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March 11, 2014

CATEGORY: FQXi Essay Contest - Spring, 2012 [back]
TOPIC: The Paradigm of Kinematics and Dynamics Must Yield to Causal Structure by Robert W. Spekkens [refresh]

Author Robert W. Spekkens wrote on Sep. 7, 2012 @ 11:30 GMT
Essay Abstract

The distinction between a theory's kinematics and its dynamics, that is, between the space of physical states it posits and its law of evolution, is central to the conceptual framework of many physicists. A change to the kinematics of a theory, however, can be compensated by a change to its dynamics without empirical consequence, which strongly suggests that these features of the theory, considered separately, cannot have physical significance. It must therefore be concluded (with apologies to Minkowski) that henceforth kinematics by itself, and dynamics by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality. The notion of causal structure seems to provide a good characterization of this union.

Author Bio

Robert Spekkens is a faculty member at the Perimeter Institute for Theoretical Physics in Waterloo, Canada. His area of research is the foundations of quantum theory.

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John Merryman wrote on Sep. 8, 2012 @ 03:56 GMT
Robert,

What if you treat time as effect of action, rather than measure of events. Not a progression from past to future, but the process by which future becomes past. Not the earth traveling a fourth dimension from yesterday to tomorrow, but tomorrow becoming yesterday because the earth rotates?

That way, cause and effect is not sequence, but energy exchange. Yesterday doesn't cause today, any more than one rung on a ladder causes the next. It is the sun radiating on a rotating planet that causes the sequence of events called 'days.'

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Robert Spekkens replied on Sep. 16, 2012 @ 17:06 GMT
John,

I agree that cause and effect should not be considered a sequence. I would put it this way. Whereas many philosophers have thought that the definition of a cause-effect relationship should include the fact that the cause must precede the effect in time, it is better to take the view that causal relations are more primitive than spatio-temporal relations and what it means to say that one event is earlier than another is that the first is a potential cause of the second. In this view, time is inferred from the partial order relation on events induced by cause-effect relationships. (Of course, I'm not the first to propose that time is emergent from causal structure.) I must admit that I don't really understand what it means to say that a cause-effect relationship is defined by energy exchange.

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Stephen M Sycamore wrote on Sep. 8, 2012 @ 15:42 GMT
Hello Robert,

From a practical standpoint it does seem that an over-reliance on kinematics in quantum theory and practice does result in a very static picture, leaving us little to say about even essential processes such as emission and absorption.

The limitations of space-time kinematics are studied from a classical perspective in the essay Is Kinematics Compatible With Field Symmetries? The investigation there shows that space-time kinematics can be replaced by dynamics using a 3-vector expression of de Broglie's wave mechanics. Does that help or hinder your arguments?

Steve Sycamore

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DANIEL WAGNER FONTELES ALVES wrote on Sep. 8, 2012 @ 21:57 GMT
Dear Robert,

Definitely, very good arguments. Congratulations.

I would like to make one point.

''So we can change the kinematics from con guration space to phase space and maintain the same empirical predictions by adjusting the dynamics accordingly. It's not possible to determine which kinematics, Newtonian or Hamiltonian, is the correct kinematics. Nor can we determine the correct dynamics in isolation. The kinematics and dynamics of a theory can only ever be subjected to experimental trial as a pair.''

Apart from mathematical manipulations, there is another way to produce ''new'' kinematics: conceptual questioning. For instance, classical mechanics kinematics is specified with a background space/time structure. If one asks the seemingly purely philosophical questions ''what is space?'',''what is time?'' we could indentify something different then the space/time structure to describe physics. For instance, we could perceive that we never measure displacements against the fixed invisible background, we measure relative displacements between visible objects. Also we never measure an invisible time parameter t, we measure the motion of a visible object we call a clock. So by constraining the MEANING of space/time statements to the behaviour of physical objects we get a completely different kinematics where the background is a derived concept.

Actually these thougts can be extended to field theries, and particularly to a 3-D metric field, and the result is GR! That is, GR is almost uniquely signed out by finding a more reasonable kinematics. This is Barbour´s research, shape dynamics.

