What are strings made of?

  • #76
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Now you've hit the real crux of the ultimate question being asked by Science, "Where did it all come from?". Most of us suspect Nature is its own origin of itself. Now, that could imply that some form of space-time, or at least its primary building blocks have always been around(ala Hawking's Instanton of time), or that while the first is true a loop in time(ala Gott)brought about our present space-time structure,or that multiple vacuum states collided(ala coliding branes, etc), or you can resort to philosophy and religion and invoke the "God" equation. At the present time we've simply not got enough of a grasp on what is the proper road to a quantum gravity to actually determine exactly the right path. But the right question does start exactly at what you've just asked.
 
  • #77
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Originally posted by pelastration
Mike2,
I just try to represent 'a string' as a 2D projection of an oscillating 3D membrane peak.
This seems to imply that there is no instantaneous string state; there is only the world sheet as a whole, which completely closes at the tip of the peeks. Otherwise, there would be an instantaneous string state at present time. Then the question arises as to what plain is slicing the protrusions to produce the string at the present time.


A closed string could then represent the avarage vibration of such 'peak'. This a personal vision (different from official ideas). I just try to find out if the actual (official) concept of strings fits with the idea that strings are just part of the brane and - in second stage - can couple to become QM-baskets (second picture).

Have you been able to produce a mathematical description of all this, yet?
 
  • #78
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One aspect of what strings are made of goes back to Feynman diagrams.
Feynman diagrams are graphs that describe processes where particles interact, like this:

\ / Two particles come in,
\ /
----- they exchange a virtual particle,
/ \
/ \ and two particles go out.

The number we compute from a Feynman diagram gives the amplitude
for the process to occur. Now this all relates to Loop Quantum Gravity, which, it is assumed for the sake of argument at present, relates to String Theory as far as the building blocks go.

In the quantum field theory called "phi^3 theory", the
diagrams are trivalent graphs with three edges meeting at
each vertex, like the one above. The basic building blocks are the
edge:


---------


and the vertex:

\ /
\ /
\ /
|
|
|

We can draw these in any rotated fashion. The parameter
corresponding to the edge is called the "mass" of the particle in
this theory, because in quantum theory, a particle's mass affects
what it does when it's just zipping along. The parameter corresponding to the vertex is called the "coupling
constant", because it affects how likely two particles are to couple
and give birth to a third. So the focus here, and this is where the bits and shards of space-time come from is that each of these loops formed by edges and vertexes is a fragment of a bigger composite we call space-time.

Its rather like a jigsaw puzzle. You do not have a complete picture till you put all the peices together. Those like Smolin say this type of modeling is devoid of a background. But personally one could argue that bits and peices of a background still imply a background. Smolin's main point was that the larger fabric we call space-time is absent from this type of picture or model.

One can actual see rather simply how one could build up a string from a bunch of stringy fragments. Regular everyday string is formed by combining many smaller bits of fabric. However, it is correct that even this model does not fully answer where did these fragments come from. Perhaps a prior mixing or ripping apart of a prior space-time? Actually, the list goes on when it comes to ideas.
 
  • #79
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Parden the diagrams. They did not translate right to here. But Feynman diagrams abound for you to get the idea from.
 
  • #80
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The most shocking outgrowth of the physics of branes has been the Maldacena conjecture. This conjecture states that M-theory subject to particular boundary conditions is in fact equivalent to some supersymmetric Yang-Mills theory on a manifold of smaller dimension. One example is the so-called AdS/CFT correspondence, in which string theory with boundary conditions matching the ten-dimensional manifold given by the product of 4+1 Anti-DeSitter space and a five-sphere (AdSsub5 x S^5) is conjectured to be equivalent to 3+1-dimensional super Yang-Mills theory.

The concepts involved in LQFT simply discribe what makes up these small structures themselves and in essence discribe how the String, that is the particle as an extended object, is formed.

Part of the question being asked is what is the most fundamental part of nature? Is it the String, the Branes, or the Loops?

In addition to strings, M-theory contains a zoo of higher dimensional objects; e.g. 2-dimensional membranes (aka 2-branes), 3-dimensional `3-branes', etc. An object with p spatial dimensions is known as a p-brane. These branes are now thought to be as fundamental as the string itself. The various branes are related to fundamental strings by powerful symmetries known as dualities.

The branes can form up into Strings and Strings can also form up into branes, but both objects are composed of something more primary themselves. Take String and one can weave a fabric which well term a brane or sheet. Yet, that same sheet can be decomposed into its basic string which in turn can be decomposed into its basic fabric parts itself.

If the quantum loops are actually the basic fabric then they could be seen as the most basic parts to be found in nature. However, at the present this has yet to be fully worked out or proven. Also any solid quantum theory will have to also account for where these basic bits of fabric actually came from. So a deeper fundamental question one can start with is Loops of what?

A starting point might be concentrating on the coupling constant issues. For example, the beta function has been calculated to four loops, in QED and in general matter flavor QCD/SQCD or SU(N_c). But even in QED, where Abelian Ward identities cancel divergences of wave function and vertex leaving only vacuum polarization logs, that doesn't tell you what "the running coupling" does at high orders. But the fact that this coupling exists can cause us to ask the question of coupling of what or to what?

