html
    you say that the cosmological (non-)constant problem might predict new physics at a scale of 35 TeV:
    "They find that the scale beyond which we should already have seen the effect of the vacuum fluctuations is about 35 TeV. If their argument is right, this means something must happen either to matter or to gravity before reaching this energy scale"
    Is this argument still valid in your eyes?

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  45. Showing that GR is incomplete and requires modification at large scales could falsify Dark Matter. As I understand it, that is what "Modified Gravity" hypotheses are all about.

    Alternatively, finding Dark Matter could falsify "Modified Gravity".


    Perhaps. There is no reason, though, that one could not have both. On the one hand there is Occam's razor, which says that we should prefer the simplest hypothesis which explains all the data. On the other hand, looking at the big picture, both dark matter and modified gravity might be simpler than either one contrived to fit all the data.

    I hope to learn more at a conference next week on dark matter and modified gravity.

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  46. Philip Thrift wrote: I have found something wrong in every philosophy of science I have read

    How about instrumentalism?

    If you find something wrong with it, could you give a real-world example of how it causes an actual problem?

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  47. One odd thing to me is that there are apparently interpretations* of OFT without any Fs (fields).

    * https://plato.stanford.edu/entries/quantum-field-theory/

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  48. Here is a proposal (https://phys.org/news/2019-01-dark-alternative-theory.html) for non-MOND modification of gravity to explain dark matter. The authors claim the theory is falsifiable. It seems the *justification* they have for the theory is that it matches current observations (aka the Bullet cluster) better than MOND.

    As a lay person, how can I figure out if the supposed justification they have for the theory is a good one even if I assume that they are correct when saying it is falsifiable?

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  49. Sabine Said, ...What reason did the physicist have to think that any of those predictions are good predictions?

    This kind of rationale you often use is why I read your blog.

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  50. Bee,

    ok, but what about the case that the FCC is a discovery machine. the reason to build it is just to discover if there is any new physics up to 100TEV. how is spending money on this any different than spending money on a telescope or robot to Mars or space station? maybe it will find something new, maybe it won't, but science is based on discovery and the only way to discover any new physics up to 100 TEV is to build the machine and see what happens.

    not discovering any new physics up to 100TEV could also revolutionize physics much as the null result of the Michelson–Morley experiment failure to detect the luminiferous aether.

    non-discovery of any new particles up to 100TEV at FCC would mean that the arguments regarding the Higgs sector need to be seriously rethought, and could inspire a revolution similar to special relativity from Michelson–Morley experiment. my bet is higgs is conformally invariant and that conformal gravity is a more complete theory of gravity than GR.

    so building an FCC and not discovering any new physics up to 100TEV could also be progress to HEP and science bc it will rule out many more models.

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  51. Sometimes I read that a new kind of maths may be necessary for the foundation of physics. Being a layman I have two questions:

    1. Any clue how this could look like? Can it be compared the way Einstein had a moment of genius and thought in a completely different way about gravitation?

    2. You criticize that physicists use arguments of beauty for building their theories. Isn't it also a (not validated but successful) assumption that the laws of nature can be expressed with mathematical theories? Maybe the laws of nature are beyond maths?

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  52. This is a subject that every grad student should be familiar with, although their advisors may prefer they focus on publishing and not concerning themselves with such matter. Before subjecting a hypothesis to testing, it should be shown to be at least plausible. If your hypothesis is not demonstrably plausible, then any statistical test goes ka-bluey. Even nonsense hypotheses will ring bells occasionally just by chance. A scientific result should never rest entirely on experimental or statistical results - it should be supported by a thoughtful rationale based on existing evidence.

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  53. Philip Helbig said I think that you are misunderstanding the literature. Of course, a paper discussing a dark-matter candidate assumes that it exists

    I am not misunderstanding the literature. Dark Matter is in a situation where it is "inferred" to match mass equations with measured velocity of dust in regions of galaxies, and alternatively with measured bending of light for lensing, or alternatively to match observed galaxy formation in the early cosmos given the relatively smooth CMB. The supposed evidence/inference is tied up with galaxy rotations etc. where the visible matter is not enough for the equations as they stand.