I invite you to read my essay

, where I explore how different conceptions of motion, thus different kinematics, originated from conceptual questioning may lead to new and known physics.

Good luck in the contest,

Best Regards

Daniel

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Author Robert W. Spekkens replied on Sep. 21, 2012 @ 16:31 GMT
Dear Daniel,

I’m very much in agreement with you that Newtonian kinematics, with its background of absolute space and time, is inferior to a relational kinematics, of the sort that Julian Barbour has espoused, following Leibniz and Mach. Indeed, I would say that the reasons that have traditionally been...

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Daniel Wagner Fonteles Alves replied on Sep. 24, 2012 @ 00:12 GMT
Dear Robert

I agree we´re being drived by the same motivation. Thanks for reading my essay and for the comments.

''Empirical indiscernables are physically identical''

Something very nice may happen if we impose that. One of the puzzles of QM is the nature of observation: why is observation so different from other physical phenomena? Observation makes wave functions collaps, but how can we classify a physical process as an observation? If we impose that two configurations of the universe MEAN the same if they are OBSERVED to be the same, the observation can be given a precise mathematical meaning... something like ''observation is that thing that identifies any two configurations of the universe as being the same''. In the last section of my essay I propose a way to express this more concretely using category theory. Maybe something similar could be done in your approach.

Best regards,

Daniel

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Member Benjamin F. Dribus wrote on Sep. 9, 2012 @ 08:23 GMT
Dear Robert,

I really enjoyed your essay. It is clearly expressed, rich in context, and advocates a view with which I have great sympathy. I have a few remarks and questions.

1. Since dynamics in conventional physics involves time evolution, and since causal graphs incorporate their own notion of “time” given by the directions on the edges, how would you characterize the...

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Jayakar Johnson Joseph wrote on Sep. 9, 2012 @ 18:09 GMT
Dear Robert Spekkens,

In Coherently-cyclic cluster-matter model of universe, dynamics and dimensionality coexists in time; in that the kinematics of macro objects includes disjunction and conjunction of string-matters on their Tribology and thus the union of dynamics and kinematics is predicted.

With best wishes,

Jayakar

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Phil Warnell wrote on Sep. 10, 2012 @ 00:29 GMT
Dear Dr. Spekkens,

This not is just to have you know I found your essay quite interesting and thought provoking, that is if for no other reason as perhaps suggesting a way of having the formalisms of physical theories be found to be more consistent and less ambiguous as they relate to their corresponding interpretations. However I'm also cautious when theory is to be restricted to such bare bones foundational limits that those elements not suggested by observation or consistent with existing or proposed theory would become as a consequence at risk to being totally ignored. That is I find it difficult to imagine how if such restriction if rigidly adhered to would allow intuition to continue to play as an important as it currently does respective of the expansion of physics, or lend the inspiration required to having it pursued.

In such regard I'm reminded of what Einstein warned about developing physical theory when he said, "The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience". That is I'd contend he would also have included experience as to take in what one could imagine how the physical world might be and not only as it's able to be observed or what our conceptualizations relating to theory would have them found needed to be. That is in short I find your argument to be a good one in the sense that we need examine new perspectives as to explore all the possibilities, yet not at the exclusion of the ones which have thus far proven to have served us so well.

Regards,

Phil

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Travis Norsen wrote on Sep. 15, 2012 @ 11:52 GMT
Here is an email I sent to the author before the essay was posted here. He suggested moving the discussion here.

---

Hi Rob, [...] I thought I’d share some thoughts I had while reading it. In no particular order…

* Despite your attempt to distinguish your basic methodological principle (“any difference between two physical models that does not yield a difference at...

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Robert Spekkens replied on Sep. 16, 2012 @ 16:53 GMT
Thanks for your thoughtful comments. Let me try to respond to each in turn. (By the way, I'm sorry for the delay in replying to your email -- I've been on holiday for the last two weeks.)

* Concerning the methodological principle and operationalism. A longer paper would be required to properly answer questions about the kind of scientific realism I'm espousing here. First,...

