Relative information at the foundation of physics by Carlo Rovelli

Thanks Carlo for replying...

On 1), I did not mean to regulate the temperature during the entropy increase, but the temperature AT the time of energy introduction. From that equation, which I presume correct since you dont question it, if T is made very, very, very low, will the resulting entropy change following a small energy introduction not be very, very, very large?

On 2), I didnt want to mix up discreteness with gravitational theory. To avoid confusion, discreteness implies occurring in separate representations, so that we can count 1, 2, etc. What usually enables us to do this, e.g. for grains of sand is separation by space. Or if you like let us take the space far away from any walls or gravitational field, in order not to argue over the statement "...because distance is a function of the gravitational field", will that far away space have a discrete nature?

On 3), Leibniz did not originate Monads, the Pythagoreans did. Also apart from the initial 8 paragraphs of his Monadology, the remaining were more concerned with spiritual not with physics. Interestingly, an essayist here pointed out a reference that Wheeler suggested that his "elementary quantum phenomenon" was like a monad (JA Wheeler, The computer and the universe, International Journal of Theoretical Physics, vol.21, nos. 6/7, 1982)here.

I know you are a busy academic, but if you have the time you may reply on these points.

Regards,

Akinbo

@Carlo Rovelli: "... for all quantum systems, the orthogonal states are in finite number per each finite region of phase space." If there is a multiverse finite automaton then all possible measurable states are a finite set. If the multiverse is infinite and really needs an infinite phase space, then what is the explanation for the space roar? The space roar is supported by: FIRAS and low frequency radio data, ARCADE2 and low frequency radio data, and combined data sets from ARACADE2 and FIRAS.

http://asd.gsfc.nasa.gov/archive/arcade/pubs/arc2_apj_interp_2011.pdf INTERPRETATION OF THE ARCADE2 ABSOLUTE SKY BRIGHTNESS MEASUREMENT by M. Seiffert, D. J. Fixsen, A. Kogut, et al., The Astrophysical J., 734:6 (8pp.), 2011 June 10

Is any quantum theory of gravity that contradicts the space roar guaranteed to be wrong?

Dear Carlo -

I'm very glad to see a new essay of yours revisiting some themes of Relational Quantum Mechanics. I've always considered that paper a milestone, or rather a signpost pointing a way that remains to be explored. Maybe the time is ripe... there are a few other essays in this contest - Knuth's, for example - working with the idea that all of physics concerns "the information systems have about other systems."

I very much agree with your conclusion - "The universe is not just simply the position of all its Democritean atoms. It is also the net of information that all systems have about one another. Objects are not just aggregates of atoms. They are particular configurations of atoms singled out because of the manner a given other system interacts with them."

However, I agree with Walter Smilga's comment above - in order to grasp what it means for things to have information, even in physics, we need to deal with contexts of meaning. You want to stick with Shannon's definition, as you wrote, to show "that there are meaningful notions of information and relative information in simple physics, without need to refer to semantic meaning." As in the RQM paper, here also you define "having information about" a system just as "being correlated" with it. (Knuth's contest essay likewise uses an abstract notion of systems "influencing" each other. And even Smilga, who wants to bring semantics into the picture, uses a very generalized notion of "semantic frames of reference.")

I don't doubt that your approach gets at something very important about the structure of physics. But the point of my essay is that something else that's important is missed when we abstract from the specific kinds of contexts in which information actually becomes measurable.

These contexts are not mysterious - we know all about how to assemble them when we make measurements. There's nothing subjective or mental about them - the same physics we use in the lab describes how any system gets information about other systems. But there are major obstacles to formulating any realistic general definition of a "measurement-context". It's not just that such arrangements are never physically simple, but also that any way of measuring something depends on other ways of measuring other things. I argue that this complex interdependency of different ways of "observing" is really what's behind the measurement problem in QM.

In physics we're always trying to show how the underlying structure is basically simple - so the many different ways in which things actually "have information about each other" give us a picture that hardly seems as though it could be relevant to the physical foundations. Yet if we only think about abstract and generalized information-processes, we lose touch with the way information is physically present in the world.

My suggestion is that measurement can be conceived as fundamental, if we can see it as an evolving process. Though it takes a very complex interactive environment to communicate definite information about and between its subsystems, this kind of environment can exist and maintain itself for the same reason that life does, if it's the kind of system that can evolve through random selection.

