Elementary Particles, Quarks and Quantum Chromodynamics 243
The proton and neutron are continually emitting and reabsorbing
mesons. The mesons can never wander more than 10-13 cm from the
proton or else they will no longer be masked by the uncertainty principle
and a violation of energy conservation would be detected. If another
nucleon wanders into the meson cloud, a meson exchange will take place
and the two nucleons will exert a nuclear force upon each other. This is
illustrated in Feynman language with the following diagram where
nucleon N 1 emits a pion at time t 1 which is absorbed by nucleon N 2 at
time t 2 :
232 The Poetry of Physics and The Physics of Poetry
and a violation of energy conservation would be detected. If another
nucleon wanders into the meson cloud, a meson exchange will take place
and the two nucleons will exert a nuclear force upon each other. This is
illustrated in Feynman language with the following diagram where
nuc 1 emits a pion at time t 1 which is absorbed by nucleon N 2 at
Figure 24.2
The transformations of the proton can be more complicated since the
protons can emit more than one meson at a time in which case a
transformation like the following is possible: p % p + 'o + '- + '+ % p
% n + '+ + 'o % p. These kinds of transformations can lead to scattering
between nucleons where multiple mesons are being exchanged. The
proton and the neutron behave in a completely symmetric way as far as
the nuclear force and their interaction with mesons are concerned.
The virtual mesons hovering about the nucleon are unobservable
because of the requirements of energy conservation. The proton or
neutron seems to borrow energy to produce the meson and must repay
that debt before anyone can detect the deficit by reabsorbing the meson
or exchanging it with another nucleon, which is within a convenient
distance. If the proton is provided with a source of energy, however,
there is no reason why the meson would have to be returned. On the
basis of Yukawa’s theory, therefore, one would expect to produce
mesons by providing a nucleon with enough energy to provide for the
rest mass energy of the meson. One mechanism for providing this energy
is to knock one nucleon against another hard enough so that the kinetic
Fig. 24.2
The transformations of the proton can be more complicated since
the protons can emit more than one meson at a time in which case
a transformation like the following is possible: p → p + πo + π– + π+ →
p → n + π+ + πo → p. These kinds of transformations can lead to
scattering between nucleons where multiple mesons are being
exchanged. The proton and the neutron behave in a completely
symmetric way as far as the nuclear force and their interaction with
mesons are concerned.
The virtual mesons hovering about the nucleon are unobservable
because of the requirements of energy conservation. The proton or
neutron seems to borrow energy to produce the meson and must repay
that debt before anyone can detect the deficit by reabsorbing the meson
or exchanging it with another nucleon, which is within a convenient
distance. If the proton is provided with a source of energy, however,