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Travis Norsen replied on Sep. 16, 2012 @ 19:05 GMT
Thanks for the interesting replies. Some follow-ups:

* Re: Ptolemy and Copernicus, my understanding is that Copernicus only made distinct predictions because he updated a few of the empirical parameters using the data that had come in since Ptolemy's time. But Ptolemy -- had he still been around -- could have updated his parameters in an exactly parallel way, such that the differences in...

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Author Robert W. Spekkens replied on Sep. 17, 2012 @ 15:55 GMT

* Re: Ptolemy and Copernicus. It seems to me that simply because one choice of coordinate system may be especially perspicuous or useful for making theoretical progress, as the coordinate system with the sun at the origin helped Galileo and Newton in a way that the earth-centered coordinate system did not, this does not imply that formulations of a...

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Helmut Hansen wrote on Sep. 18, 2012 @ 12:46 GMT
Dear Robert,

I think you are right: There is an ambiguity about how to make the separation between kinematics and dynamics.

A somehow dramatic case is the relativistic kinematics. It is not only compatible with the wave-like version of the constancy of light as it is stated in the second postulate of SRT, but it is also compatible with a particle-like version of the constancy of light c.

Reference: Stachel, John. Einsteins Light-Quantum Hypothesis, or Why Did not Einstein Propose a Quantum Gas a Decade-and-a-Half Earlier? (Einstein. The formative Years, Einstein Studies 2000, p. 240)

In his 1905b-paper Einstein has noted that the velocity of light V cannot be altered by composition with any subluminal velocity.

This kinematical notion - if connected with the particle model of light - implies a far-reaching consequence : Even if the speed of light depends on the speed of the emitting source, the speed of light is always measured of being constant.

Consequently, all measurements concerning the second postulate of SRT are not unambiguous. There is - at least in principle - the possibility that something different has been measured - a sort of a particle-like version of the constancy of light.

Kind Regards

Helmut

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Sean Gryb wrote on Sep. 20, 2012 @ 11:46 GMT
Hi Rob!

I was happy to see that you've also entered this competition. The last time we saw each other I didn't get time to hear about your new insights. Now I get a chance to read about them!

Very thought provoking essay. I must say that I endorse the idea that causal structure should be fundamental. In fact, in shape dynamics we've reached the same conclusion through different...

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Author Robert W. Spekkens replied on Sep. 21, 2012 @ 16:41 GMT
Hi Sean,

Always good to hear from you!

I’m intrigued that you’ve reached a similar conclusion about the primacy of causal structure from a completely different starting point. That being said, I think that there is a bit of similarity in our starting points: we have both been guided by the same philosophical motivations I think. As I mentioned in my response to Daniel...

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Sean Gryb replied on Sep. 24, 2012 @ 12:17 GMT
Hi Rob,

Always good to hear from you too! Thanks for your detailed comments.

It's encouraging to hear that we seem to be coming to similar conclusions from the same philosophical motivations but different physical problems. I think it points to the strength of the principle that: "empirical indiscernables are physically identical" (not that "snappy" I have to admit!!). I've often thought of this as the core idea in Mach's principles but haven't been able to come up with a catchy slogan either. Regarding Leibniz, I don't think he explicitly mentions scale (or Mach either) but you should really check with Julian, who could tell you for sure.

The theorem I mentioned is one of the primary motivations for Causal Set theory, so Rafael could probably give you an exhaustive list of references (and he could probably explain the theorem more carefully than me). However, I think the original result was in: Journal of Mathematical Physics, July 1977, Volume 18, Issue 7, pp. 1399-1404. There are probably more modern versions though. I think there is a discussion and proof of this in Hawking and Ellis.

Regarding global structures like anomalies, boundary terms, and the AB effect. It would be interesting to see if one could reproduce these effects through a restriction of knowledge. Maybe this is naive, but wouldn't this restriction itself be just a kind of replacement for holism in the sense that it acts as a kind of global restriction on the system? In any case, I am coming to think more and more that these kinds of effects might be very fundamental.

