The Myth of the ‘Observer Effect’ in Quantum Physics

Why the von Neumann-Wigner interpretation of quantum mechanics is so popular but remains a fringe speculation that almost no physicist supports.

You may have heard about the so-called ‘observer effect’ in quantum physics (QP). It is a particular interpretation of QP, also known as the "‘von Neumann-Wigner interpretation,’ and that relates to one of those many weird aspects of QP that has sparked so many speculations, conjectures, and controversies. Much too often I hear people saying that in QP the outcome of an experiment depends on the observer’s mind or consciousness. Some go even so far as stating that this supposedly demonstrates how reality comes into existence only because of our observations or, because of a conscious observer.

First of all, without going too much into the technical details, let us see what the facts are and what this ‘observer effect’ is really about.

In the microscopic world of QP, things have a strange and unintuitive indeterministic character. For example, according to Heisenberg’s uncertainty principle, we can’t measure with absolute precision both the position and the momentum (the quantity of motion, just imagine the speed) of a particle. If you try to find out with increasing precision the position of a particle you will see an increase in the uncertainty over its speed, and vice versa. In practice, this translates into the fact that, when someone makes several measurements, the outcome of every measurement–say, for example, of the position of a quantum particle like an electron–is always a bit indeterminate, uncertain, just fuzzy, even though the overall number of measurements will center around an average expected value. This uncertainty has nothing to do with the imprecision of our measurement devices, it is an inherent uncertainty that will always show up, no matter how precise your measurement will be.

Contrary to some common misleading beliefs, quantum indeterminism isn’t caused by the interaction between the measurement device and the particle either. This quantum uncertainty is misleadingly interpreted as the uncertainty arising due to the interaction between an observer and the quantum system. Because, as the saying goes, when we interact with microscopic objects by observing them, say with light particles through a microscope, we inevitably perturb the system and modify it. This tiny but inevitable perturbation–that is, the ‘observer effect’– modifies reality only because we observe it and, thus, in a sense, reality is in the eye of the beholder.

This interpretation of the observer effect in quantum physics has become pervasive for a simple historical reason: it was none other than Werner Heisenberg’s first interpretation of his own uncertainty principle. He showed that if we try to determine the position of a particle through a microscope, the photons hitting it will inevitably displace it, making it impossible to observe its position with absolute precision. While this is a correct description of the physical process, it turned out to be an overly simplistic understanding of what the uncertainty principle truly means. First, because it can be shown that quantum uncertainty is an inherent property of particles that exists even without interactions, and, more importantly, because this setup with a microscope and a human observer might suggest to some (though not to Heisenberg) that the mind or consciousness of the observer is participating in the process.

First of all, notice that, in physics, with ‘observer’ one means a measurement device, such as a photodiode, a CCD camera, a photographic plate, etc. The ‘observer’ needs no consciousness or mind to ‘observe’–that is, to perform a measurement.

Secondly, nowadays, using modern electronic and quantum optical devices, one can perform so-called ‘interaction-free measurements’ which are a very smart way to test quantum effects, such as the uncertainty principle, without interacting with the system at all. Yet, the uncertainty remains ineliminable–there are no hidden causes or ‘hidden variables’–showing that quantum uncertainty is fundamental and intrinsic in the quantum nature of things, it is not induced as a result of a noisy observer effect.

In other words, every measurement will be affected by some random fluctuations that are unpredictable, and there is nothing we can do about it. It is not due to a lack of knowledge about the real position of a particle, rather this uncertainty is an inherent aspect of reality, an ontological aspect of QP. First, the quantum particle exists in a state where multiple measurement outcomes are possible. However, at the moment the measurement takes place, it 'collapses' into a single determinate state (the famous 'collapse of the wave function'). Which outcome becomes reality is a purely random process. This is something that notoriously Einstein didn’t like at all, and that prompted him to declare that “God doesn’t play dice.”

