Theories without Fundamental Space and Time

[kiki_danc]

What is the difference between spacetime and fundamental space and time?

Fundamental space and time is indeed the classical spacetime. And I guess all quantum gravity theories are going beyond fundamental space and time. The following list is taken from the quantum gravity entry of Wikipedia (they are in addition to the leading candidates of string theory and loop quantum gravity). There are just so many possibilities and models. I'm specifically looking (or filtering) for ones where the quantum degrees of freedom (of whatever) that makes up or create emergent space and time can be directly influenced or manipulated. Anyone care to share what models can do this? With so many models and possibilities. We need guidance from any data (no matter how unconventional) to have any chance to arrive at the right quantum gravity theory.

• Asymptotic safety in quantum gravity
• Euclidean quantum gravity
• Causal dynamical triangulation[52]
• Causal fermion systems
• Causal Set Theory
• Covariant Feynman path integral approach
• Group field theory
• Wheeler–DeWitt equation
• Geometrodynamics
• Hořava–Lifshitz gravity
• MacDowell–Mansouri action
• Noncommutative geometry
• Path-integral based models of quantum cosmology[53]
• Regge calculus
• Scale relativity
• Shape Dynamics
• String-nets and quantum graphity
• Superfluid vacuum theory a.k.a. theory of BEC vacuum
• Supergravity
• Twistor theory[54]
• Canonical quantum gravity
• E8 Theory
• Quantum holonomy theory[55]

 

[MathematicalPhysicist]

Fundamental space and time is indeed the classical spacetime. And I guess all quantum gravity theories are going beyond fundamental space and time. The following list is taken from the quantum gravity entry of Wikipedia (they are in addition to the leading candidates of string theory and loop quantum gravity). There are just so many possibilities and models. I'm specifically looking (or filtering) for ones where the quantum degrees of freedom (of whatever) that makes up or create emergent space and time can be directly influenced or manipulated. Anyone care to share what models can do this? With so many models and possibilities. We need guidance from any data (no matter how unconventional) to have any chance to arrive at the right quantum gravity theory.

• Asymptotic safety in quantum gravity
• Euclidean quantum gravity
• Causal dynamical triangulation[52]
• Causal fermion systems
• Causal Set Theory
• Covariant Feynman path integral approach
• Group field theory
• Wheeler–DeWitt equation
• Geometrodynamics
• Hořava–Lifshitz gravity
• MacDowell–Mansouri action
• Noncommutative geometry
• Path-integral based models of quantum cosmology[53]
• Regge calculus
• Scale relativity
• Shape Dynamics
• String-nets and quantum graphity
• Superfluid vacuum theory a.k.a. theory of BEC vacuum
• Supergravity
• Twistor theory[54]
• Canonical quantum gravity
• E8 Theory
• Quantum holonomy theory[55]

Aren't superstring theories already incorporate supergravity and supersymmetry?

 

[Fra]

IMO the way stringtheory treats spacetime is too conservative. Sure, it does include strange extra dimensions and things which to some is weird, but it is still fairly faithful with respect to the geometric programs that presume a spacetime continuum.

And from my perspective of inference, order and countability is extremely important to warrant stability and computability to be able to actually get some expectations out from it. And I prefer to start from elementart starting points such as distinguishable states, and to construct expectations on the future states.

But when complexity gets very HIGH, it is often easier to consider things embedded in a continuum. This is fine but To maintain control when you step into that one must distinguish between the physical and the mathematical degress of freedom, and extremely careful integration measures must be defined to prevent mathematical divergences which obviously are not physically motivated. Here we have imo a gigantic mess in current models.

I think a program must step back, analyze and rectify these problems to bring back order and computability in order to not get lost on fake landscapes that is created by physicists messing with complex mathematics of continuum models, where we since long lost track of what we are really doing.

I see many reasons to suggest that we need a discrete starting point, and in these programs the generic idea is that regular spacetime will be recovered in the large complexity limit as embedding dimensions or similar. Thus the spacetime continuum in the sense of background for all the happens is IMO likely an approximation only - rather than the other way around! However, one would probably expect that the complexity limit where the continuum should be effectivel be recovered is still beyond experimental reach except for the "indirect support" that a discrete model may come with explanatory power that extrapolates into states of unification etc.

