Answer your string questions for a nickle!

[Martin]

Since you brought it up, I guess I'm obliged to respond.

This is why Martin's index about 'String Research Quality' is pretty useless. Everybody is citing Maldacena's AdS/CFT paper, which was written ten years ago, and so falls outside of Martin's arbitrary five year window..

 

To take an example, the ISI Impact index uses a two-year cutoff, because they are interested in measuring current performance. This is a widely known professional citation index. It's not unusual to consider recent citations and I think five years is a pretty wide window. I don't see that the existence of highly influential papers in the past is relevant to measuring current performance trends.

 

I'm not especially interested in string, or the present troubles of the US string research community, so I don't want to spend too much time on this, but I will show Fredrik and ajb the trend I discovered in current research citations because I think it is misleading to call it useless. It is actually pretty significant and it correlates with a bunch of other things (people getting out of the field, remarks by string leaders, trends in representation at major conferences, projected employment in the US etc)

 

Average cites for top eight recent string papers

2002: 357

2003: 243

2004: 145

2005: 117

2006: 119

(based on Stanford-SLAC Spires database)

http://www.scienceforums.net/forum/showthread.php?t=28255

[vincent]

I'm not especially interested in string

 

Then why are you posting in this thread? Does the no hijacking rule not apply to moderators?

[Martin]

Then why are you posting in this thread? Does the no hijacking rule not apply to moderators?

 

Please read my post, vincent. I'm certainly interested enough in string to try to keep the record straight. Ben calls me into the thread when he makes statements like "String has no competition". Because in my view it does.

And when he says things like this:

" string theory is the only way to quantize gravity that constrains the number of dimensions. In other QG approaches, this number is put in by hand."

 

This is simply not true AFAIK and time permitting I'll try to explain. The approach Smolin and co-workers are have been exploring since mid-2005 would fail completely if there were more than 3 space dimensions. If evidence of extra dimensions are found it's out, for topological reasons. As sensitive to dimension as string approaches are---only Smolin's insists that spacetime must be 4D (not 5D or 6D or 10D, must be exactly 4)

 

Like some string approaches don't work except in 10 dimensions, so a string advocate might say "string PREDICTS 10 dimensions". Well Smolin's doesn't work in anything but 4D spacetime----exactly in the same sense it "predicts" 4D.

Also Reuter QEG and Ambjorn Loll CDT PREDICT DIMENSION. they are very different approaches and both have been under development for almost 10 years and are farther along than smolin's---more visible. Curiously the both predict a fractional spacetime dimension around 2D at planck scale growing contuously up to 4D as you go up in scale.

So you could FALSIFY both Reuter and Ambjorn's if you could show experimentally that the microscopic dimension was not around 2. (Not that this would be a practical test, because the fractal behavior is down at planck scale, but they do constrain and indeed make predictions about dimension). It is a factual matter than needs correction.

 

I have limited time and also don't want to post too much, so I held back from mentioning this until I saw your post. But I don't think I can let uninformed or flatly inaccurate statements go by THAT INVOLVE QUANTUM GRAVITY approaches, not merely string, without saying something.

 

It just aint true that non-string QG approaches don't predict dimensionality. Some do in various ways, some don't.

====

And then of course Ben addresses things I've said in other threads, and POLLS in other threads, so I necessarily have to respond.

====

 

But perhaps you are hinting that I am secretly interested in string research Perhaps I should take back or qualify what I said about not being interested. It may have been put to categorically.

I AM actually interested in a number of string aspects. And I think what is happening to the string program can teach us things.

There is a lot to be learned by watching. You can't totally separate science from the institutions and communities that do it. They are different things but they are going to influence each other. Ultimately it's all one human process and by watching you learn all sorts of things about research communities, science policy, politics, and plenty more.

[fredrik]

Well, ask yourself... how big is the parameter space in quantum field theory? How many different quantum field theories can we build? Well, there are AT LEAST as many quantum field theories as there are string vacua, because every string vacua (to my knowledge, at least) is a consistent quantum field theory.

 

In fact, I would wager a guess that there are MUCH fewer string theories that quantum field theories. (In fact, I think there is a paper about it, by Cumrun Vafa and Lubos Motl, called something about the ``Swampland''.) And no one doubts quantum field theory's ability to describe nature. So it may turn out that string theory is just a framework for quantizing gravity, and it's predictions are all vrey general.

 

I'll see if I understand view of your own endeavours.

 

Clearly QFT isn't a theory, it's a framework which has builtin to it a number of assumptions, that constraints the possible theories. So are you suggesting that you view string theory sort as a "framework" somewhere at the same level? Except more specific and better? in the senese that string theory just tells us what class theories we should bother trying?

 

Is that close? (roughly speaking)

 

This is what I have gathered about non-stringy QG---they don't explain things like the standard model, and are completely fine with that.

 

To make a fair comparation I am not sure how much resources that has actually been invested in other approaches.

 

But this is exactly the approach that one SHOULD take. You have to know what you're picking before you know how to pick it.