Moreover, it turns out that quantum theory is also a ‘contextual theory,’ meaning that the results of our measurements not only fluctuate but also depend on how we set up an experiment that provides us with information about the quantum system (such as the position of a particle, which slit it went through, its momentum, its energy, etc.). For example, in certain experimental contexts, we will observe a particle-like behavior while in other contexts a wave-like behavior, of the very same object (a photon, an electron, etc.) with the very same initial conditions. This is the famous ‘wave-particle’ duality. For example, if you don’t try to extract from the system the information about which slit an electron went through a plate with two slits, it will displace itself on a distant screen according to a statistical distribution that shows up with interference fringes–that is, it behaves like a wave.

If, however, one positions a detector at one of the two slits to control whether a particle passes through it, then the interference fringes disappear and the particle behaves like a point moving in space. The act of measurement ‘collapses’ the wave function from a wave representation to a point-like particle.

The wave-like or point-like behavior depends on what information we have about the system and that can be read out by machines, without any necessity for human observers. This is what is meant by saying that QP is a ‘contextual theory’, contrary to Newtonian classical mechanics, which is ‘non-contextual,’ because in the macroscopic world things’ properties don’t depend on how we observe them (for example, the size, color or shape of an object does not depend from which angle we look on it.). Or, to put it in terms of the famous physicist Eugene Wigner, in the quantum realm, Nature answers according to how we frame a question. This is what physicists have shown to be the case with endless laboratory experiments. However, Wigner spoke also about the “participatory universe,” meaning that we are part of this universe observing itself and, by our observations, are participating not only in the observation but also in determining its history. This is one of Wigner’s sidenotes that sparked so much sympathy among idealists and supporters of the “consciousness causing collapse”-theory.

There are also several other effects, such as quantum entanglement and the superposition of quantum states (for example, a particle seemingly being in two places at once), that suddenly 'collapse' from an indeterminate to a determinate state. For instance, the entanglement of particles as a single quantum entity 'collapses' into two distinct particles at the time of measurement, or a particle in multiple positions simultaneously 'collapses' to a definite position once measured. For more on these aspects of quantum physics, see here.

The question then is, how should we interpret this ontic uncertainty and contextuality, and this ‘collapse’ from an indefinite to a definite physical state or property of a quantum system? As an effect of a conscious observer? The point is that these quantum effects are present always, even without anyone looking at the experiment, the particles, the slits, or whatever part of the quantum system or measuring device. And these effects were already present since the time of the creation of the universe. Quantum effects are the very first thing that determined the universe’s fate, long before the existence of any physical conscious observer.

Nevertheless, many try to save the ‘observer effect’ as having something to do with our mind or consciousness, pointing out that, after all, the outcome of an experiment is meaningless if not interpreted by someone. Ultimately, every measurement result registered by a device must, sooner or later, be read out by a conscious observer. A measurement is not a measurement unless someone controls the outcome of…. well, the measurement (say, you read out a number on a pointer.) And, since every time the measurement furnishes a (more or less fluctuating) different and contextual result that is caused neither by the interaction nor due to some unknown ‘hidden variables’ in the measured object, then some conclude that it is the observer’s mind that causes the particle whizzing in one direction and the next time towards another one, causing what is technically called the ‘collapse of the wavefunction’ (the ‘collapse’ from a wave-like to a point-like behavior.)

The problem is that we even don’t know if that wave, particle, or wave function is a real object or a fictitious mathematical abstract entity that tells us only something about our knowledge and the expectations we must have about the next measurement. We even don’t know what really a measurement is. In the microscopic quantum world, things appear to be uncertain, contextual, in superposition, or entangled until someone measures it (or ‘observes’ it, if you prefer.) Then suddenly everything collapses to a point-like single particle. The question is why don’t we observe these weird effects also in our macroscopic everyday life? This is, put bluntly, the so-called ‘measurement problem’, a conceptual loophole in quantum theory (an otherwise quite well-established theory) that didn’t find a complete resolution until nowadays, and that is at the root of the much debated ‘observer effect.’

