QM: Why I Find Many Worlds Compelling

#0 What this is, and what this isn’t

This isn’t an attempt to convince anybody of anything. I don’t intend to change anybody’s mind, and if you reject standard physics wholesale (I know a lot of this board does) then this is probably meaningless to you. That’s ok by me.

This is two things: first, it’s a journal of sorts for me - I want to be able to refer back to this to remember why I found this conclusion so compelling in the first place.

Second, I suppose I would like, at the very least, for it to be a demonstration for people who are knowledgable (or at least curious) about the current state of physics and QM that Many Worlds has reasons for it’s popularity. You may not find those reasons compelling yourself, but at least I would like you to see why other people find them compelling.

#1. Brief intro to QM and Many Worlds

Quantum Mechanics is most commonly introduced to people through the double-slit experiment. When you send a series photons through a double-slit one at a time, and you don’t try to detect which slit it goes through, you see a wave-like interference pattern on the other side. When you do try to detect it, you don’t see the interference pattern.

A more simplified experiment is an experiment involving beam-splitters (or half-silvered mirrors) and normal mirrors. In classical terms (which we’ll soon find out is insufficient), you can think of a half-silvered mirror as a mirror that has a 50% chance of reflecting the photon, 50% chance of allowing it to fly through. The normal mirror will reflect 100% of the time. If you arrange these mirrors as below, and send photons through one at a time, half of the photons fly out into nothingness, and half of the remaining mirrors go into detector 1 and the other half go into detector 2 - exactly what you’d expect.

However, when you add another mirror, B below, something very strange happens: 100% of the photons go to detector 2 and 0% go to detector 1. If we go back to what I said about how half-silvered mirrors works in classical terms, we see that it’s actually not able to account for this. If you think of photons as little balls being reflected around, there’s no reason why adding a mirror should completely remove all instances of photons hitting d1. A quarter of them were taking a path to d1 before, and adding the mirror hasn’t in any way cut off that path, so a quarter of them should keep on hitting d1. And yet they don’t.

The reason for this, like the double-slit experiment, is interference. But if you’re sending through a photon one at a time, what is there to interfere? A single ball of light can’t really interfere with itself. And herein is one of the most important concepts of QM and what makes it so interesting - you can’t explain the path of the photon as a ‘ball flying through space’. It’s impossible. It’s incompatible with the experiments. A ball cannot interfere with itself. If it were just a ball, 50% should still go to detector B. If it were just a ball, the double-slit experiment should show no interference.

The mathematics of QM explains this by something I’ll call ‘configuration amplitudes’, which I won’t go into detail about, but basically imagine it as each possible path of the photon is being calculated, and each possible path has an amplitude, and those amplitudes can cancel out. Those amplitudes cancelling out is where we see ‘interference’, and those amplitudes cancelling out is why 0% go to detector B when you add the mirror.

What Many Worlds says is, when the “computer of reality” so-to-speak calculates each possible path to determine where the photon ends up, all possible paths are real. They all happen. So, in the double-slit experiment, you send one photon through, the photon can end up on any place that doesn’t get cancelled out by the amplitudes - Many Worlds says that it ends up EVERY place that doesn’t get cancelled out by the amplitudes, in separate worlds. There’s a version of you that sees the photon in each of the possible landing places.

The primary alternative to this, and the more intuitive one, is that there’s only one world, and which place the photon ends up in is decided randomly. What I want to show here is why I don’t think that view is sufficient.

#2 Relativity of Simultaneity and Preferring Locality

Einstein’s ideas about relativity were revolutionary, and they predicted things that we didn’t see until many decades later. If he was a prophet, his prophecies were born true many times over. I know there are some here who don’t agree with relativity, and… well, that’s their right I suppose, but I don’t think they’re my target audience here.

One of the important aspects of relativity is relativity of simultaneity - if Einstein’s theory of relativity is true, then when you think two events separated in space happened simultaneously, if you looked at the same event from a different inertial reference frame, they wouldn’t have been simultaneous. But no reference frame is correct, and there is no objective truth about simultaneity.