 

The fact that we pose a question is an investment, a risk. This should IMO be balanced against the potential gain. One of the most confirming points of a question is that is has a good, useful answer. To ask a question, there is no discrimination of answers in sight seems like unmotivated.

 

You look at the ways to write the action down in ten dimensions, and think of the ways you can get consistent solutions in four dimensions. This means compactifying on a Calabi-Yau three-fold (six dimensional space), of which there are many. Generally there are many ways to put conditions on internal degrees of freedom, and some moduli that you have to deal with.

 

This is how I understand the vacuum problem---there is only a few ways to write down a ten dimensional theory, but many ways to get four dimensional physics.

 

Ok, consistent with the string framework itself that is.

 

Again, this is simply not the way things are done. There is now way for a low energy effective field theory to know very many things about dynamics in the UV---I can give you two or three examples, if you like.

 

IMO a relation should be inferred from the corrections. The deviations should I think induce a prior in the new spaces. If not, this spaces is not needed, as it's not supported by the interactions.

 

My twisted comments originate from my own views of course. Which is no more valid than yours, but the comparation is interesting.

 

So it doesn't address YOUR fundamental questions! I'm not of the opinion that physics should answer to anybody:)

 

Yes it doesn't address MY questions, I wrote that on purpose What I mean is just that don't we all answer our own questions? I'm not trying to answer somebody elses question. BUT, the fact that many of us do ask questions that are very very similar is apparently not a conincidence

 

This is what the quantum gravity people like Martin are doing. (I assume he's a scientist.) But they all have their problems. For example, string theory is the only way to quantize gravity that constrains the number of dimensions. In other QG approaches, this number is put in by hand. Scroll up to see the heated discussion

 

I definitely agree with you that dimensionality should not need to be put in by hand. But neither should IMO things that STRING THEORY put in by hand. The idea that all things are made up with a vibrating string in a background space is comptletely ad hoc to me. Note that I do not say this is wrong, I say that it is not sound to put it in by hand. If strings are the game, then a more fundamental theory should tell us so! So MAYBE if you guys can rework the entire stuff to get a more sensible master theory that explains things from more fundamental things, then... "string theory" does have hope even for me... but currently I see nothing in it for me. The really interesting questions are not even asked in the string approach as I can see.

 

I want a scientific strategy, not a framework, which is in essense a simple strategy combined with as it seems a random selection principle.

 

To be honest, the closest thing I get to a string in my own reasoning is the following. You start with a boolean observable (two state). Then if the information capacity of the environment increases beyond the two states, the two state inflates to a multiple state, and ultimately this turns in the continuum limit (which is an idealisation anyway, that doesn't ewally happen) into a string, where the position on the string represents the intermediate values of the boolean 0 and 1. Further this "string" can grow in more dimensions into planes and spheres. I am working on this and I dno't know yetwhat I will find. perhaps things will turn out to suggest a certain dimensionality, but in the general case only real data can say so. To predict dimensionality on my deks, I need to put in some physical assumptions.

 

Anyway my starting poitns are notthing near string theory, and in this comment my string is really physically locate in the environments state and correlation, the observer "mirrors" the environment.

 

/Fredrik

 

Ben, set aside my previous comments I have another question.

 

In line with my comments, what I admit that I am a bit curious about is exactly what the more fundamental theory (that I guess many string theorists look for) will actually look like, and I don't mean in detail but I mean more in principle. Will it still be a framework? Or will it be a specific theory? or more like a strategy?

 

I am curious if you could briefly look into your crystal ball and give you personal view (as a string advocate) of what sort of thing you expect to end up with in the end so to speak? And what kind of answers could possibly remain unanswered still?

 

/Fredrik

[vincent]

…in GR there is an object g which tells the geometry of the whole universe Is there something like that in the string framework? Never seen it. It seems curious to me that I never see a stringy equation for the quantum state of the geometry of the universe.

 

One objective of quantum gravity is to obtain the correct Hilbert space of states of any given spacetime. If you like you can refer to these states as different quantum spacetime “geometries”, but the difference in usage of the term “geometry” among different groups of researchers is more cultural than anything else since we’re all after the same thing in the end: A quantum theory of gravity. It should be said though that the term quantum gravity may be a bit safer than quantum spacetime geometry since spacetime may turn out to be an emergent concept in a way that makes the term quantum spacetime geometry inappropriate.

 

The object describing spacetime geometry in string theory is the same object that describes spacetime geometry in General Relativity which is the metric. This is because string theory contains General Relativity. In fact, General Relativity is encoded in string theory at the quantum level since the background fields in the world-sheet theory must satisfy the gravitational field equations of General Relativity if there is to be no quantum conformal anomaly. Quite remarkably, these equations turn out to be nothing less than the conditions on the beta functions that ensure conformal invariance beyond the classical level. These conditions also determine the number of spacetime dimensions. Such theories give us perturbative descriptions of "quantum spacetime geometry".

