8 The Most Accurate Theory in Physics
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theory that can describe the electron–electron interaction, and the electronphoton interaction. Such a theory, called Quantum Electrodynamics (or
QED for short), will be outlined in the next Section. It is very relevant,
even in view of our simplified approach in this book, for three reasons:
first, because it is arguably the most precise theory ever to be developed in
any field of science, second because it can be applied to all interactions in
nature except gravity and radioactivity, and third because it has been used
as a template for another theory, the Standard Model of Fundamental Particles, which is currently the most widely-accepted explanation for the “zoo” of
newly discovered particles, that we shall encounter in Chap. 9.
8.4 Quantum Electrodynamics (QED)
QED owes its development largely to three physicists, who shared the 1965
Nobel Prize for their “fundamental work in quantum electrodynamics, with
deep-ploughing consequences for the physics of elementary particles”. These scientists, who worked independently, were Sin-Itiro Tomonaga, Julian Schwinger
and Richard P. Feynman, and their approaches to the problem were quite
different.
It is not uncommon in physics that different ways of tackling a problem
lead to the same answer. For instance, Newton and Lagrange approached
classical mechanics very differently. Newton employed forces, velocities and
acceleration, which are vectors, 3 whereas Lagrange used a sophisticated mathematical technique, known as the Calculus of Variations. Almost two centuries
later, Quantum Mechanics was formulated using differential equations by
Schrödinger and matrices by Werner Heisenberg. Both of these apparently
disparate methods have been shown to be mathematically equivalent. In the
case of QED, the approach developed by Feynman is the most transparent
and will be discussed in the following.
Let us begin with a simple illustrative example: the reflection of light from
a mirror (see Fig. 8.7). In the classical representation of Maxwell, light is a
wave and its reflection is no more difficult to explain than the reflection of
ripples from the side of a pond. But, as we have seen in Chap. 5, in QM
light is composed of a stream of particles (photons), whose distribution is
controlled by a probability wave function.
In the upper figure we represent rays of light, transiting from the source at
A and arriving at B, after having been reflected by a mirror. The ray reflected
3 Vectors are mathematical entities, representing physical quantities, which possess both a numerical
value (called the modulus) and a direction.
155
theory that can describe the electron–electron interaction, and the electronphoton interaction. Such a theory, called Quantum Electrodynamics (or
QED for short), will be outlined in the next Section. It is very relevant,
even in view of our simplified approach in this book, for three reasons:
first, because it is arguably the most precise theory ever to be developed in
any field of science, second because it can be applied to all interactions in
nature except gravity and radioactivity, and third because it has been used
as a template for another theory, the Standard Model of Fundamental Particles, which is currently the most widely-accepted explanation for the “zoo” of
newly discovered particles, that we shall encounter in Chap. 9.
8.4 Quantum Electrodynamics (QED)
QED owes its development largely to three physicists, who shared the 1965
Nobel Prize for their “fundamental work in quantum electrodynamics, with
deep-ploughing consequences for the physics of elementary particles”. These scientists, who worked independently, were Sin-Itiro Tomonaga, Julian Schwinger
and Richard P. Feynman, and their approaches to the problem were quite
different.
It is not uncommon in physics that different ways of tackling a problem
lead to the same answer. For instance, Newton and Lagrange approached
classical mechanics very differently. Newton employed forces, velocities and
acceleration, which are vectors, 3 whereas Lagrange used a sophisticated mathematical technique, known as the Calculus of Variations. Almost two centuries
later, Quantum Mechanics was formulated using differential equations by
Schrödinger and matrices by Werner Heisenberg. Both of these apparently
disparate methods have been shown to be mathematically equivalent. In the
case of QED, the approach developed by Feynman is the most transparent
and will be discussed in the following.
Let us begin with a simple illustrative example: the reflection of light from
a mirror (see Fig. 8.7). In the classical representation of Maxwell, light is a
wave and its reflection is no more difficult to explain than the reflection of
ripples from the side of a pond. But, as we have seen in Chap. 5, in QM
light is composed of a stream of particles (photons), whose distribution is
controlled by a probability wave function.
In the upper figure we represent rays of light, transiting from the source at
A and arriving at B, after having been reflected by a mirror. The ray reflected
3 Vectors are mathematical entities, representing physical quantities, which possess both a numerical
value (called the modulus) and a direction.