/Fredrik

 

[kiki_danc]

Einstein tried to unify general relativity with electromagnetism but failed because he missed the weak and strong forces. Could we say that our present attempt to unify the forces can only fully succeed if we take into account other possible forces or dynamics besides that in the Standard Model? How many acknowledge this scenario to be the possible case.. or is our attempt to unify spacetime with the quantum is regardless of whether they are other unknown forces, etc.?

 

[kiki_danc]

Einstein tried to unify general relativity with electromagnetism but failed because he missed the weak and strong forces. Could we say that our present attempt to unify the forces can only fully succeed if we take into account other possible forces or dynamics besides that in the Standard Model? How many acknowledge this scenario to be the possible case.. or is our attempt to unify spacetime with the quantum is regardless of whether they are other unknown forces, etc.?

For perspective... LQG is the attempt to unify spacetime with the quantum regardless of whether they are other unknown forces, etc. While string theory is said to be still trying to find the basic guiding equations. For other forces than the standard model, there is the proton radius problem where some force could be at work but not greatly debated (for example reference: https://phys.org/news/2016-08-deuterium-nucleus-proton-radius-puzzle.html)... but could it affect unification significantly or only have small contribution? I was wondering about none-gauge forces. They say the Higgs boson can be thought of as mediating a "fifth force" that is not a gauge force. It is an example of a type of interaction (force) called a "Yukawa interaction" rather than a gauge interaction. What other interaction forces other than them?

So if there are new forces.. could it be normal gauge forces.. or none gauge ones.. or if gauge theory was just emergent.. could the new forces be the more elementary constituents.. or are they in the form of other objects like branes and extra dynamics or degrees of freedom, etc.

Ok. I need reference (articles, books..) that give more clarity on the above lines of thoughts concerning possible new forces of nature and what forms they may take.

 

[kiki_danc]

The most famous example is of course string theory.

The general idea is that
- in order to unify or explain what are currently fixed or theoretically "unexplained" or to explain something in a coherent way as opposed to patchwork of effective theories -
one needs to put these things in a larger context which relaxes them. This is the idea behind explaining law as evolution or negotiation.

The idea of strings is in tradition of kaluza klein to consider compactified small extra dimension. Ie in each 4d point there is a 6d manifold that can varying topplogy etc. Then try to "explain" and unify all forces from the interaction propertirs of this manifold in 4d space. This increase the complexity and sometimes this has more than one solution.

The story is that in string theory is that people conjectures that there are so many ways to compactify the 6d manifold while constraining the cosomlogical scale of 4d part to deSitter space that one speaks of the string landscape. Now a RECENT debatw in string community is that larger part of this landscape is rather wrong (they call it swampland)

Originally there was some hope that there would not be a landacape. Once realized even string theorists startew to talk abouy evolution of law. Smolins evolving law was originally proposed as a conceptusl solution to string landacape problem. But right now i think it transcends itm

There are real string theorists on here that can give you better answers.

I just relate to other researc programs and have opniona on their logic but my own view does not contain strings or no continuum in the starting points.

I am not sure how you want to combine lqg and st. I have no meaningful comments.

/Fredrik

Fra. Do you know how to compute the probability (like 1 in 20 million chance) that our academia supported physicists would be able to crack quantum gravity or arrive at the correct unification of forces or other final theory thing by doing it blind or without any experimental guidance?

This is in contrast to arriving at the theory by having accessed to the data. I think the problem with our physicists is they are expecting the unexpected yet looking for familiar data or guidance even when aware something is wrong (for example Hossenfelder is not immuned to it in spite of her anti-mainstream stance). I stand corrected if this is not the case that's why I mentioned this.

When replying. Please use simple words or ones where people can relate by giving references to others works and clarifying the issues. Because when your writing is too complex and deep that even Urs can't fathom it. What does it leave us normal citizens? For example.. about Smolin evolving laws.. are you saying that different theories can connect by some kind of adaptive evolving laws that hinted by Smolin? Create a simple FAQ or something that you can point to people in the future because as years passed by. Your writing would be even deeper and more complex using unfamiliar words that even knowledgeable physicists not familiar with the concepts would be unable to understand much of the points even if they are lurking somewhere in the arxiv pool.

