Roger Penrose shows in his writings that he is more favorable to the theory of general relativity and to determinism in physics, and that he is more critical towards quantum mechanics, its description of reality, and its probabilistic formulation. Other physicists or scientists have somewhat similar or comparable views or opinions.
Many physicists seem to be trying to formulate a theory of quantum gravity. But there is a different or opposite approach highlighted by some insightful remarks by Penrose.
In a 2013 paper entitled “On the Gravitization of Quantum Mechanics 1: Quantum State Reduction”, Penrose wrote:
” This paper argues that the case for “gravitizing” quantum theory is at least as strong as that for quantizing gravity.Accordingly, the principles of general relativity must influence, and actually change, the very formalism of quantum mechanics. Most particularly, an“Einsteinian”,rather than a“Newtonian” treatment of the gravitational field should be adopted, in a quantum system,in order that the principle of equivalence be fully respected. This leads to an expectation that quantum superpositions of states involving a significant mass displacement should have a finite lifetime[…]”
Penrose continues:
” The title of this article contains the phrase “gravitization of quantum Mechanics” in contrast to the more usual “quantization of gravity”. This reversal of wording is deliberate, of course, indicating my concern with the bringing of quantum theory more in line with the principles of Einstein’s general relativity, rather than attempting to make Einstein’s theory—or any more amenable theory of gravity—into line with those of quantum mechanics (or quantum field theory).[…]
I think that people tend to regard the great twentieth century revolution of quantum theory, as a more fundamental scheme of things than gravitational theory. Indeed, quantum mechanics, strange as its basic principles seem to be, has no evidence against it from accepted experiment or observation, and people tend to argue that this theory is so well established now that one must try to bring the whole of physics within its compass.Yet, that other great twentieth century revolution, namely the general theory of relativity,is also a fundamental scheme of things which, strange as its basic principles seem to be, also has no confirmed experiments or observations that tell against it[…]”
Penrose thinks that it is essentially quantum mechanics that ought to be changed, not general relativity. In his book The Road to Reality, Penrose states:
” My own viewpoint is that the question of ‘reality’ must be addressed in quantum mechanics—especially if one takes the view (as many physicists appear to) that the quantum formalism applies universally to the whole of physics—for then, if there is no quantum reality, there can be no reality at any level (all levels being quantum levels, on this view). To me, it makes no sense to deny reality altogether in this way. We need a notion of physical reality, even if only a provisional or approximate one, for without it our objective universe, and thence the whole of science, simply evaporates before our contemplative gaze![…]
We must think of a wavefunction as one entire thing. If it causes a spot to appear at one place, then it has done its job, and this apparent act of creation forbids it from causing a spot to appear somewhere else as well. Wavefunctions are quite unlike the waves of classical physics in this important respect. The different parts of the wave cannot be thought of as local disturbances, each carrying on independently of what is happening in a remote region. Wavefunctions have a strongly non-local character; in this sense they are completely holistic entities.
[…]there are powerful positive reasons […] to believe that the laws of present-day quantum mechanics are in need of a fundamental (though presumably subtle) change. These reasons come from within accepted physical principles and from observed facts about the universe. Yet, I find it remarkable how few of today’s quantum physicists are prepared to entertain seriously the idea of an actual change in the ground rules of their subject. Quantum mechanics, despite its extraordinary exception-free experimental support and strikingly confirmed predictions, is a comparatively young subject, being only about three-quarters of a century old (dating this from the establishment of the mathematical theory by Dirac and others, based on the schemes of Heisenberg and Schrodinger, in the years immediately following 1925). When I say ‘comparatively’, I am comparing the theory with that of Newton, which lasted for nearly three times as long before it needed serious modification in the form of special and then general relativity, and quantum mechanics. […]
Moreover, Newton’s theory did not have a measurement paradox.[…]
Newton’s gravitational theory has the particular mathematical elegance that the gravitational forces always add up in a completely linear fashion; yet this is supplanted, in Einstein’s more precise theory, by a distinctly subtle type of non-linearity in the way that gravitational effects of different bodies combine together. And Einstein’s theory is certainly not short on elegance—of a quite different kind from that of Newton.[…]
Einstein’s theory […] involved a completely radical change in perspective. This, it seems to me, is the general kind of change in the structure of quantum mechanics that we must look towards, if we are to obtain the (in my view) needed non-linear theory to replace the present-day conventional quantum theory. Indeed, it is my own perspective that Einstein’s general relativity will itself supply some necessary clues as to the modifications that are required. The 20th century gave us two fundamental revolutions in physical thought— and, to my way of thinking, general relativity has provided as impressive a revolution as has quantum theory (or quantum Field theory). Yet, these two great schemes for the world are based upon principles that lie most uncomfortably with each other. The usual perspective, with regard to the proposed marriage between these theories, is that one of them, namely general relativity, must submit itself to the will of the other. There appears to be the common view that the rules of quantum Field theory are immutable, and it is Einstein’s theory that must bend itself appropriately to fit into the standard quantum mould. Few would suggest that the quantum rules must themselves admit to modification, in order to ensure an appropriately harmonious marriage. Indeed, the very name ‘quantum gravity’, that is normally assigned to the proposed union, carries the implicit connotation that it is a standard quantum (field) theory that is sought. Yet, I would claim that there is observational evidence that Nature’s view of this union is very different from this! I contend that her design for this union must be what, in our eyes, would be a distinctly non-standard one, and that an objective state reduction must be one of its important features.”
