The Third Road to Quantum Gravity

[Careful]

Careful and Jarek
Firstly, allow me to say that it is quite clear that you have not read and thought about what I have already said.
Be that as it may, as soon as I get a chance I will do as you ask, and attempt to answer the question.

Sure with category theory, you can do anything you want (again a tautology) Unfortunately, it does not help you with *solving* a problem.

 

[Careful]

Careful and Jarek
Firstly, allow me to say that it is quite clear that you have not read and thought about what I have already said.
Be that as it may, as soon as I get a chance I will do as you ask, and attempt to answer the question.

Oh yeh, I did, but you started off bad. You referred:

``The Computational Universe: Quantum gravity from quantum computation
Seth Lloyd
http://arxiv.org/abs/quant-ph/0501135´´

If you look up the word CRACKPOTISM 2005, this paper should be in the top ten. It is not only utterly naive, but it contains elementary mistakes as well.

 

[Careful]

Let us begin with a short list of topics that have previously been mentioned, albeit briefly in some cases:
Confinement mechanisms
Mass generation
Particle Number non-conservation
Quantum Mechanics
Quantum Computing protocols
Knots in condensed matter systems
Cosmological problems
Machian principles
I'm curious as to which of these you consider to be of no physical relevance.

As I said you can define virtually anything in the framework of category theory: the questions are (a) what computational benifit does it give ? (b) has anything *extra* been reached with these methods already (apart from mathematical abstraction), that is does there exist a real physics problem which has been solved thanks to the use of category theory? (c) has it provided any further *physical* insight ?

 

[Kea]

Careful

I would never have mentioned Seth Lloyd if this was entirely my thread. But the thread was actually started by someone else, and I always try to be considerate of others' ideas.

 

[Kea]

(a) what computational benifit does it give? (b) has anything extra been reached with these methods already (apart from mathematical abstraction), that is does there exist a real physics problem which has been solved thanks to the use of category theory? (c) has it provided any further physical insight?

I think there is a very fair claim for an answer of yes to (c) and possibly even (b). As an answer to (b) one might mention the clarification (and hence increase in computational power) of the Racah-Wigner calculus used by spectroscopists. Without impressively concrete results, it is hard to make a claim for (a), but I think Strings, LQG and all other approaches are in the same boat here.

Perhaps to open this discussion:

When String theorists tell me that we cannot even in principle calculate the rest masses of fundamental particles, I get quite distressed. The LHC is not so far away, and as far as I can tell nobody has a good idea of what it should be able to see. This would be less worrisome if I didn't think there was more we could do, but I do.

The reason I often launch into categorical or logical jargon is because I believe physical intuition and categorical intuition have a great deal in common. To do GR, one certainly does not need category theory. To do lattice QCD, one does not need category theory. To some extent the problem with the jargon is a lack of physical terminology to go beyond these domains.

It is my personal opinion that the following two kinds of principle are both necessary and sufficient for writing down a unified theory:

1. Measurement The necessity of internalisation (the "context" or "environment" must be taken into account in determining the nature of propositions) forces an acceptance of, amongst other things, a categorical comprehension scheme. This must, as in the mathematical treatment, be an axiomatic issue.

2. Machian The String intuition of scale dualities is useful here. I also think a GR intuition is useful. Very briefly, think of the standard model (flat spacetime) as one particular domain of this generalised general covariance, which operates under a constraint of "conservation in time" which is given a priori. In general, physical geometry is determined by the logic of the propositions being asked. Alternatively, allowable propositions follow from geometrical constraints.

Clearly the real physical justification of this can only lie in the eventual computation of new physical quantities. This relies on an understanding of (something very mathematical) higher descent theory (categorical cohomology) that I do not yet have, but perhaps others do.

As an example, let us now consider the dimension raising nature of the Gray tensor product. Observe that Gray categories have already been shown to be important in understanding SU(3) confinement from a kinematical point of view. Moreover, they arise automatically out of a consideration of 1.

Thinking quantum mechanically for a moment, a representation space should be sufficiently internalised (in the categorical sense) to be able to describe states. Assuming for now that this leads to bicategory objects one is forced to take Gray tensor product for combinations of physical systems, because only this product has the universal property. This means that there is a link between particle number, or some measure of complexity for a system, and categorical dimension. Other aspects of Gray categories are also pertinent to QM, eg. weakened distributivity.

I have actually spoken quite a lot about this with people, and a common reaction is that it is all a pile of junk unless one can rigorously recover the standard model. Then again, a number of people are already working in this direction.

