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Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences

Uncertainty in quantum mechanics: faith or fantasy?

Roger Penrose

Published Oct 31, 2011• 31 citations
Publisher

Abstract

The word 'uncertainty', in the context of quantum mechanics, usually evokes an impression of an essential unknowability of what might actually be going on at the quantum level of activity, as is made explicit in Heisenberg's uncertainty principle, and in the fact that the theory normally provides only probabilities for the results of quantum measurement. These issues limit our ultimate understanding of the behaviour of things, if we take quantum mechanics to represent an absolute truth. But they do not cause us to put that very 'truth' into question. This article addresses the issue of quantum 'uncertainty' from a different perspective, raising the question of whether this term might be applied to the theory itself, despite its unrefuted huge success over an enormously diverse range of observed phenomena. There are, indeed, seeming internal contradictions in the theory that lead us to infer that a total faith in it at all levels of scale leads us to almost fantastical implications.

DOI
10.1098/rsta.2011.0179

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The word 'uncertainty', in the context of quantum mechanics, usually evokes an impression of an essential unknowability of what might actually be going on at the quantum level of activity, as is made explicit in Heisenberg's uncertainty principle, and in the fact that the theory normally provides only probabilities for the results of quantum measurement. These issues limit our ultimate understanding of the behaviour of things, if we take quantum mechanics to represent an absolute truth. But they do not cause us to put that very 'truth' into question. This article addresses the issue of quantum 'uncertainty' from a different perspective, raising the question of whether this term might be applied to the theory itself, despite its unrefuted huge success over an enormously diverse range of observed phenomena. There are, indeed, seeming internal contradictions in the theory that lead us to infer that a total faith in it at all levels of scale leads us to almost fantastical implications.
In classical physics there is, in accordance with common sense, an objective world ‘out there’. That world evolves in a clear and deterministic way, being governed by precisely formulated mathematical equations. This is as true for the theories of Maxwell and Einstein as it is for the original Newtonian scheme. Physical reality is taken to exist independently of ourselves; and exactly how the classical world ‘is’ is not affected by how we might choose to look at it. Moreover, our bodies and our brains are themselves to be part of that world. They, also, are viewed as evolving according to the same precise and deterministic classical equations. All our actions are to be fixed by these equations - no matter how we might feel that our conscious wills may be influencing how we behave. Such a picture appears to lie at the background of most serious 1 philosophical arguments concerned with the nature of reality, of our conscious perceptions, and of our apparent free will. Some people might have an uncomfortable feeling that there should also be a role for quantum theory - that fundamental but disturbing scheme of things which, in the first quarter of this century, arose out of observations of subtle discrepancies between the actual behaviour of the world and the descriptions of classical physics. To many, the term ‘quantum theory’ evokes merely some vague concept of an ‘uncertainty principle’, which, at the level of particles, atoms or molecules, forbids precision in our descriptions and yields merely probabilistic behaviour. Actually, quantum descriptions are very precise, as we shall see, although radically different from the familiar classical ones. Moreover, we shall find, despite a common view to the contrary, that probabilities do not arise at the minute quantum level of particles, atoms, or molecules - those evolve deterministically - but, seemingly, via some mysterious larger-scale action connected with the emergence of a classical world that we can consciously perceive. We must try to understand this, and how quantum theory forces us to change our view of physical reality.
The quantum mechanical uncertainty principle for position and momentum plays an important role in many treatments on the (philosophical, physical and other) implications of quantum mechanics. Roughly speaking, the more precisely the momentum (position) of a (quantum mechanical) object is given, the less precisely can one say what its position (momentum) is. This quantum mechanical measurement problem is not just an interpretational difficulty, it raises broader issues as well. The measurement (of a property) of a (quantum mechanical) object determines the existence of the measured. In brief, the quantum mechanical uncertainty principle challenges some fundamental principles of Science and especially the principle of causality. In particular, an independently existing (external) objective reality is denied. As we shall see, that the quantum mechanical uncertainty principle for position and momentum is based on the assumption that 1⩽0, which is a logical contradiction.
