Can Observing Something Change Its Outcome?
Observing a phenomenon can affect its outcome (observer effect). In science, this refers to particles existing in a state of probability until measured. This effect of quantum particles is best understood by the dual-slit experiment explained below, and through the understanding of concepts like quantum field theory, “superposition“, and “the uncertainty principle“.
Some with a metaphysical curiosity debate whether the observer effect is a problem with the measurement process, or simply a behavior of quantum mechanics that we don’t understand yet.
That said, today most respected scientists would likely err on the idea that the observer effect is a result of the measurement process (as the tools we use to measure are cumbersome on a quantum level; or that the measuring process is part of quantum entanglement, as we, the photon, and the measuring device are all at our core, quantum). No one knows exactly what the effect is, but the answer will likely be no more mystical than quantum physics itself (…as it is quantum physics).
How the Quantum Eraser Rewrites the Past | Space Time | PBS Digital Studios. This video from PBS Space Time is the truest answer on how to understand the double slit experiments and observer effect. That said, it is heady. Generally, the answer (from what I gather) is “uncertainty” and “quantum entanglement” AKA “Copenhagen interpretation“. In other words, the photon (or given quantum particle) essentially retroactively decides what state it is in, but not because it is weird or there is no free will, but because it is entangled with another photon (not just in space, but in space and time it seems). This makes sense when you consider the photon is actually a wave form of possible excitations in a quantum field traveling at light speed, and experiencing phenomena like superposition and entanglement, while everything else experiences relative time. So can a photon in the past be entangled with a future photon and react to the future photon based on observation and measurement? Certainly that is the sort of questions the data seems to lead to…. With that said, the only true answer is that we don’t know what the observer effect is exactly (we being physicists; but also me). All we do know is that the underlying theories of quantum physics seem to be in play. That said, watch the video, as it seems someone needs to figure out a more specific answer; also, comment below.
A video explaining the difference between Heisenberg’s Uncertainty Principle, the Observer effect, and the dual wave-particle nature of sub-atomic particles like electrons.
What Do We Mean By Observe? When we say that we observe something, we mean that we determine the properties of a given thing as a result of an experiment. “Measurement” does not mean only a process in which an observer takes part, but rather an interaction between classical and quantum objects regardless of an observer. So for instance, using technology to measure the outcome of an experiment is “observation”. This is different from mathematics where measurement is based strictly on numbers.
TIP: Massless energy particles, like the photon, are fields with excited states called particles (quantum field theory). It’s assumed that our measuring devices affect the field and result in the “observer effect”. Metaphysical theories pertaining to the observer effect are fun to explore, but it is highly doubtful that there is any “mind magic” involved in the observer effect.
TIP: There are also a few a non-physics observer effects too, this is a comment on how people’s behavior changes when it is being watched. This is generally true and is backed up by data (but is a theory).
Quick Summary of the Observer Effect
Keeping in mind that no-one, including me, understand exactly what is causing the observer effect, below is a list of four key concepts related to understanding what we do know about quantum physics and the observer effect.
- All elementary sub-atomic particles, like quarks and electrons, have a dual nature. They are both a particle and a wave and they exist in a state of probability (a state of “quantum superposition”) until observed (measured). This is shown to be true with the double-slit experiment.
- The double-split experiment not only proves the dual nature of particles, further testing shows that the behavior of particles seems to be affected by our observation (measurement process). If we look for (measure for) a particle in spot A it appears in spot A, if we look for it in B, it appears in B.
- The observer effect shouldn’t be confused Werner Heisenberg’s uncertainty principle which says we can’t measure both a particle’s position and its momentum with “certainty” at the same time. It’s confusing because we call both “measuring”, but in Heisenberg’s case we mean math, and for the observer effect we mean the observation of an experiment.
- The observer effect should also not be interpreted to mean that we could change the behavior of particles with our mind (maybe we could, but this remains completely unproven by science, despite attempts).
FACT: The observer effect is rooted in scientific experiments, but it can be applied to almost any other field in some degree of practical and philosophical effectiveness. For instance, a focus group is affected by knowing they are being watched and a computer program may run slower if being monitored. The observer most certainly affects the outcome, but the subtleties need to be understood as it applies to each field.
A video where scientists discuss the Observer effect in Quantum Mechanics in a rational way.
