The everything-is-a-quantum-wave interpretation of quantum physics
arxiv.org
arxiv.org
Other interpretations always posit some extra stuff, like wave function collapse, or pilot waves. Many Worlds just takes the Schrödinger equation seriously on its own.
Therefore it is in a very real sense the most austere interpretation, even though it posits all those worlds.
I go back and forth myself on whether I buy the austere interpretation. Mainly I struggle with the open question of probabilities. Something about the combination of probability and philosophical argument - the two most hard to intuit things in the world - makes my head spin.
Though there are also so many compelling advantages, like providing an arrow in time in that branches of the wave function never re-merge.
I'm also fascinated by superdeterminism. I don't have the same philosophical issues with it that others have. I settled on the "useful fiction" view of free will a long time ago anyway. But I've yet to see any logic supporting the idea that the entire universe would, or even could conspire in this way. But I also used to think many worlds was inherently illogical, so I don't know.
Then there's the voice in me that says "it's just a collapse, it just has to be when there's enough moving parts", but again, can't think of a justification for it other than intuition.
And now there's a 4th shouting at me "why are you thinking about this, you're a programmer". I guess I'm just wired that way, I can't not ponder the things I don't understand, no matter how irrelevant they are to my life.
Man got to sit and wonder 'why, why, why?'
Tiger got to sleep, bird got to land;
Man got to tell himself he understand.
― Kurt Vonnegut, Cat's Cradle
Or perhaps more precisely: "There is no wave function. The wave-function we talk about is just a mathematical recipe for computing the expected test-observations".
Functions are abstract things, they don't exist in the physical world. They only describe the physical world, at best.
So that really leaves the question why do our measurement results follow the predictions of the wave-function unanswered. I think we would like to come up with some theory of why the wave-function so closely predicts our observations.
"Also, are the ultimate equations that govern the universe “real,” while tables and chairs are “unreal” (in the sense of being no more than fuzzy approximate descriptions of certain solutions to the equations)? Or are the tables and chairs “real,” while the equations are “unreal” (in the sense of being tools invented by humans to predict the behavior of tables and chairs and whatever else, while extraterrestrials might use other tools)? Which level of reality do you care about / want to load with positive affect, and which level do you want to denigrate?"
Abstract things are representations of many different concrete things, they are abstractions of concrete things. Abstractions are "real" but they exist on a different ontological level than concrete things. They only exist in our head, and therefore many say they don't "really" exist by which we commonly mean that they don't exist in the physical world.
There is clearly a big difference between what exists in the physical world, and what we SAY or write about it. The latter are descriptions, which are often abstractions. Like say "redness" is an abstraction of the common properties of all red objects.
I strongly disagree.
Wave function collapse is the best description for a randomized phenomena we can observe. That exact same phenomena exists in many worlds as well, just that many worlds invent whole different universes to try to get away from the fact that to us the event is random. So instead of saying "our universe is random" you say "Our universe is not random, we just observe a random part of the universe and can never observe the real whole part of it", that isn't solving anything at all, its just a more elaborate way to say "the universe is random".
That doesn't mean you should choose to believe one or the other, but it means that one model requires fewer mechanisms than the other.
At least that's my understanding.
That is wrong, quantum state collapse just makes the quantum wave take the shape of another quantum wave, nothing in it requires it to be related to macro state nonsense like pointwise particles etc. If that is the reason you don't like wavefunction collapse then you just misunderstood quantum mechanics basics, all wave function collapse is is that it is a rule for how quantum waves can transform, there is nothing about it that connects it to our macro world view.
> and one where there is only the one set of rules and no collapse.
MWI still has wave function collapse, the "we observe random part of the universe" part is the wave function collapse, that remains unexplained, why do we only see a random subset? You can't explain that. Many worlds make it harder to see that this part is unexplained, that makes it strictly worse as an interpretation in my opinion.
Anyways, that's still an additional mechanism.
> MWI still has wave function collapse, the "we observe random part of the universe" part is the wave function collapse, that remains unexplained, why do we only see a random subset? You can't explain that.
That's not wave function collapse. The wave function just keeps evolving as normal.
I don't know enough about this to explain how the MWI maps on to our subjective experiences, I could probably find some links but I'm sure you're as good at that as I am. I'm not arguing that MWI is a better interpretation here, just that it has fewer mechanisms.
Wave function collapse is an observed phenomena, this has no interpretation at all, its just taking what we observe and say "this is what we observe". I'm not sure why you call out "wave function collapse" as something strange or alien to quantum mechanics, it is one of the core parts.