 

There are nonperturbative approaches as well which include the theories that satisfy the so-called gauge/gravity correspondence. These theories are the only known complete and self-consistent quantum theories of gravity we have. The reason we know that these theories are complete and self-consistent is that the theories on the gravitational side of the correspondence are dual to various Super Yang-Mills theories which are well-understood. It’s quite amazing that theories that don’t involve gravity should be equivalent to theories whose degrees of freedom are purely gravitational.

[the tree]

Although the conversation seems to have moved on with these super long posts, I'd just like to say thankyou for the clarification of what it means for a dimension to be big. It's always nice to understand a little bit of physics now and then.

[Martin]

Hello again Vincent!

 

One objective of quantum gravity is to obtain the correct Hilbert space of states of any given spacetime. If you like you can refer to these states as different quantum spacetime “geometries”, but the difference in usage of the term “geometry” among different groups of researchers is more cultural than anything else since we’re all after the same thing in the end: A quantum theory of gravity.

 

Actually I think those words cover a formidable gap of understanding since as far as I can tell string researchers mean something entirely different from other QG people. They don't seem to be talking about either a General Relativistic quantum physics or a quantization of the gravitational field. My question was aimed at clarifying that issue.

 

thanks for quoting my question and responding. This question was my contribution to this exciting and voluminous thread back at post #22. What I would like you to do is give me a URL where i can SEE a string formulation of the quantum state of spacetime geometry. IOW a quantum state of the Einstein metric, or something with equivalent degrees of freedom.

 

I had something else to ask about too. ...

 

It seems curious to me that I never see a stringy equation for the quantum state of the geometry of the universe. Ben Dundee would you please comment?

 

The best theory of gravity we have working so far is GR and in GR there is an object g which tells the geometry of the whole universe

 

Is there something like that in the string framework? Never seen it.

 

g is the metric like a distance function that tells distances between places or events

 

so in the classical or pre-quantum picture, g is the state of the geometry of the whole universe.

 

and of course g is also the gravitional field, because gravity = geometry, so the state of gravity is the state of geometry.

 

So it's natural to expect that when you go to a QUANTUM model of gravity, a quantum version of Einstein GR in other words, that in place of a classical state of the geometry of the whole universe you would have some object

say g* which is the quantum state of a dynamically evolving geometry.

 

In a sense, a "wave function" over all possible geometries.

 

==================

And this is what all the non-string QGs have. Or almost all (one or two don't have it yet but they are getting there.)

I think it would be a really interesting scientific question, if Ben would comment, why doesn't string have a quantum state of the geometry of all spacetime, or if it does what are some arxiv numbers of papers where one could see such a thing. Thanks.

 

I've highlighted arxiv numbers of papers to help focus on what I'm looking for.

 

Vincent you say:

The object describing spacetime geometry in string theory is the same object that describes spacetime geometry in General Relativity which is the metric.

 

One way to phrase my question would be OK spacetime geometry is described by the metric. Einstein called this the "gravitational field". Does stringy formalism have a quantum state of this or is the metric just a classical metric?

 

I suspect that your post is a way of saying that a quantum state of the gravitational field is not present in stringy formalism, and that the post is interpretive---intended to show this is a good light and suggest that it would actually be a bad thing to have a quantum state of the gravitational field in the theory (because perhaps spacetime geometry is not fundamental and is merely an appearance which emerges from some more fundamental degrees of freedom.) But I actually find your post somewhat hard to interpret. Not sure what you are saying. So maybe you would clarify by a yes or no.

If we can establish, say, that stringy approaches do NOT have a quantum state of the metric then we can move on and discuss whether they should or if that is a good thing--but interpretation seems properly secondary.

[BenTheMan]

Curiously the both predict a fractional spacetime dimension around 2D at planck scale growing contuously up to 4D as you go up in scale.

So you could FALSIFY both Reuter and Ambjorn's if you could show experimentally that the microscopic dimension was not around 2. (Not that this would be a practical test, because the fractal behavior is down at planck scale, but they do constrain and indeed make predictions about dimension).

 

Martin! How odd! When I suggest ten space-time dimensions at the planck scale, you go on long rants about how unphysical this is, because you only SEE four dimensions. Yet, in your response to criticisms about this, you point to research that claims LESS space-time dimesnions at the Planck scale, AND fractional dimensions, no less!

 

Excuse me for thinking you a bit hypocritical in all of this! Aside from this glaringly obvious hypocricy, I will again point you to your own statements, that say that Smolin's aproach is ``on the fringes'', and he doesn't realy work on things that the rest of the community does.

======================

 

So are you suggesting that you view string theory sort as a "framework" somewhere at the same level? Except more specific and better? in the senese that string theory just tells us what class theories we should bother trying?

 

I think that some people have this opinion, yes. Certainly it was hoped that we could find a vacuum selection mechanism, and that the solution would be unique. Right now, however, we can't even find ONE vacuum that works (although we CAN get close).

 

The idea that all things are made up with a vibrating string in a background space is comptletely ad hoc to me.

