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R. N. Mohapatra
5.4 Nuclear Force
The strongest force in nature is the nuclear force, which binds the protons
and neutrons together in the atomic nucleus. It only extends within the
short domain of the nucleus, which is ten trillionths of a centimeter (or
mathematically written as 10
−13 cm—also called one Fermi in honor of the
great Italian physicist Enrico Fermi). The strong force is about hundred
times stronger than the electric force and about hundred trillion, trillion,
trillion times stronger than gravitational force. Without the nuclear force, we
could not exist. The universe would only be filled with hydrogen atoms, and
no other elements will be there—no dust, no trees, no animals. This force
was discovered in the early part of twentieth century and only came to be
understood beginning in the mid-1970s.
5.5 Weak Force
The force that plays a vital role in our daily existence is the weak force,
a force which is weaker than the electric and the nuclear forces, but it is
stronger by about a trillion, trillion, trillion times than the gravity. Unlike the
electromagnetic and the gravitational force however, the weak force is felt only
in a very short distance inside the atomic nucleus. The existence of the weak
force is responsible for nuclear fusion in the core of the sun that provides us
with the warm glow of sunlight and sustenance of all life. As we will see, this
force is intimately connected to the main actor in the book, the neutrino, and
in fact, the neutrino is the only particle out of the proton, neutron, electron,
etc. that exclusively feels the weak force. However, they all feel the force of
gravity.
Weak force is also different from gravitational and electric forces, in that the
weak force can change one particle to another. For example, the weak force
acting between an electron and a proton can change the proton to a neutron
and electron to a neutrino. In short hand notation, it is written as e
−
+ p →
ν +n. By the same token, we can have a neutrino hitting a neutron, converting
it to a proton and electron i.e. ν + n → p + e
− (see Fig. 5.1). This is very
different from the way electromagnetic and gravitational forces work. They
preserve the identity of the particles they act on, whereas as we see from the
above examples, weak forces change the identity of particles i.e. a neutron to
a proton and vice versa. This understanding got expanded in the 1970s, when
a new class of processes called weak neutral current processes was discovered.
R. N. Mohapatra
5.4 Nuclear Force
The strongest force in nature is the nuclear force, which binds the protons
and neutrons together in the atomic nucleus. It only extends within the
short domain of the nucleus, which is ten trillionths of a centimeter (or
mathematically written as 10
−13 cm—also called one Fermi in honor of the
great Italian physicist Enrico Fermi). The strong force is about hundred
times stronger than the electric force and about hundred trillion, trillion,
trillion times stronger than gravitational force. Without the nuclear force, we
could not exist. The universe would only be filled with hydrogen atoms, and
no other elements will be there—no dust, no trees, no animals. This force
was discovered in the early part of twentieth century and only came to be
understood beginning in the mid-1970s.
5.5 Weak Force
The force that plays a vital role in our daily existence is the weak force,
a force which is weaker than the electric and the nuclear forces, but it is
stronger by about a trillion, trillion, trillion times than the gravity. Unlike the
electromagnetic and the gravitational force however, the weak force is felt only
in a very short distance inside the atomic nucleus. The existence of the weak
force is responsible for nuclear fusion in the core of the sun that provides us
with the warm glow of sunlight and sustenance of all life. As we will see, this
force is intimately connected to the main actor in the book, the neutrino, and
in fact, the neutrino is the only particle out of the proton, neutron, electron,
etc. that exclusively feels the weak force. However, they all feel the force of
gravity.
Weak force is also different from gravitational and electric forces, in that the
weak force can change one particle to another. For example, the weak force
acting between an electron and a proton can change the proton to a neutron
and electron to a neutrino. In short hand notation, it is written as e
−
+ p →
ν +n. By the same token, we can have a neutrino hitting a neutron, converting
it to a proton and electron i.e. ν + n → p + e
− (see Fig. 5.1). This is very
different from the way electromagnetic and gravitational forces work. They
preserve the identity of the particles they act on, whereas as we see from the
above examples, weak forces change the identity of particles i.e. a neutron to
a proton and vice versa. This understanding got expanded in the 1970s, when
a new class of processes called weak neutral current processes was discovered.