CHAPTER FOUR
two different substances freely falling simultaneously, V. Cavasinni and
his team initiated a series of Galileo-type tests of UFF and WEP, the
most recent of which reached a precision that competes with that of the
Princeton experiment.
51
The E
¨
otv
¨
os experiment and its improved versions not only confirmed
the weak principle of equivalence with high precision but also provided
some inferential evidence for the strong principle of equivalence, which
also requires the validity of m
i
= m
p
for bodies containing nonnegligible
amounts of self-energy or binding energy. The earliest inference of this
kind was made in 1955 by Aaldert Hendrik Wapstra and his assis-
tant G. J. Nijgh.
52
Assuming that matter consists of protons, electrons,
neutrons, and nuclear binding energy, thus neglecting electromagnetic
binding energy, and using a simple mathematical analysis from the
E
¨
otv
¨
os data for glass, corkwood, antimonite, and brass, they derived
the conclusion that for these substances the ratio m
p
/m
i
for protons
and electrons (hydrogen atoms) is equal to m
p
/m
i
for neutrons with an
accuracy of one part in 10
5
and that m
p
/m
i
for neurons is equal to this ratio
for nuclear binding energies with an accuracy of about one part in 10
4
.As
the electromagnetic binding energy is of the order of 10
−4
of the nuclear
binding energy they could not derive any significant results from the
E
¨
otv
¨
os data for the electromagnetic energy. But since it constitutes some
tenths of the nuclear binding energy they conjectured that the m
p
/m
i
ratio for this kind of energy cannot be significantly different from that
of the other constituents of matter.
Four years later, Leonard I. Schiff, in a study of the gravitational
properties of antimatter, an issue to be discussed later on, criticized
Wapstra and Nijgh for having made use of only the earlier and less
accurate work of E
¨
otv
¨
os, which, he said, limited the conclusions they
could draw.
53
As he showed, again by a mathematical analysis, the
51
V. Cavasinni, E. Iacopini, E. Polacco, G. Stefanini, “Galileo’s Experiment on Free-
Falling Bodies Using Modern Optical Techniques,” Physics Letters A 116, 157–161 (1986).
T. M. Niebauer, M. P. McHugh, J. E. Faller, “Galilean Test for the Fifth Force,” Physical Review
Letters 59, 609–612 (1987). K. Kuroda and N. Mio, “Test of a Composition-Dependent Force
by a Free-Fall Interferometer,” Physical Review Letters 62, 1941–1944 (1989). S. Carusotto,
V. Cavasinni, A. Mordacci, F. Ferrone, E. Polacco, E. Iacopini, G. Stefanini, “Test of g
Universality with a Galileo-Type Experiment,” Physical Review Letters 69, 1722–1725 (1992).
52
A. H. Wapstra and G. J. Nijgh, “The Ratio of Gravitational to Kinetic Mass for the
Constituents of Matter,” Physica 21, 796–798 (1955).
53
L. I. Schiff, “Gravitational Properties of Antimatter,” Proceedings of the National
Academy of Science 45, 69–80 (1959).
114