 

Why? In this sense many things are ``ad hoc''. People try something, and see if it works. This is how all theoretical physics works---space-time is ad hoc, particles are ad hoc, ...

 

IMO a relation should be inferred from the corrections. The deviations should I think induce a prior in the new spaces. If not, this spaces is not needed, as it's not supported by the interactions.

 

My twisted comments originate from my own views of course. Which is no more valid than yours, but the comparation is interesting.

 

There are ALWAYS problems when you try to analyze the UV while sitting in the IR, which is why Martin and I are always arguing The point is, it is easy to integrate a theory DOWN in energy scales, but to go the other way is quite tricky, and, in fact, it is not unique. Proof of this is found in the fact that there are about a dozen ways to make the higgs mechanism work---scalars, technicolor, little higgs, ... And this is only over an energy scale of a few GeV! No imagine the same problem, extrapolated out 17 orders of magnitude! There are so many things about physics in the low energy, and we are trying to do physics at the Planck scale!

 

So MAYBE if you guys can rework the entire stuff to get a more sensible master theory that explains things from more fundamental things, then... "string theory" does have hope even for me... but currently I see nothing in it for me.

 

Some (M)aster Theory, you say?

 

]The really interesting questions are not even asked in the string approach as I can see.

 

I guess it depends on what you consider interesting questions.

 

You start with a boolean observable (two state).

 

But this is just as ``ad hoc'' as assuming a string, with quantized energy

 

I am a bit curious about is exactly what the more fundamental theory (that I guess many string theorists look for) will actually look like, and I don't mean in detail but I mean more in principle. Will it still be a framework? Or will it be a specific theory? or more like a strategy?

 

You're talking about looking at M-Theory, which is what most people believe unites all of the string theories. I can't talk much about this research, unfortunately. I will say that there is still hope for a vacuum selection mechanism, as far as I can tell. The stock answer that you will get is that the problem is very hard, and it needs a lot of smart people working on it.

 

I am curious if you could briefly look into your crystal ball and give you personal view (as a string advocate) of what sort of thing you expect to end up with in the end so to speak? And what kind of answers could possibly remain unanswered still?

 

I'm interested in getting the standard model out of strings, which is, in some sense, like looking the answer up in the back of the book. Once you know which vacuum you're looking for exactly, it should be easier to find out how to get there. I think that should happen in the next ten years or so---someone will find a compactification which gives the standard model. Once this happens, it should be easier to find out how to fit things together.

 

You'll forgive me, of course, for stopping here, as there are others who are more qualified to finish this response than I

[vincent]

Hello again Vincent!

 

Hello again Martin!

 

…as far as I can tell string researchers mean something entirely different from other QG people. They don't seem to be talking about either a General Relativistic quantum physics or a quantization of the gravitational field.

 

If you’re unsure what string people do mean, how can you be sure what they don’t mean?

 

I already answered your questions with clarity and precision. In fact, what I posted was strings 101. I suggest you take a look at any of the by now numerous introductory textbooks on these topics. (Perhaps a look at some of the popular literature might make sense for you. I mean no offense by this). Unless you have any honest questions, I don’t know what else I can say to you.

[Martin]

I don’t know what else I can say to you.

 

Figures.

 

I guess that means the answer to the yes/no question I asked is NO.

 

In all of stringy formalism there is no mathematical object that you can identify as being the quantum state of the metric quantum state of the geometry of spacetime.

 

That seems incredible, after all these years, but it's what your post seems to be telling me, Vincent.

 

From a Quantum Gravity perspective that is a huge gap. I'd suppose people involved would have a strong desire to plaster over it with verbal spin, somehow put a good face on it.

 

Martin! How odd! When I suggest ten space-time dimensions at the planck scale, you go on long rants about how unphysical this is, because you only SEE four dimensions. Yet, in your response to criticisms about this, you point to research that claims LESS space-time dimesnions at the Planck scale, AND fractional dimensions, no less!

 

Excuse me for thinking you a bit hypocritical in all of this! Aside from this glaringly obvious hypocricy, I will again point you to your own statements, that say that Smolin's aproach is ``on the fringes'', and he doesn't realy work on things that the rest of the community does.

 

1. I never went into rants about the fact that 10D is unphysical. I just say it is unphysical. Every physical experiment so far is consistent with 4D and no physical experiment or observation detects 10D. Period (Maybe some will in the future. They're always talking about this )

 

2. My long posts are about the fact that your statements tend to be unreliable. You make flat statements about non-string business which arent true. I have to respond to set record straight.

 

3. Smolin work 2005-present IS a very new approach. Naturally it is not central though it might become so. He is innovative. You made a false statement when you said NO nonstring QG predicts dimension. Because Smolin's approach is an important one that does require spacetime 4D and he has a bunch of people working on it and reporting it at conferences etc.

That is just one illustration that your statement was false and it comes from not knowing very much about the competition. Have to point this out.

