Quantum Realities: Twelve Ways to View the Subatomic
An Introduction to the Main Scientific Interpretations of Quantum Phenomena
I was recently reading a book in which the author argued that civilization should be structured principally around scientific observation rather than abstract philosophical and religious ideas. One of the main issues with this argument (although it is not entirely unwarranted) is that the author fails to realize that even rigorous scientific observation requires abstract interpretation.
No matter how much empirical scientific research is conducted, it is always subject to the idiosyncratic parsing of the human mind. Thomas Kuhn recognized this when he wrote his book, The Structure of Scientific Revolutions.
Science is only capable of advancing in its grasp of reality in as much as it is able to transcend its own limiting paradigms which rigidly hold onto certain models to the exclusion of others.
These paradigms can become dogmatic, refusing to fund or publish research that implies worldviews outside their own.
The claim that scientific observation is subject to multiple interpretations is perfectly demonstrated by the fact that there are no less than 12 interpretations of quantum physics.
While the Copenhagen Interpretation is often assumed to be the correct interpretation by various authors as well as the lay public, it is but one of a dozen ways to interpret the data in quantum physics.
So, in the interest of getting a better “lay of the land” in terms of quantum physics, let’s take a look at the 12 main schools of thought around quantum mechanics.
1. Copenhagen Interpretation
“If I were to sum up in one sentence what the Copenhagen interpretation says to me it would be ‘Shut up and calculate!’"
—N. David Mermin1
This is considered to be the "standard" view of quantum physics, with emphasis on wavefunction collapse upon measurement, and probabilities governing outcomes. It’s pragmatic but vague on what constitutes a measurement.
Fundamental Principles
Quantum systems are described by a wavefunction, a mathematical tool that gives probabilities for outcomes.
When you measure something (like a particle’s position), the wavefunction “collapses” to one outcome.
Before measurement, the system is in a mix of all possible states (superposition).
Doesn’t explain what causes collapse or what a “measurement” really is.
Main Thinkers/Scientists
Niels Bohr developed the core ideas of the Copenhagen interpretation like complementarity and the role of classical concepts.
Werner Heisenberg formulated the uncertainty principle and emphasized observable outcomes.
Max Born introduced the statistical interpretation of the wavefunction.
Erwin Schrödinger contributed the wave equation, though he was skeptical of some of the Copenhagen ideas.
Key Books
Atomic Theory and the Description of Nature by Niels Bohr (1934)
The Physical Principles of the Quantum Theory by Werner Heisenberg (1930)
Quantum Mechanics by Albert Messiah (1961)
Scientific Experiments
Double-Slit Experiment (ongoing since 1927): Shows wave-particle duality; Bohr used it to explain complementarity.
Stern-Gerlach Experiment (1922): Demonstrated quantized spin, supporting the need for probabilistic outcomes.
EPR Paradox Thought Experiment (1935): Einstein, Podolsky, and Rosen challenged Copenhagen’s completeness, prompting debates.
2. Many Worlds Interpretation (MWI)
Proposes that all possible outcomes of a quantum event occur in separate, non-communicating parallel universes. Instead of a collapsing wavefunction, the universe branches.
Fundamental Principles
All possible outcomes of a quantum event actually happen.
Each outcome occurs in a separate, parallel universe that can’t interact with others.
In the absence of a wavefunction collapse, the universe just branches into new realities.
Explains probabilities as how likely you are to end up in one branch.
Main Thinkers/Scientists
Hugh Everett III proposed MWI in his 1957 PhD thesis.
Bryce DeWitt popularized MWI in the 1970s, coining the term “many worlds.”
John Archibald Wheeler served as Everett’s advisor and initially supported MWI.
David Deutsch advocated for MWI’s implications to be applied to quantum computing.
Key Books
The Many-Worlds Interpretation of Quantum Mechanics by Bryce DeWitt and Neill Graham (1973)
The Fabric of Reality by David Deutsch (1997)
The Hidden Reality by Brian Greene (2011)
Scientific Experiments
Decoherence Experiments (ongoing since 1990s): Studies like those by Wojciech Zurek show how quantum states lose coherence, supporting MWI’s branching via environmental interactions.