 

[Careful]

Careful
I would never have mentioned Seth Lloyd if this was entirely my thread. But the thread was actually started by someone else, and I always try to be considerate of others' ideas.

Science, for me, consists of reading papers, being open to ideas and working out your own stuff. Then, you *think* about it and see if they make sense or not. If they don't, because either some elementary unrepairable mistake is made (under the pleitoria of technical details), or because the idea is obviously naive and would spring to the mind of anyone with some intelligence after one hour of thought, THEN you should debunk it and warn people for it. That is your *duty* as a scientist, being considerate is the work of a politician.

 

[Careful]

**
When String theorists tell me that we cannot even in principle calculate the rest masses of fundamental particles **

What do you mean by this ? Are you just saying that the masses of elementary particles are not predicted from string theory calculations ?
This should tell you something about string theory, not about the method of physics.


** The reason I often launch into categorical or logical jargon is because I believe physical intuition and categorical intuition have a great deal in common. To do GR, one certainly does not need category theory. To do lattice QCD, one does not need category theory. To some extent the problem with the jargon is a lack of physical terminology to go beyond these domains.**

But for that, you probably do not need category theory either! You just need an entirely new *vision* (just as Einstein had).

**
1. Measurement The necessity of internalisation (the "context" or "environment" must be taken into account in determining the nature of propositions) forces an acceptance of, amongst other things, a categorical comprehension scheme. This must, as in the mathematical treatment, be an axiomatic issue.
**

A question: is the moon a part of your context when you are doing a lab experiment ? You seem to be saying that the set of propositions must be dynamically generated relative to its environment. This is certainly true in GR (and there such idea makes sense); the problem is that it is probably impossible to achieve this in a purely unitary scheme for QM (one has to impose by hand a preferred set of macrostates). Are you claiming that you are going to solve the micro-macro problem in QM through categorization ?


**The String intuition of scale dualities is useful here **

Can you explain me what this has to do with Mach (I shall disgard here that these dualities are not even rigorous at all ) ??

** Very briefly, think of the standard model (flat spacetime) as one particular domain of this generalised general covariance, which operates under a constraint of "conservation in time" which is given a priori.**

Give me your principle of generalized covariance ! Are you referring to the Kretchmann debate here (that one can write flat space physics as a generally covariant theory with constraints - through Lagrangean multipliers ?).

Sorry, but all your comments are just to vague.

** In general, physical geometry is determined by the logic of the propositions being asked. Alternatively, allowable propositions follow from geometrical constraints. **

This statement needs some clarification: you can recover the causal structure but not the local scale factors unless you go over to a fundamentally discrete scheme such as causal sets. If so, you should add that such line of thought which gives up manifoldness, imposes the almost impossible problem of recuperating it on appropriate scales (people really got *almost* nowhere in this problem). And certainly category theory is not going to solve it.


**
This relies on an understanding of (something very mathematical) higher descent theory (categorical cohomology) that I do not yet have, but perhaps others do.
**

I have given such ideas some thought (in the context of the manifoldness problem) and it occurred to me that all these constructions are too sensitive to combinatorical ``accidents´´ and hence not very useful. My view in this matter that a more robust scheme in the spirit of a ``coarse grained´´ version of metric geometry (a la Gromov) is much more useful.

**As an example, let us now consider the dimension raising nature of the Gray tensor product. Observe that Gray categories have already been shown to be important in understanding SU(3) confinement from a kinematical point of view. Moreover, they arise automatically out of a consideration of 1.**

Could you specify this more? As I said, you can almost do anyting with category theory KINEMATICALLY (this applies also to all other ``virtues´´ you mention), but the DYNAMICAL aspect is obscure to me (example: causal sets do not have a quantum dynamics yet.).

 

[Kea]

As someone who claims to be familiar with higher descent theory I am surprised you have this attitude towards it. We would be most keen to hear about your alternative program (Gromov's) on another thread. I am sorry I do not have the time at present to discuss all these points in great detail. Briefly, however:

Are you just saying that the masses of elementary particles are not predicted from string theory calculations? This should tell you something about string theory, not about the method of physics.

Quite true. But readers following this discussion are aware of my opinion that some current M-theoretic thinking is not all that different from the categorical approach, and I am more upset because I see them as allies than because I think it is all a complete waste of time.

But for that, you probably do not need category theory either! You just need an entirely new vision (just as Einstein had).

Not being Einstein will not discourage me from continuing this thread for the benefit of those who are interested.