    Presuming that the equations are 100% right even in pathological cases outside of the domain where no Dark Matter is inferred puts Dark Matter in an equivalent domain to epicycles. "Wandering stars" knowing from historical observations that planets are fixtures visible from the start of history, we know they are not going to do something like suddenly move randomly. In which case, no matter how they are moving across the sky, epicycles can be constructed to fit observation.

    Similarly with "Wandering velocities of stars" on the outskirts of Galaxies, we know intuitively that they are bound and move in an approximate circle. Thus, since they move faster (never slower) than expected, Dark Matter can always be constructed to fit observed velocities.

    So far so good. We have to start somewhere, and premises that our beloved mass equivalence, is as correct as our perception that the Earth is the centre of the Universe. Correct until we find relations (eg "wanderers'" relationship with the Sun, or in DM's case galactic rotation relations) that place doubt on our beloved geocentrism or mass equivalence.


    When things in even bigger scale than galaxies appear to reverse Gravity altogether (Cosmic acceleration), does it not put into doubt our beloved equations? Gravity doesn't just stop working altogether, it reverses (incidentally to a similar acceleration to the dust on edges of galaxies, just in the opposite sense) requiring another construct placeholder until we figure out what is going on, Dark Energy.


    Michael Sharples says: Showing that GR is incomplete and requires modification at large scales could falsify Dark Matter


    Surely the Galactic Rotation relations, far from being evidence for Dark Matter, are more reasonably interpreted as evidence that GR is incomplete at the lowest observed cosmic accelerations!?


    If this is not the case, the only alternative is to suggest that Dark Matter, as a concept placeholder, is just as unfalsifiable as epicycles in their heyday, possibly for similar ideological reasons.

    regards
    Marco Parigi

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  54. Thomas,

    I understand what you are saying, but please note that hbar=0 and G=0 is not the correct semi-classical limit you need to reproduce.

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  55. MartinB,

    I do not buy the conclusion of this argument because of the assumptions below Eq (22), which they clarify in footnote 1, in which it is not mentioned, but should have been mentioned, that this assumes the equivalence principle to remain valid.

    Having said this, I do consider it possible that an argument of this type could be used to arrive at better predictions than naturalness arguments, but it doesn't seem to have caught on. Thanks for reminding me (and others) of this though. Maybe it could be turned into an argument of the sort: Either new physics below XX TeV, or violations of the equivalence principle, which would be interesting either which way.

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  56. Johannes,

    It is possible that a new type of math is necessary or that maybe we've reached the limits of what math can do. I have toyed with this idea (wrote about this elsewhere), but I don't think it is likely to be the culprit in the foundations of physics at present (though it's a problem in other fields). I think that some of the problems we currently have in the foundations are solvable with the existing mathematical methods. The problem isn't so much the absence of good mathematical tools, as in theorists putting intuition ahead of math, and not learning from their failures.

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  57. Neo,

    "ok, but what about the case that the FCC is a discovery machine. the reason to build it is just to discover if there is any new physics up to 100TEV. how is spending money on this any different than spending money on a telescope or robot to Mars or space station?"

    I don't think it makes sense to lump together space exploration with the foundations of physics. For what space exploration is concerned, personally I would say it is an obvious investment into the future. Just exactly what one should invest into in this case, I am not the right person to ask.

    The foundations of physics, too, I consider to be an investment into continued progress of society in the very long term, thinking here thousands of years, at least. But the payoff isn't as obvious as in the case of "robots on Mars" where, if nothing else, you get pictures from Mars. I think that in the foundations of physics we should invest into those experiments that have the biggest promise to lead to breakthroughs. At the current state of knowledge, it doesn't look like a larger collider would do that.

    As I have stressed many times, this situation can change every day, but the way it presently looks there is no reason to think a larger collider would see any physics beyond the standard model. On the other hand, if we have more information about dark matter, that might help us pin down what it is made of (if anything) and then make better predictions. Maybe those will be testable with colliders, or maybe you'll need some other experiment. We just don't currently know.

