edit: seems like it is lazy loaded, so revised my summary.

> Among the fundamental differences is the fact that classical information can be copied but quantum states cannot be cloned.

The no-cloning theorem says that there exists no universal quantum machine that can perfectly clone an arbitrary quantum state. However, that does not preclude a machine that can imperfectly clone any quantum state, or machines that can perfectly clone some but not all quantum states [1]. (Clearly the information transferred to my brain is not a perfect copy of your brain's state, and your DNA is not perfectly copied every time.)

[1] https://arxiv.org/abs/quant-ph/9607018

This gets used to explain entanglement but it really has absolutely nothing to do with it. This is nothing that the ancient Greeks wouldn't have known.

Not to pick on you specifically, but do people really think it took a major revolution in physics in order to understand that if there are two balls, one is blue and one is red, then if you see one of the balls is red, you can conclude the other ball is blue?

It's something that I think humans can solve at the age of 3.

The failure in your explanation is right when you state that "one of the balls is red and the other is blue". The entire point of entanglement is that such a statement is not possible, that's a strictly classical interpretation. Rather, both balls are in a superposition of being both red and blue simultaneously, and it is not possible in principle to assign a color to either one of them until the moment a measurement is made.

To be fair, this usually crops up in entanglement discussions to deomonstrate how it can't be used for FTL communication and not to actually explain what entanglement is.

I don't disagree, and (clearly) I make a measurement when I show you the color of a ball. Before I show you a ball, I would also say that the colors of the balls are in a superposition.

> major revolution in physics in order to understand that if there are two balls, one is blue and one is red, then if you see one of the balls is red, you can conclude the other ball is blue?

Entanglement is really just this simple — entanglement itself is a statement about a wave function, classical or quantum. The major revolution in physics is that transformations of the wave functions do not behave as we would classically expect. Entangled particles are a tool that we can use to measure those transformations (and get surprising results).

Entanglement is not a property about wave functions and really has nothing to do with waves. It's a logical consequence of the uncertainty principle and was ironically deduced by Einstein, Rosen, and Podolsky (EPR Paradox) as a way to argue that quantum mechanics is an incomplete description of physical reality. Being that it's strictly a consequence of the uncertainty principle, it applies equally well to non-wave function formulations of quantum mechanics such as the matrix formulation which does not use a wave function.

Entanglement is precisely the principle that a physical system can exist such that no part of the system can be described without describing the rest of the system as a whole. Einstein argued that this made quantum mechanics incomplete, the idea that somehow two properties of a physical system separated potentially by light years could not be decomposed into two physical systems that behaved independently of one another violated basic notions of local realism.

The issue is that as soon as you stated that one ball is red you have made a statement about some property of the physical system that is independent of the rest of the system. That is fundamentally what entanglement states you can not do. All you can state is that there are two balls that are in a superposition of being red and blue and there is no way to describe one ball as red and the other as blue, they are both red and blue simultaneously.

That is what entanglement is and that is the new principle that was neither known to the ancient Greeks or something that a 3 year old could figure out. Not the idea that if there are two balls and one ball is red and the other is blue, then if you see the red ball you know that the other ball is blue. Nothing about that ever baffled any physicist.

I don't follow, and I can't find anything online that makes this claim. Could you explain more?

Maybe we disagree about the definition of entanglement. I'll take one from Griffith's Introduction to Quantum Mechanics. On page 422, Griffith writes [1]:

> An entangled state [is] a two-particle state that cannot be expressed as the product of two one-particle states....

(There is no mention of uncertainty in this section either.) Here I read "state" to mean "wave function" which implies that entanglement is a statement about a wave function, as I earlier claimed. "Cannot be expressed as a product" means not independent, just like the balls in my analogy (or electrons from neutral pion decay).

When I say "see the color of one ball," I am collapsing the wave function of the balls by making an observation (in the Copenhagen interpretation). This is analogous to measuring an electron's spin. If you replace "ball" with "electron," "bag" with "decay of a neutral pion", "red/blue" with "spin up/down," and "see the color of one ball" with "measure the spin of one electron," that's a completely valid statement in QM.

[1] https://notendur.hi.is/mbh6/html/_downloads/introqm.pdf

There has to be some observation that would be different in a universe with entanglement than in a universe without entanglement, and you haven't described what that difference is. There must be one out there, though -- it's just not clear to me what it is. Does it have to do with the fact that the fastest I can spread the message "I just looked at ball A and it's red!" is the speed of light, and ball B could be very very far away? But I thought entanglement doesn't actually allow FTL communication?

But Bell's theorem provides a very measureable counterexample to this type of explanation of entanglement. Sure, in the article they talk about electron spins instead of ball colors, but the analogy is that there isn't a well defined "color of the ball" before it's measured.

Of course, the analogy breaks down a bit: electron spin can be measured in multiple axes with somewhat complicated interactions.

No, it does emit two electrons with total spin zero which is not the same thing.

> We can clearly say ahead of time one electron will be spin up, and the other will be spin down.

Let’s imagine that one was really up and the other was down. But you decide to measure instead the spins along a perpendicular axis. You would expect to find no correlation between them.

However, what you actually see is that if you measure both spins along any (common) axis they will point in opposite directions.

It doesn’t make any sense to say that before any measurement one was up and the other down. The red and blue balls analogy is very misleading and has nothing to do with entanglement.

this is exactly why classical analogies should not be used to describe quantum entanglement - it gives the layperson a wrong impression. Those analogies makes it easy for the layperson to imagine the hidden variable hypothesis, which is proven to be wrong.

https://ocw.mit.edu/courses/physics/8-04-quantum-physics-i-s...

My explanation is that entanglement is when there is no red ball or blue ball, there are simply two balls and the color of both balls is both red and blue simultaneously. It's not simply that one ball is red, the other is blue, but we don't know which one is which until we measure them. It's that fundamentally there is no red ball and blue ball, there are just two balls whose colors are in a superposition of red and blue.

I will try to come up with an observable difference but it's hard to do so with colors because the typical examples used for entanglement involve properties that can cancel one another out, so that two entangled particles exhibiting a superposition of two properties will, after many trials, end up forming some kind of destructive or constructive interference that would not be possible if those two particles were in a definite state.

They really are in a superposition, not just ‘not known’ until one is measured.

Just like light was proven to (truly, actually) be both a light and a wave through the double slit experiments. It doesn’t feel right, but it is - and that is where the progress is made, and why the pushback on some examples. It hides the actual truth behind a misleading, but easy to understand example, that teaches people the opposite of what is really going on.

I would expect similar here. Intuition is terrible at understanding what is going on at the atomic and smaller level, or anywhere relativistic anything is happening.

Isn't it true that if you entangle two particles, separate them, then measure one it'll tell you something about the other particle? That's all the example is trying to communicate.

Yes that's true, but that's also true of things that aren't entangled. I assure you if I went to Socrates, showed him a red ball and a blue ball, put them in a bag, and took out a ball at random that happened to be red, Socrates would have no problem realizing that the other ball must be blue. I am sure if I went to my 4 year old daughter, she'd figure it out as well because nothing about quantum mechanics or entanglement would be needed to understand this.

