String Theory creating a vacuum

[J.C.MacSwell]

If String Theory sucks does this increase interest in other kaluza-klein theories or put a damper on the whole thing?

[Johnny5]

JC what exactly is string theory?

[J.C.MacSwell]

JC what exactly[/b'] is string theory?

 

 

I don't know exactly but it's a multi-dimensional (10, 11 or 26?) theory based on 1 dimensional strings many times smaller than the particles we know/don't know so well. Hoped to explain all the known forces.

[Johnny5]

I read about Kaluza-Klein string theory years and years ago, I was just a boy. So far as I am aware, space is three dimensional. That pretty much puts a damper on that.

[Martin]

If String Theory sucks does this increase interest in other kaluza-klein theories or put a damper on the whole thing?

 

JC what exactly is string theory?

 

strictly speaking it is not a theory

but possibly a theory-under-construction

traditionally a scientific theory must make predictions about the outcome of future experiments that could falsify or refute the theory.

 

for instance Gen Rel was published in 1915 and had a make or break test in 1919, it predicted a certain bending of light passing the sun and there was an eclipse and Eddington observed the light and Gen Rel passed the test.

 

As science has traditionally been practiced, a theory must bet its life on the outcome of some future measurement, otherwise it is meaningless

 

a bunch of words and math symbols that can happily accommodate any future outcome of any new experiment is not predicting anything, it can adapt to whatever, so it is mush. It is not a theory.

 

at present string theorists are sadly unable to predict the outcome of any future experiment.

it was hoped that they would predict something about supersymmetry or about electroweak symmetry-breaking to be observed at the LHC when it starts up in 2007 or 2008 but recent papers by Mike Douglas and Michael Dine have disappointed this hope.

 

Feynmann (who didnt like what string theorists were doing) once said "String theorists dont make predictions, they make excuses."

this seems increasingly now to be a fair objection.

 

So how to answer Johnny5's question? String theory is strictly speaking not a scientific theory but let's just say it is what the people called string theorists do, and what can be read in books called string theory textbooks It has been worked on for over 25 years. It still has not been brought to the point of making predictions. so it is in a kind of extended adolescence and not a grownup theory.

 

It is possible to say what string theory has been about in the past, but it is not possible to specify what it will be about in the future. It used to be about the surfaces swept out by of one-dimensional things called strings (imagined as vibrating in lots of different ways corresponding to the different particles of matter) but now it appears to be less about that and more about stuff called membranes and conformal field theory and twistors. What it comprises is rather mushy and string theorists say jokingly that whatever theory eventually proves successful they will call it string theory (it is amorphous enough to engulf other kinds of mathematics like a giant mathematical amoeba). They say this as a joke but it has a real element of truth.

[Martin]

If String Theory sucks does this increase interest in ...

 

JC the way you put the question earlier, before editing, was broader IIRC.

 

It got me thinking. what areas of research are likely to get new energy as people get out of string theorizing?

 

Posting of new stringy research has been declining. It is down some 10 or 20 percent from a couple of years ago, to the best of my knowledge. Hard to get reliable figures.

 

I see individual cases of people who used to do stringy research who are now doing some other kind. that is just annecdotal evidence though.

 

The two growing areas they could be going into are Astrophysics/Cosmology on the one hand and Condensed Matter physics on the other.

 

there is a general decline in particle physics these days and the fastest growing neighbor area is condensed matter. But astrophysics is highly visible too and closely akin to particle physics. there is a crossover field called "astroparticle physics"

the thing is the new orbiting instruments are doing astronomy with Xrays and Gammarays there is groundbased Neutrino astronomy and detection of UHECR (ultrahighenergycosmicray) air showers, so it is like

the universe is providing us with a giant "accelerator" that is almost better than the LHC they are building at Cern.

So Astrophysics/Cosmology is probably absorbing a fair number of those who are getting out of string.

And probably some just go over into finance, get a good job outside physics.

[fuhrerkeebs]

I read about Kaluza-Klein string theory years and years ago, I was just a boy. So far as I am aware, space is three dimensional. That pretty much puts a damper on that.

 

The Kaluza-Klein unification attempt was neither a string theory nor was it in 3 dimensional space. It extended the metric tensor to a (4+1) dimensional spacetime and used the extra spatial coordinates for the electromagnetic components.

[Guest Rounder]

This question was posed yesterday on the ilovephilosophy boards that I am a member of, since I don't wish to write the whole thing over again I'll just copy and paste it here.

theres not much to it. the main difference between classical quantum mechanics and string theory is that in classical' date=' the fundamental particles, protons, electrons, they are tiny points with no visible characteristics other than their influence on other particles.