You seem to be saying that the set of propositions must be dynamically generated relative to its environment... The problem is that it is probably impossible to achieve this in a purely unitary scheme for QM (one has to impose by hand a preferred set of macrostates). Are you claiming that you are going to solve the micro-macro problem in QM through categorization?

First of all, and this is not a small point, you use the word set casually, which in this context it is important not to do. Probably impossible does not mean impossible. Besides, you seem to have a picture of a fixed set of macrostates but one thing categories do very nicely is allow us to dodge this kind of problem. Of course, I'm not claiming that this has been solved as yet, but I will express my opinion that category theory can do it.

Can you explain me what this has to do with Mach?

I simply use the term Machian to refer to anything that relates the small scale to the large in such a way that there is a correspondence of physical observables. The principle of GGC must then be formulated with the understanding that descent topologies somehow encode observables. Since scale with duality loosely corresponds to categorical dimension, GGC takes the form of a generalised Poincare duality (I simply don't know how to express this better) in the (higher) topos cohomology.

Are you referring to the Kretchmann debate here?

No. I am not familiar with this debate.

...And certainly category theory is not going to solve it.

Really? We would appreciate it if you could substantiate such a large claim.

I'm afraid we will have to leave Gray categories to a later time. You seem to view categories as no more than an organisational tool. Even if that were true, which it is not, it may still be that is something that physics requires. This remains to be seen.

 

[Careful]

**As someone who claims to be familiar with higher descent theory I am surprised you have this attitude towards it.**

I do not claim to be actively familiar with it anymore but there were times that I considered it (a sin of youth).

**
Not being Einstein will not discourage me from continuing this thread for the benefit of those who are interested. **

Good ! You shouldn't


**First of all, and this is not a small point, you use the word set casually, which in this context it is important not to do. **

Could you clarify this (I think my use of word set is quite harmless there)?

**Probably impossible does not mean impossible. **

Oh, but I am quite confident that in this context it does ! There is no no go theorem yet (true) but I have the unmistakable evidence that it is an eighty year old wound.

**
I simply use the term Machian to refer to anything that relates the small scale to the large in such a way that there is a correspondence of physical observables. **

I guess you mean energy scales. But the use of Machian is very confusing here.

**The principle of GGC must then be formulated with the understanding that descent topologies somehow encode observables. **

In simple terms, you mean that handles glued to space represent observables (such as particles), no? I would kindly request you, for the general readership, to use the most common terminology possible (I am sure that can be done). If so, you must be informed that it is quasi impossible to obtain a non perturbative gravitational dynamics which includes such topology changing spaces (and as such it is a wild, speculative idea which has been around for at least thirty years now).


**Since scale with duality loosely corresponds to categorical dimension, GGC takes the form of a generalised Poincare duality (I simply ?**

What scale (so what is your model of spacetime, how do you put a measure stick and so on..) ?? I can see how the above idea of GGC relates to cohomology classes, but you have to tell me what this duality is about (since I see no dynamical model here).


**Really? We would appreciate it if you could substantiate such a large claim.**

I will, in due time, when you have told me what your spacetime model is (to which category do you restrict?)


** You seem to view categories as no more than an organisational tool. **
Yes

**Even if that were true, which it is not, it may still be that is something that physics requires. This remains to be seen**

Why would it not be true?

 

[Kea]

Could you clarify this (I think my use of word set is quite harmless there)?

In an elementary topos, a proposition is understood in terms of its interpretation in terms of truth values. This is an axiomatic setting outside of ordinary set theory. This is simply a fact.

In simple terms, you mean that handles glued to space represent observables (such as particles), no?

No. The point is that categories can do more subtle geometry than this. If all we were going to do was work with ordinary manifolds then I would agree: categories would not be enough. This is, however, very far from being the case.

What scale (so what is your model of spacetime, how do you put a measure stick and so on)?

One does not begin with a model of spacetime, which is clearly a highly derived concept. And yes, when I say scale I am thinking of energy scales, but then again even this is an entirely classical concept. Physically, energies are no different to quantum numbers: they need to be looked at in the context of the experiment. So, as I often say here on PF, the question what is scale is by no means trivial, and I will certainly not be answering it in a few lines. One does not work in a simple 1-dimensional category. Hence the question what category do you restrict to is completely meaningless. As I am sure you know, categorical cohomology allows different categories to act as coefficient spaces.

I can see how the above idea of GGC relates to cohomology classes...

Good! You are the first to say that.

