Emergent Phenomena in the Universe

[ste]

I was recently reading through a thread on physicsforums.com about the elegant universe video production(PBS). People seemed to be truly wrapped up in the trivial, such as fretting over who in the docu mentary was Ed Witten. Needless to say, I hadn't been terribly impressed with any of the posts I had read, until I stumbled on a particular post that caught my eye; It comes from user ZapperZ, whom I shall quote here:

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I probably should have just let sleeping dogs lie, but against my better judgement, I will jump into this one... :)

The one major disappointment, but not surprising, of The Elegant Universe (both the book and the TV docu mentary) is the omission of the significant point of view of the Anderson-Laughlin-Pines (ALP) "axis". It appears that, at least in the docu mentary, the only dessenting view was presented by Sheldon Glashow (which, BTW, was one of the rumored reasons why he left Harvard for BU - that he thought most theorists at Harvard in that field have abandoned phenomenology in favor of String, Superstring, etc...)

The ALP axis (as I would like to call it) contradicts the popular views among particle/high energy physicists, championed by Steven Weinberg, that the unification of all the 4 basic forces that includes the varification of quantum gravity, signifies a "Theory of Everything" (TOE). This point of view was alluded to several times in the docu mentary - that getting GR and QM to mearge would mean a TOE.

ALP - who are all condensed matter theorists and who are well-known in their own rights (Anderson and Laughlin are both Nobel Laureates) - argues that what Weinberg is arguing is not a TOE for physics/universe, but a TOE for REDUCTIONISM. A grand unified theory (GUT) would only be a complete explanation of the behavior of the universe at the elementary, single-particle scale, but not does not necessary mean that we have a complete description of all the phenomena in the universe. ALP points out that there are so-called EMERGENT phenomena that can't be explained simply by knowing all the elementary interactions and by simply adding more and more interaction - i.e. this isn't simply a matter of higher complexities. As Anderson likes to say "More Is Different!"

In his Nobel speech, Laughlin described an exercise he once did onto his poor, unsuspecting students taking a graduate cla ss in QM.[1] He gave the students a take-home exam in which he asked the students to derive superfluidity from First Principles - meaning knowing the full set of microscopic equation of motion, derive the phenomena of superfludity. Of course, the students could not, and no one can! Superfluidity, superconductivity, fractional quantum hall effect, magnetism, phase transition, etc, etc., are all "emergent" phenomena that occur as a collective effect. These phenomena disappear, as Laughlin points out, when you take the system apart and analyze each individual component within the system. These are many-body effects that simply can't be "derived" with the individual properties as the starting point.

Condensed matter physicists have long known of this, and various principles that came out of condensed matter, such as the Higgs mechanism and the principle of broken gauge symmetry, have now been adopted in various other fields of physics, including particle/high energy. However, the fact that these emergent phenomena are different and not simply just added complexities, seem to not have been heard by many camps, especially among popular views. I think it is why those who are working in the field of quantum gravity, string, etc, still may have an impression that such unification signifies a TOE. ALP have clearly pointed out why such notion may be a fallacy.[2,3] A unified theory doesn't not imply a theory of everything.

Anyway, didn't mean to throw a wrench into the whole thing, but I feel that it should be pointed out that eminent and large number of physicists do not share the same philosophical view on GUT=TOE thingy.

Zz.

[1] R.B. Laughlin, Rev. Mod. Phys. v.71, p.863 (1999).
[2] R.B. Laughlin and D. Pines, PNAS v.97, p.28 (2000) or get it at www.pnas.org/cgi/reprint/97/1/28.pdf .
[3] R.B. Laughlin et al., PNAS v.97, p.32 (2000) or get it at www.pnas.org/cgi/reprint/97/1/32.pdf .

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[Next Post (still ZapperZ)]
Quote:
Originally Posted by Mike2
Could a reduction of entropy account for these "emergent phenomena"? For all the phenomena you mention represents emerging states of order. Does particle physics account for entropy?