Cheers,

Sean.

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Stephen M Sycamore replied on Sep. 26, 2012 @ 11:28 GMT
Dear Sean and Robert,

When you make that important statement (Sean):

"However, even in this rigorous setting there is a problem with the interchangeability of kinematics and dynamics: there can be global properties of the fibre bundle itself that can show up in the physics. An example of this is the Aharonov-Bohm effect that would be relevant to your model of the electromagnetic fields vs potentials. Similar things, like boundary terms, can appear during Legendre transforms which imply real differences between the Lagrangian and Hamiltonian. The chiral anomaly is yet another example relevant to the Standard Model."

Does it follow that dynamics is to be preferred to kinematics where there is that departure? In other words, kinematics has a larger set of constraints and may not be as malleable in conforming to global properties and boundary terms. A case in point is the Aharonov-Bohm effect you mention which is not readily modeled by U(1) topologies. Relativistic kinematics seems to require a force fit into any even marginal compliance with SU(n) topologies.

Steve Sycamore

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Peter Jackson wrote on Sep. 20, 2012 @ 17:01 GMT
Robert

I applaud causal structure denouncing distinctions between kinetics and dynamics. But you must forgive me for already testing this unknowingly and proving it's worth, the results reported my essay.

I agree and indeed show the consequences of lambda (but also its derivative frequency) changing and the wave function being conserved with causality on all transformations. I'm not a quantum physicist so my language is different (even theatrical!) but the emergent causal structure of reality is self apparent, deriving classical relativity from a causal quantum mechanism. I hope you can read and comment for me. The physics is flooding out rather uncontrollably at present and needs help. My essay (to mix metaphors) is the tip of the iceberg.

Have you looked at the structure of truth functional logic with respect to compound systems. I only refer to dynamic logic (PDL) in my own essay but it is based on the hierarchical structure of 'nested' kinetic states with similarities to the infinite multiple components of ontic states, each only initially definable wrt the 'next state up' (local background state)?

As for your own essay I found it excellent. Clear, well argued, well written and correct, so a good score certainly coming. I hope you may feel the same of mine, if very differently presented.

Very best wishes for the contest.

Peter

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Lidia del Rio wrote on Sep. 21, 2012 @ 07:11 GMT
[adapted from an email exchange with the author]

Hi Rob,

I presented it in our group seminar, and some questions arose:

1) Your notion of kinematic locality on page 4:
$\lambda_{AB} = (\lambda_A , \lambda_B).$

You say that this is the same of separability, but it looks an awful lot like product states.

2) Newtonian physics.

Some people insisted that the kinematics, as they learned it, should be
$\{q_i, \dot{q}_i\}_i$
(with the velocities), and not just the positions
$\{q_i\}_i.$

3) Practicability.

Is it always clear how to compute the causal-statistical parameters of a theory? For instance, how are they in your two examples (Hamiltonian and Newtonian physics) ? An expansion of the equations of motion?

4) Second page, your methodological principle vs operationalism

The definition of operationalism here wasn't super clear to me. After re-reading, I'd guess you take it to mean:

"make only claims about the outcomes of experiments, and not about the underlying reality."

Is this correct? The Plato Cave example illustrates what you mean by your principle very well, but I was left without understanding what kind of theories would fit operationalism in the example.

I have a guess:

The claim "shadows grow in the afternoon" (assume there is a concept of time and they call the hours before the dark "afternoon") respects operationalism.

The claim "shadows grow in the afternoon because there is a source of light sinking" does not respect operationalism, because it makes a claim about something (the source of light) that you cannot measure. It would however fit your methodological principle, because it helps explain something empirical.

Is this right? Is that why the 3D shape theory is not operational(ist)?

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Anonymous replied on Sep. 21, 2012 @ 18:53 GMT
[also adapted from our email exchange]

Hi Lydia,

Nice to hear for you, and thanks for the comments.

