Ontology: what's really there

[marcus]

In the history of physics there are moments of crisis now and then when questions of ontology get confronted. Mostly ontology is ignored and it is business as usual (the business is largely predicting experiment outcomes) without worry about what is really there. Ontology comes from the greek word for Being.

Ontology is about Being----what really is there.
Phenomena (from greek word for appearance) is about what you see, how it looks, what you measure.
Ontology is about the basic underlay that gives rise to the appearance.

It is a philosophical quagmire so wear hip-boots and approach with caution. Working physicists shun philosophical discussion nearly all the time (but really good ones, like Newton and Einstein, now and then grapple with those issues during times of crisis)

In another thread--serving as a collection thread for links to sourcematerial---Mike asked what i think is an ontological question.

Are "gravitons" really there, or are they just convenient approximations that you can use in certain limited circumstances to approximate the field?
If "gravitons" really exist, could the world be made of them?

This was my reply. I want to make a separate thread for any discussion that might ensue because otherwise it clogs the collection of reference-links.
----here's to start an Ontology discussion---
I believe not, Mike. That is, this paper does not indicate that gravitons are real----rather that they are a mathematical fiction which plays a part in a possibly useful approximation. Analysis of the gravitational field using gravitons would be appropriate, as this paper suggests, in the weak field case.

We should start a thread about ontology. You seem to me to have an abiding interest in ontological questions---what is really there, what is reality made of. I would say, in answer to such questions, "the field is the field."

To say it in a lot more words: the field is the field and it is not made of anything more basic---it is not made of gravitons or anything else, it is really there. It may or may not sometimes be useful (as an approximation) to describe it in some special case in terms of the mathematical device of postulated gravitons and then it may or may not be helpful to talk among ourselves about "gravitons". But that is an overlay of mathematics, it is not ontological. Ontologically speaking there is nothing more basic than the field.

The field is not something defined "in space and time" because space and time arise from the field. space and time are appearances or phenomena which emerge from the field. We must arrive at ways of describing the field which do not depend on imagining a prior space and time in which to define it.

The field is a quantum animal, living in a Hilbertspace of all possible fields. The central problem in physics today is to find a satisfactory formal way of to describe the gravitational field, and the Hilbertspace of its possibilities.

When and if that is found, everything else will be describable relative to, and on top of, the field.
----let's continue this in a separate thread, so as not to choke the linkbasket---

you are cordially invited to agree or disagree or put forth alternative ontological views

 

[marcus]

Just last month (September) Rovelli posted a new article bearing on questions of ontology. Maybe it would contribute to a possible discussion here. This is my post flagging the article when it came out, with but with some ontology parts bolded:

Daniele Colosi, Carlo Rovelli
Global particles, local particles
http://arxiv.org/abs/gr-qc/0409054

brief sample from conclusions section:

---quote---

...the distinction between global and local states can therefore be safely neglected in concrete utilizations of QFT. However, the distinction is conceptually important because it bears on three related issues: (i) whether particles are local or global objects in conventional QFT; (ii) the extent to which the quantum field theoretical notion of particle can be extended to general contexts where gravity cannot be neglected; and furthermore, more in general, (iii) whether particles can be viewed as the fundamental reality (the “ontology”) described by QFT. Let us discuss these three issues separately. ...

...Can we base the ontology of QFT on local particles? Yes, but local particle states are very different from global particle states. Global particle states such as the Fock particle states are defined once and for all in the theory, while each finite size detector defines its own bunch of local particle states. Since in general the energy operators of different detectors do not commute ([H_R, H_R'] nonzero) there is no unique “local particle basis” in the state space of the theory, as there is a unique Fock basis. Therefore, we cannot interpret QFT by giving a single list of objects represented by a unique list of states. In other words, we are in a genuine quantum mechanical situation in which distinct particle numbers are complementary observables. Different bases that diagonalize different H_R operators have equal footing. Whether a particle exists or not depends on what I decide to measure. In such a context, there is no reason to select an observable as “more real” than the others.

