Pi fun fact:
As you may have learned in high school geometry (unless you went to my yeshiva), pi is defined as a circle's circumference (the distance around) divided by its diameter (the distance across). It is approximately equal to 3.14 (that's why Pi Day is 3/14).
Now imagine a circular disk. If we measure its circumference and diameter, we find that their ratio is pi. What if we start to spin the disk (for example, a CD in a CD player)? According to Einstein's Special Theory of Relativity, a moving object's length is shortened along its direction of motion as it moves (for example, if you throw a yard stick, its length becomes less than a yard while it is moving). Now, the outer edge of the disk is moving, thus its circumference is shortened. But the diameter remains unchanged, since it is not along the direction of motion. Thus the ratio of circumference to diameter is now less than pi!
What does this mean? It means that the geometry you learned in high school ("Euclidean Geometry") is not sufficient to describe relativistic motion. In fact, the spinning disk in free space is indistinguishable from a stationary disk in a gravitational field (that's Einstein's "equivalence principle") so this must mean that space under the influence of gravity is not describable by Euclidean geometry. In other words, space can be curved!
Yep kids, the universe is amazing, even without angels and witches.
Incidentally, I remember learning a gemara which said that the ratio of a circle's circumference to its diameter is 3 (I think it was talking about fitting the Torah into the holy ark). I guess you could say that the gemara was just being approximate (I think some meforshim say that), but I'd guess that Babylonian rabbis at the start of the dark ages just weren't math experts. Of course if you're a true believer then you'd say that the chazal knew everything there is to know, even though there is another gemara which says that the sun goes behind a curtain every night.
Edit: I've been informed that is today is merely American Pi Day. The British Pi Day does not occur until the 31st of April, which is never.
Sheva Yipoil Tzadick V’cum
4 weeks ago