Short answer is that that kind of shrinking is impossible by the same laws of physics you’re wondering about.

Assume a miracle happens and people shrink down to electrons and are shot at some double slits.

Assume a miracle happens... — RogueAI

...then anything follows.

Is imagination dead here?

Quantum size, Quantum rules

If people "shrink down to electrons", then they behave exactly like electrons, because now they are electrons.

As for what the experience of those electrons is, which I think is what you really want to get at, it's nothing particularly special. The electron doesn't experience any kind of self-interaction, as in the electron's charge, spin, mass, momentum, all of its properties remain unchanged by the interference of its wavefunction with itself. It only experiences something when it interacts with the screen it hits, and it only hits the screen at once place... per world. Exactly the distribution of places it hits across the possible worlds is what changes from its wavefunction's self-interaction, but it had a range of possible places it could have hit anyway before that.

As for what it's like to have your wavefunction collapse upon interacting with something else, that's basically the whole story of the Many-Worlds Interpretation: when the scientists watch the double-split experiment, they only see each photon hit in one place per world, but upon firing each photon, and its "wavefunction collapsing" to that one location from their point of view, they get entangled with the electron's wavefunction distribution, and a different version of them sees each possible outcome of the experiment in a different possible world. But none of them are any the wiser of their other selves.

And since everything is quantum, this is happening everywhere all the time, including to you right now, so you're intimately familiar with what it's like already. It's pretty ordinary.

If people "shrink down to electrons", then they behave exactly like electrons

You misquoted me. If X is shrunk to the size of Y, X does not turn into Y. In the thought experiment, people shrunk down to the size of electrons would not "behave exactly like electrons". They would behave like people.

What would that tiny person experience as they go through one at a time if the MWI of QM is correct? If the Copenhagen Interpretation is correct?

Particle behavior will manifest as the electron-size person would know which slit he went through. What happens if s/he closes his/her eyes or if s/he was blind is a different story.

Would you get the same results? — RogueAI

Probably; “Bucky balls” give an interference pattern, and they are monstrous compared to elementary particles.

What would the experiences of the people be? — RogueAI

If they’re still people, why wouldn’t they have people experiences?

Einstein imagined riding a light-wave like a train.

But there aren't many Einsteins on the forum.

It only experiences something when it interacts with the screen it hits, and it only hits the screen at once place... per world. Exactly the distribution of places it hits across the possible worlds is what changes from its wavefunction's self-interaction, but it had a range of possible places it could have hit anyway before that. — Pfhorrest

But it's a little person right, so it has eyes :-), what does it experience before the wavefunction collapses/splits, all possible positions at once... and then they all but one disappear when it hits the screen?

It only experiences something when it interacts with the screen it hits, and it only hits the screen at once place... per world. Exactly the distribution of places it hits across the possible worlds is what changes from its wavefunction's self-interaction, but it had a range of possible places it could have hit anyway before that.
— Pfhorrest

But it's a little person right, so it has eyes :-), what does it experience before the wavefunction collapses/splits, all possible positions at once... and then they all but one disappear when it hits the screen? — ChatteringMonkey

Or would it, because it has eyes instantly collapse/split because it gets entangled with itself and as such never see all positions at once?

The OP question is not as stupid as it sounds. I would reformulate it as "What does it feel like to be in a quantum superposition state?" There is some discussion of this and related questions in the literature on the foundations of quantum mechanics.

The OP question is not as stupid as it sounds. I would reformulate it as "What does it feel like to be in a quantum superposition state?" There is some discussion of this and related questions in the literature on the foundations of quantum mechanics. — SophistiCat

Presumably, that depends mainly on your interpretation of the equations, i.e. on metaphysical speculation. If it's many worlds, maybe you are an infinite number of persons at once.

The OP question is not as stupid as it sounds. I would reformulate it as "What does it feel like to be in a quantum superposition state?" — SophistiCat

all over the place, I imagine.

'What did you do to the cat, Erwin? It looks half-dead' ~ Ms Schrodinger.

what does it experience before the wavefunction collapses/splits, all possible positions at once... and then they all but one disappear when it hits the screen? — ChatteringMonkey

Living cats don't smell poison.

Living cats don't smell poison. — InPitzotl

Maybe hypothetical mini-electron sized cats do?

Maybe hypothetical mini-electron sized cats do? — ChatteringMonkey

Normal sized Schrodinger's cat is in superposition; why would mini-electron sized cats be different?

Normal sized Schrodinger's cat is in superposition; why would mini-electron sized cats be different? — InPitzotl

If a normal living cat is in superposition why doesn't it smell poison then? Doesn't superposition entail that it's neither exclusively living nor dead?

If a normal living cat is in superposition why doesn't it smell poison then? — ChatteringMonkey

"Normal sized living cat" is not in superposition; "normal sized cat" is (or more realistically, the contents of the box). The box is in a superposition between two states; A and B. State A has a living cat that smells no poison. State B has a dead cat in it. In MWI terms, once "Schrodinger" opens the box, he just gets entangled with this system. Then you have State A, Schrodinger sees a living cat, and State B, Schrodinger sees a dead cat. Then, the Schrodinger who saw a living cat "smells no poison" (sees no broken vials).

