i’m not an academic and can’t follow [this paper](https://www.science.org/doi/10.1126/sciadv.aaw9832) but i’m very intrigued. any help is appreciated.
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So in order to understand the paper you need to understand some basic quantum mechanics concepts. The first is the basic idea that at the atomic level and smaller, all things exist as probabilities. That elementary model of the planet like atom is not factually correct. It’s an excellent teaching tool, but it doesn’t resemble reality. The reality of an atom is that the electron “orbit” is really just a spike of high probability that an electron will be found somewhere in that area around the nucleus of the atom. All electrons exist as this cloud of probability around the nucleus.
Yet when we look at an atom we can observe the action of a single electron as a particle not this uncertain wave. That’s where the “local observer effect” comes in. That is that measuring aka observing a probability will cause that probability to collapse into a singular outcome. Until that observation is made, the electron is in every position at once as well as none of them. It is only through observation that the electron particle becomes “real”
This brings up the question of whose observation collapses the probability into a single outcome. A physicist by the name of Wigner designed a thought experiment to simplify this idea. In this experiment, Wigner sets up a device. This device contains a single photon. Photons like electrons are governed by probability. The photon can be in one of two states, let’s call them state A and state B. The device measures this state and produces a readout that is then recorded by Wigner’s friend. Through the concepts previously established we know that Wigner’s friend has just collapsed that probability into a single state, we’ll say state A. At the same time this is going on Wigner is watching his friend perform the experiment. However, he can neither see the readout or the result his friend recorded. From Wigner’s local observation, that photon is still in a probability state of being both A and B at the same time. Then, Wigner asks his friend to tell him his result, this collapsing that probability into both observers knowing the photon is in state A.
Therefore during that experiment you had 3 states of a photon. First was the probability state of it being both at once. Then you had the observation states of either A and B. The end resutling being that during the experiment both the probability state and state A were known to be the “truth” by people at the same people at the same time. It calls into question whether at the quantum level we can ever really make an objectively “real” observation.
The referenced paper attempted this experiment in real life. In the end they got a result that seemed to confirm Wigner’s idea that each individual observer experienced a different reality at the same time. Now, many other physicists do have logical arguments against Wigner’s original thought experiment which may invalidate the results of the actual experiment. but that’s a whole can of worms as this is still the cutting edge of scientific discovery. There are a lot of unanswered questions when it comes to the quantum world.
You might want to check out this page, which are filled with rebuttals against the conclusion of the experiment: https://dailynous.com/2019/03/21/philosophers-physics-experiment-suggests-theres-no-thing-objective-reality/
You might have heard of Schrodinger’s cat, it’s a thought experiment. A cat is locked in a box, with contains a vial of toxin that will kill the cat. The vial is only broken based on the outcome of a radioactive decay, which as far as we can tell, is random (though we can compute its probability). So until we open the box, we won’t know if the cat is alive or dead. Schrodinger then ask, is that cat in the state of being both alive and dead, and we will collapse that state into 1 possibility by opening the box?
The reason for this Schrodinger’s cat thought experiment is because of the standard interpretation of quantum physics. In this, everything do not have specific values for its properties, each property are (in general) has multiple values at the same time until a measurement is made about it. After this measurement, the object change so that that property has only one value among these different possible value. Hence the Schrodinger’s cat: it is both alive and dead until someone look at it.
Schrodinger originally thought up this experiment as a parody of the standard interpretation of quantum mechanics, he think that the theory is incomplete. After all, it’s inconceivable that a cat is both alive and dead. Unfortunately, as we discover more about quantum physics, it seems harder and harder to dismiss the idea that objects at quantum level do have properties with multiple values at the same time until it’s measured; yet at the same time, objects at macroscopic level, those we seen normally in our everyday life, doesn’t seem to be able to have multiple state like that. But if quantum physics are supposed to be the law of physics, and big objects are made up of quantum objects, shouldn’t big object has multiple values as well? Also, shouldn’t an observer or a measurement device just part of the physical process as well, why would there be something magical about measuring a property that force it to choose one value?
This conundrum leads to various different interpretation of quantum physics. One important question is this: what happen if an observer is also part of a quantum system? Would they have multiple states as well? Would they measure the same thing as someone outside? Is there something special about consciousness that change how physics work? And so on and so forth.
This leads to the Wigner’s friend thought experiment. The gist of the idea is that you have an experimenter making measurement inside a lab, and another experimenter making measurement outside the lab. The one outside should see a superposition of states, but the one inside doesn’t. It’s more complicated than this, but that’s the gist of what make it interesting anyway.
So in any cases, we currently can’t actually perform that experiment, because trying to isolate a lab from outside influence is practically impossible. The “experimenter inside the lab” is replaced by a small quantum system, which the authors argue to be just as good.
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