5 The Incredible Quantum Mechanics
85
The energy of each photon is proportional to its frequency, and the photons
can be identified with the quanta of Planck.
Readers will by now be querying why it is so difficult for physicists
to distinguish between waves and particles. Surely the two phenomena are
nothing like each other. We’ve all seen ripples on a pond, we’ve all held a
pebble in our hand. So, what’s the problem? Is light a form of electromagnetic
waves, or is it made up of photons shot out like bullets?
The answer, however, is not as simple as the question: sometimes light is
one thing, sometimes the other. Being a truly Pirandellian creature, it has a
third, more complex nature, in which both the wave and particle personalities
coexist. We will try to explain this duality in the following Sections.
5.4 The QM Revolution
We have already commented on the scarcity of Common Sense in the world
at large. The Italian poet, Giuseppe Giusti (1809–1850), has written an
epigram to denounce sarcastically what he perceived as the disappearance of
Common Sense in the school room:
Il Buonsenso, che già fu caposcuola,
ora in parecchie scuole è morto affatto;
la Scienza sua figliuola
l’uccise, per veder com’era fatto
Common Sense, who used to be
school master,
is now in many schools dead and
buried;
the reason is that Science, who is his
daughter,
killed him to see how he was made
Now that we are exploring Quantum Mechanics, we have to do precisely
the opposite to what Giusti was advocating, i.e. we must learn to abandon
common sense in favour of experimental evidence. Otherwise we will never
understand how an object such as a photon, can be simultaneously both a
particle and a wave. As we learned in Chap. 2, to understand sometimes
means simply to accept a premise and explore its consequences. This was
the approach adopted by Max Planck with his “explanation” of black body
radiation.
This trait appears to be much easier for a young, uncluttered mind. So
it happened that a Ph.D. student, Louis-Victor Pierre Raymond (Louis) de
Broglie, with a thesis of just 70 pages [5], obtained both his Ph.D and the
Nobel prize (in 1929), by postulating a dual nature, not only for photons,
but also for matter. (Before this, he had already obtained a degree in history
and one in science.) De Broglie’s bold assumption meant that electrons, the
85
The energy of each photon is proportional to its frequency, and the photons
can be identified with the quanta of Planck.
Readers will by now be querying why it is so difficult for physicists
to distinguish between waves and particles. Surely the two phenomena are
nothing like each other. We’ve all seen ripples on a pond, we’ve all held a
pebble in our hand. So, what’s the problem? Is light a form of electromagnetic
waves, or is it made up of photons shot out like bullets?
The answer, however, is not as simple as the question: sometimes light is
one thing, sometimes the other. Being a truly Pirandellian creature, it has a
third, more complex nature, in which both the wave and particle personalities
coexist. We will try to explain this duality in the following Sections.
5.4 The QM Revolution
We have already commented on the scarcity of Common Sense in the world
at large. The Italian poet, Giuseppe Giusti (1809–1850), has written an
epigram to denounce sarcastically what he perceived as the disappearance of
Common Sense in the school room:
Il Buonsenso, che già fu caposcuola,
ora in parecchie scuole è morto affatto;
la Scienza sua figliuola
l’uccise, per veder com’era fatto
Common Sense, who used to be
school master,
is now in many schools dead and
buried;
the reason is that Science, who is his
daughter,
killed him to see how he was made
Now that we are exploring Quantum Mechanics, we have to do precisely
the opposite to what Giusti was advocating, i.e. we must learn to abandon
common sense in favour of experimental evidence. Otherwise we will never
understand how an object such as a photon, can be simultaneously both a
particle and a wave. As we learned in Chap. 2, to understand sometimes
means simply to accept a premise and explore its consequences. This was
the approach adopted by Max Planck with his “explanation” of black body
radiation.
This trait appears to be much easier for a young, uncluttered mind. So
it happened that a Ph.D. student, Louis-Victor Pierre Raymond (Louis) de
Broglie, with a thesis of just 70 pages [5], obtained both his Ph.D and the
Nobel prize (in 1929), by postulating a dual nature, not only for photons,
but also for matter. (Before this, he had already obtained a degree in history
and one in science.) De Broglie’s bold assumption meant that electrons, the