In other words, what it is like to be in superposition is the same thing as what it's like to not be in superposition. You're just a classical-ish thing that is a portion of the wavefunction, not interacting meaningfully with other portions of the wavefunction in superposition, even if that other thing is "a you" that evolved differently. (In MWI terms your "classical" portion would be a world).

"Normal sized living cat" is not in superposition; "normal sized cat" is (or more realistically, the contents of the box). The box is in a superposition between two states; A and B. State A has a living cat that smells no poison. State B has a dead cat in it. — InPitzotl

So then what does the cat in superposition experience, is still the question.

Which one? Dead cats tell no tales, but the living cat smells no poison. (Make sure to see all edits above).

Which one? Dead cats tell to tales, but the living cat smells no poison. (make sure to see all edits above). — InPitzotl

So the branches are allready there before they 'branch'? Makes sense... for conservation of energy and the like.

So the branches are allready there before they 'branch'? — ChatteringMonkey

Not quite. The cat branched when it "observed" (smelled) a system in superposition (between poison in the air and no poison in the air, resulting from broken vial and no broken vial, due to detection/no detection). That observation entangles the cat with this system, but that makes two "worlds". To the one Schrodinger, those two worlds are in superposition, until he opens the box; then his wavefunction entangles with this result, branching him into two Schrodingers.

Not quite. The cat branched when it "observed" (smelled) a system in superposition (between poison in the air and no poison in the air, resulting from broken vial and no broken vial, due to detection/no detection). That observation entangles the cat with this system, but that makes two "worlds". To the one Schrodinger, those two worlds are in superposition, until he opens the box; then his wavefunction entangles with this result, branching him into two Schrodingers. — InPitzotl

Alright, I'm not sure i'm getting it entirely yet. Does this mean that when something branches it doesn't create an 'entire world'? Say when the cat branches the wavefunction, there are two cats but still only one schrödinger until he observes it and 'joins' the two branches. Or does the cat observing it create a entire second world, and then two schrödingers observing it create another third and fourth entire world? I guess from your wording, it's the former?

Edit: Or I guess that there is yet another possibility that they each branch entirely seperately, and that branching does not create an entire world in each instance?

Does this mean that when something branches it doesn't create an 'entire world'? — ChatteringMonkey

Correct. The worlds aren't fundamental; they're emergent. Also the name MWI is a bit of a misnomer; MWI doesn't posit multiple worlds... it posits that wavefunction collapse isn't "real". That leaves only the evolving wavefunction. In fact, the title of Everett's seminal work is "The Theory of the Universal Wavefunction".

Worlds are, rather, simply portions of the universal wavefunction that don't meaningfully interact with other portions. The wavefunction never collapses; instead, when an "observer" measures a system in superposition, the observer simply entangles with it, creating a new wavefunction state where the observer too is in superposition, which in essence becomes multiple portions of the wavefunction that don't interact with each other meaningfully, aka "worlds".

But in SC, the "original" split is the decay versus non-decay of the radioactive material, which is in superposition. Then the detector observes this, thus entangling with it, making a detected decay versus undetected non-decay, resulting in a broken versus non-broken vial of poison (as the vial "observes" the detector), and so on. MWI is simply the idea that we keep going this way when Schrodinger opens the box, rather than apply a brand new rule ("real" wavefunction collapse) to him. So think of this as not an absolute split, but rather, a "propagating" split; observing a split splits you.

Thanks, my mistake was indeed in thinking 'classical' worlds were created. This was really helpful, much appreciated.

You misquoted me — RogueAI

Assume a miracle happens and people shrink down to electrons — RogueAI

Or would it, because it has eyes instantly collapse/split because it gets entangled with itself and as such never see all positions at once? — ChatteringMonkey

This.

:100: :clap: I was hoping someone would give a more complete explanation of MWI while I was gone.

Presumably, that depends mainly on your interpretation of the equations, i.e. on metaphysical speculation. If it's many worlds, maybe you are an infinite number of persons at once. — Echarmion

Not infinite, the number of superposition states in a finite system would be finite. And assuming that we are in a superposition state at any time (or at all times, as per Everett), then there had better be a coherent account of how it is that we feel as if we were always in a pure state, i.e. all the classical observables always seem to have definite values. A number of such accounts, more or less detailed, have been proposed using somewhat different assumptions regarding conscious observers and with different interpretations of QM.

Note that one does not necessarily need to have a fully worked out theory of consciousness to answer these questions, nor is there necessarily a need for any mysticism. Some explanations posit nothing more than a system with memory, like a photographic plate for instance, one that can keep a record of measured eigenvalues.

'What did you do to the cat, Erwin? — Wayfarer

Schrodinger's Cat was not originally meant to be taken seriously. It was an illustration of the problems with emerging quantum mechanics at the time.

A lot of this confusion about things not happening until we 'observe' them has to do with a conflation between detection and observation, as if they were the same thing. But they are not.

Observation is when a scientist looks at the results of an experiment. That has nothing to do with how the experiments takes place or what the results are.

Detection is when a particle in the quantum universe/spacetime collides with an object (experimental apparatus) in physical spacetime. This is what determines the result of the experiment. Observation has nothing to do with it. After all, a scientist could wait months before observing the results of an experiment. Does that mean there are no results until he observes those results? I don't think so.

A lot of pseudo books have been sold on this 'changing reality by observing it' notion...