68
R. N. Mohapatra
found that the emitted electrons in beta decay of this nucleus did not obey
mirror symmetry. The Goldhaber et al discovery came the following year and
not finding the right-handed neutrino was consistent with mirror symmetry
breaking suggested by Lee and Yang. Things were happening at a break-neck
speed. Lee and Yang were awarded the Nobel Prize in 1957 (Fig. 9.4).
Until the time Lee and Yang proposed the weak forces as being somehow
oddly different from other forces and violate parity (mirror symmetry), all
forces (including weak forces) were believed to be parity invariant. In other
words, they all looked the same in their outcome when viewed in a mirror. In
atomic physics, this rule was called La Porte’s rule, named after Otto Laporte,
who announced this rule for atomic spectroscopy. The Lee–Yang parity
violation idea was completely contrary to Laporte’s rule and was therefore so
disturbing to even Lee and Yang that they suggested a way to preserve it. Their
idea was that there may be another universe with identical particles and forces
as our universe. Parity takes particles and forces of our universe to those in the
second universe. As a result, parity would be a good symmetry of forces when
both universes are taken together. Since we are doing experiments only in our
universe, the weak forces look like they break mirror symmetry. The Lee–Yang
parity violation idea was so dramatic that in a letter Pauli wrote to V. Weiskopf
in 1957 [42] “Now, after the first shock is over, I begin to collect myself. Yes,
it was very dramatic.” In fact, Pauli is reported to have said of parity violation
hypothesis that: “I cannot believe God is a weak left-hander [71]”.
This idea of a second parallel universe lay dormant for many years and has
acquired a lot of traction in the context of dark matter of the universe recently.
It will be discussed in a separate chapter in this book. The second universe is
called the “mirror universe” in modern parlance.
More events came in quick succession after the discovery of neutrino and
parity violation in weak forces. New discoveries that shook the field and added
to more understanding of neutrinos as well as weak forces followed. In 1957,
Bruno Pontecorvo [31] the Italian physicist who defected to Soviet union with
his family in 1950, suggested that neutrinos could spontaneously transform to
an anti-neutrino in free flight. This is similar to the already suggested and
observed transformation of K-mesons in free flight to anti-K mesons (also
called oscillations, since the reverse of this, i.e., an anti-K meson transforming
to a K-meson, also occurs, giving rise to a back and forth motion, like a swing)
by Murray Gell-Mann and Abraham Pais in 1955. K-meson oscillation was
discovered soon after by O. Piccioni and collaborators.
R. N. Mohapatra
found that the emitted electrons in beta decay of this nucleus did not obey
mirror symmetry. The Goldhaber et al discovery came the following year and
not finding the right-handed neutrino was consistent with mirror symmetry
breaking suggested by Lee and Yang. Things were happening at a break-neck
speed. Lee and Yang were awarded the Nobel Prize in 1957 (Fig. 9.4).
Until the time Lee and Yang proposed the weak forces as being somehow
oddly different from other forces and violate parity (mirror symmetry), all
forces (including weak forces) were believed to be parity invariant. In other
words, they all looked the same in their outcome when viewed in a mirror. In
atomic physics, this rule was called La Porte’s rule, named after Otto Laporte,
who announced this rule for atomic spectroscopy. The Lee–Yang parity
violation idea was completely contrary to Laporte’s rule and was therefore so
disturbing to even Lee and Yang that they suggested a way to preserve it. Their
idea was that there may be another universe with identical particles and forces
as our universe. Parity takes particles and forces of our universe to those in the
second universe. As a result, parity would be a good symmetry of forces when
both universes are taken together. Since we are doing experiments only in our
universe, the weak forces look like they break mirror symmetry. The Lee–Yang
parity violation idea was so dramatic that in a letter Pauli wrote to V. Weiskopf
in 1957 [42] “Now, after the first shock is over, I begin to collect myself. Yes,
it was very dramatic.” In fact, Pauli is reported to have said of parity violation
hypothesis that: “I cannot believe God is a weak left-hander [71]”.
This idea of a second parallel universe lay dormant for many years and has
acquired a lot of traction in the context of dark matter of the universe recently.
It will be discussed in a separate chapter in this book. The second universe is
called the “mirror universe” in modern parlance.
More events came in quick succession after the discovery of neutrino and
parity violation in weak forces. New discoveries that shook the field and added
to more understanding of neutrinos as well as weak forces followed. In 1957,
Bruno Pontecorvo [31] the Italian physicist who defected to Soviet union with
his family in 1950, suggested that neutrinos could spontaneously transform to
an anti-neutrino in free flight. This is similar to the already suggested and
observed transformation of K-mesons in free flight to anti-K mesons (also
called oscillations, since the reverse of this, i.e., an anti-K meson transforming
to a K-meson, also occurs, giving rise to a back and forth motion, like a swing)
by Murray Gell-Mann and Abraham Pais in 1955. K-meson oscillation was
discovered soon after by O. Piccioni and collaborators.