Is light a wave or a particle? Significant Experiments in Quantum Mechanics
In the late 17th century, the scientific consensus was that the fundamental elements of light acted as particles. This was true until Thomas Young designed an experiment that would show this wasn’t so clear. The Double Slit Experiment involved Young shining light across two slits. It was expected that if light acted as a particle, two parallel slit shaped lines of light would present themselves on the other side. However, Young surprisingly observed that the light produced interference patterns on the wall behind the slits. Interference patterns occur when the peaks of waves combine to make higher peaks, while when peaks and troughs combine, they then cancel each other out and smoothen. This showed that light was acting as a wave and not a particle.
Fast forward a couple of centuries and the Double Slit Experiment was reworked this time with quantum particles being fired one at a time through slits to determine if they individually acted as a wave or particle. Surely single electrons could not act as waves since they have no particles to collide with. They would either have to go through one slit or the other, not both. However, to the experimenters surprise, the Quantum Particles formed an interference pattern against the wall indicating that they had somehow gone through both slits and interacted with themselves. This stunned scientists since they didn’t understand how a single particle can simultaneously go through both slits and interact with itself, since it is only one particle. The experiment was therefore reworked with a detector added to the slits to determine which slit the QP actually went through. This was done since the former experiment seemed to indicate that the QP was somehow going through both slits and the detector would conclusively determine what was happening at each slit. The crazy part was that this time not only did the detectors only detect a particle going through one of the two slits, but also showed the particle leaving a line on the wall indicating that there was no interference pattern and that the particle had acted as a particle and not a wave. This indicated that the presence of the detector alone somehow influenced the state of the electrons and the simple act of measuring them seemed to change their whole states of existence.
While there are many interpretations as to why this occurred, the consensus throughout much of the last 100 years has been the Copenhagen Interpretation of Quantum Mechanics. The Copenhagen interpretation posits that only when a photon or quantum element is actually measured or compelled to select a state (in this case determining a slit to go through), does it actually differentiate itself into a determinstic form where it goes through one slit or the other as an individual particle. Before, it merely exists in a superposition of both a particle and wave as depending on the circumstances it can be one of either. This assumes that the without the need to be measured, the photon or electron is in an indeterminate state of existence. Additionally, while it is not being measured it acts a wave. Only when it needs to be measured does the waveform collapse and actually differentiate itself into a single deterministic particle or manner of existence. Early 20th century Physicist Pascual Jordan famously stated “observations not only disturb what has to be measured, they produce it… We compel [a quantum particle] to assume a definite position.”. This meant to say that without any subjectivity, there does not exist anything objective at all. Einstein was notably frustrated with this and famously remarked “Just because we are not looking at the moon, does not mean it doesn’t exist” .
In the 1970’s physicist John Wheeler conducted an experiment that sought to determine whether the act of measuring photons after they should have already selected a path influences their state of existence. This experiment showed that even when the measurement of the photons path is delayed, they still change states based on the existence of that measurement at all, so long as it is before they themselves actually go through the detector. Wheeler noted that this seemed to suggest that it was the act of a subjective force that prompted the Quantum Particles state of existence. While Interpretations of whether these experiments actually showed the need for subjectivity in the existence of objectivitiy are still heavily debated to this day, with some positing that the particles division into two different universes (Many Worlds Theory) also explains this.
Note: There is a misconception out there that this shows that the Quantum particle is itself conscious and knows when it is being detected and therefore decides to change its state. Rather, in reality this interpretation just notes that when the Quantum Particle is forced to enter a deterministic world it abides and differentiates itself into an individual particle, while when it doesn’t it remains in a superposition of states since the world it lives in is not deterministic.
How this relates to Consciousness
This seems to suggest that without a subjective perspective existing to bring the particle into a deterministic world, the QP remains in an indeterminstic world where its state of existence is a probability and where its waveform has never collapsed. For example in the popular thought experiment “Schrodingers Cat”, one is asked if a cat in an unopened box is alive or dead. The answer is that before the box is actually opened the cat is in a superposition of being both alive and dead, since both possibilties are true up until the box is actually opened. Take the simple distinction of content and context. Content generally refers to anything that objectively exists. In the case of Schrodingers Cat, content refers to different timelines, one where the cat is alive inside the box and one where it is dead inside the box. Objectively, both possibilties exist as content itself does not have to choose just one state. Context on the other hand represents a single situation. It requires that all the states of content (the two timelines of the cat being alive and dead) devolve into only one in order to fit into the specific subjective context. Therefore until there is any context, content by definition always exists in every state of being. It is only when there is context does the content have to collapse into just one possibility for itself. Furthermore, there is only one way to ever bring about context or anything subjective- Something capable of action or decision must interact with content and bring it into the world of its subjective context. Without anything capable of action to interact with the objective, what is objective can never enter the world of subjectivity. Since subjective perspectives exist each in their very own world of subjectivity, only when they take action (or in the case of the cat, open the box), does the content (or objective states of being for the cat) actually devolve into a single state of existence to fit in with the world of the subjective experiencer. This shows that consciousness (or simply a subjective observer) is required for any content to ever enter a subjective state of being where it can only itself exist in one state, per the Copenhagen Interpretation.
Note that this is not to say that consciousness is required for anything physical to exist at all, but rather that consciousness is required for anything physical taking on just one state in one context.