Sunday, April 13, 2008

Emergence and Reductionism

My last week's post on 'Theories and Models' was actually meant to be about emergence and reductionism. While wring however, I figured it would be better to first explain what I mean with a model since my references to sex occasionally seem to confuse the one or the other reader.

Brief summary of last week's post: we want to describe the 'real world out there' by using a model that has explanatory power. The model itself captures some features of the world, it uses the framework of a theory, but should not be confused with the theory itself. I found it useful to think of this much like a function (the theory) acting on a set (some part of the real world out there) to give us a picture (the model).


The model describes some objects and the way they interact with each other (though the interaction can be trivial, or the system just static). To complete the model one usually needs initial conditions and some data as input (to determine parameters). In the following I will refer to the part of the real world out there that the model is supposed to describe as 'the system'.

To reiterate what I said last week: I don't care whether you like that use of words or not, it's just to clarify what I mean when I use them.


I. Emergence

Today's topic is partly inspired by the book on "Complex Adaptive Systems" I just finished reading (see my review here), and partly by Lee's lecture on "The Problem of Time in Quantum Gravity and Cosmology" from April 2nd (PIRSA 08040011 and 08040013). Please don't ask me what happened in the other 13 lectures because I wasn't there.

Hmmm... I missed the first ten minutes on April 2nd. After watching the video I can now reconstruct what was written on the blackboard before I came and what the not completely wiped-off words said. I feel a bit like a time-traveler who just closed the loop. Either way, here is a brief summary of min 11:38 to 20:24. Lee explains there's three types of emergence:
  1. Emergence in scale:
    In which a system described on larger scale has a property that it wouldn't have on smaller scales. As an example he mentions viscosity of fluids that isn't a property which makes sense for an atom, and the fitness of biological species that wouldn't make sense for molecules. "Atoms don't have gender but living things have gender."

  2. Emergence in contingency:
    In which a system develops a property only under certain circumstances. As an example he mentions the temperature dependence of superfluidity.


  3. Emergence in time:
    In which a system develops a property in time. As an example he mentions biological membranes, and that more than 3.8 billions years ago it wouldn't have made sense to speak of these.

As somebody in the audience also pointed out, these are basically different order parameters to change a system (e.g. scale, temperature, or time).

I was somewhat confused by distinguishing between these three cases, and that not only because I don't know what the plural of emergence is. (It can't be emergencies, can it?) No, because I always understood emergence vaguely as a feature the whole has but its parts don't have. Not that I ever actually thought about it very much, but that would be an order parameter like the number of constituents and and their composition - which could, or couldn't fall among point one or two.

Part of my confusion arises because in practical circumstances it isn't always clear to me which of the three cases of 'emergence' on actually has at hand. For example, take the formation of atoms in the early universe. Is this an emergence in time? Or is this an emergence in contingency? After all it's the temperature that matters I would say. Just that the temperature is related to the scale factor, which is a function of time. Also, in most experiments we change the contingent factors in time - like e.g. the cooling of the superfluid medium. So, the second and third cases seem to be very entangled. I think then I should understand emergence of a system's properties in time as it taking place without being caused by a time dependent change of environmental conditions of the system. Like e.g. the emergence of emoticons in the written language ;-) or that of the red spot on Jupiter - cases in which it 'just' takes time.

Here is a nice example for patterns that I'd say emerge in time, an oscillating chemical reaction:



    [An example for a particularly pretty oscillating chemical reaction with emerging patterns. Unfortunately, the video description doesn't contain information about the chemicals used, instead it provides a very bizarre connection to migraine and 'stimulus points'. Either way, this sort of reaction is called a Belousov-Zhabotinsky-Reaction.]



II. Strong and Weak Emergence

Okay, so after some back and forth I figured out why I was feeling somewhat uneasy with these three cases. Besides that I think - as said above - in practical circumstances distinguishing one from the other is difficult, in the second and third case I'd have said a property might be emergent in the sense that it 'arises' and becomes relevant, but was present already in the setup of the model (and if not, you should come up with a better model). E.g. Bose Einstein condensation was predicted to arise at low temperatures. Likewise, I'd say if one knows the initial conditions of a system and its evolution then one knows what will happen in time - it might turn out only later emergent properties become noticeable and important, but it's a predictable emergence. Like e.g. stars that have formed out of collapsing matter or something like this.

