One contributor to the comments here (JC) has pointed out that Susskind has withdrawn from the arXiv his recent paper on the stupendous Landscape of sting theory. This is pretty unusual, but often when it happens the author puts in the withdrawal statement some indication of why the paper was withdrawn, something Susskind didn’t do in this case. Another contributor to the comments (Serenus Zeitblom) points out that one should look at recent changes to Douglas’s paper on the arXiv, which is now up to its fourth version.

One feature of the arXiv is that all posted versions of papers are available, so one can compare them and see what changes the author made. The history of Douglas’s paper is quite something. The original version was posted on May 30. Susskind’s now withdrawn paper was posted on June 17, and in it he claims that Douglas’s paper showed that Susskind’s argument in an earlier (May 21) paper (which exists in three versions) was wrong. The latest version (4) of Douglas’s paper now says that earlier versions of the paper are wrong. So, one reason Susskind withdrew his paper is presumably that its claims that his earlier paper was wrong were now wrong because they were based on Douglas’s wrong paper. Got that? This all seems to me to be a new and original version of the “Not Even Wrong” phenomenon.

Some other high points of the changes in the four versions of Douglas’s paper:

1. Going from version 1 (May 30) to version 2 (June 2), he changes

“If I had to bet at the moment, I would still bet that string theory favors the low scale, for the reasons outlined above, but it is not at all obvious that this is what will come out in the end.”

to

“At this point, it is not at all obvious whether high or low scales will be preferred in the end.”

2. Going from version 2 (June 2) to version 3 (June 22), he adds a reference to Susskind’s June 17 paper, some criticism of it, and the sentence

“The correct assumptions could be determined from string/M theory considerations with more work, and we are optimistic that this can be done in time to make convincing predictions before LHC turns on in 2007.”

3. Going from version 3 (June 22) to version 4 (June 29), he removes the sentence above (I guess he became less optimistic last week) and announces that the argument in the previous versions was wrong.

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I wanted to add this as well.

“

Quantum gravity is the field devoted to finding the microstructure of spacetime. Is space continuous? Does spacetime geometry make sense near the initial singularity? Deep inside a black hole? These are the sort of questions a theory of quantum gravity is expected to answer. The root of our search for the theory is a exploration of the quantum foundations of spacetime. At the very least, quantum gravity ought to describe physics on the smallest possible scales – expected to be 10-35 meters. (Easy to find with dimensional analysis: Build a quantity with the dimensions of length using the speed of light, Planck’s constant, and Newton’s constant.) Whether quantum gravity will yield a revolutionary shift in quantum theory, general relativity, or both remains to be seen.”http://academics.hamilton.edu/physics/smajor/quantgrav.htmlJC,

The Elegant Universe, by Brian Greene, pg 231 and Pg 232

“But now, almost a century after Einstein’s tour-de-force, string theory gives us a quantum-mechanical discription of gravity that, by necessity, modifies general relativity when distances involved become as short as the Planck length. Since Reinmannian geometry is the mathetical core of general relativity, this means that it too must be modified in order to reflect faithfully the new short distance physics of string theory. Whereas general relativity asserts that the curved properties of the universe are described by Reinmannian geometry, string theory asserts this is true only if we examine the fabric of the universe on large enough scales. On scales as small as planck length a new kind of geometry must emerge, one that aligns with the new physics of string theory. This new geometry is called, quantum geometry.”

You were right to point this out and from a common perspective, as a starting point .

But these discription were not limited to string theory alone as we have come to witness from the participants of LQG or dynamical traingulations of quantum gravity(quantum geometry).

Again you were right to point out the many facets of the attempts here, including Penrose and his twistors.

I am trying to find a common bound between them all, as we all are?:) Some of my perspectives are being revealled on physicsforum, and the imput back to me, is pointing towards the usage of Glast as a possible discriptor of the metric.

All speculation of course.

sol,

What is your definition of “quantum geometry”? Over the years I’ve noticed the term “quantum geometry” being used and abused for all kinds of things, depending on who you’re speaking to.

