Hugh Everett published his famous many-worlds theory in 1957. He was a graduate student under the great physicist John Wheeler. The title of his paper is The ‘Relative State’ Formulation of Quantum Mechanics. It has never been fully understood. It only makes sense completely when you bring in the concept of world superposition.
The problem Everett solves is the ‘collapse of the wave function’. As described in Quantum Reality, everything is defined by the wave function. This is the fundamental definition of the physical world. There is no question this is correct, it is the most thoroughly and deeply researched theory in the history of our race, and it predicts the results of experiments perfectly. It has never been wrong. The problem is that the wave function defines all possibilities. But we find ourselves in a world where everything is the embodiment of just one precise possibility, determinate and specific.
Clearly, therefore, along with the wave function and the way we know it works, there has to be something which makes the world the way it is, just one particular version of things. The infinite possibilities of the wave function have to ‘collapse’ to form one specific version of physical reality. This is the Copenhagen interpretation. This was not only the first generally accepted version of quantum theory, but continues to be presented in many textbooks.
But collapse of the wave function does not make sense because it is only on observation that this happens. As shown by the famous double slit experiment, described in Quantum Reality, unobserved reality is all possibilities, but when it is observed it mysteriously transforms into just one outcome.
Everett’s solution to this great puzzle is in essence very simple. There is no collapse; but there is the appearance of collapse. In this case, if there is no collapse, then all possible versions of events get played out. And this means that all possible versions of the world come into being. This is where the Many Worlds concept originally came from in physics.
It has been suggested that quantum decoherence solves the measurement problem. However, this is as wrong as can be and “… deservedly attract the wrath of physicists” (Bacciagaluppi, 2012), as described in Measurement Problem.
The picture, gratis Max Tegmark, illustrates this idea with Bob asking Alice out. She may say yes or no. If there is no collapse, then both possibilities happen. She says yes in one version of reality and no in another version. Effectively therefore, the world splits in two, and both versions exist.
An excellent article that includes a description of this progression, was written by John Wheeler and Max Tegmark 100 Years of Quantum Mysteries.
The problems arise in the details. It has not been possible to explain exactly what is happening here. Everett essentially states that only in experience are there separate realities. In physical reality, he says, both of the possible situations exist superposed, as illustrated in the picture below. But in experience, on the inside view, just one specific version of the outcome is encountered.
Since experience cannot be relevant in physics it is assumed that he was referring to the experience of some physical process. But in that light it has not been possible to make sense of this idea, or to solve the great paradox of quantum theory, the measurement problem. A description of this paradox, and the resolution in the light of logical type, is given in Measurement Problem.
In order to see exactly what he did mean we need to go into a bit of detail about the theory. His concept centres on the technical process of making an observation. We are constantly observing all the things in reality we can see and hear. The human body uses the sensory apparatus, the eyes, ears and so on, to detect the sights and sounds of the world. And the neural system of the brain turns all this information into a visual image. Right now you are experiencing a visual image, a view of reality, specifically some words in black on a white background. That is simply the information, in the form of an image, that you are actually experiencing ‘in here’. The brain produces the visual representation ‘in here’ of the reality ‘out there’. This, of course, is simply how we formulate the perceptual reality, as described in The World Hologram, and thus get to experience the real world.
The brain records this image in memory. This is the process that Everett defines as the making of an observation: an observation is made when this sensory experience is recorded in memory.
The final, key component of his theory is the ‘state of the memory’. This is defined as the record of all of the observations that have been made. So the state of the memory is the sum total of all the sensory information that gets experienced and recorded in memory. This is the total record of one’s sensory experience. This is formulated as a three-dimensional virtual reality that is mentally projected onto the real world, as described in The World Hologram. This is the navigation equipment of the human entity, enabling us to find our way about in the world and interact with the environment.
Now for the bit that gives rise to all the difficulty. This is what he actually says in his conclusion. When the observer interacts with the environment, and an observation is made, the result:
… is a superposition of states, each element of which assigns a different state to the memory of the observer. (1957, 462)
In other words, the physical reality itself does not split as shown in the picture above. Instead, the physical reality is literally the superimposed sum of both situations at once, as in this picture.
That is the superposition. This is what no collapse means: the wave function remains unchanged, and the wave function defines all possibilities, superposed.