 

string theory is an attempt to decribe what they look like. imagine you have a string in the formation of a wave, wrapped in a loop. when the crest of the wave is one inch away from the trough, thats a proton. when that amplitude is half an inch, thats an electron. [/quote']

 

The problem with quantum mechanics is that it cannot incorporate gravity, the difference is that string theory can. When we try to put Einstiens equations into quantum mechanics we get non-sensicle answers, we get infinity's. Quantum mechanics can only incorporate 3 of the four forces, Strong and weak nuclear force, and electro magnetism. What string theory does is unify all of the four forces, in a simplistic, and elegant manner. String theory seems to automatically incorporate all of the other theory's . String theory doesn't change quantum mehcanics, it incorporates it with Relativity.

 

What I mean by automatically, is that when doing equations in string theory, and not previously assuming the other theory's, the other theorys automatically pop up. This is the strongest attraction to string theory, is that they found when they extended the original Kaluza-Klein model to (N) dimensions that the Yang Mills Feild theory(the key to the standard model, which explains how sub atomic particles interact) automatically popped out!!! as if by magic. The yang mills feild was found virtually by trail and error for over 80 years!!! And it just automatically pops up in string theory. Also by doing calulations using only the self consistancy constraints alone it pops out precisley Einstiens theory of Gravity. So basically without previously assuming the equations, The field theory's that compose the entire scientific ascent of man within the past two millenia, automatically pop up in string theory!! String theory wasn't tailor made to fit the theory's, the theorys are automatically included!!

 

Why is it strings? String theory is not some farfetched idea, where someone thought that the world could be described as strings of energy. The origin of string theory really dates back to Reimann back around 1860. Reimann was Gauss's protege, and gauss had him do a paper on Eucilid geometry. At the time both Reimann, and Guass had stong reservations about our world only being 3 dimensional, but to think of other dimensions was unheard of. Reimann held a public address, where he basically showed how mathematics became simplified when expressed in higher dimensions. Yet the public view at that time utimately made theory's which incorporated extra dimensions die off for many years. It popped its head here and there only to die off again and again, that is until Einstien.

 

Einstien knew the physical properties of Gravity, what he lacked was a mathematical expression. He tried for some time to write the equation yet it was beyond him. Until a friend trying to help him out stumbled upon Reimanns work of some 60 years prior. Einstien found that it was an exact fit. He didn't have to tinker with the mathematics at all, Riemanns metric tensor just ate it up!! Giving Einstien his equation, and his place in history, and introducing another dimension, space-time.

 

Future man used an example of the worm, heres another example that I think would be easier to picture. You have a piece of paper which is actually a universe in itself. This universe is called "flatland", and all of flatlands inhabitants are two dimensional beings. To these two dimensional beings any talk of higher dimensions is strickly frowned upon, its insane!!.

What Reimann did was crumple the paper up, and asked the question what would these two dimensional beings think? His answer was that they would still only believe in two dimensions, yet if they were to try and walk straight across the paper they would be pushed by some unseen force left, right, forwards, or backwards. How would these two dimensional beings go about describing this force? They would use they're two dimensional mathematics, and find it very difficult.

 

This is basically what we have done over the past two millenia, is found the properties of the forces, yet we can't explain them. Why does light travel unempeded through a vacuum? Current physics can't explain this. In string theory it is because of a vibrating fifth dimension.

 

Strings were not just arbatrarily picked, its just that the mathematics of higher dimensions gave us the properties of strings. The strings vibrate like any string you've seen in day to day life. Like a voilin string, differnent

vibrations create different resonances. In string theory all point particles, are just resonances of a vibrating string.

 

one of the weird things about string theory is that its not a one dimensional string on a 3d surface like the strings we are familiar with' date=' but there are supposedly strings of varying dimensions, a 1d line, a 2d membrane, etc. and they wave around in more than 3 dimensions, i think 6 or 7.

 

these extra dimensions supposedly exist all around us. imagine a worm who lives in a tube. the tube is as big as he is, and in order for him to see, he shoots out a ball that is also the width of tube, and it bounces off of the object in front of him and comes back. he can 'see' the universe by counting how long it takes for the ball to come back. his entire world consists of one constantly changing number, the distance between him and his closest neighbor.[/quote']

 

In the current heretic string theory model, strings rotate clockwise in 10 dimensional space, and counterclockwise in 26 dimensional space. String theory only works when dealing with 10 and 26 dimensions.