I don’t really have a good precise definition for the term “quantum geometry”, other than perhaps (in a vague sense) looking at what happens to the geometry of classical general relativity when quantum corrections are added in. Since not many of the quantum gravity paradigms are particularly that successful, I don’t feel there’s really any easy way to even quote a universal definition of “quantum geometry” that everybody can agree upon. At this point in time, string theory has the furthest progress in terms of looking at a “quantum geometry”.

In a non gravity context, perhaps “quantum geometry” could be defined as examining the “geometry” underlying quantum Yang-Mills theory.

Anyone else have a better or more precise definition of “quantum geometry”?

Alejandro,

All I meant was that values of atomic masses are to some extent due to historical accident. The allowed ranges are of course too small to really affect the viability of human life.

I was always fascinated by the relationship to the isometrical relationship orbitals presented in terms of self similarity. To cosmological situations the representations eem awfully uncannny.

Arivero, and from that standpoint, could we have indeed found a escoteric( has it been removed?) way to speak on the nature of quantum geometry?

Last week I was informally presenting to my elders my work on nuclear masses, and someone mentioned Rydberg but I was unaware of all the history. Thanks very much for bringing it here. Although I can not see how the isotope theory is anthropic-environmental (?). Well, of course, a sort of anthropicity principle could be to request the existence of Dalton’s atoms. Plausibly this requires the proton mass to be well smaller than the ones in the higgs/electroweak sector, but this is too modern for Rydberg ðŸ™‚

Aside, I believe to remember that the original isotope proposal was linked somehow to esoterism.

There is one obvious example successful of anthropic, or at least environmental, reasoning that I am surprised not to have seen mentioned: the isotope theory. 120 years ago, Janne Rydberg was probably Sweden’s most famous physicist. Nowadays he is remembered for the series and the constant, but his main interest was to derive some deep explanation for atomic masses. When it eventually turned out that atomic mass is due to a rather random mixture of isotopes, he became so depressed that he had to seek professional help.

There are of course many differences, e.g. that we can successfully explain the masses of individual isotopes, at least in principle. But I don’t see a problem if some numbers must be explained by historical accident, as long as the main predictions of your theory (extra-dimensions, SUSY, massless scalars, proton decay, huge and negative CC, etc.) agree with experiments.

JC, indeed it is easier and a lot more honest simply to point out the empirical data your theory needs. Newton does no predict the mass of the Earth nor Moon, and still it is a pretty theory.

The point here is that the “monovacuum” and “anthropic” folks actually share a common goal of defining a single theory having a single solution. But the second group has evolved towards a tricky, not very honest, methodology. The original anthropic principle, as I remembered it, claimed that we can not determine theoretically some fundamental constants because they could have any random value in some range, and we just happen to be in one of the possible ranges. The now-selling A.P. claims that the value of the fundamental constants is determined theoretically just because we are here.

The “monovacuum” folks follow a different argument. They are on the [very extended, but rarely explicit] oppinion that there is only a consistent way to describe spatial change (ie movement) in a mathematically consistent manner. In fact it is surprising how few methods do we have to describe dynamics, so it could be. In this view Classical Mechanics is logically incomplete or inconsistent (zero limits, incompatibility with electromagnetism) and the same happens with Classical Field Theory (self-energy of electromagnetism) and Quantum Field Theory (Renormalisation), while the fundamental yet to be string theory should be completely sound. The argument is antropic in a deeper sense than the antropic principle: it assumes that Reality must be exactly described my using [matematical] Words.

Hmm I feel I am not answering your comment but simply expanding or re-stating the previous of mine. Still, I wanted to go over it because of your mention of “compactness”. A side of the “compactness” of a theory is related not to its mathematical complexity, but to its degree of uniqueness.

I supposse that at the end one can reduct this uniqueness to some counting of the axioms and postulates needed in the theory (while complexity could be a count of lemmas and theorems), and to count the external input too.

