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Ken Seto: on 5/17/13 at 3:23am UTC, wrote Dear Sean and Flavio, If we accept the existence of absolute time and that...

Georgina Parry: on 11/25/12 at 3:07am UTC, wrote Dear Zbigniew, It may interest you to know that I have addressed this...

Zbigniew Modrzejewski: on 11/24/12 at 20:52pm UTC, wrote Hello! Ultimately, physics is all in the eyes of the beholder. This...

Sean Gryb: on 10/5/12 at 16:34pm UTC, wrote Hi Olaf, Thanks for the detailed questions! I'll try to respond in order. ...

Olaf Dreyer: on 10/5/12 at 16:18pm UTC, wrote I finally managed to read your essay. It is a very nice read. I have a...

Frank Martin DiMeglio: on 10/5/12 at 2:55am UTC, wrote Sean, you will need to consider the following. Time is dependent upon the...

Sean Gryb: on 10/4/12 at 10:01am UTC, wrote Thanks for the heads up. There are definitely better systems.

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To build the ultimate artificial mimics of real life systems, we may need to use quantum memory.

September 24, 2017

CATEGORY: Questioning the Foundations Essay Contest (2012) [back]
TOPIC: Right About Time? by Sean Gryb and Flavio Mercati [refresh]
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Author Sean Gryb wrote on Sep. 4, 2012 @ 12:08 GMT
Essay Abstract

Have our fundamental theories got time right? Does size really matter? Or is physics all in the eyes of the beholder? In this essay, we question the origin of time and scale by reevaluating the nature of measurement. We then argue for a radical scenario, supported by a suggestive calculation, where the flow of time is inseparable from the measurement process. Our scenario breaks the bond of time and space and builds a new one: the marriage of time and scale.

Author Bio

Sean Gryb worked on his PhD at the Perimeter Institute and is now enjoying a postdoc at Utrecht University. Flavio Mercati received his PhD from the University of Rome "Sapienza" and is currently starting a postdoc at the Perimeter Institute. Both are working on developing Shape Dynamics and are generally interested in the foundations and experimental tests of quantum gravity.

Download Essay PDF File

DANIEL WAGNER FONTELES ALVES wrote on Sep. 4, 2012 @ 18:37 GMT
Dear Sean and Flavio

First of all, congratulations. You have written a very clear essay, and I´m deeply impressed by your proposals. The definition of entropy in shape space is very compelling and the derivation of the entropy formula is fantastic. It will be very interesting to investigate in full details your idea of linking measurement and time.

Flavio, you may remind of me, I´m the brazilian student that visited Julian Barbour earlier this year in college farm.

The most interesting aspect of your idea is that it all comes from questioning few very natural assumptions. A (close minded) string theorist could argue that our world is simply too bizarre for mundane conceptual questioning like asking what is space, time and motion, and would look solely for ''mathematical hints'' for building a theory of QG. But upon these first questions, one may choose to build physics on shape space and once this happens the whole mathematical structure, and consequently, the whole theory is changed. As a result, you may get new path to quantum gravity by changing its concepts, or ''building blocks'' at the classical limit.

It is then evident how different conceptions of motion at the classical level may lead to new physics. I feel shape space is a more natural arena for building physics then the traditional configuration space.

In my essay Absolute or Relative Motion... or Something Else? I propose the following question: how can we conceptually conceive motion? I argue that Machian´s philosophy (which leads to Barbour´s relational physics) may be part of something bigger and give hints on how to take these questions foward. You may find it interesting.

Good luck in the contest, and once again, congratulations for one of the best essays I´ve read so far.


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Author Sean Gryb replied on Sep. 5, 2012 @ 12:24 GMT
Dear Daniel,

Thanks for your enthusiastic comments. I am happy to see other young people interested in these foundational issues. I certainly agree with the relative merits of Shape Space. The real question is: what new physics can we hope to see and what could shape dynamics teach us about the quantum theory?

I will take a look at your essay, which seems very interesting. I hope to see you some time soon!


Pentcho Valev wrote on Sep. 4, 2012 @ 19:48 GMT
Sean, Flavio,

You wrote: " is still true that the spacetime framework is incredibly useful and, as far as we know, correct."

Incredibly useful for what? If you mean the destruction of human rationality - yes, I agree:

Brian Greene: "Now, however, modern physics' notion of time is...

view entire post

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Author Sean Gryb replied on Sep. 5, 2012 @ 12:38 GMT
Dear Pentcho,

I take your point that there are aspects of the spacetime picture that appear to be at odds with our experience of reality. The purpose of this statement was to make the simple observation that the predictions of the spacetime picture are extremely well tested and cannot be ignored, even if the spacetime picture turns out to be problematic. Any alternative way of viewing reality must reproduce these observed phenomena. Shape Dynamics achieves this and so do other approaches either exactly or in some limit (like Horava gravity, for instance).


Pentcho Valev replied on Sep. 5, 2012 @ 13:27 GMT
Minkowski spacetime (more precisely, special relativity) implies that an arbitrarily long object can be trapped inside an arbitrarily short container, and that the bug from the bug-rivet paradox can be both dead (according to one observer) and alive (according to another). Does Shape Dynamics reproduce these predictions?

view entire post

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Author Sean Gryb replied on Sep. 5, 2012 @ 18:50 GMT
For the same initial data, Shape Dynamics will make the same predictions as general relativity (there are some technical caveats that might be interesting for black holes but, more or less, this is true). The situation you are talking about is in special relativity where there are no accelerations and where one has rigid rods and clocks. I don't know what Shape Dynamics would look like with these unnatural assumptions so I can't answer your question directly.


