**Gravitational
interaction discussion**

My last publication as a physicist was “Measuring the Gravitational Interaction of Elementary
Particles,” *Physical Review D* 1 (1970) 961-78. Its purport is as follows:

Of course you must exert effort to lift something while standing on earth;
i.e., you put energy into the object. But
this fact can be expressed by saying that the gravitational potential energy of
the object is negative (in an amount equal to a certain number characteristic
of the earth, multiplied by the object’s mass). To get the object to
completely escape the earth, as with a space probe, you must add that entire
amount of energy so that its gravitational energy will go from something
negative to zero.

Now consider the unstable elementary particles that people began to discover
coming to the earth from space during the period between the World Wars, and
that have been created artificially at large laboratories beginning in the
second half of the 20th century. If such a particle had no
gravitational interaction but coupled more or less normally with other particles
via the other known interactions (strong, electromagnetic, weak), and if it
were traveling fast enough so that the energy of its motion would cancel the
(negative) gravitational potential energy of another particle or particles with
which it shared one of the other interactions (with enough left over to take
care of other matters, depending on details), it would create the other
particle or particles. In particular, a sufficiently fast
electrically charged particle with no gravitational interaction would
spontaneously radiate electromagnetic waves such as visible light, since the
particle of electromagnetic waves, the photon, has a normal gravitational
interaction. (The latter fact is shown by the bending of starlight
that travels near the sun to get to us, among other ways.)

In this article I worked out the theory of such processes and calculated the
rates at which they would take place. I noted that in fact no
spontaneous emission of electromagnetic rays from certain electrically-charged
particles coming to the earth is observed to take place. Therefore
such particles have normal gravitational interactions.