6
Forces Are Also Caused by Particles
What is the origin of forces? Where do they come from, or were they just there
from the beginning of the universe for some mysterious reason?
6.1 Photon, Mesons, and Forces
The mystery of the origin of forces remained until into the 1920s when it was
realized that the exchange of a particle, called the photon, between objects, was
the source of electric force. The photon as the light quanta had already been
postulated by Albert Einstein to explain the photo-electric effect for which he
got the Nobel Prize. Hideki Yukawa (1907–1981) was the first to point out that
nuclear forces arise due to an exchange of a different kind of particle in much
the same way as the cartoon in Fig. 6.1, where the boomerang represents the
exchange particle. If you throw a stone at someone, your energy is transmitted
via the stone to the “some one” to whom the stone hits and gives him or her
a sting (i.e., a force). See Fig. 6.1. Yukawa gave his theory for nuclear forces as
arising out of the exchange of mesons, which were later discovered in 1947,
in cosmic rays. Yukawa’s suggestion solidified the idea of forces arising out of
particle exchange. This meson, called the pion, is created through a temporary
violation of conservation of mass–energy and travels from the proton to the
neutron or a proton and is recaptured. It is not directly observable and is
called a virtual particle. Three pions denoted by π
± , π
0 were soon discovered
substantiating Yukawa’s hypothesis. Yukawa was awarded the Nobel Prize for
this theory in 1949.
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_6
43
Forces Are Also Caused by Particles
What is the origin of forces? Where do they come from, or were they just there
from the beginning of the universe for some mysterious reason?
6.1 Photon, Mesons, and Forces
The mystery of the origin of forces remained until into the 1920s when it was
realized that the exchange of a particle, called the photon, between objects, was
the source of electric force. The photon as the light quanta had already been
postulated by Albert Einstein to explain the photo-electric effect for which he
got the Nobel Prize. Hideki Yukawa (1907–1981) was the first to point out that
nuclear forces arise due to an exchange of a different kind of particle in much
the same way as the cartoon in Fig. 6.1, where the boomerang represents the
exchange particle. If you throw a stone at someone, your energy is transmitted
via the stone to the “some one” to whom the stone hits and gives him or her
a sting (i.e., a force). See Fig. 6.1. Yukawa gave his theory for nuclear forces as
arising out of the exchange of mesons, which were later discovered in 1947,
in cosmic rays. Yukawa’s suggestion solidified the idea of forces arising out of
particle exchange. This meson, called the pion, is created through a temporary
violation of conservation of mass–energy and travels from the proton to the
neutron or a proton and is recaptured. It is not directly observable and is
called a virtual particle. Three pions denoted by π
± , π
0 were soon discovered
substantiating Yukawa’s hypothesis. Yukawa was awarded the Nobel Prize for
this theory in 1949.
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_6
43