Thanks again for the new essay - Conrad

Dear Carlo

I read your essay with pleasure. It is very well written, clear, and easy to understand. I share essentially all points, though just at the qualitative level, i.e. as a general philosophy. I have been always curious about your relational quantum theory, and I now understand that it is meant to be an axiomatization program. That's is even more interesting for me, since, pragmatically, I do not pay much attention at the purely opinionated interpretational issues. I will consider to which of our axioms your postulates may be connected (I'm referring to the Pavia axiomatization http://pra.aps.org/abstract/PRA/v84/i1/e012311). I just downloaded your IJTP paper of 1996, and I notice a third axiom, which looks quite quantum. You don't mention it in your essay. Do you have a more recent version of your derivation of QT without it?

Second, about LQG, it seems to me that, in a sense, you are not so far from my cellular automaton approach, and I was wondering if e.g. your loops maybe related to my loops on the Cayley graph. I'm very curious.

My best regards

Mauro

Dear Dr. Carlo,

Your essay is short but contains enough information on 'Information', but you haven't touched up on 'reality' in the same way; so I couldn't see your valuable views on reality and disappointed. I hope you will make it up to it soon.

You have identified entropy with information, but is this identification universal? For example, if two systems are in equilibrium with each other there will be no change in the entropy of the two systems but yet there can be exchange of information between them.

You have reviewed the current trend prevailing in physics to unite such different fields as thermodynamics, gravitation and quantum physics on the basis of the concept of entropy as yourself being one of the champions of LQG. There are lots of expectations to see how far you succeed in your endeavor.

I also expect you to go through my essay and post your comments. http://fqxi.org/community/forum/topic/1827.

Best regards,

Sreenath

Carlo - thanks for your response, and I get your point. In fact, I pulled out my old marked-up copy of the RQM paper and was reminded again what a thorough piece of work it is, given its limited scope. It lays out - more carefully than any work of philosophy I know of - the basic philosophical issues involved in the meaning of objectivity.

It is just the notion that events are indexed by the observer-relative context that's important to me. The world only exists from the standpoint of some observer. This isn't subjective (mental), in that anything counts as an observer. It's not solipsistic, in that communication between observers is as fundamental as observation itself - in fact, from the QM viewpoint there's no difference between these two. But as you say, it's an error to describe this world of multiple observers as if it could be envisioned "from outside", from no point of view - as if there could be well-defined information without a context to define it from a specific point of view.

This is a very radical notion, and I think it will be some time before we have the conceptual tools we need to be clear about it.

So I understand your "only possible solution" - treating any interaction as a measurement. But I would remind you of the point you make in RQM, that even the correlation between two systems is only definable from the standpoint of a third system. And the position of the atom "measures" the spin, insofar as something else observes the atom, in some context in which its position is definable over time.

There's no specific level of complexity at which interactions become measurements, or systems become observers. To that extent I agree, it's better to treat all systems as observers and all interactions as measurements. But this does not really "solve" any problem. Many different kinds of interactions are still needed to define / measure any physical information, and though I well understand your preference for "the good old physics", ultimately I think we can't set this fact aside as insignificant.

In my essay I acknowledge the difficulty of dealing with it, and try to show how they can be addressed. In the end this points to a way of answering the basic question that's left - in my mind, anyway - by RQM: how and why do things work out so that at the macroscopic level, the quantum world of communicating observers ends up looking so much like the objective, deterministic reality of classical physics?

Carlo,

Interesting essay. As I dwell on the same questions you are raising I focused on the following statement you make:

"The information contained in any finite region of the phase space of any system is finite."

I would agree this is true to the level of precision allowed to the level of error imposed upon us by the uncertainty principle. However, the error does represent information, a vast amount of it, and it is this information that ultimately forces us to only accept an approximate reality. In general, I have to agree with Democritus that life is change. In general I think these ideas seem to be manifest in several of the essay provided. I was wondering what your thoughts are on the apparent prevalence of the same ideas?

My essay if you're interested.

Carlo,

If given the time and the wits to evaluate over 120 more entries, I have a month to try. My seemingly whimsical title, "It's good to be the king," is serious about our subject.

Jim

Dear Professor Carlo Rovelli:

I am going to refer myself to the last part of your essay.The main finality of a living system is to survive, in the case of the Galapagos cormoran its "selected structure" which "original finality" was to be a "flying bird" is not flying, environment (as you said, making use of the information they have about the exterior world) more than enough food around the island, and the absence of predators, result in the opposite of what you said "finality define the structure" he cease to be a flying bird because his wings become a third of the necessary size to be able to fly. Every living thing strong tendency is to survive and "they would make almost "every and I mean everything of the necessary changes of their structure to adapt to its new finality", if given the necessary time for all necessary changes to adapt, ( 30 Kg. horses with five fingers in swamp fields, become three or four hundred Kg with one finger on hard floor. Etc.) if environment change to fast the specie and its finality structure would not adapt and would cease to exist (selection). How they change?. How they would adapt? When extremely slow ( comparing with their life length) environment changes, "secure", long endurance changes, allowing an also slow chromosomes modification that would rule the bird reproduction with a paulatine body changes (structure) like diminishing wing size through 2 million years when specialists say those cormorans came from the American continent flying.

