Wigner's Friend - A thought experiment.

Wigner's Friend is a thought experiment surrounding the properties of quantum physics and consciousness. IT's an extension of the Schrodinger's Cat experiment, which is as follows: One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter, there is a tiny bit of radioactive substance, so small that perhaps in the course of the hour, one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges, and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts. It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself, it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks. - Erwin Schrodinger

Wigner's Friend is essentially, that someone ELSE is performing the experiment, in a seperate room, where you don't know the results. The official wording is as follows:

The Wigner's Friend thought experiment posits a friend of Wigner who performs the Schrödinger's cat experiment after Wigner leaves the laboratory. Only when he returns does Wigner learn the result of the experiment from his friend, that is, whether the cat is alive or dead. The question is raised: was the state of the system a superposition of "dead cat/sad friend" and "live cat/happy friend," only determined when Wigner learned the result of the experiment, or was it determined at some previous point?

So...discuss.

So "Wigner's Friend" is an extension of a thought experiment that was made for the sole purpose of satirizing people who make up thought experiments.

I'm claiming it invalid on the basis that "Schrodinger's Cat" is invalid.

Why SC is invalid:

Someone doesn't believe the observer effect.

The whole point of Schrodinger's Cat was indeed to make an argumentum ad absurdum about the inner workings of quantum mechanics and how absolutely insane they are. The thing is, most interpretations accepted by modern day physicists in some way reflects a respect for the observer effect. When we observe something on a quantum level, we DO affect it. This also has to do with time and space. Wigner's Friend brought about a response known as decoheres, that is, every time an even happens, a decohere is created, which means that alternate realities split off in different directions, all of which containing a different outcome. You might live in the reality where the cat dies, but there might be a reality where the cat lives.

I mean it's like you didn't even try. Instead of performing the thought experiment you simply say, "Screw Schrodinger's Cat. There's no such thing as an observer effect, that's pure nonsense."

Well congratulations for belittling the quest to understand the universe in an intricate way.

Schrodinger's Cat states that until you look in the box to see the outcome of the experiment, the cat itself is in a state of being alive...and dead...at the same time. And you're essentially just brushing it all off as just being nonsense, without any good explanation as to why.

I prefer to think of it as understanding the universe rationally.

My observation of the event cannot have an effect on the cat's survival. The cat's survival is, technically, up in the air until I observe the cat, but only because I'm missing knowledge. The cat itself is already dead or alive; although there are multiple/(infinite?) realities in which the cat is alive/dead, I only exist in one, and there is only one outcome that has taken place.

Understanding the universe rationally? Is that what you call rejecting anything that goes against your intuition concerning your preconceived notions about how the universe works?

The whole point of the experiment is to show how absurd and chaotic the laws of quantum mechanics are under what's known as the Copenhagen Interpretation, and all it did was show how the Copenhagen Interpretation was actually more viable. The concept that the cat IS alive, or IS dead, prior to you opening the box is wiped away by the acceptance of any sort of multiple realities, or an observer effect, or anything concerning the mechanics of a quantum realm. Not only don't you know, and can't know whether the cat is alive or dead, but the cat is in a place of superposition, being both alive, and dead. Schrodinger's Cat, violates the Logical Law of excluded middle, and it's right.

You can go ahead and keep rejecting Schrodinger's Cat all you want, but everyone educated on the matter, philosophers of science, theoretical physicists, quantum physicists, they all disagree with you.

I used to be against the SC. Then I realized I'm just spouting nonsense if I can't properly explain in what way it is wrong.

Einstein tried man, he tried.

Firstly, I don't reject everything that goes against my intuition, I reject everything that follows its own tail into absurdity.

Second, a debate is between those arguing, not mystical men who are educated on the matter. You do not speak for the scientific community, nor do I.

My point is that things happen. There may or may not be other realities in place, but I am only in one, and the cat is either dead or alive. I cannot be certain whether the cat is dead or alive until I observe it, but my observation is not necessary for the event of the cat's death or lack thereof to have already taken place. Things happen whether we perceive them or not, and they are not in some ambiguous state that somehow transcends the third dimension of reality simply because we haven't observed them yet.

And all you've said is that, "Pfft, it's absurd to say that there's such a thing as the observer effect." That's not an argumentum ad absurdum, that's an appeal to how you intuitively understand the universe.



