Unless you refuse to acknowledge collectively agreed-upon, concrete facts, Darwinism should be a word in your vocabulary, but what about quantum Darwinism?
A set of two words almost seeming like something out of a science-fiction dictionary (photon torpedoes anyone?), quantum Darwinism is one of the latest ideas attempting to reconcile the quantum world with that of the reality that we all share today.
And therein lies the key nugget of information—the reality we share.
When two people observe something, say, a leaf on a tree, they may both say that the leaf is green, or that it is pointed at it’s tip, but when both parties describe these characteristics, the information is usually agreed upon. Unless one person has some kind of disability, the two will, in most cases, see the same thing.
This is kind of how quantum Darwinism takes effect.
When physicists describe a quantum particle as being in a superposition, it essentially means that the particle has a range of possible outcomes, each with their own probabilities, described by a wave. It is only when the observer comes to take a measurement, that the wave “collapses” into a single entity.
But why does this happen? Why can’t the observer see the range of possibilities on the classical scale?
This is likely due to a phenomena known as quantum entanglement.
When two quantum particles become entangled, their properties become interdependent. Essentially, what that means is that the state of one will have an effect on the state of the other and vice versa. To give an example, if one quantum particle is spinning clockwise, the other will spin counter-clockwise. Einstein referred to the phenomena as “Spooky action at a distance”, as it has no limits in terms of distance—one particle could be on one side of the universe, and the other could be at the other side, their properties would still be interdependent.
So, when we have a quantum particle in the vicinity of other quantum particles, say, in literally every situation in the universe, they become entangled with one another so much so that their superpositions disappear and are instead described by a list of possibilities that are more fitting for the classical world—the one that we, as much larger, classical objects, inhabit.
This is referred to as decoherence, and it occurs very, very fast, hence the reason we always see a classical world, free from the almost illogical experience that is the quantum undertone of reality.
Though decoherence was first identified in the 70’s by a German physicst named Heinz- Dieter Zeh, a Polish-American physicist Wojciech Zurek built upon his work a decade later, arguing that for multiple observers to agree upon the properties of a quantum system, two things must be true: Quantum states must be resilient enough to maintain themselves when exposed to decoherence by the surrounding environment, and information about the quantum object must be imprinted in said environment.
And this is where quantum Darwinism comes into play. In order for an observer to see an object, photons come into contact with said object and are reflected into your retinas, thereby relaying the information to you in the form of ‘replicas’. The more replicas, the better.
In terms of a quantum object and its possible properties, the same sort of process occurs. The only quantum states that the observers ‘agree upon’ are those that are able to replicate themselves in the environment the most. Those that are not able to imprint themselves enough times will be discarded, or selected against, just like natural selection.
An example of this can be calculated for a grain of dust a mere one micrometer across. It is estimated that after only a millisecond of illumination by the Sun, it’s location will be imprinted in the photons it came into contact with 100 million times over.
Now, one must also take note that an ‘observer’ doesn’t necessarily have to be anything living. The observer can be the environment itself. Otherwise, reality before anything was conscious of it would be just a big jumble of quantum possibilities. As Jess Riedel, a physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada explained to Quanta Magazine, “A system doesn’t have to be under study in any formal sense [to become classical]. QD putatively explains, or helps to explain, all of classicality, including everyday macroscopic objects that aren’t in a laboratory, or that existed before there were any humans.”