Something that has puzzled me in popular descriptions of the double slit experiment is that they usually describe the observation of the detectors as though it is the end of the story for the elements of the experiment, but it seems they always leave out the most important part of the story.

Isn't the observation of the detector requiring photons to be emitted in some way from the detection apparatus to the eyes of the scientist, which are then transmuted into a cascade of neurons firing inside the brain, and after some processing in the brain and the creation of our simulated reality, an observation of the detector is made in a particular state?

In the case of nonlocality, the information about the states of the pair of electrons in superposition needs to travel to the simulated reality in the brain of an observer, so how could we know that it travels faster than light, if the whole observation of the experiment and information about it is happening inside the observer's head and the information about the light travelling from the detectors to the eyes and so forth?

Could the observations we are seeing have something to do with the way the brain puts the information together to make the world we observe, that only seems in someway coherent to us after some processing?

If we consider the reports coming from other observers as a kind of detector, then the information has to travel from the other person to me through the movement of atomic particles, and what is the state of that information in transit to me as my reality is being generated?

Are other people, objects, etc, in a possibility state until I observe them in my brain?

The molecules in my brain acting together as a network in some way is selecting one of the possible states to observe. What is happening in the brain to collapse the possibility into an observation of a particular measurement?


  • 1
    Dan, you have several questions at once here. Can you please narrow this down a bit and solve one question at the time instead of asking something, so that you do not go on churning out questions without the previous ones having been resolved?
    – MichaelK
    Jul 4 '18 at 8:11
  • Yes. Interesting question but difficult to discuss as it is. .
    – user20253
    Jul 4 '18 at 12:20
  • Okay. Sorry, it was sort of building up to the questions: What is an observation? When at what point does it occur? And is it final and immutable? Jul 4 '18 at 16:33
  • @DanBoice If the first question is not resolved, why go on and ask the following questions? You have a branching tree there. "What is an observation" can lead you down many different branches. "At what point does [the observation] occur" assumes the answer to the first question. And so on. so: one question at the time. Get an answer to the first thing so you know the context for any followup questions.
    – MichaelK
    Jul 5 '18 at 9:08
  • Okay, I’m sorry for the string of questions, although they all seemed related to the same point about the observations of the experiment in the minds of the people doing the experiment and why that is left out of the description of the experiment. Perhaps I could have worded it better. Jul 5 '18 at 16:10

My PhD supervisor had a deep interest in such questions, and had published several papers on things like Bell's theorem, locality, etc. One day I asked him what Bell's theorem really means. He replied "it depends on the meaning of the verb 'observe.'" Then he changed the subject.

In the double slit experiment you can use devices that record the information fairly permanently. Things like photographic paper. Then you can give that record to somebody who has no idea where it came from or what it means, and ask them to describe it. They will report "fuzzy parallel bands" exactly as somebody who, for example, helped to put the equipment together. The bands won't be reported differently today from tomorrow. They won't be reported differently by different people. They have no indeterminate character, at least, no more than any other thing.

So any part of any possible quantum weirdness is all happening before those holiday snapshots start getting passed around. It does not depend on internal brain states, at least not in any non-constant way. At the level of looking at the results it's all very determined and local and "clockwork" as the poetic expression goes.

As to non-locality. Quantum field theory rejects determinism. It does not reject locality. It was a tedious homework assignment during my MSc to prove that quantum field theory does not allow messages faster than light. And this is consistent with all known experiments. Determinism out, locality still in.

The whacky thing is, how do we wind up seeming to be in a determinate world when quantum mechanics says it's not? That's a lot of math that I barely remember. But basically, it's the least action principle. The most likely path, by a very large amount, is the classical non-quantum path. Other paths are possible but very much less likely. And the more particles involved the more strongly that less likely becomes. And objects such as people contain huge numbers of particles.

So in most circumstances the quantum behavior is extremely strongly suppressed. It requires some very special situation, such as double slit and some other well known experiments, to see it.

