The many-worlds theory, explained + Universe is not purely mathematical in nature

No, The Universe Is Not Purely Mathematical In Nature

The Many-Worlds Theory, Explained

EXCERPTS (John Gribbin): . . . If you have heard of the Many Worlds Interpretation (MWI), the chances are you think that it was invented by the American Hugh Everett in the mid-1950s. In a way that’s true. He did come up with the idea all by himself. But he was unaware that essentially the same idea had occurred to Erwin Schrödinger half a decade earlier. Everett’s version is more mathematical, Schrödinger’s more philosophical, but the essential point is that both of them were motivated by a wish to get rid of the idea of the “collapse of the wave function,” and both of them succeeded.

As Schrödinger used to point out to anyone who would listen, there is nothing in the equations (including his famous wave equation) about collapse. That was something that Bohr bolted on to the theory to “explain” why we only see one outcome of an experiment — a dead cat or a live cat — not a mixture, a superposition of states. [See Origin of Copenhagen Interpretation.] But because we only detect one outcome — one solution to the wave function — that need not mean that the alternative solutions do not exist. In a paper he published in 1952, Schrödinger pointed out the ridiculousness of expecting a quantum superposition to collapse just because we look at it. It was, he wrote, “patently absurd” that the wave function should “be controlled in two entirely different ways, at times by the wave equation, but occasionally by direct interference of the observer, not controlled by the wave equation.”

[...] There is no collapse of the wave function. Schrödinger anticipated the reaction of his colleagues in a talk he gave in Dublin, where he was then based, in 1952. ... In fact, nobody responded to Schrödinger’s idea. It was ignored and forgotten, regarded as impossible.

So Everett developed his own version of the MWI entirely independently, only for it to be almost as completely ignored. But it was Everett who introduced the idea of the Universe “splitting” into different versions of itself when faced with quantum choices, muddying the waters for decades. [...] Everett did point out that since no observer would ever be aware of the existence of the other worlds, to claim that they cannot be there because we cannot see them is no more valid than claiming that the Earth cannot be orbiting around the Sun because we cannot feel the movement.

Everett himself never promoted the idea of the MWI. [...] It wasn’t until the late 1960s that the idea gained some momentum when it was taken up and enthusiastically promoted by Bryce DeWitt, of the University of North Carolina ... The power of the interpretation began to be appreciated even by people reluctant to endorse it fully.

[...] The precise version of the MWI came from David Deutsch, in Oxford, and in effect put Schrödinger’s version of the idea on a secure footing, although when he formulated his interpretation, Deutsch was unaware of Schrödinger’s version. ... Deutsch became a pioneer in the field of quantum computing, not through any interest in computers as such, but because of his belief that the existence of a working quantum computer would prove the reality of the MWI.

This is where we get back to a version of Schrödinger’s idea. In the Everett version of the cat puzzle, there is a single cat up to the point where the device is triggered. Then the entire Universe splits in two. [...] Deutsch argues that when two or more previously identical universes are forced by quantum processes to become distinct ... there is a temporary interference between the universes, which becomes suppressed as they evolve. It is this interaction that causes the observed results of ... experiments.

[...] What makes a quantum computer qualitatively different from a conventional computer is that the “switches” inside it exist in a superposition of states [...] either on or off, corresponding to the digits 1 or 0. ... Each switch in a quantum computer, however, is an entity that can be in a superposition of states. ... they are both ... 0 and 1 [ the same time...] Each switch is called a qbit, pronounced “cubit.”

[...] A computer with just 300 qbits would be equivalent to a conventional computer with more bits than there are atoms in the observable Universe. How could such a computer carry out calculations? The question is more pressing since simple quantum computers, incorporating a few qbits, have already been constructed and shown to work as expected. They really are more powerful than conventional computers with the same number of bits.

