On Jan 25, 2006, at 6:22 AM, Stephen A. Lawrence wrote:
Thank you for the summary. I had one comment (really just one,
this time!)
Horace Heffner wrote:
Mass in the conventional spacetime metric is considered invariant.
There's a semantic problem here. "An invariant" is a well-defined
mathematical concept. However, it's just that -- a mathematical
concept. Saying "this is an _invariant_" doesn't mean it's some
simple physical property which always has the same value.
Wheeler and Taylor say the mass of any isolated system is invariant.
In other words:
m^2 = E^2 + p^2
in one frame then
m^2 = (E')^2 - (p')^2
in another for that isolated subsystem. Problem is, no subsystem of
mass is isolated. Stuff comes in and out of the vacuum constantly.
A significant portion of the magnetic field of the proton comes from
strange quark pairs popping in and out of the vacuum, for example.
Acceleration affects how things pop in and out of the vacuum and how
long they stick around.
It's easy to forget that relativity theory says _nothing_ about
what is "real" and what is not.
Who's relativity? Certainly not mine! You make it sound like there
is only one version! 8^)
With all that said, when someone refers to the "invariant mass"
they mean the rest mass.
Not Wheeler and Taylor.
Horace Heffner