 

[Careful]

**In an elementary topos, a proposition is understood in terms of its interpretation in terms of truth values. This is an axiomatic setting outside of ordinary set theory. This is simply a fact. **

I did not mean to define what a proposition is, I wanted to speak about a set of propositions such as : ``the moon is there, or the Earth is round, etc... ´´

**No. The point is that categories can do more subtle geometry than this. If all we were going to do was work with ordinary manifolds then I would agree: categories would not be enough. This is, however, very far from being the case.**

I KNOW that, but (a) it is always GOOD to give an example which is understandable for everyone (you have to learn to communicate an idea intuitively, and many mathematicians often can't - they are stuck in their details) (b) you seem not to appreciate my comments that deviating from manifoldness too violently highly likely leads to nonrenormalizable theories.


**One does not begin with a model of spacetime, which is clearly a highly derived concept. And yes, when I say scale I am thinking of energy scales, but then again even this is an entirely classical concept. **


So what do you start with (we need to know what we are talking about!)?? The use of energy scales in a fundamental theory is IMO highly anti relativistic, but ok, the high energy community would back you up here.

**Physically, energies are no different to quantum numbers: they need to be looked at in the context of the experiment.**

So, you stick to the reduction postulate in QM? Right?


**So, as I often say here on PF, the question what is scale is by no means trivial, and I will certainly not be answering it in a few lines. One does not work in a simple 1-dimensional category.**

That is a difficult question REGARDLESS of categorical considerations.

**Hence the question what category do you restrict to is completely meaningless.**

It is not ! If you do not do that, it is impossible for you to define a controllable dynamics! I would appreciate it if you would comment on my other remarks too and not only select those which are specifically category theory oriented.

 

[Kea]

I did not mean to define what a proposition is, I wanted to speak about a set of propositions such as: "the moon is there" or "the Earth is round" etc...

Yes, but the idea that physical propositions can form a fixed set is IMHO exactly the problem. The notion of a fixed classical reality is tantamount to the inclusion of a universal observer in one's framework. In the reduction of the general picture to ordinary QM one must of course recover some such description, but I believe it is a prejudice that needs doing away with.

...it is always GOOD to give an example which is understandable for everyone.

OK. Fair enough.

...you seem not to appreciate my comments that deviating from manifoldness too violently highly likely leads to nonrenormalizable theories.

Except that, to my knowledge, the best understanding of renormalisation that we have comes from the current Connes, Marcolli, Kreimer et al work, which is beginning to use motivic cohomology and such things rather heavily...

So what do you start with (we need to know what we are talking about!)?

I guess what you want to know is: what higher dimensional categories should one operate into be able to do either (a) GR or (b) the standard model. For the latter it would seem a suitable choice of Gray categories (with the ability to do quantum logic), such as a rich form of Vect, would do the trick.

So, you stick to the reduction postulate in QM? Right?

Well, not exactly. Although the only way I know how to speak about observables is in a language that sounds like QM, it is quite certain that the topos-like axiomatics are naturally written in a form that only reduces to the usual case on the choice of a particular model.

The interplay between theories and models is an important aspect of the logical point of view, and one of the main reasons that I make the claim that categories are much more than an organisational tool.

 

[Careful]

**Yes, but the idea that physical propositions can form a fixed set is IMHO exactly the problem. The notion of a fixed classical reality is tantamount to the inclusion of a universal observer in one's framework. **

AH, but that depends upon what you want to do with QM (and that is the whole crux of the story). I mentioned previously that for a classical theory, there is no problem, the set of physical propositions we can make is DYNAMICAL (I think I explicitely mentioned this already in post 97). Example: put some differential equation in your computer with exotic intial conditions (possibly with boundary conditions). Suddenly you notice that very complex patterns form in time for this particular solution mankind has never seen before. At that moment you learn something more and your set of propositions gets enlarged. All you need for that is a classical theory of the brain which allows for pattern recognition and an (classical) arrow of time.

Now, in ordinary QM you are screwed, the propositions are merely put in by the experimentator and not dynamically generated at all. So, this leaves a few possibilities :

(a) you introduce a double world picture, both with its own dynamics and a principle which interrelates them. This is for example done in the work of Aerts et al (based upon work of Piron). He considers quantum words embedded in different classical entities (the problem is that there is no dynamics yet). The kinematical setting of this work is very abstract but concrete (they work in a specific category as you would call it)
(b) Everything is quantum but then my guess is that you have to make QM nonlinear to make sense out of the macroworld (and as such out of a dynamical set of propositions)
(c) Everything is classical and the Schroedinger equation is nothing but a statistical divise containing macroscopic parameters (like mass and charge) to compute outcomes of experiments. Therefore, we have to look for an underlying deterministic mechanics (my preferred approach)

If you have something to add, please go. You see: you can adress this problem within a fixed ``master´´ category (you just have to choose it big enough so that it suits your desires).

