The

**many-minds interpretation** of

quantum mechanicsQuantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

extends the

many-worlds interpretationThe many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternative histories and futures are real, each representing an...

by proposing that the distinction between worlds should be made at the level of the

mindThe concept of mind is understood in many different ways by many different traditions, ranging from panpsychism and animism to traditional and organized religious views, as well as secular and materialist philosophies. Most agree that minds are constituted by conscious experience and intelligent...

of an individual observer. The concept was first introduced in 1970 by

H. Dieter ZehHeinz-Dieter Zeh , is a Professor Emeritus of the University of Heidelberg and theoretical physicist...

as a variant of the

Hugh EverettHugh Everett III was an American physicist who first proposed the many-worlds interpretation of quantum physics, which he termed his "relative state" formulation....

interpretation in connection with

quantum decoherenceIn quantum mechanics, quantum decoherence is the loss of coherence or ordering of the phase angles between the components of a system in a quantum superposition. A consequence of this dephasing leads to classical or probabilistically additive behavior...

, and later (in 1981) explicitly called a many or multi-consciousness interpretation. The name

*many-minds interpretation* was first used by

David AlbertDavid Z Albert, Ph.D., is Frederick E. Woodbridge Professor of Philosophy and Director of the M.A. Program in The Philosophical Foundations of Physics at Columbia University in New York. He received his B.S. in physics from Columbia College and his doctorate in theoretical physics from The...

and

Barry LoewerBarry Loewer is a philosopher and Chairperson of the Rutgers University Department of Philosophy and director of the . He obtained his BA from Amherst College and his PhD from Stanford...

in their 1988 work

*Interpreting the Many Worlds Interpretation*.

## The central problems

One of the central problems in interpretation of quantum theory is the duality of time evolution of physical systems:

- Unitary evolution by the Schrödinger equation
The Schrödinger equation was formulated in 1926 by Austrian physicist Erwin Schrödinger. Used in physics , it is an equation that describes how the quantum state of a physical system changes in time....

- Nondeterministic, nonunitary change during measurement of physical observable
In physics, particularly in quantum physics, a system observable is a property of the system state that can be determined by some sequence of physical operations. For example, these operations might involve submitting the system to various electromagnetic fields and eventually reading a value off...

s, at which time the system "selects" a single value in the range of possible values for the observable. This process is known as wavefunction collapseIn quantum mechanics, wave function collapse is the phenomenon in which a wave function—initially in a superposition of several different possible eigenstates—appears to reduce to a single one of those states after interaction with an observer...

. Moreover, the process of observation occurs outside the system, which presents a problem on its own if one considers the universe itself to be a quantum system. This is known as the measurement problemThe measurement problem in quantum mechanics is the unresolved problem of how wavefunction collapse occurs. The inability to observe this process directly has given rise to different interpretations of quantum mechanics, and poses a key set of questions that each interpretation must answer...

.

In the introduction to his paper,

*The Problem Of Conscious Observation In Quantum Mechanical Description* (June 2000), H.D. Zeh offered an empirical basis for connecting the processes involved in (2) with conscious observation:

### The many-worlds interpretation

Hugh EverettHugh Everett III was an American physicist who first proposed the many-worlds interpretation of quantum physics, which he termed his "relative state" formulation....

described a way out of this problem by suggesting that the

universeThe Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

is in fact indeterminate as a whole. That is, if you were to measure the

spinIn quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...

of a particle and find it to be "up", in fact there are two "yous" after the measurement, one who measured the spin up, the other spin down. Effectively by looking at the system in question, you take on its indeterminacy.

This relative state formulation, where all states (sets of measures) can only be measured relative to other such states, avoids a number of problems in

quantum theoryQuantum mechanics is the body of scientific principles that explains the behavior of matter and its interactions with energy on the scale of atoms and atomic particles....

, including the original duality – no collapse takes place, the indeterminacy simply grows (or moves) to a larger system.

Everett claims that the universe has a single

quantum state, which he called the

universal wavefunctionThe Universal Wavefunction or Universal Wave Function is a term introduced by Hugh Everett in his Princeton PhD thesis The Theory of the Universal Wave Function, and forms a core concept in the relative state interpretation or many-worlds interpretation of quantum mechanics...

, that always evolves according to the

Schrödinger equationThe Schrödinger equation was formulated in 1926 by Austrian physicist Erwin Schrödinger. Used in physics , it is an equation that describes how the quantum state of a physical system changes in time....

or some relativistic equivalent; now the measurement problem suggests the universal wavefunction will be in a

superpositionIn physics and systems theory, the superposition principle , also known as superposition property, states that, for all linear systems, the net response at a given place and time caused by two or more stimuli is the sum of the responses which would have been caused by each stimulus individually...

corresponding to many different definite macroscopic realms ("macrorealms"); that one can recover the subjective appearance of a definite macrorealm by postulating that all the various definite macrorealms are actual – it seems to each observer that "we just happen to be in one rather than the others" because "we" are in all of them, but each are mutually unobservable.

### Continuous infinity of minds

In Everett's conception the mind of an observer is split by the measuring process as a consequence of the decoherence induced by measurement. In many-minds each physical observer has a postulated associated continuous infinity of minds. The decoherence of the measuring event (observation) causes the infinity of minds associated with each observer to become categorized into distinct yet infinite subsets, each subset associated with each distinct outcome of the observation. No minds are split, in the many-minds view, because it is assumed that they are all already always distinct.

