Dear Karen Crowther,

Sorry for misspelling your name. Hopefully you nonetheless understood my point. Let me try and say it with other words:

Let's never stop digging in the treasure of possible corrections.

Admittedly, I am not ready to expect finding any theory to be unified, unique, UV complete, etc. by means of your nine criteria as long as commonly agreed assumptions are treated like a taboo. Elapsed time is definitely more weird to physicists than to common sense.

Kadin pointed to several possibly overlooked treasures. Just a single one out of them seems to be worth digging, at least to me. What about McEachern/Traill?

Eckard

Hi Karen,

An almost encyclopedic treatment. A couple of things, though. You prescribe conditions for theories, but you left out the premise of a unified spacetime -- " ... independent in its physical properties, having a physical effect but not itself affected by physical conditions." ~ Einstein, The Meaning of Relativity .

If, as you admit space and time are fundamental, why is not spacetime more fundamental?

Nevertheless, good essay.

Mine: https://fqxi.org/community/forum/topic/3124

    Ah yes, I see what you mean now. It would obviously be a sufficient condition, but I'd hope it's not a necessary one!

    Best,

    Karen

    Dear Eckard,

    Thanks. Yes, I'm sorry to say I don't understand what you mean. Could you perhaps elaborate a bit more on what you mean by "possible corrections" and "commonly agreed assumptions", please?

    I haven't yet read Kadin's essay, and am unfamiliar with McEachern/Traill.

    Best,

    Karen

    Dear Karen,

    Klingman followed Phipps Jr. who tried to fundamentally correct Einstein and rescue ubiquitous simultaneity. I guess, the treasure of unseen alternatives might be larger. In my essay, I even questioned Maxwell's guess as the correct fundamental of gamma. Being not an etherist, I rather share Michelson's preliminary agnosticism. I feel intrigued by Foucault's pendulum which is nicely to be seen in Magdeburg and also by the late Michelson's experiment.

    Kadin questions a lot of mandatory tenets, maybe too many as to get accepted. In particular, I admire his older essay "Just too many people". W"hile I don't feel myself right in political sense, I consider Kadin's judgement as alerting. The money given by "good" people like me to the exploding population in poor regions

    does not solve the problem of lacking responsibility, on the contrary ...

    When Kadin confronted us with the prediction that QM will never fulfill the hope for hugely improved computers, the cautious reaction here seems to confirm that he again put his finger squarely on a moot point. Szangolies could only point to a DQC1 that is not yet based on entanglement which, if I recall correctly, corresponds to the situation about two decades ago. Others said a lot by saying nothing.

    The mentioned hope was theoretically confirmed by Bell. In discussions at FQXi, McEachern gave a completely documented MATLAB simulation with a result that looks at least similar to the result by Traill. McEachern was perhaps deeply disappointed because peers and admins like John Baez simply rejected it. He decided to not participate in the contest this year.

    Best,

    Eckard

    Dear Terry Bollinger,

    Thanks very much for taking the time to read and vote on my essay, and to provide useful feedback; I really appreciate it. I also greatly appreciate your voting pledge, and will strive to implement it myself more consistently.

    Yes, the contest's question drew me in so I used it as an opportunity to explore some new ideas, and to understand issues surrounding quantum gravity from a different perspective. Writing the essay has been very beneficial for me, and I'm really glad to hear that you enjoyed it and think it useful for the community.

    In regards to the first two critical comments.... aaah yeah, these are fair---the stance I adopted in the essay was, indeed, to view the question from the perspective of mainstream physics, and my aim was to distil and make palpable the conditions that are being assumed as consensus in high-energy physics. So, it is rather status quo in that respect.

    However, I did not mean to sound as though I actually advocate all these conditions myself (especially without further refinement and provision of their precise definitions, as required particularly for the conditions of naturalness, unification, and no-weirdness). I certainly do not want to side with mainstream high-energy physics just because it is mainstream. Nor am I a supporter of string theory, so I'm (very! haha) sorry if the essay comes across like that. I considered string theory because it is the only approach to more-fundamental physics (that I know of) that claims to be a ``final theory'' (or, rather, final framework).

    Instead, I am a philosopher, and this is just the first step of a bigger project: what I really want to do, but could not here given the time and length constraints of the essay, is to now go on and more thoroughly examine each of these conditions. I want to better understand what they each mean, what their motivations are, and especially what their implications are, particularly when combined with other theoretical desiderata. I agree completely with what you say in your second comment, and believe that progress can be made by re-examining, and perhaps giving up some of the implicit, deeply-held assumptions that turn out to be not well-founded or useful. So, I'm very glad you pointed this out, and I regret that I wasn't able to do more justice to this fact in the essay itself.