Physicists have had a long history of preferring locality in physics - any physical phenomenon must only be caused by the things in its immediate surroundings. The alternative is of course that physical events can be caused by things far away. The discovery of relativity of simultaneity makes this alternative difficult to justify - if something happens (A) at one location, and it immediately causes something else (B) 100 miles away… how could it? From our point of view, A happened first and that caused B to happen, but relativity tells us that, in a different intertial reference frame, B happened first and then A happened. So A couldn’t have caused B.

Things causing other things far away was an unattractive concept to physicists before Relativity, but after Relativity’s circulation and later experimental validation, it’s almost worth rejecting the possibility of non-local causality without question (but only almost - we’re always open to contrary evidence).

#3 Entaglement, Local “Hidden” Variables and “Spooky Action at a Distance”

The simplest way for me to talk about entangled photons is in terms of measuring ‘spin’. When you send two entangled photons in opposite directions, and measure their spin across the same axis (eg up/down, or left/right – we’ll stick with up/down for simplicity’s sake), then one photon’s spin will be opposite to the other one, every time. If you measure one as up, the other one will be down.

Now at first glance, this doesn’t seem particularly spooky. Imagine a situation where I have a bag, and in the bag I have a red ball wrapped in brown paper, and a blue ball wrapped in brown paper. I take each ball out of the bag, I send one to New York and one to Los Angeles. When the person in New York unwraps the ball, they find theirs was blue, and - it should come as no surprise - when the one in Los Angeles is unwrapped, that one is red! There’s absolutely nothing spooky about it.

However, in QM we have this concept called Bell’s Inequality (or Bell’s Theorem). Bell’s Inequality is a proof that the spin of the photon does not have a definite value before it’s measured. I discuss how Bell’s Inequality proves that here.

Imagine yourself as God, and you’re able to fast forward and rewind time at will and go observe anything anywhere at any time. So you’re curious about the red and blue balls. You know blue was in NY and red was in LA, so you rewind time to before their delivery. The two wrapped balls are on their way, one to New York and one to Los Angeles. You’re God, so you use your x-ray vision on the ball heading to NY and you can see inside the warpping, and it should come as no surprise that the ball is Blue. Then you go have a look at the one heading to LA, and again, no surprise, this one is Red.

Bell’s Inequality tells us, to the contrary, that if God himself went to go look at the spin of each photon before it’s measured, that information is not there. It’s impossible for it to be there. I won’t go into detail on exactly why that’s the case, but it is. And experiments have shown Bell’s Inequality to be true. If someone wants an explanation of why or how Bell’s Theorem could prove something like that, I can go into more detail, but for the purpose of this post, suffice it to say that that’s an experimentally verified fact.

The balls heading to NY and LA is an example of a ‘hidden local variable’ - that there’s a fact that we don’t know, but that is true about the balls, and when we unwrap the ball we simply discover that fact that was always true. And this is what Bell’s Inequality says is impossible for the spin of our photons. We are not discovering a fact that was always true. Photons are fundamentally unlike the red and blue balls.

What’s interesting is that Einstein himself supposed that the ‘hidden variable’ theory was to explain for the correlation of the entangled particles. The alternative is too unattractive, because the alternative violates locality. If one photon is measured up, the other photon will be measured down. But Bell’s Inequality proves that both photons weren’t up/down while they were travelling, before the measurement, which implies that the measurement of one photon’s spin causes the other photon’s spin to take a definite value. But that can’t be possible, because of Relativity of Simultaneity. If you measure both photons at the same time, you can’t say one photon’s measurement caused the other photon’s value, because depending on your reference frame each one might have come first! And there’s no objective fact about which measurement happened first!

And that’s why it’s spooky. It’s spooky because we can’t have it be based on local hidden variables, and the only apparent explanation is non-local causality, which as we established above in the conversation about Relativity is (nearly) impossible.