The idea of many-minds was suggested early on by Zeh in 1995. He argues that in a decohering no-collapse universe one can avoid the necessity of distinct macrorealms ("parallel worlds" in

MWIThe many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternative histories and futures are real, each representing an...

terminology) by introducing a new psycho-physical parallelism, in which individual minds supervene on each non-interfering component in the physical state. Zeh indeed suggests that, given decoherence, this is the most natural interpretation of quantum mechanics.

The main difference between the many-minds and many-worlds interpretations then lies in the definition of the preferred quantity. The many-minds interpretation suggests that to solve the measurement problem, there is no need to secure a definite macrorealm: the only thing that's required is appearance of such. A bit more precisely: the idea is that the preferred quantity is whatever physical quantity, defined on brains (or brains and parts of their environments), has definite-valued states (eigenstates) that underpin such appearances, i.e. underpin the states of belief in, or sensory experience of, the familiar macroscopic realm.

In its original version (related to decoherence), there is no process of selection. The process of

quantum decoherenceIn quantum mechanics, quantum decoherence is the loss of coherence or ordering of the phase angles between the components of a system in a quantum superposition. A consequence of this dephasing leads to classical or probabilistically additive behavior...

explains in terms of the Schrödinger equation how certain components of the universal wave function become irreversibly dynamically independent of one another (

*separate worlds* – even though there is but one quantum world that does not split). These components may (each) contain definite quantum states of observers, while the total quantum state may not. These observer states may then be assumed to correspond to definite states of awareness (

*minds*), just as in a classical description of observation. States of different observers are consistently entangled with one another, thus warranting

*objective* results of measurements.

However Albert and Loewer suggest that the mental does not supervene on the physical, because individual minds have trans-temporal identity of their own. The mind selects one of these identities to be its non-random reality, while the universe itself is unaffected. The process for selection of a single state remains unexplained. This is particularly problematic because it is not clear how different observers would thus end up agreeing on measurements, which happens all the time here in the real world. There is assumed to be a sort of feedback between the mental process that leads to selection and the universal wavefunction, thereby affecting other mental states as a matter of course. In order to make the system work, the "mind" must be separate from the body, an old

dualityDualism denotes a state of two parts. The term 'dualism' was originally coined to denote co-eternal binary opposition, a meaning that is preserved in metaphysical and philosophical duality discourse but has been diluted in general or common usages. Dualism can refer to moral dualism, Dualism (from...

of

philosophyPhilosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

to replace the new one of quantum mechanics.

In general this interpretation has received little attention, largely for this last reason.

## Objections

Objections that apply to the

many-worlds interpretationThe many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternative histories and futures are real, each representing an...

also apply to the many-minds interpretation. On the surface both of these theories expressly violate

Occam's RazorOccam's razor, also known as Ockham's razor, and sometimes expressed in Latin as lex parsimoniae , is a principle that generally recommends from among competing hypotheses selecting the one that makes the fewest new assumptions.-Overview:The principle is often summarized as "simpler explanations...

; proponents counter that in fact these solutions minimize entities by simplifying the rules that would be required to describe the universe.

Another serious objection is that workers in no collapse interpretations have produced no more than elementary models based on the definite existence of specific measuring devices. They have assumed, for example, that the

Hilbert spaceThe mathematical concept of a Hilbert space, named after David Hilbert, generalizes the notion of Euclidean space. It extends the methods of vector algebra and calculus from the two-dimensional Euclidean plane and three-dimensional space to spaces with any finite or infinite number of dimensions...

of the universe splits naturally into a

tensor productIn mathematics, the tensor product, denoted by ⊗, may be applied in different contexts to vectors, matrices, tensors, vector spaces, algebras, topological vector spaces, and modules, among many other structures or objects. In each case the significance of the symbol is the same: the most general...

structure compatible with the measurement under consideration. They have also assumed, even when describing the behavior of macroscopic objects, that it is appropriate to employ models in which only a few dimensions of Hilbert space are used to describe all the relevant behavior.

In his

*What is it like to be Schrödinger's cat?* (2000), David Lewis argues that the many-minds interpretation of quantum mechanics has absurd implications for agents facing life-or-death decisions.

In general, the many-minds theory holds that a conscious being who observes the outcome of a random

zero-sumIn game theory and economic theory, a zero-sum game is a mathematical representation of a situation in which a participant's gain of utility is exactly balanced by the losses of the utility of other participant. If the total gains of the participants are added up, and the total losses are...

experiment will evolve into two successors in different observer states, each of whom observes one of the possible outcomes. Moreover, the theory advises you to favor choices in such situations in proportion to the probability that they will bring good results to your various successors. But in a life-or-death case like getting into the box with Schrödinger's cat, you will only have one successor, since one of the outcomes will ensure your death. So it seems that the many-minds interpretation advises you to get in the box with the cat, since it is certain that your only successor will emerge unharmed. See also quantum suicide and immortality.

Finally, it supposes that there is some physical distinction between a conscious observer and a non-conscious measuring device, so it seems to require eliminating the strong Church–Turing hypothesis or postulating a physical model for consciousness.

## See also

- Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...

- Quantum immortality
- Quantum mind
The quantum mind or quantum consciousness hypothesis proposes that classical mechanics cannot explain consciousness, while quantum mechanical phenomena, such as quantum entanglement and superposition, may play an important part in the brain's function, and could form the basis of an explanation of...

- Many-worlds interpretation
The many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternative histories and futures are real, each representing an...

- Biocentrism

## External links