Infinite dimensions in string theory

[Cult of Reason]

In this thread:

http://www.revolutionaryleft.com/index.php...topic=50075&hl= (http://www.revolutionaryleft.com/index.php?showtopic=50075&hl=)


Originally posted by "ComradeRed"
That is to say, String theory uses an infinite number of dimensions. If you can't see the absurdity of this, you are no scientist.


Having not yet started university yet, I ask ComradeRed that he would please explain why this is so. I just hope I have not missed anything obvious.

Some other questions:

On Dark Matter:

It is my (possibly erroneous) impression that ComradeRed's answer to the idea of Dark Matter is that the orbit of stars around the centres of galaxies can be correctly worked out using Einsteins relativistic theory of gravitation rather than Newton's non-relativistic one, which is more commonly used for the purpose for reasons of convenience. This is an attractive idea (although ComradeRed is my only source on this), as evidence for Dark Matter does not seem forthcoming. However, if I remember correctly, Anthony Fairall in his book Cosmology Revealed (which is a good read) claims that simply the use of General Relativity would not explain the larger scale structures of the universe (such as clusters and superclusters of galaxies etc., and various walls in the "frothy" structure of mass distribution. Something to do with considering the whole universe a fruit cake (sorry if I am being incoherent)) without the addition of extra matter, nor the solution to the problem of the critical density of the universe. What does ComradeRed say about this?

A small general question: The second law of thermodynamics only works in one direction. Are there any other major physical laws that also only work in one direction? Will those that work in both directions eventually have to be modified in some way so that they take account of the second law of thermodynamics?

Shape of the universe:

Based on what ComradeRed knows about the amount of matter int he universe etc. what shape does he think the universe is? Is it negatively or positively curved? Flat? Is it infinite in extent outside of what Anthony Fairall terms the Cosmic Egg (the limit to what we can see), or is it finite but with no boundary?

Small mathematical question: is the surface of a torus negatively curved but with no boundary and finite extent? It seems to be a natural extension of a saddle shape, though I probably made a mistake somewhere.

Potentially long and confusing question:

I am currently reading (while skipping the questions due to getting stuck on one and giving up... ugh) The Road to Reality, and I am wondering if, possibly, ComradeRed could give, in layman's terms, a brief explanation of: What the hell is twistor theory?

Thankyou.

[ComradeRed]

Ask me to elucidate where needed, I go quick.

Also, please do not be offended if I become overly pedogogical or pedantic; I am assuming that those reading this do not know much physics.



Originally posted by ComradeRed
That is to say, String theory uses an infinite number of dimensions. If you can't see the absurdity of this, you are no scientist.
Having not yet started university yet, I ask ComradeRed that he would please explain why this is so. I just hope I have not missed anything obvious. (After re-reading this, look at chapter 26.9 in the Road to Reality by Penrose, he goes over the renormalization procedure for canonical quantization. After that, you can skip down below.)

So, this is involved with quantum field theory which has to do with quantizing classical field theory.

Classical field theory is an extension of classical mechanics to explain fields, and how matter interacts with fields. So if we had a particle travelling through an electromagnetic field, this particle of ours would be affected by the electromagnetic field and its path would deviate from what we expect it would be.

Remember Old Newton's saying "A body moves in a straight line unless acted upon by an outside force." (Paraphrased ;))

Classical field theory explains fields in terms of scalars (magnitudes), vectors (magnitudes with directions, e.g. The Wind is blowing 30 mph [magnitude] due East [direction], which is then represented as a line whose length is the magnitude), and tensors (which is like a collection of vectors).

Now, what we do is we have this field quantity, right? It can be a scalar, vector, tensor, whatever! What we are going to do is introduce the Uncertainty Principle into the field.

How we do this is rather long winded, though interesting nonetheless. It involves something called the Fourier Transform.

What the Fourier Transform is involved with is: suppose we have a signal. We can express the frequency of the signal (units of "per second" = 1/s) or we can express it in units of time (units of "seconds" = s).

Because these are conjugate quantities (s and s^-1) we need a Fourier transform to change it from f(s) to g(s^-1). That's all it really does.

