Oh, I see what you mean. Since the usual, but not always, independent variable in differential calculus is time, the question is whether or not time is discrete.
I am not sure whether or not space or time is discrete. It is possible, I suppose. **In any case, the real line is not discrete in a mathematical sense, since between any two points on the real line, you can find one in between. **This would not be true AFAIK with a thin rod.
Your thought process is somewhat mysterious.
Originally, you wrote:
“The differential calculus is built on the assumption of the continuity of the real line, and yet AFAIK, matter is discrete and not continuous. therefore the math model is in this case an approximation.”
More recently, you wrote (see above for the full quote):
“In any case, the real line is not discrete in a mathematical sense, since between any two points on the real line, you can find one in between.”
Given any two rational numbers, there is a rational number between them. So it’s becoming less clear (rather than more clear) what you meant originally when you wrote about “the assumption of the continuity of the real line.”
Do you know of a way to develop differential calculus using merely the set of rational numbers rather than the set of real numbers? That is not a rhetorical question. There is a mathematician named “Norman Wilberger” (who has videos on Youtube and also his own website) and he would probably be very interested in such a development.
Now, relating back to the topic of this thread,
Mathematical representations of space and time can be very good approximations, but they are not exact. Or perhaps I should say that eventually there might be a mathematical representation of space and time that is exact, but we would not know that it is exact. There are at least two reasons for this. First, our measurements have limited precision. At best, we could say the correct value of something lies within some interval, but it is an interval. If the interval is made too small then we can no longer say whether or not the correct value lies in the interval. There are also sources of error. So if we want to reduce the chance of making a statement that will eventually be discovered to be definitely false, then we need a safety margin that makes our interval bigger, rather than smaller.
That is why, if we are interested in focusing on mathematics that may be difficult to explain from the point of view of materialist philosophy, then we should focus on mathematics that deals with the properties of non-negative integers.