Quantum mechanics is regarded as one of the crowning achievements of 20th century physics with it’s predictions backed up by countless experiments in the decades since its formulation in the 1920’s. Along with it’s success as a physical theory for all things microscopic it has also garnered notoriety in the mainstream for its perceived complicated and abstract subject matter and it’s reputation for being impenetrable to any layman. The reason for this singling out of quantum mechanics from the great canon of physical theories is due to its unique philosophical position in relation to the physics it describes, or better put: it’s not necessarily what quantum mechanics tells us, rather how we interpret what we are told.
To begin this discussion of interpretations of quantum mechanics it is best to start with the most widely accepted and universally taught interpretation, The probabilistic interpretation. This is the belief that quantum mechanics doesn’t tell us what has happened in a given system but more precisely how likely it is to happen in a given system. Within this framework we can imagine that all possible results of a measurement of a quantum system have assigned to them a particular probability which represents how likely one is to find the system in that arrangement when measured.
To clarify this idea we can consider a widely understood concept, Pokémon cards! We know that the only way to ‘measure’ what Pokémon we have is to remove the card from the pack and ‘observe’ it. If we know beforehand that there are only 3 types of Pokémon available, let’s say, fire, water and electric and we have heard from others who have bought the same cards that 20% of people get fire cards, 50% get water cards and 30% get electric cards. We can describe our card before we open it as follows:
(card type) = 0.2 (fire) + 0.5 (water) + 0.3 (electric).
All information about the card is represented in this statement (i.e. the type of card and the probability of getting it). We also know that after we open the card and ‘observe’ it we will only possess a single card belonging to only a single card type and it will not change. Therefore, (assuming we got a fire card) after it has been opened the card can be described as:
(card type) = 1.0 (fire)
This change in the description of the card is fundamental to this interpretation of quantum mechanics and is said to take place instantly upon measurement.
The many worlds interpretation of quantum mechanics is an alternate interpretation which proposes a different view on the ‘collapse’ of the description of quantum systems. It states that every possible result of an observation is realised in it’s own universe. Using this point of view, at the moment when the card is opened we can imagine the arrow of time branching into 3 distinct paths and in each new path a different type of card was obtained.
This interpretation was formulated in the 1970’s with contributions from physicists such as Hugh Everett and Bryce DeWitt and aimed to resolve some of the paradoxes of quantum mechanics, the most famous of which being Schrödinger’s cat. While sounding like nothing more than a purely science fiction concept it remains a very real and respected academic hypothesis to this day.