What entanglement tells us is that if two balls had their colors entangled, then both balls are both red and blue at the same time and it's simply not possible to reason about one ball being blue and one ball being red while they are entangled. They are in a superposition of both colors and remain so until a measurement is performed.

Once the measurement is performed, they are no longer entangled and only at that point can you call one ball red and the other blue.

You “make a measurement” well before that, when you say that you have a red ball and a blue ball.

The point of entanglement is that until you make a measurement they don’t have a color. You could measure something else than color and you would also find a correlation.

But if they have a defined color the entanglement is broken. Sure, one is red and the other is blue. But if you measure anything else (a non-commuting observable, that is) there will be no correlatiom.

And not knowing which one is what (already defined) color is not a superposition. It’s just a mixture.

"one of the balls is red and the other is blue"

IS a statement you can make. However, it's surprisingly not equivalent to asserting

    (xor (and (red?  'left) (blue? 'right))
         (and (blue? 'left) (red?  'right)))

In terms of oft-used Bell pair states to demonstrate what I'm talking about, you can definitely say that total S^2=0.

The uncertainty principle here then relates to how much this probability density function 'peaks' in position space or momentum space. A higher peak in one space results in a wider spread in the other. This is because position and momentum are Fourier transforms of each other.

But it is possible to imagine usually unrelated properties of a particle being entangled, e.g. a two-peaked position function, spin up if it's over here and spin down if it's over there. So that's possible. Usually when discussing entanglement, though, we're talking about 'distinct'* particles. Electron A's spin entangled with electron B's spin. Not that it has to be spin, of course. But that's a common case because of how naturally this sort of entanglement occurs, for example, in atoms where electrons have to form spin pairs.

* This is complicated by QFT where particles are not exactly distinct, but exist as excitations in a particle field. E.g. there aren't two electrons but the electron field is excited by two quanta. At least, that's my understanding; I never went to grad school for physics, so I'm limited to undergraduate knowledge and some extracurricular reading.

Yep, sorry, artifact of the editing process.

> they intrinsically have to be related to each other, and the position state (i.e., function) a particle is in fully determines its momentum state.

Sure, but the momentum doesn't determine the position (due to the constant of integration) so you can have two particles with the same momentum functions and different locations, and that leads to my next question...

> Usually when discussing entanglement, though, we're talking about 'distinct'* particles.

That's what I actually meant to ask but didn't phrase clearly: since position and momentum are described by wave functions, can you entangle the positions of two particles? or entangle their momentum?

There's no constant of integration since the integral will be over all of space (or momentum space).

> That's what I actually meant to ask but didn't phrase clearly: since position and momentum are described by wave functions, can you entangle the positions of two particles? or entangle their momentum?

Certainly! I couldn't think of any examples of how it might occur, but I googled it and found an answer on Quora that seems to be correct: https://www.quora.com/In-quantum-mechanics-how-do-I-comprehe...

[1] https://en.m.wikipedia.org/wiki/Kochen–Specker_theorem

The non-classical properties of entanglement start appearing once you start measuring combinations of the redness and blueness of those balls.

Let's say that instead of looking at the balls, you pass them through some machine that will let a red ball pass through with some probability P that you control; if the ball is blue, the machine will let it pass with probability 1-P. Let's say further that you have three such machines. You set the first machine to P=1. You pass each ball falling from this machine through a second machine, which has P = 0. You will never see a ball pass through to the end - if it were red, it would pass the first machine, but not the second; if it were blue, it would not pass the first machine at all.

But, let's say you now put a third machine between the other two, and you set P = 0.5. With classical balls, nothing changes - a blue ball doesn't make it past the first machine, while a red ball goes through the first, may or may not pass the second, and never makes it through the third regardless.

However, a quantum ball actually has a chance to pass through the 3 machines if you set it up this way. In fact, that chance is pretty large - more than half of the balls will start passing once you add the middle filter machine.

Still, this is easy to explain if we assume that the middle machine actually paints the ball instead of just detecting its color. This is where the entanglement experiment comes in: if you pass the pair of balls through the three machines, with ball 1 passing through machines P=1 and P=0.5, and ball 2 passing through P=1, you will find that sometimes both balls make it through, even though both balls can't be red at the same time, and they can't communicate about passing through the P=0.5 machine (you can repeat the experiment with the balls being taken arbitrarily far away before passing through the filters).

I've heard of the apocryphal "half-silvered mirror", but I don't get why reflection isn't an observation/interaction there either.

I know this comment is going to get lost in the noise, but that is a really excellent point, one of the best that has been raised here so far. This is a point that is often glossed over, but it is actually really important, and quite challenging to explain without getting deep into the weeds. The answer is that passing through a half-silvered mirror is an observation/interaction, but it is special because it can be practically reversed by using additional mirrors so that you can get back to a state where you can no longer tell what the outcome of the "measurement" was. All measurements are reversible in principle, but some are irreversible in practice because the number of things you'd have to reverse is just too large. And in particular, by the time a measurement has affected the state of any macroscopic system (like a ball) it is absolutely impossible to reverse in practice, though not in principle. This process of becoming irreversible-in-practice is called "decoherence".

See [1] for a more detailed explanation.

[1] http://blog.rongarret.info/2014/10/parallel-universes-and-ar...

The weird part is precisely this: "you can get back to a state where you can no longer tell what the outcome of the 'measurement' was." In other words, at lunchtime you believed that a horizontally polarised photon hit your nose at 10am in morning, and you were right. Now it's dinner time, you don't believe that, and you would be wrong if you did. If the Everett interpretation doesn't pose a massive challenge to your ideas about reality and human identity, you haven't understood it. There are physics professors who picture photons choosing which way to go at a beam splitter, then transmitting the news backwards in time, because that seems more plausible to them.

Of course, interpretations are not science. Everyone agrees how an experiment would go: any attempt to reverse the interaction of the photon with your nose and brain would fail, because thermodynamics. From a purely scientific viewpoint, it simply doesn't matter how many other yous are superposed in parallel universes, because their existence or lack of it has no consequences that (any of?) you can observe. But scientists are as fascinated by this as everyone else is.

No, it isn't. I've said nothing about many-worlds, only reversibility. And on that point everyone agrees.

> Now it's dinner time, you don't believe that

You really need to read the link above. It goes into all that in great detail. But the TL;DR here is that if it's dinner time, you haven't actually reversed the measurement, notwithstanding your current mental state with respect to the photon.

I don't like claims to authority, but maybe you should read the papers I've published about Bell inequalities too? :-p

It sounds like you're saying that, in principle, physical processes are all reversible. (Although that is often thermodynamically impossible in practice.) You're also saying that it's impossible in principle for someone to learn the result of a measurement in the morning, then unlearn it when the measurement is reversed during the afternoon. I don't see how there could be a self-consistent interpretation of quantum measurement where both those things are true.

