Relativist mass

[Jacques]

From http://homepage.mac.com/ardeshir/EssayOnGeometry.pdf

according to

the Theory of Relativity, an object which is accelerating — i.e., gradually moving faster and

faster — should be increasing in mass as time goes by, while an object which is decelerating —

i.e., gradually moving slower and slower — should be decreasing in mass as time goes by. But,

and this is a really big “BUT”, the Theory of Relativity also insists that acceleration and deceleration

are equivalent to one another in every way: or in other words, that there is no way to tell

of an object whose velocity is changing, whether it is changing in the direction of an increase in

velocity or a decrease in velocity! Indeed according to Relativity, any particular object can be

both accelerating and decelerating at the same time — that is to say, accelerating relative to a second

object, and decelerating relative to a third.12 So if an object’s velocity is at all changing, according

to the Theory of Relativity its mass could be both increasing and decreasing simultaneously

… which is of course quite impossible.

 

Is what is told in this quote, conform to Relativity ?

[swansont]

I think the quoted part is confusing reference frames, as well as the standard "which mass do we use" problem. The observer whose mass you are measuring never "sees" a change in mass in his own frame, just as he thinks his own clock is ticking properly.

[J.C.MacSwell]

the Theory of Relativity also insists that acceleration and deceleration

are equivalent to one another in every way: or in other words, that there is no way to tell

of an object whose velocity is changing, whether it is changing in the direction of an increase in

velocity or a decrease in velocity!

 

This part is wrong. Pick a reference frame and SR insists that (wrt the chosen frame) this is wrong.

[luc]

Is this why physicists prefer the formulation of SR in which there's no relativisitic mass. The notion of rest mass makes easier the calculations