Nonetheless, the state of the memory – the definition of the experience of reality – is different in each element of the superposition. Thus in the experience of reality, in each element of the superposition, there is just one specific outcome, and just one version of reality, as shown in each branch of the first picture. In other words, physical reality works like picture 2, but experience works like picture 1.
This is Everett’s solution. Although in physical reality, both of the different possible outcomes are superimposed – so there is no collapse of the wave function – in each element of the superposition, it appears that the possibilities have collapsed to a single physical actuality.
Frames of Reference
The problem is this seems to make no sense. How can the experience of the physical world be different to the physical world? He is saying that it is in experience, and only in experience, that different, discrete versions of the physical world exist. In the current scientific worldview this sounds like complete nonsense. So the obvious assumption is that is not quite what he actually meant.
There is a great deal of literature devoted to trying to establish exactly what he did mean. The Quantum Mechanics of Minds and Worlds by Jeffrey Barrett (1999) gives an excellent overview of the decades of thinking. He goes through all the arguments about how Everett could be understood in precise but accessible detail.
There is only one way of taking all this that works. It gives the same result as QBism. The state of the memory is not just the inside view of a specific world on the outside view. It is a frame of reference, and one of ontological significance. It seems it could not be because it is only the frame of reference of consciousness. However, this turns out this frame of reference is absolutely fundamental. The inside view, and thus the field of information defined, are of direct and absolute ontological significance, as described in Universe Consciousness.
This frame of reference is defined by the record of observations. From the point of view of this frame of reference, one specific version of events is experienced, observed, recorded and becomes part of the definition of the determinacy of the world of this individual. Since, as Everett points out, the physical body is in a state of superposition, this individual cannot be the same thing as the physical observer. As described here, this individual, the protagonist of the dynamics and the subject of the reality encountered is simply and solely the world hologram itself. This is a big part of the conceptual revolution.
This seems crazy in the current paradigm because it seems totally obvious I am the whole of the physical entity. I am a body-mind. But the correct identity of the subject in physics is precisely what is missing from the current paradigm. This is what gives rise to all the problems in quantum theory. We think we are bodies that have minds in them, and we are. But primarily we are world holograms. It is the record of observations in Everett’s theory that defines the operational frame of reference. As he states, it is : “… judged by the state of the memory”, that the quantum mechanical dynamics are enacted. As described here, the world of such an entity is the QBism type of world, and this resolves all the great paradoxes.
Everett’s formulation of quantum mechanics states that only in experience is there just one specific version of an outcome to events in the world. This cannot possibly make sense in the science of objective physical reality, which is why his theory remains the subject of controversy. In fact, however, his theory describes what happens at different levels of logical type. The linear dynamics of quantum mechanics is the dynamics of the physical. This is the wave function. The collapse dynamics is the dynamics of the inside view, the world hologram. Everett’s solution has been incomprehensible because it describes the appearance of collapse, which is what takes place as the frame of reference is altered by the addition of the observation to the record of observations, in experience, on the inside view. On the inside view, this is the step from one frame of the holographic movie to the next. It is a second-logical-type phenomenon. This is graphically illustrated in Measurement Problem.
As Tegmark states, important scientific discoveries go though three phases:
… first they are completely ignored, then they are violently attacked, and finally they are brushed aside as well known. Everett’s discovery was no exception: it took more than a decade before it started getting noticed. But it was too late for Everett, who left academia disillusioned.
Everett’s no-collapse idea is not yet at stage three, but after being widely dismissed as too crazy during the 1970s and 1980s, it has gradually gained more acceptance. At an informal poll taken at a conference on the foundations of quantum theory in 1999, physicists rated the idea more highly than the alternatives, although many more physicists were still ‘undecided’. I believe the upward trend is clear.
Why the change? I think there are several reasons. Predictions of other types of parallel universes from cosmological inflation and string theory have increased tolerance for weird-sounding ideas. New experiments have demonstrated quantum weirdness in ever larger systems. Finally, the discovery of a process known as decoherence has answered crucial questions that Everett’s work had left dangling.
It seems increasingly obvious Everett is right. The remaining puzzles persist because the final hurdle has not been cleared. This is the nature of the identity of the subject of the dynamics, the protagonist in the reality defined by the equations. This is the entity ‘in here’, the record of observations, in human observers the world hologram. In the world of this type of entity, the reality is a many-worlds reality, and this resolves all the massive puzzles and paradoxes. The world encountered is the world superposition, a second-logical-type phenomenon.