 

4. Two other quite different approaches Reuter QEG and Ambjorn CDT ("quantum einstein gravity" "causal dynamical triangulations") both which got a big play at Loops 05, the 2007 School, and Loops 07

DO PREDICT DIMENSION AND ARE COMPLETELY CONSISTENT WITH OBSERVATIONS. So there is nothing unphysical about them. they happen to predict a running of dimension from 4D down to 2D at Planck scale.

So far no experiment has indicated that dimensionality down at Planck scale has to be the same as macroscopic 4D, so that is interesting side aspect. It's not a way that Ambjorn or Reuter have offered for their theories to be tested. It is just a forced outcome.

 

You say I'm hypocritical. Perhaps I am. that is an issue about my moral character which I don't feel any need to discuss.

 

what I have to say is simply that your statements are MISLEADING. you often say things which are simply wrong when you refer to any kind of non-string QG. I don't blame you for this or say you are a bad person. Indeed you seem very nice and forthright on the whole. I have the impression that it is NORMAL for string researchers not to have accurate impressions of nonstring QG approaches. But innocent or not, I have to try to correct at least some of the mistatements.

[BenTheMan]

Martin---

 

It certainly isn't my intent to attack your character, because I don't know who you are. (Conversely, you have quite a bit of information about me.) ``Hypocrite'' is kind of a strong word, I agree---perhaps I should have said that you were very John-Kerry-ish about it

 

Either way, I just wanted to point out that you spent a long time crticizing the fact that string theory predicted ten dimensions (I could cut and paste if you REALLLY want me to), only to say that some quantum gravity approaches predict TWO dimensions, and FRACTIONAL dimensions, no less.

 

Perhaps if we ever meet, we can have coffee and talk about baseball

[fredrik]

Why? In this sense many things are ``ad hoc''. People try something, and see if it works. This is how all theoretical physics works---space-time is ad hoc, particles are ad hoc, ...

 

Yes it apparentl is, and that's what I don't like I'm trying to do something about

 

We can not get rid of all ad hoc, we can not get rid of gambling. But my view of science is that it's supposedly the perfect gambling strategy.

 

There are ALWAYS problems when you try to analyze the UV while sitting in the IR, which is why Martin and I are always arguing The point is, it is easy to integrate a theory DOWN in energy scales, but to go the other way is quite tricky, and, in fact, it is not unique.

 

Yes, not unique. Which is why I think we need a betting strategy? Random betting works, but it is hopelessly inefficient, and apparently not the one advocated by nature.

 

I guess it depends on what you consider interesting questions.

 

That sure is true. Or as I would like to put it, what I consider to be the most "useful" questions in the context of my mission. I define useful to be whatever I "benefit" from.

 

Or in the general case, what a system benefits from in the evolutionary perspective, which I view as a game of self organisation, dissipation vs stability, and so on.

 

The complication that there seems to be no clear objective reference here, is really part and key of howto generate dynamics and complexity from almost nothing.

 

You start with a boolean observable (two state).

But this is just as ``ad hoc'' as assuming a string' date=' with quantized energy

[/quote']

 

I think not

 

You certainly have a point but I've given that some thought in the past and had some headache over it.

 

My argumentation why my starting point is less ad hoc than your is roughly as follows:

 

I was looking for the "least speculative" starting point in terms of making assumptions over missing information. What is relative to any observer or system, the "simplest possible change", simple as in requiring the least amount of information to encode.

 

To even do logic, or a comparasion, it seems you need to at minimum be able to distinguish(*) one state from another. Either you can distinguish "impulse" or you can't. We can call this whatever we want. True or false, 0 or 1, A or (not A), Exist or not exist.

 

So the notion of "change", defines the minimal starting point for me. Either the observer detects a change or it doesn't. For example a two state observer simply have no means to relate to superpositions, because the information capacity is constraining it.

 

So the amount of missing information and thus speculation to specify a string is massive as compared to a boolean state, which is why I think my starting point is far less ad hoc.

 

In my thinking the information capacity is pretty much to be associated with mass or energy. This way the concept of intertia is obvious. The intertia of the prior distribution is it's information capacity relative to the new input working to revise it. I claim thta concepts like attractions and also radiation can be explained in this way in the dynamic view. The structure would radiate off excess information unless there is supporting incoming pressure to keep it.

 

Also out of the relational changes, time can be defined. But the confidence level in the detection of the arrow of time is too low to be seen at microscopic level since the arrows fluctuations are so large.

 

But if you have a better starting point, I am open for suggestions, because it bothers me at times still. It's just thar it's the best I see so far. Occams razor can basically be given a probabilistic formulation, rather than just and old saying.

 

My ideas is composed of an evolutionary equation (which I needless to say haven't finished yet which describes prior dynamics as well as the space dynamics. So both the space and the distributions are dynamical variable at the same level, the difference is only in complexity and "information mass".

 

The complex part is that the environment as well as the observer itself are descrived by similar dynamics. Probably making it nasty to solve even onec found.