The world is far more subtle than a bunch of particles that interact.
---end quote---

 

[marcus]

So the notion of particle is contingent.

when describing the world, or some situation in it, you can't give a once-and-for-all list of what particles are there because that has no fixed meaning----it what particles and how many depends on what is being measured

I have to run, but want to give this link to Ashtekar recent talk
http://www.phys.psu.edu/events/index.html?event_id=934;event_type_ids=7;span=2004-08-20.2004-12-25

Look at slide 12 and 13 where he discusses the "deep Planck regime" at the heart of a black hole. certain things like the distinction between spacetime and matter may break down, the audio discussing these slides is interesting

 

[Curious6]

I think ontology is a really interesting subject. The ontological view of the world should be described by a theory of quantum gravity which states what the fundamental objects really are. In string theory, they are made of strings. In loop quantum gravity (if I have understood it correctly) the elementary constituents are discrete loops of spacetime (which give rise to the name "loop"). However, I believe that gravitons do really exist, as they are described as the lowest possible vibrationary mode of the string (and since a string does exist what impedes it from having the lowest gravitational vibration)? Just an observation.

 

[Mike2]

This thread is in response to my post:

Since the graviton is supposed to be quantized gravity which is also supposed to be quantized geometry, would gravitons exist everywhere and constitute the construction of spacetime itself? This would be opposed to gravition moving through space. Instead, are graviton space itself, always motionless with respect to the observer?

Ontology... And how would we know what really is the case as opposed to just some curve fitting, effective theory using some mathematical construct for our convenience? I suppose that we would see a theory as truly fundamental (and ontological) only if it were derived from abstract principles that we accept as the most basic to reasoning... in other words, it would have to be derived from logic itself.

However, my comment on gravitons above is a question about the underlying mathematics involved, whether effective or not. I wonder if gravitons can be derived from the attempts to quantize spacetime itself, as opposed to coming from some mode of string vibration. I wonder if string theory can be derived from quantized geometry? Or maybe string theory is a low energy limit of some quantized geometry scheme.

 

[RingoKid]

Please correct me...

In string theory, there is an underlying reality not percievable except by abstract mathematics in which according to the vibrational activity of operating in 4d or less determines whether a string registers as an effect or an object.

This underlying reality is the field/landscape is what is referred to as background dependence and is static in a multiverse scenario ?

An analogy might be of the wind passing over a field of wheat embedded in the ground where we register the wind and it's effect on the wheat but we can't see the wind or the ground it is planted in.

 

[Curious6]

Could anybody please post the link for the thread that is being referred to?

 

[Garth]

I believe that phenomena are the things that "really do exist". We receive data and then have to make sense of it all by making conceptual models. All our theories are a conceptual modelling of the reality 'out there'. We may verify these theories and falsify them but never 'prove' them as Karl Popper pointed out. Popper did not mean that final truth did not exist, as if all truth were culture dependent, but that we never know if we have arrived at it. No matter how consistent and well fitting our theories may be today, something may be discovered tomorrow that disproves or modifies them.
Normally the set of theories, physical and otherwise, serve us well, however we could all be existing in a 'Matrix' type virtual reality - but I doubt it!

 

[setAI]

those of us in the cognitive and computer sciences are still waiting for you physicists to fully understand/embrace the full implications of Computation

 

[Garth]

That was a neat cross posting!
Garth

 

[marcus]

Could anybody please post the link for the thread that is being referred to?

good question, I should have given this link at the outset
https://www.physicsforums.com/showthread.php?p=353430#post353430
this is Mike2 post that, to me, raised a basic issue of what reality is
made of----btw that is not the kind of question I ordinarily think about either!
this is where Mike2 said:
"Since the graviton is supposed to be quantized gravity which is also supposed to be quantized geometry, would gravitons exist everywhere and constitute the construction of spacetime itself? This would be opposed to gravition moving through space. Instead, are graviton space itself, always motionless with respect to the observer?"

I am trying to use that thread as a substitute "sticky" to collect Loop QG source material---it tends to overload it to have discussions in it too, and then it doesn't work as well as a reference shelf or link-basket. I put new LQG articles there, and announcements of conferences etc. Other people contribute useful stuff like that.

Must say that it is great to the range of ideas here. I think I benefit from seeing other people's concepts of what's basic. Also very fine image by RingoKid of the imprint of wind on a field of wheat.

No one right answer. but each attempt is valuable. I am moved to keep silent for now at least.