 

according to crazy math and nothing more' date=' thats the world we live in. with 6 or 7 more dimensions "curled up" so that anything smaller than the plank length (the size of a tree on earth if an atom is the universe. something like that) can move about in 6 or 7 dimensions we cant comprehend.

 

 

the main reason why string theory was invented is because when a black hole is created, or when the big bang happened, science doesnt have any way of thinking about that stuff. there are two main theories that describe the universe, einsteins relativity explains large scale gravity, and quantum mechanics explains small scale other three forces. when you have lots of gravity in small places, it doesnt compute. black holes and big bangs have infinite gravity according to non-string theories and so dont make sense.

[/quote']

 

Obviously its not crazy math. Critics of string theory do not site the math as the problem at all, they point to the fact that currently it cannot be tested. Its the math of higher dimensions that gave us Einstiens theory of relativity. Without the math we would not have seen one of the greatest breakthroughs of the 20th century.

 

The reason it can't be tested is as Futureman said that we do not have machines capable of of testing it. String theory's home lies at the Planck energy, this energy was only released at the instant of creation itself. So string theory is basically a theory of creation, and therefore cannot be tested directly. We would need a machine capable of producing energies trillions of times larger then what we can now create in our atom smashers. In string theory, at the beggining of time our universe was a perfect 10 dimensions, but this 10 dimensional universe was unstable, and so the big bang happened literally creating a tear in space time, four of our dimensions expanded rapidly, while the other six curled up.

 

And there really is no reason why string theory was invented, string theory more or less was fell into ass backwards. The reason we have string theory today is largely Due to Riemann, a letter sent to Einstien by Kaluza which Incorporated his equations along with Maxwells in a fifth dimensional model using Riemanns metric tensor, and the fact that the mathematics become simple, and elegant when expressed in higher dimensions. The reason we have string theory today, is that we have as yet failed to create a unified theory, and string theory does this automatically with grace, and ease. The problem is that we can't test it.

 

im not sure exactly what conclusions can be drawn from a string theory big bang or black hole that cant be drawn from a normal one. maybe someone else knows.

 

in the elegant universe by michael greene' date=' string theory also seems to explain time dilation as a result of high speed. something about the string entering the world-perception-time-cone of the observer at an angle. or something. if someone could please explain.[/quote']

 

I just recently bought the elegant universe by micheal green, but have not read it yet. I'm going to read it next week, so when I come to the explanation of time dilation I'll come back and post what Greene had to say if someone else has not already posted it.

 

Anyways the basic attraction to string theory is that, as Reimann showed back in 1860, mathematics becomes simpler, and "elegant" when calculated in higher dimensions. String theory just seems to eat up all the other theory's, they are automatically included.

 

hyperspace is pure fantasy. there is no reason to think that the curvature of space allows for one section to curl up into another. it is nothing except wishful thinking.

 

however' date=' some crazy scientisists have predicted, probably wrongly, that a black hole can spin so fast that instead of collapsing into a tiny dot, it collapses into a donut shape.

 

if you go into a donut, and its big enough or your lucky or something, you can go through the middle of it and the forces will cancel out. when your in the middle of a donut, infinite gravity wont hurt because it pulls on all sides.

 

then, if we contact some 4d aliens, we can move "flooob" and "dooob" (as opposed to 'up and down), and connect to another point of the universe somewhere. or maybe, the donut blackholes will randomly connect somewhere on their own.

 

nobody knows the slightest tiniest detail about hyperspace.[/quote']

 

Hyperspace is just a result of string theory. Hyperspace is basically defining that we live in a world of higher dimensions. If string theory is right, then in fact we do know a great deal about how hyperspace universe would function. Our minds can't visualize higher dimensions, yet the mathematics of it our relativly simple.

 

One last note about string theory, is that there is some hope in testing the theory indirectly. So it is not a lost cause in this respect at all. Think of the mathematicians, and scientists in the 19th century who thought that a 4 dimensional world was complete nonsense. Then Einstien came along!!

 

The reason why Green's book is entitled the elegant universe, is simply because the mathematics of string theory are just that elegant. We have various complex models, such as quantum theory, that are very ugly. Quantum theory really doesn't incorporate the other theory's very well. The three theorys that are incorporated in quantum theory alone all have they're own inherent symmetry. What Quantum theory does is splice these three symmetrys together to make one theory. Its like a jiggsaw puzzle, if you couldn't figure out the currect configuration you could always use tape!! This is what quantum theory does, and the mathematics are hence very ugly. When we add extra dimensions, the mathematics easily incorporates all of the theorys, and creates a supersymmetry!! Thus supersrting theory.

