1. Introduction.

A non-collapse objective reality is one in which both the wave function - with all its branches - and a separate, objective reality exist together.  We will give three arguments against such a scheme.  First, there can be no evidence which implies there is such a scheme unless quantum mechanics is found to be wrong.  And so far, it has always been right.  Second, there is  no way to show that objective reality theories achieve their intended goal of explaining why we perceive a particular quantum mechanical outcome.  And third, there are technical difficulties encountered in attempting to meld quantum mechanics with an objective reality theory.

2. No Experimental Evidence for an Objective Reality

In the various attempts to interpret quantum mechanics, its weaknesses are often emphasized while its strengths are not fully appreciated.  We feel that a proper appreciation of its strengths significantly narrows the field of potential interpretations.

 

The Strengths of Quantum Mechanics.

To illustrate how well the theory of quantum mechanics does, suppose we again consider Schrödinger’s cat.  The wave function is the sum of two parts, two potential versions of reality – a version with the cat alive and a version with the cat dead.  We perceive one or the other.  The point is that, no matter which possibility we perceive, quantum mechanics includes within its wave function an exact description of our perceptions.  (The problem, of course, is that it includes more than just what we perceive in a given instance, but never mind for now.)

 

Exactly the same thing occurs in the scattering of an electron (section IID.4) off a proton surrounded by a sphere of film emulsion.  The wave function for the end result is the sum of many possible versions of reality, each with just one grain of film exposed.  And one of those possible versions of reality will correspond exactly to what we perceive.

 

This can be generalized.  In a given experiment (or in real life), the wave function will contain many versions of physical reality.  And it will always be found that one of those versions corresponds exactly, quantitatively, to what we perceive.  In short, quantum mechanics always contains the right answer -  a correct, accurate description of what we perceive.

 

No Experimental Evidence for Objective Realities.

There are two consequences of this observation.  The first is that as long as quantum mechanics always gives the right answer, there can be no experimental evidence for a separate objective reality, for quantum mechanics has co-opted all the evidence.  The only hope for those who advocate a separate, objective reality is that some experiment will show quantum mechanics to be wrong.  And after all the tests quantum mechanics has been put through and passed – especially those involving Bell-like situations – that seems like a vain hope. 

 

Perception of the Wave Function.

The second consequence is that, since the wave function always contains an accurate, complete description of what we perceive, we must, in some sense, be perceiving the wave function!  (This, of course, also holds in collapse theories.)

 

3. How does an Objective Reality Lead to Perception of a Particular Branch?

Not only is it very unlikely that an objective reality exists, but also, even if it does, it is not at all clear that it leads to conscious perception of one particular branch.  To illustrate the problem, suppose we do the Schrödinger’s cat experiment yet again.  Ignoring for the moment the reputed objective reality, the two-version wave function, including the cat and the observer’s brain, is

[cat alive][observer’s neurons correspond to perceiving cat alive]

+

[cat dead][observer’s neurons correspond to perceiving cat dead]

Now we include the objective reality.  If we think in terms of the Bohm model, for example, all the particles corresponding to the cat and the observer will be on one branch or the other.  (The argument is essentially the same for all objective reality theories.)  Suppose the branch with the particles is the cat alive branch.  Then the state, {alive}, of the system, wave function plus particles, is

{alive}=

[cat alive]_pa[observer’s neurons correspond to perceiving cat alive]*_pa

+

 [cat dead]_{no pa}[observer’s neurons correspond to perceiving cat dead]_{no pa}

where the asterisk denotes the particled, conscious version of the brain. 

The implicit assumption, normally made without comment in particle theories, is that the branch which the particles travel on is the branch that enters our awareness.  The point is that this is an assumption which I believe it is most difficult to defend.  And if it cannot be defended—if it must simply be assumed—then the presumption that there is an objective reality does not really give an explanation for why we perceive one and only one particular version of reality.

Conjectured Defenses of the Consciousness-Particle Connection.

The onus is on the objective reality advocate to defend the particle-perception connection but as far as I know, that is never explicitly done.  So I will guess at the defenses and comment on them.  Before doing that, however, I will list four relevant points.

• Existence in objective reality theories consists solely of the objective reality plus the wave function.  There is nothing apart from these two that would correspond to consciousness.  There is no inherent intelligence within the particles, for example, nor is there an “outside” observer perceiving the state of the particles or the wave function.

• Because wave functions alone—with no assumption of the existence of particles—have been found sufficient for very accurately describing (low energy) reality, at least in simple cases, we assume the wave function of the neurons of the brain is not substantially changed by the presence or absence of particles. 

• More generally (aside from the problems associated with understanding many branches), quantum mechanics gives a complete (as far as we know) and accurate accounting of the properties of the physical universe.  Whatever we perceive has qualities corresponding to those of the wave function.

• Particles on the other hand add nothing (as far as we know) to the quantitative description of nature.  In particular, particles are not needed to explain the Compton effect (IIIA4), localization (IIIA5), particlelike trajectories (IIIA5), the discrete properties of matter (IIIA6), atomic spectra and so on.

Conjectured Defense 1.  The particles (or more generally the objective reality) are the “actual” reality, with the wave function being a subsidiary, nonperceived reality. 

Comments:

• Everything we perceive corresponds to properties of the wave function.  How does one justify saying we do not perceive the wave function?

• Why are particles given the role of arbiter of consciousness when they play no role in the quantitative description of the physical universe (and when there is not even any evidence for them)? 