Quantum Interference Experiments (e.g., Mach-Zehnder Interferometer, 1980s–present): Demonstrate superposition, consistent with MWI’s non-collapse view.
3. Transactional Interpretation
Suggests quantum events involve a "handshake" between forward- and backward-in-time waves, resolving probabilities in a time-symmetric way.
Fundamental Principles
Particles send out “offer” waves forward in time and “confirmation” waves backward in time.
When these waves meet, they form a “handshake” that decides the outcome.
Explains quantum weirdness (like entanglement) as events connected across time.
Time-symmetric: past and future both matter.
Main Thinkers/Scientists
John G. Cramer developed the interpretation in 1986.
Ruth Kastner expanded it with a “possibilist” version, addressing criticisms.
Key Books
The Transactional Interpretation of Quantum Mechanics: The Reality of Possibility by Ruth Kastner (2013)
The Quantum Handshake by John G. Cramer (2016)
Scientific Experiments
Delayed-Choice Quantum Eraser (1999): Experiments like those by Yoon-Ho Kim et al. show retrocausal effects which aligns with the interpretation’s symmetrical view of time.
Wheeler’s Delayed-Choice Experiment (1978–present): Supports the idea that quantum events may depend on future conditions, which is consistent with the handshake model.
4. Bohmian Mechanics (Pilot-Wave Theory)
“In Bohmian mechanics a system of particles is described in part by its wave function, evolving, as usual, according to Schrödinger's equation. However, the wave function provides only a partial description of the system. This description is completed by the specification of the actual positions of the particles. The latter evolve according to the "guiding equation," which expresses the velocities of the particles in terms of the wave function. Thus, in Bohmian mechanics the configuration of a system of particles evolves via a deterministic motion choreographed by the wave function.”
—SpaceandMotion.com2
A deterministic view where particles have definite positions guided by a quantum wavefunction. Non-local effects explain correlations.
Fundamental Principles
Particles always have exact positions and follow clear paths.
A “pilot wave” (part of the wavefunction) guides particles like a map.
Deterministic: if you knew the starting conditions, you could predict everything.
Non-local: particles can instantly affect each other, no matter how far apart.
Main Thinkers/Scientists:
Louis de Broglie proposed the pilot-wave idea in the 1920s.
David Bohm revived and formalized it in 1952.
John Bell supported Bohmian mechanics and explored its non-locality.
Partha Ghose extended Bohmian trajectories to bosons and photons.
Key Books
Quantum Mechanics by David Bohm (1951)
The Undivided Universe by David Bohm and Basil Hiley (1993)
Bohmian Mechanics by Detlef Dürr, Stefan Teufel, and Sheldon Goldstein (2009)
Scientific Experiments
Weak Measurement Experiments (2010s): Experiments by Aephraim Steinberg and others traced particle trajectories, which match Bohmian predictions.
Hydrodynamic Analog Experiments (2006–present): Yves Couder and Emmanuel Fort’s work with oil droplets supports the pilot-wave idea by its mimicry of quantum behavior.
5. Objective Collapse Theories
Proposes that wavefunction collapse happens spontaneously (e.g., GRW model), independent of measurement, with specific physical mechanisms.
Fundamental Principles
Wavefunctions collapse randomly at tiny scales (like atoms) without needing an observer.
Collapse is a physical process, like a law of nature.
Explains why big objects (like a cat) don’t act quantum-weird.
Examples: GRW (Ghirardi-Rimini-Weber) model.
Main Thinkers/Scientists
GianCarlo Ghirardi, Alberto Rimini, and Tullio Weber developed the GRW model in 1986.
Philip Pearle contributed to continuous spontaneous localization models.
Roger Penrose linked collapse to gravity in speculative models.