    In regards to your last point, yes, I see what you mean and also agree. Given the incredible success of the standard model, together with all the difficulties in trying to fit gravity into this framework, I agree that this seems unlikely to be the right way of going about it. Both the standard model and GR might emerge from a more-fundamental theory, without having to do so in the same way (this is one reason why I'd like to more deeply question the requirement of unification). In fact, there are compelling reasons for not treating gravity as a force at all, as Maudlin says (in On the Unification of Physics), ``Objects do not couple to the gravitational field, they merely exist in space-time.''

    Also worth noting that most approaches to quantum gravity (apart from string theory) don't seek to fit gravity into the framework of QFT.

    Thanks again, and also for your handy summary of the conditions! Even I'm finding it useful. I particularly like the alternative titles for 6 and 7, because they're a bit more evocative.

    Just a couple of notes... firstly, I realised this from other comments, as well, that there are different uses of uniqueness: the stronger one is as you state it, but it may be too strong a constraint to be realistically implemented, so I only meant to refer to the weaker notion of a theory being unique, which is just that there be only one fundamental theory we have... not that we have to rule out the possibility of there being any other theories that could do the job (in other words, I don't know how to solve the problem of underdetermination!)

    And secondly, I don't know about probabilistic in requirement 4. I just meant not reliant upon approximations. But it is interesting to ask now whether being non-proababilistic is also a requirement...! It seems like it could well be, actually.

    Best,

    Karen

    Dear Don Limuti,

    Thank you! OK I will try to have a look at your essay when I can, and let you know whether or not I agree that it's easy-peasy ;)

    Best,

    Karen

    Dear Mozibur Ullah,

    Thanks very much! Yes, I agree, I love mathematics too, but an essay is an essay, and I wanted to make it as accessible as possible. I'm glad you enjoyed reading it.

    Yes, you're right that it's easy sometimes for people to forget the origins of QFT. Certainly it is a very successful step towards unifying our most fundamental theories---and, indeed, the most successful framework for physics that we have! And yet it has so many conceptual and theoretical difficulties. Also, it's interesting now to explore how QFT in curved spacetime can give insight into a greater unification of QM with GR, and approximate quantum gravity.

    Thanks again,

    Karen

    Dear Conrad,

    Thanks very much! I'm really happy to hear that there are people out there finding my work useful!

    Yes, thanks, I had wanted to bring in some discussion of emergence from that paper for the essay, or at least mention it, but couldn't manage it in the end. So, I'm glad you discovered the paper, as well as the book, and can advertise them here!

    I'm intrigued by your arguments regarding unification and naturalness, especially since I'm very interested in better understanding the definitions of each, their motivations and implications myself (I'm quite suspicious of them, in spite of their apparently being so central to the business of physics!), so I'll certainly take a look at your essay when I can.

    Thanks again,

    Karen

    Dear Branko,

    Thank you! OK, I am interested in the heuristic role of the Planck units, so I will try to have a look at your essay. But what do you think, does your approach satisfy these conditions?

    Best,

    Karen

    Dear Adel,

    Thank you!

    I think your quote here captures the requirements that a fundamental theory be simple and that it be explanatory (additionally, the quote suggests how the theory should be explanatory), maybe also the requirement that the theory be self-consistent. I did not explicitly have the requirements of 'being simple' and 'being explanatory' as criteria in my list, although several of the criteria may be related to simplicity (e.g., unification, uniqueness, no-weirdness), and all of them are based on the principle that a fundamental theory not leave anything that apparently requires explanation.

    I like your idea that a fundamental theory should explain current physics, I think that is certainly desirable, and unfortunately not something that I discussed enough in my essay.

    There are also criteria on my list that I think are not captured by your quote here, though. I will have to read the rest of your essay.

    Best,

    Karen

    Hi Peter,

    Thanks very much! I'm embarrassed to say that I had not heard of Hestenes before, so I'm glad you mentioned his work, it indeed seems very interesting. I'll read up more and see how it can apply to my work, as you suggest. Sorry I'm not sure how to answer your question, though. Will reply to your other post now, too.

    Best,

    Karen

    Thanks again, and sorry for the delayed response. Haven't yet read the essay, but this sounds good to me!

    In regards to uniqueness... I knew I picked the wrong word here, because of its different uses, but struggled to think of a better one! But, the idea is supposed to be that we have just a single theory, as in alone -- rather than being the only possible theory. So, your model may satisfy this criterion, after all, I think.