...So I shouldn't include that all the educated people on the matter laugh at your position? Fine. Doesn't change it from being true.



You are not in one reality, so your argument has failed from the very first premise. You're in three, and the universe plays by different rules on all three scales. It plays by one set of rules on the relativistic scale, one set on the mesoscale, and a 3rd set on the quantum scale.

You have just assumed "the view from nowhere," an omniscient god-like perspective that assumes the unobserved world functions the same as your observed world and according to the scientific rules you know about. You do this intuitively, and that's why I'm saying you're not 'understanding the universe rationally' you're coming to an intuitive conclusion about the universe that's unjustified, as the nature of quantum mechanics is, quite frankly, completely counter intuitive.

So essentially your argument is that anything could have happened because nothing is constant between realities? At this point, I'm trying to understand exactly what your argument is.

...No....I mean, if you had paid attention to one of my first responses to you, in accordance to the prevailing interpretation of quantum mechanics and how they work, the superposition of a cat both alive and dead at the same time until the observer effect kicks in(be it from waiting too long and the timer causing the necessary wave collapse, or opening the box and the wave collapsing. You're saying: "Nope. That's absurd. So I reject it." Which isn't an argument. It's not a rejoinder, it's just an opinion formed from intuition, which, by nature, isn't rational.

From my current understanding, the observer effect is what causes the wave function to set on one occurrence, and until observed, pretty much everything is ambiguous. If that's the case, I can conclude that not only do my observations affect my surroundings, but so also do others' observations, making the world, among other things, a complicated web of wave functions springing up that are settled into a single occurrence by people observing them.

Is that the case?

Not only that, but the 'observer' doesn't always have to be a person. Something can hold an observer function on the mesoscale, for example, that is simply an act of physics that hold predictability.

To illustrate it simply, an observer effect can be replicated by winding a minute on a kitchen timer clock, and letting it go. The mechanisms inside are determined by the clock's construction and the physics involved to ring off after the minute is over, and the observer effect is filled...without you.


But that's a side issue.

Interesting shit. I'll look into it more.

well first things first :
1. can anyone explain me what is quantum science in the nutshell
2. the purpose of schrodinger Cat experiment?

I'm not really familiar with this topics

Quantum science(mechanics actually) is simple a name for the part of science which deals with things on the atomic level(well, even smaller than that currently but not initially). It is one of the 2 'fiels' of study today, the other being Relativity.

The so called experiment is more like a parody, Schrodinger didn't agree with the interpretation of others so he elaborated the 'experiment' to show how absurd it is.

Anyway the important thing that pretty much everyone that talks about it forgets is that we can't actually observe anything on the atomic level. Do you know about Uncertainty principle of Heisenberg? It illustrates that fact pretty well.

Basically it is this, due to it's size we cannot observe an atom. Assume that its initial momentum has been accurately calculated by measuring its mass, the force applied to it, and the length of time it was subjected to that force. Then to measure its position after it is no longer being accelerated would require another measurement to be done by scattering light or other particles off of it. But each such interaction will alter its momentum by an unknown and indeterminable increment, degrading our knowledge of its momentum while augmenting our knowledge of its position.

The whole field of quantum mechanics has this problem. We can't observe things so we introduce known variables to the system and see how it changes. That's why in the contest of quantum mechanics the 'observer' affects the system. It is not that making the question affects the answer but that in the process of obtaining the answer you change it.

You can then expand on the experiment(as absurd as it is) by saying that the only way to verify if the cat is alive or dead is to force the box open which shatters the flash and kills the cat...

Saying the state of a huge physical cat is in superposition is absolutely oversimplified and that's where the paradox arises. The cat is not in superposition, it is too large of a system to only have two states of |dead> and |alive>. It has a large number of degrees of freedom and is continually interacting with the environment, therefore, it is either dead or alive when you open the box, not both. Small microscopic systems cooled close to absolute zero may have these properties but not a cat in a box. Another point is that information about the state of the poison release already leaked out of the box long before you opened it. Thermal interactions from the box, radiation, etc. give you an observation even when not recorded. Because the thought experiment is simplified, it gives you a misleading intuition about how macroscopic systems work.

Please stop talking about cats and instead talk about particles.