    The point is that if you do it the other way round you just risk more null results that will not help us. Best,

    B.

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  58. Manyoso,

    Well, no, you can't tell because they don't mention it. I had a brief look at the paper. It's a case of bimetric massive gravity which I wrote about here. A certain industry has developed around this because it's an extension of general relativity with several parameters that allows you to make a lot of calculations.

    Note that in addition to modifying gravity, they also have a dark matter component. So it's rather unsurprising that they find they can explain things that have been more difficult to accommodate in pure theories of modified gravity.

    In the abstract they write

    "We quantify how large a deviation from GR one actually finds, how much of it is tolerable and maybe even favourable in the sense of improving the fits to the data."

    So in a nutshell they find that the best way to fit the data is a combination of dark matter and modified gravity. We have known this for a long time.

    What can I say in summary? It's a good work, but I wouldn't pay too much attention to the particular model that they are using. This may be the right model or it may not be. The relevant finding here, I think, is that the best explanation for the data has aspects of modified gravity and dark matter. We would be well advised to first find a model-independent way to quantify this situation before guessing specific explanations for it. Best,

    B.

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  59. Marco Parigi said: Surely the Galactic Rotation relations, far from being evidence for Dark Matter, are more reasonably interpreted as evidence that GR is incomplete at the lowest observed cosmic accelerations!?

    The only test of reasonableness is which hypothesis best fits the observations. Gut instinct is no real substitute here.

    If this is not the case, the only alternative is to suggest that Dark Matter, as a concept placeholder, is just as unfalsifiable as epicycles in their heyday, possibly for similar ideological reasons.
    There is a risk of confusing mathematical models, which may be perfectly self-consistent, with the physical reality they purport to represent.

    Epicycles work as a mathematical model. However they represent a geocentric cosmological view which could be (and has been) falsified.

    It is the same with Dark Matter. No one can falsify a mathematical model that assumes its existence. However one can, in principle, prove the DM is not there through some advance in cosmology or particle physics.

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  60. God is not falsifiable by science.

    That does not mean that believing in God is good science.

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  61. Michael Sharples saysThe only test of reasonableness is which hypothesis best fits the observations

    The hypothesis that best fits the data for galactic rotations is that GR is incomplete. The hypothesis that Dark Matter exists in the exact quantities that is required by Newton, can be made to fit in precisely the same way that epicycles can be hypothesised to fit any planet.

    The hypothesis that best fits Galactic Rotations is a modified inertia. There is even peer reviewed papers that describe how it outperforms predictively any other way of estimating velocities at the edges of galaxies.


    Gut instinct is no real substitute here.

    Precisely, and the gut instinct that GR is complete has to be set aside for *Observations* and *evidence* correctly interpreted.


    Epicycles work as a mathematical model. However they represent a geocentric cosmological view which could be (and has been) falsified.

    Yes, but falsification criteria had been thrust onto epicycles by the elegant and predictive formulae that do not have adjustable parameters. ie. a lot of time is saved in predicting orbits for new objects by skipping the formulation of the epicycle parameters.


    In the same way MoND type mathematics in a modified inertia can do the same thing to Dark Matter that Heliocentrism did to epicycles - show it up to be an embarrassment to evidence and predictive hypotheses.


    Usually the evidence I perceive in favour of Dark Matter is in the "authority of the literature". I accept that myriad papers come to the conclusion of Dark Matter, but the *evidence* is the measurements that can be made of the velocities of the elements of the galaxies. An argument from measurement rather than an argument from authority. I hope those authors of peer reviewed papers are not as self-righteous as the authors of the Bible, peer reviewed by other biblical scholars.

    regards
    Marco Parigi

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  62. Steven Mason said...
    "How about instrumentalism? If you find something wrong with it, could you give a real-world example of how it causes an actual problem?"

    Instrumentalism is a rather strict type of antirealism. (I am not an academic philosopher of science, so I don't claim to be an authority.)