Jayakar Johnson Joseph wrote on Sep. 5, 2012 @ 01:44 GMT
Dear Sean Gryb,

As time is within a dynamic system, it emerges with dynamics, in that the measurement process is spontaneous. Thus in a Coherently-cyclic cluster-matter universe model, time emerges with the eigen-rotations of strings, in that a cyclic time of universe is expressional.

With best wishes,


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Member George F. R. Ellis wrote on Sep. 5, 2012 @ 05:57 GMT
Dear Sean and Flavio

a very interesting essay. I applaud your emphasis on coarse graining, a key process in understanding how physics works in practice, as well as on the measurement problem and the limitations of theories of the universe as a whole. I also agree on the central importance of conformal degrees of freedom for gravity.

However I don't get one thing. You say time can come from coarse graining. Now I agree that time and measurement are inseparable, provided one means by "measurement" any interaction with a well-defined outcome. But I could not see in sections 3.2 and 4, where time actually emerged. You derive expressions for entropy but never for time.

Please can you clarify where/how time emerges?


George Ellis

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Author Sean Gryb replied on Sep. 5, 2012 @ 13:21 GMT
Dear Prof. Ellis,

Thank you for your comments. I am glad for your interest in these ideas.

Your question is fair and I wish I could provide a more concrete answer. We are currently investigating the details of our proposal, which is still very much open for discussion (an important reason for writing the essay). Nevertheless, the text, in hindsight, is a bit vague on this issue and I...

view entire post

Author Sean Gryb replied on Sep. 6, 2012 @ 11:08 GMT
After a night's sleep, I realize that there is a simpler way to answer your question. Time emerges through the following sequence of steps.

1. Start with a theory with no time and no scale.

2. Allow for measurements with finite precision.

3. The coarse graining of these measurements breaks scale invariance.

4. The emergent scale defines a natural preferred clock in the system.

5. Time evolution emerges in terms of this preferred clock.

We think that it is possible that the time evolution we will get from this procedure will match that of the SD Hamiltonian. This, of course, would be highly non-trivial but we think that principles like universality and locality will come to our rescue.

Hope this is a better answer!


ps. Steps 2 and 3 are necessary because of the expected Weyl anomaly.

Pentcho Valev wrote on Sep. 5, 2012 @ 22:27 GMT

You wrote: "The situation you are talking about is in special relativity where there are no accelerations and where one has rigid rods and clocks. I don't know what Shape Dynamics would look like with these unnatural assumptions so I can't answer your question directly."

Is Shape Dynamics incompatible with special relativity? Can you derive time dilation and length contraction in Shape Dynamics? Does the travelling twin return younger according to Shape Dynamics?

Pentcho Valev

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Author Sean Gryb replied on Sep. 6, 2012 @ 10:54 GMT
This is, of course, an important question and the final answer is basically 'yes'. The complete answer has a lot of technical and interpretational caveats that would require a full paper to properly explain. I haven't written such a paper yet but it is on my list. What I can do is give you a short answer and explain why the full answer is tricky.

The simple answer is that Shape Dynamics...

view entire post

Pentcho Valev replied on Sep. 6, 2012 @ 14:25 GMT

You wrote: "Minkowski space is a solution to SD, but only in a preferred reference frame. Thus, all the physical predictions of special relativity - like the younger travelling twin and the fact that certain muons created in the upper atmosphere don't decay until they hit the surface of the earth - are reproduced."

Sounds confusing. Please elaborate. How is the younger...

view entire post

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Author Sean Gryb replied on Sep. 6, 2012 @ 15:11 GMT
In the same way that modern either theories can reproduce the results of the travelling twin experiment. In SD, there is one frame where physics is scale invariant. That frame behaves much like an either.

Yuri Danoyan wrote on Sep. 6, 2012 @ 13:00 GMT

Quote from your essay "i) time and space should be treated on the

same footing, ..."

My questions is next.

I don't like 4-D space-time. I will try to explain .... Why are you went to bed, a night for all spatial scales changed in ten time.You are notice anything? Absolutely sure that no, but now the usual time period when you sleep, increase or decrease by 10 times. Did you notice this?

The same footing?

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Author Sean Gryb replied on Sep. 6, 2012 @ 15:00 GMT
I'm sorry I don't understand your question.

However, the quote you gave is preceded by "We have questioned the basic assumptions that:" which means we are doubting whether this is true! The reasons are section 2.1 of our essay.



Yuri Danoyan replied on Sep. 6, 2012 @ 18:32 GMT

It turns out we are allies in this matter

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Author Sean Gryb replied on Sep. 6, 2012 @ 18:36 GMT
It seems we are, though our motivations are different.

Pentcho Valev wrote on Sep. 6, 2012 @ 16:23 GMT
Sean: "In SD, there is one frame where physics is scale invariant. That frame behaves much like an either."