Reality, is not, that because we have big brains (comparing with other animals) we can relate and analyze more data coming from sensors, but the opposite "Because we had many data coming from sensors to be analyze by our brains they become biger".

When you are referring to DNA etc. saying "it is by dealing with information that these systems effectively persist" you are being drag by the same wrong approach. The real thing is that "by dealing with information is that these systems change and adapt continuously to this information to be able to persist"(DNA code, immune systems etc. etc.)

"The world is not just a blind wind of atoms, or generally covariant quantum fields " I agree with that.

But when you said "formed by the correlations among the structures formed by the elementary objects". "Correlations" means relations between the structures, I suppose this means informations that comes and goes between them. And when we say "comes" and "goes" what ever is what do that, I suppose that this action imply "motion".

When I read your book What's time? What's space? I find out, that you was very interested since you was a young boy to know what is time specially more than space. That your interest motivate you to study physics, this didn't clarified the definition and specially the empiric meaning of time, so you went to Pittsburg and study philosophy you new knowledge did not answer your question either, so after many years of trying with no results and taking into account the failure to do it, since at least 25 hundred years by Heraclites, Plato, Aristotle, Newton, Einstein, after those grate minds didn't find it, you as physicist Barbour felted back up to decide that "time" did not exist. I recognize it was a logical conclusion, I understand he made his theory to do physics without "time" and that you are trying to do yours.

I realize that you and Julian Babour who are recognized physicists all over the world, both of you when decided that "time" didn't exist, because nobody reach its definition and empiric meaning, simultaneously implied the not existence of "motion" or "movement" as you like, which has a clear definition and empiric meaning.

So I ask myself why? couldn't be, that because time empiric meaning is not know, you don't know what you are leaving out? So there was no change at all.

Since Heraclites "time" was related with "motion" that's why now days people talk of the "flow of time" "the arrow of time", "time direction" " back to the past, forward to the future" which nobody ever proved, but all those sayings implied "motion". Nobody imagine himself measuring time, if absolutely nothing moves.

So to know what happen leaving "time" out, you felt force to leave "motion" out, to make a difference. None of you ever ask yourselves?. Couldn't be that when you think, you are measuring "time", you are not conscious that instead (or in fact) you are measuring "motion" ?. even in Einstein book "Ideas and Opinions" pg. 354,he recognize that "time" is a man creation, he called them pre-scientific concepts. In fact is a remnant word from which mankind forgot its meaning, probably refering to a system to measure "motion".

I think nobody can't ignore "motion" I think also that is the first physical thing that us and all animals know of its existence. Nobody that insist in its no existence, cross a high-way blind folded, a galaxy and a subatomic particle move. I think that every physically existent thing moves. I think that because you didn't find the door you are trying to open one through the wall by force, like you did about the living sytems,. Just because we are in this contest I will finish this note with one of John Wheeler sayings "I would like to stand for. We can and will understand.".

My best whishes to you

Héctor

Dear Professor Carlo:

On my hard drive, you have existed as a bunch of arXiv articles; in my memory, your name is associated with the name of Professor Lee Smolin, the author of many books that I learned physics from.

You are on my hard drive, you are in my memory, and now you are here. It's a pleasure to be in your company!

I have downloaded your article, and I'm reading it with as much intelligence and diligence that a non-physics major can muster about a topic "It from Bit" that is deep and has many facets to it. I dread making pronoucements about it, but having entered a public contest, I had to.

I am the author of FQXi essay entry titled "Analogical Engine", and my belief is that 'Nature is thoroughly Analogical,' and to make it sound less of a slogan, I made a subsequent statement: "Planck's constant is the Mother of All Dualities, and a necessary condition for existence of thoughts and things."

And to make the statement picturesque, I have included in the body of my essay a thought-experiment based on an intuitive distinction between the (subjective) and the (objective) by working out an interpretative, non-mathematical derivation of what I believe to be the simulacrum of Planck constant, different from the one that is in textbooks.

Within that framework, I find your essay greatly illuminating, especially section IV.