    My own concept of science is that it (I say "it", but really science can be viewed as a collection of domain-specific languages) should (at least endeavor to) inform us about what nature really is. Nature may forever be "noumenon" (ultimately inaccessible), but that doesn't mean the quest for better languages that can inform us of what nature "really" is should be abandoned. A purely antirealist philosophy is a "problem" if it says "don't even bother pursuing that quest." On the other hand, one shouldn't commit to realism without even considering that what you are committing to may not be "real" at all, like much of the entities of the language of current physics.

    cf.
    Codicalism: Between realism and antirealism
    https://codicalist.wordpress.com/2019/01/30/codicalism-between-realism-and-antirealism/

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  63. "I am not misunderstanding the literature."

    If things are as you say, the case is closed and everyone believes that dark matter exist, why do people still write papers on it, have whole conferences about it, etc?

    Maybe you are not misunderstanding the literature but misunderstanding how science works.

    And the cosmological constant, and hence the observed acceleration of the universe, is perfectly compatible with GR.

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  64. Phillip Helbig askswhy do people still write papers on it, have whole conferences about it, etc?

    It really baffles me, quite honestly. In the same way that supposed scientists are doing everything in their power to hype the utility of things such that a new collider is a good idea. If "science" is made to be the "raison d'etre" to continue to spend billions with nothing to show for it, then to believe in DM for decades with no tangible on-prediction to the inference of DM is natural and the way science is meant to be - an expensive farce. The real action is in Dark Matter engineering. Like with all sciences, the very repeatability of science opens up using that repeatability to predict new facts or engineer a new widget. Where's the Dark Matter widget? Where's the new facts derived from Dark Matter? If Dark Matter is so "scientific" why is DM Engineering not a thing?

    And the cosmological constant, and hence the observed acceleration of the universe, is perfectly compatible with GR

    Before having observed the acceleration of the universe, GR would have predicted that the mutual gravitation would be accelerating inwards. Rather than accepting that *one* of the possible hypotheses to explain outward acceleration is that GR is incomplete at these scales. We have jumped from the lack of predictive ability of GR, to GR determining the need for Dark Energy.


    One could say that Dark Matter and Dark Energy gives more jobs to more theoretical physicists and obviates the need for those physicists to be subject to the pressures of engineering. One could say something similar for the Large Hadron Collider. One could say that for the study of Epicycles.


    The point is - Not enough theoretical physicists have any incentive to disprove DM, DE, or GR or SUSY. There is a distinct disincentive to allow infinite studies to narrow down what may not actually exist. As Sabine says for SUSY, this is wasteful.


    regards

    Marco Parigi

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  65. Now we have a pithy term - "carrot rain" - for hypotheses that don't have anything going for them but for falsifiability. I can see the phrase "it's raining carrots in there" being a useful way to summarize certain meetings and seminars.

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  66. Based on this paper https://arxiv.org/abs/1809.00673 it seems that the recent gravitational wave measurements put very strong constraints on the graviton mass.

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  67. Bee,

    the other point i made is that null results from a 100tev collider would also progress HEP much as the null results from the Michelson Morley experiment.

    ruling out proposals that extend the SM motivated by dark matter or naturalness (SUSY or technicolor) or finding hidden sectors is also an important task.

    100TEV collider can either discover new particles, perhaps not anticipated by any current theory, or rule out many BSM proposals, esp those motivated by the higgs sector.

    i agree this is a hard sell but it appears CERN and China might build the FCC.

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  68. @Sabine
    Thanks for the clarification and keep up the good work - your criticism is really needed and well-posed in my opinion.

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  69. @neo
    "the other point i made is that null results from a 100tev collider would also progress HEP much as the null results from the Michelson Morley experiment"
    Really? Did the null results from the LHC (nothing found but the Higgs) advance physics like MM did? (O.k., perhaps the ever-increasing shifts in SuSy energy concepts etc. are the modern-day equivalent of the ether drag...)
    Or is there anything special about the 100TeV-range?

