I put the prefix as intermediate because I wasn't really sure how complicated of a question this is, I am currently a junior in high school... So basically if you were to have two spaceships with people the exact same age in them travelling at 99% the speed of light and they were traveling parallel to each other, but in opposite directions, then when ship A passes ship B, to ship A ship B will be traveling slower through time, and ship A will feel normal, and vice versa with ship B. So my question is, who is actually traveling slower through time? If both people were to meet each other then who would be younger? Also, from the perspective of someone on earth, they will both be the same age right? I kinda had a hypothesis (that I know is most likely wrong) that from the perspective of ship A ship B will be younger when they meet and from the perspective of ship B ship A will be younger when they meet, and then if both of them were to meet someone on earth, the person from earth would see them as being the same age... Thanks in advance any help much appreciated!