 

[Curious6]

It might be interesting now that we are discussing ontology to include the equivalence of mass and energy. Does anybody know how this concept is addressed in quantum gravity approaches? This mass energy equivalence can be interpreted by saying that matter is actually made up of concentrations of energy. But what is the physical meaning of this energy? Anybody that would like to comment on this point?

 

[marcus]

I don't know if you others have any favorite online two-page summaries of a basic picture of reality.

I agree rather much with what Garth said which is pragmatic enough.
what exists are the phenomena (which are seen and measured)

and we have these descriptions which can be more or less restricted
and more or less comprehensive in their applicability-----there is the idea of: the more universally applicable the more basic it is.

If you have an effective theory that works well in a narrow range but fails badly outside that range then you suspect it is less fundamental than a theory which applies over the whole range----but that kind of judgement is partly aesthetic or involves some choice.

So Ontology is partly a matter of choice and is a feature of this moment in history. How people picture the basic reality is something that can change from one historical period to another.

To what two-page summary of basic reality do I personally SUBSCRIBE?
I like the word subscribe. I don't believe. I don't insist its right. I just am willing to sign on----for better or worse---and so i subscribe to this version of what's basic.

If you had to pick a two-page summary of what ...yeah I know Douglas Adams said it was 42. what would you personally pick?

At the moment the best i can think of is the first two pages of this 5 page article by Rovelli that Ashtekar has scanned and put at his website:

http://cgpg.gravity.psu.edu/people/Ashtekar/articles/rovelli03.pdf

It is a general audience, totally non-technical article with a bit of historical perspective (which I think is an important part of elucidating ontol. issues)
At least for now that is the best I can come up with.

Anybody have anything they like better?

 

[arivero]

Marcus, to me the virtue of ontology (and the main reason to invoke it in this sub-forum) is that we are free of its grasp. And that this freedom is, in the long run, predictive. From the start we renounce to speak about anything unspeakable in mathematical language; and then the constraints of mathematical language become constraints in our equations. Things as having D=3+1 or having a determinate spectrum of particles are imposed upon us not because of some anthropic nor empirical principle, but because we have choosen a specific language. At the end, Reality lives in the language.

 

[Curious6]

A question I believe that underlies almost all of ontology:

Are the fundamental constituents tangible things or aren't they?

By this I mean that if it were possible to examine the most fundamental constituents (such as strings in string theory) would we be able to touch them or wouldn't we (i.e. are they solid?)?

I don't know what the fundamental constituents of loop quantum gravity are but at least in string theory I believe the strings are made up of something solid (even if they are described as vibrating strings of energy sometimes this energy might be solid).

 

[Mike2]

A question I believe that underlies almost all of ontology:

Are the fundamental constituents tangible things or aren't they?

According to QM, one thing is as real as the next alternative

 

[marcus]

Curious6 we will be getting to your question, I expect. Several people have hinted at some criteria of tangibility. Tangibility would I guess include the ideas to probe to test to manipulate to predict and experiment with.

I just saw a paper by George Svetlichny,
http://arxiv.org/abs/quant-ph/0410230
Nonlinear Quantum Mechanics at the Planck Scale
He is someone to pay attention to IMO because of a monograph of his (preparation for gauge theory) which I believe is widely respected and well written. Maybe this thread is the place to check it out and see if he says anything.

have to go, back later this evening.

 

[marcus]

here was a key exchange in this thread. post #8 was this:

I believe that phenomena are the things that "really do exist". We receive data and then have to make sense of it all by making conceptual models. All our theories are a conceptual modelling of the reality 'out there'. We may verify these theories and falsify them but never 'prove' them as Karl Popper pointed out. Popper did not mean that final truth did not exist, as if all truth were culture dependent, but that we never know if we have arrived at it. No matter how consistent and well fitting our theories may be today, something may be discovered tomorrow that disproves or modifies them.
Normally the set of theories, physical and otherwise, serve us well, however we could all be existing in a 'Matrix' type virtual reality - but I doubt it!

about a minute later setAI posted #9:

those of us in the cognitive and computer sciences are still waiting for you physicists to fully understand/embrace the full implications of Computation

tho more an onlooker (not a computer science or physics professional) I find I agree with the spirit of both posts

And i think that asking ontology-type questions and occasionally trying to get answers is a good habit [CAVEAT alejandro has pointed out that it may be built into the rules of the language game that you cannot actually answer certain questions in a satisfactory way, you can only evolve your language to be better----which is a collective undertaking since no individual can have a language by themselves---but let's forget about alejandro's warning]


