godelian wrote: ↑Mon Oct 28, 2024 3:34 am
Physicalism fails because it cannot deal with the abstract, platonic phenomena that do not have a counterpart in the physical universe but which are essential to explain the ones that do.
For example, the 18th century is replete with philosophers and mathematicians who rejected calculus because infinitesimals were not physically "real" as they do not map to anything in physical reality:
[..]
I am afraid you're distracting yourself by confusing my positions with those of others.
You're trying to shoehorn me into one of the common philosophies of mathematics: physicalism, platonism and formalism.
That's not a good idea.
I am not rejecting infinitesimals. I see absolutely no reason to do so. It's not something that follows from the way that I think.
My claim was merely that concepts, such as the concept of infinitesimal, are physically real.
There is a difference between concepts and quantities. A quantity is not a concept. The concept of a quantity is a concept. Concepts are meanings attached to symbols and they represent the rules that determine what can be represented by these symbols. The concept attached to the symbol "4" tells us that we can only use that symbol to represent the quantity that is 4. That's not a quantity. It's a set of rules.
As such, the statements "Concepts exist" and "Quantities exist" are two different statements meaning two different things.
Then you have to consider that there are more than one realm of existence. There are the physical realm of existence, the conceptual or platonic realm of existence and the oxymoronic realm of existence.
The physical realm of existence refers to what actually physically exists.
The conceptual realm, or the platonic realm, refers to what can be conceived or imagined regardless of whether it physically exists. Whatever exists in the conceptual realm, does not necessarily exist in the physical realm, but it can exist. Whatever does not exist in the conceptual realm has no possibility of existing in the physical realm. The latter are things such as square-circles. They only exist in the oxymoronic realm.
In mathematics, when we say that a quantity exists, we're saying that it exists in the conceptual or platonic realm. We're not saying that it physically exists.
A quantity is said to physically exist if it can be found in the actual physical existence. For example, if there are three apples on my table, then the quantity "three" physically exists. That's what it means. Quantities aren't physical objects, the way rocks are, but they are nonetheless aspects of physical existence.
The concept of quantity that does not physically exist is potentially useless -- why talk about it? -- but that's not necessarily the case. Circles may not exist anywhere in the physical world but they are still useful as an approximation for real life shapes.
And when it comes to infinitesimals, one has to understand that they are fractions, like "1/2". Fractions aren't
proper quantities. They are actually relations between quantities. A fraction answers the question, "How many times a number is larger than some other number?" But rather than telling us that the number is larger, it tells us that it's actually smaller. "1/2" means "two times smaller". "1/3" means "three times smaller". And so on. The same goes for infinitesimals. Thus, if you want to determine whether or not infinitesimals physically or conceptually exist, you have to focus on the relation between quantities.
As an example, the set A = { 1 } is infinitely many times smaller than the set N = { 1, 2, 3, ... }. More specifically, if we use the symbol "infN" to denote the number of elements in the set N, then the answer to the question, "How many times is A larger than B?", the answer is "1 / infN" times. "1 / infN" being an infinitesimal. The would be a proof that infinitesimals exist in the conceptual realm. And that might be enough for mathematics.
If you want to prove that infinitesimals exist in the physical realm, it should be easy if you happen to already believe the space is infinite in all directions. If you're sure that the length of the universe in one direction is "infN" meters, then it follows that the number of times one meter is larger than the length of the universe in that direction is "1 / infN" times. That's an infinitesimal and an actual one.
But the question is, do you really have to do that? Just to appease the physicalists?