Because it’s very straightforward and has less assumptions and weird features than most other interpretations, and it has seen the most advancements in quantum fundamentals research
Complete layman here -- does that theory say that every time a quantum effect does or does not occur, in fact both possibilities happen but in different worlds?
The entire universe instantly splits up in two for every quantum event anywhere in it?
Edit: I read more comments and no, it's not literally that.
These are just mathematical tools we use to make predictions. Assuming they represent objective reality and somehow prove an infinite number of universes doesn’t seem very scientific to me.
That's way too instrumentalist. The math also describes how atoms work and many other things. Modern physical understanding is based on those descriptions. Cosmology and nuclear physics would be useless without an understanding.
How do the predictions work if they aren't in some way modeling the way reality is? Why does the technology based on them work? Instrumentalism gives no answers to those questions. Science is about understanding the world, and using that to make predictions.
They work because they use human logic which has evolved to understand the universe just enough to “work” and where that logic doesn’t work we use probabilities to ensure we’re only calculating the odds and deriving from there. You can devise probabilistic systems of equations to describe stock prices and account for when you could be wrong, but this is not you describing some objective set of equations the market emanates from.
It working doesn’t mean it in anyway reflects some objective truth (if such a thing even exists.) It just breaks things down into small enough parts you can then model those parts and make predictions. This does not mean those small parts are “real” just that they are convenient ways to describe the flowing of energy for our purposes.
> atoms work and many other things
Atoms are still just a human created mathematical abstraction we use to describe and make predictions about matter. All there really is is energy and atoms are just a mathematical tool we use to study energy.
This is quite literally the oldest debate in natural science and it seems like one half of the debate just decided they’re right a few centuries ago and stopped caring about the fact that’s not something they have (or can) ever proved.
They’re tools, don’t get me wrong they are very useful ones, but the second you start pretending they’re anything else or that your interpretation of them is how reality really works you become just another religious zealot and that goes against everything science is supposed to be about.
> Atoms are still just a human created mathematical abstraction we use to describe and make predictions about matter. All there really is is energy and atoms are just a mathematical tool we use to study energy.
We can see atoms with electron microscopes. A mathematical tool to study energy doesn't say anything. A tool describing how chemistry arises from atomic structure does.
> This is quite literally the oldest debate in natural science and it seems like one half of the debate just decided they’re right a few centuries ago and stopped caring about the fact that’s not something they have (or can) ever proved.
Not proved, but imagine using this sort of argument against evolution being a true account of life's history on Earth. Of course it won't get everything right, but in general there is simply no other way to explain how life forms changed over time. Similarly, there's no other way to understand microscopic physics than quantum mechanics. Maybe a more complete theory combining gravity and QM would be more true, just like Newtonian physics was incomplete and superseded by relativity.
> This is quite literally the oldest debate in natural science and it seems like one half of the debate just decided they’re right a few centuries ago and stopped caring about the fact that’s not something they have (or can) ever proved.
Yet earlier you asserted one side of the argument without proving it nor even acknowledging that there is a debate
I mean, that's obviously a huge matter of debate, but most of us physicists at least hope that our theories reflect objective reality in some way. Also, there are of course explicitly ontological aspects of quantum mechanics, such as PBR theorem and Bell's inequalities
Quantum mechanics tells us that, in order to predict the outcome of a measurement, we have to compute a specific probability based on the amplitude of the wavefunction.
We can explain this probability as some kind of collapse, or we can explain it as some measure of the number of observers making the measurement in parallel "worlds". Neither is inherently closer to the math.
> Quantum mechanics tells us that, in order to predict the outcome of a measurement, we have to compute a specific probability based on the amplitude of the wavefunction
Even this is already wading into interpretational waters. The math says nothing about whether a given POVM should be thought of as a measurement or an interaction (or both, or neither).
Sure, it's not part of the math, but it is part of the physics. There is a very clear distinction in the theory between "interactions", governed entirely by the Schrodinger equation (or its relativistic versions, or QFT), and a "measurement", where you have the apply the Born rule not only to predict what the measurement device will show, but also to correctly predict what will happen in a subsequent experiment on the same particle.