Alejandro,

Many years ago I use to think of physical theories as a “compact” way of representing information about a particular phenomenon, in a vague sense. If a theory is so complicated and cumbersome, that it takes up more computer “storage space” to represent the mathematical formulas than it takes to represent the original experimental data, it would be easier just to quote the experimental data instead of the cumbersome “theory”. (This is sort of an abuse of “Occam’s Razor” without being too precise). The obvious case is that of Newton’s laws representing many different phenomena like Kepler’s laws, pendulum motion, free fall motion, etc … With quantum mechanics, the n-body Coulomb problem for the Schrodinger equation can account for the spectral lines of atoms, etc … The theories of Newton and Schrodinger are a very “compact” mathematical representation, compared to quoting all the experimental data for all the possible phenomena they represent. (I think it was Gregory Chaitlin who advocted this point of view over the years).

For really highly nonlinear systems that show up in fields like economics, biology, politics, psychology, etc … a lot of them are so mathematically cumbersome to the point that they are hopelessly complicated, where the most “compact” way of representing the phenomena is just to quote the original empirical data. A typical example of this is the empirical weather data, compared to the complicated nonlinear fluid dynamics systems which attempt to approximate the weather (in a less than satisfactory manner for the most part).

I’m being somewhat vague on purpose, since I don’t have a precise definition for “compact” representation of a physical phenomenon. Over the years I have changed my views on some of these ideas. I may very well end up dropping the entire framework in the future if I can’t find a way to resolve the issues that I have been deliberately vague about.

With respect to string theory, the “monovacuum” folks want a single unique vacuum solution which in a vague sense gives a “compact” representation for a quantum theory of gravity. With a proliferation of a zillion Calabi-Yau manifolds and many other solutions in the String Landscape, then string theory becomes one of those nasty cumbersome theories which becomes hopelessly complicated to deal with. It may very well be easier just to state the empirical data from the particle physics data books and the Standard Model, along with whatever empirical data is coming from the astrophysics folks (ie. cosmological constant, etc …) as the most “compact” representation of the phenomena that string theory originally was “advertised” to represent.

I had always though of it as a cosmologist/philosopher gadget. The Weak Anthopic Princriple and all that.

A decent motivation for it can come from

“Things are words” (20, 21st century AD), as Larsson quotes Polyakov. But forget the explanation from P. I understand that the “things are words” principle can be used to tell us that any theory of Reality must be done with words, and thus all the physics we do is limited to this. A physicist can say “words, and more concretely mathematical words”, and then look for a proof of existence and uniqueness of mathematical theories fitting the known data. This was the spirit of GUT and it is the spirit of string field theoretists, to use the “things are words” principle to get a single unique theory.

My understanding is that string is failing to get uniqueness, and then they perturb their own philosophical principle in order to say “things are words coming from empirical input”, or something so. But then it loses all its appeal.

Alejandro,

Do you have any insight as to why exactly some physics people end up believing in anthropic arguments and ideas?

If I didn’t know any better, I get the sense that a person using the anthropic principle is attempting to justify a particular idea/theory (whether popular or unpopular) that they are not willing to give up on easily. In the days when I was still a true believer in string theory, I would have found it very difficult to give up on it as a solution to quantizing gravity. I probably would have been making every possible excuse and argument to rationalize my own personal biases and prejudices in favor of string theory. If the anthropic landscape ideas were around when I was still doing string theory, I certainly would have tried to use them as my own personal justification to continue to believe in string theory.

For some folks, it may possibly be an “ego” thing where they don’t want to admit that they spent many years of their life, time, and energy on something that may very well be completely wrong in the end.

JC-

One thing that comes immediately to mind is Poincare and his wrestling with the metaphysics of F=ma (see “Science and Hypothesis” and “Science and Method”). If he had just forged ahead without worrying too much about how people are related to physics, he might have hit on relativity before Einstein.

-drl

I keep telling, supposse that we ask for sentient persons able to measure an earthly acceleration of 9.8 meters/second^2. Is this an anthropic requeriment? To me, it seems just experimental input. As people become aware that antropic=empirical input, the club will dissolve. I hope.

It will be interesting to see how many “monovacuum” folks will still be left actively working on string theory, if the anthropic folks end up having the most influence on the string research agenda.

It would be interesting to go back into physics history and see which paradigms and research fields had a “kiss of death” once the experts were starting to use the anthropic principle in a “serious” manner.