Deutsch’s answer is that the calculation is carried out simultaneously on identical computers in each of the parallel universes corresponding to the superpositions.[...] when we build a 300-qbit machine ... we will, if Deutsch is right, be involving a “collaboration” between more universes than there are atoms in our visible Universe. It is a matter of choice whether you think that is too great a load of metaphysical baggage. But if you do, you will need some other way to explain why quantum computers work.

Most quantum computer scientists prefer not to think about these implications. But there is one group of scientists who are used to thinking of even more than six impossible things before breakfast — the cosmologists. Some of them have espoused the Many Worlds Interpretation as the best way to explain the existence of the Universe itself.

Their jumping-off point is the fact, noted by Schrödinger, that there is nothing in the equations referring to a collapse of the wave function. And they do mean the wave function; just one, which describes the entire world as a superposition of states — a Multiverse made up of a superposition of universes. [...] Cosmologists are excited by this, not because they are included in the wave function, but because this idea of a single, uncollapsed wave function is the only way in which the entire Universe can be described in quantum mechanical terms while still being compatible with the general theory of relativity.

The universal wave function describes the position of every particle in the Universe at a particular moment in time. But it also describes every possible location of those particles at that instant. And it also describes every possible location of every particle at any other instant of time, although the number of possibilities is restricted by the quantum graininess of space and time. Out of this myriad of possible universes, there will be many versions in which stable stars and planets, and people to live on those planets, cannot exist. But there will be at least some universes resembling our own, more or less accurately, in the way often portrayed in science fiction stories. Or, indeed, in other fiction. Deutsch has pointed out that according to the MWI, any world described in a work of fiction, provided it obeys the laws of physics, really does exist somewhere in the Multiverse. There really is, for example, a “Wuthering Heights” world (but not a “Harry Potter” world).

That isn’t the end of it. The single wave function describes all possible universes at all possible times. But it doesn’t say anything about changing from one state to another. Time does not flow. Sticking close to home, Everett’s parameter, called a state vector, includes a description of a world in which we exist, and all the records of that world’s history, from our memories, to fossils, to light reaching us from distant galaxies, exist. There will also be another universe exactly the same except that the “time step” has been advanced by, say, one second (or one hour, or one year). But there is no suggestion that any universe moves along from one time step to another. There will be a “me” in this second universe, described by the universal wave function, who has all the memories I have at the first instant, plus those corresponding to a further second (or hour, or year, or whatever). But it is impossible to say that these versions of “me” are the same person. Different time states can be ordered in terms of the events they describe, defining the difference between past and future, but they do not change from one state to another. All the states just exist. Time, in the way we are used to thinking of it, does not “flow” in Everett’s MWI... (MORE - details)

RELATED: Six Impossible Things: The Mystery of the Quantum World, by John Gribbin
"Schrödinger pointed out the ridiculousness of expecting a quantum superposition to collapse just because we look at it."

The most sensible statement I have heard (IMHO) about Quantum Mechanics!

Why not just say the truth. The cat is in an indeterminate state. It is neither alive nor dead.
Its state of life mathematically is approximately 50% depending on the details of the experiment. (The actual mechanism might be biased).
(May 22, 2020 05:03 AM)Catastrophe Wrote: "Schrödinger pointed out the ridiculousness of expecting a quantum superposition to collapse just because we look at it."

The most sensible statement I have heard (IMHO) about Quantum Mechanics!

Why not just say the truth. The cat is in an indeterminate state. It is neither alive nor dead.
Its state of life mathematically is approximately 50% depending on the details of the experiment. (The actual mechanism might be biased).
If only it was so simple. The Double slit experiment is a classic conundrum where knowing the path of the photon (which slit it went through) destroys the interference pattern. The delayed choice setup allows the path (optionally) to be determined after (8ns later) the interference pattern has been detected (or diffraction pattern if no interference).
If the path is detected (later) then the (earlier) interference pattern is not seen.

The double slit experiment is one of my favourites. Maybe new thread if you would like to discuss it further.

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