#4 Tieing It All Together

My concept of physics leaves me strongly preferring locality, and I believe that’s within reason. But of course the data shows one thing unequivocally: the measurement of the spin of an entangled photon will always correlate to the spin of its sister photon, separated in space by potentially great distances. And the spin can’t be decided by a local hidden variable - it can’t be something that was true about that photon the whole time.

If the spin is decided randomly at the time of measurement, then in order for the other spin to correlate, the information of the first photon’s spin has to be immediately transferred across great distances. But then you view the experiment from another reference frame and now you’re not sure which photon was measured first. So this concept is very difficult to square with Relativity, and therefore doesn’t seem like the best option to me.

The only interpretation I’ve seen which allows for fully local physics, doesn’t violate relativity, and allows for the measurement of these photons spin to still correlate with each other is Many Worlds. I’m not an expert, I’m just a filthy casual, but this is why it works for me:

First, let’s get specific about these photon spins and how they’re measured. Let’s say the entangled photons are sent from a central location to Location A and Location B: A is 100m to the east of the central location, and the phycisist there is named Adam. B is 100m to the west, and the physicists there is named Barbra. The measuring aparatus is set up to measure each photon’s spin as close to simultaneously as possible, in their reference frame.

The reason in Many Worlds that photon A doesn’t have to send information 200m immediately, faster than the speed of light, to photon B in order for their measurements to correlate, is that at both places both measurements actually happen. Adam sees his photon measured Up, and another version of Adam sees his photon measured Down. Barbra sees her photon measured Down, and another version of Barbra sees her photon measured Up. Adam’s “world”, so to speak, doesn’t actually find out any information about Barbra’s “world” immediately - the state of each world propogates outward, at the speed of light or slower. So in Barbra’s office, one version of her sees Down, and then she calls Adam, and, slower than the speed of light, she tells Adam “I saw down”. It’s at this point that Adam’s two different worlds have to correlate with the world Barbra’s in. The world where Adam saw “down” is incompatible with the world where Barbra saw “down”. And the same sort of thing happens in the world where Barbra saw “Up”, and the same things are true for both of Adam’s worlds - the worlds created at A match up to the worlds created at B at a speed slower than light.

So Many Worlds is able to maintain locality and account for the correlation of space-separated measurements without hidden variables. And that makes it an inherently attractive possibility to me, over many of the other possibilities for interpreting what QM is telling us.


The most interesting thing in all of this, in my opinion, is the bit I gave the least details on: Bell’s Inequality. If you understand Bell’s Inequality, it remains hard to accept how we could know, for certain, that the spin of these photons is not a constant fact about the photons, like the color of the balls heading to NY and LA were constant facts. At some point I want to post a detailed explanation of exactly why that’s the case. Maybe in this thread, maybe in another. [edit] I’ve done it now! ilovephilosophy.com/viewtopic.php?f=4&t=197257

Also, check out this video for another perspective on Many Worlds: youtu.be/kTXTPe3wahc

I’m going to say this a million times simpler than you did.

By definition: non existence can’t be, thus all that’s left is existence

Thus: existence is by definition asymmetrical

As for the multiple worlds theory…

That’s horrific.

That means any possible world is real.

Fortunately for us, we have a non substantiated dimension of imagination.

I thought James put all of these distortions away on this board.

Why do you want people to believe them?

So when there is no possibility of something happening - it doesn’t happen.
This is a revelation? :confused:

  • Or when it is calculated that it is possible that mass fraud took place in the US elections - the Many Worlds theory says that it certainly did occur (as long as you are not allowed to see the evidence).

  • And when during the trial it is revealed that any of 3 men could have possibly murdered the victim - all are guilty and all must be put away.

  • It is possible that my neighbor stole my bicycle - therefore he did.

  • It is possible that the vaccines will cause birth defects or other deleterious effects - therefore they do.

