gaz_hayes

Thanks everyone! Especially DrRocket, you gave me the "ah huh" moment.

Hi all, I was just wondering if someone can explain this to me. If [mass increases] and [speed of time decreases] as speed increases, what is the speed relative to? Can there ever be absolute rest? If something is at absolute rest, what happens to the speed of time (to outside observers), or is it just relative to the outside observer's speed? And what about the mass of the object at rest? Can mass just disappear when an object slows down enough (is mass created by speed)? If everything is just relative, then where does mass fit in? I can understand with time because time 'appears' no to change for the objects that are changing speed, but the change in mass is actually observable to the object that is changing speed, right? Also, to an outside observer (moving), something moving at speed y along a body that is at rest would appear to be moving faster than y due to time having been sped up to that observer. If that is the case, then what is speed y in terms of mass/time? Is it the speed to the outside observer or the object at rest?