Clever etherists know that, in a frame moving relative to the ether, the speed of light is variable:

The Mystery of the Einstein-Poincaré Connection, Olivier Darrigol: "It is clear from the context that Poincaré meant here to apply...

view entire post

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Author Sean Gryb replied on Sep. 6, 2012 @ 18:02 GMT
The results of the Michelson-Morley experiment are no different in SD then they are in GR. That's all that matters. Any words one would like to use to describe this prediction are nothing but a rose with another name!

Pentcho Valev replied on Sep. 6, 2012 @ 19:22 GMT
Originally the Michelson-Morley experiment confirmed Newton's emission theory of light:

Relativity and Its Roots, Banesh Hoffmann: "Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone...

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John Merryman wrote on Sep. 7, 2012 @ 10:42 GMT

I think the traditional emphasis on measurement only compounds the confusion about time. We perceive time as a series of events and measurement only re-enforces this perception, but physics is supposed to be about understanding the underlaying dynamic processes, not just how to model them. It is not that reality consists of a four dimensional geometry in which all events are somehow...

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Jeff Baugher wrote on Sep. 10, 2012 @ 15:49 GMT
Sean and Flavio,

Interesting essay.

"Consider a world with no scale and no time. In this world, only 3 dimensional Platonic shapes exist. This kind of world has a technical name, it is a fixed point of renormalization {"fixed" because such a world does not flow since the renormalization scale is meaningless. This cannot yet be our world because nothing happens in this world. Now, allow for something to happen and call this "something" a measurement. One thing we know about measurements is that they can never be perfect. We can only compare the smallest objects of our device to larger objects and coarse grain the rest. Try as we may, we can never fully resolve the Platonic shapes of the fi xed point. Thus, coarse graining by real measurements produces ow away from the xed point."

This quote makes me think of the cosmological constant as the fixed point of renormalization and the accompanying dynamic stress energy tensor as your measurement. As Eddington stated:

"matter does not cause the curvature of space-time. It is the curvature"

I look forward to reading more in depth. We may have quite a bit in common.



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Author Sean Gryb replied on Sep. 10, 2012 @ 17:30 GMT
I agree with your intuition about the importance of the cosmological constant at the fixed point. As the universe continues to expand, the cosmological constant starts to dominate the dynamics of the universe. In our scenario, the infinite future corresponds to the fixed point. This means that the cosmological constant dominates the behaviour of the system near the fixed point. We've investigated some of this in: ,

where we compare some results of shape dynamics with some well known results from AdS/CFT (we will be updating this paper shortly). As we point out in the paper, there are similarities between the cosmological constant and the trace anomaly in the CFT (i.e., the expectation value of the trace of the energy momentum tensor of the CFT). However, I'm not sure if this is related to your comments about the energy momentum tensor.

Jeff Baugher replied on Sep. 10, 2012 @ 19:53 GMT
Yes it is related but I would be some ways from being able to give you a comparison of a reinterpretation of the EFE (my essay) into shape theory, but it is very closely related to AdS/CFT. There are some concepts in your paper and essay that may be helpful to me.

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Author Sean Gryb replied on Sep. 10, 2012 @ 20:02 GMT
Hopefully! When the volume of space is large, there is not much difference between the SD Hamiltonian and the GR Hamiltonian (they converge to the same thing). That might help. Glad to hear your interested in these ideas.


ps. I don't know why the last post came up as "anonymous"... I should have been logged in. Sorry about that.

Jeffrey Michael Schmitz wrote on Sep. 11, 2012 @ 01:31 GMT
I would like you to read my essay "Billy Pilgrim Blues". I cover the same issues as your essay, but in a very different way. Please honestly tell me what you think.

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Author Sean Gryb replied on Sep. 11, 2012 @ 09:45 GMT
You're right that we are tackling similar issues from a very different perspective.

In our proposal, there might be a way to relate time, as a renormalization group flow time, to a measure of complexity. This could indeed be a kind of entropy of configurations. However, I believe this is quite different from the kind of relationship you are suggesting.

I don't agree with your statement that "entropy is needed to define time". Your pendulum example is misleading because clocks don't have to be cyclic. In Julian Barbour 2009 essay: The nature of time, he describes a relational notion of time that is perfectly well defined without a notion of entropy. This is what astronomers use to define time. So I don't understand your argument.



Jeffrey Michael Schmitz replied on Sep. 11, 2012 @ 20:31 GMT

Thank you for your comments and taking the time to read my essay.

Clocks do not have to be cyclic. I used the example of a perfect cyclic timepiece to isolate time from all other factors. The Earth spins on its axis and the stars move in relationship to each other, but the Earth is different each day and the stars burn a little of their store of hydrogen each momentum. Entropy is very much a part of Astronomy. At the quantum scale, when enthopy change is harder to come by, postion relationships between indivual particles are uncertain. Please show me a way to mark time that does not change enthopy.

All the best,


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Author Sean Gryb replied on Sep. 11, 2012 @ 23:23 GMT
You need to define entropy more precisely. In particular, if you're talking about thermodynamic entropy then this is not even defined for systems outside of thermodynamics equilibrium. Surely you are not suggesting that time is not defined for systems (such as the sun and humans) far from equilibrium?

