Meet Mr. Xiao-Gang Wen

[Martin]

I came across a paper that was so strange I needed to share it with someone.

 

this is a guy who is at MIT and who publishes in peerreviewed journals like Phys. Rev. series B. and Oxford U. Press is publishing his book this year, called Quantum Field Theory of many-body systems

 

so you or I probably can not so easily dismiss him, if we wanted, but look at the title and abstract of this paper.

http://arxiv.org/abs/hep-th/0109120

 

Origin of Light

Xiao-Gang Wen

4 pages,

Phys.Rev.Lett. 88 (2002)

 

author's summary:

"The existence of light (a massless U(1) gauge boson) is one of unresolved mysteries in nature. In this paper, we would like to propose that light is originated from certain uantum orders in our vacuum. We will construct quantum models on lattice to demonstrate that some quantum orders can give rise to light without breaking any symmetries and without any fine tuning. Through our models, we show that the existence of light can simply be a phenomenon of quantum coherence in a system with many degrees of freedom. Massless gauge fluctuations appears commonly and naturally in strongly correlated systems."

 

introductory paragraph:

"In an attempt to explain the meaning of “emptyspace” to a young child, I said “space is something not made of atoms.” He replied “Then you were wrong to tell me last time that only light is not made of atoms.” Indeed, light and gravity are two singular forms of “matter” which are very different from other forms of matter such as atoms, electrons, etc.

(Here I assume space=gravity.) The existences of light and gravity–two massless gauge bosons–are two big mysteries in nature.

 

Massless particles are very rare in nature. In fact photon andgraviton are the only two massless particles known to exist.

 

In condensed matter systems, one encounters more kinds of gapless excitations. However, with a few exceptions, all the gapless excitations exist because the groundstate of the system has a special property called spontaneous breaking of a continuous symmetry.[1, 2] For example, gapless phonons exist in a solid because a solid break the continuous translation symmetries. There are precisely three kinds of gapless phonons since the solid breaks three translation symmetries in x, y and z directions. Thus we can say that the origin of gapless phonons is the translation symmetry breaking in solids."

 

I'm not getting too much from this on first encounter. I'm looking at XG Wen because Olaf Dreyer (whose QG work I know) has made a point of refering to XG Wen book (the Oxford U Press 2004 one)

in a paper of his that appeared today.

[Martin]

here are 15 papers by XG Wen from March 1993 to July 2004

http://arxiv.org/find/hep-th/1/au:+Wen_X/0/1/0/all/0/1

 

his book, that Olaf Dreyer cites, is not available online.

I am looking for an online substitute---dont want to have to make a trip

to the physics library for something I just want to taste the flavor of

 

Olaf Dreyer paper purports to solve the Cosmological Constant problem of QFT. the paper is just 4 pages. it is possible that he has seen how to do it.

this is a dizzy stretch of the imagination for me and maybe you (if anyone is reading this) I dont dare dismiss it

 

 

It has been known for decades that standard QFT predicts a vacuum energy that is hugely too big----like too big by a factor of 10¹²³ .

 

the celebrated Steven Weinberg has written about this. It is well known. It is the worst prediction in the history of theoretical physics. It is called the Cosmological Constant problem

because when the CC was measured in 1998 it turned out to be

10¹²³ times smaller than what people said QFT predicted.

 

now in a 4page paper Olaf Dreyer (one of Lee Smolin's Quantum Gravity team of researchers at Perimeter Institute) has shown an argument that seems to resolve the problem and show that a (Background Independent) QFT does not, after all, make this huge mistake.

 

http://arxiv.org/hep-th/0409048

Background Independent Quantum Field Theory and the Cosmological Constant Problem

[Martin]

Here is how Olaf Dreyer starts off.

 

"There are currently two competing views of the role quantum field theory plays in our theoretical understanding of nature. In one view,quantum field theory describes the dynamics of the elementary constituents of matter. The job of the physicist is to figure out what the elementary particles are and to find the appropriate Lagrangian that describes the interactions. The Standard Model of elementary particle physics is the epitome of this view (see[1] for an authoritative exposition of this view).