1) This is a confusion of terminology, which I'm sorry I didn't clarify in the paper. The term "separability" is used by quantum information theorists to describe quantum states that are convex combinations of product states. In quantum foundations, the same term is sometimes used to describe an assumption about ontological models, namely that the ontic state space satisfies kinematical locality. You're right that lambda_AB is just the ontic state for AB. The consequences of kinematical locality on the epistemic states is just that we can write P(lambda_AB) = P(lambda_A,lambda_B) and we can therefore talk about whether lambda_A and lambda_B are correlated or uncorrelated, etcetera. Kinematical locality does not imply the quantum information theorists' notion of separability.

2) The information that needs to be specified to make predictions is certainly the positions and the velocities, but I don't think one should consider the velocities to be part of the kinematics. Maybe this argument will clarify why I think so: in a variational approach to classical mechanics, one could specify the initial position and the final position and deduce the trajectory followed by the particle in the intervening time. But one would not thereby conclude that the kinematics included the initial and final positions (at least, that's not how people usually talk about kinematics). So one shouldn't, I think, identify the variables used for boundary conditions with the kinematics.

3) The bit where I present the causal diagrams for Hamiltonian and Newtonian mechanics shows that one can easily translate a theory from the kinematical-dynamical paradigm into the causal paradigm. Deterministic dynamics is represented by a conditional probability distribution which is a point distribution on the conditioned variable for every value of the conditioning variable. For instance, in the Hamiltonian scheme, the conditional probability P(p2|q1,p1) is just delta(p2,f(q1,p1)) where delta(.,.) is the Kronecker delta and f(q1,p1) is just the function that defines p2 in terms of the earlier phase space point. That being said, these causal diagrams don't yet capture all and only the nonconventional bits. I'm not exactly sure what mathematical formalism does this. People in machine learning have introduced the notion of an equivalence class of causal diagrams, and this strikes me as promising.

4) As I see it, an operationalist is a kind of empiricist. Empiricism in the philosophy of science is the idea that the goal of science is simply to "reproduce the phenomena", for instance, to provide an account of what we experience. We should not ask "why", according to the empiricist, only "how". Empiricists were motivated to build knowledge on top of statements about experience because they thought that in this way it would be immune from error. This motivation was later convincingly shown to be misguided by people like Popper and Quine but in physics we still have a strong empiricist streak in our attitude towards quantum theory. The operational brand of empiricism is that the primitives in terms of which experience is described are experimental operations.

So, yes, "not about the underlying reality" is a good description of operationalism. If you look at any of the recent work on operational axioms for quantum theory, you'll get a feeling for the operational interpretation. Basically, an operationlist talks about preparations, transformations and measurements of systems, not about properties of systems or evolution of those properties. Your example of shadow growth is spot on.

The first couple of sections of this short paper that I wrote with Lucien Hardy describes in more detail the difference between realism and operationalism.

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Author Robert W. Spekkens replied on Sep. 21, 2012 @ 18:57 GMT
Oops, that last post should have appeared as mine, rather than anonymous.

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Amanda Gefter wrote on Sep. 22, 2012 @ 06:18 GMT
Hi Robert,

I really enjoyed your essay. It's a fascinating idea that kinematics and dynamics might be two aspects of a more fundamental causal structure. It leaves me wondering *why* causal structure should be so fundamental?

As I touch on in my essay, theoretical developments in understanding black hole physics, such as the holographic principle and horizon complementarity, seem to suggest that reality is radically frame-dependent, where frames are delineated in terms of causal structure. Do you suspect that this frame-dependence might shed light on the foundational role of causal structure?

All best,

Amanda

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Anonymous wrote on Sep. 24, 2012 @ 19:04 GMT
I just read your essay. I need to read it again for greater depth. I usually give these a couple of readings. I am pondering what you are saying. I think it comes down to the Bell statement

P(XY|ST) = sum_λP(X|Sλ)P(Y|Tλ)P(λ),

where the ontic variable is ultimately a summation or dummy variable. This means that what ever the analyst assigns to λ it is...