How am I supposed to do that? You haven't provided and references and your profile is empty.

> in principle, physical processes are all reversible

Correct. This is a straightforward mathematical property of the Schroedinger equation.

> it's impossible in principle for someone to learn the result of a measurement in the morning, then unlearn it when the measurement is reversed during the afternoon

That's right. But that's not because it's impossible to reverse the measurement. It's because when you reverse a measurement you don't just "unlearn" the result.

You really should read the reference I gave you.

Here you're hitting on the heart of the Measurement Problem. In QM as it is understood today, unlike classical mechanics, there are two fundamentally different kinds of interactions between objects: quantum interactions and measurement. Quantum interactions are linear changes to the wave function, while measurements perform a non-linear update to the wave function (it becomes one for the measured value and 0 everywhere else).

Unfortunately, we do not have any theory so far that explains what is the difference between a quantum interaction and a measurement. The experiment I described works with 'machines' that interact quantically with the 'balls', but does not reproduce if the machines measure the state of the balls.

I will note that in the Many Worlds Interpretation, the measurement problem is somewhat different - it states that the state of the universe is always described by a wave function, but that parts of the wave which are sufficiently separated can no longer perceive each other somehow, usually called branching. Precisely when, why or how this happens are just as unknown, though decoherence seems to play a role

However, the wave function at different places interacts with the environment and start to shift in phase, eventually becoming unable to interfere with itself - this is called decoherence, and is a valid explanation about why and how we can't observe wave-like behaviors at large scales or in hot systems.

On the other hand, we can only postulate, based on observations, that when a particle interacts with a measurement device, the measurement device will show a single value with a probability determined by the amplitude of the particle's wave function at that point. We can postulate that the wave function collapses, or we can postulate that the device branches out into different devices in different worlds (enough such devices&worlds to achieve the probability distribution through observer selection somehow), or many other ways of formulating the Born rule. But whichever way you put it, this rule must be added to your system to predict experimental results, it does not derive from the Schrodinger equation.

I suppose it's destructive interference. It's qualitatively interesting, but its observation is complicated by orthogonal states: when you multiply orthogonal states you get zero. If you can thoroughly dismantle the state to observe it, you still can do it only on microscale, then you'll have a problem lifting it to macroscale evading destructive interference while orthogonal states are all over the place. Anyway, Schrodinger equation describes behavior of quantum states with mathematical precision and the math is quite conclusive that a linear equation behaves in a linear way. When you feel intuition doesn't get you much, you can resort to math, that's why math is seen as an indispensable part of science, because intuition isn't guaranteed to work, which is exactly your case.

>it does not derive from the Schrodinger equation

MWI derives it from the Schrodinger equation. Observation is experience of the observer and can be calculated. Unless you assume that the observer is supernatural and is thus unknowable.

This posits the notion of an observer that only observes one outcome, whereas the SE predicts that an observer will observe several different outcomes with different amplitudes. The MWI is postulating that we should only look at each outcome separately.

Furthermore, it is not possible to derive the actual probability value from the wave function amplitude without some additional postulate equivalent to the Born rule, for example that the number of observers that observe one outcome is proportional to the wave function amplitude of that outcome.

>that the number of observers that observe one outcome is proportional to the wave function amplitude of that outcome

If you mean the number, the norm of each state of observer that observes the respective outcome can be calculated. The statistics over the outcomes can be calculated too.

But this sheds no light on quantum wave functions and quantum entanglement.

Bell showed that the correlation is even greater than you can get using that sort of thinking. Reality is more like this:

Bob and Alice each get a pair of bags, one black and one white. They open one of the bags in which they get either a red ball or a blue ball.

If they both choose the white bags, their balls are different colors. However if either or both of them choose the black bag, the colors of the balls are the same.

If you think about it, there's no way to put the balls in the bags to satisfy these conditions in all cases. This is a simplification of what's going on with Bell's theorem.

https://www.scottaaronson.com/democritus/lec11.html

scroll down to the section titled Relativistic Causality

A proper (but less elegant) would be: you have two balls with the same color or a pattern.

You take one out. If you check the color first, you will find the other’s color the same, but the pattern sometimes different. If you check the pattern first, you will find the pattern the same, but the color sometimes different.

I disagree. Suppose that I create a machine that chooses which ball to place in each box. This machine makes the choice based on some measurement of a quantum particle (electron spin). Then the colors of the ball are entangled with the state of the quantum particle, which cannot be described by some local hidden variable.

It is equivalent to a hidden variable, just a non-local one.

If I look through the holes, I will see that one ball is blue and the other is red.

If I touch them through the holes, I will feel that one ball is hot and the other is cold.

However, I cannot look and touch at the same time. And once I check the color or the temperature of one of the balls (so I know it for both) the link is broken.

If I look first, I’l see that one is red and the other is blue. But if now I touch them, each one will by hot or cold with 50/50 probability. Finding the temperature of one doesn’t tell me anything bout the temperature of the other. And when I touch a ball I don’t know its color anymore: if I look at it again it could be red or blue with 50/50 probability.

Bell's theorem describes the highest possible upper bound of correlations for spin measurements along different axis if it was as you say. But it turns out that in practice they are more correlated than what would be possible according to Bell's theorem, ergo, that analogy (which, in general, is plausible and reasonable) is not compatible with the physical reality we live in.

Here is an example that may make it more obvious:

There exists a game that can be played cooperatively between two players that share two random bits. It is possible to win this game only 75% of the time if the bits are not entangled. If the bits are entangled there is a strategy for winning the game about 85% of the time. The details of the game and a good explanation can be found here: https://www.scottaaronson.com/blog/?p=2464

Basically, there is a game that involves sharing two bits, if they are entangled, it can be won 85% of the time. If they are not entangled but otherwise random (like the red and blue ball example), it can be won only 75% of the time.

That's the spooky part.

This is one of many interpretations, I don't think it's fair to label conjecture as "reality" yet.

My argument is that not only that we do not know a way to conduct such category of copy->measure->compare experiments for human subjects, even with advancement in BCI, etc, it is perhaps impossible to conduct such experiment due to some nature of consciousness that we do not yet understand concerning “information”.

I used the word “mimicking” earlier as apparently when concerning “information” with humans, a (somewhat) “conscious” act has to be performed for the whole phenomenology to be interpreted as that of “copying”. We are encoding “information” in an extremely none-“traditional” way as information is studied and made sense of in computer science.

Similarly, the notion of “semantics” opens up two categorically different sets of paths for inquisition in programming language theory vs linguistics. There is something mysterious and trippy about what “meaning” and “information” really are (eg in regards to qualia).

Being "in a simulation" doesn't imply that we're in simulation created by later humans, it doesn't give any indication how fine-grain the approximations are, etc. etc.

"We're in a simulation" fundamentally discard Occam's Razor in the fashion of the belief in God as controlling everything. And thus this belief has the same weight as belief in the Flying Spaghetti Monster [1].

