Are Real Numbers Real?
Let's talk about the different sets of numbers. First, we have integers, which are a simple and intuitive concept. It's a series of numbers going in both directions (positive and negative) to infinity. Rational numbers are not hard to understand either, as the name suggests they are ratios of integers. But what about the real numbers? Are they a valid mathematical concept? There is one fact that made me question it: most of them are "unreachable", which means we cannot create any formulas that "pinpoint" them. The number of types of mathematical symbols is finite, and the number of symbols in a formula is finite too. This means that the number of all possible formulas is "countable infinity", while the number of all possible real numbers is "uncountable infinity". So most of the real numbers can't be expressed as formulas. This also applies to any continuous subset of them, for example the set of all real numbers between 0 and 1.
But I still think the real numbers are a valid concept (or are "real" in Platonic sense). What convinces me is that there exists a way to construct them all. But instead of constructing one at the time (like we do with integers, where we're just adding one number after another to the set), to create an "uncountable infinity" we need to make the number of elements added in each step grow exponentially. For simplicity we're using the binary code, but it can be also done in decimal or any other base. The point I use here works like the decimal point.
First we create 0.0 and 0.1. Then, in every step, we split every series of digits created so far into two, by adding 0 and 1 at the end. Here's how it works:
step 1
0.0
0.1
step 2
0.00
0.01
0.10
0.11
step 3
0.000
0.001
0.010
0.011
0.100
0.101
0.110
0.111
and so on.
After an infinite number of steps, we will create all the real numbers between 0 and 1. Expanding it to all the real numbers is not a problem and can be done in many ways, for example by adding integers to them, or by changing the position of the point. This procedure convinces me that the real numbers make sense as a mathematical concept. Of course it requires an infinite number of steps (after finite steps we can't even create any irrational number), but it's understandable when we're dealing with infinite sets.
Edited by PawelS
- 3
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