 

[Fra]

I don't think its rational for science to expect to learn about something without interacting with it, or without having access to observational data.

That said, there is plenty observational data including the condensed form of the patchwork of well corroborated theories we have for physics. But things does not only concern HEP or probing space, we also have more ready access to complex systems here on earth, whose relevance for understanding IMO is underestimated. Mainly due to the common reductionist philosophy of physicists. To speak for myself, I gained a lot of insight from observing and trying to understand how complex systems organise, interact and evolve. This involves biological systems, economical systems, and social systems. If you ponder about evolution of law at the level i do, all these things are potentially at some level described by the same mathematical abstractions as is evolution of physical law. This is indeed a kind of generalisation of probability theory. After all, logic of science has common roots with probabilit theory as it has to do with quantifying degrees of believe in a rational way.

My imprecise writings concerns first of all these abstractions, and the exact mathematical imlpementation of this is something i work on. Unfortunately i am not aware of an existing research program that is in line with mine. But several are related to it. Also once my arguments are precise and actually accomplishes something current programs dont, they will be published but not sooner.

So to speak for myself, the data today is decent enough to feed me trying to find a coherent framework instead of a patchwork of effective theories. A researcher can "experiment" with its own ideas, by exploring logical implications of conjectures analytically/formally and numerically by using computers. I do not blame too low energies at LHC for my lack of progress, I think there are "cheaper sources" of observational data that are relevant. So what is the probability that someone like me will succeed in my lifetime? Surely the vision is an a priori hard and difficult, and looking at history, a human once in a few hundred years will succed at such a task at best. So the odds are skyhigh, but its enjoyable nonetheless and there is no shame for not succeeding ;-)

The creative process of research or learning about anything for that matter can IMHO not be described as a deductive process, where you use only precise steps and arguments. The more precise describtions emerge when progress is made. During the process things may remain "somewhat precise" only to people within the same research community, or alike thinkers.

Precise things can be communicated to the outside of the community only when substantinal progress is made. But at this point the creative part of the problem will be largely done ;)

/Fredrik

 

[kiki_danc]

I don't think its rational for science to expect to learn about something without interacting with it, or without having access to observational data.

That's not entirely accurate.
I'll explain a bit. In the time of Newton. They didn't have access to any relativistic or quantum data.. but that doesn't mean they didn't exist. Scientists in that era were conditioned and accustomed to Newtonian physics. In our age. Physicists were conditioned to relativistic quantum field theory and general relativity (and separately because they couldn't unite the two (yet)). So conditioned are they that the data they seek must be related to the two (or some a bit of modification since quantum gravity has new prediction but only in the Planck scale). Nature is always wiser so the new physics could be not just theories without fundamental space and time but other degrees of freedom. Therefore don't expect the expected.. but prepare for the unknown. However, Because our funding of science were done by universities and departments so stuck with certain line of thoughts. Physicists need to comply with them or else they lost funding. Even Sabine Hossenelder agreed with this in her book "Lost in Math yet she was still a victim of it in spite of trying to look at it from the outside. Hossenfelder still want to think of the ordinary and thought observational data must only be related to expectations from our ordinary senses ..

At this point I'd better stopped commenting about it lest this thread get locked and I'd lose access to answers to my questions so let me proceed with my questions now.

That said, there is plenty observational data including the condensed form of the patchwork of well corroborated theories we have for physics. But things does not only concern HEP or probing space, we also have more ready access to complex systems here on earth, whose relevance for understanding IMO is underestimated. Mainly due to the common reductionist philosophy of physicists. To speak for myself, I gained a lot of insight from observing and trying to understand how complex systems organise, interact and evolve. This involves biological systems, economical systems, and social systems. If you ponder about evolution of law at the level i do, all these things are potentially at some level described by the same mathematical abstractions as is evolution of physical law. This is indeed a kind of generalisation of probability theory. After all, logic of science has common roots with probability theory as it has to do with quantifying degrees of believe in a rational way.

Are you familiar with Shape Dynamics.. which uses Weyl Transformation which is a shape-preserving transformation. Shape-preserving means that angles are unchanged, but overall scale can change. This is in contrast to General Relativity where length is preserved. Is this related to the idea of the relativity of observers (and how to relate the concepts)? What transformation must you use in GR and what are you trying to preserve? And what is the connection of relativity of observers to Smolin evolving laws?