[1] https://en.wikipedia.org/wiki/Flying_Spaghetti_Monster

You are using Occam's Razor incorrectly. A preference for parismony in problem solving is not identical with parsimony being the only state of the world.

As a side note, which directly applies to your comment, Occam's Razor was invented by Friar William of Ockham as a defense of divine miracles.

You are fundamentally misunderstanding Occam's Razor. It is not a law - Occam's Razor is a preference for how to view the world, not a law that was violated. [1]

There are alternate rules-of-thumb, such as one by Ockham's contemporary, Walter Chatton. Chatton created Chatton's anti-razor in opposition to Ockham's Razor: "Consider an affirmative proposition, which, when it is verified, is verified only for things; if three things do not suffice for verifying it, one has to posit a fourth, and so on in turn [for four things, or five, etc.]. (Reportatio I, 10–48, paragraph 57, p. 237)" [2]

[1] https://plato.stanford.edu/entries/ockham/#OckhRazo

[2] https://plato.stanford.edu/entries/walter-chatton/#AntiRazo

Yes, Occam's Razor isn't a law but a method of understanding reality. My point is that if you throw out Occam's Razor in total, not in one or another situations, you're left with nothing to understand the world with.

The "God wants it that ways" and "because it's simulation" can be substituted for any proposition at all under any circumstances and there's not counter argument to such substitutions. This approach is also "the paranoid worldview" - "because they want to think that" also has this "insert everywhere" quality.

And you're link describing the original ideas of William of Occam doesn't what you'd imagine. "Occam's Razor" is broad approach that's evolved over time and just takes that label for convennience. Virtually no one is evoking the authority of William of Occam or claiming to follow his Nominalism or whatever. The generally means that adding unneeded hypotheses should generally be avoided. If you can never follow that guide, you're in trouble.

Same thing if someone engineers a super complicated method to murder someone while appearing to physically be at a different place. It isn't the simplest explanation, but it can still be correct!

Sure. But if the entirety of reality is created by magicians, then one's concept of reality collapses. The "simulation" view point is indeed pretty much the idea that magicians control everything.

If you read the argument above, my point isn't that Occam's Razor is always correct but if you posit a world where it is generally/always incorrect, your ability to coherently understand reality collapses.

This is the logical fallacy with what you wrote. You don't know what is needed or unneeded.

A logical fallacy is an error in reasoning that is based on poor or faulty logic.

Lol, it seems clear you are the one setting up a debate and attempting to win it. I actually am working on the implications of the "simulation" argument. All of my positions are based "plausible reasoning" with similarities to formal logic being only incidental.

EDIT: maybe we need another word in this context besides 'creationist' since it has a lot of baggage in the culture at this point. What else to call someone who hypothesizes that there is some kind of intelligence behind the universe? The simulationists seem to fit into that category as do the various flavors of 'creationist', 'intelligent design', 'theistic evolutionist' and probably even Hindus, etc.

Interestingly, I think some of the distinction as to why this idea is more palatable is that it doesn't require "supernatural" or "magic" deities. The "creator" could be just like us. We already have evidence that creating virtual worlds is possible--we do it ourselves with games, so I think it takes a lot less faith, as we have a limited proof of principle already.

Also, most magical creationism is totally untestable. You can make some predictions about a simulation, though. If simulations are subject to constraints, which is likely, you should be able to ascertain, in the design of the universe, that items with the biggest O might be subject to performance optimizations. If you find lazy loading, caching, or other performance optimizations at the smallest scale (biggest O), which is what this might predict, you at least have some hints.

[1] https://www.simulation-argument.com/simulation.html

I respect people who believe in a bearded White omnipotent homophobic God who lives in a sky palace more than I respect people who believe in this insane drivel about the probability of living in a simulation. At least the former were indoctrinated as their brain was forming.

I think you've expressed a number of confusions.

First, I think you contradicted yourself. The line you quote says that posthuman civilizations are unlikely to create simulations, but you say this is false because a universe simulation requires more power than available in the universe. So you're agreeing with the outcome while saying you're disagreeing.

Second, I suggest reading the the paper fully, because Bostrom explains that we don't need full universe simulations, we need only consciousness simulations (kind of like the Matrix). The very premise of a post-human civilization is that they have knowledge sufficiently advanced that they have algorithms to simulate human minds.

Much like how video games only render the part of the world that is visible to the players, so a consciousness simulation only needs to simulate minds and their perceptions of a macroscopic, classical world, they do not have to simulate a full quantum universe. Our brains are great at filling in information that we expect to be there, so even the parts that we directly perceivedon't need to be simulated with complete fidelity.

Frankly, I don't think you've given the argument sufficient thought, but by a happy accident you picked exactly the outcome that I think is most likely, and I elaborate on why here:

https://higherlogics.blogspot.com/2021/02/why-we-are-likely-...

Right, but the simulation is nonetheless bottlenecked by whichever system requires the greatest fidelity, and the more technology advances, the more of a problem that becomes. For instance, medieval times would likely be far easier to simulate than modern times, because the latter requires simulating our entire computer infrastructure.

And I think that infrastructure is harder to simulate than you'd think: I could use a solver on a big NP problem (we'll assume that P != NP), get a solution after an hour, and in theory, with some practice, I could probably check if the answer is correct in my head. So the simulator can't simply give me what I "expect". It has to actually compute the thing, and then it's clear that the faster our computers get, the slower the simulation has to run.

Alternatively, the simulation could mess with our minds so we never notice anything out of place, but at that point I'm not sure I understand the point of it. Might as well wonder if this is all a dream.

Agreed.

> because the latter requires simulating our entire computer infrastructure.

Maybe, that isn't clear. There are probably plenty of optimisations here too if given some thought.

> I could use a solver on a big NP problem (we'll assume that P != NP), get a solution after an hour, and in theory, with some practice, I could probably check if the answer is correct in my head.

Yes, but note that we very rarely solve NP or EXPTIME problems exactly due to the costs. We often solve them heuristically or approximately, which wouldn't pose a problem for a simulation either.

Then there's also the possibility that we are simply not free to choose the problem to solve. When running a solver for an NP problem, we just need to input any kind of NP problem, and a simulation could easily have large sets of precomputed solutions available.

> Alternatively, the simulation could mess with our minds so we never notice anything out of place, but at that point I'm not sure I understand the point of it

Depends on whether any such changes affects the point of the simulation. If the simulation is to test world-scale economic models, then isolated tribes wouldn't have much influence on those outcomes.

Then again, maybe the point is simply entertainment. Maybe we're just The Sims for post-humans, in which case there's no point anyway.

Idle curiosity is drives a lot of human behaviour, particularly in philosophy!

No, they are saying the opposite. The argument that simulating the universe requires more atoms than the universe says that a later civilization would not simulate the entire universe. IE, #2 of the refutations really true.

The simulation only needs to produce observations that are consistent with the knowledge of the first observer. Sometimes bit even that, as I describe in the blog post, because eyewitness testimony is known to be quite unreliable.

I'm not sure what sort of history you're thinking of specifically.

