A determinist holds that everything is determined by the physical world around them and free will is an illusion.
A multiverse suggests there are an infinite number of alternative universes in existence, of which we only experience one.
But if the world does not have free will, and everything is determined, then a multiverse will never exist because the existence of our universe determines it cannot exist.
Is this true? A lot of determinists also believe in a multiverse, but how?
You might be misunderstanding the Everett ("many-worlds") interpretation of quantum mechanics. On the Everett interpretation, there's one universe, and its change in time is described deterministically by the Schrödinger equation. But observers inhabit different "worlds," meaning that they will give different macroscopic/classical reports of events. One observer will report that the cat in the box is dead, another will report that the cat in the box is alive. Both observers inhabit the same, single universe; but their macroscopic/classical experiences of that single universe are different. The change of worlds in time is only described probabilistically by the Schrödinger equation.
Or, you might be thinking of classical universes, described by Newtonian physics. Newtonian physics isn't deterministic. But bracket that point. A system is deterministic if its future state is necessitated by its past state and the laws that govern its change over time. So you can have many deterministic classical universes with different future states so long as either their past states or the laws that govern them are different.
Free will is not the opposite of causality but of coercion. Free will means that I have agency, based on my own internal mental states as well as the situation around me. It does not mean I can violate the laws of physics. It means I'm awake, aware, and don't have a gun pointed at me. (Or some other physical threat, etc.) An entity is said to have free will when it has internal mental states that can change its behavior.
Non-determinism would not save the notion of free will that people say is impossible. If I'm walking down the street and then, for no apparent reason, my arm flings out and smacks somebody, that's not free will. The un-caused isn't free will. The randomly produced without cause is not free will.
Multiverse theory is a (fairly abstruse) variation of quantum mechanics. It was suggested as a way to interpret certain things in QM that people had difficulty adding to their list of things they thought they understood.
It better not be required to understand anything about human behavior, since the idea only arose a little more than 60 years ago. Whatever did people do about late-night arguments over too much alcohol before that?
https://www.newscientist.com/article/dn26261-hugh-everett-the-man-who-gave-us-the-multiverse/
And, so far, nobody has managed to formulate an experimental test of multiverse theory. That is, nobody has managed to show that the existence, or non-existence, of these other universes, can be shown to make any detectable difference.
Free will is not compatible with physicalist materialism, except in a compatabalist sense of being a useful illusion. Whether there is true randomness in the world cannot account for free will, or not.
The multiverse is not a fixed eternal visitable place, and neither are parallel universes. The past exists as it is embodied in now, in conserved quantities and so on (including information conservation, in the Many Worlds view). Alternative probabilities exist in probability space, which has real measurable impacts on our reality, over certain specific -compactified- scales. https://www.universetoday.com/48619/a-universe-of-10-dimensions/
Many Worlds recovers determinism in quantum mechanics, but in a higher dimensional space that ours is a subset of.
the existence of our universe determines it cannot exist.
What does that mean? It doesn't make sense to me.
Although the question has been asked and answered more than a year ago, I'd like to add my INPUT which I believe is missing and will make it more clear that there's no contradiction (or confuse further).
Consider the multi-verse or better let's say meta-verse as a tree. Every branch is a universe which develops and may or may not depend on other branches when it is the time to branch out again (satisfy the branching condition, make a decision, etc.). See how sound this is with real tree. One branch depends on the weight of the other one for the tree to balance itself and also there are things that are not inter-connected like an animal eating leaves from only one branch. The tree still grows deterministically.
All those things are inputs to THE deterministic program/algorithm which behaves different depending on the input. Where inputs come from? From meta-verse. These inputs are also generated in a deterministic way, as you will see later. It is hard to say if the number of inputs is limited or not, but the values an input can have is limited, like digit, for example. Not every input is set at the same time, it is set by THE program when it needs to satisfy a branching condition. All the possible values are tried. Which I think is the reason to believe there's a multiverse. Basically, every universe answers to the question "what would happen if this thing would go this way". Note, however, that not everything is possible. Everything is determined by the laws of the whole meta-verse.