 

The other point of view likens the use of quantum field theory to its use in other areas of physics, most importantly in solid state physics. Here, quantum field theory is not used to describe the dynamics of elementary particles. In solid state physics, this would be fruitless, since the dynamics of a large number of atoms is usually beyond anyone’s ability to compute.

 

It turns out, however, that these large numbers of constituents often have collective excitations that can be well-described by quantum field theory and that are responsible for the physical properties of the material.

 

The view is then that the elementary particles of the Standard Model are like the collective excitations of solid state physics. The world we live in is just another material whose excitations are described by the Standard Model. The point of view was introduced by P. W. Anderson[2] and has since found a large following (seee.g. [3, 4, 5] and references therein). "

 

Reference 5 that Olaf Dreyer cites is the 2004 book from Oxford press by Xiao-Gang Wen.

 

 

BTW Olaf Dreyer echos the usual scandal about the Cosmological Constant problem a bit later in the paper right after equation number (1) where he says: "...If one takes this cutoff to be the Planck energy the vacuum energy is some 123 orders of magnitude away from the observed value of the cosmological constant [6], making this the worst prediction in theoretical physics. (For a detailed discussion of this problem see [7,8])..."

 

Anyway it is getting clearer that some attention is due to PW Anderson's work and X-G Wen. theirs is the solid state, or "condensed matter" way of looking at Quantum Field Theory and it is gaining adherenets. At arxiv there has been a leveling off or even decline of papers in the category hep-th and a rapid surge in the category cond-mat. Michael Peskin's (stanford-SLAC) annual review of what's hot in physics has moved astrophysics and condensed matter physics up over particle physics (string, HEP, whatever).

so there is some kind of shift happening. and at the moment it looks like

Olaf Dreyer has found a window on it---a clear perception. break in the fog.

[Martin]

Xiao-Gang has a nice home page

http://dao.mit.edu/~wen/

 

look at this animation

http://dao.mit.edu/~wen/talks/alight/alight_6.png.html

 

if you press run/start it will begin to run and

if you drag the thing on the side upwards it speeds it up

 

I have no sure feeling of whether Xiao-Gang is reasonable or not. but he is a successful and original physicist with many graduate students (how crazy can he be?) he sometimes quotes Dao sayings of LaoZi the sage, but then, people do all sorts of stuff.

 

He puts a blurb for his book on his home page:

"Quantum Field Theory of Many-Body Systems ---from the Origin of Sound to an Origin of Light and Electrons

 

For most of the last century, condensed matter physics has been dominated by band theory and Landau's symmetry breaking theory. In the last twenty years, however, there has been the emergence of a new paradigm associated with fractionalization, topological order, emergent gauge bosons and fermions, and string condensation. These new physical concepts are so fundamental that they may even influence our understanding of the origin of light and electrons in the universe.

 

This book is a pedagogical and systematic introduction to the new concepts, as well as quantum field theoretical methods in condensed matter physics. It discusses many basic notions in theoretical physics that underlie physical phenomena in nature, including a notion that unifies light and electrons. Topics covered are dissipative quantum systems, boson condensation, symmetry breaking and gapless excitations, phase transitions, Fermi liquids, spin density wave states, Fermi and fractional statistics, quantum Hall effects, topological/quantum order, spin liquids, and string condensation. Methods discussed include the path integral, Green's functions, mean-field theory, effective theory, renormalization group, bosonization in one- and higher dimensions, non-linear sigma-model, quantum gauge theory, dualities, slave-boson theory, and exactly soluble models beyond one dimensions. This book is aimed at bringing students to the frontier of research in condensed matter physics."

 

If you click on the title of the book you will get some sample pages including a table of contents for the book.

[Martin]

two recent papers by X-G Wen

 

http://arxiv.org/abs/cond-mat/0406441

An Introduction to Quantum Order, String-net Condensation, and Emergence of Light and Fermions

 

http://arxiv.org/abs/cond-mat/0407140

A unification of light and electrons based on spin models

 

these are posted June and July 2004

the first of these looks like a condensation of the message of his book,

so it would do as online substitute, to get a taste

it is essentially a talk he gave at SantaBarbara in January 2004 in which

he was plugging his book, scheduled to come out in the fall. so it has

to be reflective of the book or paralleling it, but only 16 pages