Now the Uncertainty principle says that if we know momentum, p, then the position is ih(p^-1) (due to the limitations of this forum, h is supposed to be dirac's shorter constant, that is Planck's constant over 2*pi). The same is true for position, x, the conjugate momentum is ih(x^-1).

So we take the field itself as the position component, and take a fourier transform to find its conjugate momentum.

The conjugate momentum and position are turned into "operators" (like addition, subtraction, multiplication, etc.). The momentum is the "Creation operator" that creates virtual particles, the position is the "Anhilation operator" which destroys virtual particles. This quantized field is defined everywhere on spacetime.

These operators obey the Uncertainty principle.

Part of the quantizing procedure, the Fourier Transform part, is supposed to "converge" to a number; take, for example, an infinite series SUM^{infty}_{n=0} 2^-n -- it converges to 2. (1 + .5 + .25 + ... = 1 + (n-1)/n = 1 + 1).

Sometimes bad things occur, like particles interact with themselves, and then instead of converging to a number, it goes to infinity :o This then requires a "coupling constant" -- something that prevents the series from going to infinity.

This is called the "renormalization process" to prevent needless infinities. It is relatively contraversial in physics for a variety of reasons (e.g. Math with infinities is often counter-intuitive and doesn't simply "cancel each other out").

Stop skipping here.

In String theory, the approach is to add more dimensions. There exists no coupling constant to the number of dimensions; it would go to infinity.

The reason why there is a need to add more dimensions is because String theory works in a background dependent spacetime as opposed to General Relativity's background independence. This is a contradiction! :lol:

That's just my interpretation, and I am an avowed foe of String Theory; if you ask, say, Brian Greene (a pioneering String Theorist) he'd probably laugh this criticism off. String theorists don't like criticism.




On Dark Matter:

It is my (possibly erroneous) impression that ComradeRed's answer to the idea of Dark Matter is that the orbit of stars around the centres of galaxies can be correctly worked out using Einsteins relativistic theory of gravitation rather than Newton's non-relativistic one, which is more commonly used for the purpose for reasons of convenience. This is an attractive idea (although ComradeRed is my only source on this), as evidence for Dark Matter does not seem forthcoming. However, if I remember correctly, Anthony Fairall in his book Cosmology Revealed (which is a good read) claims that simply the use of General Relativity would not explain the larger scale structures of the universe (such as clusters and superclusters of galaxies etc., and various walls in the "frothy" structure of mass distribution. Something to do with considering the whole universe a fruit cake (sorry if I am being incoherent)) without the addition of extra matter, nor the solution to the problem of the critical density of the universe. What does ComradeRed say about this? ComradeRed says ComradeRed likes to hear ComradeRed talk about ComradeRed...ComradeRed!

It really depends how you approach cosmology. For example, there is this quantity -- the "Cosmological constant" -- which holds the data for the radius of the universe and the mass of the universe.

Lazy physicists like me love it because it drastically simplifies Einstein's field equation to help determine the metric tensor (the gravitational deformation of spacetime).

Well, even lazier physicists say "Screw this, I'm going old skool to Newtonian Cosmology!" That's where the notion of Dark Matter, to my knowledge, comes from. (Quantum Physicists even want the resurrection of Aether :lol: check out Quantum Cybernetics for details).

Anthony Fairall, based solely on your expose, appears to forget that gravity works based on Energy of any sort (regardless of what it is). It's irrelevant that it's one way or another.

But gravity is only relevant to a point...for example, taking the entire universe as an object, finding its gravitational field, then complaining about how unrealistic the conclusion is does not qualify as a critique of General Relativity.

Though, granted, I have read nothing from this Fairall fellow.



Based on what ComradeRed knows about the amount of matter int he universe etc. what shape does he think the universe is? Is it negatively or positively curved? Flat? Is it infinite in extent outside of what Anthony Fairall terms the Cosmic Egg (the limit to what we can see), or is it finite but with no boundary? What the hell am I, a demigod? :lol:

I think that this is an irrelevant question, very much like asking "Who's buried in the tomb of the unknown soldier?"

