[akvadrako]

They have not been explicitly looked at, but they have been observed in the QM sense. That’s because decoherence has spread those records to conscious observers.

If the results had been kept completely isolated from all people, you could still say a measurement hasn’t occurred.

[millstone]

That's just not what traditional QM says. Traditional QM separates quantum systems (microscopic) from measurements devices (macroscopic). A measurement occurs when the measurement device interacts with the quantum system. You do QM by predicting the results of these measurements. Consciousness does not enter into it.

[TheOtherHobbes]

So why doesn't a measurement and/or decoherence occur when double slits or a half-silvered mirror interact with a passing particle? Are they not macroscopic objects which interact with the quantum information?

Perhaps it's only a "measurement" if the (alleged) particle has nowhere else to go after the interaction. But how does the (alleged) particle know which macroscopic interactions are terminal and should be counted as "measurements" and which are part of the rest of the experiment?

There is no answer to this in QM. You can calculate the probabilities and you will get predictable answers, but there are still >20 interpretations of what is really happening, and they all disagree with each other in important ways.

[BadThink6655321]

Until you get information from the measurement, it didn’t happen.

[rbanffy]

Can it be considered as until it causally affects something else (the observer), its state is not defined? Isn't it a causal relation that collapses the superposition?

[trenchgun]

Why from all people?

What if there is a person in an lab which is isolated from the rest of the people?

[kgwgk]

Wigner’s friend?

[akvadrako]

Then he will certainly be able to say a measurement happened.

That’s something only conscious beings can do.

[rbanffy]

But then isn't Wigner's friend also in a superposition until Wigner talks to them?

[akvadrako]

Traditional QM does not allow Wigner’s friend to be in superposition.

[rbanffy]

Until he talks to them, how can Wigner tell? ;-)

[akvadrako]

Wigner can’t tell, but the friend knows. If he thought he was in a superposition he would believe in many worlds.