The arguments given in No Evidence for Particles and Bohm’s Hidden Variable Interpretation show we can be quite (although not absolutely) certain there are no particles or hidden variables. And the arguments in No Evidence for Collapse, Mathematical Collapse Interpretations and Observer-Induced Collapse indicate we can be fairly certain there is no mathematical or consciousness-triggered collapse. We thus arrive at the following set of ‘idealized’ requirements on an interpretation.

Requirement 1. There are to be no particles or hidden variables.
Requirement 2. There is to be no collapse.
Requirement 3. One version must be singled out as the one corresponding to my perceptions on each run (principle [P18] from Probability and Constraints on Interpretations).

How do we proceed from here? To see, we go back to principle

[P3] from Schrödinger’s Cat—that our perceptions always correspond exactly to those of one and only one version of the observer. It is as if there is a “Mind,” outside the laws of quantum mechanics, that is, in some sense, concentrating on and perceiving one quantum version of physical reality. This supposition forms the basis for the Mind-MIND interpretation.

1. The individual non-physical Mind. Associated with each individual person is an individual Mind that is not subject to the mathematical laws of quantum mechanics. In particular, the Mind has no wave function associated with it. We use a capital M to distinguish this Mind from the usual usage of the word mind. Because quantum mechanics describes the physical world so well, we will define anything outside its laws to be ‘non-physical.’ So with this definition, the Mind is non-physical.

2. The Mind perceives only the brain-body. The individual Mind perceives only the wave function of the individual brain (brain-body); it does not directly perceive the quantum state of the external world. This is consistent with the fact that we are not directly aware of the external world; we are only aware of the neural state of our brain. The process of perception of the wave function by the Mind is not understood.

3. The Mind picks out one version of the wave function. The individual Mind concentrates on one version of the wave function of the brain-body, and it is the concentrated-upon version that enters our conventional awareness.

4. No collapse. The Mind does not collapse the wave function or interfere with the mathematics in any way.

A primary objection to dualism—a non-physical Mind separate from a physical brain-body—is that the non-physical aspect must exert a force or otherwise have some effect on the physical world. The Mind scheme circumvents this objection because the non-physical aspect only perceives; it does not affect the physical world (which is made up of wave functions) in any way.

The model as it has been given so far leaves two important questions unanswered—why observers agree on what they perceive, and why the probability law holds. To make the first question specific, consider again the Schrödinger’s cat experiment and suppose we have two observers. Then according to the rules of quantum mechanics, the wave function is

Suppose observer 1’s Mind focuses on the version of the associated brain corresponding to cat alive so that observer 1 perceives, in the everyday sense, a live cat. We know from everyday experience that observer 1 and observer 2 (and the cat) must be in agreement. And we know from property [P7] in Classical Perception that two observers can never disagree. But still, how do we guarantee in our Mind model, that observer 2’s Mind is also focused on the ‘alive’ version of its brain? There is a way to bring about agreement but it is bound to make scientists uneasy about this proposal because it is outside the realm of contemporary science.

5. The overarching MIND. Instead of each individual Mind being separate from all others, each Mind is a fragment or facet of a single overarching MIND. Each individual Mind is that aspect of MIND that is responsible for perceiving the state of the associated individual physical brain. Concentration of perception on a particular version of the wave function by one individual Mind is then presumed to set the concentration of perception on that same version by the overarching MIND. And that in turn sets the perception of the same version by all the other individual Minds. Neither the MIND nor the individual Minds alter the wave function in any way.

So to obtain conscious agreement among observers in this scheme, we are forced to substitute the MIND assumption for the conventional particle or collapse assumptions that give a single-version physical world. The scientist will say there is no evidence to justify such an outrageously non-scientific assumption. But the counter-argument is that there is no evidence to justify the particle or collapse schemes either (see No Support for Materialism). And if there is no collapse and there are no particles—the option we are exploring here—we are apparently forced to a “Mind” interpretation. Agreement among observers then forces us to the Mind-MIND scheme.

Freedom of choice. Freedom of choice enters the Mind-MIND interpretation in the sense that the individual Mind can (presumably) choose to perceive any possible internal quantum state—states in which the versions of reality (branches of the wave function) are versions of the brain wave function alone; that is, the freedom applies to thoughts and preparations for muscular actions. (See Quantum Mechanics, the Brain and Free Will for the argument that the brain has many simultaneously existing internal quantum states.) But this freedom of choice of the individual Mind does not apply to external events, where the different versions of reality include objects besides the brain. We cannot choose to perceive a live Schrödinger’s cat instead of a dead one, nor can we choose to perceive a decayed nucleus instead of an undecayed one.


There is a problem with the concept of probability if we assume no particles and no collapse. Probability as it is traditionally understood, say in the example of rolling dice, refers to the probability of a specific, actual, ‘single-version’ event; there is an actual die that has a specific reading after each roll. But in quantum mechanics, the wave function does not give a specific, actual, single-version event; instead, it gives several versions of reality (equivalent to all six readings of the die occurring at the same time), each potentially corresponding to an ‘actual, perceived’ event. So the direct use of classical probability is not appropriate in the Mind interpretation, where all versions exist forever.

In spite of this problem, there is a way to salvage the probability law in the Mind-MIND scheme. To do this, we make the following (relatively weak) assumption:

6. Probability. The overarching MIND is ‘much more likely’ to perceive a version of reality that has a much larger norm than other versions. The MIND doesn’t have to follow the usual |a(i)|² probability law or any stable probability law at all; it just has to be much more likely to perceive those versions with a relatively large norm.

Now suppose we run an experiment many times. Then this assumption implies (see Probability in the Mind-MIND Interpretation) that the observer will perceive a result consistent with the probability law; that is, she will perceive state i on close to a fraction |a(i)|² of the runs.

It is worth emphasizing three points here.

•The probability law in the Mind-MIND interpretation only pertains to a large number of repetitions of the experiment (which, of course, is pretty much true in classical probability theory also).
•The probability law for long runs holds in the Mind-MIND interpretation only if individual results are not observed (which is quite different from classical probability theory).
•This approach adheres to principle [P10] in The Probability Law, which says that the probability law must be derived primarily from within quantum mechanics itself, rather than being superimposed on the theory by some mechanism which is entirely outside the mathematics of quantum mechanics.