Sorry - small ammendment! On page 4, I refer to M-theory as "the meta-theory in which the five known versions of string theory are seen as distinguished points in eleven-dimensional spacetime". This should read that the five known strings theories, and 11-dimensional supergravity, are points in multi-dimensional moduli space, moduli space being a form of geometric space used to identify equivalent mathematical objects.

Hi Jessica, a very nicely written essay and very easy to read yet containing complex study matter. I was particularly taken with this last comment "Perhaps reality IS easy to visualize". I totally agree and think that I have the visual model for the graviton: Archimedes screw. How did Newton miss that one!?

If a graviton helical screw travelled around a wraparound universe then it would emerge on the other side as a force of repulsion i.e. dark matter. Too much of a coincidence imo, what do you think to this backwards idea Jessica?

    The one problem with LQG, causal sets and dynamic triangulation and the rest is that one assigns degrees of freedom to a spacetime manifold. The dynamics is encoded into space as if space were composed of atoms. This leads to a massive accounting of degrees of freedom with entropy S = nNK/2, for N the number of degrees of freedom. This means the universe has intrinsically huge entropy. This is one reason people can't get LQG to reproduce classical gravity easily, for the classical spacetime has energy or entropy content which is wrong.

    In a sense this seems to me as a problem with ether theories over 100 years ago. People insisted there was a dynamical flow to space itself. This was replace by Einstein and Lorentz by a symmetry. In this setting the degrees of freedom in the system are contained in the particles and systems in spacetime, but not in spacetime itself. Curiously we seem to have a similar trend in physics today.

    Cheers LC

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      Jessica,

      I found your essay beautifully written, you definitely have a 'literary' flair. When I saw the title of your essay, I thought of Jonathan Swift and braced myself for a truly outrageous proposition, but, as it turns out, many other entrants to this contest have proposed ideas that seem somewhat similar.

      In my view, a duality between things that in their essence appear to be incompatible with one another which fails to show the conceptual bridge between them presents an incomplete picture of the relation between those things, and so I cannot accept that, say, the wave-particle duality alone (i.e. without an explanation of how the two incompatible representations 'fit' each other) is a description that reflects our most fundamental understanding of quantum objects. I think that it really is within our grasp to understand what these kinds of dualities really 'mean', in the sense that a deeper reflection ought to reveal that two concepts related by a duality but apparently mutually exclusive are in some definite sense still compatible with one another.

      From this perspective, it seems incumbent upon anyone who proposes such dualities to also explain in what specific sense the two ostensibly incompatible concepts can be understood to be compatible with one another after all. Without this sort of explanation, such propositions run a serious danger of degenerating into a kind of mysticism, in my opinion. Unfortunately, I fail to see much in this regard in the essays that I have read which propose that reality may be both continuous and discrete.

      In the case of your essay, I do have the impression that you were actually too modest to venture into this area, as it (unsurprisingly!) will force the proposer to go out on limb and suggest ideas that are likely to be highly unfamiliar. It is not that difficult (or 'immodest') to point out places in a given theory where one or the other concept may be usefully substituted. It is much, much harder to explain in specific terms how the different conceptions can be understood to be connected to each other as clearly as we understand, say, how the the ear and the trunk of an elephant are connected to each other.

      Anyway, don't let my criticism discourage you, it is was sincerely meant to be constructive. Within the scope of what you set out to do, you did extremely well!

      Take care,

      Armin

        Jessica,

        I don't get a sense that you believe it is one or the other or both, separating yourself from a decision.

        Do you have a preference? I would like to hear it.

        Jim Hoover

          5 days later
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          Jessica,

          I can tell you put a lot of care into this essay. I wish you used a term other than "research programs" in relation to things like string theory. There has been no experiment to prove or disprove string theory, Hawkins radiation or quantum gravity. I know what you mean, there have been great advances in these fields. In a paper like this, that is accessible to non-physicists a small point like this could be confusing.

          Overall, this a very good essay.

          Jeff

            Jessica

            I enjoyed your analysis and modest proposal, definitely worth more than a modest score. Lawrence had a good point about degrees of freedom, but I'm struggling to find anything wrong with an even more modest proposal, that there are simply multiple manifolds. This allows covergence of the quantised mechanism as Newton discovered in our current community leaders essay.

            I put this through thorough if naive empirical falsfication in my own essay, (2020 vision, a model of discretion..) which I do hope you'll find time to read and comment on. It suggests a slightly different 3rd way, between an absolute ether and zero field, with the attributes of both, and seems to produce all the results of SR and GR without patches or paradoxes. It's far to simple to believe, but has only yet been faulted on beliif grounds - so also needs some some scientific ones'

            I'd really love to hear your views.

            best wishes.

            Peter

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            Thank you, everyone, for your kind and helpful comments!

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            True, that IS an interesting coincidence. What do you think might be the implications for the relative 'amounts' (strength might be a better word) of gravity and dark energy in such a wraparound universe?

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            I am not sure what you mean by 'degrees of freedom'. Are you referring to background independence? Sorry if I have misunderstood!

            • [deleted]

            Thank you :-) Yes, I did steal my title from Swift, and also did not go so far out on a limb as he did!

            I would, indeed, have liked to have suggested a more concrete picture of the dualities I was describing. To be honest, I was not sure myself of precisely the form such a duality would take. Possibly this is a lack of knowledge on my part - I look forward to exploring such ideas more in future. Do you have any thoughts on the matter?

            • [deleted]

            I confess to being a bit of a fence-sitter: as yet, I can't see that there is any clear 'winner' between analog and digital realities, nor do I necessarily think that a dualistic approach will turn out to be completely correct. What I was suggesting was more a third line of inquiry - the answer may be in any one of the three camps, or neither, but restricting the debate to two camps only seems to be ignoring some interesting material.

            • [deleted]

            Thank you! I know - I wasn't completely happy with the phrase, either, but couldn't think of an adequate alternative. 'Theory' didn't quite fit... What would you have used, that might be clearer in future?

            • [deleted]

            In slicing and dicing up spacetime there are fields or connection terms assigned to the edgelinks. These are degrees of freedom. This means any two-chain has a curvature 2-form associated with it. Summing all of this up means there is a huge amount of entropy per volume. For this reason LQG people are not able to recover a classical gravitational limit.

            With string theory the counting of degrees is on boundaries of relevant spacetimes. This reduces the entropy enormously and so black hole quantum field theory can be computed.

            The background indpendence is the one strong card the LQG folks have in their hand. However, there is something terribly wrong with the basic approach. It is similar to ether theories, where space was thought to be filled with some sort of "gas." From a stat-mech perspective that is like putting many degrees of freedom into the problem.

            Cheers LC

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            Jessica,

            I would say that these models seem to explain the data, but can not be tested at this time.

            Jeff

            11 days later
            • [deleted]

            Hello Jessica, and a belated congratulatory note on your excellent essay. Hard to keep up with all that is going on with this contest!

            I want to share with you an astounding result that just days ago I posted on the web. I think it may help you with your fence-sitting. Two fundamental assumptions made by Einstein more than 100 years ago were the constant speed of light (CSL) that lead to Special Relativity and the Photon Hypothesis (PH) that eventually lead to QM. In my short paper I mathematically prove that CSL contradicts PH! More specifically, I prove the following proposition:

            "If the speed of light is constant, then light is a wave".

            It is an easy read! If you have the time, check it along with my essay and comment if you are so inclined. And if you find these results worthy of your support, I ask that you help me put the essay before the panel of experts for review.

            Best wishes,

            Constantinos