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Until we have a solution to the wave function collapse, it kind of freaks me out.
My understanding is that the tools that are used to observe it cause the wave function to collapse. Like how putting a thermometer into meat to check the temp makes a little hole.
It doesn’t work like this, popular misconception. It is cool in sci-fi though.
The easiest way to understand this is in terms of mutual information.
If we both flip a coin independently of one another, then both coins have a 50%/50% chance of being heads/tails and the distributions are independent of one another and thus uncorrelated, but imagine the two coins are initially attached to one another, flipped, and then we separate them. Now they’re both still 50%/50% for heads/tails but are perfectly correlated, so they are guaranteed to have the same value, and so if you know one, you know the other. In this case, the coins are said to have mutual information on one another.
It turns out in the physical world that mutual information, or more specifically quantum mutual information (QMI), plays a very important role. The marginal statistics on the behavior of a system can depend upon whether or not it shares mutual information with something else. You see this in the double-slit experiment because if you record the which-way information of a particle, then necessarily it must have interacted with something to record its state, and thus whatever measured it must possess QMI between itself and the particle, and thus the particle’s marginal statistical behavior will change.
This is in no way unique to human observers or human measurement devices. You can introduce just a single other particle into the experiment that interacts with the particle such that they become statistically correlated and it will have the same effect.
QMI is rather counterintuitive because you can establish QMI in ways that you would intuitively think would not impact the system being measured. For example, you can have an entirely passive interaction whereby only the measuring device’s state is altered and not the particle in order to establish QMI between them.
You can also establish QMI without an interaction at all, such as, imagine that the measuring device is only placed on 1 of the 2 slits and you only fire a single photon and that photon is not detected. If it’s not detected, you still know where it is, because it must have traversed the slit the measuring device was not on. Hence, the non-detection of something can still be a detection and thus can still establish QMI.
Intuitively, you would think a passive measurement, or a measurement that does not even involve an interaction at all, should not alter the system’s behavior. But the mathematical structure of quantum mechanics is such that the system’s marginal stochastic behavior is genuinely statistically dependent upon the quantity of QMI, and so things you would intuitively believe should not affect the system do, in fact, affect the system.
You can even use this effect to detect the presence or absence of something without ever (locally) interacting with it.
In the Mach-Zehnder interferometer, the photon can take two possible intermediate paths, we’ll call them A1 and A2, but both end up at the same place. Then, at the end of the experiment, it can take two possible paths again, B1 and B2, with a detector placed on both paths. You find, in practice, that there is a 100% chance the photon will show up on B1 and 0% on B2, unless you block either A1 or A2 with your hand, then it will have a 25% chance of showing up on B1, 25% chance of showing up on B2, and 50% chance of not showing up at all (because it was blocked by your hand).
The reason this is interesting is because, without your hand blocking an intermediate path, there is a 0% chance it will show up on B2, but with your hand blocking one, it changes to 25%. Thus, if you measure a photon on path B2, you know with certainty that someone’s hand must be blocking A1 or A2, yet, clearly the photon did not traverse the path of the hand or else it would have been absorbed by the hand and you would have detected nothing. You thus can deduce the presence/absence of the hand from a particle’s behavior that never (locally) interacted with it, and so logically speaking, the hand must be having a non-local influence on the statistical behavior of the particle.
This influence is due to the fact that if the particle interacts with the hand, it will be absorbed into it and slightly will alter the states of the particles in the hand, and if it does not interact with the hand, it will not do this. Thus, you could in principle look very closely at the particles that make up the hand and deduce whether or not the particle took the path the hand is on based on whether or not this alteration occurs, and thus there is QMI between the hand and the particle’s path, regardless of whether or not the particle actually interacts with the hand. The mere presence or absence of this QMI changes the particle’s behavior.
Agree to disagree!
Nothing to agree or disagree with, you’re factually incorrect. The observer effect has nothing to do with whether someone’s eyes are looking toward it or not. It basically just means when a process is happening and anything external occurs to it then that will change the way the process is happening.
I was curious, so I went to Wikipedia, as one does.
A notable example of the observer effect occurs in quantum mechanics, as demonstrated by the double-slit experiment. Physicists have found that observation of quantum phenomena by a detector or an instrument can change the measured results of this experiment. Despite the “observer effect” in the double-slit experiment being caused by the presence of an electronic detector, the experiment’s results have been interpreted by some to suggest that a conscious mind can directly affect reality.[3] However, the need for the “observer” to be conscious is not supported by scientific research, and has been pointed out as a misconception rooted in a poor understanding of the quantum wave function ψ and the quantum measurement process
Edit: erhm. this isnt an ad for Wikipedia. the words just shook out that way. lol
If anybody still doesn’t understand, when the wave function collapses, that is called observation. Again, from Wikipedia:
In various interpretations of quantum mechanics, wave function collapse, also called reduction of the state vector, occurs when a wave function—initially in a superposition of several eigenstates—reduces to a single eigenstate due to interaction with the external world. This interaction is called an observation and is the essence of a measurement in quantum mechanics, which connects the wave function with classical observables such as position and momentum.
