Question

Twins A and B live on Earth. On their 20th birthday, Twin B climbs into a spaceship and makes a round trip journey at 0.94c to a star 25 light-years distant, as measured in the Earth-star frame of reference. What are their ages when the twins are reunited?
y (twin A)
y (twin B)

Answer 1

For Twin B, the distance between the star and the Earth will be contracted due to Lorentz Length contraction.

The new length will be:

= 7.806 light years.

So, the time taken for this trip according to Twin B will be:

therefore Twin B's age will be: 20 + 16.61 = 36.61 years old.

For twin A, the time will be dilated. And so, the amount by which Twin B would have aged by the time twin B comes back will be:

= 48.682 years.

So Twin A will be: 20 + 48.682 = 68.682 years old.