Before we get into the “oooh” and the “aaahh,” or maybe even “huh? I don’t get it,” we took a little of time to talk about what is it mean by “countable?” A couple of our classmates argued that if infinity is boundless and has no limit, there is no way it’s countable. However, at the end we came to an agreement that countable is a special kind of infinity and that in order to be countable, it has to have one-to-one correspondence, and it can be put in order. For instance, natural numbers (N) are considered to be countable because we can say that 1 comes after 0, 2 comes after 1, 3 comes after 2, and so on, whereas P (N) or even the real numbers (r) are uncountable because they do not have one-to-one correspondence, nor can they be put in order. We don’t exactly know what comes after 1.278563; is it 1.278564 or is it 1.2785631 or is it 1.27856305?
After understanding that the idea of infinity has the first, second, third, and so on is the essence of it being countable, we went on to talk about paradox. What is paradox? It’s not just a contradiction, but it’s a statement that could be false and true at the same time, which does not suit very well with Aristotle’s “law of excluded middle.” There are different types of paradoxes, one of which is the self-referential type that can be shown in a famous Russell’s paradox, stated “R be the set of all sets that are not members of themselves.” There is no right or wrong answer here, thus in order to “resolve” this problem, Russell decided that a huge set is not a set but a class.
Regarding the paradoxes, we went ahead and looked at 4 of the Zeno’s paradoxes that Aristotle tried to compile things to give an answer to each of them. Each paradox does not work individually; hence they work as a group. The four paradoxes are:
1. Dichotomy: in order to reach a certain location, you first have to get to half of that distant, and to get to that half of that distant, you have to get to half of the half of that distant, and so on. This is the infinite half-way points, which has no end, yet we have to pass all these infinite steps to get to that certain location.
2. Achilles: By letting his tortoise starts out first, it doesn’t matter how fast Achilles runs, he will never catch his tortoise. This is because before he can overtake the tortoise, he first has to reach p1, but when he reaches p1, the tortoise is still ahead, reaching p2. Again, when Achilles reaches p2, the tortoise is still ahead, reaching p3, and so on.
When looking at these two situations, one might think that this is easy; if time and space has the smallest unit and is not infinitely divisible, of course, we will be able to move one unit of space at one unit of time to reach that certain location and catch that tortoise. However, let move on to the third and the fourth paradoxes:
3. Arrows: clearly, we can definitely see the movement if the arrow moves from point A to point B. Assume that time is indivisible like we mentioned above, we will use the word “instant” as the smallest unit of time. If the word instant cannot be divisible, there wouldn’t be a start or an end, and thus the arrow never moves at an instant. The entire of time that the arrow moves from point A to point B will just consist of a bunch of “instant” moments. This means that the arrow has never moved, yet we see movement as the arrow goes from point A to point B.
4.Stadium: The picture below assumes A is stationary, B is moving on unit to the right of A, and C is moving one unit to the left of A at the same time. If it takes one smallest unit of time to move the purple box of B to match with the red box of A, the time that it will take for the black box of C to match with the blue box of A is also one smallest unit of time. However if time can be atomic like one assumes in the first two paradoxes, then how long will it take to have a black box of C match with the purple box of B?