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Comment by vpfaulkner | Hacker News Reader

From a layman’s point of view, it seems like we grasping at straws when it comes to these thorny quantum questions. Is fair to say, for example, that we are about as clueless as our ancestors were with the bubonic plague?

To a non-expert it can be difficult to separate which theories lay on solid ground and which theories are highly speculative.

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QM is hard to visualise, but we have extremely sophisticated equations and principles for determining how quantum systems will evolve, and can engineer complex functioning systems using that knowledge. For example transistors only work because we understand QM well enough to precisely engineer the energy level state behaviour of electrons in semiconductors.

It would be like accidentally discovering antibiotics during the plague. You might not know how it works or why, but you know what it does and it absolutely gets the job done.

That applies to a lot of medicine right now - we don't know how Tylenol or antidepressants work, and Semmelweiss's invention of handwashing was rejected because he couldn't explain why it was working.

That would not be fair, though it's understandable why a layman might feel that way. The fact is, most physicists don't particularly feel the need to have an explanation for that kind of thing. We have the math, and most people agree on how to use it to make very accurate predictions. Collapse was always a little silly, but there are other possibilities as to why you'd get that kind of effect just from wavefunctions.

"It's only a model" Patsy says, but then they cut to a whole big song and dance routine, so it must be a pretty good model. Or course it is unsurprising that Monty Python's Holy Grail would provide deep physics insights, they were a pretty clever bunch.

> which theories are highly speculative.

So QM itself is on very, very solid ground. You're using it now on your computer.

The interpretations of QM and the attempts to reconcile the exceptionally well tested mathematics of QM and the reality that we experience which is not-QM at all are all philosophical with zero evidence. Everyone just tries to make compelling arguments based on things like Occam's razor about why their horse is the best one in the race without actually knowing anything at all.

We have place a few bounds around things like Bell's inequality so we know that local hidden variable theories are ruled out, but that is about it.

The title article is very interesting because its one of the first few actual tests to probe if there really is a transition between QM reality and classical reality. Regardless of who actually wins the horse-race the important thing here is that there's slow progress being made on trying to experimentally test theories. This is why I've always liked the Penrose models of collapse better than the MWI models since the former have some chance of being actually testable, while with MWI you just blindly decide it is true or not and then you argue a bunch about philosophy and never do any experiments, which isn't science. Penrose models of collapse might be wrong but at least they're in principle testable, which is incredibly exciting about this article.

Many worlds is absolutely testable, since if we observe collapse in even a single one of these experiments then that completely falsifies many worlds. If one of these experiments discussed in the article had actually observed a collapse, then I have no doubt we'd be seeing headlines like "many worlds theory disproven", and Nobel prizes for the physicists involved. It would be the biggest discovery in physics for decades.

You don't get there from WMI though. You get there from trying to prove collapse happens and testing some other theories predictions.

We "observe" collapse all the time, and can calculate the probabilities of the different possible collapsed states of a not-yet-observed superposed or entangled state using the Born rule. What we don't know, and can't tell, is whether we have seen an "objective collapse" (we live in just one universe, that undergoes a discontinuous change at the time of measurement) or in something like MWI. That is question for philosophers afaik. The experiment in the title falsifies certain models of objective collapse, but others are harder to falsify.

I agree that's it's possible to create objective collapse theories that are arbitrarily difficult to falsify, but the difference between objective collapse and regular old decoherence due to interaction with the environment has experimentally measurable implications. In particular, if you expect a certain probability of objective collapse in a certain period of time, then do an experiment with a coherence time longer than that, while keeping your system carefully isolated from interaction with the environment. Then if the wavefunction collapses anyway, that would prove objective collapse and disprove many worlds.

I thought an objective collapse theory was one where the observation (whatever that is) causes the collapse. An observation is necessarily an interaction with the system, where the observer is part of the environment. So if the system is that isolated from the environment, the collapse or lack of it can't be observed. I didn't think it meant the collapse happens after some amount of time like radioactive decay, even without an observation (interaction). Maybe I'm wrong.

> Is fair to say, for example, that we are about as clueless as our ancestors were with the bubonic plague?

“We” in the collective sense are not clueless about quantum mechanics at all. We have an extremely exact model, and pretty much every attempt At proving that it’s insufficient fails. The only “problem” with quantum mechanics is the same as the “problem” we had in Newtonian mechanics when we found that a tennis ball and a bowling ball falling from head height hit the ground at the same time. This was a problem because intuition would have the heavier object fall faster than the lighter. It wasn’t an actual problem with Newtonian mechanics though mind you. Our intuition was counter to reality, the problem was the intuition not the model of reality.

Naturally there were other actual problems with Newtonian mechanics, but none of that had to do with making it more intuitive. And the same is true of quantum mechanics. It doesn’t sound intuitive to most people, but that’s not problem, it just means your intuition about how systems should behave at these scales is wrong.

> From a layman’s point of view, it seems like we grasping at straws when it comes to these thorny quantum questions. Is fair to say, for example, that we are about as clueless as our ancestors were with the bubonic plague?

> To a non-expert it can be difficult to separate which theories lay on solid ground and which theories are highly speculative.

Sure, but isn't that the point of doing these experiments?

I'm all for trying to understand these phenomena and running these experiments. Just trying to get a sense for how much of a grasp we have on these phenomena.

Based on the other responses, it seems like we can mathematically model these phenomena very well and make very good predictions. However, when it comes to explaining why these phenomena exist in the first place, we are like a medieval doctor trying to explain why antibiotics work.

It's like we had miasma theory of disease, but miasma theory was actually highly accurate at predicting disease.

So... not really like how our past misunderstanding of disease, which was useless as well as being wrong.

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