Physics has this problem with naming things. They use words like “particle”, “observation”, and “spin”, among others, which are words that every English speaker knows, but then they use those words to describe stuff that’s actually only similar to the words everybody knows. This makes physics a lot more approachable for people who know nothing, but then completely confuses people with only a little knowledge.
There isn’t a scientific definition for “observation.” In the Copenhagen interpretation, it really is treated just as vaguely as the colloquial definition, something the physicist John Bell complained about in his article “Against ‘Measurement’”, that the textbook axioms of quantum mechanics are inherently vague because they refer to “observation” or “measurement” which is not itself defined in the axioms. Saying that observation is just “when the wavefunction collapses” is a circular definition and doesn’t answer anything, because then we can just ask, “when does the wavefunction collapse?” and the only answer the textbook axioms give is “when you observe/measure it.”
Nah, man, it’s literally how it works (for all we know). The wave function doesn’t collapse until the data is read. You can’t prove otherwise, so people are free to believe it.
This was a joke. This is a joke community. I was being facetious when I said “literally”.
However, there’s truth in what I said. How do you know that the entire experimental setup is not in a superposition right up until you observe the result. I mean, you obviously have to look at the result of the experiment before you know what happened in the experiment, and until you do, the entire experiment could be in a superposition of [interference pattern] and [no interference pattern].
However, this is not really what the meme is saying, so I guess my joke was dumb, and I deserve the downvotes.
But the way it works is only the top one if im not mistaken
Well, no. Not if you put a detector in one of the slits. It collapses the wave function, and the interference pattern disappears. The meme is a joke that your eyeballs are the detector, which is not true.
I was making a bit of a joke myself to get people to think about when the collapse actually happens. It could occur as late as when you look at the screen, and you can’t prove otherwise. You know… like, “is the moon still there when you’re not looking at it?” Except for real.
Well that’s basically the bohr-einstsein problem isnt it?
Not exactly. At least I don’t think. Einstein didn’t believe in quantum mechanics at all, or that it was inherently random until measured. Bohr said it was, but I don’t think he necessarily equated conscious observation with measurement. Einstein believed there must be hidden variables, but if there are, they’re non-local.
So, really the problem was about Einstein saying that if Bohr is right then there is information moving faster than the speed of light. Einstein wasn’t saying that he didn’t believe it, but rather if true, then it violated the speed of light in a vacuum. Bohr seemed to actually not understand what Einstein was trying to say, so he interpreted it as Einstein trying to tell him he was wrong.
https://www.youtube.com/watch?v=NIk_0AW5hFU
I think you’re right that Einstein’s instincts wanted QM to be wrong, but he couldn’t argue with the math and experimental results.
Yes, Bohr, and most physicists, are very confused on this subject, and do not properly understand Einstein’s point. Physics doesn’t even really exist anymore, because the term “physics” comes from Greek referring to the study of nature, but modern day physics is better described as “empirical mathematics.” It is solely concerned with nothing else other than mapping what is observed to mathematical equations, and if you ask a more philosophical question of “okay, what do those equations actually tell us about the natural world?” it is typically dismissed. You see this with physicists like Lawrence Krauss and Niel deGrasse Tyson who dismiss philosophical questions as useless.
Einstein’s concern was that he did not see them as useless but to want to talk about reality, and he understood quite well that special relativity is not “really” (in the sense of referring to reality) compatible with non-local influences since he had developed it. In fact, this was his motivation for developing general relativity to begin with. When Einstein introduced special relativity in 1905, it actually made no new empirical predictions, because it was mathematically equivalent to a theory Lorentz introduced in 1904.
Einstein’s criticism of Lorentz’s theory in Einstein’s paper was that Lorentz’s theory required a preferred slicing in spacetime, which Lorentz put there to take into account non-local effects from Newton’s theory of gravity. Einstein argued that he believed this preferred slicing would later be proved to be superfluous, and after he published his paper, he sought to remove the non-locality from Newton’s theory, and then subsequently sought to remove the non-locality from quantum mechanics, by fitting them both to local field theories.
It is quite trivial to see why non-locality is not “really” compatible with special relativity. Giving a definition of “realism” is quite difficult, but we can adopt a minimal, but not sufficient, criterion. This criterion is what I like to refer to as the “no solipsism” criterion. I experience in the world in a definite way, and so I assume you do as well, and how you perceive the world should not depend upon whether or not, or how, I look at you. Mathematically, this criterion is to say that relativity/variance should not bubble up to the scale of the mental states of human beings. The mental states of other humans should be invariant.
