Most physicists believe that the universe is governed by comprehensible laws. They dedicate their lives to the discovery of those laws. A majority of them believe that the laws are part of a single theoretical framework. This belief system and the research program towards finding that single unifying framework is known as the unification program.
It is ironic that the goal of having a single theoretical framework – sometimes referred to as the “Theory of Everything” – gave birth to multiple research programs (group theoretical approaches, String Theory, Hypergraph, primordial qubit network, and many more). The idea of unification seems to inspire multiple approaches. Are these simply candidates in the sense that only one of them will prove to be correct? Or, are these theoretical frameworks all contain elements of truth reflecting different aspects of Reality? My personal opinion is that no single theoretical framework can be declared as the truth. I am convinced that we will keep discovering new perspectives. There is no end to this process.
When I say “perspectives” I mean those conceptual frameworks with strong explanatory and predictive power. There will be many others that will be dismissed. It is clear to me that eventually we will have not single but multiple useful “perspectives”.
History of the unification efforts in physics
James Clerk Maxwell unified electricity and magnetism under the theoretical umbrella of Maxwell equations. We now refer to electricity/magnetism as the electromagnetic force. In the 70’s physicists were able to construct a single theoretical framework for the unification of the electromagnetic force with the weak-nuclear force which is a very short range force responsible for the transmutations of electron, muon, tau into neutrinos and vice versa. Weak-nuclear force is also responsible for some of the nuclear decays.
Physicists failed to unify the electroweak force with the strong-nuclear force which is a very short range force holding the nucleus of atoms together. Strong-nuclear force is also responsible for the stability of the proton. There is a theory known as GUT that tries to unify the electroweak force with the strong-nuclear force. GUT has not been experimentally verified yet.
Physicists also failed to unify the electroweak force with gravity. Einstein spent a lifetime trying to unify gravity with electromagnetism but failed. Other physicists did not have any luck either.
Problem: there are 4 forces and many fields
Unifying forces is different from unifying fields. There are 4 known forces: electromagnetic force, weak-nuclear force, strong-nuclear force, and gravity. Fields are many. Too many!
Some might argue that ‘field’ and ‘force’ are just two different words referring to the same entity in QFT (Quantum Field Theory). There is a subtlety here. There is the electron field and there is the electromagnetic field. The units of these fields (electron and photon, respectively) interact. QFT does not unify the electron field and the electromagnetic field. Rather, QFT describes the interactions among the units of these fields.
According to QFT each type of particle has its own field. This does not make sense to me. I hope physicists work towards unifying the fields. This effort is known as UFT (Unified Field Theory). UFT is an old fashioned name. UFT is an old fashioned project. Nobody talks about UFT these days.
Unification of the collective entities (fields) is more difficult than finding a unified description of the interactions among the units of those fields. With QFT we are able to explain the interactions between electrons and photons but we are unable to explain what electron is or what photon is. If we could unify the electron field and the electromagnetic field we would then have a unified description of electrons and photons.
Two different types of guiding principles
One of the broadly accepted guiding principles in physics is that the description of physical reality should be independent of the coordinate system we use. Einstein struggled with this during his ordeal to construct the covariant theory of gravitation.
Do not confuse “coordinate system” with “frame of reference”. The term “coordinate system” is about mathematical description whereas the term “frame of reference” is about physics. When we say “the speed of light in vacuum is the same in all frames of reference” we are stating a physics law. We are declaring an empirical fact. We should discriminate between the guiding principles Nature provides and the mathematical guiding principles rationality dictates.
Discovering symmetries (group theoretical approaches)
Discovering existing symmetries or proving that a particular symmetry appears to be broken now but it was in effect in an earlier epoch is considered as “unification”. There must be hundreds of articles and books about the importance of symmetries in the description of physical reality. I will point you to the PNAS article written by David J. Gross (winner of Nobel Prize in physics in 2004) for a grand overview.
“The role of symmetry in fundamental physics” by David J. Gross
Discovering equivalences or correspondences (also known as physics dualities)
Einstein noticed that it is impossible to distinguish gravity from acceleration. This is sometimes expressed in fancy wording like this: “The local effects of motion in a curved space (gravitation) are indistinguishable from those of an accelerated observer in flat space, without exception.” – Wikipedia. Starting from this observationally supported assumption (gravity/acceleration equivalence) Einstein was able to construct his theory of gravitation which later proved to be correct.
Juan M. Maldacena‘s AdS/CFT correspondence is widely discussed among theoretical physicists. This subject is above my head but I mention it here because many physicists discuss the unifying potential of it. AdS/CFT correspondence sheds light on this question: What can we learn about gravity from particle physics (gauge field theory)? (see Maldacena’s public talk )
A related correspondence is the applicability of gauge field theory in condensed matter physics.
“Physics duality” is different from “philosophical duality” or “mathematical duality”. In physics, “duality” means equivalence or correspondence. There are many types of dualities identified by physicists. It is worth considering dualities from a mathematician’s point of view as well.
“Duality in Mathematics and Physics” by Michael F. Atiyah
Discovering correspondences/dualities bring us closer to the unification ideal in physics.
Effective field theory as a unifying framework
The article titled “Philosophical Foundations of Effective Field Theories” summarizes the pros and cons of effective field theories and provides insights into the unifying potential in such theories.