Michael Popov wrote on Sep. 12, 2012 @ 13:58 GMT
Dear Sean,

I'd like to remark only that

1. Einstein the physicist was agree to simplify mathematics, in particular, he used the 3-dimensional simplified version of the Pythagorean theorem in the form x2 + y2 + z2 = t2 ( i.e in a rectanglular box, the square of the space diagonal is equal to the sum of squares of the three sides ). Purely mathematically, however, it is not correct,...

view entire post

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Eckard Blumschein wrote on Sep. 12, 2012 @ 14:58 GMT
Dear Sean Gryb,

"an experiment by Michelson and Morley ... measured the speed of light to be

independent of how an observer was moving". Isn't the speed of a wave in general independent of how its source as well as its many possible observers are moving?


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Author Sean Gryb replied on Sep. 12, 2012 @ 16:14 GMT
Sounds waves don't have this property. Their speed measured by some observer depends on the speed of the source and the observer relative to the medium of propagation (like the air).

Pentcho Valev replied on Sep. 12, 2012 @ 16:58 GMT

You wrote: "Sounds waves don't have this property. Their speed measured by some observer depends on the speed of the source..."

Are you sure? An undergraduate would fail the exam for this.

Pentcho Valev

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Eckard Blumschein replied on Sep. 12, 2012 @ 17:11 GMT
They definitely have. The speed of sound in air refers to the medium air and has a constant value c that is determined by the medium: about 330 m/s dependent on temperature, humidity, etc. but NOT by the observer.

There is no acceptable reason why this should not hold for electromagnetic waves including light too. There was such reason, and indeed it led first to FitzGerald's and Lorentz's...

view entire post

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Peter Jackson wrote on Sep. 12, 2012 @ 16:59 GMT
Sean & Flavio

Speed of sound depends on speed of source!? I've just picked myself up off the floor, and am still wondering if you're serious! Sure the detected absorbed wavelength thus the frequency depends on the source speed.

I agree there is also a case of course where the observer/detector is in the same frame as the source, and the speed is calculated by using coordinated clocks, but in this case we have to ask speed wrt what, so we need a background frame, and then the calculated speed would be inverse to the source speed (with no Doppler shift on detection. I struggle to think you considered this case as, simply, nobody does. Can you explain?

Nicely written and argued essay all round with some interesting views. Well done for getting to the top, hold on for the sleigh ride!

I agree with your point that; "The measurement problem results from the fact that quantum mechanics is a framework more like statistical physics than classical mechanics." And have offered a solution to this via a mechanism in my own essay, which I hope you will read.

I look forward to your comments.

Best wishes


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Flavio Mercati replied on Sep. 12, 2012 @ 19:29 GMT
Sean meant that "the speed of soundwaves depends on the speed of the observer relative to the medium of propagation".

"source" was a slip of course.

I'm reading your essay with interest...

All the best,


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Pentcho Valev replied on Sep. 12, 2012 @ 19:45 GMT
The speed of the sound/light waves, relative to the observer, varies with the speed of the observer, doesn't it? Is Sidney Redner right?

Professor Sidney Redner: "The Doppler effect is the shift in frequency of a wave that occurs when the wave source, or the detector of the wave, is moving. Applications of the...

view entire post

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Peter Jackson replied on Sep. 12, 2012 @ 20:11 GMT

Correct but incomplete. Like saying; 'music is the variation in sound made by instruments'. It misses the critical mechanism of 'HOW'.

My post below of 20.01 was in answer to Flavio's message above. The fluctuation must have crossed the media boundary (refractive plane) and be propagating within the detector medium BEFORE it reaches any brain cells or sensors.

Old assumption, including Einstein's, was, let's say; 'incomplete'. You might well of course equally say 'wrong'.


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Peter Jackson wrote on Sep. 12, 2012 @ 20:01 GMT
Sean, Flavio,

It may be a very moot point wrt light as well, as you're hopefully finding in my essay.

As the source of sound is NOT also the detector the only way to get a relative speed is by calculation, of c over the flight distance.

Of course it's exactly the same with light when calculated with that same data. That's where the paradox is, because that gives c + v, yet...

view entire post

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Author Sean Gryb wrote on Sep. 12, 2012 @ 21:42 GMT
Let me respond to the many previous responses concerning the interpretation of the Michelson-Morley experiment.

I do not think it is correct to say that one interpretation is "right" or "wrong". An interpretation is an just an interpretation after all. Instead, I think it is more constructive to think of an interpretation as being "useful" or "not useful".

Einstein's interpretation was incredibly useful because it made definite new predictions, like the equivalence of mass and energy (E=mc^2), and because it led to a deeper theory: general relativity, which has been wildly successful.

It is perfectly valid to question the usefulness of a particular interpretation. That is what we are doing with Shape Dynamics and it is part of a healthy scientific discussion. However, for a new interpretation to be useful it must pass the same test as Einstein's: it must make novel predictions and it should lead to a deeper understanding. This is the challenge for Shape Dynamics and it is also the challenge for any alternative view: show how new predictions and a deeper theory could emerge from your interpretation. That is the ultimate goal of physics.



Eckard Blumschein replied on Sep. 12, 2012 @ 23:12 GMT

Einstein did not interpret the MMX. Allegedly he even denied knowing it.

Almost all physicists of that time including Hertz and Einstein accepted the as now turns out wrong conclusions from the unexpected outcome of MMX.

Whether or not the MMX disproved the aether wind is definitely not a question of interpretation but it can now clearly be decided as either a correct or a wrong conclusion.