However, unlike that question, this one is unanswerable because we all are stuck in the universe. We can't walk "outside" of the universe and look at it, like we would look at a clock or a computer screen. The universe would deform its shape so that the observer would still be in it.

In this sense it is like a fish in a bag full of water. When it approaches the edge of the bag, we could deform it, so the flow of water pushes the fish back. The fish observes this as moving forward (relative to his frame of reference). So this fish of ours would think it was moving for an infinite period of time and never reach the end of the bag.

What shape is that? :P



Small mathematical question: is the surface of a torus negatively curved but with no boundary and finite extent? It seems to be a natural extension of a saddle shape, though I probably made a mistake somewhere. It depends on where you are on the torus, whether you are examining it locally or nonlocally, and the signature of the metric tensor.

Though this is probably over analysing your question in the wrong direction.



I am currently reading (while skipping the questions due to getting stuck on one and giving up... ugh) The Road to Reality, and I am wondering if, possibly, ComradeRed could give, in layman's terms, a brief explanation of: What the hell is twistor theory? You poor bastard! I sympathize, I read it without heading Rosa's warning that Penrose is a damn Platonist.

Are you familiar with light cones? I shall assume that you are.

What Penrose proposes is that we take a hypothetical event at point X in spacetime. If there is relation to point Y, then X will lie within the light cone.

Twistor theory quantizes the light cone (essentially), so the momentum and angular velocity is used to determine if the point lies on the path of the photon.

That's the significance of the fourth equation in Chapter 33.6 (in the hardcover, page 979).

Geometrically, if point A is in incidence on ray B, that means somewhere on the ray point A is on it.

Learn about phasors, they're really damn useful when talking about spinors. Twistors are an extension of spinors, and spinors are a pair of phasors ;) Look at Chapter 22.11, the first two equations in the fifth paragraph are examples of simple spinors.

Twistors are so damn indescribable that it makes those spinors (they're simple spinors too) look like child's play. That's why no one graphs them out :lol:

If you want a good introduction to loop quantum gravity (from chapter 32 Einstein's Narrower Path), there's a damn good textbook Quantum Gravity by Carlo Rovelli on it. You'd have to request it as it is a graduate level textbook :(

[ComradeRed]

Some more stuff on twistors!

If you take the determinant of a matrix:
[[ A B ]
[ C D ]]
it would be AD - BC, right?

Well, look at how Penrose formed the entries of his Twistor matrix:
[[ t + z x + iy ]
[ x - iy t - z ]]
Take the determinant and you get:
t^2 - x^2 - y^2 - z^2.

If we notionally set this to zero (as we do in the practice of light cones), we set up a coordinate system around a given event, thus:
t^2 - x^2 - y^2 - z^2 = 0

We can rearrange this to be more elegant! Add the spatial dimensions to the other side:
t^2 = x^2 + y^2 + z^2
which is remniscient of the equation for a radius in spherical coordinates
r^2 = x^2 + y^2 + z^2 .

However, there is uncertainty in the position and momentum of particles, like -- say -- photons.

What a coincidence! Photons ( remember that photons = light!) are very damn important in what we are doing!

This would quantize the causality from classical special relativity! :o

Look at the Robinson congruence for a "simple" two spatial dimensional light cone at time t=0. Boy isn't that damn simple? :lol:

A word to the wise: Penrose was trained as a mathematician, so he is more comfortable talking about 27 dimensional twistor manifolds to the nth degree that incorporates the x manifold of the conjugate components of yadda yadda yadda.

But just remember that there are three ways to use twistors: the right way, the wrong way, and the ComradeRed way!

[Cult of Reason]

Some parts of your answers I will leave for later when I have got further through Penrose's book, and I prefer to go through it all rather than skipping ahead.

String theory:

So string theory is background dependent while General Relativity is not? OK. So you view it that any TOE (string theory is an attempt at a TOE, right? What relation is quantum gravity to a TOE?) must be consistent with General Relativity? This is because General Relativity has empirical evidence supporting it? Are there any instances of GR producing erroneous results on the macro scale, as opposed to the micro scale?