OK. right now I am reading this paper
Dynamically Triangulating Lorentzian Quantum Gravity
and maybe it should suit setAI because the proof of the pudding is
in the computing

and I am reading the two followups
Emergence of a 4D World

and
A Semiclassical Universe from First Principles

and when you get something emerging from a kind of minimal combinatorial program setup and you get a universe to show familiar features that you didnt put into the model but developed out of
primitive Regge rules. well then that seems to me to verge on the
ontological-----as if THOSE rules might really be there

and of course we all know that such hopes are doomed to disappointment
but the setup has a certain simple persuasive verisimilitude

 

[Kea]

computation and ontology

about a minute later setAI posted #9:

I remember that post! The reference to 'cognitive' implies
a level of mathematical logic way beyond what I think
happens in CDT. I tend to agree with Lubos on this, but
without having looked at CDT carefully can't really say.

Another quote by Heisenberg: "one had also to assume that
any particle was really a complicated compound system, because
with some degree of truth one can say that any particle consists
virtually of any number of other particles..."

The logical conclusion of this statement alone (if formulated
more carefully) appears to be that ordinary set theory isn't
good enough to characterise 'fundamental systems'...
hence categories!

Now there is a really cool book on programming category theory,
which I just discovered at:

http://www.cs.man.ac.uk/~david/categories/index.html

 

[marcus]

... Heisenberg: "...
with some degree of truth one can say that any particle consists
virtually of any number of other particles..."

I suppose there is some benefit from approaching ontology in a conceptually simple way. Newton.

he wondered about the spinning bucket of water
WHAT IS THERE relative to which the water is spinning?

we know when the water is spinning and when it is not spinning, because when it spins the surface curves and becomes concave instead of flat. But what is it spinning relative to?

various people have answered different things----the distant stars, absolute space.

BTW early on in this thread there was the paper of Rovelli and Collosi
which argues that particles do not have any absolute or unconditional existence. What particles are in a region depends one what the observer is measuring. This sounds like it is too philosophical to matter. But the arguments they give are actually physical.

what particles are in the box is contingent on the observer. what a bummer!
and they are arguing physics, it is not just some teaparty sophistry.
and they are saying this is simply a fact, not something "one can say with some degree of truth". So at every turn things are getting more and more relative!

It seems that quantum mechanics can only tell us about what information one system gets from another-----it is only about me and the box---it cannot tell me the absolute unconditional truth about the box alone, with me out of the picture. Damn. they have told me this for years and it hurts every time.

 

[Kea]

no ontology

Newton.
He wondered about the spinning bucket of water
WHAT IS THERE relative to which the water is spinning?

An ancient philosophical idea often brought up by people I
know is the idea of the Elephant: everyone is feeling
different parts of the elephant, so they think they're
looking at different things.

The problem with this picture is that it is a very classical
elephant - out there in some objective classical reality.
If one looks up "I think, therefore I am" in Descartes

http://www.literature.org/authors/descartes-rene/reason-discourse/

it's quite clear that Descartes wasn't happy with an ontological
view - but he resigned himself to it anyway (inventing Cartesian
geometry) - seemingly because of his faith in Him - a premise
that I believe we can now do without.

Similarly, Newton worried about these things...buckets and all
that...and eventually Mach and Einstein (interesting that there
was a close connection between Mach and Pauli).

In summary, a real (in my mind anyway) philospher here gave
a talk recently entitled "Spacetime without spacetime ontology".

Regards
Kea

 

[marcus]

...In summary, a real (in my mind anyway) philospher here gave a talk recently entitled "Spacetime without spacetime ontology".
...

Intriguing title, who was the lecturer pray tell?

 

[Kea]

Intriguing title, who was the lecturer pray tell?

Philip Catton

 

[Demystifier]

It seems that quantum mechanics can only tell us about what information one system gets from another-----it is only about me and the box---it cannot tell me the absolute unconditional truth about the box alone, with me out of the picture. Damn. they have told me this for years and it hurts every time.

This is not so in all possible interpretations on QM. Those who are already familiar with my ideas will easily guess that now I will say that this is not so in the Bohmian interpretation.