In replying, try to refrain from saying it's your theory because remember personal theory are not allowed. I got nervous whenever you reply afraid the thread may get locked. Instead mention the references and give comments how they could be related or future programme that may be possible.. emphasize on references (and possible improvement that is in the radar mark of the Perimeter Institute Advanced Physics). Another thing. You are so familiar with your ideas that you sometimes assume people understood them. I don't think so.. so please make some kind of FAQ or none can pick them up. This is exactly the reason why Urs earlier in this thread commented what in blazes where you talking about (wondering if it's crackpottish (his word)). Without a FAQ, it will remain like this for years to come. So kindly really make one (or maybe try to point to earlier message of yours for the introduction of the terms you were using and concepts because they are quite foreign even to experts.

My imprecise writings concerns first of all these abstractions, and the exact mathematical imlpementation of this is something i work on. Unfortunately i am not aware of an existing research program that is in line with mine. But several are related to it. Also once my arguments are precise and actually accomplishes something current programs dont, they will be published but not sooner.

So to speak for myself, the data today is decent enough to feed me trying to find a coherent framework instead of a patchwork of effective theories. A researcher can "experiment" with its own ideas, by exploring logical implications of conjectures analytically/formally and numerically by using computers. I do not blame too low energies at LHC for my lack of progress, I think there are "cheaper sources" of observational data that are relevant. So what is the probability that someone like me will succeed in my lifetime? Surely the vision is an a priori hard and difficult, and looking at history, a human once in a few hundred years will succed at such a task at best. So the odds are skyhigh, but its enjoyable nonetheless and there is no shame for not succeeding ;-)

The creative process of research or learning about anything for that matter can IMHO not be described as a deductive process, where you use only precise steps and arguments. The more precise describtions emerge when progress is made. During the process things may remain "somewhat precise" only to people within the same research community, or alike thinkers.

Precise things can be communicated to the outside of the community only when substantinal progress is made. But at this point the creative part of the problem will be largely done ;)

/Fredrik

 

[Fra]

Are you familiar with Shape Dynamics..

I will comment more when i get more time to explain.

Note that I haven't discussed my personal theories at all. A theory consists of a mathematical framework, an so does mine; but they will not be introduced on this forum for sure. But obviously my reasoning about the logic of various issues are strongly coloured by my perspective, and i have at times tried to explain my way of reasoning, but that is not a theory per see.

/Fredrik

 

[kiki_danc]

Here is a new question.
Wiki described about that gauge symmetries can be viewed as analogues of the principle of general covariance of general relativity in which the coordinate system can be chosen freely under arbitrary diffeomorphisms of spacetime. Quoting it:

​

"Gauge theories are also important in explaining gravitation in the theory of general relativity. Its case is somewhat unusual in that the gauge field is a tensor, the Lanczos tensor. Theories of quantum gravity, beginning with gauge gravitation theory, also postulate the existence of a gauge boson known as the graviton. Gauge symmetries can be viewed as analogues of the principle of general covariance of general relativity in which the coordinate system can be chosen freely under arbitrary diffeomorphisms of spacetime. Both gauge invariance and diffeomorphism invariance reflect a redundancy in the description of the system. An alternative theory of gravitation, gauge theory gravity, replaces the principle of general covariance with a true gauge principle with new gauge fields. "

First. It is just analogue so classical general relativity has no fundamental gauge symmetry.
But is it a requirement that all our ultimate theories need to reflect redundancy as in "Both gauge invariance and diffeomorphism invariance reflect a redundancy in the description of the system.". In the case of General Relativity what if there is no redundancy in the description of the system?

If redundancy and gauge principle need to be obeyed by any fundamental theory. If spacetime was really emergent from more primary constituents or ingredients (like spin networks, etc.). Can the redundancy instead be reflected in the more primary ingredients meaning the theory is no longer sensitive to shapes, scales, lengths or time? In other words, can the gauge transformation be made instead to these more primary ingredients (like spin networks, etc)?