Without the Born rule, QM makes nonsensical predictions that don't explain what happens. Decoherence helps explain certain things directly from the math without appealing to the extra Born rule, but not fully, and not quantitatively (not the specific probabilities).
> Sure, it's not part of the math, but it is part of the physics.
"the physics" here is a specific interpretation
> Decoherence helps explain certain things directly from the math without appealing to the extra Born rule, but not fully, and not quantitatively (not the specific probabilities).
No, "the physics" here is the way we are supposed to tie the math to physical observations. You can't explain all of our experiments if you don't make a distinction between interactions which preserve quantum properties and measurements which lead to classical observations. For a specific example, you can't explain the double-slit experiment with a detector at one slit if you don't make this distinction.
> You can derive the Born rule using decoherence
No, you can't. I have actively looked for such derivations and found none (at least none that are considered credible), and there is literature that explicitly says that this hasn't been convincingly done, e.g. [0]:
> My main conclusion is that there is no way to derive the Born rule without
additional assumptions. It is true both in the framework of collapse theories and,
more surprisingly, in the framework of the MWI. The main open question is not the
validity of various proofs, but what are the most natural assumptions we should add
for proving the Born rule.
> Again, that's a matter of interpretation. The different quantum interpretations say different things here.
In my view, a physical theory has two parts: a mathematical model, and a series of rules to relate the model physical experiments. For example, the theory of Newtonian mechanics isn't just F=m×a, it also includes the observation of how to measure the mass of an object and its speed etc.
Without these extra rules, you just have a mathematical theory, not a physical theory.
> Yes, you can. Look up Quantum Darwinism.
I did, and as far as I understand (e.g. from here [0]), it is an exciting candidate for explaining the Born rule based only on the other equations, but it's not fully accepted and it has its own limitations so far. Still, very interesting, thanks for pointing me to it.
> PS. throwing "nuh uhs" back to a professional in the field is not appropriate. Get your respect in order.
I did not throw a "nuh uh", I explained what I looked for and why I came to my conclusion, including a citation from a professor in the field. I think that's about as far from disrespecting you as I can get, while still disagreeing. Not to mention, I didn't know you were a professional in the field.
Why should we not just take it as a probability based abstraction for something we don’t have a true understanding of and move on? Anything else seems like weird theology to me.
Sure, it's perfectly valid to say we don't understand it - but the ambition of physics is to actually understand things like that. So if we agree that it is something that we don't know yet, then it remains a target for new theory development or new experiments.
Physics is ultimately not about predicting the outcomes of experiments. It goes farther than that: it is about coming up with a model of the world that humans can understand. The experiments and predictions are just there to validate that the model actually corresponds to the world, but they are not an end in itself.
And all of this speculation about what the Born postulate actually means has in fact lead to new experiments and new theories. If we had only ignored it, we probably wouldn't have discovered Bell's theorem, and we probably wouldn't have discovered decoherence.
1) Because physics has had an ontology, what there really is, since like Aristotle. Even if ontology changes, posing one has worked for roughly 2500 years to partially guide science. It really does inform all kinds of experiments, even thought experiments. BUT, you might be right the trade off you propose is more worth it
2) Reichenbach's principle says any correlation must have a cause. Even without an idea of an ontology like in 1) this looser principle is hard to give up as well. It explains the mystery behind Simpson's for example. And why without the causal model behind correlations, you could easily take the wrong drug for you specifically.
Again though, these are guiding principles and trade offs I am curious to see how we could progress without them
I really think it’s best to leave such metaphysical speculation out of it (or rather leave that to metaphysics.) Sure it could be right, and reality is definitely weird as hell, but it just seems like theology to me when you start pushing such things as fact when nothing says it is.
Don’t get me wrong I have weird beliefs about the universe too but I would always stress they’re my weird beliefs and not something we’ve proved. The many worlds interpretation is pretty mainstream at this point and it leads the masses to believe it’s either true or that scientists are batshit crazy. Not a good look imo.