Key Books
Sneaking a Look at God’s Cards by GianCarlo Ghirardi (2005)
Do We Really Understand Quantum Mechanics? by Franck Laloë (2012)
Scientific Experiments
Collapse Tests (ongoing since 1990s): Experiments like those by Markus Arndt test for spontaneous collapse by probing large molecules in superposition.
Gravitational Collapse Experiments (proposed): Penrose’s ideas inspire tests like those using optomechanical systems to detect gravity-induced collapse.
6. Quantum Bayesianism (QBism).
Treats quantum states as subjective probabilities reflecting an observer’s knowledge, not objective reality. Emphasizes personal belief over physical ontology.
Fundamental Principles
Quantum states are just your personal bets on what a measurement will show.
Wavefunctions are tools for updating your knowledge, not physical things.
Reality is subjective: different observers can have different “truths.”
Focuses on experience, not what the universe “really” is.
Main Thinkers/Scientists
Christopher Fuchs is the leading proponent of QBism.
N. David Mermin has advocated QBism’s subjective approach.
Rüdiger Schack developed Bayesian foundations for QBism.
Key Books
Coming of Age with Quantum Information by Christopher Fuchs (2011)
Bananaworld: Quantum Mechanics for Primates by Jeffrey Bub (2016)
Scientific Experiments
Quantum State Tomography (1990s–present): Experiments reconstructing quantum states align with QBism’s view of states as knowledge.
Bell Test Experiments (1980s–present): QBism interprets non-locality as constraints on observer beliefs, consistent with results.
7. Consistent Histories
Focuses on sets of possible histories for a system, assigning probabilities to consistent sequences of events. Avoids collapse but is mathematically complex.
Fundamental Principles
Quantum systems have many possible histories (sequences of events).
You can assign probabilities to “consistent” histories that don’t contradict each other.
No collapse; you just pick a history to focus on.
Useful for cosmology but hard to apply practically.
Main Thinkers/Scientists
Robert Griffiths introduced the interpretation in 1984.
Murray Gell-Mann and James Hartle extended it to quantum cosmology.
Roland Omnès developed mathematical frameworks for consistent histories.
Key Books
Consistent Quantum Theory by Robert Griffiths (2002)
The Quantum Universe by Roland Omnès (1999)
Scientific Experiments
Decoherence Studies (1990s–present): Experiments by Zurek and others support the role of environmental interactions in selecting consistent histories.
Quantum Cosmology Models (1980s–present): Theoretical models test consistent histories in early universe scenarios.
8. Relational Quantum Mechanics
“In a theory of this kind, time and space are no longer containers or general forms of the world. They are approximations of a quantum dynamic that in itself knows neither space nor time. There are only events and relations. It is a world without time of elementary physics.”
—Carlo Rovelli3
Argues quantum states are relative to the observer or system, with no absolute state. Context is key; resembles QBism in some ways.
Fundamental Principles
A quantum system’s state is only meaningful relative to an observer or another system.
There is no absolute “truth” about a system; it’s all about relationships.
Measurements are interactions between systems, not cosmic rules.
Similar to QBism but emphasizes interactions over beliefs.
Main Thinkers/Scientists
Carlo Rovelli proposed the interpretation in 1996.
David Mermin influenced relational ideas through QBism connections.
Časlav Brukner explored relational aspects in quantum information.
Key Books
The Order of Time by Carlo Rovelli (2018)
Scientific Experiments
Quantum Contextuality Experiments (2000s–present): Tests like those by Adán Cabello show observer-dependent outcomes, supporting relational views.
Wigner’s Friend Thought Experiment (1961, revisited 2018): Extended versions test observer relativity, aligning with RQM.
9. Modal Interpretation
Assigns definite properties to systems between measurements, avoiding collapse, but struggles with defining which properties are "real."
Fundamental Principles
Quantum systems have some real properties at all times, not just when measured.
Which properties are “real” depends on the system’s state.
Tries to avoid collapse but struggles to pick which properties matter.
Less popular due to technical issues.
Main Thinkers/Scientists
Bas van Fraassen introduced modal ideas in 1972.
Dennis Dieks developed the interpretation in the 1980s.