**Except that, to my knowledge, the best understanding of renormalisation that we have comes from the current Connes, Marcolli, Kreimer et al work, which is beginning to use motivic cohomology and such things rather heavily...**

I don't know that and I would like to hear what NEW insight is gained vis a vis the methods physicists normally use.

**I guess what you want to know is: what higher dimensional categories should one operate into be able to do either (a) GR or (b) the standard model. For the latter it would seem a suitable choice of Gray categories (with the ability to do quantum logic), such as a rich form of Vect, would do the trick. **

Sure, everyone would like to know this ! So, I suggest that you concentrate on explaining the virtues of these two categories.


**The interplay between theories and models is an important aspect of the logical point of view, and one of the main reasons that I make the claim that categories are much more than an organisational tool. **

Hmmm, but it are in the end only the models which form the *physical* theory. So your level of abstraction is good for mathematics, but in the end physics concentrates itself on a specific kinematics endowed with a specific DYNAMICS.

Cheers,

Careful

 

[Kea]

So, this leaves a few possibilities :
(a) you introduce a double world picture, both with its own dynamics and a principle which interrelates them. This is for example done in the work of Aerts et al (based upon work of Piron). He considers quantum words embedded in different classical entities (the problem is that there is no dynamics yet). The kinematical setting of this work is very abstract but concrete (they work in a specific category as you would call it)
(b) Everything is quantum but then my guess is that you have to make QM nonlinear to make sense out of the macroworld (and as such out of a dynamical set of propositions)
(c) Everything is classical and the Schroedinger equation is nothing but a statistical divise containing macroscopic parameters (like mass and charge) to compute outcomes of experiments. Therefore, we have to look for an underlying deterministic mechanics (my preferred approach)

My preference is for a mixture of (a) and (b). My work is probably most closely related to (b). Piron's ideas have led many people to topos theory. Quite frankly, as a physicist, I don't see how you can take (c) seriously.

I don't know that and I would like to hear what NEW insight is gained vis a vis the methods physicists normally use.

The renormalisation studies are about the methods physicists normally use. Sure, it's very mathematical, and I can well understand why any physicist would be reluctant to touch it...but I reserve the right to burden myself with any mathematics that I have good reason to think supports this approach.

So, I suggest that you concentrate on explaining the virtues of these two categories.

That is, naturally, the long term goal of this and some other threads. If I could do this in the next 5 minutes, I would be busy calculating things and not wasting my time here. Moreover, PF has no facility for drawing lots of diagrams.

Hmmm, but it are in the end only the models which form the *physical* theory.

Well, time will tell, won't it? Careful, you have not given us a single solid argument to deter people from this approach. Once again, I urge you to begin another thread, introducing us to your own ideas.

 

[Careful]

**My preference is for a mixture of (a) and (b). My work is probably most closely related to (b). Piron's ideas have led many people to topos theory. Quite frankly, as a physicist, I don't see how you can take (c) seriously.***


My God, you are completely unaware of the fact that the best thinkers in physics have mostly taken (c) seriously (and continue to do so). To name a few: Einstein, de Broglie, 't Hooft, A.O Barut (partly) etcetera... . ¨I want to stress that (c) is a logical possibiltiy which has NOT been experimentally refuted. Moreover, (a) as I said is really *inexistant* in the sense that there is no DYNAMICS yet (although this approach goes along for some twenty years too no?) (b) has been the subject of intense research without any conclusive outcome so far. Considering (c) is usually frowned upon albeit there exist already some partial results in that direction (SED, Self field approach etcetera)! These theories partly reproduce in a (semi) classical way quantum results (so they left the kinematical stage already for a some 25 years) and have a clear (classical) ontology.


**The renormalisation studies are about the methods physicists normally use. Sure, it's very mathematical, and I can well understand why any physicist would be reluctant to touch it...but I reserve the right to burden myself with any mathematics that I have good reason to think ssupports this approach. **

So, you cannot tell us why it brings us anything extra while you used this argument to ``counter´´ my objection that if you make the category too wild, the dynamics you are interested in is probably nonrenormalizable. There is serious evidence for this claim: check out the literature in dynamical triangulations to start with. Moroever such debating tricks are not serious : you should consider going into politics since you clearly do not like to answer real objections.


**That is, naturally, the long term goal of this and some other threads. If I could do this in the next 5 minutes, I would be busy calculating things and not wasting my time here. Moreover, PF has no facility for drawing lots of diagrams. **

You can still explain in words...

