The Personal Website of Mark W. Dawson
Containing His Articles, Observations, Thoughts, Meanderings,
and some would say Wisdom (and some would say not).
The Copenhagen Interpretation
"Reality is the business of physics." - Albert Einstein
There are several important issues regarding the current science of Quantum Theory. The most basic is what is the reality underlying the Quantum world. The Copenhagen Interpretation is a collection of views about the meaning of quantum mechanics principally attributed to Niels Bohr and Werner Heisenberg. It is one of the oldest of numerous proposed interpretations of quantum mechanics, as the features of it date to the development of quantum mechanics during 1925–1927, and it remains one of the most commonly taught.
There is no definitive historical statement of what the Copenhagen interpretation is. There are some fundamental agreements and disagreements between the views of Bohr and Heisenberg. For example, Heisenberg emphasized a sharp "cut" between the observer (or the instrument) and the system being observed, while Bohr offered an interpretation that is independent of a subjective observer or measurement or collapse, which relies on an "irreversible" or effectively irreversible process, which could take place within the quantum system.
Features common to Copenhagen-type interpretations include the idea that quantum mechanics is intrinsically indeterministic, with probabilities calculated using the Born rule, and the principle of complementarity, which states that objects have certain pairs of complementary properties which cannot all be observed or measured simultaneously. Moreover, the act of "observing" or "measuring" an object is irreversible, and no truth can be attributed to an object except according to the results of its measurement. Copenhagen-type interpretations hold that quantum descriptions are objective; in that, they are independent of physicists' mental arbitrariness.
Over the years, there have been many objections to aspects of Copenhagen-type interpretations, including the discontinuous and randomness nature of the "observation" or "measurement" process, the apparent subjectivity of requiring an observer, the difficulty of defining what might count as a measuring device, and the seeming reliance upon classical physics in describing such devices.
The Copenhagen Interpretation is generally accepted by Quantum Physicists as the proper scientific theory about the Quantum world. However, it has been challenged by several notable physicists since its formulation, most notably by Einstein, who spent the latter part of his life on this challenge. The core objections to The Copenhagen Interpretation are:
Two Questions about Reality
- Does the natural world exist independently of our minds? More precisely, does matter have a stable set of properties in and of itself, without regard to our perceptions and knowledge?
- Can these properties be comprehended and described by us? Can we understand enough about the laws of nature to explain the history of our universe and predict its future?
Two Classes of Interpretation
- The Copenhagen Interpretation is essentially correct
- The Copenhagen Interpretation is incomplete
Two Classes of Quantum Physicists
- Anti-Realists - There is no underlying reality of Quantum Physics
- Realists - Quantum Physics should attempt to explain an underlying reality
Epistemology and Ontology Impacts
- Epistemology - The philosophical theory of knowledge
- Ontology - The metaphysical study of the nature of being and existence
Issues to be Resolved
- Nonlocality
- Superposition
- Entanglement
- Measurement
Deterministic vs. Probabilistic Universes
- Deterministic - An inevitable consequence of antecedent sufficient causes
- Probabilistic - of or relating to the probability of occurrence
Locality and Universality
- Locality - A particular area; the surrounding or nearby region
- Universality - The quality of being universal; existing everywhere
The Two Classes of Interpretation are that if you believe that the Copenhagen Interpretation is all there is to the Quantum world, or if you believe that the Copenhagen Interpretation does not explain the underlying reality of the Quantum world. The Two Questions about Reality reveal what type of Quantum Physicist you are. The realists answer yes to these questions, while anti-realists answer no. This reminds me of the two types of persons in the Harry Potter novels: Muggles (realists) and Wizards (anti-realists). Muggles take the side of Einstein, while Wizards take the side of Bohr and Heisenberg.
The Copenhagen Interpretation challenges the Ontology of our universe, as one of its foundations is that reality doesn't exist until we measure it. This idea led Einstein to ask, "Does the Moon exist only when someone was looking at it?" This question is at the heart of the ontological question of the Copenhagen Interpretation. By not addressing the ontological question, the Copenhagen Interpretation relies on the Epistemology of Quantum Physics and responds that the Quantum world is unknowable and, therefore, need not be examined. Ontological and Epistemological questions need to be answered by science to understand the reality of our Universe. By avoiding these questions, the Copenhagen Interpretation is not meeting the requirements or expectations of physics to explain the fundamental properties of the Universe.
The Copenhagen Interpretation has four issues that bedevil it regarding the question of the Copenhagen Interpretation being a description of reality.
Quantum nonlocality is a principle in quantum mechanics that says quantum particles can "know" the states of other quantum particles, even at great distances, and correlate their behaviors with each other instantaneously (i.e., instantaneous action-at-a-distance). While classical physics assumes locality, the principle of nonlocality is a feature of many interpretations of quantum mechanics. Nonlocality appears to be a feature of even the original interpretation of quantum mechanics, the Copenhagen Interpretation, though it remains implicit in this interpretation rather than being explicitly called out. The equations which describe quantum entanglement seem to tell us that two particles across the universe from each other can correlate their behavior simultaneously. Simultaneous is faster than the speed of light, and lab experiments that demonstrate quantum entanglement have shown this to be true.
