Disclaimer: Although my maths is quite good and I have a background in computer science and software engineering, I am a philosopher specialising in information theory (and what is called the philosophy of information) so please be kind if you can. I am terribly nooby and may say dumb things.
I have a very basic understanding of the concept of first and second quantised theories. I also more or less get the following (see the disclaimer above):
- M-Theory is the current best version of string theory, having been unified from several (five - I think) separate string theories by Whitten in the late 1980s
- There is ample physical/experimental evidence in support of QFT and the quantum field, but not very much at all for String theory and its membranes.
- The quanta of QFT are excitations in (emerging from) the quantum field, and these are the (reductive) basis of the existence of the different particles of the standard model of quantum/particle physics
- Strings are not quanta qua/per QM and QFT: they are mathematically and presumably ontologically (this goes to my question) different beasts
- Membranes might intersect (M-Theory) with membranes in other universes, providing a physico-mathematical formalism that accomodates many worlds interpretations of QM (I think - I am not too sure about that)
- String theory is apparently very mathematically elegant with respect to representing/modelling many phenomena
Now. I realise that there are a lot of mathematical constructs deployed in QM and QFT and that there are debates relating to such things as interpretations of QM about which ones correspond to physical entities (like operators for example) in the actual mind, mathematics, and language independent physical/material natural world that is the subject of investigation in experimental physics (i.e. - the physical universe or multiverse depending on which one we turn out contingently to be living in).
I also understand that string field theory is much less developed than quantum field theory. However, when I try to get a quick concept of how the string field relates to the quantum field ontologically, I end up facing what seem to be contradictions (which I am sure are largely down to my ignorance.)
For example - there is a book available (which book is probably fantastic - I have not read it) the title of which is "Quantum Field Theory of Point Particles and Strings (Frontiers in Physics)" and for which the abstract says:
The purpose of this book is to introduce string theory without assuming any background in quantum field theory. Part I of this book follows the development of quantum field theory for point particles, while Part II introduces strings. All of the tools and concepts that are needed to quantize strings are developed first for point particles. Thus, Part I presents the main framework of quantum field theory and provides for a coherent development of the generalization and application of quantum field theory for point particles to strings....The book is unique in that it develops all three representations of quantum field theory (operator, functional Schrödinger, and path integral) for point particles and strings. In many cases, identical results are worked out in each representation to emphasize the representation-independent structures of quantum field theory.
So it's clearly the case that many mathematical apparatus deployed in QFT can be deployed for string field theory. HOWEVER - is this supposed to correspond to identity of the fields referred to by the two theories in the physical ontology of the natural world (each theory has a theory-ontology: do both map to the same external physical ontology w.r.t the field of each)?
Moreover, the wikipedia page about string theory starts thus: "String field theory (SFT) is a formalism in string theory in which the dynamics of relativistic strings is reformulated in the language of quantum field theory."
Note that it says "language of quantum field theory", which leads me to believe it is probably a text to get QFT theorists to understand string theory and the string field using language they understand.
So my dumb question boils down to this: is the field of string field theory (meant to be identical to) the quantum field in ontological terms?
Presumably string theorists and QFT physicists are ultimately shooting at the same ontic and explanatory objective, but then (and remembering that I understand basically there are arguments about the interpretations of QM and their ontological commitments) string theorists say stuff like:
However, string theory is not a quantum field theory, and this shows in the "stringy Feynman diagrams" it uses to compute perturbative string amplitudes. Here, one might start to think that the string becomes analogous to the particle because the diagrams simply are two-dimensional manifolds that look like "fattened Feynman diagrams", with string interaction corresponding to higher-genus 2D manifolds.
And they say stuff like:
To start addressing this question I will first say that while I think that string theory has something to do with fundamental physics I do not particularly see it as all (strings uber alles), but as something which may reflect a pattern in the structure of reality.
Presumably both fields have to account for the ample experimental evidence proving the existence of many (all?) of the particles of the standard model, and presumably both have to accomodate the vacuum (which seems to be ontologically primitive in QFT)? Or - maybe not??
Another way of putting my question is as a T/F:
The string field and the quantum field of SFT and QFT respectively are (taken to be/represent) the same field in the physical world but modelled using very different mathematical constructs: True or False? Why?