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Originally Posted by Doggg
The link that was supplied was very scarce in information. I just bowed out because it seemed to be the kind of link that one throws up when they want to respond, but not answer.
I'm a little hesitant to try to provide a detailed explanation because I'm fairly sure there are several other posters who are more formally versed in the specific physics, but I'll give it a shot and you can just take it with a grain of salt and keep in mind that I learned some QM from the Feynmen Lectures on Physics, and some from Neal Stephensen novels :P
The important snippet from the wiki for "Universal wavefunction" is this: The universal wave function is the wavefunction or quantum state of the totality of existence, regarded as the "basic physical entity"
We can take "totality of existence" to mean totality of the physical existence to try to make as few assumptions as possible. The wiki language assumes materialism, by which I mean the physics of QM says nothing about existence beyond the physical, so if that's the totality, then materialism.
It's actually easier to talk about quantum states or wavefunctions of much simpler physical systems, for example a system that involves a single photon interacting with an electron. The universal wavefunction is just an extrapolation where the scope of the system is expanded to the entire physical reality. Such an expanded system is entirely unfeasible to actually deal with mathematically, but the idea that it exists in QM is reasonable. In the more common interpretations of QM, the state function is not a physical reality in itself, but its range represents a weighted distribution of possible states of the system at a given set of space-time coordinates. So you evaluate the function at (x, y, z, t) and interpret it as saying there is an A% chance of A1 occuring, a B% chance of B2 occuring, etc etc. The number of possible states and probabilities grows as the complexity of the system you are modeling grows, and so you can imagine that the state function of the entire universe is mind-bogglingly large. When a measurement actually occurs at (x, y, z, t) only one of the possible states is actually observed. This is what is referred to as the "collapse of the wave function", and it is somewhat mysterious as to what counts as a "measurement" and "how" one state is selected out of the possibilities, other than the fact that if you repeat measurements that have similar outcome distributions, you will observe results that statistically match up with that distribution. There are many other subtleties about the collapse of the wave function. A good place to start googling is the Young's Double Slit Electron experiment.
And so, the mysteriousness of the connection between the mathematical description (wavefunction) and the reality we observe has famously caused physicists some consternation (see: Einstein's "God doesn't play dice") and the interpretation from the model to what the underlying reality is "actually" like is interesting. Multiple-worlds resolves the mystery of the wavefunction collapse by simply doing away with it. MW says that the wavefunction represents the actual reality, but we only observe one tiny part of it. For every physical interaction in which there is a multiplicity of possible states according to the wavefunction, there is a "branch" of the cosmos in which that state was selected. Note that MW doesn't have to imply that a new branch is created at each interaction, you can model the MW-cosmos as a kind of giant configuration space of possible physical states, and each individual "branch" represents a path through that space, with paths splitting apart from each other at each interaction.
Hopefully that description is not too incorrect.
Now, you wrote that this is another way of saying "everything [possible] exists" (I'm assuming the word possible but it's helpful and I think doesn't change your meaning). As zumby helpfully pointed out, there's a difference between physical possibility and logical possibility. The kinds of possibilities that are represented by quantum states are possibilities involving collections of fundamental particles with particular masses, electric charges, spins, energy levels and etc etc. Such states are the only possibilities that are made actual in MW. So unless "God" is some collection of such particles, MW does not imply that "God" exists. Such a conception of God is not perhaps immediately self-contradictory, but it is not what most religions have understood God to be, and there would be numerous theological problems. For example, how can such a God be present everywhere or hear all prayers?
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I remember Carl Sagan opened up (Cosmos, maybe) one of his books with the statement that: "the universe is all there is, and all there was. and all there ever will be." If there are other universes, then what is a universe, really? It is certainly not all there is, or all there was, and all there ever will be. "All there is," then, is now redefined. You still have to get there. You still need an all-encompassing macrocosm. Which is the point-- that it doesn't matter what you call the first cause, or where you place it-- you still need it.
I think you are making a mistake to take Carl Sagan's cosmology as a given from a religious perspective. It's correct that under MW the universe is not exactly a "uni"verse any longer, although in another sense it still is a single physical reality (mathematically represented by the single wavefunction), just one that is not very intuitive for us. But the problem is not that, the problem is that when Sagan says the universe is all there is, he is espousing materialism and in general theists are not materialists.
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Also, just because we can get to God through logic, or even through science, does not mean that God is a consequent of logic or science. It is simply a kind of viewing station in which we can appraise the creator.
I agree to the extent that if Christians believe there can be rational proofs of the existence of God, then if you were to understand MW as a rational proof of the existence of God, that would be no different. The problem is that MW doesn't function in that way. But the point of what zumby was saying I think is more that a physicalist conception of God would displace God as the ultimate ground of reality. God could not be "fundamental", He would be some physical matter, and the matter itself and the laws that it obeys would be more fundamental, and if you were to surmise that God could break the laws of physics then at that point you've rejected the original assertion that the existence of such a God is implied by MW, since MW in no way implies the existence of matter that does not follow the laws of QM.