Originally Posted by **topsquark** Point in fact this is the way I was taught, at least beyond casual comments in High School. I'm not trying to tell people what to think I'm merely telling them what the standard convention is. (At least to the best of my knowledge.)
-Dan
Edit: Okay, I'm looking at this from the POV of a particle Physicist. Perhaps a Relativist would describe things differently. |

But you have to think of it like this: There are various applications of relativity in which its more convenient to use proper mass. One of them is in particle physics. In applications such as cosmology and general relativity (when you're speaking of the active gravitational mass) then relativistic mass is more convenient to use and actually better. Also when one is learning relativity. If one has a very good teacher and wants to give the student a thorough education on the concept of mass then he should teach them all possible scenarios one can run into. Then the reason for the use of relativistic mass becomes very clear. But teachers just don't do that anymore. They just don't want to spend time teaching tensors in SR. They leave that to their GR class. But when they get to their GR class they learn about the stress-energy-momentum tensor, which describes completely the mass of an object, but they don't teach about mass because they assume you learned everything you need to know in your SR class.

There just aren't teachers who know about all the possible scenarios that mass has to cover.

But in the end, the number of particle physicists dominate the relativity community. Therefore the use of proper mass dominates relativity. That's how people view what the standard convention is. They never learn why its like that. It in no way means that it's better to use it all around. That's why Alan Guth did that video for me on this. It's also why he makes a point to place it in his lecture notes for his Early Universe course. These lecture notes will eventually be made into a text. You read my website and article on this subject, didn't you?