I'm not sure what or why particle physics have anything to do with this, since the emerging phenomena that I cited are all in condensed matter physics. In many of the emergent phenomena, such as superconductivity and superfluidity, the transition into those phenomena is a phase transition, typically a 2nd order phase transition. In such cases, there need not be any change in the thermodynamics state variables, or equation of state.

Zz.

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[ste]

Here is a much better format of the information, directly from ZapperZ's blog, physicsandphysicists.blogspot.com:

There have been frequent claims, both from legitimate sources and quackeries, of the possibility of finding something called the Theory of Everything (TOE). Supposedly, such a theory would contain ALL the necessary interactions that would be able to, in principle, describe ALL the phenomena (at least the existing ones) that we have observed.

We won't talk about the quackery aspect of this. The legitimate aspect of the belief in a TOE is due to the fact that there are only 4 fundamental interactions that are responsible for all the phenomena in our universe that we know of: gravity, electromagnetic, strong, and weak interactions. There is a strong belief (and desire) that all 4 of these fundamental interactions can be unified into a single consistent description. Already the electromagnetic and weak interactions have successfully been unified into an electroweak theory. There are every indication that the strong interaction will be next. Gravity might be the last and most difficult. However, assuming that it can be unified with the others, one then have what is called the Grand Unified Theory (GUT). Most people claim that then, we have achieved the TOE.

The implicit assumption in making such a claim that GUT = TOE is that the principle of Reductionism works. Reductionism is a philosophy which, to state rather crudely, everything in the universe can be reduced to the basic interaction at a single particle case. Then, by simply adding a higher level of complexities, one can then recover all the other more complicated, macroscopic phenomena. So if you know all the interactions that an atom in a human skin has, then by including more and more of the number of atoms/molecules, you will eventually be able to describe all the properties of the human skin. Hence, once you know all there is to know at the single particle scale, then everything else is just a matter of complexities. This then leads to the notion that GUT = TOE.

Most particle and high energy physicists espouse this point of view. I would single out Steven Weinberg as the prominent champion of this school of thought. String theoriests have also been known to slip up now and then by claiming that unification of gravity with quantum mechanics is a step towards GUT and TOE.

However, there is another school of thought that would contradict the idea that GUT = TOE. This school of thought is made up of condensed matter physicists, which make up the largest percentage of practicing physicists. The most prominent condensed matter physicists who have stated their opposition to the reductionists idea are Phillip Anderson, Robert Laughlin, and David Pines. They brought up examples that are described as "emergent" phenomena, often seen in condensed matter. These are phenomena that only occurs, or can only be defined, when there are a gazillion interactions occurring. Examples of these are superconductivity, fractional quantum hall effect, magnetism, etc. Laughlin, for example, argued that if you try to write down all the interactions of a single electron in a conductor, no matter how many electrons you add up in your interactions, you will NEVER recover the superconductivity phenomenon. Superconductivity is an emergent phenomenon that is a result of a many-body interaction. The starting point in describing such a phenomenon MUST start not from a single particle scenario, but from a many-body ground state scenario. This effect emergers out of a many-body interaction and will simply disappears if one tries to take it apart to a single-particle level.

What this boils down to is the claim that GUT is the TOE for reductionism, not the TOE for physics. Anyone claiming the existence of any form of TOE will have to seriously address the glaring omission of a huge body of phenomena from condensed matter physics, which holds some of the most highly verified observations with the highest degree of certainty in any field of physics.

For more resources on emergent phenomena from condensed matter physics and why they contradict the claim of GUT=TOE, read the references below:

1. www.pnas.org/cgi/reprint/97/1/28.pdf
2. www.pnas.org/cgi/reprint/97/1/32.pdf
3. ar[SPAMFILTER]Xiv.org/abs/hep-th/0210162
4. R.B. Laughlin, Rev. Mod. Phys., v.71, p.863 (1999).