The amount of information science could infer on many questions is strictly bounded and in those cases we could only reason stochastically. The data presented at time of first observation can then be generated randomly from the set of answers consistent with what's already known.

The place to implement an optimization like this would be at the items with the biggest O in your world, which is usually the smallest building block--what you'd have the "most" of, which would drive the largest memory and processing demands.

Also, why the assumption that post-humans are running the simulations (as in the paper)? Couldn't it be any ultra-advanced civilization that's playing with an evolutionary simulation?

> Also, why the assumption that post-humans are running the simulations (as in the paper)? Couldn't it be any ultra-advanced civilization that's playing with an evolutionary simulation?

Sure, potentially. The paper makes no assumptions about the existence of other life forms, it instead extrapolates the likelihood of a simulation given the only intelligent life we know to exist: us.

Therefore you can see the simulation argument from that paper as a lower bound on the probability we live in a simulation. Positing the existence of other life forms that run random simulations can only increase the probability we're living in a simulation, assuming one of the other outcomes isn't more likely.

I think the parent poster was noting that it is a pretty fundamentally different argument than say, positing the existence of a creator, because we exist at all - and that said creator has certain specific requirements of us regarding what we do on Sundays, for instance, or with whom and when we have kids.

Is that a requirement of every flavor of creationism? Actually, maybe I shouldn't use 'creationism' in this context because that's a loaded term with a lot of baggage at this point. What else to call a hypothesis that asserts there's some kind of intelligence behind the universe that we see? Simulationists would seem to fall into that broader category as would old-school creationists.

Seems like first you'd need to have some kind of falsifiable evidence that we were in a simulation first before jumping there? Plenty of folks trying to do that though, without falling into the first case.

Personally it seems to have little to no real impact on anything I care about one way or another, so filed in the 'cute but who cares' bin.

Assuming any kind of simulation at all leads to more questions than answers - simply delegating the creation of the universe to the next turtle down. It's not a matter of how "persuasive" an argument is or isn't. It is the evidence the scientific method has produced from which we draw our conclusions.

A. The idea that intelligence beyond human beings would grant it's possessor power that are in ways absolute in very specific, rigid fashion. Human being can accomplish a lot of things. It's notable those things human beings do better than computers seem very tenuous. Humans seem to drive rather haphazardly yet humans drive much better than computers and driving overall seems a "bucket chemistry" sort of activity. Humans calculate much worse than computers and calculation is an exact, defined activity (arguable, the exact, defined activity). But for the singularians, transhuman devices will do the uncertain, tenuous activities that humans do but with "no mistakes". And for a lot human activities, "no mistakes" actually might not even mean anything. Despite humans driving better than computers, humans probably wouldn't even agree on what absolute good driving even means.

B. Simulation as exact map. Any human created simulation of some system is going to be an approximation of that system for the purpose of extracting particular phenomena. Some things are discarded, other focused on and simplified. A model of the solar has to consider conservation of energy or tiny deviations will produce instability over time since errors overall on unavoidable in current hardware. Even a simulation of a computer chip isn't useful unless one knows the chip's purpose is logical operations. But for Bostrom and partisans of

C. Incoherent ontology. If we could produce an exact model of a thing, which is the real subject and which is simulation? What if we could produce twenty "exact simulations", which is real? In a realm of unlimited hypotheticals and unlimited exact simulations, wouldn't a least a countable infinite simulations of "everything" exist. Which is real is quite a conundrum but this problem itself only exists in a world of multiplied objects which we actually have no reason to suppose exists.

As for aging and life extension, I honestly don't understand how anyone could reasonably think we shouldn't stop or reverse aging.

I can certainly comprehend why one would wish to become an immortal being incapable of death. But I just want to be human. Sure you can live forever, but at what cost? A fear for sunlight, garlic, and crosses? For me, "Death is very likely the single best invention of Life."

Not true! It implies we might find performance optimizations, especially at the lowest level. Lazy loading, caching, pointers to constants, that sort of thing. It also doesn't discard Occam's razor. We actually have examples of simulated worlds (physics engines in games), so we know they are possible, unlike the flying spaghetti monster.

Nah, as other have noted, no simulation could have a 1-1 relationship between data humans observe and data in a physical device that exists in a world congruent to what humans observe - because there aren't enough atoms in the reachable universe for this. So such simulation either compresses the actions it simulates using higher level constructs or its happening in some universe congruent to the world we're in. Any such machine is going be a product of a future we don't know about yet and so it's constraints could be wildly different. Moreover, since the standard assumption of this simulation foolishness is that future humans or future post-humans want to learn about their ancestors, one can naturally assume you mechanisms that compensate for any "glitches" that might otherwise be obvious. Which just adds to my original claim.

The issue is that you can only learn whether you're in a simulation if the simulator allows you to do so. Otherwise, the moment that you discover a performance optimization, the simulator could just pause the simulation, delete the discovery from your mind, and resume.

Perhaps. I suspect, though, that it would be subject to the same information theoretical constraints which would provide convergent evolutionary pressures.

It seems at least likely that some level of optimization would be useful if there is any type of cost (energy, materials, resources, space) to the computing substrate, whatever that may be, and that would lead to similar optimizations to what we might be able to imagine.

Practically, the simulator theory may be testable, but probably not. Every religion I’ve run across is pretty clearly not okay to even test.

So that’s progress maybe?

As you say pointer to shared memory location is basically hidden variable theory, you could also move faster than the speed of light by simply updating your location to any value, I have done this in game hacking before you just need a WriteProcessMemory api, might get caught by anti-cheats.

This is part of the premise of the fantastic novel "Permutation City" by Greg Egan.

Edit: OP edited their original comment to be more accurate.

I think this model kind of works and some scientists are working on it, but it is not the preferred interpretation.

One side doing their interaction may cause a "spooky action at a distance" (according to some QM interpretations), but if you have only one side of readings and don't know what the other party measured in their interactions, you can't tell anything about what "the other side" did, so it does not help communication at all because you still need to transmit as many bits in a non-quantum way until you can do anything.

If they didn't follow the plan and measured orhogonal/same (can't remember which) spins, then your results are uncorrelated but you can't know until you meet back up (maybe barring superdeterminism that is also accessible to the individual).

Doesn't the traveler have more information than anyone else on ship about whether an assassination attempt was made in Russia or America? and have it faster than the speed of light? We don't have it with certainty, but we have shared knowledge that is unknowable to others and instantaneous.

The universe either had to break the light barrier to make the measurements correlated (predetermining the outcome isn't generally possible because you could choose how to make the measurement based on another quantum measurement from something outside of the other participant's then-current light cone), or make the same choice through superdeterminism (the other measurement and all others were predetermined too and exact simulation of entire future universe's measurement decisions was shared between every particle when they were within some distance at big bang or something). But even though the universe broke the light barrier, you yourself aren't able to use it for communication.

In the many-worlds interpretation you've both branched into the same branch of the multiverse, but couldn't choose which branch. You do have private knowledge of which branch and the consequences of that, assuming you both followed the agreed on procedure.