    As you say, it's difficult to see how we could establish that a given model is the only possible one able to describe the physics. I'm not sure if the problem of underdetermination can be solved -- however, Dawid's book is an extensive argument trying to demonstrate the limitations on theoretical underdetermination (I am still trying to work through his arguments, though).

    In regards to "not weird" haha! well, this is the one I am not so sure of myself. I was mainly thinking of it as a response to the general frustration surrounding the measurement problem.... but now I realise that may have more to do with how the theory links back to observations, rather than the weirdness apparently described by QM. Maybe we can be OK with fundamental weirdness if everything else is satisfied, and the weirdness is inherent? I guess it depends on how otherwise happy people are with the approach, whether they'll tolerate some weirdness for its other virtues, or whether they'll keep searching for something else (even if in vain).

    Dear Peter,

    Thanks very much!

    ooops!10 ^- 33 cm yes you're right, thanks for pointing it out!

    Best,

    Karen

    Dear Wayne,

    Thanks very much!

    In regards to your mathematically formal criteria, I'm interested in what you mean by causality and how you define it? (If you're importing the notion from GR, you mean that you have a spacetime, and that it shares the same topological and metrical structure as GR spacetime? Or something less than this?)

    Also, I'm assuming by "non-renormalisable" as a criterion, you mean a theory that doesn't require regularisation, rather than that it actually be non-renormalisaable (because that would mean it has infinities)?

    But I'm most interested in what you mean by when you say that the theory must "replicate [older theory] when evaluated at [relevant length scale]", because this is a large part of my own research (which I regret that I didn't have opportunity to include in my essay, due to the various constraints on it). You mean that the older theories should be derivable from the new one, under some relevant conditions, I gather?

    And yes, agree with your practical point, that we may stop digging when the cost (whether in terms of energy, time, or money, etc.) is estimated to be greater than the anticipated rewards of continuing beyond a certain point. But of course that's a response to a different interpretation of the question (or perhaps under different assumptions) than what I adopted here.

    Best,

    Karen

    Dear Avtar,

    Thank you. Your paper sounds interesting, particularly the potentially empirical aspects.

    Best,

    Karen

    Dear Gary,

    Thank you!

    I am similar, I find I can only fully understand things, or work out my own arguments, by writing (though it's not always essay form!)

    Yes, I agree that there may be many different conceptions of fundamentality, depending on different contexts. For this exercise, I explicitly chose to write from the perspective of high-energy physics, and certainly do not mean to imply that such an account is appropriate for other contexts, or that it is the only perspective on offer. In fact, I am more inclined towards "emergentist" accounts (e.g., those offered by condensed matter theorists), where what is fundamental is scale-dependent, so I agree that much is lost when we consider only a single fundamental "theory of everything" (you may like to see some of my published work on emergence).

    However, the FQXi question: What is "Fundamental?" invites a singular response; otherwise the question would be framed: What are "Fundamental?" The only exception to that interpretation is to respond to the FQXi question with the answer: 'Yes'

    I'm sorry, but I don't really understand what you're saying here. I read the question as asking about the meaning of the word "fundamental", as in, what it means for something to be fundamental. I don't see how that requires just a one-condition answer? It's just that they are only asking about one word. And what is the interpretation of the question that could be answered by "Yes"?

    Best regards, and good luck to you too,

    Karen

    Dear Karen,

    you've produced an interesting list of conditions for fundamentality (fundamentalness?). Your argumentation is exceptionally clear and down to the point, and you present your points in an enormously comprehensible way that nevertheless never runs the danger of leaving out something important.

    I have one question, though, regarding the need for unification: it seems possible to imagine a universe ruled by Newtonian mechanics, or a universe ruled by Maxwellian electrodynamics. But it's also possible to combine the two: adding charge to a massive ball and putting it into an electromagnetic field means that its behavior is no longer solely governed by Newtonian gravitation, but that additional effects due to electromagnetism play a role; but both theories seem to be well capable of existing side by side. Furthermore, they seem to do well with respect to the other criteria you mention. So isn't it possible to have a universe with several equally fundamental theories?

    It would certainly be aesthetically dissatisfying if the universe were like that, but well, the universe probably isn't under any obligation to appear pleasing to us.

    You seem to be dissatisfied with the fact that in such a case, there's something 'left open' to explain; but then, isn't that also true if there is a single fundamental theory? Are we not always left with an ultimate, 'but why this?'

