[deleted]
Henk,
You refer to mathematics, algebra, logic and set theory as though you think mathematics can be taken for granted: something that is assumed to exist that requires no further explanation. But surely "the right starting point" is to ask what mathematics is, and where it fits into the scheme of things? I think 4 points about mathematics are relevant:
First there is the question of a Platonic realm. I start from the assumption that there is no Platonic realm - that is, I think everything exists within this universe including mathematics: mathematics is part of the universe - it is not external to the universe. Unfortunately, even physicists who profess to not believe in a Platonic realm seem to treat their mathematical equations (laws of nature) as though they were external to the universe i.e. things unable to be explained, or things not requiring explanation in the context of this universe.
Second, I assume that mathematics arises out of the reality of living things: mathematics started out as, and continues to be, a system of symbolic representation. We are made out of the underlying reality of the universe; we are not separate from this underlying reality: I consider that mathematics could only make sense to us if and only if the basic elements /symbols of mathematics faithfully represented corresponding basic elements and relationships in the underlying reality. So there was no mathematics in the early universe - there was only the underlying reality, much of which we can represent using symbols*. These symbols include "+ - テキ テ--" and "=", which presumably represent aspects of the underlying reality in this universe, not things that exist in a Platonic realm. These symbols, alone or as part of "law of nature" mathematical equations, seemingly represent aspects of reality that are not measurable, whose existence can only be inferred.
Third, while the basic elements/symbols of maths can be utilized to represent the underlying reality (e.g. as laws of nature), mathematicians or physicists can also creatively assemble mathematical symbols to represent artificial realities: this is similar to the way words in a story, or colour and line in a painting, can be used to represent actual experienced reality or to represent imagined, artificial realities**.
Fourth, the above views might lend support to a view that numbers found in nature, instead of being seen as mysterious Platonic objects, might be seen as being constructed out of the same "component parts" as laws of nature. E.g. if we say that "a + bc = d" represents a law of nature, then "(d +d + d)/d" represents a number similarly constructed. This view implies that that numbers found in nature have a hidden structure, but a structure that may be impossible to determine: there are many possible ways to construct the number 3 using mathematical symbols.
Lorraine
* But seemingly not all aspects of the underlying reality are able to be represented with mathematical symbols e.g. the precise "random" outcomes of quantum events are seemingly not representable as one side of a mathematical equation.
**This view would indicate that mathematics is both discovered AND invented: the type of symbols used in mathematical equations, and the form of a mathematical equation, represent discoveries about aspects of the nature of reality; but mathematics is invented in the sense that it is a creative reworking using these types of symbols.