Pi can be seen in real life (obviously not with full precision, but close enough). Simply make a 1 cm rod on a lathe and measure its circumference, and you’ll see it’s ~3.141 cm

The same goes for root 2. Simply measure the diagonal of a 1 cm square

Not sure where you’d see e in real life, though (excluding as the base of an exponential, because any exponential can be trivially rewritten with any base)