There are compelling arguments to believe in the many-worlds interpretation.
No sign of a Heisenberg cut has been observed so far, even as experiments involving entanglement of larger and larger molecules are performed, which makes objective-collapse theories hard to consider seriously.
Bohmian theories are nice, but require awkward adjustments to reconcile them with relativity. But more importantly, they are philosophically uneconomical, requiring many unobservable — even theoretically — entities [0].
That leaves either many-worlds or a quantum logic/quantum Bayesian interpretations as serious contenders [1]. These interpretations aren't crank fringe nonsense. They are almost inevitable outcomes of seriously considering the implications of the theory.
I will say that personally, I find many-worlds to focus excessively on the Schrödinger-picture pure state formulation of quantum mechanics. (At least to the level that I understood it — I expect there is literature on the connection with algebraic formulations, but I haven't taken the time to understand it.) So I would lean towards quantum logic–type interpretations myself.
The point of this comment was to say that many-worlds (or "multiverses", though I dislike the term) isn't nonsense. But it also isn't exactly the kind of sci-fi thing non-physicists might picture. Given how easy it is to misinterpret the term, however, I must agree with you that a self-aware science communicator would think twice about whether the term should be included, and that there may be not-so-scrupulous intentions at play here.
Quick edit: I realise the comment I've written is very technical. I'm happy to try to answer any questions. I should preface it by stating that I'm not a professional in the field, but I studied quantum information theory at a Masters level, and always found the philosophical questions of interest.
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[0] Many people seem to believe that many-worlds also postulates the existence of unobservable parallel universes, but this isn't true. We observe the interaction of these universe's every time we observe quantum interference.
While we're here, we can clear up the misconception about "branching" — there is no branching in many-worlds, just the coherent evolution of the universal wave function. The many worlds are projections out of that wave function. They don't discretely separate from one another, either — it depends on your choice of basis. That choice is where decoherence comes in.
[1] And of course, there is the Copenhagen "interpretation" — preferred among physicists who would rather not think about philosophy. (A respectable choice.)
I think the key point that makes the quoted statement sciencey gibberish is that the Many Worlds Interpretation is just that - an interpretation. There is no way to prove or disprove it (except if you proved that the world is not actually quantum mechanical, in which case MWI might not be a valid interpretation of the new theory). Saying "this is more evidence for MWI" is thus true of any quantum mechanical experiment, but anything that is evidence for MWI is also exactly as much evidence for Pilot Waves (well, assuming it is possible to reconcile with quantum field theory), the Copenhagen Interpretation, QBism, and so on.
As a side note, there is still a huge gap between the largest system we've ever observed in a superposition and the smallest system we've ever observed to behave only classically. So there is still a lot of room for objective collapse theories, even though that space has shrunk by some orders of magnitude since it was first proposed. Of course, objective collapse has other, much bigger, problems, such as being incompatible with Bell's inequalities.
Edit: I'd also note some things about MWI. First, there are many versions of it, some historical, some current. Some versions, at least older ones, absolutely did involve explicit branching. And the ones that don't have a big problem still with explaining why, out of the many ways to choose the basis vectors for a measurement, we always end up with the same classical measurables in every experiment we perform on the world at large. Especially given that we know we can measure quantum systems in another other basis if we want to. It also ultimately doesn't answer the question of why we need the Born rule at all, it still postulates that an observer only has access to one possible value of the wave function and not to all at once. And of course, the problem of defining probabilities in a world where everything happens with probability 1 is another philosophically thorny issue, especially when you need the probabilities to match the amplitude of the wave function.
So the MWI is nice, and it did spawn a very useful and measurable observation, decoherence. But it's far from a single, satisfying, complete, self-consistent account of the world.
This would be true if we were talking about something like String Theory, or Loop Quantum Gravity.
But it is not true for MWI: MWI was designed from the ground up as an interpretation of the mathematics and experimental results of quantum mechanics.
It is designed specifically to not match all of the predictions of quantum mechanics, and to not make any new predictions. Other interpretations are also designed in the same way.