Either way, to come back to my rather naive sense of 'emergence' by increasing the number of constituents. If you look at a part of some larger system, specifying or examining its properties just might not be enough to understand how the whole system will behave: it can just be an incomplete description. It can be one needs further information that is the interaction with other parts of the system. As an example take one of these photographic mosaics:


[Picture Credits: Andrea Planet, Click to enlarge.]

If you'd only look at one of the smaller photos you'd have no chance of ever 'predicting' that something will 'emerge' if you zoom out.

After looking at the Wikipedia entry on Emergence I learned that this essentially is the difference between 'strong' and 'weak' emergence. In the danger of expressing my total ignorance of various words and names in that Wiki entry I've never heard before and am presently not in the mood to follow up upon, let me say that weak emergence is - at least "in principle" - already contained in a model you use to describe the system, and is thus at least "in principle" predictable, whereas strong emergence isn't.



III. Reductionism

If you want to go back to Lee's lecture, fast forward to min 37:00, where the topic emergence and reductionism comes up again. Somebody in the audience (I believe it's Jonathan Hackett), asks (min 40:00): "Is there a phenomenon which is emergent which is not derivable and is not expected to ever be derivable from something else?" This is essentially the question whether strong emergence actually exists.

Let me paraphrase reductionism as the believe that a system can "in principle" be understood entirely by understanding its parts. Then the argument of whether or not reductionism can "in principle" explain everything is that same question: does strong emergence actually exist? Or are all emergent features 'weakly' emerging, in that they are "in principle" predictable?

Now you might have noticed a lot of "in principles" in the previous paragraphs. I'd think that most physicists believe there is no strong emergence. At least I don't believe it. As such, I do think reductionism does not discard any features. However, this believe is for practical purposes often irrelevant since the models that we use, however sophisticated, are never complete descriptions of reality anyway. Even if you had a 'theory of everything', and there was no strong emergence, it wouldn't automatically provide a useful "model for everything". If we'd find the one fundamental theory of elementary matter it wouldn't describe all of science for the same reason why specifying the properties of all atoms in a car doesn't help you to figure out why the damned thing doesn't want to start. And I doubt we'll be able to derive the 'emergence' of, say, blog memes from QCD any time soon.


[Even if we had a Theory of Everything, it wouldn't give us a model for everything we want to describe. Cartoon XKCD.]

But besides these practical limitations that we encounter when making models that still have to be useful, there is the question whether it is possible to ever figure out if a system has the potential for a 'weak emergence' of a new property. Since it's impossible to rule out something unpredictable will happen, I'd say we can never know all the 'non-relevant' factors or 'unknown unknowns' as Homer-Dixon put it in his book. For example I'd say it is possible that tomorrow the vacuum expectation value of the Higgs flips to zero and that's the end of the world as we know it. Not that I am very concerned this will actually happen, but what the bleep do we know? Anybody wants to estimate the risk this happens and sue somebody over it because we irresponsible physicists might all have completely overlooked a lot of unknown unknowns? Just asking.

I'm not actually sure what Lee is saying later about Stuart Kaufman's view since I didn't read any of Kaufman's books (got stuck in 'At Home in the Universe' somewhere around the history of the DNA or so). But I guess this argument points in the same direction: "What [Stuart] claims is that if you know all the properties that are relevant to compute the fitness function of all the species at some time, you do not know [...] enough to predict what will be the properties that will be relevant for the fitness function 100 million years later."

Thus, no matter whether there is some fundamental theory for everything or not, or whether strong emergence exists or not, we will be faced with systems in which features will unpredictably emerge. Like probably in the evolution of species on our planet, possibly in the climate, but hopefully not in the global economy.

Besides this, since it's impossible to prove that our inability to accurately make a prediction is due to the system and not due to the limitations of the human brain, the hypothesis that strong emergence doesn't exist is unfalsifiable (In other words: if you find an emergent feature you can't explain, you can't prove it can never be explained within any model). So I think I leave this domain over to philosophy.


VI. Summary

Properties of system can emerge in various ways, they can emerge by changes in scale, under certain conditions, or in time. One can distinguish between strong and weak emergence, where weakly emergent features are in principle predictable and strongly emerging ones aren't. However, this difference is a rather philosophical one as all of our models are incomplete descriptions of the real world anyway, so there always can be a 'strong emergence' simply because the description is incomplete. Further, it is of little use to know whether a feature is in principle unpredictable or if it is in practice unpredictable. Weak emergence is not in conflict with reductionism.