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  70. Given the measured masses of the assumed "Higgs" and the apparent top quark, I am not so certain that CERN should be as certain as it is of what it thinks it has.

    https://arxiv.org/abs/1512.01222
    … Figure 2
    http://docplayer.net/docs-images/70/62086541/images/27-0.jpg

    The universe is then metastable, though apparently inert to LIGO mergers, galactic core black holes, supernovae, magnetars, LHC paired proton and paired heavy ion collisions, EeV cosmic rays, pseudovectors (axial vectors), etc. Add naughty information manipulations like quantum eraser and delayed-choice quantum eraser experiments.

    https://www.youtube.com/watch?v=Ztc6QPNUqls&t=4m48s
    … The Higgs field is decimal trim to total mass.
    https://hackadaycom.files.wordpress.com/2016/09/er_01.jpg
    … Did not destroy the universe

    Leavening and fermentation are ancient. It was yeast.

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  71. @MartinB

    it's calling into question naturalness.

    there are SUSY proposals and other BSM theories that obviously are just beyond the reach of LHC, but accessible to FCC

    i.e arXiv:1901.09966 [pdf, other] hep-ex hep-ph physics.ins-det
    Physics Beyond Colliders at CERN: Beyond the Standard Model Working Group Report


    not finding any SUSY in the 100TeV-range would more strongly dis confirm naturalness, than 14 TEV LHC. perhaps there is something else going on with the Higgs and the cutoff, such as conformal invariance.

    IMHO i'd prefer CERN and China pool resources for a 200km, 200TEV or even larger ring (or stronger magnets)

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  72. Bee,

    this paper put out by CERN, dated 20 Jan 2019)

    arXiv:1901.09966 [pdf, other] hep-ex hep-ph physics.ins-det
    Physics Beyond Colliders at CERN: Beyond the Standard Model Working Group Report

    lists all the new physics and their motivations for the proposed FCC at CERN.

    do you have any issues with the topics and theories they hope to test for the proposed FCC at CERN.?

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  73. neo,

    I am basically reading it right now. But, well, it's 120 pages long, so I cannot comment on this quickly, sorry.

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  74. @Marco Parigi
    Dark matter and dark energy are there because, in combination with the SM and GR, they make up the so-called concordance model of cosmology, which can pretty much explain all current observations with good accuracy, and this with a rather small number of free parameters. That's a pretty good reason for taking them seriously, isn't it?
    Certainly, the situation is not ideal, because nobody knows what DM really is, or even if it really exists (or should be replaced with a modification of GR).
    But the current cosmological model works, and anybody is welcome to find another one that works even better without DM or DE. Any physicist who was able to do so would become instantaneously very famous! And it's not that people are not trying, they do (for instance, here: https://arxiv.org/abs/1110.3054). It's just that it is very difficult not to run into inconsistencies.

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  75. What a new theory needs is an interesting question. Any theory should arrive at a set of outcomes, and I think we would all agree that set should not contain an element that is immediately falsified by what we already know. But I think it also has to be useful, and to do that, it has to go somewhere where current theory does not go, or at the minimum, does not go easily. The carrot rain obviously fails not only the standard model of carrot growing, but it does not go anywhere rational. Where I disagree with some opinions is that it does not (in my opinion) have to use the mathematics of current models; a significantly simplified approach using a different mathematical approach should be considered. I also do not think it has to account for everything the current model does, in part because a model developed over years by the input of dozens of physicists should not have to have everything replaced immediately. As an example of what I mean, think of the standard model of particles. One cannot accuse the Lagrangian of being over simple, so supposing someone proposed a relatively simple model with no free parameters that correctly arrived at the energy/mass of all the particles would that not be worth consideration? (Caveat - I have no idea how to do that.)