According to this line of reasoning, somehow reality depends in the end on our observations and the context in which we make them. Thus, ultimately, there must be a connection between our mind, or consciousness, that ‘collapses’ reality to be the way it is through this weird ‘observer effect.’ In a sense, nothing exists until someone observes it.

This is, in simple words, what again Wigner thought to be the case. He illustrated this with a thought experiment (‘Wigner’s friend’ thought experiment) and that has become an interpretation of QP that nowadays we find especially in the popular literature. Nevertheless, it does not receive too much favor from most physicists. Because the implications it suggests seem to go a bit too far. For example, should we go so far as to defend the idea that the entire universe came into existence only once humans (or, at least, some conscious beings in whatever galaxy) began to observe? Frankly, in my opinion, this looks like a desperate attempt to save the quantum ‘observer effect’ interpretation in order to preserve a paradigm that would like to connect at any cost quantum physics to human mental processes or consciousness.

More recently, especially people who believe in the observer effect, mention an experiment in Psi-research. It has been reported that subjects focusing their attention on a double-slit experiment, which is the paradigmatic experiment to illustrate quantum interference, could modify the statistics of the measured outcomes. This purportedly demonstrates how the mind influences quantum phenomena–that is, collapses the wavefunction–and is considered to be evidence for the quantum observer effect. But, even if the experiment is correct, it only shows that the mind might have telekinetic powers, not that it is responsible for quantum effects. It could equally well be that similar effects could be demonstrated with non-quantum objects, say by the ability to move a grain of sand or a feather. If such psychic abilities exist, there is no reason to connect them so straightforwardly to QP, since they may well be operative also in our macroscopic everyday non-quantum realm.

These are the facts about the infamous observer effect in QP. Of course, you must not take my word for a final truth and may continue to believe that there is such a thing as an ‘observer effect’ because, unfortunately, also several physicists, when they speak to a popular audience, like to perpetuate this myth, that they would never mention in an academic lecture. While the von Neumann-Wigner interpretation gained significant favor among the general public, it remains an interpretation supported by only a tiny fringe minority of physicists. At any rate, please, don’t present it as a scientific fact, it was and remains wild speculation.

Having said that, let me digress with my personal (more or less wild) speculation as well. Paradoxically, I am one of those who believes that QP has something to do with consciousness, but I start from a completely different perspective. Let me unpack this.

In physics, only an exclusively scientific third-person perspective is allowed. The ‘observer’ is just a dead, unconscious, and mechanical measurement apparatus that registers data without any need for us to know what the result is.

This is how science is supposed to work. However, the interpretation of scientific facts depends heavily on our belief system, ideological background, and personal preferences.

If you are a materialist, or reductionist who believes there is nothing other than blind and purposeless (more or less random) phenomena ruling the universe with our conscious experience and mental phenomena being only evolutionary emergent surface epiphenomena of brain activity, you might prefer this third-person interpretation: There is no ‘observer effect’ to begin with. In QP phenomena can be driven by blind chance, just ‘random’ (whatever that means) events. We don’t need to inject ‘observers’, ‘minds, or ‘consciousness’ into a rock-solid quantum theory that never mentions it. Any further philosophical extrapolation is unnecessary metaphysical speculation.

This worldview, however, does not answer the question of wherefrom the ‘causeless’, apparently self-determining, and intrinsic quantum randomness comes from. It simply labels quantum theory a ‘theory without hidden variables’ and does not question this state of affairs further.

On the other side, if you find the attempt of reducing mind, life, and consciousness–that is, ourselves–to mere mechanistic processes unconvincing, you might lean towards more metaphysical speculations and those interpretations that see in QP the proof that reality comes into existence because of conscious observers and consciousness itself as a fundamental, non-derivative entity. It is the observer that determines reality, and the universe exists because we are observing it.