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31 comments:

Doug said...

Hi Bee and Stefan,

I enjoyed the U-tube video on the oscillating chemical reaction [OCR].

It sort of resembles a number of little bangs exapnding and merging in 2D.

You may be interested in this introduction to the mathematics of Dynamical Systems and OCR by Irving R Epstein, PhD
Brandeis University
.

Phil Warnell said...

Hi Bee,

I have to agree that emergence is a slippery concept. For instance you mentioned that viscosity held no meaning for an atom; and yet I would contend that while it has little to do with the limit of scale yet rather where within the scales it is found. For between the relation of the nucleus and the electrons this has no meaning, yet within the confines of the constituents of the nucleus it does. For it has been found that viscosity has been observed to be relevant in relation between the quarks and gluons where a gaseous nature was first expected, to then find by experiment that is more liquid and one of very low viscosity (quark soup).

However, I consider all such things belong to the subjective, rather then objective. My idea of emergent is to consider what is perhaps truly fundamental and what is simply a subjective description resultant of such. These for the most part I would call phenomena. As you can recall in an earlier quote I made of Einstein, he was not interested so much in the phenomena but rather the fundamentals from which it sprang and then evolved to develop. My take on Smolin is that his definition of emergent and fundamental is much the same as this and for similar or same reasons. That is why he asks if time then is fundamental or emergent and as of late suspects it to be fundamental. I think it simply is a recognition that if there was a beginning(s) then from what did it spring forth from? I would call all these fundamental and the rest phenomena which are referred also as entities or qualities of what emerged.

Best,

Phil

Bee said...

I dunno. Honestly, I didn't comment on the time-question because I still don't get it. If you'd say we live in a manifold that has a timelike coordinate, full stop, I'd have said this is fundamental. But it seems to me Lee means something different, like all that stuff with the succession of present moments etc, that I'd have attached to the 'flow of time' (can't come up with a better word), which I however believe is an illusion. But yes, possibly the mentioning of emergence in said lecture was a backwards construction to underline the argument. Anyway, this was not what I had in mind when writing. To use your words, you'll have to ask yourself then whether the 'fundamental' quantities can change with time (meaning, e.g. new ones show up). And since they are fundamental, they can't change in a predictable way. This would be what I mean with 'strong emergence'. Likewise, what I tried to say with this in practice being of little relevance is the questions whether you'll ever be able to know a set of 'fundamental' variables is really complete. Best,

B.

Phil Warnell said...

Hi Bee,

“To use your words, you'll have to ask yourself then whether the 'fundamental' quantities can change with time (meaning, e.g. new ones show up). And since they are fundamental, they can't change in a predictable way. This would be what I mean with 'strong emergence'.”

As I have mentioned many times I am certainly no guru in all this. Also, I may have gotten Smolin’s meaning all wrong. What I’m then left with is my own feeble notions. Whether or not the interactions of the fundamental are predictable I would say it has to do with if the quantities of each is relevant rather then the qualities. That is to say that even though there may exist what would truly be fundamentals, and all these fundamentals have quality(s) of there own; what we observe as emergent or phenomena may relate as much to the proportions they combine to form as to what we call that which is real. This is certainly not the task of philosophers to discover, yet rather the task of science. The job of philosophy is to remind the scientist not to limit what might form to be a possibility. What Einstein became aware of is that at such a tenuous moment as now it would be better if perhaps these people and their disciplines be more not less one in the same

Best,

Phil

Bee said...

“Magnetism is one of the Six Fundamental Forces of the Universe, with the other five being Gravity, Duct Tape, Whining, Remote Control, and The Force That Pulls Dogs Toward The Groins Of Strangers.”
~ Dave Barry

;-p

Garrett said...

Hi Sabine,

Thanks for describing the exciting career in mathematical modeling. (Boy was I confused when I first walked into that class at UCLA.)

One of the comics you posted was actually from xkcd:

http://xkcd.com/171/

xkcd is great. The other one I didn't recognize.

Best,
Garrett

Bee said...

