History of knowledge
Can we believe in absolutes? Will we ever know it all? For me these are relevant questions for which I didn't have any fundamented answer even a few years ago. I remember that when I left the church my only argument was that "something is just not right, god's not anywhere". Then of course I started that angry atheist stage which I think many people suffer of.
People around me often tell me that I always wanna be right like telling you that you have a defect. Is it bad? I don't think it is but what I probably did wrong all this time was to believe in absolute truth. I already adopted years after leaving my faith and convictions an agnostic point of view about god. However, what I didn't know about was how truth works in science in general. It's harder than it seems, epistemology is a branch of philosophy that's related to knowledge and of course, an important part of acknowledging something is how can we consider it as valid (or not) without fooling ourselves (a phrase that reminds me of Richard Feynman, the first scientist I bothered to read).
The thing is that we didn't always have the same view as to how to come by knowledge. Probably the first theory of knowledge is empiricism which claims that we learn through the senses, experiencing something. Empiricism considers that there's no mental exercise from the perception of an event or a fact and we knowing that besides a derivation.
An evolution of that idea was Inductivism which is very similar but argues that you first adopt a generalization and then after repeated experiences we confirm that generalization and that way we get closer to knowing something.
The problem with that is that it doesn't really explain facts whatsoever, only the probability of them being true. Also, there are several things that we cannot experience at all like atoms which indeed were rejected by many people when electronic microscopes didn't exist and atoms couldn't be yet seen.
What's interesting is that empiricism is in some way alive today, especially among common people. I think most of us have fallen into this, trying to explain phenomena by what we perceive. It makes us incapable of understanding ideas and our comprehension of observable phenomena very poor because it doesn't even attain the reason behind it. There's even yet another wrong source of "knowledge" which is authority (the Bible, your boss, a religious authority, your mom).
However, after all that eventually some scientists realized that we don't attain knowledge neither derived from experience nor from repetition but from explanations. Francis Bacon believed in laws that had to be proven through repeated experience. Karl Popper discredited all these ideas quite well with his idea of falsifiability which means that every statement needs to be put in a position where it could be false in order to be proven or refuted. For example, you can refute the idea that the Earth is flat or (in theory) that I have a bill in my pocket but can you prove that god doesn't exist? You can't because it's not a testable problem. Tests alone aren't enough but they are important once you have possible explanations for a phenomenon. These tests allow you to formulate a theory that, based on the hypothesis that was proven before.
Yet, in the same way that you can't experience everything you can't test everything. There is where you can formulate hypothesis and explain a phenomenon as best as it's possible at the moment awaiting for the better technology or a situation that allow humanity to test it in the future. Therefore, even if you formulate a hypothesis about something hard to prove like the existence of god or ghosts there has to be such a formulation of the idea that has both conditions: It has to be a reasonable explanation and it has to be falsiable. There are other conditions that a conjecture has to accomplish in order to be a theory but I don't wanna repeat what Wikipedia says.
Explanations and particularly good explanations are thus, constructed not derived or "downloaded" from somewhere. We as human beings develop them. Even learning a language or mimicking someone are processes of learning where we create something completely new, even if it seems similar to achievements made by other people, otherwise we would all speak in the same way without mistakes. This doesn't mean that we are not influenced by others.
Today what we live thanks to the modern scientific model and the consequential success at achieving good explanations for different phenomena that surround us is a sort of Enlightenment of knowledge on which the society indeed seeks good explanations instead of the stagnation, especially in the Western world.
Knowledge is unbounded
Is it? Some people don't think so but why would it be anyway?
First off, infinite means that something has no end, not just that its end is hard to perceive. Knowledge as I explained above is constructed by human beings. As problems arise which is inherent to solutions to other problems the human being has to devise a solution to them, so there's always something else yet to be learned. Corrections, amendments or possible improvements are all different kinds of solutions to problems.
Connecting this idea to the one above about the human beings and our ability to explain the world I conclude that creativity is infinite, so are problems and therefore knowledge (which is what in the end we build with our creativity).
Problems + creativity = human knowledge
There's yet another branch of this which is what genetics study. DNA is the structure that contains all the information needed to create a new life of any kind. It's not life on itself but it contains information that will be replicated. The theory of evolution explains that genes who are suited to replicate themselves survive (which is not exactly the same as the strongest).
Even though genes and DNA work in a different way than creativity, it's just as adaptative as human knowledge. It faces problems when manifested in living beings and whichever survives is the one that could overcome those problems, not the others. The difference between living beings is the mutations they manifest, understanding mutations as the variant situations in which life displays itself.
Problems (selection) + mutations = biological knowledge
It doesn't have to be confused with the Lamarckian idea of adaptation of genes during the life of living beings. Mutations are just that, they happen randomly but they stay only if they manage to replicate themselves through the living beings they have created.
Human knowledge replicates itself too but it always changes (because of learning). At the same time, if it can't manage to replicate is because it died. We call that memes and the source of study of it all is called memetics.
Selection + creativity = collective knowledge
For a truth to be true, it has to be valid for all situations, given a context of course, you can't remove context from a statement if you want it to be a truth or at least if you wanna test it. For example, shoes hurt is an incomplete statement but it's understood by context. What I meant is that shoes hurt me (and probably a specific kind of shoes that I have) and then I'm right. Maybe I have flat feet which is a good explanation for that statement to be true.
We don't always have all the evidence and that's why science exist. In fact many people believe that scientists are such know-it-alls but their raison d'etre is ignorance.
There are many other concepts in the book but I can't reproduce them all and it's not meant to be a faithful summary of the book so don't hit me if I misunderstood some idea from the book.