I think you can use what you are describing in a series of correlated measurements to set up a provably secure one-time-pad, and then do secure classical communication with it. But you don't communicate the actual bits of the pad, you just both get correlated ones.

You can take actions that will later turn out to be correlated with each other, but you can only find that out once you meet up again, bounded by the speed of light.

If the Universe were {analogy} is {real thing} related to {analogous thing}?

See for example: https://www.frontiersin.org/articles/10.3389/fphy.2020.00139...

My point is, locality and superdeterminism aren't mutually exclusive, they are independent. All 4 combinations are logically possible with current experimental evidence.

https://www.americanscientist.org/article/quantum-randomness

If so GP's statement is just backwards: Super-determinism is a kind of forgoing statistical independence

Yes, the idea is that the past of both the detectors, experimenters, and particle producer were once interacting, relatively recently in the scheme of the human race (let alone civilization, the big bang, etc.) These correlations would be responsible for the entanglement correlations, not a shared nonlocal RNG reference, but rather an inherited local piece of an old reference.

Nonetheless, superdeterminism doesn't have to be doing anything conspiratorial, but the possibility of doing so, lets it violate Bell/CHSH inequalities.

The only difference in quantum physics is that there are actually two parallel universes: One in which you took out the red marble & one in which you took the blue one. You don't know what universe you're in until you look at the marble, but still it doesn't help you to transmit a message to your friend.

(This is assuming the "multiple universes" interpretation- In the other interpretations there is "spooky action at a distance", but this action happens in EXACTLY THE RIGHT WAY to prevent you from transmitting a message to your friend)

I don't think it is helpful to talk about multiple universes, that makes a strong implication towards a many world interpretation. It is better to say that the difference is that in the classical case the decision who gets which marble happens when one of the marbles is taken out of the pouch while in the case of entanglement we do not really know when the decision happens but it does provably work differently than in the classical case. It might be that the decision is never truly made, that both outcomes happen in two parallel worlds, it might be that the decision is only made when one party inspects their marble, it might be that it happens at the same time as in the classical example, ...we don't know.

You say that like it's a shortcoming. :)

There are many who take the (very reasonable) position that the many worlds interpretation is the most epistemologically parsimonious one. Contrary to some misunderstandings of it, it doesn't "add" extra worlds; it removes the concept of "wave function collapse", and leaves all the other known laws of quantum mechanics completely unchanged. The "worlds" arise naturally as more and more particles in the environment become entangled with the measured system, and "wave function collapse" turns out to be the predicted observation of an observer who is themselves made out of quantum states.

The only difference between many worlds and the "standard" Copenhagen interpretation is that Copenhagen adds that, at some point, the entanglement process stops, and a bunch of states in the wave function disappear. And it doesn't specify how, or why, or how to calculate when it will happen. Those that advocate for many worlds would point out that this extra epistemological burden is questionable, given that the correct prediction is made without it.

The contention seems to be that the Copenhagen interpretation elevates wave function collapse from mathematical artifact to real phenomenon.

No, this is the misunderstanding that I'm talking about.

The extra "worlds" follow directly and exclusively from the existence of the various basis states in a wave function, and the laws of entanglement. No other postulates are needed.

Before the measurement/entanglement, the system and environment are independent, and can be written (|0> + |1>) ⊗ (|0> + |1>). After the entanglement, the wave function of the universe can no longer be factored that way, and the system and environment are in a joint state of |00> + |11>. The |00> and the |11> are the multiple "worlds", they show up— in both interpretations— whether you want them to be there or not.

Copenhagen doesn't want them to be there, so it says that one of the |00> or |11> goes away... at some point... because [waves hands and mumbles]. Many worlds merely declines to do this, and that is legitimately the only difference between the two.

The many worlds are in the entangled state but then the collapse postulate reduces them to one world. If you remove the collapse postulate you put them back in. And sure, the collapse postulate is an awful solution breaking unitary evolution and you have every right to reject it, but that does not change the fact that many world introduces - or at least not removes - additional worlds that are not there in Copenhagen.

The "worlds" are there in both theories; Copenhagen adds a new phenomenon (non-unitary evolution) which makes some of them disappear at unspecified times. The "worlds" are direct consequences of suppositions shared with Copenhagen.

Many worlds has N postulates, Copenhagen has no fewer than N+1. One theory is a strict subset of the other's premises. It is not at all accurate to say that many worlds is the one that "introduces" suppositions.

If you argue that the collapse postulate is stupid because it is non-unitary and therefore in conflict with experimental evidence, then sure, I totally agree with this. But just because it is an additional postulate it does not per se make many worlds the better theory. Relativity without the constant speed of light is also a theory with one fewer postulate but it of course in much worse agreement with reality.

The problem with the interpretations is that we are currently unable to distinguish them experimentally which unfortunately adds much more personal preferences to the discussion then there should be.

>But just because it is an additional postulate it does not per se make many worlds the better theory.

The postulate of collapse contradicts the postulate of Schrodinger equation and makes the system of postulates contradictory. By removing the contradiction MWI is strictly better, this in turn also removes non-locality and achieves a strictly better agreement with observation, like special theory of relativity.

> Yes, it gets rid of the collapse postulate, but no, it actually introduces many worlds. [...] but in the end many worlds makes a metaphysical claim that two cats exist, [...] while Copenhagen claims only one cat exists in the end.

If you are saying that many worlds makes a greater number of claims than Copenhagen, that's incorrect, as explained above. The claims made by many worlds are a strict subset of Copenhagen.

If you are claiming that many words "introduces" the worlds but Copenhagen does not, that's also incorrect, because the worlds (it seems we agree) are also there in Copenhagen. If they weren't, there would be nothing to "collapse" in the first place!

If you're not saying one of those things, then I'm not sure what that paragraph is trying to say.

> But just because it is an additional postulate it does not per se make many worlds the better theory

It absolutely does, given that both agree equally well with observation.

Each additional assumption in a theory is an opportunity to be wrong. Therefore, given two theories which are in agreement with observation, the theory with fewer unchecked assumptions has a higher probability of being right.

A theory which disagrees with observation (like your altered relativity example) has zero percent chance of being right, so those kinds of examples aren't applicable.

This is just a somewhat more rigorous way of explaining why Occam's Razor is so effective.

For example, take [the dragon in Sagan's garage][1]. We have two models of reality: A garage containing (a) a dragon, who is (b) invisible, (c) dodges touch, (d) floats in air, (e) gives off no heat (f) etc, etc. Or we have a world/garage where none of those things are true.

Both models agree with observation— any measurement we make will not contradict either "empty garage" or "undetectable dragon". And yet one of them is a better theory. How do we know which one is which? The Undetectable Dragon Theory has far more unchecked assumptions (a...f) than the Empty Garage theory (everything in Undetectable Dragon, minus (a...f)).