 

/Fredrik

[Martin]

But they all have their problems. For example, string theory is the only way to quantize gravity that constrains the number of dimensions. In other QG approaches, this number is put in by hand...

 

This is a misstatement. String theorizing is not the only approach that constrains the number of dimensions. I gave you 3 nonstring examples. One requires pure 4D to work, just as some string seems to require 10D. Two others happen to predict dimensionality varying with scale so that there is a kind of fractal-like spacetime foam at very small scale. Just a byproduct of otherwise rather minimalist approaches. Fractals often have some low fractional dimension like 1.9 or 2.1. I think that is interesting but I wouldn't say it was typical of nonstring QG, simply that there are various approaches which constrain dimensionality in various ways. Some have a foam structure at Planck scale, others don't.

 

The point is your statement is wrong. Instead of retracting it you partially retract calling me a hypocrite, but I did not object to the attack on my character. You are welcome to call me any names you can think of

 

"Hypocrite'' is kind of a strong word, I agree---perhaps I should have said that you were very John-Kerry-ish about it

 

Either way, I just wanted to point out that you spent a long time crticizing the fact that string theory predicted ten dimensions (I could cut and paste if you REALLLY want me to), only to say that some quantum gravity approaches predict TWO dimensions, and FRACTIONAL dimensions, no less.

or sneer at John Kerry if that is what you wish to do. What concerns me is not the insults but the content of your statements.

 

We are in a serious discussion. You have made more false statements about non-string QG than I can keep track of. I will do my best to assemble and correct them.

 

You have suggested that string is the only approach that attempts to reproduce the results of the Standard Model. You havent finished doing that, you say, but when you have done that you will proceed to make NEW predictions.

 

Your statement is false because Alain Connes and John Barrett did that in 2006 with NCG, not only reproducing the Standard Model which stringfolk are still trying laboriously to do but actually going ahead with NEW predictions so that there work can be tested by future experiment. Further, this version of NCG is being put together with LQG by Grimstrup et al. That will mean that Grimstrup's extended-LQG will give particle physics.

 

Also Smolin's new research since 2005 is about getting the standard model in a spin-network QG context. That by itself should be enough of an example that your statement was wrong.

 

Anyone who wants can get the papers on arxiv easily since the names Connes, Barrett, Grimstrup, Smolin are distinctive. There aren't a lot of Grimstrups on arxiv.

 

One solution might be for you to stop talking as if you knew anything about rival approaches. Just talk about string without making groundless claims like string is "the only approach to do this or that" or "has no competition as an approach to quantum gravity".

 

Another possibility would be to learn something about the leading nonstring approaches. I suggested Reuter to you several weeks back and I'd be more than happy to help you get a quick and dirty introduction to Quantum Einstein Gravity (Reuter QEG).

[BenTheMan]

Your statement is false because Alain Connes and John Barrett did that in 2006 with NCG, not only reproducing the Standard Model which stringfolk are still trying laboriously to do but actually going ahead with NEW predictions so that there work can be tested by future experiment. Further, this version of NCG is being put together with LQG by Grimstrup et al. That will mean that Grimstrup's extended-LQG will give particle physics.

 

Will give? Before you told me that these people already HAD gotten the SM out of quantum gravity?

 

Now, I haven't been able to think about why someone would claim that the top quark and the tau neutrino Yukawa couplings should be the same.

 

Secondly, what of generations? They seem to be put into Connes' model by hand (I missed this before). In strings they come from topology. Finally, in another paper (http://arxiv.org/PS_cache/hep-th/pdf/0608/0608226v2.pdf), he seems to get a top quark mass of somewhere around 200 GeV (=173 x 1.102 GeV), which is wrong. (See equation 39.)

 

He also predicts a higgs mass of 170 GeV, which is pretty far out of line with what all of the electroweak data are telling us, which point to a fit of somewhere less than 150 GeV.

 

And lastly, this scentence, in the conclusion:

 

It is not clear what the physics meaning is since unlike in grand unified theories one is still lacking a renormalizable theory that would take over above the unification energy.

 

This seems to mean that he's working independant of any quantum gravity approach? I don't know. This is, of course, the caveat that you forgot to mention

 

Oh, and if you don't believe me about the top mass, I could ask some OSU undergrads...

[fredrik]

My ideas is composed of an evolutionary equation (which I needless to say haven't finished yet which describes prior dynamics as well as the space dynamics. So both the space and the distributions are dynamical variable at the same level, the difference is only in complexity and "information mass".

 

In this sense I believe in that structures (strings included IF they are needed in the first place) are what many call emergenet properties. I do not consider space to be truly fundamental, I think it's a dynamical thing that is emergent from stabilised relations, which in principle applies also to the dimensionality.

 

/Fredrik

[Martin]

Ben, you seem to be picking up information fast about Alain Connes work. I have a FOUR PAGE more recent paper for you!

