# Explanations Provide a Fundamentally Different Structure and Search Process
Let's start with the following claim: in order to improve the world around you, you must interact with it. This requires that *something* is physically instantiated. Now let us consider the space of all possible physically instantiations. This includes rocks, water molecules, ink on the page of a paperback book, text rendered on an LCD screen, your brain, and so on. This is an enormous, infinite space. Let's call this the **P**hysical **I**nstantiation space, or $\Pi$ for short. We can call some specific physical instantiation, such as the polycarbonate lens of my glasses, $\pi$.
$\Pi = \{ \pi \mid \pi \text{ is a possible physical instantiation} \}$
We can now consider how [Evolution](Evolution.md) navigates this space. It does so via *local* trial and error. Imagine we are in the corner of this space that is occupied by sea turtles. In order to create a variant of a sea turtle with a harder shell, evolution will proceed by a random mutation of a gene which leads to the phenotype of a harder shell. If that proves useful in solving some of the [Problems](Problem.md) posed by the environment, it will be preserved and propagated through the gene pool.
Notice how local this jump was. The turtle already had a set of genes that coded for a shell. The shells functional *purpose* was to provide protection. But evolution was never going to jump to a shell made of steel or titanium, which would also provide (increased) protection. This is because there is no local viable path to jump from the current chemical composition to one so drastically different. For the purposes of this note, evolution can be thought of as falling in the class of [Local Search](Local%20Search.md) algorithms: evolution uses trial and error to locally search $\Pi$. There is no sense of direction (each jump is random) and no sense of where a certain $\pi$ is in the full space of $\Pi$. Mathematically, we could of course compute a distance between two $\pi