You have the opportunity to ride in a Klingon hyperdrive spaceship that cruises at 0.9 the speed of light.
Its engines are so powerful that it accelerates from rest to cruising speed in just 5s.
Using advanced spacewarp technology, the occupants of the spaceship easily tolerate the resulting acelerations.
Your 25-year-old brother watches you leave and wishes you well on your trip.
When you return, the chronometer on the spaceship indicates that your trip lasted exactly one year.
How old is your brother?
The expert examines the age of brother on earth after one year trip in a spaceship.