In one sense, this selection of the classical path is itself an observation. And it happens automatically without the intervention of any mind.

  • Hmm. I'm sceptical. I see no reason to state that anything happens without the intervention of mind, or to suppose that the universe is not deterministic. It is a common view but not yet proven.
    – user20253
    Jul 4 '18 at 15:51
  • 2
    "I don't believe it" is not an argument.
    – user34017
    Jul 4 '18 at 15:56
  • I like your answer, but It could be that the information that comes to me about what other people observe when they look at the photograph has entered into a large superposition that my brain keeps consistent or joins in some way. What they say has to travel through sound waves (unobserved movements of particles) to my ears. What they write has to be transmitted to my eyes through photons.It does all seem very odd that the electron would "know" it is being observed without some sort of interaction with it. Photons need to stimulate nerves in the back of my eyes to see that something is there. Jul 4 '18 at 16:24
  • Be careful not to project superposition of states into regions it does not belong. It's hard enough to get it to happen for single particles. Getting it to happen for large numbers of particles is quite stupendously much harder.
    – user34017
    Jul 4 '18 at 16:28
  • So If the number of particles is sufficiently large, relatively close together, or somehow moving as a unit, the brain takes some sort of amalgam of the probability states and makes it into a distinct observable object in one state. Is that right? Jul 5 '18 at 2:22

The double slit experiment raises a simple question. Is the world observed or created by expectation?

When we observe the photon it is our expectation that determines how it behaves. To us this is impossible, because our thoughts do not appear to drive anything, rather we observe something and then derive a model to explain it.

If the universe is created to appear a certain way to us, this breaks down at the boundaries, when the outcome is only decided based upon what the observer wants to see. If one is a determinist this is difficult to accept because it suggests that we have a purpose and a creator rather than merely a product of an engine of existence.

Similarly if life exists only because of a very complex interaction of DNA strands, it could never have come from chaos. Some though say life came from chaos, ie a faith statement, so its complexity can be created from chaos, which is a tautology, and not a proof of anything.

It is always hard to work against ones faith or assumption bias, which is why scientific observations are so difficult. So if you reduce people to a machine, a brain, so discounting the observation and the reality we are self aware beings, without proof of how or why, you end up with a dilemma which is not easily resolved because of the assumption one is just a brain. If you can make the leap into we maybe more, then alternatives exist.

  • 1
    Actually, it's fairly easy to show that what we expect has nothing to do with it. The pattern sits there completely unmoved by what the experimenters think of it. It shows up the same today, yesterday, last week. It works the same for seasoned cynical experimenters who have worked on multiple Nobel winning experiments, and for newbs who have not finished 2nd year high school yet. It works the same for Hindu, Mormon, Jew, Moslem, Budhist, atheist. Even Pastafarians get the same answer.
    – user34017
    Jul 5 '18 at 14:02
  • The double split experiment is one level more difficult as explained in this example popularmechanics.com/science/a22280/… It is the behaviour that responds to what you are looking for.
    – PeterJens
    Jul 5 '18 at 15:49

Systems behave in a 'quantum way' whe they are fully isolated from their surroundings. Photons are significant because they are the limit of lowest mass-energy signal, so disturb observed systems the least.

It is about https://en.m.wikipedia.org/wiki/Quantum_state#Mixed_states becoming https://en.m.wikipedia.org/wiki/Quantum_state#Pure_states above the https://en.m.wikipedia.org/wiki/Quantum_decoherence limit.

Anything which breaks the isolation of a quantum system counts as an observer, and the state of the observed propagates as a pure observed state instead of a mixed 'quantum' state.

In the entangled particle case, the quantum mixed state propagates in a way that is spatially divided. They are correlated, but not identical in a way that preseves the https://en.wikipedia.org/wiki/No-cloning_theorem and prevents non-local information transfer.

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