Same thing for (forgive the extreme example) conspiracy theories. Moon landing hoaxers' ideas agree with observation— they just pile on a mountain of unchecked suppositions in order to avoid contradictions. If we're holding ourselves to good standards of belief, we pick the world model without all those extra unchecked assumptions. This becomes crucially important when there's disagreement about which theory is the Invisible Dragon theory.

Of course Copenhagen isn't nearly as bad as either of those, but the point is to call attention to the epistemological weight of each assumption we add, and what strategy we use for picking between two theories that are not (yet) contradicted by data. Copenhagen is doing more epistemological lifting, and so if we want to be good skeptics and efficient world model-builders, we should require its unchecked assumptions to be checked before we prefer it over other, more parsimonious theories which also agree with the data.

> which unfortunately adds much more personal preferences to the discussion

I quite disagree. The question is of "which strategy to use for picking models of reality which are most likely to be right". There are objectively good and bad strategies for doing that, in the same way that there are good and bad strategies for designing an airplane, or winning at chess, or proving a theorem. Of course no strategy guarantees success, and a "good" strategy might occasionally perform worse than a "bad" one— But without advance access to the solution, we don't know what those exceptions are, so our best bet is to go with the strategy which performs best a priori. In this case, for the sake of avoiding accidental belief in Dragons, the number of unchecked assumptions is centrally important!

[1] https://en.wikipedia.org/wiki/The_Demon-Haunted_World#Dragon...

Many mathematically and physically theories that are perfectly reasonable are rejected by such people out of hand because it doesn't mesh well with their preconceptions of "The Earth is Special", "I have a unique soul that is me", "Jesus came to us, here, specifically", etc...

I know I'll probably get voted down for this, but these are the literal arguments that I was given once I pressed some of my fellow students hard enough on why they reject MWI.

It's not because they investigated the logic of the situation, like you have. They just "feel" like MWI makes them less special and unique in Creation.

1. It doesn't have anything to do with the topic at hand. It is, at best, a distraction. 2. It is impossible to design an experiment which is capable of distinguishing between a universe where many worlds is the correct interpretation of quantum mechanics or a universe where Copenhagen is the correct interpretation. Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed. We simply do not have the tools to arrive at the truth of the matter. 3. You guarantee that everybody is going to stop discussing entanglement+FTL communication and will start arguing about interpretations of quantum mechanics. I'm not sure if anyone's started talking about De Broglie–Bohm theory yet, but it'll... oops I just did.

I say this as someone for whom many worlds feels truthier.

To the contrary, it provides an intuitive model that produces correct predictions. That is inherently valuable and extremely relevant.

> Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed.

Strongly disagree— See further discussion[1] under my original post for support.

> You guarantee that everybody is going to stop discussing entanglement+FTL communication and will start arguing about interpretations of quantum mechanics

Not wrong >_>

[1] https://news.ycombinator.com/item?id=27900738

Uh. No. It definitely -- definitely -- doesn't do that. Many worlds, for all its many virtues, gives us "There's another dimension where you -- you -- are Batman!" Because that's what the phrase "many worlds" means to most people.

> > Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed.

> Strongly disagree— See further discussion[1] under my original post for support.

So in that discussion, you made the argument:

> Both models agree with observation— any measurement we make will not contradict either "empty garage" or "undetectable dragon".

...which is literally the argument people make when they're arguing Jesus vs Mohamed. It's just that nobody agrees on which holy being is the empty garage and which one is the undetectable dragon.

> Not wrong >_>

Woooo! I won an argument on the internet!!

You're correct but the point is "many worlds" or Copenhagen interpretation having no implications, they each describe the same mathematical/experimental results. They're just "ways to think about the results". They matter as much as whether you label the axes of a graph x and y or A and B. So any theory that "requires" many worlds is inherently not looking using the standard interpretation of many worlds and quantum mechanics.

It depends what one considers "significant differences". If I go from caring about the practical implications of an interpretation to some other implications, I could make all sorts of distinctions. Explanation X might be written in French and explanation Y might be written in Spanish. Even if one is a translation of the other, you could say they're different in various ways. Or maybe one explanation contains swear words and makes the reader feel bad and so the reader might not "like" that explanation.

But my point above is more specific. Since the two interpretations have the same practical implications, a practical prediction can't really "need" one interpretation - the other interpretation gives you the result. This is the point about all the hidden objects/states explanations have classical analogues.

And if we're getting metaphysical, Copenhagen doesn't say live cat or dead cat but says superimposed state.

This is saying the interpretations "exist". The interpretation like intermediate values in some calculation process that are never returned. If the interpretations are true, they can be seen, not just "locally".

It seems like a lot of this basically involves people who've "suspended disbelief" provisionally, accepted a violation of their intuition provisionally but still are hankering for their intuition to spring back into validity. It's like people who accept that general relativity specifies curved space, understand the implications but are still expecting to somehow find a higher dimensional space that all this is suspended in 'cause that's what a fundamental reality feels like to them.

It's like people who accept that general relativity specifies curved space, understand the implications but are still expecting to somehow find a higher dimensional space that all this is suspended in 'cause that's what a fundamental reality feels like to them.

General relativity works just fine without an embedding space but there still could be one. Not that you should think about it in this way without good reasons but only because it is more intuitive. But in the case of quantum mechanics we do - at least that is what I think - understand things so poorly that it is hard to judge what one should reasonably consider while making contact with questions about the fundamental nature of things.

You take a marble out of the bag without looking and give the bag to your friend. Your friend also take a marble out of the bag without looking. Both you and your friend now look at your marbles and they will both be the same colour every time.

You can't send information this way because you don't know the colour until your friend has already taken a marble too. You cannot do anything with the fact that they are both the same colour unless you can control or know the colour in advance, which you can't. When you look at your marble and see that its red, your friend looks at their marble and sees that its red, all you know is you both have red marbles.

The only way to send information would be if you took multiple marbles, looked at them until you found one that's blue (say, the third) and then told your friend to look at the third marble. But since you can't tell your friend to do that without using traditional information sending, you may as well just tell them that the third marble is blue and forego the marbles altogether, you're not sending faster than light information anymore anyway.

Your above experiment could be done with just a simple bag and two marbles without the need to contort yourself around looking or not looking.

Here's an attempt to fix your example:

You and your friend each take a marble out of the bag, go very far away from each other and make an agreement to look at the marble at a given time in the future and not before or after. If you look at the marble before or after the agreed upon time, the result will be random. If you both look at it at the exact same time, the marbles will be equal.

Maybe you have many bags of marbles so you can do this experiment many times over. You decide to fudge some results by looking at some marbles before or after the agreed up time. You and your friend will see the same marble color for all marbles seen at the agreed upon time and potentially different marble colors for ones that were opened at different times.

How do you tell if your friend fudged the result? How does your friend tell if you fudged the result? The marbles have a 50-50 distribution of being red and blue, and the extra probability of it flipping to one color or no if it's fudged is lost in that noise.

If you then reconvene and compare notes on what you observed, you can see a very clear correlation of which experiments were fudged and which weren't but now you've done the work of getting in close proximity and destroyed any chance of faster than light communication.

