Two twin sisters, Gwen and Jackie, are both 20 years old in the year 2020. Jackie takes off on a round-trip to Vega, 25 light-years away. She travels at an average speed very close to the speed of light—say, 0.9999c. According to Gwen back on Earth, about how long does it take Jackie to reach Vega?
A. about a month
B. about 10 years
C. about 25 years
D. about 100 years
Answer:C
Two twin sisters, Gwen and Jackie, are both 20 years old in the year 2020. Jackie takes off on a round-trip to Vega, 25 light-years away. She travels at an average speed very close to the speed of light—say, 0.9999c. According to Gwen back on Earth, about how long does it take Jackie to reach Vega?
A. about a month B. about 10 years C. about 25 years D. about 100 years