Hi Garrett,

Thanks. I figured it was from xkcd, but couldn't find the exact link, I've updated this. The other one? In case you're referring to the one with the Garfield, that's a crime I committed myself for last week's post.

Yeah, actually when I read the chapter in the Miller & Page book about mathematical modelling I couldn't quite figure out what its supposed to be good for. Like, I also wouldn't take a lecture in 10 finger typing or so. So I thought I'd cook it up for a blog post.

Best,

Sabine

theoreticalminimum said...

May I recommend one book I have only partially skimmed through, but which I think might help towards understanding some of the questions that usually arise when thinking about these phenomena. It is "The Nonlinear Universe: Chaos, Emergence, Life", by Alwyn C. Scott.

I would be very interested to know what Gell-Mann, after that many years at the Santa-Fe, would be able to tell us about these kinds of phenomenological questions.

michaeldcassidy said...

emergence = emergences

no 'i'

Neil' said...

Here's my long-nursed question about string theory, which gets right to what is perhaps the ultimate "emergence and reductionism" issue: how to explain and predict how and why strings are and do as they do. Note that for example, a literal "string" we know is made of atoms in various arrangements, and those in turn of constituents (in everyday interactions, electrons being the most directly relevant.) Hence, we can predict and explain the properties of real strings and other everyday objects by building up from their constituents. We predict melting points, chemical reactions, elastic coefficients, magnetism, etc. But if strings are "fundamental" then there isn't anything they are "made of" to predict from, right? You could just decide to say, well strings are a given, a fait accompli. Then, once you pick a way for them to be, the rest follows.

That seems a bit arbitrary, doesn't it? Even if you need to avoid infinite causal turtle series, it just doesn't address the issue of the "logic behind" strings. I know that theorists look for some consistency about mathematical design in hypothesizing about strings etc., but we can imagine all sorts of such constructions. Just food for thought.

Also, at the higher level of emergence, I nominate superconductivity as a good candidate. It seems a delicate situation, involving odd collective behavior of charged particles, and isn't really fully understood. "Money quote" from Wikipedia:


... During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957). Generalizations of these theories form the basis for understanding the closely related phenomenon of superfluidity, because they fall into the Lambda transition universality class, but the extent to which similar generalizations can be applied to unconventional superconductors as well is still controversial. ...

Uncle Al said...

Given N physical dimensions, no fewer than N+1 points can have a chiral confiuration. Given N+2 points, chirality can continuously deform into its mirror image without passing through an achiral intermediate (J. Math. Chem. 17 185 (1995)). When does the flip occur?

Beware emergent phenomena. Physics thinks the world is continuous; recursion: See "recursion."

stefan said...

Dear Bee,


thanks for the careful discussion of the different instances of "emergence"! It seems to me that to have "strong emergence", one just may be missing some important ingredient in the model, or even the theory, just as you said - or, as the example with the mosaic photo shows, that there is some "designer" ;-).

But my (maybe naive) impression is that physics usually is dealing with "weak emergence". But even when there is "predictability in principle" this does not imply predictability, if we think about deterministic chaos, for example. And if I remember correctly, just in "chaotic" systems, there can be surprising patterns emerging (isn't this Belousov-Zhabotinsky-Reaction often mentioned in connection with "chaos", or nonlinear dynamics, at least?)

And Homer-Dixon discusses "unknown unknowns"? Does this mean, perhaps, that Donald Rumsfeld has been reading Homer-Dixon ;-) ?

Best, Stefan

Arun said...

Dear Bee,

It may be we are capable of understanding only weakly emergent properties of systems. Our very notion of what constitutes an explanation requires weak emergence.

We would make any strongly emergent property into a fundamental, given, unexplained property of the system.

Phil Warnell said...

Hi Bee,

““Magnetism is one of the Six Fundamental Forces of the Universe, with the other five being Gravity, Duct Tape, Whining, Remote Control, and The Force That Pulls Dogs Toward The Groins Of Strangers.””

I would submit that the first five to be emergent or phenomena, while the last most definitely fundamental :-)

Best,

Phil

Plato said...

Nice post Bee.

Symmetry considerations dominate modern fundamental physics, both in quantum theory and in relativity. Philosophers are now beginning to devote increasing attention to such issues as the significance of gauge symmetry, quantum particle identity in the light of permutation symmetry, how to make sense of parity violation, the role of symmetry breaking, the empirical status of symmetry principles, and so forth. These issues relate directly to traditional problems in the philosophy of science, including the status of the laws of nature, the relationships between mathematics, physical theory, and the world, and the extent to which mathematics dictates physics.