Than Tin

Dear Prof. Carlo Rovelli,

Let me quote you first from your essay:

"...I think, from the basis of genetics, to the

foundation of quantum mechanics, to the basis of ther-

modynamics, all the way to sociology and to quantum

gravity, it appears that the notion of information has a

pervasive and unifying role. The world is not just a blind

wind of atoms, or generally covariant quantum elds. It

is also the innite game of mirrors reecting one another

formed by the correlations among the structures formed

by the elementary objects. To go back to Democritus

metaphor: atoms are like an alphabet, but an immense

alphabet so rich to be capable of reading itself and think-

ing itself".

Thanks for the sentences and also similar many others in your essay. I'm agree with you.

Moreover I think that its really a quantized mirror world. It simply depends on from which side we are looking that world on the mirror. I'also invite you to my essay if possible.

Regards

Dipak

Hi Carlo,

Interesting essay. I have always had a certain affinity for your relational approach having studied Eddington's work in great detail (if you are not familiar with it, it might be worth a look despite its age). But I wonder about some of the specific conclusions you have reached. In addition to the concerns shared by Matt Leifer, I'm not sure I buy the argument that recovers objectivity in the macroscopic limit while maintaining a relative approach. While I agree that a relational view is inescapable, so too do I think is some level of subjectivity.

In regard to the favored "starting position" in dynamical evolution, it is entirely possible to explain that without any reference to a form of description. Large systems of random processes can be shown to favor very specific macrostates simply via combinatorics (e.g. a pair of dice are the classic example, but much larger systems can be shown to have even narrower distributions).

Related to your example of the broken cup, I think there are some subtle issues that you have missed. Certainly by redefining "information" I could create a situation in which the entropy of the broken cup appears to be less than the entropy of an unbroken cup. But I do not see how to do this without completely redefining information in which case you're not really talking about the same quantity anymore. I think the problem here is that the exact relation between Shannon entropy and thermodynamic entropy is not as well-understood on a foundational level as many people think it is. I have no doubt that they are, but I think there are some deep foundational issues that still need to be resolved here.

At any rate, my only other criticism is that you seem to have avoided taking a specific stance on the actual question of the essay contest itself: does your argument imply "it from bit" or "bit from it" or, perhaps, neither?

Cheers,

Ian Durham

Dear Carlo

Warren McCulloch an American neurophysiologist and cybernetician, known for his work on the foundation for certain brain theories and his contribution to the cybernetics movement once told:"Greatest riddle of the World "What is "the same information?"

That is modern version question of Plato.

Do you agree with him?

Regards

Yuri

Mr. Carlo Rovelli , I am sure You do not Know who I am, as any other

participant.

I can say , to be in this contest is an historical goal.

Can I ask to read my essay , actually with zero score ?

Into my best hope the basic idea of the script is the first classic law for

quantum physics. I also need suggestions about the idea.

Best Regards. Giacomo Alessiani.

Dr. Rovelli,

I enjoyed reading your essay and appreciated several of your insights. In particular, I thought you pointed out a couple of vital distinctions, such as the fact that, "Objects are not just aggregate of atoms. They are particular configurations of atoms singled out because of the manner a given other system interacts with them." You also noted that, in addition to the fact that inanimate objects are not simple an aggregate of atoms, that "living systems are those that selection has led to reproduce continuously their own structure by, in particular, making use of the information they have about the exterior world."

It would seem, then, that both living things and inanimate objects in our universe somehow interact with information, which, as you also point out, "has a pervasive and unifying role." I would be curious to know if you think it might be possible that the universe is, in fact, some sort of information system. The fact that, "The world is not just a blind wind of atoms, or generally covariant quantum fields," and that so many various fields of study suggest there is an exchange of information occurring seem to suggest an information system of some sort. Might it be possible that quantum field theory offers us a description of a form of information software at work? Perhaps the Theory of Relativity describes the hardware?

Again, thank you for your thoughts on the matter. Best to you in the future.

Sincerely,

Ralph

Dear Carlo,

thank you for interesting essay; this kind of ideas lead to the theory of fundamental physical informational interaction between objects and other kind of objects selected and controlled by us to become experimental devices (material reference frames, etc.), which can be called "subjects". Your time would not be lost if you check my essay where I show that on this way one may unify quantum and relativity principles in one single principle based on Object-Subject informational interaction:

http://fqxi.org/community/forum/topic/1612

Valentin Koulikov

P.S. I believe that I have mailed to you my article on this matter a couple of years ago, but unfortunately got no response ("Time Loops and Unification of Quantum and Relativity Principles"), you may find the link to it in References to my essay.