Emergence as a unification theme
David Pines defines emergence as “collective phenomena or behaviors in complex adaptive systems that are not present in their individual parts.” [1] In another article R.B. Laughlin and David Pines declare that:
“The central task of theoretical physics in our time is no longer to write down the ultimate equations, but rather to catalogue and understand emergent behavior in its many guises, including potentially life itself. We call this physics of the next [21st] century the study of complex adaptive matter. For better or worse, we are now witnessing a transition from the science of the past, so intimately linked to reductionism, to the study of complex adaptive matter, firmly based in experiment, with its hope for providing a jumping-off point for new discoveries, new concepts, and new wisdom.” [2]
Speaking of complex adaptive systems and emergence, I think that the observations of theoretical biologist Howard H. Pattee are very relevant in the discussions of unification.
“Physical systems require many levels of models, some formally irreducible to one another, but we must still understand how the levels are related. Evolution also produces hierarchies of organization from cells to societies, each level requiring different models, but the higher levels of the hierarchy must have emerged from lower levels. Life must have emerged from the physical world. This emergence must be understood if our knowledge is not to degenerate (more than it has already) into a collection of disjoint specialized disciplines.” [3]
“There are fundamental reasons why physics and biology require different levels of models, the most obvious one is that physical theory is described by rate-dependent dynamical laws that have no memory, while evolution depends, at least to some degree, on control of dynamics by rate-independent memory structures.” [3]
Computation/Hypergraph
I find the computation/hypergraph approach of Stephen Wolfram very compelling.
“…even when the underlying rules for a system are extremely simple, the behavior of the system as a whole can be essentially arbitrarily rich and complex. And this got me thinking: Could the universe work this way? Could it in fact be that underneath all of this richness and complexity we see in physics there are just simple rules? I soon realized that if that was going to be the case, we’d in effect have to go underneath space and time and basically everything we know. Our rules would have to operate at some lower level, and all of physics would just have to emerge.” [4]
Please find my comments on Stephen Wolfram’s approach here. Even though he uses the term “emerge” I wouldn’t include his approach under the “emergence” theme. I think that the hypergraph approach is in a category by itself.
Primordial qubit network
Primordial qubit network paradigm is closer to the computation approach to unification. This hypothesis is in the early stages of development. Note that the “primordial qubit network” perspective is not the same as the “universe is a simulation in a quantum computer” perspective even though both assume qubit to be the most fundamental element. In the “primordial qubit network” perspective physicists are talking about the emergence of space-time-matter from the primordial qubits. Once the emergence takes place space-time-matter evolves according to its own laws. Even though the term “emergence” appears here I would treat the “primordial qubit network” approach as a distinct perspective.
Simulation
In the “universe is a simulation” perspective, the idea unification would be meaningless because one is not dealing with the laws. Everything happens according to the logic of the simulation code which can be very complex and sophisticated. The logic of the “code” is not necessarily expressible in terms of laws therefore “unification of laws” is meaningless.
An important contrast between the “Simulation” and “Hypergraph” is that the “rules” of the Hypergraph are presumed to be very simple. In the Hypergraph universe complexity emerges from repeated application of the simple rules. In the Simulation universe complexity does not emerge, complexity is built-in.
Information is physical approach
Scott Aaronson has a long commentary on the slogan “information is physical” which originated in this article by Rolf Landauer.
It from bit approach of John Wheeler
I found a very readable article written by Rachel Thomas on John Wheeler and his “it from bit” (original paper).
“It from bit symbolises the idea that every item of the physical world has at bottom — at a very deep bottom, in most instances — an immaterial source and explanation; that what we call reality arises in the last analysis from the posing of yes-no questions and the registering of equipment-evoked responses; in short, that all things physical are information-theoretic in origin and this is a participatory universe.” – John Wheeler
I think Wheeler is expressing Bohr’s views in different words. Someone else would interpret his words differently and find similarities between his views and Indian metaphysics. Regardless, I think that the term “all things physical are information-theoretic in origin” is probably too simplistic. The mystery is much deeper.
“this is a participatory universe” : I agree. But, not in the way Bohr (or Wheeler) meant it. See next section.
After the emergence of individual minds (agency)
It is clear that after the emergence of agency (individual minds) natural laws acquire new operational characteristics. Intelligent beings start taking advantage of the natural laws and determine the outcomes by using technology. This is different from the discussions of observer dependence in Quantum Mechanics. Participatory universe through “wavefunction collapse” sounds too simplistic.
Microvita
“Microvita are described as subatomic living entities giving rise to the formation of matter, life and mind in the universe.” – Richard Gauthier [5]
Microvita theory is not part of the scientific discourse yet but it will be. If I am so convinced why didn’t I write more on this subject? I don’t have a good answer. Microvita theory seems to be developing a new language not only for science but for spiritual philosophy as well. For the unification promise of the Microvita theory to be realized, researchers have to shrink the language gap by pointing out the correspondences as well as the differences between the developing Microvita theory and the existing theories of science. For more information on Microvita please visit the links mentioned in ‘Microvita links‘.
Search for a simpler theory
Unification of theories may not be possible after all…but there is value in this effort. The unification research program reflects the basic human desire to find a simpler theory.
References
[1] David Pines, Emergence: A unifying theme for 21st century science
[2] R.B. Laughlin & D. Pines, 2000. The Theory of Everything. PNAS 97: 28.
[3] Howard H. Pattee, “The Physics of Symbols: Bridging the Epistemic Cut”, Biosystems Vol. 60, pp. 5-21 (2001) https://www.informatics.indiana.edu/rocha/publications/pattee/pattee.html
[4] Stephen Wolfram, Finally We May Have a Path to the Fundamental Theory of Physics…
and It’s Beautiful
[5] Richard Gauthier https://www.academia.edu/43238583/Cosmology_and_Microvita also https://www.academia.edu/34184179/Microvita_Cosmic_Seeds_of_Life
Suresh Emre
Renaissance Universal 