Say a brother and sister are twins on Earth, and at the ages of 20 years old, the sister boards a spacecraft that is traveling to Alpha Centauri while the brother remains on Earth. Alpha Centauri is approximately 4.367 light years or 4.1315 * 1016m away from Earth, and if the spacecraft that the sister boards is traveling at a velocity v = 0.9c where c = 3 * 10 " a) How long does the trip take (in years) in the reference frame of the brother on Earth? b) How long does the trip take (in years) in the reference frame of the sister who is traveling on the spacecraft? c) When the sister arrives at Alpha Centauri, is she still the same age as her brother? If not, is she younger or older, and by how many years?