B Does Quantum Eraser Prove That Intention Does Not Create Physical Reality?

[lashinko]

TL;DR Summary

The past influenced by the present

If you perform a double slit experiment but never look at the results could we say that the experiment never actually happened? The beginning of the experiment would show intention to find results but we believe intention does not create physical reality. Quantum Eraser could be preventing us from ever knowing which slit the photon came through or rather if it ever came through at all.

 

[Nugatory]

If you perform a double slit experiment but never look at the results could we say that the experiment never actually happened?

No. Whether someone looks at the result of an experiment or not is completely irrelevant to the result. You may have been misled by some of the pop-sci garbage about Schrodinger’s cat and how a conscious observer ”collapses the wave function”; your best bet is to forget all of that.

A good layman-friendly starting point would be David Lindley’s book “Where does the weirdness go”.

 

[StevieTNZ]

You may have been misled by some of the pop-sci garbage about Schrodinger’s cat and how a conscious observer ”collapses the wave function”; your best bet is to forget all of that.

How is the consciousness causes collapse garbage? To the OP: don't forget about all that, despite what Nugatory has told you. It is, at least I'm aware, still a valid interpretation of quantum theory. The "Where Does The Weirdness Go?" book advocates for decoherence which we all know does not produce classical outcomes, despite claims in that book saying otherwise.

 

[Nugatory]

I didn't say that consciousness causes collapse is garbage, I said that the pop-sci treatments of it are.

A good starting point for a non-garbage treatment of the problem would be Schrodinger's 1935 paper "The Current Situation in Quantum Mechanics" (Google will find decent translations online) in which he introduces his cat as a demonstration of the problems with the then-current collapse interpretations.

The point of decoherence is not that it might "produce classical outcomes". It can't, because we're applying unitary evolution according to Schrodinger's equation to an initial quantum state, and that can only yield a probability of various outcomes, not any single outcome. Instead decoherence shows how a quantum superposition will quickly evolve into a mixed state in which all the possibilities are classically reasonable; just as a classical tossed coin is heads or tails whether we look at it or not, the cat has died or not and we'll find out which it is when we open the box.

 

[vanhees71]

One should however stress that the statement that consciousness causes collapse indeed is garbage. Nowadays at large experiments like the big particle accelerators (like the LHC at CERN) experiments are done by detectors storing the measurement results on some computer storage device and it may take a long time until some conscious observer (aka physicist) looks at these data. The measured particles are long gone and it doesn't make any sense to associate any quantum state to them anymore at the moment the physicists starts to take note of the data a and evaluates them. Rather the measurment has been finished by the readout electrons when it stored automatically the data on the storage device. Even if you subscribe to the collapse interpretation (which I and many other physicists don't and it's not even part of all followers of the one or the other kind of the Copenhagen doctrine) then the claim that there's any need of a conscious observer is not at all founded in quantum theory as a physical theory. As Bell once ironically asked, what should this mean at all: Hasn't there been any "collapse" before the advent of life (on Earth)? Is an amoeba enough to cause a collapse or do you need some higher developed animal or even a human being? Does the human have to be trained in physics to cause a collapse?

The problem is that for quite some decades popular physics books on quantum theory often are sold by referring to some "weirdness" or, even worse, relate QT to esoterics. That's only because the publishers think such books will sell better to the general public than a serious attempt to explain QT to the public.

There are some rare good popular-science books on quantum theory like Anton Zeilinger's "Dance of the Photons".

 

[StevieTNZ]

Re-read what you wrote.

 

[StevieTNZ]

One should however stress that the statement that consciousness causes collapse indeed is garbage.

Nonsense. Its still a valid interpretation.

 

[StevieTNZ]

Instead decoherence shows how a quantum superposition will quickly evolve into a mixed state in which all the possibilities are classically reasonable; just as a classical tossed coin is heads or tails whether we look at it or not, the cat has died or not and we'll find out which it is when we open the box.

Basically saying a classical outcome has occured, no?

 

[Nugatory]

Basically saying a classical outcome has occured, no?

Yes, but not yet a particular classical outcome. Decoherence gets us from “the cat is in a quantum superposition of live and dead” to “the cat is either classically alive or classically dead even though we don’t know which” which addresses Schrodinger’s objection. But there’s another step to get from there, a mixed state whose density matrix is diagonal, to a classical outcome and decoherence doesn’t help with that step.