Why do we need confinement mechanisms in physics theories?
- There is a fundamental binding agent in nature, that needs to be explained. The limiting, localizing, encircling, singularity seeking confining action of the fundamental binding agent is independent of theory construction. In other words, binding action is not epistemic; it is ontic which means real. Reality of the binding action can only be explained by confinement mechanisms of the theory.
- There are aspects of nature that can only be described by the “interaction” concept. The “interaction” is real (ontic) therefore needs to be explained. It is possible to explain the “interaction” aspects of nature by various confinement mechanisms.
- There is also an epistemic reason for devising confinement mechanisms in theories. We are trying to explain a multitude of observed properties with a small number of variables of the theory. For mostly psychological reasons but also for reasons related to predictive power, the smaller the number of variables the better. This can only be achieved by establishing constraints on our variables. We try to establish a connection between the specific constraints and observed properties.
- Nature has ‘freedom seeking’ aspects as well but obviously those cannot be explained by confinement mechanisms. But, one can specify which confinement mechanism would result in which ”freedom seeking’ mechanism. This is rather an optimistic view because most probably there are uncountable number of ”freedom seeking’ mechanisms.
Confinement by curvature of space-time
Gravity is the dominant form of the fundamental binding agent at the astronomical scales. Gravity holds galaxies and star systems together. Gravity can also confine matter to Black Holes. At the atomic scale the electromagnetic force is the dominant form of the fundamental binding agent confining electrons to the atom. Inside the atomic nucleus and inside protons and neutrons the strong nuclear force is the dominant form of the fundamental binding agent.
Einstein’s theory of General Relativity explains gravity by a constraint on the space-time. It explains gravity by saying that matter (energy and momentum) distorts (curves) space-time. The curvature of space-time is the constraint. The curvature of space-time is a confinement mechanism. Not just the space-time, the curvature in any medium is a confinement mechanism. Curvature on a field, for example, is certainly a confinement mechanism.
Confinement by field
Another confinement mechanism in physics is the concept of field. Charged particles like electrons or protons emanate electric fields. Moving charged particles emanate magnetic fields. Other charged particles feel these electric and magnetic fields and get confined in various ways.
Confinement by “force”
The “force” concept is related to the “field” concept but still different. Force is a different kind of confinement mechanism. A “force” is not a geometrical concept therefore we cannot use the “curvature” concept to describe a “force.”
Force is sometimes described as interaction-by-particle-exchange. When you throw a ball the catcher feels a force. There is an interaction or force between the thrower and the catcher. The force is transmitted to the receiver by exchanging an object. According to this paradigm all forces work like this. Electromagnetic force is mediated by exchanging photons; the strong nuclear force is mediated by exchanging gluons and the weak nuclear force is mediated by the exchange of W and Z particles.
I am uncomfortable with the “force” concept. But, I know that, at this point in history, the “force” is the only confinement mechanism to describe the “interaction” aspects of nature.
At the scales smaller than quarks the concept of “force” is abandoned. Physics theories dealing with the physical phenomena at the tiniest scales typically resort to modifications of the ordinary space as a confinement mechanism.
Confinement by compact extra dimensions (microstructure of space)
Strings move in superspace. What is superspace? 3 dimensions of external space plus the time dimension plus 6 compactified extra dimensions of space. In addition to these 10 degrees of freedom, each point in superspace has additional degrees of freedom that can be represented by a 2-component Weyl spinor.
This is strange! We are adding degrees of freedom (more flexibility) to our theory but at the same time we are constraining those degrees of freedom. Very clever but very tricky! This approach may not succeed in the end.
What are the compactified extra dimensions? It is the microstructure of space? Does space really have microstructure? We don’t know! There is no experimental evidence yet? Why does the String Theory theorize a microstructure for space? Is the microstructure needed? Yes, otherwise String Theory cannot explain the observed properties of elementary particles. Fundamental strings have to be confined otherwise they cannot have discrete frequencies and distinct vibrational modes. The distinct vibrational modes supposedly correspond to different elementary particles. The correspondence between the vibrational modes and the observed properties of elementary particles is only partially done. There are great mathematical difficulties. String Theory does not yet have a principle that can fix the topology (shape) of the compactified dimensions. There are too many choices. That’s why the correspondence to observed particle properties cannot be established yet.
To summarize, the confinement mechanism in the String Theory is the microstructure of space. There are different types of string theories but in all of them the confinement mechanism theorizes a microstructure to space.
Confinement by discrete (granular) space-time
The confinement in the “Causal Dynamical Triangulations” approach is achieved by approximating space-time as a mosaic of very small triangles. Fundamental dynamic components of nature have to move or vibrate within the confines of these small triangles. This is a big assumption but it removes the ambiguity regarding the topology of compactified extra dimensions.
So far, all experiments and astrophysical measurements have shown that the speed of light in vacuum does not depend on its frequency. If space-time was discrete (granular) then light would have a different speed in vacuum depending on its frequency. This has not been observed yet.
Confinement by spin networks
Spin networks were first introduced by Roger Penrose as a purely combinatorial description of the geometry of space-time. Later, Rovelli and Smolin discovered that spin networks can be used to describe states in loop quantum gravity. A spin network is a mathematical graph. Nodes of the graph correspond to quanta of volume (atoms of space). Edges of the graph correspond to quanta of area. Spin networks evolve in time. The main strength of this proposal is its background independence property. Spin-network proposal combines nicely the “discrete space-time” and the “quantum-space-time” proposals and shows how “quantum space-time” can emerge from the spin-network.
So in these types of quantum gravity theories the confinement is accomplished by “atoms of space” and “quanta of area.”
Confinement by primordial thread forms
There is no experimental evidence for any proposal that tries to extend space by theorizing micro-structure to space. There is no experimental evidence for “atoms of space” either. So I feel comfortable proposing an alternative mechanism for confinement.
I have been talking about the “primordial threads” in various posts. What is a primordial thread? Primordial thread is NOT an extra dimension of space. The primordial threads do not try to extend the space-time. They represent primordial flows in nature. They have similarities to strings and fields but there are also major differences. For example, strings vibrate but primordial threads do not vibrate in my opinion. Primordial threads are forms. What does “form” mean? The term “form” refers to a confinement mechanism. Instead of imposing size restrictions on the compact extra dimensions of space we can impose curvature on the primordial threads and establish connections between the observed properties of particles and fields and the various forms of the primordial thread. Instead of making extra assumptions like vibrating strings confined to compact space dimensions we can establish connections between the forms of the primordial thread and dynamic aspects of observed physics. In other words, we can achieve many goals with the same theoretical construct. 1) explain charge, spin, mass 2) explain “time effect” 3) explain dynamic features of nature. Well, the mathematical theory of the primordial threads does not exist yet. So, it is premature to talk about the virtues of the “primordial thread” approach.
My point is this: we should think about alternative mechanisms for confinement other than “compact extra space dimensions” and “force” to improve our theories.
You might check out my earlier article titled “Proposals for space-time extensions”