 

[Fra]

Are you familiar with Shape Dynamics.. which uses Weyl Transformation which is a shape-preserving transformation. Shape-preserving means that angles are unchanged, but overall scale can change. This is in contrast to General Relativity where length is preserved. Is this related to the idea of the relativity of observers (and how to relate the concepts)?

Shape dynamics is a development from ideas of Julian Barbour, which essentially focues on the nature of time at its core, arguing time as dimension has no place in physics, going back to Machs ideas. I have not read any of his books, but some of his papers. Smolin also mentions Barbour in his own talks and papers as someone that explain the view of "end of time" clearly, in constrast to Smolins reality of time. But Smolins "reality of time" is not anything like Newtonian time. He seem to think of it more like an evolution parameters of laws.

https://fqxi.org/community/forum/topic/360
http://www.platonia.com/FQXi_Full_Proposal_2011.pdf

Barbour says time shall be operationally defined in terms of relative change of position in space, and given initial conditions (state and tangent) the timeless dynamical laws yield the future state. This is why he considers the shapes in 3D and their tangent changes as the right starting point. This corresponds to singling out a preferred 3D+1 of 4D; where the next 3D layer deductively follows from a timeless law.

Paradoxally it seems Smolin was Barbours phd supervisor, but today they seem to hold competing views on the nature of physical law and time.

While I symphatise with the relational ideas (I could even argue that they are not take far enough), set aside issues that SD disagrees with GR except for special cases, i have several conceptual issures, a couple are:

1) 3D space is a non-trivial starting point, that just like time, also begs an explanation. Just like 4D space ca be thought of as evolving 3D structures, why not see 3D space as an evolving 2D space, and 2D as evolving 1D, and 1D as an evolving point? Exactly where does the dimensionality 3 come from?

I will just say that i symphatise partly with this, but stopping at 3D breaks the beauty. I envision that you can keep reducing it further.

2) Another problem is that 3D space and "points" are classical concept. What is the generalization of the "point configuration space", into something that makes sense in a modern inference perspective, which i take to be the founding core of QM. Well represented by this famous quote

"It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature."
-- https://en.wikiquote.org/wiki/Niels_Bohr

"What we can say about" to me, means what an observer can infer (measure + abduce) from interactions. This implies also preconditions such as formulating questions (~ preparing measurement devices etc). This is the reason why i analyse the inference.

So what is the minimal starting point for this scheme? Is it positions in classical 3D space? If not, what?

3) Julian argues that things should be operationally defined in terms of relative changes of positions, by why not argue that laws should also be operationally defined. If the argument is that physical law is there even if we do not know about it, then this lacks perspective. An external observer can easily predict what understanding we have of physical law, by observing the technology our civilisation uses. This the way in which is does make a difference. Then translate this to subatomic particles, explain if there is any principal difference beyond complexity scale?
This is related to my critique against Rovellis relational QM as well. It starts out well, but the failure is that at some points in the hierarcy the "relations" are detached from observation and gets places outside the inference process.

See old thread: https://www.physicsforums.com/threa...able-in-classical-and-quantum-gravity.220841/

Here is a new question.
...
First. It is just analogue so classical general relativity has no fundamental gauge symmetry.
But is it a requirement that all our ultimate theories need to reflect redundancy as in "Both gauge invariance and diffeomorphism invariance reflect a redundancy in the description of the system.". In the case of General Relativity what if there is no redundancy in the description of the system?
...
If redundancy and gauge principle need to be obeyed by any fundamental theory. If spacetime was really emergent from more primary constituents or ingredients (like spin networks, etc.). Can the redundancy instead be reflected in the more primary ingredients meaning the theory is no longer sensitive to shapes, scales, lengths or time? In other words, can the gauge transformation be made instead to these more primary ingredients (like spin networks, etc)?

This is a good focus but a big one. About questions on gauge symmetries vs observer relativity.I commented on this in a way that I suspect no one understood either here (explaining this properly requires no less than a paper and backing it up with other stuff, and this isn't the place)
https://www.physicsforums.com/threads/ed-witten-on-symmetry-and-emergence.927897/

So I would not look at SD in order to understand evolving law. Much deeper grips are needed.