Easy to glance over and also the most recent available.

http://arxiv.org/abs/0706.3690

A Dress for SM the Beggar

Ali H. Chamseddine, Alain Connes

4 pages

Submitted on 25 Jun 2007

 

"The purpose of this letter is to remove the arbitrariness of the ad hoc choice of the algebra and its representation in the noncommutative approach to the Standard Model, which was begging for a conceptual explanation. We assume as before that space-time is the product of a four-dimensional manifold by a finite noncommmutative space F. The spectral action is the pure gravitational action for the product space. To remove the above arbitrariness, we classify the irreducibe geometries F consistent with imposing reality and chiral conditions on spinors, to avoid the fermion doubling problem, which amounts to have total dimension 10 (in the K-theoretic sense). It gives, almost uniquely, the Standard Model with all its details, predicting the number of fermions per generation to be 16, their representations and the Higgs breaking mechanism, with very little input. The geometrical model is valid at the unification scale, and has relations connecting the gauge couplings to each other and to the Higgs coupling. This gives a prediction of the Higgs mass of around 170 GeV and a mass relation connecting the sum of the square of the masses of the fermions to the W mass square, which enables us to predict the top quark mass compatible with the measured experimental value. We thus manage to have the advantages of both SO(10) and Kaluza-Klein unification, without paying the price of plethora of Higgs fields or the infinite tower of states."

 

In the main body of the paper he says 170 +/- 10 GeV. You say that UNDER 150 GeV would be more reasonable to expect based on some data. I am sure he knows the same data. So he is taking a risk isn't he? He has had 8 months to change his prediction and he still holds to the 170. Well we will see who is right.

 

I should emphasize and correct any mistaken impression I've given. None of these derivations of the SM are COMPLETE.

As you have indicated, stringfolks are not completely finished deriving MSSM from string framework.

THESE PEOPLE ARE NOT COMPLETELY FINISHED EITHER

My hunch is that they have a decent shot at beating you to the finish line, however the finish line is ultimately defined.

 

what I see is a prediction of Higgs 170 GeV and a POST-DICTION of top quark mass. That is, they derived a prediction for top quark which turned out to compatible with experimental measurment. They say.

==============

Anyway that's a side issue. I think what is obvious is that there are several parties out there on the road going for a derivation of the Standard Model. Nobody is at the finishline. And String is not the only car on the road. If this is acknowledged, I'm happy.

 

Glad to see you taking a look at these papers! I got the impression that you were unaware of this work earlier. I know of 2007 Grimstrup papers in the works but I'd prefer to just talk on the basis of what is available on arxiv, which is 2006.

 

This Grimstrup paper sums up the situation pretty well as of January 2006, you might like to glance at it.

 

http://arxiv.org/abs/hep-th/0601127

Intersecting Connes Noncommutative Geometry with Quantum Gravity

Johannes Aastrup, Jesper M. Grimstrup

19 pages, 4 figures

(Submitted on 18 Jan 2006)

 

"An intersection of Noncommutative Geometry and Loop Quantum Gravity is proposed. Alain Connes' Noncommutative Geometry provides a framework in which the Standard Model of particle physics coupled to general relativity is formulated as a unified, gravitational theory. However, to this day no quantization procedure compatible with this framework is known. In this paper we consider the noncommutative algebra of holonomy loops on a functional space of certain spin-connections. The construction of a spectral triple is outlined and ideas on interpretation and classical limit are presented.

 

Now it is a over a year and a half later. I believe their program has succeeded. This is the paper we have to go on. If you take a look you will see what their program is.

=====================

[BenTheMan]

Anyway that's a side issue. I think what is obvious is that there are several parties out there on the road going for a derivation of the Standard Model. Nobody is at the finishline. And String is not the only car on the road. If this is acknowledged, I'm happy.

 

I won't acknowledge anything until you or someone explains to me how in the hell a top quark and a tau neutrino can have the same Yukawa coupling This is pretty instrumental in their top quark mass prediction (or post-diction), because if the tau neutrino coupling is small (as it SHOULD be), then the top quark mass in the model is 198 GeV, which is clearly wrong.

 

This is coupled with the fact that all of the precision electroweak data say that the higgs mass has to be less than 150 GeV, with a preferred value of somewhere around 120 GeV. Otherwise there are tremendous fine tuning issues.

 

All of this aside, there is still no UV completion of the Connes model---only your hand waving that this is ``probably been done''.

[Martin]

 

...I think what is obvious is that there are several parties out there on the road going for a derivation of the Standard Model. Nobody is at the finishline. And String is not the only car on the road. If this is acknowledged, I'm happy.

 

I won't acknowledge anything until...

 

... there is still no UV completion of the Connes model---only your hand waving that this is ``probably been done''.

 

Ben, it's certainly fine with me if you want to keep to the position that String is the only car on the road and not acknowledge the existence of others! The attitude is a familiar one and in a sense normal to your community, in my experience. What needs to be addressed is when you make flatly inaccurate statements to support your denial of other cars. If you simply deny that other cars on the road exist, without giving faulty reasons, that seems quite fine. So please continue.