In the basic quantum mechanic course every physics student takes nowhere do they say "quantum waves collapses to pointwise particle states", they say "quantum waves collapses to eigenstates of quantum waves". So, wave function collapse is just what we call the observed phenomena that when we measure a quantum wave it takes the shape of one of the eigenstates of the measurement. That is all it is, and that is true regardless if you have a MWI or a Copenhagen, or like me a "quantum waves behave weirdly during some interactions" interpretations of quantum mechanics. And I think my interpretation makes the least assumptions, we have quantum waves, and during some interactions they collapse to one of its eigenstates of that interaction. That is the purest form of quantum mechanics, no need to do more than that.
Edit: And trying to argue about more interpretations than that is like trying to invent some divine interpretation of Newtons laws of motions etc. Those are just descriptions of how things behaves.
Edit: Or to make it clearer that it isn't magic, the event where some parts of the wave function suddenly stops interacting with the other parts of the wave function, that is a wave function collapse, and yes it does happen in MWI, you can't just change the laws of quantum mechanics so it has to work that way.
I said it has fewer mechanism. Which it does. Because it does not have the wave function collapse mechanism.
If you refuse to understand that, you have some reading to do. I don't believe further discussion is fruitful.
No it doesn't? After a wave function collapse, a particle's (or quantum system's) wave function is reduced from representing a superposition of eigenstates to representing one eigenstate. That does not happen in MWI. I don't understand why you find that so difficult to accept.
If a particle is in a superposition, and an observer observes the particle, MWI says that the observer also enters a superposition with one eigenstate for each of the particle eigenstates, following the normal "rules" of interaction/entanglement since the observer is also a quantum system. There is no collapse.
So if I use a series of quantum collapses to move a particle a meter forward, a state it wasn't originally in, how would that work in MWI? To do that you just make a long series of "measurements", each perturbation so small that the chance is basically 100% since the chance is squared with the overlap, how did that particle get moved according to MWI? How do you explain that without wavefunction collapse?
You would need new rules for the wave function in order for MWI to work, one that handles the collapses. But if you do that I wouldn't call the theory "just standard quantum mechanics without collapses".
Is my understanding correct that you put the particle in a superposition, observe it a little bit further along, then put it in another superposition, observe it further along again, etc until it has moved a meter?
I don't see why you would expect there to be some probability to see the particle as having moved a whole meter after the first observation. Obviously you putting it in a superposition in between steps is an important factor. And each time you've first put it in a superposition and then observed it, you've created two branches of what we would classically call the universe.
The only thing which really changes between an interpretation with collapse and an interpretation without collapse, is that in one without collapse (i.e MWI), the universal wave function splits into two "branches" which can't interact after the split.
Sadly, I don't know much about the math though, so it's completely possible that I've missed some detail in your question and given a reply which doesn't address what you're getting at. If that's the case, I've probably reached my limit and you'd have to ask someone who has studied this way, way more than me.
And how is that different from "wave function collapse"? How is that purer? To me that just looks like a wave function collapse with another name, and a whole slew of universes as extra garbage.
Say you have two isolated particles A and B, and A is in a superposition between eigenstates 0 and 1. If those two particles interact, we say that they have formed a quantum system in a superposition between "A is in state 0 and B interacted with A in state 0" and "A is in state 1 and B interacted with state 1", right?
MWI "simply" lets the same happen with observers. You have a particle in a superposition between states 0 and 1. You observe (i.e interact with) the particle, which puts the "you + particle" system in a superposition between "the particle was in state 0 and you observed the particle in state 0" and "the particle was in state 1 and you observed the particle in state 1".
There is no wave function collapse mechanism, what we describe as "wave function collapse" is nothing more than the particles in the macro world becoming entangled with the particle we're testing.
... and no clear relation with the states that we observe as it includes no rules defining macro systems?
The extent to which you can model a system as truly isolated depends on its size and quality of quantum isolation. This can be calculated theoretically as well as measured empirically.
Isn’t the universal wavefunction supossed to be able to accomodate distinct realities where that system may be in different states?
A poster above posted something to explain this a bit:
http://www.paradise.caltech.edu/~cook/Workshop/Physics/QMQue...
But you're wrong. Any serious researcher working on the foundations of quantum mechanics agrees that MWI is the most austere. That includes the ones who prefer a different interpretation. You can disagree with the whole field if you want. You do you, I guess.
Edit: To add, all quantum mechanics interpretations are equivalent when you ignore wavefunction collapse. So only experts on wavefunction collapses would have a credible say here. But there is very little research in that area, so there aren't many experts on it.
These probabilities aren't just numbers produced by the theory, they are the predictive content of the theory, the very thing we're supposed to be interpreting, and MWI has no place for them.