The continued effort to clarification helps one with knowing what one knows? As too, what they mean?:) Defines, the limits to which their conclusions had been drawn.

Now in a philosophical sense even Lee Smolin had to contend with these issues. See here

I struggle here too.

Neil' said...

Plato (and anyone), I wonder how it is that mere space-time symmetries {per Noether theorem] can prove conservation laws regardless (IIUC) of the particulars of the physical laws involved. For example, the following exercise shows the danger of simplistically interpreting e.g. “Homogeneity in space implies conservation of momentum, and homogeneity in time implies conservation of energy.” Let’s assign different values of G; G1 and G2, to two otherwise physically normal masses m1 and m2. (Hence, we keep the standard, non-gravitational definition of “mass” for inertia and kinetic energy.) We connect them with a rod. The forces between them will be unbalanced, because we have: f12 = G1m1m2[r]12/r^2 but f21 = G2m1m2[r]21/r^2. (The forces on the masses are a function only of mg, since we are by fiat just adjusting G and not inertial mass.) Hence the closed system will accelerate - “reactionless drive.”

Energy and momentum are not conserved unless perhaps we make awkward demands on general relativity etc. Note that although different G were assigned to the masses, those values of G are attached to the masses and are not characteristic of regions of space as such.

Aren't there hidden or not so hidden assumptions that go into Noether type claims, making their "proof" of conservations laws more dependent on particulars than the usual description seems to imply?

Bee said...

Dear Arun,

That's what I was trying to say in reply to Phil above. If there was 'strong emergence' it would imply changing the 'fundamental' properties. But the question is whether you can possibly ever find out this is bound to happen. I.e. take the example with the photomosaic above (the analogie to the multiverse is obvious). Is there any possibility to ever know what's in the neighboring parts, if you only have access to your own patch?

Best,

B.

Bee said...

Dear Stefan,

Actually, I didn't mean it model dependent. If you have an incomplete model, you can likely witness all kinds of surprising emergences. The worse the model, the more 'strong emergence' you'd have. What I meant to say is that there might be no model in which you can make the prediction that something will emerge. As I said above, the hypothesis that this isn't possible isn't falsifiable, so I don't particularly like it, but that's what I was talking about. Think about the example with the photomosaic. I think the claim that Kaufman makes is somewhat different (it appears also in the book I'm presently reading). Basically it says, there is no 'model' that can make a prediction for the real world that isn't isomorphic to the real world itself. There is no simplification possible. So the only thing we can do is sit and watch. (For me the argument misses something clarification about timescales, i.e. how fast a prediction would fail, depending on the complexity of the system, but one can probably straighten it out somehow.)

Best,

B.

Bee said...

Neil',

You have asked the same question at least two times previously, the last time here, and I've already replied to it. If you're not interested in my answer, then please omit repeating it. Besides this, the question is completely off topic, and you know that I don't appreciate this.
Thanks,

B.

Neil' said...

Well Bee, I was wondering what Plato would say about my example since he brought up the issue of symmetry (so it was already mentioned in the thread, and Plato has not yet commented on my thought-experiment AFAIK.) I don't imply that I expect you too to answer every question I bring up, and certainly not, if you already did. It seems to me as well, that implications of symmetry are indeed connected to questions of emergence (emergence from symmetry?) Maybe not, but I sincerely thought it was. May I gently suggest, that your standard of being on-topic is too strict? In any case I don't mean to be OT.

Arun said...

Dear Bee and Stefan:

The comments section of your blog is a strongly emergent property of the blog :)

-Arun

Phil Warnell said...
This comment has been removed by the author.
Phil Warnell said...

Hi Bee,

“If there was 'strong emergence' it would imply changing the 'fundamental' properties. But the question is whether you can possibly ever find out this is bound to happen. I.e. take the example with the photomosaic above (the analogie to the multiverse is obvious). Is there any possibility to ever know what's in the neighboring parts, if you only have access to your own.”

