May 1, 2012

Can a child become elder than his own father?

Albert Einstein was the one who proved that time itself does not always pass in the same way (“time is relative, you know”), and he came up with a little problem so ordinary people could understand his postulation:
Some astronauts that were travelling through the space in a futuristic vessel, managed to reach a speed close to The Speed of The Light.  These astronauts would not become older as fast as their fellows on Earth.

If A stands for their age when they started their journey, t stands for the time and Av for the astronauts’ age at any time; we have the following expression (which is nothing but an affine function)

Av = 0,3t + A

Imagine that one of them left in the year 2000 being 20 years old…

a) Get his real age measured using Earth’s Timeline in both the years 2010 and 2020.

b) When will he become a 25-years-old person?

c) If his son was born the on the same day as he enrolled in this mission, how old will this child be when his father gets to his 30s?