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Hou Ying Yau wrote on Sep. 25, 2012 @ 04:58 GMT
Dear Robert,

In related to the hidden variable theories you mentioned in the essay, I have a different thinking that I hope you may find it interesting. Nothing mathematical fancy, I find that the bosonic quantum field can be reconciled from a system with vibrations in space and time. The model has some unique features that seem to be extendable to gravity and non-locality of quantum theory.

Is there really no reality in quantum theory

Hou Yau

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Member Tobias Fritz wrote on Sep. 26, 2012 @ 20:09 GMT
This is a very insightful essay!

It might be worth mentioning that computer scientists have long recognized the fact that kinematics and dynamics do not have separate observational meaning. This can be formalized in terms notions like bisimulation. There ought to be a definition of bisimulation for theories of physics!

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Author Robert W. Spekkens replied on Sep. 26, 2012 @ 22:44 GMT
Tobias,

Can you tell me more about the notion of bisimulation? I'm intrigued.

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Member Bob Coecke replied on Oct. 3, 2012 @ 19:24 GMT
It's the cornerstone to concurrency theory:

http://en.wikipedia.org/wiki/Bisimulation

The right mathematical context in which it lives is coalgebra. Next year in Barbados: coalgebra + quantum foundations. Both of you are of course invited!

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Anonymous replied on Dec. 7, 2012 @ 15:32 GMT
Robert Spekkens,

I recently made a comment on the viXra blog about bisimilation and its relevancy to your causal structure in the sense that it allows the incorporation of bi-directional causation! I made the comment before I read these comments here and as soon as I saw this comment I thought I would direct your attention to a good paper on bisimilation: http://www.cs.unibo.it/~sangio/DOC_public/history_bis_coind.pdf. This paper examines the history of bisimilarity in the context of computer science, Modal Logic, and set theory.

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Hoang cao Hai wrote on Sep. 27, 2012 @ 05:08 GMT
Dear Professor Robert W. Spekkens

I very approval with the statement of Professor.

In my opinion: the Causal Structure is the principle of every problem.

Kind Regards !

Hải.Caohoàng of THE INCORRECT ASSUMPTIONS AND A CORRECT THEORY

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

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Vladimir Rogozhin wrote on Sep. 27, 2012 @ 10:23 GMT
Dear Robert! Excellent in-depth analysis in your essay. But why not have the depth of the ontology? Modern physics and mathematics - science not ontologically grounded. Today dominate the operational theory without the necessary ontological foundation.

Correctly, you have to look deep first structure. Bourbaki is a good title "mother" or "generative". Now, as for the physics and mathematics necessary first structure-mother. The concept of "causality" - a category of relationship (Immanuel Kant) ... What are the most fundamental relationship that is unconditional?

There is a fine principle of "coincidence of opposites." Also there is another good old principle of the triunity, who was not Isaac Newton.

In my absolute generating structure to form the basis of dialectical triad only absolute (unconditional) state of matter. This structure, which Umberto Eco calls "missing." "The truth must be drawn ..." (A.Zenkin) ... and ontologically grounded .... There is no other way to truth... My rating-9. Sincerely, Vladimir

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Anonymous wrote on Sep. 28, 2012 @ 12:19 GMT
Robert,

Congratulations, your excellent essay is in the top 35 essays of this contest. I wish you good luck in the final evaluation too.

As a final conclusion of your essay, please summarize in a few sentences, which of our 'Basic Physical Assumptions' are wrong in your opinion?

Anonymous

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Author Robert W. Spekkens replied on Sep. 28, 2012 @ 15:13 GMT
My essay argues against the prevalent assumption that any proposal for a physical theory should separately specify kinematics and dynamics, that is, a space of physically possible states and a law describing how these evolve in time.

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Member George F. R. Ellis wrote on Oct. 3, 2012 @ 12:21 GMT
Dear Robert

a deep and intriguing essay. The core about causal sets sounds right: I believe there are many indications that gravity is really described by conformal degrees of freedom, and I learned the other day that all of the Standard Model interactions except one term are conformally invariant. Causal set theory is surely a good way to explore. But one somehow has to introduce a scale too at some point.

