Koobee Wublee wrote:
On Feb 16, 12:45 pm, Tom Roberts wrote:
The energy-momentum tensor automatically includes the motion of an
object. One must include both its kinetic energy and its momentum, in
addition to its mass.

Kinetic energy is observer dependent, and so is the momentum. This is
also true for the observed mass. Thus, the energy-momentum tensor
must be observer dependent as well.

(sigh) You just do not understand tensors, and the distinction between
tensors and their components. Kinetic energy, momentum, etc. are related
to COMPONENTS of the energy-momentum tensor, and THEY are observer
(coordinate) dependent. The tensor itself is not coordinate dependent --
that's why we use tensors. shrug


Yes. A collection of non-interacting pointlike masses is called "dust",
and the energy-momentum tensor for dust with a mass density \rho is:
T^ij(x) = \rho(x) U^i U^j
Where U is the 4-momentum of the infinitesimal element at x.

This still does not make much sense. It still has nothing to do with
the field equations that Hilbert derived before 1916.

Perhaps if you had READ WHAT I WROTE you would not be so confused. I
said nothing at all about the field equation, I was talking about the
energy-momentum tensor. shrug


[I only occasionally respond to Koobee, because it is useless to do so.
I do it only to prevent others from being fooled by his idiocies, and
thinking that no response implies he is correct. He isn't.]


Tom Roberts