Ockham's Razor and the Many Worlds Interpretation of Quantum Mechanics

The history of physics from ancient times to the modern day, focusing on quantum mechanics and the subjective nature of the mind. Some argue that the many worlds interpretation of quantum mechanics violates Ockham's razor, the idea that the simplest interpretation is most likely. This is untrue because the many worlds interpretation is simplest in this sense, it is mathematically simplest and does not violate any laws of physics.

Last updated on 5th June 2017 by Dr Helen Klus

1. Everett's many worlds interpretation

Proponents of American physicist Hugh Everett's many worlds interpretation of quantum mechanics claim that this approach solves the main problems faced by both the wave function collapse approach and the Bohm interpretation[1].

The measurement problem, which shows that it is impossible for quantum and classical objects to interact, is resolved by accepting the idea that macroscopic objects are described by the same laws as quantum objects. If we accept this, then the preferred basis problem, which asks why the universe is split into the 'separate worlds' we experience if it is really part of a multiverse, may be resolved with decoherence theory.

The problem of action at a distance does not occur within Everett's many worlds interpretation of quantum mechanics because all events are actualised, and so information regarding a specific result does not need to be sent.

Everett's many worlds interpretation of quantum mechanics is also preferable to other approaches because it applies to the universe as a whole, and so it can be used on a cosmological scale.

Everett's many worlds interpretation claims to resolve all of these problems without modifying the basic equations of quantum theory, but, by taking the theory of quantum mechanics literally, it does challenge some common sense assumptions.

2. Many worlds and Ockham's razor

Some are reluctant to accept Everett's many worlds interpretation because it relies on the existence of an infinite amount of other, unobservable worlds to account for our experiences in this one. It's sometimes claimed that this makes it unnecessarily extravagant, violating Ockham's razor, the idea that the simplest approach is preferable.

American physicist Bryce DeWitt admitted having these reservations when he first read about Everett's interpretation. He stated:

"I still recall vividly the shock I experienced on first encountering this multiworld concept. The idea of 10100+ slightly imperfect copies of oneself all constantly spitting into further copies, which ultimately become unrecognisable, is not easy to reconcile with common sense"[2].

However, proponents of Everett's many worlds interpretation reject the idea that it contradicts Ockham's razor and argue that, in fact, Ockham's razor favours Everett's many worlds interpretation.

Ockham's razor states that entities must not be multiplied beyond necessity, but this does not refer to the number of unobservable objects that a theory invokes. It refers to the number of mutually independent assumptions that a theory makes, and their individual complexity.

Everett's many worlds interpretation is simpler in Ockhamist terms because it solves all of the problems faced by the collapse and Bohm interpretations without adding extra structure to the theory of quantum mechanics. It is also mathematically simpler to describe a superpositional universe than to define all of the eccentricities of any particular one.

Everett responded to DeWitt's worries in a letter written in 1957. Everett stated that:

"A crucial point in deciding on a theory is that one does not accept or reject the theory on the basis of whether the basic world picture it presents is compatible with everyday experience. Rather, one accepts or rejects on the basis of whether or not the experience which is predicted by the theory is in accord with actual experience...Now in your letter you say, 'the trajectory of the memory configuration of a real physical observer, on the other hand, does not branch. I can testify to this from personal introspection, as can you. I simply do not branch.' I can't resist asking: Do you feel the motion of the earth?"[3].

Everett argued that it may be easier for us to believe that the Earth is stationary than to learn Newtonian physics, but in doing so we are making many assumptions that cannot be verified. Newtonian physics is preferable to the idea that the Earth is stationary because it can be derived from very few basic assumptions, and explains a wide variety of phenomena.

If we reject theories on the basis that they postulate unobservable entities, then we are taking an instrumentalist approach to science. This may involve rejecting the existence of anything that we cannot verify with our own eyes, including objects such as bacteria and the moons of Jupiter.

Instrumentalism has not been acceptable in astronomy since the 1600s, and also seems implausible when applied to fields such as chemistry and biology, which manipulate microscopic objects in order to produce macroscopic results.

Everett stated that objections to his interpretation on the grounds that it contradicts common sense seem:

"to be founded on the notion that the only purpose of a theory is to serve as a summary of known data, and overlooks the second major purpose, the discovery of totally new phenomena. The major purpose of this viewpoint appears to be the desire to construct perfectly 'safe' theories which will never be open to contradiction"[4a].

Everett concluded that:

"strict adherence to such a philosophy would probably stifle the progress of physics"[4b].

3. References

  1. Everett, H., III, 1957, ''Relative State' Formulation of Quantum Mechanics', Reviews of Modern Physics, 29, pp.454.

  2. DeWitt, B. and Graham, N., 1973, 'The Many Worlds Interpretation of Quantum Mechanics', Books on Demand.

  3. Everett, H., III, 1957, 'Everett's Letter to Bryce DeWitt of May 31, 1957', NOVA.

  4. (a, b) Everett, H., III, 1957, 'The Theory of the Universal Wavefunction', PhD thesis.

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Mind & Multiverse

Theories of the mind

1. Socrates' Rationalism

2. Descartes' Mind-Body Dualism

3. Locke's Empiricism

4. Hume's Epistemology

5. Materialism and Consciousness

6. Material theories of the Mind

7. Material Mind vs. Descartes

8. Scientific Realism

The mind and quantum mechanics

1. Many Worlds Interpretation

2. MWI and the Preferred Basis

3. MWI and Probability

4. MWI and Ockham's Razor

5. Many Minds Interpretation

6. Emergent Multiverse

7. Evidence of Parallel Worlds

8. Free will and Parallel-selves

9. Many Worlds and Biology