/Fredrik

 

[kiki_danc]

Shape dynamics is a development from ideas of Julian Barbour, which essentially focues on the nature of time at its core, arguing time as dimension has no place in physics, going back to Machs ideas. I have not read any of his books, but some of his papers. Smolin also mentions Barbour in his own talks and papers as someone that explain the view of "end of time" clearly, in constrast to Smolins reality of time. But Smolins "reality of time" is not anything like Newtonian time. He seem to think of it more like an evolution parameters of laws.

https://fqxi.org/community/forum/topic/360
http://www.platonia.com/FQXi_Full_Proposal_2011.pdf

Barbour says time shall be operationally defined in terms of relative change of position in space, and given initial conditions (state and tangent) the timeless dynamical laws yield the future state. This is why he considers the shapes in 3D and their tangent changes as the right starting point. This corresponds to singling out a preferred 3D+1 of 4D; where the next 3D layer deductively follows from a timeless law.

Paradoxally it seems Smolin was Barbours phd supervisor, but today they seem to hold competing views on the nature of physical law and time.

While I symphatise with the relational ideas (I could even argue that they are not take far enough), set aside issues that SD disagrees with GR except for special cases, i have several conceptual issures, a couple are:

1) 3D space is a non-trivial starting point, that just like time, also begs an explanation. Just like 4D space ca be thought of as evolving 3D structures, why not see 3D space as an evolving 2D space, and 2D as evolving 1D, and 1D as an evolving point? Exactly where does the dimensionality 3 come from?

I will just say that i symphatise partly with this, but stopping at 3D breaks the beauty. I envision that you can keep reducing it further.

2) Another problem is that 3D space and "points" are classical concept. What is the generalization of the "point configuration space", into something that makes sense in a modern inference perspective, which i take to be the founding core of QM. Well represented by this famous quote

"It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature."
-- https://en.wikiquote.org/wiki/Niels_Bohr

"What we can say about" to me, means what an observer can infer (measure + abduce) from interactions. This implies also preconditions such as formulating questions (~ preparing measurement devices etc). This is the reason why i analyse the inference.

So what is the minimal starting point for this scheme? Is it positions in classical 3D space? If not, what?

3) Julian argues that things should be operationally defined in terms of relative changes of positions, by why not argue that laws should also be operationally defined. If the argument is that physical law is there even if we do not know about it, then this lacks perspective. An external observer can easily predict what understanding we have of physical law, by observing the technology our civilisation uses. This the way in which is does make a difference. Then translate this to subatomic particles, explain if there is any principal difference beyond complexity scale?
This is related to my critique against Rovellis relational QM as well. It starts out well, but the failure is that at some points in the hierarcy the "relations" are detached from observation and gets places outside the inference process.

See old thread: https://www.physicsforums.com/threa...able-in-classical-and-quantum-gravity.220841/

This is a good focus but a big one. About questions on gauge symmetries vs observer relativity.I commented on this in a way that I suspect no one understood either here (explaining this properly requires no less than a paper and backing it up with other stuff, and this isn't the place)
https://www.physicsforums.com/threads/ed-witten-on-symmetry-and-emergence.927897/

So I would not look at SD in order to understand evolving law. Much deeper grips are needed.

/Fredrik

I'll digest the above and reflect.

Fra, are you also adept in math besides theoretical exposition? Do you know how to manipulate the math of spacetime (or quantum gravity) to make the theory no longer sensitive to angles, scales, length or time by shifting the gauge transformations of basic elements elsewhere (perhaps to more basic degrees of freedom like spin networks (or others that can work))?

Can anyone else please comment more about this?

 

[Fra]

I'll digest the above and reflect.

Fra, are you also adept in math besides theoretical exposition? Do you know how to manipulate the math of spacetime (or quantum gravity) to make the theory no longer sensitive to angles, scales, length or time by shifting the gauge transformations of basic elements elsewhere (perhaps to more basic degrees of freedom like spin networks (or others that can work))?

Can anyone else please comment more about this?

What "will work" in the sense of succeding with unification is an open question, no one knows.

But what i would can say about something that's more primary than spacetime and that is in line with an observer-centered perspective - without diverging into details of my own hypothesis - is to ask some questions without adding my personal answers. Then ponder how/if the various research programs (lqg, strings, causal sets etc) address these.