Indeed an interesting way to look at it and yet I would say it is approachable. For instance, if to be any part of a multi-verse involves process or if say one brane is to pass through another, that would imply that time is fundamental. Also, just to pass in time, as to pass through, would also require space or dimension if you prefer. So based on this then you have two fundamentals, being space and time. The question then, is space-time fundamental or composite, such that space(other dimensions) and time are fundamental separately (of our reality or all if they exist)?

I would say that with our current thinking, where the number of each have relevance to what forms reality they are separate, with time being one that in our perspective is monopole in nature (for lack of a better expression). Einstein saw no distinction between space-time and what was contained therein, with all that is contained extended. He furthered to insist if this be true that there then was no meaning to “empty space”. This is what I understand is the difference between how those like Smolin considers things and those like Witten, where the latter still requires a scaffold on which to build a reality and the former not. I myself like the former for then we may have some true fundamentals where in the latter they still elude.

Perhaps then, the most persistent of the illusions are so because they are not.

Best,

Phil

Plato said...

"We all are of the citizens of the Sky" Camille Flammarion

Neil:It seems to me as well, that implications of symmetry are indeed connected to questions of emergence (emergence from symmetry?)

Time translation symmetry gives conservation of energy; space translation symmetry gives conservation of momentum; rotation symmetry gives conservation of angular momentum, and so on.John Baez

I refer you back to Bee's answer and just add "John Baez's comment section" for consideration. I am not about to fool with the complexities of those things I do not understand completely.:)

It is a "foundational point" for me, in context of model development. It was important to me to understand Lee Smolin's position and point this out, while considering the context of Bee's post.

Phil has gone on to point out these differences of approach.

I was also pointing out the foundational approach from Smolin's position on symmetry, asymmetry and the relationships to beauty and the kind. The whole context of the post threw me back to the very points of of emergence and Reductionism.

Why Robert Laughlins point of view(Condense Mater Theorist?) was also added for reference.

That each theory involves loops-in string theory, these are string loops; in loop quantum gravity, they're harder to describe non-mathmatically, but, roughly speaking, they're elementary loops of space-suggests there might be a connection. This possibility is further supported by the fact that on a few problems accessible to both, such as blackhole entropy, the two theories agree fully. And on the question of spacetime's constituents, both theories suggest that there is some kind of atomized structure. Page 490, Fabric of the Cosmos by Brian Greene

In terms of the Mosaic, a quote immediately came to mind that had been most troubling for me. An "enlightening moment" you might say.:)

So it turns out that if you, for instance, take a dimension - imagine its in a circle, imagine its really huge - and then you make it smaller and smaller and smaller, the equations tell us that if you make it smaller than a certain length (its about 10-33 centimeters, the so called 'Planck Length') ... its exactly identical, from the point of view of physical properties, as making the circle larger. So you're trying to squeeze it smaller, but actually in reality your efforts are being turned around by the theory and you're actually making the dimension larger. So in some sense, if you try to squeeze it all the way down to zero size, it would be the same as making it infinitely big. ... (CSPAN Archives Videotape #125054)

I understood that Lisa's writing was more palatable for you Bee , but these points cannot go unanswered as you approach the foundational perspectives?

Some of that flower power generation were perplex by what the human brain potential was capable of. While the brain power was thought to be increased by the drugs, I found it was never necessary once you applied the thinking brain to it's potential.

Not appropriate to this article Bee I know. Sorry.

Sure I thought of Lecithin., With regards to other other potentially useful drugs(?)and after reading the results of a person who thought like wise that was dear and close to me since passed on in years, I can tell you that if the mind cannot bring back where it went, there was no sense going.:)

Now we have to get past the occupation of the physical and the mental journey's to take the mind to a path for consideration. A treadmill and music for sure while the mind works?

Sure some were interesting in the philosophical introduction of Eastern concepts, while Murray Gell-Mann made fun of it. There are interesting comparisons to consider in this aspect of the Yin/Yang.

Tony Smith made them, and I am in agreement with a "deeper perspective in the probabilistic journeys" taken there. A deterministic one.

But back to your point on emergence and reductionism.

In fact, in the reciprocal language, these tiny circles are getting ever smaller as time goes by, since as R grows, 1/R shrinks. Now we seem to have really gone off the deep end. How can this possibly be true? How can a six-foot tall human being 'fit' inside such an unbelievably microscopic universe? How can a speck of a universe be physically identical to the great expanse we view in the heavens above? (Greene, The Elegant Universe, pages 248-249)

It is pushing back the boundaries of our thinking.