    The basic problem, of course, is that nobody invested in the field wants to discard the work they have already done, and proposals to do this sort of thing will not get encouragement during peer review for things like funding. The second problem is that such work would be extremely difficult. We did not get to where we are by ignoring the obviously easier approaches. But the other side of the coin is, can we be absolutely certain that everything we have done is right? If we look historically there have been a large number of "wrong tracks" pursued, but since about 1975, as far as I can tell, nothing obviously wrong. But how much of this relies on mathematical formalism that while it gets correct correlations with observation when it can actually be evaluated, and with certain parameter assignments when there are no analytical solutions? How can we be certain that an erroneous concept is not being made to work, in the same way Claudius Ptolemy got his terra-centric cosmological model to work?

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  76. "Problem is that now the data say that the standard model is just not natural, period."

    Isn't some deeper underlying symmetry still possible?

    "To explain the existing data, all you need is the standard model of particle physics and the concordance model of cosmology."

    But what about all the supposed outstanding "problems"? Shouldn't physicists try to solve them?

    It seems like your arguments could've been used against relativity. Someone could've said that the lorentz transformations explain everything you need to know about special relativity. And you apparently don't need gr to explain the classic predictions. Even black holes had already been predicted without it.

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  77. Opamanfred said: in combination with the SM and GR, they make up the so-called concordance model of cosmology, which can pretty much explain all current observations with good accuracy, and this with a rather small number of free parameters. That's a pretty good reason for taking them seriously, isn't it?

    I don't really think so, no. The concordance model cosmology is not derived from a combination of SM,GR, DM and DE. It is, however very dependent on the tunability of, especially, DM and DE. ANY free parameters is a red flag, and a possibility to continuously juggle free parameters of *unobserved* ie. dark, placeholder science concepts, is a way of making a completely wrong concordance model fit whatever new data it needs to.


    The requirement of free parameters and thousands of directionless papers and experiments is a good reason *Not* to take them seriously. I would be much happier for physicists to take any grain of truth from alternatives far more seriously than we do eg. Modified Inertia.

    regards
    Marco Parigi

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    Replies
    1. For all those who are looking for a new explanation of CDM (please, always include the”C”), the minimum requirement is, surely, to do at least as good a job as concordance cosmology does re all relevant observational results, and to be self-consistent. Then it would be nice to have some good pointers to what new astronomical observations would/could test this new explanation.

      So far, as far as I can see, no new explanation - including Modified Inertia - passes muster.

      Delete
    2. Good pointers to astronomical observations would be the orbits of "wide binaries" if a modified inertia, or modified Newtonian dynamics gives better results than Newton (assumed by concordance at these scales), then we are on the right track. The further away we go and the further back in time we go the less we can be sure about our extrapolation eg. to close to the Big Bang, or so far away that different processes may be hiding in the superclusters etc. If we stick to the observable/repeatable and close in on why there are anomalies we will get closer to complete theories.

      Delete
  78. Falsifiability of a hypothesis does not imply good science. I agree completely but at least it is a criterion to exclude a lot of bad science.

    Falsifiability plus no evidence that the the hypothesis is wrong. Better but it's still just theorising with no data. An interesting intellectual exercise and that's all. Still in agreement with you there.

    Now suppose your hypothesis also
    a) passes any tests an earlier theory does and
    b) explains some observation that earlier theory does not

    Now we are talking good science. And the filtering process started with falsifiability so I think it is still an important part of science. Without it, "A wizard did it" would be a perfectly sound argument.

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  79. "ANY free parameters is a red flag"

    Then you need to throw out a lot more. Unless you have a theory which explains the value of the parameters, leaving none to be determined by observation, it's not good science? Many would disagree with you.

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  80. Yes. A lot more needs to be thrown out. It just is not good science if it has no utility outside being self consistent and providing fodder for directionless papers. At some level, concordance cosmology is worse than useless. It wastes time and energy on its uselessness.

    The point is that DM is tuned to what it needs to be by virtue of how it is inferred. That amounts to circular reasoning on the evidence of it existing. If the inference is wrong because Newtonian Dynamics is wrong, calculating where the Dark Matter is is just chasing your tail while being paid to do it. It doesn't need a "better replacement". The fact that it is a tuneable parameter should lead everybody to search for replacements rather than beating a dead horse.

    ReplyDelete

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