From what I’ve read, according to the Many Worlds theory, every time I make a choice, a new universe springs into being in which I make a different choice. But what constitutes a choice? Does it have to be a conscious, binary choice? For example, there are a large number (infinite?) of things I’m NOT doing right now, including running around my workplace naked except for clown makeup. Does that mean that there’s a universe in which I am doing that? And am I just getting lucky to keep ending up in the universe in which I’m behaving well? Or does the theory only apply when I have to actually consider what to do next? (Until now I’ve never considered running around naked at work with clown paint on).
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It seems entirely unfair that a person and a universe springs into being in which they will be punished because of the good decision made by their counterpart in another universe.
Many Worlds has nothing to do with choices or consciousness or willpower or anything human.
In order to get normal, classical mechanics out of quantum mechanics, you need something called wavefunction collapse – in effect, a particle whose state was uncertain has (some part of) its state become certain upon measurement, with the result of the measurement reflecting that certain state. This is weird, because why would a fuzzy smeared-out thing suddenly become sharp when measured?
Many Worlds just says that it doesn’t – that, in fact, the world we see with definite states is just one possible state of us along with the rest of the Universe and that, like a particle whose position is uncertain, the Universe is in fact a smeared out combination of every such possible timeline. There are many yous in the same way that an electron can be in a mixture of different orbitals in an atom.
It’s not about choices, and it’s not on a macro level like that.
Journalist and science communicators talk about it like that because it makes sense to a layperson, but it’s really not that accurate.
It’s much *much* smaller scale than that. Like individual atoms bumping into each other.
When people talk about the “many worlds theory” what they are referring to is the “many worlds *interpretation* of quantum mechanics”. I pointed out the word “interpretation” there because it’s not really a theory. The math doesn’t tell us this is true, and we have no way of testing it (as far as I know). But it’s one way to *interpret* what might be going on.
What MWI says is that there is no *wave function collapse*. You can probably already see why science communicators are oversimplifying it. Because now you need to understand what a wave function is.
But basically (this is *also* going to be not entirely correct but hopefully less incorrect than what you have heard before) in quantum mechanics we can never know the exact position and velocity of a particle until it interacts with another particle. But what we can do is describe where it probably is and what it’s most likely to be doing. This is called the wave function, it’s basically a list of all the possible states the particle could be in. Like “moving quickly coming for the left, Moving slowly coming from the top.”
Once that particle interacts with another we know where it is at that moment. There is no longer a wave function.
So what MWI says is that there is a universe out there for every single one of the state that wave function said it could be in.
“Many Worlds” theory is not falsifiable and not even testable. Common sense tells us there is only one universe. Theories like these simply highlight the difficulty of using human language to try and describe certain aspects of physics, quantum mechanics, and the like.
Every time you flip a coin in a many worlds multiverse the universe splits into the potential outcomes. Heads, Tails, being most probable (But the coin can also land on its side lol). 6 heads (H, H, H, H H, H) is less probable than any combination of 3 heads and 3 tails as there is only 1 way to get 6 heads and many to get 3 heads and 3 tails eg. (H T H T H T), (H H H T T T)
Your choices are no different than the coin flips. Just more complex. Based on your personality, experience, physical body, certain things are more probable than others. An introverted, risk avoident accountant might sky dive, but it’s unlikely. However the probability isn’t zero.
If universes are truly infinite a universe exists where all coin tosses end with heads as the outcome. Heads, Always, all coin throws purely due to chance come up as heads. However universes with more typical coin flip outcomes would be much more common.
The universe you exist in is probably very average because it’s more common. Most your choices yield pretty normal outcomes. You win some you lose some but things will typically average out to your skill level etc (think chess rating).
If you deal in risky behaviors the probabilities on average will play out it you play them enough. If you deal with smart behaviors on average these behaviors will average out. Consistency is important.
On a side note. Our solar system is pretty average, our sun is pretty average.
If simulations exist. It’s unlikely that you would be the true world, but in a simulation, simulating a simulation, but you would be somewhere in the middle of the stack of simulations because that is most probable.
As the other user said, Many Worlds isn’t explicitly focused on _your_ choices, but on the “choices” made by particles. Contrary to classical understanding, a particle doesn’t have to behave like a billiard ball bouncing around according to clear geometric rules; its location and velocity can be a bit fuzzy, which creates a certain amount of randomness in the universe. At the level of everyday life, this randomness mostly washes out, but it is noticeable at the particle level. Many Worlds says that this fuzziness represents separate universes splitting off for every single particle every time there’s more than one thing the particle could be doing, which is all the time. That’s a lot of universes.
Most of the randomness at the particle level washes out at the everyday level – for every particle that zigs instead of zags, there’s probably another that zags instead of zigs, and so on. Consequently, most universes would probably look more or less similar. But not all of them would.
Inhibitory neurons in your brain tell you that it would be a bad idea to be a naked clown. They prevent you from doing that by releasing neurotransmitters into synapses, and these neurotransmitters move through a combination of Brownian motion and chemical attraction toward receptors at the far end of the synapse to pass those signals along. That’s all a choice is, by the way – different neural circuits firing, weighing the strength of some signals against others.
It is extraordinarily unlikely – extraordinarily, I say – that every single one of those neurotransmitters in your inhibitory pathway would be nudged away from its cognate receptor by errant water molecules through otherwise-random Brownian motion. It is so unlikely that we can disregard it for any other conversation. But mathematically speaking, it is _not_ impossible. Ergo Many Worlds would have, among the infinite possible worlds in the multiverse, some where you are a naked clown.