Also, what do you mean by background dependence and independence? I have never met any concept before, I think, which uses those terms, so could you explain please? Assuming it was possible to modify GR to be background dependent, what would happen to its predictions if it was?

Cosmological constant:

Cosmological constant? I thought that was done away with decades ago, Einstein's greatest blunder, etc.? You say it simplifies the equations, but does it introduce any error?

Dark Matter and GR:

According to Anthony Fairall, with Newton's gravity working, clusters of galaxies were thought possible, and were the largest entities in the universe. To form anything larger than a cluster would be impossible, as gravity would require a time scale "tens or hundreds of times longer". He goes on to say that galaxies outside clusters were believed to be randomly scattered, but actually form large-scale structures, not predicted by Newton's gravity. Would it have been predicted by GR?

He also says this:


Or is it that we do not understand Newton's Law of Gravity? Newton devised it to solve questions about the solar system, yet here we are trying to apply it to the cosmos, and still expecting it to work. However, to make stronger gravity, rather than invoke unseen mass, the law would have to be modified. While still working precisely the same at small distances, Newton's Law would have to grow somewhat "stronger" at large distances - at the scale of galaxies, clusters of galaxies and large-scale structures. It would then have to get weaker again or it would disrupt the whole universe. But physical laws do not work this way, and this suggestion seems to contrived for comfort. The preferred choice, by far, is simply dark matter.

The only possible alternative would be a completely different conceptual approach to gravity to the one used by Newton. As we will see (in the next chapter), Einstein's thoery of General Relativity is such an alternative, but it too cannot account for "stronger" gravity on large-scales, exept by involving more mass.

Empases mine. He does not mention energy at all, that is true. Oh, and it is not different to, it is different from!


What the hell am I, a demigod? laugh.gif

Damn, but I need a hero to worship, and Lenin is obviously out of the running... :P

Anyway, so you say that anything that does not involve a defined observer is irrelevant? I suppose you apply this to all your thoughts of various physical hypotheses?


It depends on where you are on the torus, whether you are examining it locally or nonlocally, and the signature of the metric tensor.

Though this is probably over analysing your question in the wrong direction.

:huh: So a simple shape like a torus can have both negative and positive curves?

Anyway, it seems to me that you get a saddle shape if you cut out a part of the torus that is on the inside ring, and that since a saddle is negatively curved, the rest of the torus would be too.


You poor bastard! I sympathize, I read it without heading Rosa's warning that Penrose is a damn Platonist.

What is a Platonist (I assume it has something to do with the Platonic Plane of mathematical forms?) and what is bad about Platonists?


Are you familiar with light cones?

I suppose as familiar as possible if all you have read about them is from Hawking's books.

On spinors, twistors, phasers and tensors I will probably have to wait until I get to them in RTR.

Graduate level textbook? Damn, I would have to wait until 2010 before it would be worthwhile then.


If you take the determinant of a matrix:
[[ A B ]
[ C D ]]
it would be AD - BC, right?

Yes, that is about as far as I have been taught about matrices (except how to do the same for 3x3 matrices, and that was only from learning about the vector product).


Well, look at how Penrose formed the entries of his Twistor matrix:
[[ t + z x + iy ]
[ x - iy t - z ]]
Take the determinant and you get:
t^2 - x^2 - y^2 - z^2.

:huh: So a determinant of a 2x3 matrix is... Oh, wait, that is a 2x2! Sorry, just got a little confused! (for half an hour!)

Robinson congruence?

Also, twistor thery does not seem to be in fashion (while string theory is...). Why is that? Also, is twistor theory testable? Are there other theories that are testable?

[ComradeRed]

So string theory is background dependent while General Relativity is not? OK. So you view it that any TOE (string theory is an attempt at a TOE, right? What relation is quantum gravity to a TOE?) must be consistent with General Relativity? This is because General Relativity has empirical evidence supporting it? Are there any instances of GR producing erroneous results on the macro scale, as opposed to the micro scale?
1. String theory is background dependent as is QUantum Field theory (String theory is the school of thought saying quantum gravity needs to begin with quantum theory then go to quantum gravity somehow by first unifying every other field together).