**Well, time will tell, won't it? Careful, you have not given us a single solid argument to deter people from this approach. Once again, I urge you to begin another thread, introducing us to your own ideas.
**

O yeh, I have given pleanty of them: (a) it did not bring anything new yet (b) I did not hear yet any argument why it should contribute one day to physics (on the contrary, there is evidence that you have to keep your kinematical structure under control - but of course you are completely ignoring these facts or are simply not aware of them) (c) the examples you gave us are entirely *kinematical* and avoid as such the real problem: that is the dynamics (d) the good inventions in physics NEVER emerged from a twisted desire to abstraction, but always were the result of deep, albeit relatively simple ideas and calculations.

So, IMO you are a mathematician who is on a promotional tour trying to link her business to ``physics´´. Perhaps I am wrong and you can still present us some real physics = kinematics + dynamics.

 

[Kea]

Careful

You have voiced your objections and are no longer adding value to this thread. The first points above would be more appropriate on a thread that discusses your own, clearly superior, ideas.

 

[Careful]

Careful
You have voiced your objections and are no longer adding value to this thread. The first points above would be more appropriate on a thread that discusses your own, clearly superior, ideas.

Your answer clearly expresses that there is nothing to it yet otherwise you could give a clear and unambiguous answer. :zzz: BTW, some of my ideas concering QM were already discussed on the quantum mechanics forum. I shall not bother you anymore in your self promotion activities. It is clearly a waste of my time.

 

[setAI]

Oh yeh, I did, but you started off bad. You referred:
``The Computational Universe: Quantum gravity from quantum computation
Seth Lloyd
http://arxiv.org/abs/quant-ph/0501135´´
If you look up the word CRACKPOTISM 2005, this paper should be in the top ten. It is not only utterly naive, but it contains elementary mistakes as well.

the quantum computational approach is currently the most fruitful and promissing thing to happen to cosmology since the discovery of the Big Bang- you stand practically alone amongst all professional scientists in your disreguard of Seth's Thesis-

here is a section of my recent "IT from qubit" article:

...given the nature of Quantum Mechanics and Quantum Computers the next logical step was obviously the search for a theory Quantum Gravity through Quantum Computational Cosmology- in essence to recognize that quantum computers are harnessing Nature’s own processes and that the Cosmos itself should be described as a quantum computation!



Seth Lloyd and others in the field of Quantum Computational Cosmology conjecture that the 'correct' theory-of everything for our universe will be solved through universal quantum computation: “Computational universality allows a quantum computer to give rise to all possible computable structures... such a universal quantum computer that computes all possible results, weighted by their algorithmic amplitude, preferentially produces simple dynamical laws. Our own universe apparently obeys simple dynamical laws, and could plausibly be produced by such a universal quantum computer.” –Seth Lloyd- obviously the implications of this transcend even the most fantastical Virtual Reality and Time–travel concepts-



Lloyd conjectures that these physical laws will be a form of Quantum Gravity emergent from the computation of a Quantum Cellular Automaton embedded in a lattice of quantum logic gates with 4 connections [2 inputs/ 2 outputs]- this automatically establishes by it's inherent structure a 4D spacetime metric with 1 degree of freedom establishing a causal hierarchy between universe-states corresponding to the causal structure of spacetime which emerges as Time/Causality/ sets the covariant entropy bound/ and establishes the information bound that shapes the structure/ rules/ evolution of physical systems and begins to resolve the mystery of why/how time/the quantum geometric limit/ and the entropy/information bounds are complementarily interrelated!


which means the old idea of a theory-of-everything that you can print on a T-shirt is within view! the correct theory of QG [or whatever the correct theory[ies] is/are] could easily be expressed as the eigenvalues of a Quantum Cellular Automaton formulated as an algorithm for a 2input/2output quantum logic-gate matrix-



some more research in Quantum Computational Cosmology:



http://www.arxiv.org/abs/quant-ph/0506113
http://arxiv.org/abs/quant-ph/0502166
http://arxiv.org/abs/gr-qc/0403057
http://www.arxiv.org/abs/gr-qc/0503073
http://arxiv.org/abs/quant-ph/0505064
http://www.arxiv.org/abs/gr-qc/0510052
http://www.arxiv.org/abs/gr-qc/0412076

Crackpotism indead! within a decade or two we will be able to run quantum algorithmic versions of all of our cosmological theories on a quantum computer and examine their hilbert spaces to determine if spacetimes like ours are a possible result- if we run versions of String Theory and LQG and nothing like our world results- then those theories can immediately be tossed and forgotton! decades of conjecture settled and disgarded in a lazy afternoon-

this technology is actually making theory obsolete- or rather it is transorfming theoretical physics into reverse engineering! the future of theoretical science will be very different when anyone can check their theories against the Universe itself!