    Additionally, your dictum that 'physics does and must, by its nature, assume that we are able to formulate a physical description of all phenomena' strikes me very much like Hilbert's declaration that there can be no 'ignorabimus' in mathematics, and his search of a single, unified axiom system that underlies all of mathematics---which, of course, was shown to be impossible by Gödel.

    In my essay, I argue that similar restrictions may well be true of physics---and furthermore, that it's not any more of a problem than Gödel's results have been for mathematics. I would be very interested in hearing your thoughts!

      Karen,

      Thank you for your most gracious and informative response! I would have added this reply earlier, but I don't seem to get any kind of notification from FQXi when someone replies on anything except my own essay thread. I had to search manually for my own name, essay by essay to find responses. Argh! I must be missing something?

      You are very generous about my critique points, and I deeply appreciate that you used them as an opportunity to make positive, constructive suggestions. That to me is the heart of good science! I note that some of my favorite comments from one fellow essayists were the ones in which he did his best to point out holes in my argument. Delightful! The points were valid and made me both think carefully and explain myself better.

      I'm glad you liked my two title suggestions, and that they were constructive.

      Regarding your number 4 non-perturbative criterion, I must confess that was the only one I wasn't quite sure of. Why? Well, there seems to be a deep "lumpiness" to both physics and our universe in general that lurks behind such powerful mathematical concepts as renormalization. Renormalization is not really as exotic or even as mathematical is it is in, say, Feynman's QED theory. What it really amounts to is an assertion that our universe is, at many levels, "lumpy enough" that many objects (and processes) within it can be approximated when viewed from a distance. That "distance" may be real space or some other more abstract space, but the bottom line is that this sort of approximation option is a deep component of whatever is going on. I say that in part because we are ourselves as discrete, independently mobile entities are very much part of this lumpiness, as are the large, complex molecules that make up our bodies... as are the atoms that enable molecules... as are the nucleons that enable atoms... and as are the fundamental fermions that make up nucleons.

      This approximation-at-a-distance even shows up in everyday life and cognition. For example, let's say you need an AA battery. What do you think first? Probably you think "I need to go to the room where I keep my batteries." But your navigation to that room begins as a room to room navigation. You don't worry yet about exactly where in that room the batteries are, because that has no effect on how you navigate to the room. In short, you will approximate the location of the battery until you navigate closer to it.

      The point is that the room is itself lumpy in a way that enables you to do this, but the process itself is clearly approximate. You could in principle super-optimize your walking path so that it minimizes your total effort to get to the battery, but such a super-optimization would be extremely costly in terms of the thinking and calculations needed, and yet would provide very little benefit. So, when the cost-benefit ratio grows too high, we approximate rather than super-optimize, because the lumpy structure of our universe makes such approximations much more cost-beneficial overall.

      What happens after your reach the room? You change scale!

      That is, you invoke a new model that tells you how to navigate the draws or containers in which you keep the AA batteries. This scale is physically smaller, and again is approximate, enabling tolerance for example of highly variable locations of the batteries within a drawer or container.

      This works for the same reason that in Feynman's QED is incredibly accurate and efficient for modeling an electron probabilistically. The electron-at-a-distance can be safely and very efficiently modeled as a point particle with a well-defined charge, even though that is not really correct. That is the room-to-room level. As you get closer to the electron, that model must be replace by a far more complex one that involves rapid creation and annihilation of charged virtual particle pairs that "blur" the charge of the electrons in strange and peculiar ways. That is the closer, smaller, dig-around-in-the-drawers-for-a-battery level of approximation. In both cases, the overall "lumpiness" of our universe makes these special forms of approximation both very accurate and computationally efficient.

      At some deeper level, one could further postulate that this may be more than just a way to model reality. It is at least possible (I personally think it probable) that this is also how the universe actually works, even if we don't quite understand how. I say that because it is always a bit dangerous to assume that just because we like to model space as a given and particles as points within it, those are in the end just models, ones that actually violate quantum mechanics in the sense of postulating points that cannot exist in real space due the quantum energy cost involved. A real point particle would require infinite energy to isolate, so a model that invokes such particles to estimate reality really should be viewed with a bit of caution as a "final" model.

      So my bottom line: While formal formula (criterion 4) are great, our universe seems weirdly wired for at least some forms of approximation. I find that very counterintuitive, extremely fascinating, and likely important in some way that we flatly do not yet understand.

      ----------

      Enough, I'm droning on again! Thanks again for your response, and I really like what you are doing. Your broader goals are great -- please keep at them!

      Cheers,

      Terry