At work we somehow landed on the topic of how many holes a human has, which then evolved into a heated discussion on the classic question of how many holes does a straw have.
I think it’s two, but some people are convinced that it’s one, which I just don’t understand. What are your thoughts?
Take a sealed tin can. Punch a hole in it. Punch another hole in it. You now have one hole.
No, but that’s two holes. And it’s because the holes are not connect by a single, unbroken cylinder. It’s the material at the edge of those holes and the 90° turn at the corners that makes the holes disconnected.
The edges and corners mean nothing for the purposes of counting holes. Counting holes is a concept of topology that relies on continuous deformation. All non-opening features of the object just get squished and stretched away in the process of identifying holes.
For the purpose of counting holes a can with two openings punched into it is equivalent to a donut which we know has only one hole.