Hacker News Reader

Comment by username90 | Hacker News Reader

> quantum mechanics is well-understood

No it is not, we don't even understand what causes quantum waves to collapse. We call it "observation" but we don't know what that is. So you can't say we understand quantum mechanics until we have a theory which can accurately predict when wavefunctions will collapse.

When two quantum systems interact their wave functions either gets entangled with each other or they cause each other to collapse, it seems like the first happens in small systems and the second happens in large systems, we don't know much more than that.

View on HN

From what it seems, we don't actually even know if "collapse" as such is a thing, nevermind what causes it.

We are one experiment away from placing serious doubts even on counterfactual definiteness.

Observation = interaction

But what kind of interaction? Is it a tensor field? Change of spacetime? Particle mediated? Wavelike? Nonlocal string or brane vibrations? Does it interact with other known fields and particles and in what way?

What is its range and speed? Does it work same in very low or very high energies? Does temperature affect it? Does it change at relativistic speeds?

Etc. The tool we have to probe it is currently only entanglement and secondarily tunneling. Maybe some calorimetry and charge detection.

None of that is a problem if you accept MWI.

The mental benefit of MWI is that instead of worrying about both entanglement and observation/wave function collapse, you only need to worry about entanglement because what Copenhagen describes as collapse is really just entanglement of the observed system with the observer.

A group of particles can interact without it counting as an observation which is why I mentioned entanglement.

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

I would bet ssijak thinks in MWI, where observation is not a separate thing from interaction and there is no such thing as "counting as an observation" in physical reality.

The "observations" that other interpretations cause endless confusion about are simply interactions between the observed system and the observer, but "observed system" and "observer" are concepts without a corresponding physically reality. They're simply labels assigned by humans.

Entangled particles share a state, they do not interact: https://en.wikipedia.org/wiki/No-communication_theorem

Particles can entangle when they interact, ie they go from not sharing a state to sharing a state. Your link states that wavefunction collapse is random and can thus not be used to communicate information, it doesn't say anything about interactions resulting in shared state.

Note that there's no way to observe a particle without some form of entanglement, though.

Reply on news.ycombinator.com