The Observer Effect
In most of the observable and measurable world things either are or aren’t. In most computers, everything is a “1” or a “0”. The power is either on or off. You are either sitting in your chair or aren’t. Quantum computers however, are not limited to binary, instead everything is both “1” and “0” until it is observed (as they use the phenomena of “quantum superposition”).
In the quantum world (the very small sub-atomic world) particles like quarks, electrons, and photons can exist in more than one place at a time (a state of superposition). If we look for a particle in one place it will be there, if we look in another place it will be there, and if we don’t look it will exist in more than one place at the same time.
Given the above, the observer effect refers to the fact that when we actually try to observe (measure) a particle like an electron it’s behavior will change based on our observation. Recent findings are hinting that this is a problem with the way we have been measuring and not something more mystical. 
A video explaining the observer effect in a simple, rational, and understandable way.
FACT: Particles like electrons can be both a wave and a particle at the same time, essentially being in two places at once and existing as a probability.
Dual Wave-Particles and the Double-Slit Experiment
The “Double-slit” experiment presented in simplified form below is probably the most classic example used to explain the dual nature of particles. In this experiment, we will use light as an example, but it also works with other particles like electrons.
A video explaining the double-slit experiment.
- We briefly shine a light source at a plate with two closely placed slits in it.
- We have a screen behind the plate that detects where light hits.
- When we shine the light at the two slits it goes through both holes at the same time, canceling out some waves and appearing as patterns on the screen. It behaves just as we would expect a wave to behave.
- If we repeat the test we find some positions on the screen will have been hit a lot and some will not have been hit at all. This is what we would expect from a particle.
- The “interference pattern” we observe indicates that light acts as both a wave and a particle. Waves should produce an interference pattern and particles should produce solid bands on the screen. Actually, both of these happen. This is because particles can exist as both particles and waves.
- If we do the same experiment and just shoot a single electron at the screen we see that the single electron itself acts as both a particle and a wave causing the same type of “interference pattern”.
- If we try to observe the electron going through only slot A or only slot B it will do exactly that. Essentially it will change its behavior based on our observation. This is the observation effect as shown by the double-slit experiment.
FACT: This tests works with a number of other quantum and atomic particles. It has even been performed with the largest entities possible to use for the double-slit experiment: molecules that each comprised 810 atoms and whose total mass was over 10,000 atomic mass units.
The core behavior of sub-atomic particles being in a state of probability until observed has been famously stated with the Schrödinger’s Cat “paradox”:
“Schrödinger’s cat is currently in a room that will release a deadly poison at some random moment. If we can’t observe Schrödinger’s cat, can we know whether it is alive or dead at any given moment? Does the cat exist in a state of probability, like an electron, being both alive and dead until we check? At what point exactly does being in a state of probability end and the reality of becoming one thing or another begin?”
Wavefunction Collapse and Quantum Superposition
Instead, “wavefunction collapse” accounts for measuring something in quantum mechanics rather than classical mechanics. In classical mechanics a thing is in one specific state any given time and can be measured at each step of an experiment. With quantum mechanics several states are “superposed” and exist at the same time. These superposed states can be measured and collapsed into a single result at any step of the experiment. Adding these quantum states together is called quantum superposition and it is fundamental principle of quantum mechanics.
The Uncertainty Principle
Heisenberg’s uncertainty principle is often confused with the observer effect. This is probably because the two are very closely related, despite having important differences.
The uncertainty principle describes the limit to which complementary variables, such as position x and momentum p, can be known simultaneously. For instance the more precisely the position of some particle is determined, the less precisely its momentum can be known, and vice versa. In short the uncertainty principle is one of mathematics and the observer effect is one of observational science.
FACT: The uncertainty principle was introduced 1927, by the German physicist Werner Heisenberg. It is also known as Heisenberg’s uncertainty principle.
The formal inequality relating the standard deviation of position σx and the standard deviation of momentum σp can be found below (i.e. this is the mathematical equation version of the uncertainty principle).
(ħ is the reduced Planck constant, h / 2π).
What We Know Today
Today we have new data that pokes holes in the observer effect, Heisenberg’s uncertainty principle, and what we know about quantum physics.
As we get better at measuring quantum behavior we find signs that may be the measurement processes we use that are giving us ambiguous results. We will need to figure out how to measure and observe things on a quantum level before we can unveil the next step of the mystery.