The problems with this school of thought are so vast that I cannot even begin! First, the idea that "We need to unify everything in order to unify quantum mechanics and general relativity" is so tragicomically decoupled from reality, you may as well say "The flying speghetti monster makes everything work."

The idea is actually similiar to a notion from the '80s; they thought Strong force would explain the renormalization process :lol: It didn't, needless to say.

2. String theory is a crackpot attempt at a UFT, but quantum gravity is only the scafolding for a UFT (in my opinion).

3. GR is stronger at the Macro level than the micro level; there is no logical, empirical, or mathematical criticism (besides "the math is hard!") or counterproof that exists to my knowledge. That doesn't mean, however, that it is undeniably true scripture ;) It just means Newton was wrong.

4. Quantum Gravity must preserve GR (at least, in my school of thought, which begins with Relativity so I'm only relatively biased ;)). There are two main constraints: the diffeomorphism constraint (background independence), and the Hamiltonian constraint (which is extremely difficult to interpret -- there are debates on what it means, no one really knows all that much ;)).

5. The places where GR breaks down is in black holes and the beginning of the universe; that's where quantum gravity is supposed to explain everything. There is a school of thought, the black hole thermodynamicists, that argue that black holes are fundamental; who knows.



Also, what do you mean by background dependence and independence? I have never met any concept before, I think, which uses those terms, so could you explain please? Assuming it was possible to modify GR to be background dependent, what would happen to its predictions if it was? OK, lemme give you an example of background independence.

A triangle in a coordinate system X is equilateral with 1 unit length for each side. We introduce a new coordinate system Y which has 1 unit length (Y) = 2 units length (X). The triangle doesn't change because it is independent of the coordinate system, it's lengths are the same in both coordinate systems.

A better example might be: there are two bodies moving with a black background. Which is moving past the other? What rates are they going? You can't tell without other objects to judge it by.

One may observe object A passing object B, another may observe the opposite. They are both right.

The significance of this is that space and time (spacetime) is itself a field. So if we have something as background independent, it doesn't matter how deformed spacetime is; what happens is the same.

The consequences of this is profound. The universe contains everything, for example; you can't observe the universe without changing it (because you can't leave the universe). Otherwise there is a background, which contradicts relativity ;)

Basically: dynamic spacetime = background independence. The universe is composed of fields only, there is no "absolute" space or time; spacetime is itself a field, which we dub "gravity" ;)

Hope that was coherent, I gave the more mathematical example first then explained its physical significance.

If you can, I would highly recommend reading Gravitation by Kip Thorne, Charles Misner, and J.A. Wheeler; they demonstrate the impossibility of having a background dependent form of General Relativity and how it leads to the Newtonian system necessarily.



Cosmological constant? I thought that was done away with decades ago, Einstein's greatest blunder, etc.? You say it simplifies the equations, but does it introduce any error? Well, we can have the solution to the field equation because the metric tensor (the gravitational field) is equal to the Ricci tensor times 4 divided by the Ricci scalar.

Plug in Einstein's field equation and you get the metric tensor is equal to -4/3 times the stress energy tensor over (-p c^2); for the density of matter p.

This reduces to velocity vector \dot{x}^{a} over the speed of light times the velocity vector \dot{x}^{b} over the speed of light is equal to the metric tensor.

This is a hell of a lot easier to solve than the Einstein equations without the Cosmological constant (I showed all the work, for a simple body moving at a constant velocity, and it took me over 4 pages front and back; and I used lineless paper, 3 columns each side, with tiny writing too!).

There is thus, due to laziness, discrepencies in the view of the cosmological constant.



According to Anthony Fairall, with Newton's gravity working, clusters of galaxies were thought possible, and were the largest entities in the universe. To form anything larger than a cluster would be impossible, as gravity would require a time scale "tens or hundreds of times longer". He goes on to say that galaxies outside clusters were believed to be randomly scattered, but actually form large-scale structures, not predicted by Newton's gravity. Would it have been predicted by GR? I'm slightly pressed for time unfortunately, but I would suggest reading The Large Scale Structure of the Universe by Hartle and Hawking.

