(2-7)  

①  In Nefertiti’s reference frame:   c  =  y/t

②  In Cormorant’s reference frame, using Pythagoras exactly as we did in Question 2-6, when it was the sardine that was moving,    c =  √(x2 + y2) / t.

③  We know - because Uncle Albert insists - that c is a constant; in other words, it must be the same whether Nefertiti or Cormorant measures it. So how can these equations both be true?

The answer is straightforward, albeit at variance with with how we have grown up to see the world:  either y is smaller from Cormorant’s perspective than from Nefertiti’s, or t is bigger.