First: Spacetime embeds events (sets of n real numbers) in a topological space where the key is a distance metric.

What is the observational basis for these events? What is the basis for the continuum? Can an observer can represent a real number with infiite precision?

What is the observational meaning of the distance metric? What does it mean for events to be close vs beeing widely separated?

If we define also a geometry on this space what is the observational meaning to straight lines? What is the meaning of volume?

And when answering this, what is the relatiion between the originally distinguishable events and the continuum embedding and volumes of the emedding? For example when the observer does statistical inference, how do we ensure proper counting of events and prevent arbitrary integration measures in the continuous embedding?

Can a finite bounded observer of mass m count and resolve arbitrary numbers? If not, what happens when the observational process is constrained by the limitations of the observer? (Lets even think of it as a Planck scale observer)

From an single observer-perspective, what is the difference between information in general and classical information?

So what are the more basic degrees of freedom that may preceede spacetime?

Some hunches may emerge once you tried to answer the questions above. I would say that if spacetime are inderstood as relations between parta of matter or between communication observers then one can not answer this question without also answering what is the primary microstructure of matter. They unaviodably go hand in hand, which i why i think the evolutionary thinking is needed, where spacetime and matter emerge together. Here the step to evolution of law is also small. At least in my head.

This is why i think fundamwntal theories about empty space are bound to not be fruitful. Also vice versa, because without lorentzian spacetime the whole of HEP and its standardmodel would loose its backbone.

I see none of the big programs as satisfactory here. But string theory is at least most ambitious and worked on.

/Fredrik

 

[Fra]

Do you know how to manipulate the math of spacetime (or quantum gravity) to make the theory no longer sensitive to angles, scales, length or time by shifting the gauge transformations of basic elements elsewhere (perhaps to more basic degrees of freedom like spin networks (or others that can work))?

Something to think about, how to create new dimensions in a probabilistic setting, here is something to ponder about. I was thinking first about this long time agoe when exposed to field theory in the way of "second quantization". And you can make interpretations here suchas probability or probability. Here you have the possibilities to create higher dimensions, by applying a kind of statistical induction. then try to interpret this in terms of an observer.

http://www.math.ucr.edu/home/baez/nth_quantization.html

Next would be to see what to make of this if you constrain the probabilities to be discrete. Not sure if you know about causal sets, that's an idea to create spacetime as a continuum limit of discrete ordered set. I am not a fact to that particular idea, but instead try to do something similar but imagine the discrete set to be "counts" from a frequentist view. then mix this with nth quantisation. I personally always felt that from my perspective the higher order quantization interpretation makes more sense, than the field theory picture.

/Fredrik

 

[kiki_danc]

What "will work" in the sense of succeding with unification is an open question, no one knows.

But what i would can say about something that's more primary than spacetime and that is in line with an observer-centered perspective - without diverging into details of my own hypothesis - is to ask some questions without adding my personal answers. Then ponder how/if the various research programs (lqg, strings, causal sets etc) address these.

First: Spacetime embeds events (sets of n real numbers) in a topological space where the key is a distance metric.

What is the observational basis for these events? What is the basis for the continuum? Can an observer can represent a real number with infiite precision?

What is the observational meaning of the distance metric? What does it mean for events to be close vs beeing widely separated?

If we define also a geometry on this space what is the observational meaning to straight lines? What is the meaning of volume?

And when answering this, what is the relatiion between the originally distinguishable events and the continuum embedding and volumes of the emedding? For example when the observer does statistical inference, how do we ensure proper counting of events and prevent arbitrary integration measures in the continuous embedding?

Can a finite bounded observer of mass m count and resolve arbitrary numbers? If not, what happens when the observational process is constrained by the limitations of the observer? (Lets even think of it as a Planck scale observer)

From an single observer-perspective, what is the difference between information in general and classical information?

So what are the more basic degrees of freedom that may preceede spacetime?

Some hunches may emerge once you tried to answer the questions above. I would say that if spacetime are inderstood as relations between parta of matter or between communication observers then one can not answer this question without also answering what is the primary microstructure of matter. They unaviodably go hand in hand, which i why i think the evolutionary thinking is needed, where spacetime and matter emerge together. Here the step to evolution of law is also small. At least in my head.