Pieter Vermaas refined modal frameworks.
Key Books:
Quantum Mechanics: An Empiricist View by Bas van Fraassen (1991)
Modal Interpretations of Quantum Mechanics by Dennis Dieks and Pieter Vermaas (1998)
Scientific Experiments:
Decoherence Experiments (1990s–present): Support modal ideas by showing how environments select properties.
Weak Measurement Experiments (1988–present): Reveal properties between measurements, consistent with modal views.
10. Ensemble Interpretation
Views quantum mechanics as describing statistical ensembles of systems, not individual events. Sidesteps ontology but is incomplete for single systems.
Fundamental Principles
Quantum rules describe averages over many identical systems (an ensemble).
Doesn’t say much about single particles or events.
Avoids weirdness like collapse by staying statistical.
Limited because it sidesteps individual cases.
Main Thinkers/Scientists
Albert Einstein advocated a statistical view and was skeptical of the Copenhagen interpretation.
Leslie Ballentine formalized the ensemble interpretation in 1970.
Alfred Landé promoted statistical approaches in textbooks.
Key Books
Quantum Mechanics: A Modern Development by Leslie Ballentine (1998)
The Conceptual Development of Quantum Mechanics by Max Jammer (1966)
Scientific Experiments
Statistical Ensembles in Quantum Optics (1970s–present): Experiments with photon ensembles confirm Born’s statistical rule.
Bell Test Experiments (1980s–present): Ensemble interpretation aligns with statistical outcomes, though non-locality poses challenges.
11. Information-Based Interpretations
Treat quantum mechanics as fundamentally about information flow or constraints, often aligning with QBism or digital physics ideas.
Fundamental Principles
Quantum states are about the information you can know or share.
Reality might be built from information, like code in a computer.
Often aligns with QBism or ideas about digital physics.
Still developing; not a single, clear theory.
Main Thinkers/Scientists
John Archibald Wheeler proposed “it from bit” in 1990.
Anton Zeilinger linked quantum mechanics to information principles.
Christopher Timpson explored philosophical implications.
Key Books
Information and the Nature of Reality edited by Paul Davies and Niels Henrik Gregersen (2010)
Quantum Information Theory and the Foundations of Quantum Mechanics by Christopher Timpson (2013)
Scientific Experiments
Quantum Teleportation (1997–present): Experiments by Zeilinger’s group show information transfer, supporting information-centric views.
Quantum Cryptography Experiments (1980s–present): Demonstrate quantum mechanics as an information protocol.
12. Stochastic Mechanics
Proposes quantum behavior arises from underlying stochastic (random) processes, though less developed than others.
Fundamental Principles
Quantum behavior is caused by tiny, random fluctuations we can’t see.
Particles move like they’re in a choppy sea, creating wave-like patterns.
Tries to make quantum mechanics less mysterious but isn’t fully developed.
Less popular due to lack of clear predictions.
Main Thinkers/Scientists
Edward Nelson proposed stochastic mechanics in 1966.
Francesco Calogero elaborated on stochastic conjectures.
Luis de la Peña linked stochastic processes to zero-point fields.
Key Books
Dynamical Theories of Brownian Motion by Edward Nelson (1967)
Quantum Mechanics as an Emergent Property by Luis de la Peña et al. (2009)
Scientific Experiments
Zero-Point Field Experiments (1990s–present): Studies of vacuum fluctuations support stochastic underpinnings.
Stochastic Electrodynamics Simulations (2000s–present): Numerical experiments by de la Peña’s group replicate quantum distributions.
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N. David Mermin (2016). “Why Quark Rhymes with Pork: And Other Scientific Diversions,” p.38, Cambridge University Press
Spaceandmotion.com. (n.d.). Quantum physics: Bohmian mechanics, pilot wave theory. Retrieved July 10, 2025, from https://www.spaceandmotion.com/physics-quantum-bohmian-mechanics.htm
Rovelli, C. (2018). The order of time (S. Carnell & E. Segre, Trans.). Riverhead Books.