Your arguments about not separating kinematics and dynamics are intriguing. Of course in a sense that is what Einstein discovered about gravity.

Best wishes

George Ellis

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Author Robert W. Spekkens replied on Oct. 5, 2012 @ 22:11 GMT
Dear George,

I agree that Einstein’s theory of relativity provides further evidence for the conventionality of the distinction between kinematics and dynamics. Concerning the question of introducing scale, you should have a look at Sean Gryb’s comment (posted above). Sean is working on shape dynamics, which posits global scale invariance. He points out that the information left in the metric after one does away with the conformal factor is entirely about the causal structure. As I mentioned to Sean in my response to his post (and also in my response to Daniel Alves), the motivation for considering scale to be unphysical is very similar to the motivation for considering the distinction between kinematics and dynamics to be unphysical. I’m certainly sympathetic to the project of formulating our physical theories relationally, as one does in shape dynamics.

Best,

Rob

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Jonathan J. Dickau wrote on Oct. 3, 2012 @ 15:25 GMT
Hello Robert,

I have not read it yet, but your essay is on my reading list for today. However, your key point is one I have already given a lot of thought to. The notion that kinematic states and dynamic evolution are separable seems to carry over from the subject-object distinction in English and other European languages.

It is a peculiar left-brain dominated preoccupation, which necessitates measures like Korzybski's "the word is not the thing." In Chinese, by contrast; one cannot describe a thing apart from its process, and even the individual strokes in a character tell the story of how that pictogram evolved.

But causal structure is a subject I've been interested in for some time. The challenges posed by the recent Fermi and Integral probe results have called many promising theories like CDT into question, because of problems with achieving Lorentz invariance. And I had some interesting discussions about this matter with Gerard 't Hooft during FFP10, and with some loop quantum gravity folks during FFP11.

All the Best,

Jonathan

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Member Bob Coecke wrote on Oct. 3, 2012 @ 19:20 GMT
Hey Rob, nice thingy, but one thing confuses me a bit. As you well know since to told me this, causal discovery is an ill-posed problem and to even have a non-trivial causal structure a joint probability should be degenerate. So how can a causal structure underpin everything? This almost sounds a bit like the causal set paradigm, which you clearly refute in your introduction.

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Author Robert W. Spekkens replied on Oct. 5, 2012 @ 22:31 GMT
Hi Bob,

It's certainly true that causal discovery algorithms, if applied to finite sets of data, are really just heuristics for identifying likely causal structures. One kind of causal discovery algorithm actually returns a probability distribution over causal structures as its output. In that way, even if one's probabilistic data does not, strictly speaking, exhibit any conditional independences among the observed variables, if it is close to exhibiting such independence the algorithm will identify the most likely causal structure to be one that predicts such independences in the limit of infinitely large statistics. I don't see any problem with positing causal structure to be primitive while granting that we can never be 100% certain of the precise causal structure underlying finite data. Isn't it just like other idealizations in physics? The notion of an inertial observer might be critical to making sense of the special theory of relativity even if, strictly speaking, no observer is every truly inertial.

Best,

Rob

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Anonymous replied on Oct. 12, 2012 @ 19:16 GMT
...causality 20 % 40 % 60 % - well half truth or half half falsehood....

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Cristinel Stoica wrote on Oct. 5, 2012 @ 04:53 GMT
Dear Robert,

I think you are right about the "relativity" of kinematics-dynamics. Originally, I wrote a completely different essay for this contest, in which I explained that the universality of the physical laws (its independence of position and time), as well as the principle of relativity, should not be considered as assumptions, because they can be ensured by extending the configuration space and modifying accordingly the evolution laws. This was based on something I wrote in an older unpublished article, in which I discuss the theories of physics from the perspective of sheaf theory. At the end, I decided to write a completely different essay, about singularities in general relativity, where I have more concrete and published results (Did God Divide by Zero?).

I find brilliant the idea of playing with the kinematics and dynamics to yield an equivalent theory, but which is local. You may be interested in Maxim Raykin's recent Analytical Quantum Dynamics in Infinite Phase Space, who finds a more elegant dynamics for de Brogile-Bohm theory. I would also humbly suggest my own view on QM, in which I try to interpret the quantum weirdness by using only the unitary evolution of the wavefunction, constrained by global consistency conditions (which are intrinsic).