  • It is possible that O’Biden is an extremely - extremely - clever good faith actor - therefore — nah - not remotely possible.

So , objectivity of simultaniouty is a non objective property, and still happens, because the relative position of quantum measurement constantly changes, but as has been noted by the Jungian observation of individual psychology, such in a different domain disallows such.

Therefore on a differing level, which may go to behavior on a meta-nuclear level, the interference may be the result of some interaction between a two fold behavior of the single elemental particle

Just on hunch.

My problem with multiple realities is that there is eventually so many of them, due to exponentially self multiplying, that there is basically infinite of them. Creating new realities should take some kind of energy to do. There’s not enough energy to create that many universes. Do you understand what I’m trying to say?

I don’t think we necessarily know that that’s the case. The universe doesn’t have to confirm to your conceptions, rather your conceptions are the ones that should bend. We have this conception of conservation of energy and matter, and that’s certainly apparently true within a world, but not necessarily true when it comes to creating new worlds. Perhaps new worlds are free.

Some people who support many worlds actually don’t believe in world-splitting, but believe that all the worlds have always existed, and when a measurement happens, the existing worlds that were identical up to that point diverge. Not sure how widely supported that is though.

Someone asked your question on stack exchange: physics.stackexchange.com/quest … -come-from

James convinced the entire forum of his own personal ideas about physics? Somehow I doubt the rest of the forum would agree with that.

how do you mean real?

if you really want to be able to form descriptions of any and every thing, then you have to have infinite possible worlds because until the problem of infinite divisibility is solved,(spoiler alert, it cant be), there are infinite possibilities to describe. we can do types or kinds or whatever to form sets and simplify the language, but the underlying problem remains. if you want a real theory of everything, then it has to be able to account for infinite possibility given the problem of infinite divisibility.

the trick is that there are infinite possible ones, but only one actual one. so it’s not an energy problem, it’s a problem of knowing which one is the actual one…as in, the one that we’re in. we narrow it down by doing counterfactual analyses or things that we can observe here. we have to say that all the possible ones are “real” not because we know them to be concrete like the one we’re standing on, but because we cannot prove that they aren’t the one that we’re standing on until we’ve done the infinite amount of observation that would have to occur for there to be certainty about everything that there is.

counterfactual analysis is a fancy way of saying that we rule shit out deductively.

I’m sure there is something like the law of energy where you can’t create realities for free out of nothing.

Also possibility is not infinite.
It is only an aspect of Potential Energy.

I don’t think that’s been experimentally proven, I don’t know of any experiment that can demonstrably create a new world and prove how much energy it took.

I THINK quantum experiments create new worlds, but I don’t have the audacity to think we know that for sure, and we certainly don’t have a way to measure how much energy it took to create it.

Perhaps creating a new world takes as much energy as it takes you to click ctrl+c ctrl+v

what if those realities were purely abstract?

create or reveal?

And this part? -

I don’t know, I don’t have a strong preference for which of those two visions seems the most reasonable. I just know that, in Many Worlds, conservation of energy and matter is maintained within a world, and that’s the only place humans have ever been in which is why we have that rule. That rule doesn’t necessarily apply outside of a world.

impossible world are the ones that do not exhibit regularities that conform to the fundamental aspects of our ability to perceive and discern. like worlds where the law of identity doesn’t hold. you can chunk all those in the trash because there’s no way to analyze them and if it were ever going to be ok to throw a bunch of shit into a set in a theory of everything, it would be the shit that goes into the set of things impossible to perceive.

This article: thestargarden.co.uk/Everetts … orlds.html

takes the view I was talking about: worlds don’t split, there were always there.

I don’t know anything about that site or how reliable it is, just using it as an example of “world splitting” vs “worlds always existed”.

I don’t think “Many Worlds” is touching on that sort of thing. Many Worlds is just about physical quantum events being measured - a world split in QM doesn’t produce worlds that have different laws of physics or logic. Just worlds where different measurements happened.