The quantum mechanical uncertainty principle for position and momentum plays an important role in many treatments on the (philosophical, physical and other) implications of quantum mechanics. Roughly speaking, the more precisely the momentum (position) of a (quantum mechanical) object is given, the less precisely can one say what its position (momentum) is. This quantum mechanical measurement problem is not just an interpretational difficulty, it raises broader issues as well. The measurement (of a property) of a (quantum mechanical) object determines the existence of the measured. In brief, the quantum mechanical uncertainty principle challenges some fundamental principles of Science and especially the principle of causality. In particular, an independently existing (external) objective reality is denied. As we shall see, that the quantum mechanical uncertainty principle for position and momentum is based on the assumption that 1⩽0, which is a logical contradiction.
Are General Relativity and Quantum Mechanics incompatible? Each in their world, that of the infinitely large and that of the infinitely small, they did not seem to interfere as long as they avoided each other. However, it is their fundamental oppositions that prevent the scientific community from achieving a unification of physics. The proposal of this paper is to provide a mathematical proof of incompatibility, beyond the fact that they have fundamentally different principles, between the foundations of General Relativity and Quantum Mechanics, namely the deformation of the space-time geometry and the Uncertainty Principle. It will thus be possible to provide an absolute limitation in establishing a unifying theory of physics, if any. Moreover, while respecting the conditions fixed by the Uncertainty Principle, it will be tempted to determine with accuracy and simultaneity, the position and the speed of a non-relativistic particle, by application of relativistic principles and bypassing the problems raised by such an operation. The Uncertainty Principle as stated by Werner Heisenberg will be then, in the light of observations made on the measurement of the time dilatation and in accordance with its own terms, refuted by the present. - Physics Essays, Volume 31, Issue 3 (September 2018), Article 12 - https://physicsessays.org/browse-journal-2/product/1667-12-alexandre-georges-incompatibility-between-einstein-s-general-relativity-and-heisenberg-s-uncertainty-principle.html
The notion of uncertainty in the description of a physical system has assumed prodigious importance in the development of quantum theory. Overcoming the early misunderstanding and confusion, the concept grew continuously and still remains an active and fertile research field. Curious new insights and correlations are gained and developed in the process with the introduction of new 'measures' of uncertainty or indeterminacy and the development of quantum measurement theory. In this article we intend to reach a fairly uptodate status report of this yet unfurling concept and its interrelation with some distinctive quantum features like nonlocality, steering and entanglement/ inseparability. Some recent controversies are discussed and the grey areas are mentioned.
The theory of quantum mechanics, as formulated by the Copenhagen school, has been controversial since its inception. Heisenberg’s uncertainty principle asserts that certain aspects of reality are not simultaneously defined, forbidding certain questions. Recognition has recently been given to experimentalists who have asked these “forbidden questions”. Aephraim Steinberg at the University of Toronto conducted the double slit experiment using weak measurements to construct average trajectories of particles traveling through both slits. To an adherent of the Copenhagen view of reality, however, these average trajectories will constitute nothing more than a mathematical contrivance. Experiments like these will only prove fruitful if we are willing to reject quantum mechanics’ restrictive philosophical approach. This paper will isolate the controversial physical postulate of quantum mechanics (the postulate of wave collapse) and the philosophical approach that gave rise to it. This approach reflects an instrumentalist philosophy which claims that science must only account for the results of measurements, and has nothing to say about their underlying causes. Such an approach has put an epistemic moratorium on discovering the causes underlying quantum phenomena. Notable progress has been made by those who reject this moratorium. Steinberg et al. found the average particle trajectories by rejecting the idea that there is no underlying reality to our measurements. Bell, more notably, was able to discover details of quantum entanglement by using his concept of “beables” to question the built-in epistemology of quantum mechanics. Because quantum mechanics does not explicitly define wave collapse and prescribe what causes it and when it is supposed to happen, the theory cannot give explicit solutions to a certain class of experiments. This so called measurement problem is assuaged by Zurek’s theory of decoherence, which has had great success in predicting the results of recent experiments. Despite this, decoherence contains the same philosophical oversights as the original theory; it does not propose, or even address, the issue of the underlying causes for quantum phenomena. While most scientists try to steer clear of such philosophical controversies, underlying causes cannot be discovered without the conviction that it is the job of science to discover them.