Now we see the meta-verse is a pretty useless set of values for the inputs. In this case, if the number of inputs stay constant, then this means we have all the values to satisfy every branching condition. This would not allow a development (or would lead to the end) and would be the boring output of the meta-verse program fed with current set of values.
And finally, the most interesting part...If we believe the meta-verse is run once with a given "set" of values or to say so that there's no God to rerun it with different values and we don't think the meta-verse will ever finish...We need self-modification! Think of recursion. The meta-verse keeps running itself and for THE input is using the output of the previous run.
Every recursion (including trees) needs a starting value, which for our tree of life, I think, was number 0.
A multiverse provides the determinist with an explanation for randomness. This explanation hopes to avoid the suggestion that there exist events originating from the free choices of agents on statistical grounds.
First consider the anthropic principle. Here is Wikipedia's description:
The anthropic principle is a philosophical consideration that observations of the universe must be compatible with the conscious and sapient life that observes it. Proponents of the anthropic principle reason that it explains why this universe has the age and the fundamental physical constants necessary to accommodate conscious life. As a result, they believe it is unremarkable that this universe has fundamental constants that happen to fall within the narrow range thought to be compatible with life. [my emphasis]
Wikipedia links the section in bold with its "Fine-tuned universe" article.
The fine-tuned universe is the proposition that the conditions that allow life in the Universe can occur only when certain universal dimensionless physical constants lie within a very narrow range of values, so that if any of several fundamental constants were only slightly different, the Universe would be unlikely to be conducive to the establishment and development of matter, astronomical structures, elemental diversity, or life as it is understood.
A fine-tuned universe suggests there is either a tuner, which points to theism, or randomness. Randomness, by itself, is a threat to determinism. Also it is not an explanation. The multiverse attempts to provide that explanation.
Generally, whenever something appears 'random', and there is nothing to explain that randomness, that opens up a possibility that a free choice from somewhere occurred choosing one of the possibilities. Such a free choice coming from anywhere would falsify the hypothesis of determinism. To avoid that falsification, just add to the assumption of determinism another assumption that if scientific evidence forces one to accept randomness then all of the possibilities occur in some universe of a multiverse.
The OP asks whether determinism and a multiverse are contradictory.
To get a logical contradiction one needs two propositions, one being the negation of the other, that someone commits to. It may be easier to obtain a contradiction between determinism and randomness. Even there finding a logical contradiction may not be easy.
However, if one is opposed to determinism another approach taken by the Information Philosopher is to view determinism as a "dogma" that needs to be revised and then provide an alternative to it.
Wikipedia contributors. (2019, August 27). Fine-tuned universe. In Wikipedia, The Free Encyclopedia. Retrieved 13:30, September 5, 2019, from https://en.wikipedia.org/w/index.php?title=Fine-tuned_universe&oldid=912702879
Wikipedia contributors. (2019, August 29). Anthropic principle. In Wikipedia, The Free Encyclopedia. Retrieved 13:26, September 5, 2019, from https://en.wikipedia.org/w/index.php?title=Anthropic_principle&oldid=913044836
From my point of view, the theory of determinism does not rule out the existence of a multiverse. After all, if we assume that each event has both a cause and effect, that everything in nature is predetermined, then according to the theory of probability, only the most probable events should occur. But how then to explain the fact that events occur, the probability of which is extremely small? Now, if we assume that all events occur simultaneously, only in different universes, then we will get the answer to this question. Then determinism has a place to be, and multiverses.
Original text:
С моей точки зрения теория детерминизма не исключает существование мультивселенной. Ведь если предположить, что у каждого события есть и причина и следствие, что все в природе предопределено, то согласно теории вероятности, должны происходить только наиболее вероятные события. Но как тогда объяснить то, что происходят события, вероятность которых крайне мала? Вот если предположить, что происходят все события одновременно, только в разных вселенных, то мы и получим ответ на этот вопрос. Тогда и детерминизм имеет место быть, и мультивселенные.
[Translated via Google]
A determinist holds that everything is determined by the physical world around them and free will is an illusion.
This definition means that a determinist is either:
The acceptance of the popular half-idea that "free will is an illusion" suggests that the last option (misguided) is the most probable.
Anyway, being a determinist is contradicting reality, in both multi- and singleverse.
