Two brothers aged 27 years old are separated when one of them travelled through space on a journey at a constant speed. The brother in the spaceship uses a watch which he uses to measure time accurately. On his return to Earth he claims to be 35 years old, but the other brother left on Earth knows that he is 48 years old. 3.1 Explain what is meant by the following terms: 3.1.1 Proper time 3.1.2 Time dilation 3.2 How fast was the ship travelling?

Two brothers aged 27 years old are separated when one of them travelled through space on a journey at a constant speed. The brother in the spaceship uses a watch which he uses to measure time accurately. On his return to Earth he claims to be 35 years old, but the other brother left on Earth knows that he is 48 years old. 3.1 Explain what is meant by the following terms: 3.1.1 Proper time 3.1.2 Time dilation 3.2 How fast was the ship travelling?