Neil' said...

Here's another fascinating candidate for an emergent phenomenon: Sonoluminescence . We still don't truly understand what is going on in this effect. Good take (no surprise?) at http://en.wikipedia.org/wiki/Sonoluminescence. Some think IIRC that we can get enough heat from SL to achieve fusion, even usable fusion. (I heard of such an attempt using acetone, but not much since.)
Also, ball lightning might be another example.

BTW, Phil W., I too wonder about the treatment of "empty space", or let's just say "space" versus any particular content, in physics. I am looking for good answers as to how one manifold of "space", say a 3-brane holding (how?) most particles within it, is demarcated and moves inside a larger "space" which is also inherently "empty" except for quantum fluctuations. How is it circumscribed and undergo movement etc. like a "thing" would in ordinary space?

Plato said...

Sorry for being off track Bee.

Maybe Neil only in terms of the "geometrical propensities of the bubble nucleations themself?"

That was a journey I took also, but was drawn back to the very schematic realizations of the actions of expression.

Their relationships drawn by analogy to events within the cosmos, or within context of the universe itself. Gravitational collapse and the evidence released in the supernovas. A candle of measure:)

Calorimetric evidence is only as good as well want to measure it? Another foundational question in terms of Glast and the PI direction?

Rhys said...

"As somebody in the audience also pointed out, these are basically different order parameters to change a system (e.g. scale, temperature, or time)."

That seems like a silly thing to say. How can time be an order parameter? It can't, is how! Neither can either of the other examples.

I think you are rightly confused about the different categories presented by the lecturer - he seems to not actually be saying anything meaningful...

Bee said...

Rhys: Maybe that wasn't the exact wording that was used. But what is the problem with it? Time is an 'order parameter' if its fundamental, i.e. you have an observer independent definition of before, now, and after. Anyway, as I already said, I didn't comment on the time question in this lecture as I still don't understand it. Best,

B.

Plato said...

Lee Smolin:

I suspect this reflects the expectation many people have that time is not fundamental, but rather emerges only at a semiclassical approximation in quantum cosmology. If you believe this then you believe that the fundamental quantities a quantum cosmology should compute are timeless. This in turn reflects a very old and ultimately religious prejudice that deeper truths are timeless. This has been traced by scholars to the theology of Newton and contemporaries who saw space as “the sensorium” of an eternal and all seeing god. Perhaps the BB paradox is telling us it is time to give up the search for timeless probability distributions, and recognize that since Darwin the deep truths about nature cannot be divorced from time.

The alternative is to disbelieve the arguments that time is emergent-which were never very convincing- and instead formulate quantum cosmology in such a way that time is always real. I would suggest that the Boltzman Brain’s paradox is the reducto ad absurdum of the notion that time is emergent and that rather than play with little fixes to it we should try to take seriously the opposite idea: that time is real.


Somehow how, I cannot believe that "theoretical positions" are disregarding the "substance gravity places" in both cases?

Good words around the Internet and tributes to John Wheeler.

What stuck with me the most was this. As well as the new terminology and historical context assigned to the blackhole was the "Geon."

Geons, Blackholes & Quantum Foam, by John Archibald Wheeler, with Kenneth Ford, page 236, para 2.


"This hypothetical entity, a gravitating body made up entirely of electromagnetic fields. I call geon(g for the gravity, e for electromagnetism," and on as the word root for"particle"). There is no evidence for geons in nature and later was able to show that they are unstable-they would quickly self-destruct if they were ever to form. Nevertheless it is tempting to think that nature has a way of exercising all the possibilities open to it. Perhaps geons had a transitory exitance early in history of the universe. Perhaps(as some students and I speculate much more recently), they provide an intermediate stage in the creation of the blackholes."

Who in their right mind has not tried to give meaning to a "configuration space" for exemplifying an aspect of nature?

Gravitons?:) Strangelets?:) Geons?:) "Bulk perspectives" after a graduation of a kind?

Count Iblis said...

In case of strong emergence you would expect that information could get lost. So perhaps you could test this by testing for violations of unitarity...

wev said...

This may be a very simple example, but it does demonstrate the reality of strong emergence ...

http://tinyurl.com/yjrnxmv