46andTwo wrote:
Great question! I asked a former Mathamatics professor in college whom agreed with the above posters but then he dropped this nugget of confusion: "some infinities are mathematically larger then others" . Every answer comes with more questions it seems haha
He is correct.
Consider countable vs uncountable.
A set is countable if you can pair each member of the set with a unique integer. If you have a set of three items, say {red, green, yellow}, you can say red is the first member of the set, green is the second member of the set, and yellow is the third member. In fact, any finite set is countable.
Many infinite sets are countable as well. For example, the integers since each integer can be paired uniquely with itself.
A set for which you cannot pair every member with a unique integer is called uncountable.
Remember that rational numbers are numbers that can be expressed by one integer divided by another non-zero integer. For example, 1/2, 3/4, 99/5132413241235123412, ... . There are countably many rationals. Irrational numbers are numbers that cannot be written as the ratio of two integers. Pi and e are examples of this.
Another way of looking at it is that rational numbers are numbers that can be expressed in decimal in which the digits repeat after some point.
It is easy to find two integers that represent any such number where the digits repeat. First, determine how many digits repeat. For example, 5/27=0.185185185... with the three digits 185 repeating over and over. Let x=0.185185185... . Multiply the number by 10 to the power of the number of digits that repeat. For x=0.185185185, multiply by 10^3 or 1000. Thus, 1000x = 185.185185185... . Subtract the first from the second 1000x-x=185.185185... - 0.185185... . You get 999x = 185. Thus, 0.185185185... = 185/999. When you divide top and bottom by the common denominator, 37, you get 5/27.
On the other hand, the perceived size of something doesn't necessarily mean that one is larger than the others.
Consider two concentric circles of various sizes. For example, draw one circle of radius 10 and one of radius 1 with both having the same center. There are exactly as many points in the outer circle as in the inner circle and vice versa.
To see this, pick any unique point on the outer circle and draw a line between that point and the center of the circle. It will cross the inner circle at one precise point. Thus, for every point on the outer circle, there is a unique point corresponding to that point on the inner circle. Thus, the inner circle contains at least as many points as the outer circle.
Similarly, choose a point on the inner circle and draw a line starting at the center of the circle and through that point on the inner circle and extending out to the outer circle. Again, for every point on the inner circle, there is a unique point on the outer circle associated with that point. Thus, the outer circle contains at least as many points as the inner circle.
And therefore, the number of points in each circle are identical.