This is why i think fundamwntal theories about empty space are bound to not be fruitful. Also vice versa, because without lorentzian spacetime the whole of HEP and its standardmodel would loose its backbone.

I see none of the big programs as satisfactory here. But string theory is at least most ambitious and worked on.

/Fredrik

What is the difference between observer in quantum mechanics and observer in relativity? Are they not equal? Should they be made equivalent by some kind of transformation? does this already exist in our physics?

And when you say observer.. do you mean a human or a machine observer?

Also I'm looking for the model where these degrees of freedom that precede spacetime can form some kind of structure that can hold the observer.. do you know of any models that explore this?

 

[Fra]

What is the difference between observer in quantum mechanics and observer in relativity? Are they not equal? Should they be made equivalent by some kind of transformation? does this already exist in our physics?

And when you say observer.. do you mean a human or a machine observer?

Also I'm looking for the model where these degrees of freedom that precede spacetime can form some kind of structure that can hold the observer.. do you know of any models that explore this?

Good questions indeed. If its any comfort I am also looking for(working on) such models. But they are not ripe yet.

But Scrutinizing what an observer is, and what observation is, in the existing theories is a very good starting point.

I would say that an observer, is something(a physical system) that infers information about something else(called the system under study) by means of "observation". Roughly this "observation" must be some kind of physical interaction, where the observer extracts/gains information about the system.

( Note: Nowhere (classical or quantum) does observer ever mean "human". This is a persistent confusion that can't be washed away. Certainly Niels Bohr wasn't talking talking about humans. Any later claims are IMO from people who simply misunderstood all this deeplyy. )

First are two distinctions to make, or "passive"/classical vs "active"/quantum measurements.

• In classical mechanics - both special and general relativity - the physical process of observation, is assumed to be possible to make arbitrary small so that you can extract the desired information without distorting it.
• In quantum world, this is not possible becauase the process of acquiring information, changes the system. And not just at the classical way (which can be arbitrary small), but in a fundamental logical way. Ie. in quantum world you can not "copy" information without disturbing it.

It's important to understand that this is a key insight. It means that one can not treat "observations" in a different footing than any physical interaction (except that of a given observational perspective, that you can never release yourself from)

I will not ramble too much but i claim that thi difference has deep confusing consequences if you later, elevate the state of law on par with state of the system (like i think we must do)!

But beyond this, there are essentialy one overall key constructing principle for physical law

• The laws of physics must be same for all interacting observers, meaning they should be able to communicate their observations and agree.

Einsteins first consiered only the class of observers related by poincare transformations, just from this + the requirement that here exists a communication speed that all observers agree upon => Special relativity follows almost deductively.

Note that one does not need for SR, to explain or "declare" in detail what an observer is, all that matters is how they are RELATED. And that is poincare transformations. Of course its presumed the existence of 3Dspace and time (this is certainly questioned if you take this to another level and attempt to model an observer and explain exactly HOW this "structure" can encode notions such as spacetime; but that is far beyond what Einsteins did)

One can then argue that the class of observers are larger, looking at those related by 4D diffeomorphisms, and argue towards General relativity. But also here, no attempt is made to explain what and observer is.

I would say that's related to the fact that its not necessary eactly because the observers observational interations are "passive".

In quantum mechanics OTOH, an observer is a classical measurement devices that is interacting with the system during "observation" in a way that can never be reduced to a passive observation. This is a big step forward vs classical mechanics. But combining this instrumental observer with the constructing principles of classical laws, become extremely complicated, becauase so far even in quantum theory the notion of "PHYSICAL LAW" is a classical concept.

This is something I've been given a lot of thought and there is a key conflict here. And different research programs have different stances to this. But those programs that take a deep stance and try to suggest a constructing principle for the structure of the observer; and put it into the above context seems to be absent. So what to you do? This has lead me to the insight of evolving law. It is actually not too alien from the evolution of the geometry leading to Einsteins equations, but there is a much deeper twist which is that the observer can not be passive, the observer is unavoidable encoded int this mess, in a way that no one yet seems to have understood well enough to describe it mathematically.

So if you don't find what you are looking for i have the answer for you - it means you have to create it yourself ;-) If you succeed come back and enlight the rest of us.

/Fredrik