It’s not just luck that in most universes, you still have a job. The clown scenario requires extremely improbable aggregate particle behavior. Other choices you might make may face less inhibition or may have greater relative salience, so multiple competing possible results are more likely.
The idea is that anything that can happen does happen, even mutually exclusive events, they just happen in alternate realities. Is it possible that a radioactive decay causes a brain cancer that results in you running around your workplace naked in clown makeup? Call it a low probability. (still infinitely many, if it’s possible at all, but very much a smaller infinity than the ones that don’t run around naked in public with clown makeup on).
Of the universes have someone recognizable as you in it, most of them are probably pretty similar.
Its not about choices. Many Worlds is an interpretation of the maths behind quantum mechanics. Quantum mechanics have a so called measurement problem. Particles seem to exist in a weird way. They are in a superposition of may states but when they interact with something they have to “decide” which specific state to pick.
In other words we have a wave that describes a particle. That wave is a probability. Like location is a good example. The position of a particle is indefinite. The wave shows where we are more likely to find it and where we are less likely to find it. But when we measure the wave collapses and the position of the particle becomes definite. So what is going on here?
Does the particle only occupy one state and we just don’t know which one? Is the wave function real or just a mathematical model? Whats the reality? We dont know. We know that particles are really in a superposition of many states and not carrying hidden information. We can experimentally verify that.
So what happens when the wave of probabilities collapses. It appears to be truly random, its not sudorandom, there is no hidden complexity that creates so much chaos that we can call it random like a coin flip. Its random we have no way to predict exact results.
This goes again what we know about the macroscopic world. We (its uncertain) believe its deterministic. This means that if you have a perfect model and know all the necessary starting conditions of a system, you can predict its future perfectly. But that isn’t true in quantum mechanics.
So we have this problem, where does the randomness come from? How can it be this undeterministic. Many Words says that there is no randomness. Every outcome of a measurement happens.
The key idea is that every interaction creates an entanglement. You got a particle it can be in state A or B with 50% chance of each. You measure state A. What Many Worlds say happened is that the measurement caused the universe to branch in two. On where the particle is state A and one where its state B. You got entangled with the state A particle and exist in the universe with the state A particle. Another version of you got state B and got entangled with that particle in another universe.
We gave determinism back the most pointless way. Every outcome happens so the entire multiverse is deterministic but we still cant say anything about the future in the universe we are in. Quantum mechanics is no longer random its the universe we get thats random as we only see one outcome but all of them happen.
These questions are actually good questions…against other interpretation of quantum mechanics, but not Many World itself. Many World is basically the interpretation that said “I don’t have to care what ‘choice’ really mean”.
The better description of many world interpretation would be “there are no trimming of worlds, particles don’t make choices, and there are no special physical process called ‘measurement’ that has new mechanism”. The reason why many world interpretation often was described as “a new world spawn whenever a particle make a choice” is because they’re trying to contrast it against other interpretation when the particle do make choices. Unfortunately, that gives the wrong impression that many world interpretation tackle on an ad hoc hypothesis (many worlds) on top of poorly defined concepts (measurements and choices), when in fact, it’s the opposite, it removes an the poorly defined concepts (measurements and choices) commonly seen in other interpretation, and let the rest of the math happen.
Let me elaborate.
Quantum mechanics, on its own, already lead to many world. Any system has many classical states (technically speaking this is not quite correct either, but simplicity for the sake of ELI5). If you have a small system, these different states can interfere with each other easily. If you have a huge system, it’s astronomically unlikely that these states can interfere with each other. When you have a huge system, its states are so unlikely to interfere with each other, these states are called “world”.
But there is no clear dividing line between what’s a state and a world. When you have a small system – that was previously isolated – interact with a large system, the states of the small system rapidly separate from each other until they become unlikely to interfere, this process is called decoherence. This is a “measurement”. From the perspective of one state in the big system (one world), the small system made a choice. But there are no clear dividing line here. The small system gradually (but rapidly) has its states separated from each other, but there are no single instance of time where you could say it had made a choice, no single instance of time where you could say they are now in different world. The bigger your system, the more separated the states, and the less likely the interference, but there are no exact dividing line where the system is big enough that the states are now world, just a gradual decline in interference. There are no precise instance in time when the small system interact with the big system either, the amount of interactions can vary which affect how fast these states get separated.
As an analogy, asking exactly when a new world is spawned would be like asking the exactly when a baby is born: is it when its head pop out of the womb, is it when the entire body is out, is it when it takes the first breath? There are time when we are sure the baby is not yet born, and there are time when the baby is clearly already born, but there is a time gap in between when there are no clear answer. Our concept of “the baby is born” is just an imprecise description of what happened physically.
The above situation are true in quantum mechanics, and hence is true in all interpretation of quantum mechanics.
What Many World Interpretation said, is that all of the term above, “world”, “measurement”, “choice” are just our imprecise description of the underlying deterministic physics. It’s the one interpretation that does not care about what these word means exactly.
But most other interpretation of quantum mechanics care about what these word mean exactly, because they also suppose that there is only 1 world in the entire universe. Somehow, despite all of the spawning of world that keep happening, these extra world get trimmed away, somehow, so that the entire universe has only 1 world. This trimming of worlds is called a collapse, and it happens during measurement. The difficult problem of determining exactly what is a measurement – so that we know exactly when a collapse occur – is called a measurement problem.
That’s why the issue of when the particles make choices is a question for other interpretations of quantum mechanics, but not many world itself.
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