Fairall is just whistling dixie compared to what HnH have to say.



Anyway, so you say that anything that does not involve a defined observer is irrelevant? I suppose you apply this to all your thoughts of various physical hypotheses? I'm actually not too liked by mathematicians because if something can't be physically shown to me, I judge it to be irrelevant.

You know from elementary geometry, the dot represents the dimensionless point in space? That can't be otherwise we wouldn't see the dot. I rejected that proposition of Euclid's; and mathematicians reject me :P


So a simple shape like a torus can have both negative and positive curves?
It depends on the local reference frame of the observer, yes.

Nonlocally it could theoretically be both, locally it would be impossible.



What is a Platonist (I assume it has something to do with the Platonic Plane of mathematical forms?) and what is bad about Platonists? Go ask Rosa :P

It contradicts materialism, not to mention common sense.



Also, twistor thery does not seem to be in fashion (while string theory is...). Why is that? Also, is twistor theory testable? Are there other theories that are testable? Well, twistors quantize the light cones.

It is feasibly testable, but it would be difficult.

Twistors check if an event lies in "quantum incidence" with a light ray (that is, we doodle a line representing a photon particle's path, and because we are uncertain of its position/momentum, this affects the light cone; it becomes fuzzy!).

This creates a new element for quantum geometry (something I'm working my ass off on) and causality.

String theory has recently tried to incorporate twistors into it.

Twistors are part of the "third camp" -- those who begin with neither relativity nor quantum theory and tries to mesh the two together.

[Cult of Reason]

Twistors are part of the "third camp" -- those who begin with neither relativity nor quantum theory and tries to mesh the two together.

So, first camp: Start with QM, most well known result is string theory.
Third camp: Start with neither GR or QM, but try to mesh them together, for example TT.

So, what theories come from the second camp, starting with GR? And are there any other theories from camps 1 and 3?

[RebelDog]

Quantum Loop Gravity;

http://en.wikipedia.org/wiki/Loop_quantum_gravity

I've not read much about it, but its a rival to super-string theory. I read that there is a possibility it actually the same thing as super-string as there are similarities. Lets hope they are chasing the same thing, might mean there is a unified theory and more people are working toward it.

[ComradeRed]

Originally posted by Haraldur+--> (Haraldur)So, first camp: Start with QM, most well known result is string theory.
Third camp: Start with neither GR or QM, but try to mesh them together, for example TT.

So, what theories come from the second camp, starting with GR? And are there any other theories from camps 1 and 3?[/b] Yep, the second camp is beginning with GR.

The schools stemming from it are: canonical gravity, quantum geometrodynamics, dynamical triangulations, path integration in Regge calculus, Loop Quantum Gravity (probably the biggest from the camp), and others!

I am affiliated with the camp, but not especially with any particular school of thought ;)


TheDissenter

I've not read much about it, but its a rival to super-string theory. I read that there is a possibility it actually the same thing as super-string as there are similarities. Lets hope they are chasing the same thing, might mean there is a unified theory and more people are working toward it. Well, Lee Smolin certainly hopes so...though I doubt it.

String theory will (optimistically) be disproven empirically within the next several decades with the new particle accelerators at CERN.

There simply is no reason to accept String theory: there is no empirical evidence for Strings, there is no logical or mathematical evidence for Strings, there is no reason to use Klein's 5 dimensional model for GR rather than the empirically valid 4 dimensional model, and worse it contradicts Einstein!

I am, of course, openly hostile against String theory :P

[Cult of Reason]

I am affiliated with the camp, but not especially with any particular school of thought

Ah, right. Then it would be pointless for me to ask what your alternative to string theory would be. :P


Quantum Loop Gravity;

http://en.wikipedia.org/wiki/Loop_quantum_gravity

I will look into it i a few days time when there are no examinations for a week and I am less tired. ;)

[ComradeRed]

It also depends on how you view gravity: is it a field whose mediating "particles" is spacetime itself or is there some "graviton" mediating boson?