While recognizing the experimental verifications and successes of quantum physics, Penrose uses the word faith in relation to quantum mechanics, and thinks there are limitations to that “faith”.
The following quoted lines are taken from the book Fashion, Faith, and Fantasy in the New Physics of the Universe by Penrose:
” Quantum theory explains the phenomenon of chemical bonding, the colours and physical properties of metals and other substances, the detailed nature of the discrete frequencies of light that particular elements and their compounds emit when heated (spectral lines), the stability of atoms (where classical theory would predict a catastrophic collapse with the emission of radiation as electrons spiral rapidly into their atomic nuclei), superconductors, superfluids, Bose–Einstein condensates […]
When we combine quantum theory with special relativity we get quantum field theory, which is essential for, in particular, modern particle physics.[…]
Quantum theory is commonly regarded as a deeper theory than the classical scheme of particles and forces that had preceded it.[…]
The dogma of quantum mechanics is thus seen to be very well founded indeed, as it rests on an enormous amount of extremely hard evidence. With systems that are simple enough that detailed calculation can be carried out and sufficiently accurate experiments performed, we find an almost incredible precision in the agreement between the theoretical and observational results that are obtained.[…]
Perhaps the multitude of theoreticians involved in the formulation of quantum mechanics is a manifestation of the totally non-intuitive nature of that theory. Yet, as a mathematical structure, there is a remarkable elegance; and the deep coherence between the mathematics and physical behaviour is often as stunning as it is unexpected.[…]
Quantum mechanics provides, indeed, an overarching framework that would appear to apply to any physical process, at no matter what scale. There is perhaps no puzzle, therefore, in the fact that a profound faith has arisen among physicists, that all the phenomena of nature must adhere to it.[…]”
Penrose also mentions and criticizes the Copenhagen interpretation or view:
“According to standard quantum mechanics, the information in the quantum state of a system – or the wave function ψ – is what is needed for probabilistic predictions to be made for the results of experiments that might be performed upon that system.[…]
[According to the Copenhagen interpretation and] to various other schools of thought also, ψ is to be regarded as a calculational convenience with no ontological status other than to be part of the state of mind of the experimenter or theoretician, so that the actual results of observation can be probabilistically assessed. It seems that a good part of such a belief stems from the abhorrence felt by so many physicists that the state of the actual world could suddenly “jump” from time to time in the seemingly random way that is characteristic of the rules of quantum measurement.”
Moreover, Penrose is of the opinion that the de Broglie-Bohm theory, the pilot wave theory, or Bohmian mechanics
“provides an interesting alternative ontology to that provided (or not really provided!) by the Copenhagen view, and it is fairly widely studied, though certainly not qualifying as a fashionable theory. It claims no alternative observational effects from that of conventional quantum mechanics, but provides a much more clear-cut picture of the “reality” of the world.”
I think remarks, views and ideas similar to those of Roger Penrose ought to be taken into consideration. Quantizing gravity is not the only available option. It will be beneficial and useful if other alternatives such as those proposed by Penrose are considered, discussed, studied, and developed, in order to determine the best future direction for research, and formulate comprehensive appropriate consistent theoretical explanations and advances, with regard to gravity and to physics in general.
Knowledge mix 