Of course, FitzGerald and Lorentz fabricated speculative interpretations of the seeming fact in order to rescue the seemingly disproved aether hypothesis. Einstein built on these ideas his theory of SR. He incorporated length contraction and time dilution into it. Were they ever objectively measured and shown not just to be illusions explainable as Doppler effect?

I do not feel obliged to reiterate the detailed objections by opponents who questioned the ascription to SR of the many claimed predictions and confirming experiments. Some of them were already admitted in the textbook by David Bohm.

I am not the only one who considers in particular Einstein's method of (de-)synchronization and his block universe unreal and obviously flawed. I tend to at best apply the judgment by Ebbinghaus on Georg Cantor on Einstein too.

Even if you are firmly believing in Einstein's SR you might feel challenged to find an alternative explanation for my Fig. 5.



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Author Sean Gryb replied on Sep. 12, 2012 @ 23:49 GMT
I do not firmly believe in Einstein's SR but I find it extremely useful for solving a wide variety of practical problems and for providing a special limit to an even more useful theory: general relativity. If you have ever used a GPS you have benefited from special and general relativity. Would you discard this remarkable device as readily as the theoretical framework that led to its development?

I would if I had a framework that led to the development of even more remarkable devices. That is what I am looking for (although I will likely fail) and that would be my challenge to anyone who questions the physical assumptions of our fundamental theories.

Eckard Blumschein replied on Sep. 13, 2012 @ 21:51 GMT
"If you have ever used a GPS you have benefited from special and general relativity." Really?

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Member Benjamin F. Dribus wrote on Sep. 13, 2012 @ 18:45 GMT
Dear Sean and Flavio,

Interesting and well-written essay. One quick question: What exactly are the elements of the shape space of your model? Special types of 3-manifolds, I presume? Thanks,

Ben Dribus

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Flavio Mercati replied on Sep. 13, 2012 @ 19:49 GMT
Dear Ben,

first of all thanks for the interest in what we wrote!

To answer your question, points of shape space are "conformal 3-geometries" or "conformal 3-manifolds", that is 3-geometries (which are described by 3-metrics modulo 3-diffeomorphisms), modulo local conformal transformations. A conformal transformation preserves only angles but not

vector's lengths, so you can describe a conformal 3-geometry with just the angle-determining

part of a 3-metric. There is quite some mathematical literature on them:

In our next paper (it's coming soon on the arXiv, stay tuned...) Sean and I found how to describe shape dynamics in the simplified case of 2 spatial dimensions with a Cartan geometry in which

the structure group is the conformal group. You have then a description of the gravitational field

in terms of "conformal frame fields", which are useful for several reasons (in GR it's easier and somewhat more natural to couple fermions to frame fields, and they provide the best known reformulation of GR as a gauge theory). Written in this way, shape dynamics looks like a Chern-Simons theory of the conformal group.

Something about Cartan geometry can be found here:



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Flavio replied on Sep. 13, 2012 @ 22:06 GMT
Btw Ben,

I've seen your essay: interesting!

Are you familiar with Rafael Sorkin's causal sets?



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Member Benjamin F. Dribus replied on Sep. 15, 2012 @ 04:07 GMT

Thanks for the detailed response! You might have seen on my bio that I work in algebraic geometry, and the connection to characteristic classes is very intriguing. To be honest, I had never heard of shape dynamics until I read Julian Barbour's essay a week or two ago, but I will be sure to learn more about it now that I've been introduced.

I have read Sorkin, and indeed reference him in my essay. I don't feel that I can entirely agree with the axioms of the causal sets approach, but I'm fairly new to that as well. My approach is indeed similar, however.

By the way, there was another essay here about desingularization by Abhijnan Rej that has a lot of interesting geometry in it. He proposes using cycles/motives etc. Take care,

Ben Dribus

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Avtar Singh wrote on Sep. 14, 2012 @ 21:52 GMT
Dear Sean & Flavio:

I enjoyed reading your well-written and intuitive essay describing the challenges in the fundamental understanding of time. You rightly point out to the two major problems that constitute the unexplained 96% of the universe – “….(dark energy) the accelerated expansion of the Universe, which is some 120 orders of magnitude smaller than its natural value…..and the...

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Member Benjamin F. Dribus wrote on Sep. 18, 2012 @ 17:24 GMT
Dear Sean/Flavio,

Do mind telling me an email address or sending me an email at I notice you don't have addresses listed on the paper. Thanks,

Ben Dribus

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Lawrence B. Crowell wrote on Sep. 22, 2012 @ 14:43 GMT
Sean and Flavio,

I found your essay to be interesting. It takes me a while to digest the more interesting and solid works here, so it has taken me a bit of time to get to your paper. You make a number of very interesting points. I can only this morning discuss a few of these. I will try to follow up later today or tomorrow.

The relationship between shape dynamics (SD) and the...

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Author Sean Gryb replied on Sep. 24, 2012 @ 17:20 GMT
Thanks Lawrence for the detailed reply.

You point out many things that may have connections with Shape Dynamics. I am not an expert on twistors but I have heard the suggestion that they could be linked to Shape Dynamics before. One possibility way to make this more concrete is to explore the symmetry groups of the local homogeneous spaces used to model geometry in SD vs GR. In GR, the relevant group is the Poincare group ISO(3,1) but in SD we have spatial conformal symmetry so the relevant group is the conformal group in 3d, which is Conf(3) = SO(4,1). Our recent preprint ( shows that SD, in 2+1 dim, can be understood as a gauge theory of Conf(2). It might be that one can use the relation with the conformal group to make a connection with twistors. It's an option I'd like to explore a bit more.