 

Peter Freund, a leading physicist in string theory gave this analagy.

 

"Think of a cheetah that has been captured and thrown into a miserable cage in a zoo. It has lost its original grace and beauty, and is put on display for our amusement. We see only the broken spirit of the cheetah in the cage,not its original power, and elegance. The cheetah can be compared to the laws of physics, which are beautiful in their natural setting. The natural habitat of the laws of physics is higher-dimensional space-time. However, we can only measure the laws of physics when they have been broken, and placed on display in a cage, which is our three dimensional laboratory. We only see the cheetah when its grace and beauty have been stripped away"

[Martin]

If String Theory sucks does this increase interest in other kaluza-klein theories or put a damper on the whole thing?

 

Indeed there is a growing sense in the physics community that the string enterprise has failed, with increasing numbers of physicists willing to speak out on this.

 

the popular media is just beginning to pick up on this: however here is an article in the San Francisco Chronicle

http://sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2005/03/14/MNGRMBOURE1.DTL

 

Here are some comments on the article at the blog of a Columbia University mathematician where a lot of physicists post and arguments about string theorizing go on

http://www.math.columbia.edu/~woit/blog/archives/000168.html

 

the stink about string's fiasco has been building since January 2003 when a paper by some string theorists Kachru et al come out, and another string theorist Leonard Susskind started pushing the Landscape idea in what was probably a misguided attempt to save string theory (which is partly Susskind's baby). there is a lot of aspects to the controversy. departments are split around the country.

 

basically the problem is string theorists have entrenched power and can maintain their control of funding and tenured positions in the major institutions, but they have not produced a theory which can predict anything definite and so there is nothing to test experimentally.

 

there is a growing sense that it would be appropriate for researchers to be trying some other approaches to a quantum theory of spacetime.

Stringy approaches have not actually succeeded in getting a quantum version of General Relativity (the prevailing theory of gravity) and spreading the effort in other directions is looking more appropriate (of course not completely giving up on string either!).

 

So I think MacSwell question that started this thread is a very smart one.

Indeed it appears that String Sucks. So what other approaches are going to get explored? the search for a quantum theory of gravity is going to branch out. In terms of numbers of papers written per year it IS ALREADY branching out, and people are leaving string.

 

What are the other approaches to watch?

 

A close reading of a recent paper by 4 prominent string theorists can give some clues.

these are very eminent guys

Robbert Dijkgraaf (Amsterdam), Sergei Guckov, Andrew Neitzke and Cumrun Vafa(Harvard). This is the DGNV paper online at hep-th/0411073.

They dont in the least "give up" on string, in their article, but whether intentionally or not they give some clues as to where things are likely to go. One of the references in their paper was to Lee Smolin's "Invitation to Loop Quantum Gravity" http://arxiv.org/hep-th/0408048.

The DGNV paper suggests to me that as the String Titanic sinks LQG might be a lifeboat.

Lee Smolin responded to DGNV with a paper that came out this week

http://arxiv.org/hep-th/0503140 "A Quantization of Topological M-theory".

 

this paper of Smolin is probably the richest source of clues as to what lines of research will take over from string. If you check it out, notice the pointer to work in Causal Dynamical Triangulations (some work going on in Utrecht and Copenhagen with computer simulations of the quantum geometry of the universe) and the paper "Emergence of a 4D World from Causal Quantum Gravity". http://arxiv.org/hep-th/0404156

 

When DGNV talk about "topological M-theory" they are basically taking a hopeful look at FORM THEORIES OF GRAVITY of which leading examples are over in LQG territory (especially recent work of Freidel, Starodubstev, Livine). And looking to unify with 4D theories----DGNV is an important paper among other reasons because it mitigates the usual string insistance on extra dimensions. Some people will find this incredible, but look for yourself. Here is the DGNV link

http://arxiv.org/hep-th/0411073

[Johnny5]

Some people will find this incredible' date=' but look for yourself. Here is the DGNV link

http://arxiv.org/hep-th/0411073[/quote']

 

Martin, do you know anything about this Chern-Simons three dimensional theory of Gravity, referred to in that paper?

 

I see the authors talking about a simple theory of Gravity, which could be slightly modified later, to give more accurate results. I like simple, as I am just a simple man.

[Martin]

Martin' date=' do you know anything about this Chern-Simons three dimensional theory of Gravity, referred to in that paper?

