What's a cool thing you ‘invented’ as a kid, only to find it had already been invented?

This is a fun question. I have three “discoveries” as a kid that later turned out to have been discovered much much sooner than when I was born.

Geometry in 3D space

I was somewhere between 8 and 10, around the time when they start teaching at school the basic 2D geometry about x,y coordinate systems, rectangles, triangles, circles and so on. One time after school I was lying on the couch and I was looking at the corner of my room near the ceiling. I looked at it and thought how one of the lines coming out of the corner could be X-axis and the other Y and how one could draw rectangles on the wall.

Then I realized that there’s a third line coming out of the corner, perpendicular to the other ones, going straight up. I started pondering, how I could also mark units on that line. And one could do 3D shapes - cubes and parallelograms instead of rectangles, spheres instead of circles and how maybe one could even extend the formulas we had for area to get volume, and there would be different formulas for surface area and so on. I was really excited, as I thought I was really unto something.

When my elder sister came home, I ran to her, all excited, to tell about my new discovery and she just said: “Wait a few years, it’s all there, you’re gonna hate all the formulas.” I felt pretty down the entire evening.

Curvature of the Universe

It’s hard to figure out when this was. Between 9 and 12 I’d guess. I had heard that the Universe is infinite, that one can fly as far as one would want to in a space ship and it would never end. So I was pondering about how would this be possible. Then a realization came to my mind that infinity is actually curved when observed from a vantage point in the next dimension.

Take a line, a single spatial dimension. One could draw a line on a sheet of paper but it would be finite. However, one can draw a curved line - a circle. If anyone lives on the circle but is only able to experience one spatial dimension and is small enough, they would experience the circle as an infinite, straight line. Whereas anyone being able to experience at least two spatial dimensions, and big enough, would see it as a circle - a curved 1D object.

This would also extend to two dimensions. People used to think that the Earth is flat and finite. It turned out to be roughly a sphere (I thought it’s actually a sphere then). So again, if one experiences only the 2D nature of the sphere, it feels awfully lot like an infinite plane, yet for anyone who sees it in 3D it’s a sphere.

So I thought - why wouldn’t this extend to more dimensions? If we have an infinite three dimensional Universe, maybe it is something like a circle, or a sphere, so it must be somehow curved.

I lived with the thought that I have figured something new out for quite a while, I think a few months. The internet was in its infancy then, so fact checking quickly was not a thing. Later I found out that this is not a new theory. And of course, the real theory is not this naive.

100 X 100 = 10000

For this one I know exactly how old I was. I was 7. In the first grade this was a common taunt between the kids: “If you’re so smart, then, how much is 100 X 100?” Because then 100 was, like, the largest number around so consequently 100 X 100 was something akin to infinity - an unknown, mythical super large number.

Now, I don’t remember if we had had multiplication at school already. Maybe, maybe not. I would know some anyway because of my two elder sisters. In either case, I knew that 10 X 10 is 100. I was lying in my bed in this weird state between being asleep and awake when I started thinking - if 10 X 10 is 100 then 100 X 100 must be 10 X 10 X 10 X 10. So I have 100 X 10 X 10. I started counting. 100.. 200 .. 300 …. 900.. What comes after? Is there a number ‘ten hundred’? A thousand! It must be a thousand! So I have now ‘a thousand’ X 10. 1,2,3,4… 10 thousand!! 100 X 100 is ‘ten thousand’!

The next morning I ran up to my Mom who was sipping coffee and thinking about her day with a loud exclamation: “Mom, mom, I know how much is 100 X 100!! It’s 10 thousand!” She’d just look at me and say: “Sure it is, honey!” As if it was common knowledge!

The day at school was great though. An annoying girl: “If you’re so smart then how much is 100 X 100??” Me, casually: “Ten thousand, of course.”

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Jānis Gailis on Quora:

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