I'm not a physicist and I don't have a deep knowledge of this stuff. This is a toy example and may or may not be a valid reduction of quantum entanglement. The above explanation is my current understanding, which could be wrong.

Here: "they will both be the same colour every time"

> Your above experiment could be done with just a simple bag and two marbles without the need to contort yourself around looking or not looking.

They won't be the same colour every time, despite being able to be either colour prior to looking.

But ok, I see what you're saying in the attempted fix. Thanks.

Somehow they still manage to align themselves so if one person sees red the other sees blue.

Although it's even more accurate to say that if one person sees [colour] the other person sees [opposite colour].

The colours are random, but the relationship between them is fixed.

Very crudely (and rather misleadingly but never mind) this is why you can't communicate at FTL.

You need the other marble to know whether you had [colour] or [opposite colour]. And that info can't travel faster than the speed of light.

It's even more accurate to say there are no marbles anywhere - only interaction events between marble objects and people-looking-at-marble objects, and the API does not allow you to look inside either to see state.

(The state has to exist somewhere otherwise none of this would work. But Bell proves it's not inside the marbles. So it's "non-local" which is code for "we have no idea where it is".)

It is probably encoded in the cosmic horizon a la Green's Theorem.

For it to be encoded at the cosmic horizon, it has to communicate with the cosmic horizon. It's hard to see it doing so, within the time frame of the experiments, without superluminal communication.

In fact, Bell’s inequality was stated as a collaboration game that can only succeed if you use entangled particles. No classical object will get you the same results.

You still can’t communicate faster than light but the reason is more subtle. The article does a good job but for a deeper explanation I’d refer to Sean Carrol: https://youtu.be/yZ1KSJbJAng

An analogy I like for entanglement is to picture two atoms that will both decay at the same time. You could place them on other sides of the planet and until one is observed to decay nobody learns anything because the timing is unpredictable. After the observation people agree with that timing independent of distance but can’t communicate anything because the timing was random. Still, having two people both knowing some fact at the same time which can’t be observed by outsiders is a useful in it’s own way.

What I like about this is it’s clear what’s going on is different from what’s being described, it’s describing a property of something, and it separates information from communication. On the other hand it’s got plenty of it’s own problems.

The whole point of Bell’s inequality is that quantum entanglement is fundamentally different than classical correlation between two objects which have some opposite properties the observer simply does not know about before observing one of them.

It’s not helpful to use an analogy which teaches the reader the exact opposite of the point you are trying to make.

Your example with decaying atoms suffers from the same misunderstanding. Quantum entanglement is not about lack of information about some specific states, if that was the case, why would anyone talk about loss of locality?

Understanding entanglement and Bell’s inequality requires a completely different ontology than your everyday experience with classical objects. I highly recommend the video I linked above for an approachable explanation. It is not as simple as these analogies but at least it gets to the actual point of this result which tells us something profound about how nature works.

The many worlds interpretation is analogous to global hidden variables, and while out of favor, perfectly consistent with modern physics. That said, the core issue is IMO only a one dimensional property was correlated which hides a lot of the oddities involved.

https://en.wikipedia.org/wiki/Bell_test though none of them are quite definitive on their own https://en.wikipedia.org/wiki/Loopholes_in_Bell_tests. I wouldn’t read much into the loopholes, but they do demonstrate just how difficult this stuff is.

Yes, a classical bag containing classical balls doesn't reproduce quantum behavior, because of Bell's theorem. But GP's description isn't classical; it explicitly invokes multiple universes. Once you've done that, quantum behavior is reproducible, because (just as Bell's theorem says) it's no longer possible to ascribe a single hidden state to the ball/bag system, because you can't eliminate the extra universes.

What exactly does it mean? This sentence always feel like as if these particals are sentient beings and can react to when someone sees them.

If observing means performing an experiment and finding out is this information, that an experiment to observe the actual state has been performed, sent to the other half? To know the state of other half another experiment had to be carried out on it.

How is it any different from picking randomly from a set of pairs? We won't know what other half is until one of them is observed.

For one, if we don’t have free will, no one could bother one way or the other whether they argue about it.

It would also just be a feature of the universe that clouds of atoms take one position or the other :)

Neither of you can choose what the state of either particle is. You have no control, so there's no way to transmit information.

What you can do is agree in advance that you will both take certain actions based on the measured state of the particles. There's no way to be sure the person at the other end actually does so though.

[0]: https://www.ams.org/notices/200902/rtx090200226p.pdf

https://en.wikipedia.org/wiki/Something_Deeply_Hidden

Indeed, you are only sure about the state of the other particle in the instant just after they measured it. Whoever measures first instantly destroys the entanglement link, so if they chose to manipulate the particle after measurement, you will have no knowledge of these manipulations.

More generally, note that in quantum mechanics "reading" the state of a particle (i.e. performing a measurement) is drastically different than "writing" information by manipulating a particle. Most entanglement-related weirdness hinges on this fundamental asymmetry between "read" and "write" operations for quantum information.

Bell's Theorem is just a model showing how two sets of measurements of certain properties of entangled particles would differ in a “Quantum Physics” regime where there is spooky action at a distance changing the measured properties versus a “common sense” regime where both particles leave the entanglement site with those properties already set.

[0] is a fairly easy to understand graph of the correlation of the measurements at the two sites in both regimes, even if the math that generates those charts is beyond me.

Given that, just knowing what measurements you got only gives you an idea of what the other guy across the universe would see were he to measure your particle’s entangled partner - he has no more control over what those measurements actually are than you do, you just know that there’s a certain correlation between what you saw and what he saw. That’s why you can’t use Bell’s Theorem to communicate, neither one of you is actually controlling the measured property, there’s just a certain correlation between the measurements both of you got.

It seems to this layman that in order to communicate FTL using QM, you’d need a way to determine that the property being measured has already been “collapsed” (if that’s the right word) by spooky action at a distance, e.g if the other guy had already measured it. Bell’s Theorem gives us no way to determine if the other guy has actually made the measurements, it assumes that both you and he have both made those measurements.

[0]: https://en.wikipedia.org/wiki/Bell's_theorem#/media/File:Bel...

What happens in entanglement is that the two entangled objects receive say an entangled photon, it is at this point where the two objects are entangled.

Entanglement is a dance of the statistical limits and position of a particle/object given a specific space/energy configuration (initial condition). From this we know the probability of where it can be, what states it can assume, and the limits of both—given the energy it takes to traverse space and assume those states at once.

They are entangled because once information of the states of one of the entangled objects is measured (mainly by analyzing the exiting photon), we can apodictically discern the state of the other.

Say you and Bob share a bunch of entangled particles. Bob wants to send you a message using those particles, so he takes one particle at a time and encodes his information. How would you know he did so? At the very least, Bob would still have to send you a classical signal to say he did something.

There are more subtle arguments why this doesn't work even at the particle level, but that at least should give you an idea why superluminal communication won't work.