I love Physics! I've been thinking about if..... you were in a room with a window, bouncing a ball... and you were looking at another building where you could see a room with a person bouncing a ball, but ..... their time was moving at half speed (Caused by gravitational time dialation only ( not speed)) .... you weigh 170 lbs with respect your scale and they weigh 170 lbs with respect to their scale. To you.. their ball is also going half speed. .... Now, somehow you give them your weight scale. Your scale is still on your time though. When they weigh themself your scale would read 85 lbs because the gravity there is only 1/2 the gravity of your time. My question is.... Is their mass half your mass?