Also, I definitely agree that the toy model we present could be relevant to Verlinde's paper. Actually, the calculation was motivated by his paper. We wanted to ask ourselves: is shape space holographic? and could this property be used to derive gravity? It seems like that may be the case but it is still pretty early in the game and our toy model needs to be made much more precise!



Lawrence B. Crowell replied on Sep. 26, 2012 @ 02:15 GMT
The conformal group in 3+1 spacetime would then be SO(4,2) ~ SU(2,2). The connection to twisters of course is through this conformal symmetry. One can of course see this according to Desargues’ theorem; Two triangles are axially perspective if and only if they are in perspective centrally. The projective rays in spacetime have a similar correspondence ω_a = ω(0)_a + ε_{aa’}π^{a’}, π^a = π(0)^a, which in the null construction is a projective Lorentz spacetime.

Your paper on 2+1 Chern-Simons SD has much the same structure as some work I just completed and will be sending to publication soon. The AdS_3 spacetime (2 space +1 time) has the CFT_2 on its boundary S^1xR. This CFT is SL(2,R)^2/Z_2, which with

1 --- > Z_2 --- > SL(2,C) --- > SL(2,R)^2 --- > 1

constructs spacetime symmetries in 4-dim. The S^1xR is the string world sheet or tube, and the CFT constructs the gravitons states. The holography here is with the boundary of the AdS_3. However, there is an additional symmetries on the string corresponding to four dimensions

There was some interesting discussion last week about commuting and anticommuting operators with SD and with causal set theory. I think this might have some interesting implications. It might provide some category theory of functors between spacetime and supersymmetry.

Cheers LC

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Author Sean Gryb replied on Sep. 26, 2012 @ 15:45 GMT
Thanks for your comments Lawrence.

I think you're right that there could be some connections with causal set theory, but there is a subtly related to your first comment. Perhaps a point that is not clear is that, in SD, we have *spatial* conformal invariance so that the relevant group is the conformal group in 3 spatial dimensions, i.e., SO(4,1). I think the connection to causal sets could be through the causal structure of de Sitter space in 3+1 dimensions, whose isometry group is also SO(4,1).

A connection with supersymmetry in SD is hinted by the BRST algebra of the theory. This is explored in a paper by Gomes and Koslowski that you might find interesting: I could put you touch with those authors if you're interested.



Steve Weinstein wrote on Sep. 23, 2012 @ 00:52 GMT
Sean and Flavio,

Beautifully written essay. I just have a comment and a question.

Comment: You claim that the problem of time stems from the different way that time and space enter into the formalism of general relativity, and that the evolution equations cannot be solved starting from nonspacelike initial data. The latter is not known to be the case. Certainly for the wave equation, one can begin with data on a nonspacelike hypersurface and evolve in the spacelike direction. (The Holmgren-John theorem guarantees uniqueness, and the work of Craig and myself shows that a solution exists if one begins with data satisfying a nonlocal constraint.) As for the problem of time, I would think that it has something more specific to do with general relativity, since it doesn't arise in the quantization of other relativistic fields.

Question: I see where coarse-graining is important for the fascinating result you get for the Shape formalism, but where does renormalization come in?


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Author Sean Gryb replied on Sep. 24, 2012 @ 11:19 GMT
Hi Steve,

Thanks for your input and kind words. Next time I'm at PI, we should discuss your paper on the wave equation.

In regards to your comment, you are right that the problem of time is much more intricate than what we had time to discuss in this short essay and, indeed, there are many things we didn't mention or had to simplify. I remember discussing the wave equation with you...

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Steve Dufourny Jedi replied on Sep. 25, 2012 @ 18:39 GMT
Verlinde's Entropic gravity and AdS/CFT Beyond the Standard

Model discussion is just a superstrings extrapolations.In fact,they confound the theory of informations witrh a real quantization.

In fact the works are not bad, but they are weak and not sufficient. The strings theories were just a faschion. Several convergence are relevant but it is time to be rational. The entropy is proportional with my rotating 3D spheres. Me I have explaine the gravity, him no !!! them , no !!!

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Hoang cao Hai wrote on Sep. 24, 2012 @ 07:21 GMT
Dear Sean

Very interesting to see your essay.

Perhaps all of us are convinced that: the choice of yourself is right!That of course is reasonable.

So may be we should work together to let's the consider clearly defined for the basis foundations theoretical as the most challenging with intellectual of all of us.

Why we do not try to start with a real challenge is very close and are the focus of interest of the human science: it is a matter of mass and grain Higg boson of the standard model.

Knowledge and belief reasoning of you will to express an opinion on this matter:

You have think that: the Mass is the expression of the impact force to material (from the ABSOLUTE theory of me)- so no impact force, we do not feel the Higg boson - similar to the case of no weight outside the Earth's atmosphere.

Does there need to be a particle with mass for everything have volume? If so, then why the mass of everything change when moving from the Earth to the Moon? Higg boson is lighter by the Moon's gravity is weaker than of Earth?

