Part
A 10-year-old astronaut goes off on a long-term mission in a spacecraft that travels at 0.9c. The mission lasts exactly 20 years measured on Earth. Biologically speaking, the astronaut's age would be:
- exactly 50 years
- more than 30 years and less than 50 years
- exactly 30 years
- more than 50 years
Observer sees a ruler moving by at a relativistic speed and measures its length to be L'. Observer moves together with the ruler and measures the length of the ruler to be L. These two results will:
- L' = L
- L' could be greater or smaller than L, depending on the direction of motion
- L' > L
- L' < L