 

[Kea]

Thank you, setAI. It was my opinion that we should probably just ignore this empty tirade, rather than encourage it.

 

[Careful]

Thank you, setAI. It was my opinion that we should probably just ignore this empty tirade, rather than encourage it.

I actually *know* that I am far from being alone in the professional society with my opinion here. That the quantum computing community wants to self promote some own ``ideas´´ (because there really is no theory) concerning QG is only natural (and can indeed lead to such proposals). Again, I actually read the paper *in detail* (which was hard to do because he uses obscure constructions); before you SetAI make such quotations, you might (actually should) do the same effort (in the same way I guess Kea did not read it either).

Cheers,

Careful

 

[vanesch]

I would like to propose something to the different antagonists here which - I hope - will calm down spirits (or attract me a lot of trouble :-). I'm working in much more applied domains and I have to say that I cannot even follow technically several discussions around here. Nevertheless, I notice something that I consider a fundamental problem in attitude (which you do not find in other branches of science to my knowledge).

I think it is fair to say that all attempts to unify general relativity and quantum theory are more or less embryonic attempts at formulating a possible frame for a future, speculative theory. No real *theory* exists, which clearly leads to the quantum theory we know of on one hand, and to general relativity on the other, without ambiguities ; and even if such a theory one day would emerge, one should keep in mind that it is still a totally speculative endeavour.

Given the situation, two points - I think - can be made:

1) all good ideas are welcome! Nevertheless, one shouldn't forget what Feynman set out as his attitude in scientific endevour: if you have an idea, you should try, by all means, to show that it DOESN'T work. You shouldn't try to show that it works, but you should rather try to find why it doesn't work. It is only when you've tried that, honestly, in all possible ways, and you *do not find a single way to show that your idea is flawed*, that you can show it to others, who are then supposed to do exactly the same.
It is my personal impression that a lot of people working on different ideas on the unification between general relativity and quantum theory do not play that game, but rather the opposite ; that they try to convince others that their idea WILL OVERCOME all eventual troubles, and they seem to be hostile to the "normal" attitude of other scientists, which is: trying to find why the idea cannot work. I cannot undo myself from the impression that the ideas in this field are usually *strongly* oversold ; I think more self-critique is due when presenting ideas.

2) one should keep an open mind. Although it requires of course some "faith" in the idea you're working on to keep being motivated, it should not turn into a religious war. One shouldn't feel "attacked" by any other scientist who tries to point out where your idea has a problem ; in fact, normally you should have thought of it yourself and have the answer ready, and if not, you should be grateful that somebody is pointing it out for you. The attitude I have often seen has been rather to close oneself up into different "sects" where the only thing that counts is the *promotion* of the dogma at hand, and the denial of the validity of others' critiques or approaches. Although psychologically understandable, I think it leads to uselessly nasty and unproductive discussions.

So let's get back to "normal" scientific discussion which consists in:
1) pointing out where one sees a serious problem in the other person's ideas and where
2) that other person has already considered the objection and knows the answer to it (in which case the first author of the critique learns something) OR where the one pointing out a new idea is confronted with a critique he didn't think of, which sends him back to the drawing board.

Amen

 

[Careful]

I would like to propose something to the different antagonists here which - I hope - will calm down spirits (or attract me a lot of trouble :-). I'm working in much more applied domains and I have to say that I cannot even follow technically several discussions around here. Nevertheless, I notice something that I consider a fundamental problem in attitude (which you do not find in other branches of science to my knowledge).
Amen

I fully agree : let me refer people to a discussion I had with Vanesch on the philosophy forum concering consciousness in the MWI to QM. Although it is clear that I think that it stinks, I still acknowledge that it is a logical and consistent approach (although not complete) which does the trick (and in the mean time we had fun driving each other nuts ). To add a further comment to what Patrick says here: I think he and I agree that it is of extreme importance to have a *physical* theory which produces falsifiable results in a reasonable amount of time (say 5 years). Actually, I would add that the production of an experimentally refuted theory which is based upon clear physical principles actually teaches us *more* than talking about a theory which either does not exist, makes no predictions at all or is not logically well founded. As a string non believer, I must nevertheless admit that string theory is the most logical game in town we have so far (a weakness is that it did not produce any physical result so far of course , but none of the nonperturbative approaches did either.). I would like to invite Kea to do her best and try to give one detailed example with dynamics (if possible) which makes her *believe* in what she does. It is clear that I dismissed the category approach some time ago for good reasons based upon concrete calculations within what you would expect to be the most ``reasonable kinematical category´´ on which to define a dynamics. However, I would not object consideration of an honest example without the addition of buzz words.

