In another thread beginning at post 130 there is discussion defining causal determinism as
Everett’s many worlds (MW) model is then offered up as a causally deterministic alternative model to the various models that have randomness as a fundamental feature of nature.
The popularized understanding of MW is that the result of each and every quantum occurrence is that every possible outcome actually occurs and an infinite number of universes branch off forming greater and greater infinite numbers of universes.
It seemed to me that such did not fit the definition of causal determinism because the same exact identity of information within any specific box does not result in only one way out but in an infinite number of ways out that all occur: f(x) = y, y[sub]n to ∞[/sub] or something like that.
Everett’s PhD thesis was then quoted in which he apparently claimed his model was deterministic. I readily admit that the “wave equation ∂Ψ/∂t = UΨ, where U is a linear operator” stuff goes beyond my level to comprehend. Way beyond. (I’m a doctor Jim, not a quantum physicist! :))
So physics heads of the SD - in language understandable to we mere ignorant mortals wishing to marginally decrease our neverending ignorance just a bit more - does the MW model offer up determinism other than by saying that all things that can occur do so everything, literally everything ever possible, causally follows in one of the infinite number of universes?
Bonus question: do any of the Copenhagen alternative models of quantum mechanics offer up any falsifiable predictions that would differentiate them from the Copenhagen model? If not what good are they?
Bonus question 2: Your take on “shut up and calculate.” Appropriate mindset or demonstration of being “closed-minded, and intellectually incurious”?
If you take “causal determinism” to mean that, for a theory, if you are given an complete set of data about an arbitrary isolated system/the Universe at some arbitrary initial time, then you can completely determine its state at any other - then yes the many-worlds interpretation (MWI) fits this bill.
MWI specifically states:
the universal wavefunction is objectively real (up to gauge symmetry, presumably) and contains all the data about the Universe.
the only time evolution that the universal wavefunction undergoes is deterministic and unitary.
So by asserting the reality of the Universal wavefunction and specifying that it evolves in time in such a way that its state at a given time can be determined from its state at any other time, MWI is “causally deterministic”.
However there are some problems of how the universal wavefunction relates to the objective reality we see. Even if we were some supreme being with complete knowledge of the universal wavefunction it is not clear how we could, or even if we would, be able to predict the observations made by us mere mortals. So it could be argued that the causal determinism of MWI is hidden in the same manner as a hidden variables theory and worse you may still need to introduce probability to relate it to the world as we actually observe it.
As an aside, any theory/interpretation which has probabilistic behaviour as fundamental cannot meet the above definition of “causal determinism”, however being non-probabilistic is a necessary, rather than sufficient condition of “causal determinism”. For example general relativity does not have any fundamental probabilistic elements to it, but fails to meet the definition as stated above. That said, the condition is often imposed in GR at the expense of solutions that allow things like time travel or the ability to open a wormhole (for example).
DSeid, To be ignorant and attempt clarity - you use the phrase “other than as a way to say all things occur” But isn’t the the whole point to the MWI? To provide a context where our perfectly anthropic reality can make sense to exist?
If this universe is tuned perfectly to lead to Life, Humans, Consciousness, it either emerged once, perfectly, or is the result of some multi-verse Darwinian Selection amongst “mutations” or in this case, quantum variations.
Oy. I love the noodling, but fail to see the applicability other than to stop and think “whatever is underlying my reality is likely complex and filled with weird stuff that Humans can contemplate from afar at best.”
I call it the Keanu Principle: Whoa.
ETA: AFat that was all cool. Have you been reading that other thread? How do you feel about a Spinozan approach, accepting Thought as its own level of reality?
Also: hey, my other thread spawned a cool GQ thread!
WordMan - it may be the whole point of MW or not. I do not know enough to answer. We’s in the same ignorant boat. All I’m wondering is where to find a paddle!
But I think I get Asympotically fat’s response and it is cw how I was thinking of it.
In the MWI the totality of the sum of an infinitely branching infinity of worldlines is the universal wavefunction, which is not just our "universe’ (which exists only for maybe one Plank-second before branching off into another infinity of alternatives) but all multiverses that have and will ever be. That universal wavefunction is subject to causal determinism. The view from any of those one out of infinity ever branching worldlines, which is all that is ever observable, is not. The one out of infinities worldline that contains me is indeterministic in and of itself; what can be observed of reality will always be observed as having random probability at its base; this apparent randomness is unavoidable and will always be what is apparent, must be so. Only a perspective transcendent of all the infinity of all multiverses can view the totality in its ultimate causal determinism.
It creates no new falsifiable predictions over other interpretations, may as well be saying there are magical fairies that do it, and the best response may indeed be “shut up and calculate.”
There is a problem though, how can we go to from the universal wavefunction of MWI to the branches of reality? It’s not that clear and that’s before you even consider problem of how the observed probabilities from Born’s rule could be derived from MWI.
I would recommend Jess Riedel’s post on Physics StackExchange:
If, in one world, the Uranium atom decays at time=0, and in another world the same atom decays at time=1, then no complete set of data can completely determine the world’s state – because there are two different non-compatible states.
I don’t get it.
(Even conventional Quantum theory says that no amount of data will let you know in advance when the Uranium atom is going to decay. How can something you cannot predict, even with all the information there is, be “determined?”)
In MWI the state is the universal wavefunction and it evolves by unitary evolution only. That is to say the state does not evolve into one where the uranium atom decayed at t=0 or t=1 and the “illusion” that it does is in itself due to incomplete knowledge of the state.
Whew! That’s depressing. I always thought the Many Worlds idea was that there’s this world, see, where one thing happened, and another world, “somewhere else” where a different thing happened.
“Alternate History” writ small. Maybe not, “A world where Hitler won WWII,” but “A world where the Uranium atom didn’t decay.”
What MWI does say and what it can say are hotly debated. I think (as someone who is not an expert) one of the few universally-applicable things that can be said is that in MWI the complete information about the Universe is described by the Universal wavefunction whose evolution is entirely unitary. How this relate to the world we experience or the possible existence of alternate worlds are open questions.
I suppose one difference between MWI and an interpretation where the state reduces is that the state of our world (considered in isolation) would be ever so slightly different in MWI due to tiny and very quickly decaying contributions from (for want of a better description) “other worlds”.
Keep in mind that the universal wavefunction describes all of the worlds. You don’t have a wavefunction that says the atom decayed at t=0 and a wavefunction that says that the atom decayed at t=1. You have a wavefunction that says “In one world, it decayed at t=0, and in another world, it decayed at t=1”. And that wavefunction is thus completely correct and self-consistent.
