Re: Mass and Potential Energy


Tom Roberts wrote:
Mike wrote:
Tom Roberts wrote:
In SR and GR, the mass of an object is the
norm of its 4-momentum, and is thus an invariant.

Not in GR, it is impossible to define mass that way since 4-vectors are
found in different tangent spaces.

Yes in GR. For a given pointlike object, [shrug]

How convenient to define mass just for pointlike objects. But real life
is not poinlike, don't you think so?

I mean, some people should understand that physics is not a pure
extension of geometry.


I suggest GRists try to find a better definition of mass that is
convincing.

There is nothing wrong with this one. Indeed, it is probably the only
one that satisfies the basic requirements of what we mean by "mass" and
has the proper local limit for inertial frames. Certainly it is the
usual definition.

For your so called "pointlike" objects. But not for any other kind of
the usual objects you encounter in your favirite "local" experiments.

GR is to "pointlike" in every sense. Is there anything elese besides
"pointlike" physics?

Mike





Tom Roberts

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