• There is, in objective reality models, no external being that perceives either the particles or the wave function.  So it is simply an assumption—an apparently unsupportable assumption—that the particles are the actual, perceived reality.  What is perceiving them and not the wave function (which is the carrier of all the quantitative information)?  

• Finally, one cannot simply say that that is just the way the universe is; the particled version is the version that enters our consciousness.  One must explain why we perceive only the branch with the particles and, particularly, why we don not the quantum-mechanically-equally-valid branches with no particles. Otherwise one is “solving” the particular-version problem by declaration, not by fact or logic.

Conjectured Defense 2. The particled version forms a self-consistent universe which one could imagine giving rise to an artificial-intelligence-like awareness.  And objective reality theories have the potential to explain the probability law.

Comment:

• These may indeed be true.  But they still do not explain why we are aware of the particled version but not the nonparticled versions.  And the artificial-intelligence-like awareness argument cuts both ways; it can be applied to wave functions as well as particles.

In summary, until a clear explanation is given for why we are aware of the particled version but not the nonparticled versions, objective reality theories cannot even get out of the starting gate.  The presumed existence of particles or any other form of objective existence cannot solve the problem of why our awareness corresponds to one particular version of our brain.

4. Technical Difficulties with Objective Reality Theories.

Because of the reasoning in section 2, I do not believe there is an objective reality.  In addition, because of the reasoning in section 3, I do not believe that there is an acceptable explanation for why we perceive only the branch associated with the objective reality in underlying objective reality theories.  Nevertheless, we will continue our criticism of such theories by considering the technical difficulties they face.

We will use an electron scattering experiment to explain the requirements on an underlying objective reality theory and the difficulties encountered in trying to construct such a theory.  A target proton is at the center of a 1 meter sphere covered with detectors.  An electronlike wave function scatters off the proton.  The wave function spreads out and hits all the detectors, but only one registers the passage of the wave function.  We infer from this that the “objective reality that triggered the detector” (actually, there is a detector triggered on each branch) must be very small, as small as the smallest possible detector.  This essentially throws us back to the Bohmlike objective reality model of a point particle.  In that model, the point particle moves rapidly back and forth within the confines of the wave function.

A constraint on objective reality models is that there must be one and only one “particle” associated with each single-particle wave function.  This constraint must be put into the theory in a mathematical form; it cannot simply be one of the assumptions defining the theory (as it is in the Bohm model).  The mathematical form of this constraint will presumably be that of a “source” equation, with the particle being the source of the associated single-particle wave function.

The conditions that an underlying objective reality theory with a source equation must satisfy are:

• The source equation must not significantly modify the wave function.  In particular, it must not measurably affect the emitted light spectrum or the chemical properties of the elements.

• When there is a source equation, the  Bohm derivation of the probability law no longer holds in general.  So one must make sure there is a valid derivation of the probability law.

• The wave function must not be significantly affected by the rapid zig-zag “Bohmian” motion of the source.

• When the wave function splits into two or more widely separated parts, the particle (localized objective reality) must presumably still be the source for all the parts.

• Suppose the source equation takes the form of a modified Schrödinger equation,  with  being the usual Hamiltonian for the N-particle wave function and the source term  being, in general, a nonlinear function of the wave function.  Then separability ( becomes a sum and  becomes a product) implies that .  This constraint must be satisfied in an underlying objective reality theory with sources.

• The theory must allow for the creation and annihilation of photonlike states and particle-antiparticle pairs.

• The theory must be relativistically invariant.

• Internal symmetries must be integrated into the theory.  (Remember that mass, energy, momentum, spin and charge are properties of the wave function—section  IIIA2.)

To the best of my knowledge, there is not a candidate theory that even starts to address these constraints on a hidden variable theory with a source equation.

5. Conclusion.

Because quantum mechanics always gives an accurate description of what we perceive, I do not believe there is an objective reality.  In addition the two problems—explaining why only the branch associated with the objective reality is perceived,  and overcoming the technical difficulties—present formidable barriers to the construction of a satisfactory objective reality theory.  I would not like to hang my view of reality on the slim possibility that these problems will be solved.

6. The Copenhagen Interpretation.

The Copenhagen interpretation says, in essence, that the physical world divides into two aspects, a macroscopic, large-scale aspect and a microscopic, atomic-scale aspect.  It is only the macroscopic aspect—meters, cats, and so on—that we directly perceive.  So, says this interpretation, because we cannot directly perceive on the atomic scale, it is useless to speculate on the nature of matter on that scale.  (And by implication, it is useless to search for an explanation of the mysteries of quantum mechanics.)

Because of the following points, I simply don’t agree with this point of view. 

• We perceive something. 

• What we perceive agrees in every checkable instance with the characteristics of the wave function.

• We have argued that it is very difficult to defend the existence of an objective (microscopic or macroscopic) reality separate from the wave function.

So, even though we cannot verify the nature of matter by "direct perception," it still seems valid to conclude that matter, on every scale, consists of the wave function and the wave function alone.

We might consider an analogy here.  Imagine a picture of a beautiful snow-capped mountain, digitally printed.  The various pixels correspond in the analogy to the facts of science while the whole picture corresponds to the implications, or the meaning of the facts of science.  To me, the Copenhagen interpretation is like saying we are only allowed to pay attention to the pixels.  We have no business inferring what the mountain actually looks like from the picture.