Cheers,

Careful

 

[Kea]

I must nevertheless admit that string theory is the most logical game in town we have so far...

This is String theory.

 

[Kea]

Chronos!

On Not Even Wrong, Woit has mentioned this beautiful article by the mathematician Mazur
http://www.math.harvard.edu/~mazur/preprints/when_is_one.pdf

I think it is just for you.

 

[vanesch]

Chronos!
On Not Even Wrong, Woit has mentioned this beautiful article by the mathematician Mazur
http://www.math.harvard.edu/~mazur/preprints/when_is_one.pdf
I think it is just for you.

It wasn't meant for me, but it turns out to be helpful for me !

Thanks, Kea

 

[Kea]

Reference:
The Anthropic Landscape of String Theory
L. Susskind
http://arxiv.org/abs/hep-th/0302219

Perhaps it is about time that, in regard to the Third Road approach to String theory, we thought about some of the physical aspects of the landscape.

When a physicist of the calibre of Weinberg accepts the notion of an anthropic principle, one should take the science behind the idea seriously. The question is: how might one retain the landscape and yet do away with the ludicrous notion of anthropicity? Is this possible at all?

The Third Road would say that the notion that the multitude of vacua exists, in any objective sense, is erroneous. What we observe depends very much on the context of the experiment. So, until we are capable of devising experiments that step outside the conditions under which we are used to operating, we should not be at all surprised that reality has the appearance of magically fitting parameters that could, according to the standard picture, take on many other values.

There is a big challenge here: to rigorously derive the landscape in a category theoretic framework, and hence show that it is possible to place constraints upon it which give it predictive power.

Looking at Susskind's article:

This change in viewpoint is demanded by two facts, one observational and one theoretical. The first is that the expansion of the universe is accelerating...The second fact is that some recent progress has been made in exploring the landscape.

This statement is followed by a definition of the landscape. Let the landscape be parameterised by a collection of fields such that the value of V(\mathbf{\phi}) at a vacuum point gives the cosmological constant \Lambda for the vacuum. Special SUSY vacua with V \equiv 0 form a flat subspace within the hilly landscape, replete with great cliffs (domain walls) and mountain passes.

Hopefully the reader can see that already at this point the landscape picture is beginning to make all sorts of assumptions about the nature of a multitude of universes as if they actually exist. Moreover, these assumptions have been made within the context of standard M-theory, ie. with the addition of no new physical principles.

Susskind then goes on to discuss how vacua may be parameterised by
sets of integers which arise from different ways of wrapping things around compactified dimensions. It turns out to be possible to recover the Standard Model (!) with a small positive \Lambda by exploring this landscape.

OK. So to do away with the landscape rigorously we just have to begin by recovering the SM from a fully working M-theory... Sigh. It always comes down to that. :zzz:

 

[Chronos]

Thanks for the plug, Kea. Mazur has greatly influenced my admittedly naive ideas. I've never actually mentioned that on PF, and I am, well, shocked you made the connection [is it not a truly brilliant treatise?] You scare me sometimes.

Careful, you make good points. But, your criticism of Kea was disturbing and misinformed, in my opinion. She is one of the most tolerant and forgiving people on PF, along with SelfAdjoint. That aside, I am a huge fan of QIT. Not sure if that is the third road, or the fourth road, but, I'm convinced it is the right road.

ps. I forgot to mention the excellent contributions SetAI and Vanesch made to this discussion.

 

[Careful]

**
Careful, you make good points. But, your criticism of Kea was disturbing and misinformed, in my opinion. She is one of the most tolerant and forgiving people on PF, along with SelfAdjoint. That aside, I am a huge fan of QIT. Not sure if that is the third road, or the fourth road, but, I'm convinced it is the right road. **

I do not think so, I shall read the Masur paper (but at first glance it seems like an introduction to the playground of category theory accompanied with some philosophical remarks towards physics). My comments are still very adequate since I come up with CONCRETE evidence that all these generalizations probably have very little applicability (but again, nobody cares).

 

[Kea]

...but at first glance it seems like an introduction to the playground of category theory accompanied with some philosophical remarks towards physics...

Indeed! We confess.

 

[Chronos]

Looks like hand-waving to me. I see more mud than cement.