Thanks! Your topic looks interesting.

Good luck in the competition!

Sean.

Dear Wilhelmus,

Apologies for the delay in my response. You are very right: I've been hiking through the Alps over the last couple of days and haven't had email access. Also, before that I was extremely busy with two very intense conferences. It is a bad idea to schedule an essay contest in the middle of the summer: it is the height of holiday and conference season!!

In regards to your questions, I am very happy that you were able to read through the essay carefully and gets some ideas for your own thoughts about the world. You're right that many of these mathematical structures are just conventions. In the end, they are only useful if they can be used to model real-world experiments. I will admit that the model Universe that I give here is very idealized. But, I still think it could be interesting to give us some clues as to what our real Universe might be doing. The spheres are meant to stay spheres in the infinite future but this is somewhat of an idealization too.

I am really enjoying my time in Holland. It is a very nice country!

All the best,

Sean.

Dear Vladimir,

Thank you for the nice comments about the essay.

I think you are right that scale invariance seems to be in conflict with Loop Quantum Gravity and other lattice approaches to quantization.

All the best,

Sean.

Dear Ralph,

Thank you for these very flattering remarks. I am really happy that you were able to take something useful out of the essay. You are too kind.

All the best,

Sean.

Best of luck in the competition. I will try to take a look at your essay.

Sean.

Dear Leo,

Thank you for these thoughtful comments.

I will have to look into this in more detail before making a definite opinion of how my work might relate to yours.

Best of luck in the competition!

Sean.

Dear Unnikrishnan,

Thanks for the question.

The relation is between space and time and information. Since space and time provide the fundamental arena in which relationships between matter can be described, the essay addresses whether it's possible for matter to be fundamentally describable solely through information. My suggestion is 'no', because the standard arguments for the discretization of spacetime can be replaced by fundamental scale invariance. I thus don't find the arguments that matter can be described primarily by information particularly compelling.

All the best,

Sean.

Dear Tom,

Thanks for your nice comments on the essay. I will definitely try to have a look (very soon) at your essay.

Regarding Rovelli, I'm not sure I immediately see why QFT degrees of freedom are discrete or what it means for them to be static. After all, things DO HAPPEN in QCD, which seems to me to indicate some sort of notion of dynamics. On the other hand, I do agree that 't Hooft's conformal gravity stuff is very interesting and promising. I'm not too familiar with Corda.

All the best,

Sean.

Dear Adel,

It is certainly true in shape dynamics that only ratios of coupling constants have empirical meaning. However, it's not clear to me how much your ideas could be related to shape dynamics.

Best of luck in the competition!

Sean.

Sean,

Good to see another fine submission from you! I didn't have time to participate in the present contest, but I enjoyed your essay. Good luck with the contest, and take care,

Ben

    Thanks, Sean. I won't pretend to speak for Carlo Rovelli, though I think I do understand what he means by degrees of freedom in an n-particle state space (I would say n-dimension state space and use the Hilbert space) where things happen discontinuously because the field assumes t = 1 and time coordinates are therefore constant (static).

    In a continuous spacetime field, time changes with space -- dynamically, as you say. So I think what Carlo is saying, is that because a continuum theory such as shape dynamics cannot associate a definite dimensionless integer to a point of the space evolving in time, it is just as, if not more, meaningful to speak of the algebraic (Fock space) degrees of freedom as to speak of finite degrees of freedom in your continuously evolving system -- because the two descriptions, absent a simple time parameter of reversible trajectory, are equivalent.

    Personally, I don't agree with Carlo, though I understand the Fock space construction. At the end of the day, I think that if shape dynamics is mathematically complete, it allows relative degrees of freedom; i.e., time reversibility that guarantees conservation of information. That's what the 't Hooft and Corda references are all about.

    All best,

    Tom

    hmmm... I'm still not sure I understand what you're getting at. Of course, there is nothing wrong with having a Fock space in Shape Dynamics, but that doesn't mean that the degrees of freedom are discrete: the number of particles can be an integer but their energy spectrum can still be continuous. Just think of a scattering experiment. Perhaps there is something I am missing.

    Cheers,

    Sean.

    Thanks Ben!

    Hope things are well with you!

    Sean.

    Thanks Sean. I know it's extremely late, but even if you don't get a chance to look at it before the deadline I would appreciate you reviewing it at some point in the future. You seem to have an open mind, so I would value your thoughts.

