### 3. HYPOTHESIZED NEW PHYSICS

It is believed that many other vector fields exist. Perhaps the most
important of these are the *X*-fields, which may convert protons and
neutrons into energy. The observed fact that ordinary matter is
essentially stable indicates that if these *X* vector fields exist,
the associated
particles must be very massive, with masses greater than 10^{14}
or 10^{15}
proton masses. This means that it will probably not be possible to
experimentally create and detect them using accelerators for at least a
century. They are therefore considered to be outside the domain of
particle physics which we have proclaimed to be
"well-established". ^{(4)}
But there is another hypothetical direction of importance to cosmology:
the really deep question is, Do other types of fields - non-vector fields
- exist? We know for sure that the gravitational field exists. In the old
Newtonian version, the gravitational field was characterized by one
quantity which depended on the coordinates and time - it seemed to
be analogous to the Coulomb electrostatic field. The question of the
behavior of the gravitational field in the moving frame under the
Lorentz transformation did not arise, since this was two centuries
before the birth of Lorentz, Einstein and Poincaré. There was already
one hint that the gravitational and electromagnetic fields were different:
in gravitation, all masses attract one another, while in electrostatics,
positive and negative charges attract one another and like charges repel
one another.

We shall make the following statement without proof: we now
understand that this one fact means that the gravitational field is not a
vector field. It could be either a scalar or a tensor field. General
relativity (which is the relativistic theory of gravitation) shows that it is
a tensor field. Experiment confirms this brilliantly. A detailed description
of what a tensor field is would take us too far from the ultimate
goal of this paper. There are many good books at every level on
gravitation (see
Misner et al. 1973).
We shall describe scalar
fields (of which gravitation is not an example) later on.

^{4} This is the end of our discussion of
vector fields. Back.