We need to decide whether we're talking about a physical coupling, related to an amplitude, with the entire loop correction amplitudes resummed gauge invariantly; or an unphysical parameter in perturbative expansion in some particular renormalization scheme, perhaps in an asymptotic approximation that keeps only leading logs at high momentum. Also, we can have spacelike or timelike momentum transfer, depending on the physical process, and the subleading momentum terms depend on that.
But one could start this process of questioning by focusing on spacelike and timelike momentum transfer. In general with momentum we have energy coupling from one point to another. Coupling tends to imply direction to this energy flow which in turn implies a tensor field at play. But we can also have a simulation of a tensor field’s end product of direction via differences in a scalar field like the measurement of temperature. Under entropy we have flow of energy from a high temperature region into a lower temperature region. The result is a net coupling of energy from one region to another defined by tensor and scalar fields interacting.

This then sort of implies a picture where the basic building blocks of the cosmos are bits of energy. But then we have to further define exactly what energy is.

We measure energy via time, movement, etc in units expressing work. But then using time we are somewhat rather forced right back to a system with one of the original parts of the background invoked again when the whole idea was to get away from the background and form a background independent model.

Might seem a long way to bring up a point and indeed it is a long fashion to do so. But what is being shown here is that its hard to answer a question about the origin of something who’s very nature depends upon the background of time and space itself and who’s origin point would seem to be beyond some predetermined T=0 point.
 
  • #81
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Originally posted by paultrr
.... This then sort of implies a picture where the basic building blocks of the cosmos are bits of energy. But then we have to further define exactly what energy is.

We measure energy via time, movement, etc in units expressing work. But then using time we are somewhat rather forced right back to a system with one of the original parts of the background invoked again when the whole idea was to get away from the background and form a background independent model.

Might seem a long way to bring up a point and indeed it is a long fashion to do so. But what is being shown here is that its hard to answer a question about the origin of something who’s very nature depends upon the background of time and space itself and who’s origin point would seem to be beyond some predetermined T=0 point.
Thanks Paul for this very interesting analysis and overview of the various parameters involved with the fundamental question about the creation of all. String, brane , loops, coupling, .... energy, .... lots of interaction, and we have to make conceptual choices all the time such as the question: physical/unphysical.

But indeed that energy brings us back to the background.
To solve that ... don't we have to start with a unified starting concept: the background itself?

I believe the quest must start at the top. And then that background must be processed into the complexity that we see today around us, in you and everyone.
The background (das 'Feld') should include the gravity effect: stress and tension of the background. We may not throw away the gravity effect during our journey, since that is the only force that is "ALL the time" present. Where other forces change faces and values ... that inter-connective gravitational effect works all the time.
 
  • #82
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I think in general you do, though we might argue where exactly to start there. Here is the real crux of the problem somewhat reflective of Kant's own views also:

We have synthetic a priori knowledge of the spatial and temporal forms of outer and inner experience, grounded in our own pure intuitions of space and time; and to argue that transcendental idealism, the theory that spatiality and temporality are only forms in which objects appear to us and not properties of objects as they are in themselves, is the necessary condition for this a priori knowledge of space and time. Basically, these forms, weither they be string, loops, or branes are not in themselves an actual substance of reality. They are more our constructs by which our minds can get a handle on the sub-atomic world and come to understand how this world works.

Our conceptions of space and time cannot be divorced from experience of objects, because any such experience presupposes the individuation of objects in space and/or time, and that although we can represent space or time as devoid of objects, we cannot represent any objects without representing space and/or time. No matter how small one chooses to go as far as our breaking down these constructs one always returns in one fashion or another to the aspect of time and space. What we can hope to create is a fundamental theory or construct that is not dependent upon space and time.

In general, through the theory of general relativity we have a working model of just such a construct where the interplay of geometry has allowed us to begin to fathom what was once thought of as an action at a distance effect into an on stage performance of the interplay of different fields coming together to form the background we call space-time. The center stage actor in all this is energy expressed as matter telling space-time how to bend and warp and that warpage in turn telling energy how to move. So the primary question to start with is why is there energy in the first place?
 
  • #83
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On a related note, does anyone think Penrose's original idea still holds a firm basis these days?

His original suggestion was that quantum state reduction occurs at the Planck scale, where spin-networks encode proto-consciousness... so it's a quantum mechanical process and when the wavefunction collapses, we "experience"...
 
  • #84
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Jack Sarfatti, even though he follows Bohm's pilot wave model, tends to at least by implcation support such. Personally, while I believe quantum effects do have implications for the subject of consciousness I tend to rather like avoiding them in general discussions of physics. However, Penrose was a man well ahead of his time in many ways so I would not fully discount his ideas out either.
 
  • #85
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Originally posted by Mike2
.... there is only the world sheet as a whole, which completely closes at the tip of the peeks. Then the question arises as to what plain is slicing the protrusions to produce the string at the present time.
...
Have you been able to produce a mathematical description of all this, yet?
Thanks Mike2,
indeed that's a possible entry. Since the specialists found a number of mathematical significant formulaes ... but have no concept behind ... we can use our own creativity.
No, I have not explored math's behind ... and that's not my job. I am just a conceptor, an inventor interested in real things. With such membrane material I could build the world and life and consciousness we see today.
 
  • #86
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The idea that strings are made of energy does not satisfy me. To me, it makes more sense that strings are made of space which move through time and other dimensions. Strings are all conected and influencing each other. Knots of "waves interacting with each other" make up subparticles. Therefore at this level we can be considered as an interactivity among multiple dimensions; what makes existence or matter looks like a living(strings are in constant motion) bunch nothing.
 
  • #87
2,471
1
On a related note, does anyone think Penrose's original idea still holds a firm basis these days?

His original suggestion was that quantum state reduction occurs at the Planck scale, where spin-networks encode proto-consciousness... so it's a quantum mechanical process and when the wavefunction collapses, we "experience"...
No, wavefunction never collapses.
 

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