    Best of luck to you in the finals.

    Ralph

    Hi Sean,

    It's just the difference between algebra and analysis. If one speaks of a continuous energy spectrum, there's no point in the spectrum at which any element (any measured state at any instant) is discontinuous from the line. If one speaks of a state of particle interactions ("state" means "static") all degrees of freedom are discontinuous from the line, thus discrete.

    The distinction is nontrivial, because finite degrees of freedom define particle states and predict an historical path (Feynman path integral). The ensemble transformation of a continuous measurement function such as you describe results, as you say, in the absence of fundamental discreteness -- so I think what Carlo is asking, is how can anything that is not fundamentally discrete be countable? One would apparently have to either eliminate the measurement function (and thus eliminate the physics), or allow that countable bits of spacetime are already described by evolution of the state vector in standard quantum theory.

    I'm on your side of the question, with a caveat: one must choose which element of continuous spacetime -- time or space -- is finite. General relativity conventionally chooses time (the universe has a finite beginning and a finite end). If one chooses space, which surely shape dynamics does, infinite varieties of time-dependent shapes of a finite space potentially describe a universally entangled wavefunction of continuous measurement values, without assuming discrete particles with discrete degrees of freedom.

    All best,

    Tom

    Dear Sean Gryb:

    I am an old physician, and I don't know nothing of mathematics and almost nothing of physics, but after the common people your discipline is the one that uses more the so called "time" than any other.

    I am sending you a practical summary, so you can easy decide if you read or not my essay "The deep nature of reality".

    I am convince you would be interested in reading it. ( most people don't understand it, and is not just because of my bad English). Hawking, "A brief history of time" where he said , "Which is the nature of time?" yes he don't know what time is, and also continue saying............Some day this answer could seem to us "obvious", as much than that the earth rotate around the sun....." In fact the answer is "obvious", but how he could say that, if he didn't know what's time? In fact he is predicting that is going to be an answer, and that this one will be "obvious", I think that with this adjective, he is implying: simple and easy to understand. Maybe he felt it and couldn't explain it with words. We have anthropologic proves that man measure "time" since more than 30.000 years ago, much, much later came science, mathematics and physics that learn to measure "time" from primitive men, adopted the idea and the systems of measurement, but also acquired the incognita of the experimental "time" meaning. Out of common use physics is the science that needs and use more the measurement of what everybody calls "time" and the discipline came to believe it as their own. I always said that to understand the "time" experimental meaning there is not need to know mathematics or physics, as the "time" creators and users didn't. Instead of my opinion I would give Einstein's "Ideas and Opinions" pg. 354 "Space, time, and event, are free creations of human intelligence, tools of thought" he use to call them pre-scientific concepts from which mankind forgot its meanings, he never wrote a whole page about "time" he also use to evade the use of the word, in general relativity when he refer how gravitational force and speed affect "time", he does not use the word "time" instead he would say, speed and gravitational force slows clock movement or "motion", instead of saying that slows "time". FQXi member Andreas Albrecht said that. When asked the question, "What is time?", Einstein gave a pragmatic response: "Time," he said, "is what clocks measure and nothing more." He knew that "time" was a man creation, but he didn't know what man is measuring with the clock.

    I insist, that for "measuring motion" we should always and only use a unique: "constant" or "uniform" "motion" to measure "no constant motions" "which integrates and form part of every change and transformation in every physical thing. Why? because is the only kind of "motion" whose characteristics allow it, to be divided in equal parts as Egyptians and Sumerians did it, giving born to "motion fractions", which I call "motion units" as hours, minutes and seconds. "Motion" which is the real thing, was always hide behind time, and covert by its shadow, it was hide in front everybody eyes, during at least two millenniums at hand of almost everybody. Which is the difference in physics between using the so-called time or using "motion"?, time just has been used to measure the "duration" of different phenomena, why only for that? Because it was impossible for physicists to relate a mysterious time with the rest of the physical elements of known characteristics, without knowing what time is and which its physical characteristics were. On the other hand "motion" is not something mysterious, it is a quality or physical property of all things, and can be related with all of them, this is a huge difference especially for theoretical physics I believe. I as a physician with this find I was able to do quite a few things. I imagine a physicist with this can make marvelous things.

    With my best whishes

    Héctor

    Write a Reply...