 

BTW I was puzzled by what you said about UV completion and your apparent quoting me as saying "probably been done". I don't remember saying "probably been done" re Connes, or ever talking about a UV completion of Connes model. Maybe you can remind me, or get the quote of what I actually did say.

 

If you meant Grimstrup's work, it's not what I think of as a UV completion and in that case I KNOW of papers not yet posted publically, since I correspond, and I did not say "probably" in that connection. I definitely believe his program has succeeded. But perhaps you were not talking about that work. You can see what Grimstrup's program is by glancing at the paper I just gave a link to. It is presented not as a "UV completion", but as PUTTING CONNES STANDARD MODEL INTO THE LOOP GRAVITY FRAMEWORK. Mathematically grafting one kind of model to another. I only mention Grimstrup's work to illustrate the "not the only car on the road" point.

[iNow]

I must say, at this point in the thread, I am no longer learning ABOUT string theory... just why it's not perfect. That kinda saddens me. I knew it wasn't perfect coming into this, but was excited to learn more anyway.

[Martin]

I must say, at this point in the thread, I am no longer learning ABOUT string theory... just why it's not perfect. That kinda saddens me. I knew it wasn't perfect coming into this, but was excited to learn more anyway.

 

I'm kind of interested to hear more just about string theory myself and I would like this thread to move in that direction!

What I have to respond to is where Ben mentions me by name or implies something I've said in some other thread is wrong, so that I am forced to reply, or when he brings up OTHER APPROACHES---rivals to string.

If he makes statements to the effect that

string is the only approach that requires a certain spacetime dimension or predicts what the dimension has to be

then I have to try to correct that, because it is NOT the only such.

 

Or to the effect that string is the ONLY approach that tries to reproduce the standard model---that is just wrong! Lee Smolin has been working on an interesting new way to do that since 2005. The correct statement would be that string is AN approach which tries to reproduce the standard model. This may seem trivial to you, iNow, but it is a serious issue----basically the issue that Smolin took the time and trouble to write his latest book about.

 

What I am hoping is that Ben, who knows a lot about string and not so much about the other approaches going, will FOCUS on string and not make adverse comparisons with stuff he doesnt know as much about.

 

So iNow, what i would urge you to do is get busy and ASK LOTS OF QUESTIONS of Ben which just have to do with string----and not with unification and quantum gravity in general. that will give him a chance to talk constructively about what he knows.

 

thanks for the comment.

[BenTheMan]

This is what you said:

 

Now it is a over a year and a half later. I believe their program has succeeded. This is the paper we have to go on. If you take a look you will see what their program is.

 

And this:

 

You can see what Grimstrup's program is by glancing at the paper I just gave a link to. It is presented not as a "UV completion", but as PUTTING CONNES STANDARD MODEL INTO THE LOOP GRAVITY FRAMEWORK.

 

If your position is that LQG is NOT a UV completion to the standard model, then I must say---string theory IS. Then we are talking about two different things, and we can safely end this conversation, per iNow's request:

 

I must say, at this point in the thread, I am no longer learning ABOUT string theory... just why it's not perfect. That kinda saddens me. I knew it wasn't perfect coming into this, but was excited to learn more anyway.

 

I was working under the assumption that moderators wouldn't flame the thread, but...

[Martin]

 

 

 

 

 

 

If your position is that LQG is NOT a UV completion to the standard model,

 

 

I was working under the assumption that moderators wouldn't flame the thread, but...

 

Ben please don't shift the topic around so much. What you said was

*... there is still no UV completion of the Connes model---only your hand waving that this is ``probably been done''.*

 

I don't see Grimstrup's work as a UV completion of the Connes model. That is not how he presents it. So I responded. the result may turn out to be a UV completion of something else, but that is not the topic I don't take the position that it isnt. And I wasnt just handwaving and saying "probably". So I had to reply.

 

I don't particularly like to have to reply to misstatements about nonstring QG and rival unification efforts. Or to attacks on me and misrepresentations of what I've said. I'd rather you would just keep your discussion to STRING and not make adverse comparisons like *string is the only approach that does X or Y*

 

It would be great not to have to get in and make corrections.

 

About "flaming the thread". That is really an unfair insult. I'm pleased and appreciative when you stick to STRING, avoiding mistaken claims about string relative to other research.

Indeed I have and will compliment you on a job well done, if it is focused like that!

[BenTheMan]

Whatever.

 

Back to strings.

[Martin]

Back to strings.

 

Excellent!

[Reaper]

Whatever.

 

Back to strings.

 

 

May have already been mentioned in this thread, too lazy to look through it now...

 

But anyways, in most string theory literature that I've read, it is predicted that it will take a stupendous amount of energy to actually observe a string directly, or indirectly (something like on the order of 1x10^32 J ?). How did string theorists come to predict such a large amount of energy like that, and why?

 

Another thing that I've been wondering is, is there any relationship whatsoever with cosmic strings (or can they even be applied to cosmic strings)?