I think the latter is cartoonish by its inexistence. Einstein preferred the former, with the exception that he viewed spacetime as continuous rather than discretized.

In physics, we call discretization of a field the "first quantization". The actually quantization of this discretization is the "second quantization" if and only if it follows the uncertainty principle. ;)

Just some fun factoids.

[RebelDog]

The string vibrates. This in turn warps space/time ie; gravity. This string manifests itself as a one of the seemingly endless different particles. This particle has a mass that has direct relationship with the frequency of the vibration of the string. ie a string vibrates with the frequency that makes it a electron and it accordingly warps space/time to the same degree with the correct mass.

I think thats about right, String theory has appeal to me because its essentially simple in its elegance.

[Janus]

I think thats about right, String theory has appeal to me because its essentially simple in its elegance.
That's why it appeals to a lot of people.


There aren't infinite dimensions in String theory. There are an extra 6 in Ed Witten's M theory; one was added because it was necessary in order to get the math right.

[ComradeRed]

The string vibrates. This in turn warps space/time ie; gravity. This string manifests itself as a one of the seemingly endless different particles. This particle has a mass that has direct relationship with the frequency of the vibration of the string. ie a string vibrates with the frequency that makes it a electron and it accordingly warps space/time to the same degree with the correct mass. The problem with this interpretation of String theory (I call M theory, Q theory, Superstring theory, etc. "interpretations" -- like Quantum theory) is that it mimics general relativity without encompassing it fully.

As Wheeler said, matter tells spacetime how to curve, and spacetime tells matter how to move. String theory has the former yet ignores the latter, and the latter is the important part.



I think thats about right, String theory has appeal to me because its essentially simple in its elegance. Mathematically, it is very simple to quantize (the elementary examples in Quantum Field Theory texts are frequency :P).

And it has intuitive appeals to symmetry and its simple reasoning (strings + more strings = particle).

Yet what about the composition of the particle? I mean, atoms have certain compositions of protons and nuetrons which govern its nuclear state, etc. Why don't Strings have the same relation?

The cost for accepting such a proposition is background dependence :o

Something&#39;s gotta give, and it shouldn&#39;t be General Relativity (as it makes no sense to say "Quantum General Relativity is really Quantum Newtonian Gravity" <_<).


Originally posted by Janus

There aren&#39;t infinite dimensions in String theory. There are an extra 6 in Ed Witten&#39;s M theory; one was added because it was necessary in order to get the math right. And that was doubled for supersymmetry, and it was doubled again to make the math "just right".

There was no empirical justification to do it.

Since "gravitational field = spacetime" and String theory has no coupling constant (I reiterate: ABSOLUTELY NO COUPLING CONSTANT&#33; NONE&#33;) that will mathematically lead to a singularity in the number of dimensions ---- i.e. lead to an infinite number of dimensions.

Further, String theory isn&#39;t compatible with Special Relativity&#33; They had to create a "Doubly Special Relativity" (maybe they should&#39;ve said super duper special relativity), which has been proven to be inconsistent with Special relativity.

How do you expect it to be consistent with general relativity? :huh:

[Janus]

How do you expect it to be consistent with general relativity?
:blink: I thought that was the whole point of String theory: a theory of everything. It was supposed to combine the general relativity with quantum mechanics.

[ComradeRed]

blink.gif I thought that was the whole point of String theory: a theory of everything. It was supposed to combine the general relativity with quantum mechanics. No, it was originally an attempt to unify quantum mechanics and general relativity.

The line of thought is beautifully stupid: in order to unify QM and GR, we first need to make a UFT. :lol:

The same notion existed for Strong force, except instead of a unified field theory (UFT) it would explain the renormalization process (the process which prevents infinities from coming up -- which String theory lacks)...needless to say, they were wrong then and they are wrong now.

String theorists are just impatient for a UFT, if only they could examine their own work with a critical eye&#33;

[omegaflare]

Reading this (I have a rudimentary understanding of Quantum Physics, i&#39;m getting there.) makes me feel proud of being a communist.