The LHC particle accelerator used to "Smashed" until "Ejected" Higg boson, but why only when the "Smashed" can see it,and when off then not see it ?

Can be "locked" Higg particles? so when "released" if we do not force to it by any the Force, how to know that it is "out" or not?

You are should be boldly to give a definition of weight that you think is right for us to enjoy, or oppose my opinion.

Because in the process of research, the value of "failure" or "success" is the similar with science. The purpose of a correct theory be must is without any a wrong point ?

Glad to see from you comments soon,because still have too many of the same problems.

Kind Regards !


August 23, 2012 - 11:51 GMT on this essay contest.

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Author Sean Gryb wrote on Sep. 24, 2012 @ 15:50 GMT
****************** UPDATE ******************

Our ref [9] has now appeared on the arxiv. The reference is:

Sean and Flavio.

Hoang cao Hai wrote on Sep. 25, 2012 @ 05:09 GMT
Congratulations to the two of you, hope you are not so busy that forget this topic.

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Yuri Danoyan wrote on Sep. 25, 2012 @ 11:35 GMT
For Shape Dynamics theory to fit my proposal about one analogy between geometry and physics


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Thomas Howard Ray wrote on Sep. 25, 2012 @ 18:16 GMT
Sean & Flavio,

I think many will agree with me, that there are more prize winning essays in this contest than there are prizes ... yours is among the top. So good luck! -- and I hope you get a chance to vist my essay ("The Pefect First Question") that soundly agrees with your statement, "The truth is that quantum mechanics requires some additional structure, which can be thought of as the observer, in order for it to make sense. In other words, quantum mechanics can never be a theory of the whole Universe."


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Author Sean Gryb replied on Sep. 26, 2012 @ 15:30 GMT
Hi Tom,

Thanks for your kind words. You're right that there are many good essays in this competition and, unfortunately, too few prizes. I had a look at your essay. It seemed like there were some interesting points but I'm not knowledgeable enough with Joy and other's work to really make detailed comments. I certainly agree with the importance of the measurement problem though.

Good luck in the competition!


Yuri Danoyan wrote on Sep. 26, 2012 @ 13:43 GMT
"Moreover, the toy model may shed light on the nature of the Plank length. In this model, the Plank length is the emergent length arising ....

This dimensionful quantity, however, is not observable in this model. What is physical, instead, it the dimensionless ratio r=R. This illustrates how a dimensionful quantity can emerge from a scale independent framework. Size doesn't matter but a ratio of sizes does. The proof could be gravity."

Dear Sean

Be careful with Planck length and read Wilczek doubts about it

Wilczek:"we must extract roots",

"can be taken outside the square roots",

"In the strong system of units no square roots

at all appear in [M], [L], [T ]."

Read Wilczek

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Peter Jackson wrote on Sep. 26, 2012 @ 13:49 GMT

You said on Sept 12 "I'm reading your essay with interest...". I hope you have, or do, as I think it may be very important in context, and am looking forward to your comments.

Best wishes


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Lawrence B. Crowell wrote on Sep. 27, 2012 @ 21:44 GMT

Maybe my insight into this is not complete hogwash. It will take a bit to digest the Gomes and Koslowski paper. BRST quantization is a cohomology of supergenerators, where this is a modern cornerstone of SUSY. It does appear this is derived from shape dynamics without reference to causal set theory. I’d be interested in contacting these two authors.

I agree that the...

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Janko Kokosar wrote on Sep. 29, 2012 @ 20:56 GMT
Dear Mr. Sean and Mr. Flavio

Your explanation of distinction between space and time in special relativity is very similar as mine. The distinction is in minus sign in your equation (3), it implies causality. I wrote also pedagogically that imaginary distance means that interaction between two events is not possible.

But, it seems to me, that time is basis of everything and that space is only a consequence of time. I wrote also that time runs only in rest matter and that everything can be reduced to dimensionless masses of elementary particles. It seems to me that this is against your and Barbour's theory? I quickly read your and his article, but I did not found similarity. Please correct me if I am wrong. Otherwise I agree with Mach principle.

Your write also about measurement problem. I have my own solution, which is at the end of this essay . It says that every quantum collapse is a conscious decision of units of primitive consciousness. This does not disturb all quantum calculations. Thus every our decision is a quantum event.

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Georgina Parry wrote on Sep. 30, 2012 @ 11:23 GMT
Dear Sean Gryb,

I found your essay lucid, absorbing and relevant but I found the final section on solutions a little difficult to follow. That's OK though because the enjoyment of the rest of the essay more than compensated for the difficult bit at the end. (I would need to spend far more time on that bit to properly appreciate it.)You chose a really interesting selection of assumptions to consider. Well done. Good luck in the contest.

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Georgina Parry replied on Sep. 30, 2012 @ 11:30 GMT
Dear flavio Mercati,

So sorry I should have addressed that last post to you as well. Well done, it is a very good essay, and good luck to both of you. Kind regards Georgina.

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Author Sean Gryb replied on Oct. 1, 2012 @ 11:26 GMT
Dear Georgina,

Thank you for your flattering words. I understand that the last section was probably a little hard to handle. We tried to put in a little something for everyone but I'm glad that the technical discursion didn't ruin the essay for you!

Good luck to you too! I'm looking forward to having a look at your essay.



ps. Flavio is a bit swamped with bureaucracy at the moment so I'm handling most of the posts on this forum.

