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?

  • Well blow me down. I hadn't thought of this. I think you might be right. The argument holds up for me although I'm still pondering. Nice one!
    – user20253
    Commented Jul 6, 2018 at 11:23
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    I don't understand why you take determinism to only be possible in our "universe"; you can easily state that there are other deterministic systems in the other "universes" (if we're inclined to take your definition of multiverse and not the Many-Worlds theory as the answers below suggested), exactly like we (might) have in our "universe". You also imply a causal link between the "universes", which isn't necessary. Commented Jul 7, 2018 at 9:58
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    I don't see how being a determinist contradicts the possibility of existence of our universes. There could be even a universe identical to ours (for any internal observer). No contradiction. What it can contradict is many-worlds QM interpretation. But even then it is possible for determinism to be the case. In the end, determinism means the world is computable.
    – rus9384
    Commented Jul 7, 2018 at 22:46
  • If determinism means the world is computable, 100% predictable, there are no variations. If there are variations, or areas that are not predictable, that allows for choice or free will, of the freely acting agent. If there is total predictability why does there need to be alternate realities, because if they are mirrors of this world, they must be identical. This is not the popular concept of multiple universes, this is my point.
    – PeterJens
    Commented Jul 8, 2018 at 7:49
  • @PeterJens "if there are mirrors of this world, they must be identical" - a) why do you consider the "other worlds" as "mirrors"? b) why do you think they must be identical? In fact, if they are identical, they are most probably the exact same world we live in (Leibniz would use this idea to pursue his "best possible world" thesis). If there are actually other worlds, they must be non-identical, most probably with different logic system and physical laws. A nice article that follows your overall stance. Commented Jul 8, 2018 at 16:06

7 Answers 7


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.

  • Under the Everett interpretation, there can still be uncertainty about which observer I am. Perhaps this kind of indexical uncertainty would be perceived to not violate determinism. On the other hand, for example Hellie's vertiginous question suggests that there needs to be something that determines which perspective is mine...
    – present
    Commented Aug 6, 2018 at 2:46

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?


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.

  • Many Worlds is the dominant interpretation of the Measurement Problem, among professional physicists, as evidenced by Tegmark's conference surveys.
    – CriglCragl
    Commented Mar 10, 2023 at 20:05

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.

  • If in our world everything is determined by its existence in the physical world, there are not alternatives possible, or else determinism is not true. Once there are alternatives, no matter the source or trigger point of the alternatives, things are not determined.
    – PeterJens
    Commented Jul 6, 2018 at 10:10
  • @PeterJens What do you mean, exactly, by "our world"?
    – Chelonian
    Commented Jul 6, 2018 at 13:47
  • "our world" - the world we experience and know as opposed to other worlds or parts of the universe we inhabit but do not know.
    – PeterJens
    Commented Jul 6, 2018 at 13:55
  • Physicalist materialism is compatible with either a deterministic or quantum world. A quantum world can be considered determinstic across a Many Worlds interpretation. Quantum randomness cannot give you free will, causality deriving from mind states, except in a compatible sense of being a kind of supervening heuristic explanatory layer. Randomness is irrelevant to this, if you are a physicalist materialist.
    – CriglCragl
    Commented Jul 6, 2018 at 15:01

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.

  • If you have any references to those taking a similar view this is an opportunity to reference them. It would also give the reader a place to go for more information. Welcome! Commented Sep 4, 2019 at 15:20
  • Actually, I won't say this is a unique point of view, but I haven't found the exact thinking anywhere else. All I could reference are the basic things like determinism, algorithm and alike. This was my attempt to resolve issues with randomness and boring future, occasionally thinking about it within last 12 years.
    – n0p
    Commented Sep 4, 2019 at 15:29

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]

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    Welcome, Любовь Пахомова. I have enough Russian to read your answer. It's interesting and relevant but PSE is an English-language site. It really would be helpful if you were to provide an English version. Many other users would then have the benefit of undertanding your answer. All the best - Geoffrey.
    – Geoffrey Thomas
    Commented Mar 10, 2023 at 9:59

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:

  • An irrational person capable of believing in conflicting propositions simultaneously.
  • A rational person suffering from cognitive dissonance as reality does not match his beliefs.
  • A misguided person who doesn't understand determinism or free will.

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.

  • An argumented or sourced answer would be welcome.
    – armand
    Commented Mar 12, 2023 at 23:15
  • Here's the argument: The definition of determinism describes conditions very much different from reality. Believing otherwise is against either the definition (misguided person) or reality (cognitive dissonance). Commented Mar 13, 2023 at 4:43

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