Quantum superposition is a fundamental principle of quantum mechanics. It states that, much like waves in classical physics, any two (or more) quantum states can be added together ("superposed"), and the result will be another valid quantum state; and conversely, that every quantum state can be represented as a sum of two or more other distinct states. Mathematically, it refers to a property of solutions to the Schrödinger equation; since the Schrödinger equation is linear, any linear combination of solutions will also be a solution. It is also the basis for the paradox of Schrödinger's cat.
Quantum entanglement is a physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics lacking in classical mechanics.
The Measurement problem is the problem of how or whether wave function collapse occurs. The inability to observe such a collapse directly has given rise to different interpretations of quantum mechanics and poses a key set of questions that each interpretation must answer.
The Quantum nonlocality, Quantum superposition, Quantum entanglement, and the Measurement problems are often grouped together as the Copenhagen interpretation are the oldest and, collectively, probably still the most widely held attitude about quantum mechanics. N. David Mermin coined the phrase "Shut up and calculate!" to summarize Copenhagen-type views, a saying often misattributed to Richard Feynman and which Mermin later found insufficiently nuanced. Shut up and compute is useful to solve problems in Quantum Physics, but it is not useful in understanding the underlying reality of the Quantum universe. It was these problems that led Einstein and other physicists to challenge the Copenhagen Interpretation as a description of the reality underlying the Quantum world.
The Heisenberg uncertainty principle, first introduced in 1927 by the German physicist Werner Heisenberg, states that the more precisely the position of some particle is determined, the less precisely its momentum can be predicted from initial conditions, and vice versa. The uncertainty principle implies that it is, in general, not possible to predict the value of a quantity with arbitrary certainty, even if all initial conditions are specified. In a Deterministic Universe, if you knew the properties of a starting point, then the forces acting upon the starting point, you could then predict the result. In a Probabilistic Universe, you can only predict possible limited outcomes. General and Special Relativity observations and experiments indicate that we live in a Deterministic Universe, while Quantum Physics observations and experiments have shown that regarding atomic and sub-atomic particles, we live in a Probabilistic Universe. It is this dichotomy that is of concern for modern physics, leading to much scientific speculation and (heated) debates. The Uncertainty principle also has a role in determining the underlying reality of the Quantum world.
The Copenhagen Interpretation deals only with atomic and sub-atomic events, but Quantum Physics needs to be reconciled with Einstein's General and Special Theories of Relativity to be universal. The Nonlocality of Quantum Physics conflicts with Special Relativity, and logically you cannot have a universe where both are true. However, both have been proven to be true, and this issue needs a resolution to understand the reality of our universe. In addition, Quantum Physics needs to be reconciled with the gravity of General Relativity, as gravity in the Copenhagen Interpretation plays no part in Quantum Physics.
The Loop quantum gravity interpretation is one of many other Interpretations that attempt to reconcile Relativity and the Quantum universe. Loop quantum gravity (LQG) is a theory of quantum gravity, which aims to merge quantum mechanics and general relativity, incorporating matter of the Standard Model into the framework established for the pure quantum gravity case. It is an attempt to develop a quantum theory of gravity based directly on Einstein's geometric formulation rather than the treatment of gravity as a force. As a theory, LQG postulates that the structure of space and time is composed of finite loops woven into an extremely fine fabric or network. These networks of loops are called spin networks. The evolution of a spin network, or spin foam, has a scale above the order of a Planck length, approximately 10 to the minus 35 meters, as smaller scales are meaningless. Consequently, not just matter, but space itself, prefers an atomic structure.
A good book that is readable and understandable by the general public, Einstein's Unfinished Revolution: The Search for What Lies Beyond the Quantum by Lee Smolin, looks at these issues and the repercussions of the possible answers to these questions. Lee Smolin is an American theoretical physicist, a faculty member at the Perimeter Institute for Theoretical Physics, an adjunct professor of physics at the University of Waterloo, and a member of the graduate faculty of the philosophy department at the University of Toronto. He is also a Muggle and one of the originators of Loop quantum gravity, but the book presents a fair and balanced examination between Muggles and Wizard's viewpoints.
The above issues and questions, along with the correct answers, needs to be resolved for Physics to make its next great advancement. These answers will help a great deal in solving The 18 Biggest Unsolved Mysteries in Physics.
Disclaimer
Please note that my Science Articles disclaimer applies to this article, as it does to all of my science articles. These science articles are for the purposes of general scientific information that is understandable to a layperson, so that they can grasp the concepts of the topic being discussed. As such, they are neither as accurate nor as thorough as academics, scientists, engineers, and science writers strive to achieve. My hope is that these science articles will be informative and interesting, and that they will pique the reader's interest in exploring these topics in further detail via the hyperlinks that I have embedded into these articles.
If you have any comments, concerns, critiques, or suggestions I can be reached at mwd@profitpages.com.
I will review reasoned and intellectual correspondence, and it is possible that I can change my mind,
or at least update the content of this article.