Best wishes,

Cristi Stoica

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Jin He wrote on Oct. 5, 2012 @ 19:22 GMT
MAX PLANK:

An important scientific innovation rarely makes its way by gradually winning over and converting its opponents; it rarely happens that Saul becomes Paul. What does happen is that its opponents gradually die out and that the growing generation is familiarized with the idea from the beginning.

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Member Benjamin F. Dribus wrote on Oct. 13, 2012 @ 08:32 GMT
Dear Robert,

I thought you might be interested in the following idea I posted on George Ellis's thread. Since you also are interested in "nonmanifold models that emphasize the role of causality," I thought I'd copy the idea here.

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After initially struggling with the idea, I’ve been thinking a bit about how your [George’s] top-down causation idea might look...

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Eckard Blumschein wrote on Oct. 15, 2012 @ 06:11 GMT
Dear Robert Spekkens,

Your essay argues against the prevalent assumption that there are two separate basics of physics, a space of physically possible states and laws describing how these evolve in time.

Doesn't the expression "in time" guess that the future is predetermined and just unseen? Doesn't "a space of physically possible states" also guess that the world is built like a combination of discrete elements? Maybe these assumptions are good or at least clever guesses. I prefer to not assume more than what seems to be indispensable: reality and causality.

I see any causal structure real only in the past if the world cannot be seen from outside as a closed system although most of our theories do so. Is my caveat acceptable? I designed five figures in order to illustrate it and its implications.

Eckard

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Vladimir F. Tamari wrote on Dec. 1, 2012 @ 10:40 GMT
Dr. Spekkens,

Congratulations on having your beautifully written essay winning the contest. I missed reading it before and have just done so. Your conclusion that kinematics and dynamics should be considered as one causal entity sounds to me very natural in both senses of the word.

I know you have waded in your scholarly way through the whole layers of various quantum theories and applied your intuition and methodical analysis to reach this conclusion. Also working intuitively but lacking your erudition, I invented my own theory (of a universal lattice of nodes interacting locally, linearly and causally with their neighbors), which I think a priori has the above characteristics without consciously seeking them out (see attached figure). I would be grateful if you or your students can check it out half-cooked as it is, but it is the best I could do. Here is my Beautiful Universe Theory and here is my fqxi essay Fix Physics! on which it was based.

Finally I wonder if you agree with me that Eric Reiter's essay deserved a prize ? Perhaps the good people at Perimeter can check out his research and replicate his experiments if need be .

with warm regards

attachments: bu_figure_5.jpg

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Vladimir F. Tamari wrote on Dec. 1, 2012 @ 10:44 GMT
sorry I meant the fqxi essay is based on the 2005 theory not the other way round!

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Paul Reed wrote on Dec. 3, 2012 @ 04:59 GMT
Robert

As this paper won, I read it.

You have correctly identified a false distinction in the depiction of physical existence, but not actually, I think, explained why this is so. That is because physical existence can only occur in one physically existent state at a time. In terms of what exists at any time, it is not physical substance that matters so much as the physically...

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Tosin wrote on Dec. 3, 2012 @ 23:48 GMT
I usually wait for the announcement and read the winning paper.

Can't wait to enjoy this one.

Congrats.

X Bubbler

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Eric Brunhouse wrote on Mar. 26, 2013 @ 00:09 GMT
Robert,

It is practical to say we think everything we observe happens through some causality. This gives us some sense of time moving forward, therefore time is not fundamentally fixed like a map in the background. So while causality exists (at least in our thoughts) events move forward and each event has an explanation. Quantum mechanics posits there is a break in geometric causation...

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sridattadev kancharla wrote on Oct. 30, 2013 @ 18:53 GMT
Dear Robert,

Congratulations. I hope you will enjoy the following blog and videos in it.

Any Body Can Derive - Everything From Geometry

Love,