 

I see the authors talking about a simple theory of Gravity, which could be slightly modified later, to give more accurate results. I like simple, as I am just a simple man.[/quote']

 

yeah I like simple too.

 

Lee Smolin has been writing about Chern-Simon theory in connection with Loop Quantum Gravity since about 1995

and he even suggested that there was a small positive cosmological constant because that would make something work out nicely

 

and then in 1998 they actually found supernova evidence that there WAS a small lambda or cosmological constant, and all the "dark energy" talk began.

 

so I have on my list of things to do to go back to some earlier Smolin papers and try to understand better.

 

I will get you the names of some articles and some links. but I cant elucidate any of it for you.

 

going backwards in time here is a 2002 paper, I will look in it and see if there are references to earlier stuff:

http://arxiv.org/abs/hep-th/0209079

Quantum gravity with a positive cosmological constant

Abstract:

"A quantum theory of gravity is described in the case of a positive cosmological constant in 3+1 dimensions. Both old and new results are described, which support the case that loop quantum gravity provides a satisfactory quantum theory of gravity. These include the existence of a ground state, discoverd by Kodama, which both is an exact solution to the constraints of quantum gravity and has a semiclassical limit which is deSitter spacetime. The long wavelength excitations of this state are studied and are shown to reproduce both gravitons and, when matter is included, quantum field theory on deSitter spacetime. Furthermore, one may derive directly from the Wheeler-deWitt equation, Planck scale, computable corrections to the energy-momentum relations for matter fields. This may lead in the next few years to experimental tests of the theory.

To study the excitations of the Kodama state exactly requires the use of the spin network representation, which is quantum deformed due to the cosmological constant. The theory may be developed within a single horizon, and the boundary states described exactly in terms of a boundary Chern-Simons theory. The Bekenstein bound is recovered and the N bound of Banks is given a background independent explanation.

The paper is written as an introduction to loop quantum gravity, requiring no prior knowledge of the subject. The deep relationship between quantum gravity and topological field theory is stressed throughout."

 

BTW. WARNING. just because the authors say "simple" does not mean it really is simple. I find Chern-Simon NOT simple. Also it is connected with the "holographic universe" idea which excites some people but I do not find at all simple. I only have it on my list to learn something about C-S because it keeps coming up

 

Here is a 1995 Smolin paper

http://arxiv.org/abs/gr-qc/9505028

 

And a 1998 paper

http://arxiv.org/abs/hep-th/9808191

[Johnny5]

I will get you the names of some articles and some links. but I cant elucidate any of it for you.

 

Thank you kindly.

[Martin]

Thank you kindly.

 

you are welcome. I guess the tactful thing for me would be to stop now. but I have gotten interested. so even though it may not be responsive to you i will put down a little more and try to discern a pattern to satisfy my own curiosity

 

Linking Topological Quantum Field Theory and Nonperturbative Quantum Gravity

Lee Smolin

59 pages

J.Math.Phys. 36 (1995) 6417-6455

 

from the abstract

"Quantum gravity is studied nonperturbatively in the case in which space has a boundary with finite area. A natural set of boundary conditions is studied in the Euclidean signature theory, in which the pullback of the curvature to the boundary is self-dual (with a cosmological constant). A Hilbert space which describes all the information accessible by measuring the metric and connection induced in the boundary is constructed and is found to be the direct sum of the state spaces of all SU(2) Chern-Simon theories...

 

...The integer level k of Chern-Simons theory is found to be given by k= 6pi /G^2 Lambda ...

 

...,the construction of the state space for quantum gravity in a region from that of all Chern-Simon theories defined on its boundary..."

 

Sorry about all the gibberish, but one thing I can see is that to do C-S you need a finite-area surface that bounds some region of space. There is going to be some reduction of information about what is inside the region to information written on the boundary surface.

 

Now that was a 1995 smolin paper, lets take a peek at a 1998 one:

http://arxiv.org/abs/hep-th/9808191

A holographic formulation of quantum general relativity

Phys.Rev. D61 (2000) 084007

 

from the abstract

"We show that there is a sector of quantum general relativity which may be expressed in a completely holographic formulation in terms of states and operators defined on a finite boundary. ..."

 

from page 3

"...Another property of this formulation is that the bulk state which describes the physics in the interior of the boundary is the Chern-Simons state of Kodama[14], which is known to have a semiclassical interpretation in terms of de Sitter or Anti DeSitter spacetime[14, 15]. These results show that, at least for quantum general relativity, completely holographic formulations exist..."