This is a perspective that sounds appealing, especially to those who embrace some sort of philosophical idealism.  While I put myself in this latter category, I find this a view of extreme philosophical idealism, an almost solipsistic understanding of reality, and that, as I have just pointed out, has no real support in QP. While, I find it much more reasonable to take a third position that is potentially able to connect both, and even transcend them both. A view I termed ‘quantum idealism’ that tries to get the real message that QP is sending us.

The point is that the way we perceive and conceive reality, even on the macroscopic scale of Newtonian physics, is a reconstruction, a figment, a ‘symbol’ in our conscious experience filtered and translated by mental representations. That kind of reality we conceive of through our limited human sensory means doesn’t exist in the first place. No more and no less than a shadow ‘exists’ in relation to the object that projects it.

QP reminds us that the ‘shadows’ we experience in our everyday life (chunks of hard matter, particles having precise positions and momenta, etc.) do not exist ‘down there’ in the microscopic quantum realm because they don’t exist, as-we-perceive-them, also not in human’s macroscopic everyday reality. We try to inject our human-centric mental constructs into all of Nature in terms of space, time, and causality, and then, once paradoxes arise, postulate whether reality might come into existence only once we observe it. There is a ‘reality’, but it has nothing to do with the conceptual reality in our mind. That mental kind of reality doesn’t exist even when one observes it. It was and will forever remain a ‘shadow’ in our minds. Thus, it isn’t surprising that the microworld doesn’t reflect our macro-world conceptions, because there is no reason to believe that the latter has any ‘ontological superiority’ that supposedly must stand above the former. You can’t describe, let alone explain, the nature of an object with the shadow it projects. For more about this see my post here.

But, again, what about that intrinsic uncertainty, indeterminacy, and randomness that is so characteristic in so many quantum phenomena? What should we make of these ‘fluctuating shadows’ then? We might agree that everything we apprehend and comprehend is ultimately a construct and a figment in us, not the ‘things in itself’, as Kant would have said. Nonetheless, why should that mental construct jitter and wobble like mad, apparently ruled by blind chance, every time we make a measurement?

Let’s take a less anthropocentric perspective and shift from the human-centric observer to a universal-centric one. Is it rather Nature making ‘choices’ that we interpret as ‘random’ due to our limited cognitive ability to see all the phenomena in their entirety? Can we then eventually go so far as stating that, not only the interaction between a measuring device and a quantum object is a measurement, but every physical interaction between particles in the universe is a sort of conscious ‘measurement’ as well?

From a more cosmic perspective: not our human mind or consciousness determines the random quantum outcomes, but a will, or a working universal Consciousness in things, that, by an exclusive concentration in space and time causes one quantum event to become actual rather than another one. For whatever reason that we still don’t understand, it becomes more evident at a microscopic rather than macroscopic scale (the measurement problem.) But we don’t need to pursue dubious conjectures about observer effect in QP that determine the outcome of an experiment. We only need to question our ingrained principles of mechanistic causality and shift our reference frame from the little human perspective to a universal and teleological point of view.

The so-called ‘quantum random fluctuations.’

Without pretending to be able to have a God’s eye view of reality, it is plausible to conjecture that all that quantum randomness and all that mysterious quantum fluctuations are ‘potentialities,’ ‘latent possibilities’, a ’power of choice,’ that come into being by the works of a ‘self-determining Mind at large.’ A ‘super-mind’ that works in and throughout the whole universe, in and through the tiniest elementary particle in every point in space and time (for more on this see also my essay on “force, will, and agency.”) Something that, by the way, would be well in line with modern quantum field theories that work with the notion of a universal quantum field. We, as cognitively limited beings, can interpret all this work no other than as being ‘random’, and ruled by what we call ‘chance.’ But also the ordered and purposeful design of an artifact or a machine created by a human being might well appear a chaotic, and meaningless entity ruled by chance to an ant that can’t look further than its anthill.

So, I agree with Einstein. But for very different reasons than he had in mind. In fact, God doesn’t play dice. God is the dice and even tosses itself.