Frank Martin DiMeglio wrote on Oct. 1, 2012 @ 21:53 GMT
Hi Sean and Flavio. I am considering your essay. Do you agree that time is ultimately dependent upon the integrated and interactive extensiveness of physics, being, thought, and experience (and space). Time requires gravity. In the absence of gravity, we are literally out of touch with reality.

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Author Sean Gryb wrote on Oct. 2, 2012 @ 10:53 GMT
I'm not really sure exactly what you're getting at here. We're suggesting that the flow of time may be intimately connected with the measurement process. This is suggested by the observation that the mathematics of coarse graining resembles the flow of time in general relativity. We are still not entirely sure what this means concretely, but we are working on it. One thing is certain, if the idea is right, it will mean a radical rethinking of time and measurement.



Frank Martin DiMeglio replied on Oct. 5, 2012 @ 02:55 GMT
Sean, you will need to consider the following. Time is dependent upon the integrated and interactive extensiveness of space. That is ultimately dependent upon us. We fundamentally and ultimately depend upon gravity for our physical existence and physical experience (typical, ordinary, and natural experience -- seen, felt, AND touched). Time requires gravity. Physics happens in and with time. Outer space cannot be understood [fundamentally] in relation to time. The [real/actual/true/full] experience of outer space is impossible. Outer space is detached and disconnected from our thought/comprehension; as outer space destroys and precludes our being, experience, and thought/ideas. Gravity fundamentally relates to and involves distance in/of space, force/energy, feeling, visible space, invisible space, touch, and vision. Gravity, invisible and visible, is fundamental to distance in/of space. My essay proves this. Time requires distance in/of space. Importantly, vision and gravity relate to feeling, invisible space, visible space, distance in/of space, force/energy, and touch.

Einstein's GR never provided for fundamentally equivalent and balanced inertia and gravity in conjunction with: 1) Fundamentally demonstrating F=ma

2) Fundamentally balanced and equivalent attraction and repulsion 3) Fundamentally stabilized and balanced distance in/of space in and with time.

My essay, in this contest, provides for all of this.

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Sergey G Fedosin wrote on Oct. 4, 2012 @ 04:42 GMT
If you do not understand why your rating dropped down. As I found ratings in the contest are calculated in the next way. Suppose your rating is
was the quantity of people which gave you ratings. Then you have
of points. After it anyone give you
of points so you have
of points and
is the common quantity of the people which gave you ratings. At the same time you will have
of points. From here, if you want to be R2 > R1 there must be:
In other words if you want to increase rating of anyone you must give him more points
then the participant`s rating
was at the moment you rated him. From here it is seen that in the contest are special rules for ratings. And from here there are misunderstanding of some participants what is happened with their ratings. Moreover since community ratings are hided some participants do not sure how increase ratings of others and gives them maximum 10 points. But in the case the scale from 1 to 10 of points do not work, and some essays are overestimated and some essays are drop down. In my opinion it is a bad problem with this Contest rating process. I hope the FQXI community will change the rating process.

Sergey Fedosin

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Author Sean Gryb wrote on Oct. 4, 2012 @ 10:01 GMT
Thanks for the heads up. There are definitely better systems.

Member Olaf Dreyer wrote on Oct. 5, 2012 @ 16:18 GMT
I finally managed to read your essay. It is a very nice read. I have a number of questions regarding your essay. The first two are just technical:

1. In appendix A you say that equation (10) gives three constraints.  How is that?  Aren't we talking about motion in one dimension?  

2. I do not understand the first part of equation (11).  If you are looking for the moment of...

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Author Sean Gryb wrote on Oct. 5, 2012 @ 16:34 GMT
Hi Olaf,

Thanks for the detailed questions! I'll try to respond in order.

1. This is a typo. An old version of the draft was in 3d.

2. This is Julian Barbour's favourite way of writing the moment of inertia (because it is more "Machian"). It takes some rearranging, but it's possible to get it into the right form (note the M^2 in the denominator).


4. You...

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Zbigniew Modrzejewski wrote on Nov. 24, 2012 @ 20:52 GMT

Ultimately, physics is all in the eyes of the beholder.

This conclusion comes straight from the so-called "problem of perception" in philosophy, that has not been solved so far.

In simpler physical approaches to reality, we may wish to pretend that we, somehow(!), observe the independent, objective reality. This is called in philosophy: "naive realism".

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Georgina Parry wrote on Nov. 25, 2012 @ 03:07 GMT
Dear Zbigniew,

It may interest you to know that I have addressed this problem. There is an explanatory diagram in my essay and a high resolution version of the diagram correctly oriented in my essay discussion thread. In that thread there is also a link to a web site giving some more detail about it.

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Ken Seto wrote on May. 17, 2013 @ 03:23 GMT
Dear Sean and Flavio,

If we accept the existence of absolute time and that a clock second represents a different amount of absolute time in different frames (different states of absolute motion) then all the perceived paradoxes of SRT are resolved. The GPS suppoorts the existence of absolute time. A GPS second is redefined to have 4.46 more periods of Cs 133 radiation than the ground cloock second. This redfinition of the GPS second is designed to make it contain the same amount of absolute time as the ground clock second and thus making the GPS permanently in synch with the ground clock in terms of absolute time.


Ken Seto

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