So, if the people creating these interpretations succeeded in their goals when making them, then they will never be experimentally verifiable.
I think the point about it being unscientific is completely fair, as far as a press release aiming to appear scientific is concerned.
However, I also think there is a tendency among well-educated people in physics to dismiss philosophical questions out of hand. It's fair enough when the point is "let's focus on the physics as it's hard enough", but questions of interpretation have merit in their own right.
MWI or Parallel Worlds is an interpretation of QM, it is one of the 15-20 major interpretations of QM. Nothing at all wrong with MWI. Sean Carrol speaks kindly towards WMI and I have tended to agree with his views over the years. I don't see any wild claims being made that would warrant a major reaction, but I would agree Willow's results are so impressive that it should lead one to consider at minimum that it counts as evidence in favor of the WMI. I don't see how this doesn't count as evidence for MWI.
Thank you for this clarification -- for me it addresses a good part of the crank/fringe/sci-fi aspect
> While we're here, we can clear up the misconception about "branching" — there is no branching in many-worlds, just the coherent evolution of the universal wave function. The many worlds are projections out of that wave function.
That's right, I agree that Multiple Worlds isn't any less correct/falsifiable than quantum mechanics as a whole.
I've never heard about quantum logic before. The "Bayesian" part makes sense because of how it treats the statistics, but the logic? Is that what quantum computer scientists do with their quantum circuits, or is it an actual interpretation?
"Many-world interpretation" is just a religion, it has nothing to do with physics. Pilot Wave is an example of a physical theory, Copenhagen is an administrative agreement.
I'm pretty sure pilot wave is the same kind of unfalsifiable interpretation of the experimental results that MWI is. Also I think people are making too big a deal out of the comment in the article. I took it as kind of tongue-in-cheek. An expert would know MWI is unfalsifiable and inconsequential.
I'm sure they meant it refutes pilot-wave theory, though it seems that's not precisely true if you consider a non-local hidden variable to explain instantaneous interaction.
No sign of a Heisenberg cut has been observed so far, even as experiments involving entanglement of larger and larger molecules are performed, which makes objective-collapse theories hard to consider seriously.
Bohmian theories are nice, but require awkward adjustments to reconcile them with relativity. But more importantly, they are philosophically uneconomical, requiring many unobservable — even theoretically — entities [0].
That leaves either many-worlds or a quantum logic/quantum Bayesian interpretations as serious contenders [1]. These interpretations aren't crank fringe nonsense. They are almost inevitable outcomes of seriously considering the implications of the theory.
I will say that personally, I find many-worlds to focus excessively on the Schrödinger-picture pure state formulation of quantum mechanics. (At least to the level that I understood it — I expect there is literature on the connection with algebraic formulations, but I haven't taken the time to understand it.) So I would lean towards quantum logic–type interpretations myself.
The point of this comment was to say that many-worlds (or "multiverses", though I dislike the term) isn't nonsense. But it also isn't exactly the kind of sci-fi thing non-physicists might picture. Given how easy it is to misinterpret the term, however, I must agree with you that a self-aware science communicator would think twice about whether the term should be included, and that there may be not-so-scrupulous intentions at play here.
Quick edit: I realise the comment I've written is very technical. I'm happy to try to answer any questions. I should preface it by stating that I'm not a professional in the field, but I studied quantum information theory at a Masters level, and always found the philosophical questions of interest.
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[0] Many people seem to believe that many-worlds also postulates the existence of unobservable parallel universes, but this isn't true. We observe the interaction of these universe's every time we observe quantum interference.
While we're here, we can clear up the misconception about "branching" — there is no branching in many-worlds, just the coherent evolution of the universal wave function. The many worlds are projections out of that wave function. They don't discretely separate from one another, either — it depends on your choice of basis. That choice is where decoherence comes in.
[1] And of course, there is the Copenhagen "interpretation" — preferred among physicists who would rather not think about philosophy. (A respectable choice.)