If you believe particles do not have real values until you measure them, then you can imagine a “Wigner’s friend” type scenario where a friend in a lab measures a particle in a superposition of states while you are outside of the lab. From your perspective on the outside, you would have to describe both the friend and the particle in an entangled superposition of states, and thus the friend’s mental state would not have an invariant and definite value until you look yourself, which would contradict with the friend’s own experience.
You might try to “solve” this by arguing that when the friend first measures the particle, they “collapse” the state to a definite value for both observers, and so for the observer outside of the room, it’s not in a superposition, but this is not quantum mechanics. Introducing such an invariant transition is called an objective collapse theory, and objective collapse theories fundamentally cannot be mathematically equivalent to quantum mechanics, because they break the linearity in the unitary evolution, and so in principle any objective collapse theory (like GRW theory of the Diosi-Penrose model) would made different empirical predictions to quantum mechanics.
Indeed, Bell definitively proved in 1964 that the states of particles simply cannot be Lorentz invariant given stock quantum mechanics, and since particles make up the human brain, then it logically follows that the mental states of observers cannot be invariant, i.e. you run into solipsism. You thus must give up one of two assumptions. You must either give up quantum mechanics, or you must give up special relativity, if you want to preserve realism.
Giving up special relativity, interestingly enough, does not actually require modifying the mathematics at all. It only requires introducing a philosophical asymmetry in how we interpret otherwise mathematically symmetric reference frames, by assigning one particular reference frame a privileged status of representing a “real” representation of the system, and all other frames as representing an “apparent” representation. This is known as a preferred slicing in spacetime, and John Bell discusses this in his paper “How to Teach Special Relativity.”
You thus can actually fit quantum mechanics to a quite trivial realist interpretation, one where particles have real values at all times and merely evolve statistically, without modifying the mathematics at all, just by introducing a preferred slicing. But this is precisely what Einstein hated and was trying to avoid, because, like I said, his 1905 paper made no new predictions. His 1905 paper was really a bet: it was a bet that Lorentz’s preferred slicing would be proved to be superfluous because gravity and quantum effects could be fit to local field theories, a bet which turned out to be wrong.
However, what Einstein did not anticipate is how little physicists actually care about reality and nature to begin with. Most physicists did not interpret Bell’s theorem as proof nature is non-local and therefore a preferred slicing is logically necessary. Most physicists just argued that we should stop talking about “reality” at all and only talk about what is consciously observed by the experimenter, and predicting that is all that matters, and if that is all you are concerned with, then there really is no incompatibility between quantum theory and special relativity.
Einstein was baffled by this and once even asked Abraham Pais, “do you really believe that the moon doesn’t exist when you aren’t looking at it?” This is what I mean by saying physics no longer exists. Physicists often lie to your face. When they talk to Laymen and try to explain things, they will often give realist explanations, like describing vision in terms of photons reflecting off of a surface and being absorbed into the retinas of our eyes, or describing virtual particles as a “bubbling brew of particles popping in and out of existence,” etc.
Pretty much any time a physicist gives a realist explanation of something to a Laymen, they are lying, because these things literally do not exist in the theory. Objectively, quantum field theory does not anything with any definite properties at all. If I walk to my living room to my kitchen, I will feel quite strongly that I traversed a definite trajectory from my living room to my kitchen, and thus the particles that make up my body should have also traversed such a definite trajectory.
But such a definite trajectory for the particles literally does not exist in quantum field theory. This is why John Bell described modern physics as a kind of “radical solipsism,” because everything you perceive and all your memories have to be taken to be a lie, because they don’t actually exist in the physics. Only the most direct impression in your conscious experience does in the immediate moment of observation.
A lot of students who first start learning physics don’t understand this and thus remain in denial of it. They genuinely cannot fathom the absurdity that modern day “physics” merely describes predicts what is consciously observed in the moment and gives no underlying realist account of how what was observed came to be to begin with, and so they deny it by regurgitating certain statements they’ve heard through the grapevine, like that there is a “collapse” or something about “branching” that explains this, but when you actually learn more and read the academic literature, once go beyond the Dunning-Kruger effect, you will start to learn that these “explanations” don’t actually give an underlying account of what we observe at all (John Bell debunks the “collapse” argument in his article “Against ‘Measurement’” and the “branching” argument in his paper “Quantum Mechanics for Cosmologists”) and that modern physics simply does not have one.
This is what bothered Einstein so much. You must necessarily either give up quantum mechanics, or you must introduce a preferred slicing in spacetime, thereby giving up “real” relativity (whereby relativistic effects are then interpreted to be only apparent), if you actually want a realistic account. If you insist upon not modifying the mathematics of quantum mechanics at all, as well as not introducing a preferred slicing into special relativity, then when you combine the two, you inevitably run into solipsism, because you cannot have a logically consistent accounting of reality whereby each observer’s mental state is invariant.