The way this problem is often discussed is to talk about "recovering the Born probabilities", which frames the problem wrongly. It makes it sound like the problem is that MWI merely isn't producing some numbers we like. MWI proponents respond to this by going through absurd contortions involving things like decision theory as a way of causing the desired numbers to pop out of a calculation. But the problem isn't "recovering the probabilities". The problem isn't finding some way of performing a calculation that results in these particular numbers. The problem is that these probabilities have no physical meaning in MWI, and it's a catastrophic problem because those probabilities have a very real meaning in the actual world as we observe it.
It really is as simple as "how can all the things happen at once when we know some of the things are more likely than others?" And, like "why is the emperor naked?" it's a question that can literally be asked by a child.
An "interpretation" that renders the core predictive content of the theory meaningless is a bad interpretation and a waste of everyone's time.
>An "interpretation" that renders the core predictive content of the theory meaningless is a bad interpretation and a waste of everyone's time.
Given that the different interpretations do not make different predictions, the only relevant way to judge them is to ask the question "is X interpretation a useful way to think about the universe". This can be answered empirically, practitioners of both MWI and CI have both made important advances in quantum physics, therefore neither are a waste of anybody's time.
There is a reason why students generally get taught both, there is nothing wrong with having multiple ways to think about things.
In objective collapse theories, there is an "us" to do the observing, and there is a collapse event which samples randomly from the possible outcomes. Both the "us" and the sampling are additional things that we have to add to the theory.
In MWI, there is no "us" in an objective physical sense. "We" are on all the "branches" of the wavefunction, spread out in such a way that it isn't possible for any observation to see both events having happened.
We don't "observe a random part of the universe", we do observe all parts of it. It's just that "we" aren't classical in the sense that you are implying.
So why do we measure only states of |dead> or |alive>? I don't know; maybe it's evolutionarily advantageous (those simultaneously dead and alive beings sound quite bothersome). Regardless, it's irrelevant -- evidently we are only capable of making measurements in the basis {|dead>, |alive>}, so naturally that's all we'll ever see. Of course, that restriction by itself doesn't make the |dead> + |alive> state less real, only unobservable when you're coupled with the system.
Here is where the problem arises practically: The cat has an enormous number of particles, and (naturally) exists as a vector in an exponentially large number of dimensions. Observing whether it is alive or dead is a measurement along an axis that you get the equipment for by default. On the other hand, building a machine that can take arbitrary measurements of millions and millions of particles would naturally give it so much freedom within that giant space of possible axes that the smallest misalignment would take you away from the glorph basis.
The questions is why position is the preferred basis that ‘you get the equipment for by default’ - if that’s what you mean.
This takes us back to my original point, which is that although the consequences of space seem mysterious in a perspective so abstract that there is no space, they no longer seem so mysterious when you include other facts about physics, like about particles and fields. I am aware that there are some attempts underway to figure out how space could come about as a consequence of quantum stuff, but even they add extra behavior on top of the postulates of QM in order to plant the seed, so to speak, that spacetime grows from.
That said, any discussion of this theory should mention the rather puzzling issue that gravitation is nonlinear, and thus it would be impossible for there to be a superposition of worlds in each of which general relativity works as observed.
Are such superpositions not a thing in String Theory? How would gravity's nonlinearity preclude this? Quantum mechanics works fine with nonlinear systems like weird oscillators.
I'm not suggesting that we should do that -- I suspect that there's a lot that I'm missing. But I guess I don't understand why these speculative interpretations are so alluring if we can't confirm or invalidate them through experiments.
And mosts physicists actually do this; they don't worry about intepretation of quantum mechanics in their work. They use the Schrödinger equation and the Born rule for their calculations and leave it at that. This is often referred to as "shut up and calculate".
But the measurement problem, addressed through these interpretations is a foundational problem, and the tricky thing with those is you have no idea what the implications might be on other foundational problems. An understanding of the measurement problem may very well have something to say about other open questions like the arrow of time or quantum gravity. It could even have implications for the scalability of quantum computers.
And I don't think it's fair to say that this question is empirically unanswerable. A number of possible interpretations have actually been ruled out by the bell inequality, for instance. And both theoretical and empirical research on this topic has seen a resurgence in recent decades.
On a purely sociological basis I feel inclined to think that the reason the measurement problem has seemed so incalcitrant is not because it's fundamentally unsolvable, but because physics as a field has denied itself from actually trying to solve it, and actively pushed out those who dared work on it.
The point was made by Sabine Hossenfelder
I think Hossenfelder described it in the video the problematic in Chaos: The real problem with quantum mechanics