Dear Karen,

All of your 9 conditions are very real.

Among all the essays without mathematics, you are among the best.

My essay is tied to Plank's units. I would like you to tell me what conditions do not satisfy my views in the essay.

With best wishes,

Branko

    Dear Karen,

    Your contribution to our motley collection of essays here is much needed. You give a clearer picture than most physicists could give of what they're looking for in a fundamental theory, and I think it's important to understand how little clarity there is about this. To me what's most striking about physics is how much our current theories can explain about the world, while seeming to leave us almost clueless as to why a world should be based on such strange foundations.

    I want to mention that your excellent paper on "Decoupling emergence and reduction in physics" is directly relevant to this contest, since these two notions come up in many of these essays, and are usually taken to be directly opposed. Also, I was very glad to find your book/thesis on "Effective Spacetime" - it's rare to find such in-depth discussion of recent physics that a non-specialist can follow.

    I was interested in your comment, "The requirement of unification is hard to justify. Given that our manifest experience of the world is of diversity rather than a sameness of phenomena, seeking an explanation of heterogeneity seems counter-intuitive--surely a unified description would be more striking than a disunified one, and cry out for explanation?" Later you answer this by suggesting it's the "business of physics" to "explain diverse phenomena by appeal to simple, universal laws." I can't argue with that - and certainly the quest for unification has led to many an outstanding discovery, most lately in the Standard Model. But in my current essay I've tried to show that neither unification nor naturalness are reliable guides to a more fundamental theory. The essential argument is that diverse interaction-structures are necessary to make any kind of physical information measurable, or even meaningfully definable.

    I really appreciate the kind of work you're doing, digging out the real conceptual issues within the technical struggles of current research.

    Conrad

      Dear Karen Crowther

      Just letting you know that I am making a start on reading of your essay, and hope that you might also take a glance over mine please? I look forward to the sharing of thoughtful opinion. Congratulations on your essay rating as it stands, and best of luck for the contest conclusion.

      My essay is titled

      "Darwinian Universal Fundamental Origin". It stands as a novel test for whether a natural organisational principle can serve a rationale, for emergence of complex systems of physics and cosmology. I will be interested to have my effort judged on both the basis of prospect and of novelty.

      Thank you & kind regards

      Steven Andresen

      Dear Peter,

      Thanks very much for reading and commenting on my essay. I usually tend to think of the standard model as a collection of theories, but since it can be written as a single Lagrangian, it seems more usual to call it a theory (even if it is non-unified and rather inelegant one!) I also explored general relativity and quantum field theory instead of special relativity and quantum mechanics, because the latter are held to be less-fundamental than the former (SR being a special case of GR, and QFT being a combination of QM and SR).

      If we are talking about a TOE in the sense of a complete theory valid at the most fundamental level, as I do in the essay, then yes I think it is potentially within our power to formulate and understand such a theory. However, if you mean actually using such a theory to get results about everything (i.e., physics at all scales), then this is most certainly not possible. As you say, it would require some incredible level of computational power. In the essay, I used the assumption that it is possible "in principle" but, in honestly, I don't believe that -- in fact, I can't even make sense of such a statement.

      Thanks again,

      Karen

      Dear Diogenes,

      Thanks very much for your comments. Yes, in the essay I assume that it is possible "in principle" to derive results valid at larger length-scales from theories formulated at shorter length-scales. This is one sense of reductionism, but it is not one that necessarily conflicts with the possibly of emergent phenomena, particularly the examples you mention.

      Yes, I agree that there are many ill-defined concepts in mainstream physics, and I believe that part of my job is to help clarify these where needed (though being ill-defined is not always a bad thing, nor something that can in all cases be fixed). In this essay, though, I decided to work with the mainstream perspectives (this is also why I used the reductionist assumption, in spite of finding it problematic myself) --- this was partly for reasons of simplicity and accessibility for a short essay, but also because I wanted a better understanding of them. My aim next (i.e., my current project) is to critique these conditions (particularly their motivations, and consequences for other principles) from a philosophical standpoint.

      Best,

      Karen

      Sorry for the formatting in that post. The small "n"s that appear out of place at the start of some sentences were supposed to be new lines. I don't know why that happened, or how to fix it now!

      Dear Luca,

      Thanks very much for your comments! That's an interesting idea, that a fundamental theory cannot describe interactions. I will have to think about that, but there are simple systems with interactions that can be described without requiring perturbation theory.

      In regards to empirical adequacy, I did not think this to be a condition of fundamentality but a requirement for a theory in order that it be considered scientific at all. And, as I mention at the top of page 8, I take it for granted in the essay that we are considering only scientific theories. This saves me from having to explore the problem of demarcation in science, which is too complicated to discuss in a short essay! As you say, too, the issue of connecting theory with observation is certainly not a straightforward one.

      Best,

      Karen

      Sorry for the formatting in that post. The small "n"s that appear out of place at the start of some sentences were supposed to be new lines. I don't know why that happened, or how to fix it now!

      Sorry for the formatting in that post. The small "n"s that appear out of place at the start of some sentences were supposed to be new lines. I don't know why that happened, or how to fix it now!

      What do you mean "create a universe"? And how would that give us a fundamental theory?

      Dear Paul, Thanks very much! Yes, I agree the idea of naturalness is an interesting one for the reason you mention -- it may be desirable to have a theory that doesn't require fine-tuning, but we can't rule out the possibility that, at the fundamental level, we have a theory that is "unnatural". This is true of several of the requirements, including -- most obviously -- those of unification, and "no weirdness". It's very possible that, fundamentally, the world is described by an unsettling, non-unified theory. And yet, if we arrive at a theory that doesn't fulfil these conditions, then we will keep digging for a more satisfactory one. So, actually, it's possible that we have a final theory and yet continue to search in vain for something more. That's an interesting consequence of the epistemic worry that I hadn't considered, so thanks for that. Best, Karen

      Dear Lawrence B. Crowell, Thanks very much. Your comments touch on several interesting issues. Yes, I wonder about the no weirdness requirement, too, and am still not certain of its inclusion or interpretation. But, the idea generally expressed is that QM is not fundamental, precisely because of its weirdness. Many people (most prominently Penrose) argue that a more fundamental theory is necessary in order to solve these issues, particularly the measurement problem. Quantum gravity, although the moniker suggests otherwise, need not -- and probably, in fact, can not -- be a quantum theory in the usual sense. One reason is because quantum theories utilise space and time, and these are to be modified in quantum gravity. So, another reason why quantum mechanics is supposed to be non-fundamental is because of the expectation of the necessity of QG. If QG contains similar weird features, then this will push people to seek a more-fundamental theory, in turn. But, that said, you are right that QG is likely to be weird! The ideas of a shortest length scale and a shortest time scale are extremely difficult ones -- as is the possibility of formulating a theory that describes a non-spatiotemporal regime. Your suggestion that QG be an EFT valid "close to" this regime, is interesting, too. We would have to think more about the issue of UV completeness in this case. Best, Karen

      Thanks for your reply - I completely agree with what you've said here! Best, Paul

      Dear Karen

      Its nice to read an essay about physics that explores the issues without dragging in mathematics - not that I have anything against mathematics - I trained as one. But I do feel the essay ought to be about words and a pleasure to read and I very much enjoyed reading your essay. I'm glad that you pointed out that QFT = QM relativity as that particular point is not made often enough and it does show that progress has been made in integrating our two most fundamental physical theories. Congratulations on an informative essay!

      Best Wishes

      Mozibur Ullah

        It seems that the site slightly mangles up the formatting of posts by removing linebreaks for some reason.

        Hi Karen,

        I do not think, that a fundamental theory cannot describe interactions. On the contrary. But fundamental concept like mass, spin, momentum etc. are only defined in the free theory. Only if the meaning/definitions of these concepts are given, one can define, what interaction is. For instance force is something, that changes the momentum. I think that was Poincaré's view. Then whether given specific initial conditions, there exist a non perdurbative solution of the equations depends on the symmetry of that configuration. But I do not think that whether such a solution exists or not can be a criteria for a theory to be fundamental. But that might not be, what you intended to say.

        By the way I would be glad, if you could find the time to read and comment on my essay: The quantum sheep - in defense of a positivist view on physics

        Best regards,

        Luca

        Create as in cause to come into being like God is supposed to have done.

        We would have to have a fundamental (most fundamental?) understanding about cause and effect relationships. Model comes first.

        Hi Karen,

        I like very much your formalism for determining whether a theory is fundamental. It is a high gate to jump over. I believe modern physics does not clear it.

        I have a theory of quantum gravity that I believe is easy-peasy. Would you take a look at my theory and see if it clears the gate? I have looked at your credentials and think you can easily "grok" what I propose.

        Visit my essay "The thing that is space-time" and give me your opinion on if it clear the gate. I'm interested in what you really think (or feel)...not looking for mutual admiration :)

        It was refreshing to read a practical approach to fundamentality.

        Thanks,

        Don Limuti

          Hi Karen & Wolfgang,

          It is interesting to consider if physical theories are susceptible to limits in Logic - such as Godel Incompleteness. If physical theories are based upon logic, then they may also be limited as to their ability to provide a complete logical explanation.

          Don

          Dear Karen & Peter,

          How could a TOE, that could not present all levels of scale be considered a TOE? Physics seems to have so constricted it's area of applicability, to this or that level, as to no longer cover what a TOE should.

          A Theory of Everything should be of Everything, no matter the scale or arena of applicability. Physics appears to no longer strive for such a theory - since it would "require some incredible level of computational power."

          Maybe the limitations physics is hitting are not philosophical or experimental, but mathematical. Maybe we do not have the tools needed to cover casual affects that cross between all levels of scale. Maybe this is where further investigation in needed.

          Don