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Appendices
1764. However, much earlier, a Roman poet, Decimus Iunius Iuvenalis
(aka Juvenal) in Book III of his Satires had written Rarus enim ferme sensus
communis – Common sense is generally rare.” Much later, Mark Twain and
Will Rogers added their own contributions: I’ve found that common sense ain’t
so common. In any case, common sense, based as it is on our past experiences
in a macroscopic world, turns out to be a poor guide in QM.
A.5.2 Black Body Radiation
A black body, when cold, is a perfect absorber of radiation, i.e. all radiation
that falls on it is absorbed; none is reflected or re-emitted. When heated, a
black body is the most efficient emitter of radiation allowed by the laws of
physics. Normal objects, such as iron bars or lamp filaments, are less efficient
radiators than black bodies.
A black body can be approximated in the laboratory by hollowing out a
cavity in a metal ingot. Light falling into the cavity is repeatedly reflected
around inside it before being finally absorbed. (A similar effect happens with
narrow-necked bottles that are used in summer to trap flying insects.) As none
of the light that enters escapes, the cavity appears black. However, if the ingot
is heated, the cavity appears to be brighter than the metal around it, because
the cavity is a better emitter than the surrounding metal.
A.5.3 Nature Does not Make Jumps
Natura not facit saltus or Nature does not make jumps was a truism of classical
science, attributed by some to Gottfried Leibniz, co-founder of the calculus.
It is the belief that nature does not allow sudden changes. In biology, it was
used by Charles Darwin to support his theory of the evolution of species
through small gradual changes, rather than through the sudden appearance
of new species. In physics, Quantum Mechanics, with its sudden transitions
between states, violates this principle. Also in biology, the discovery of the
roles of DNA and mutations in genetics shows that sudden changes, even if
small, are indeed possible.
Appendices
1764. However, much earlier, a Roman poet, Decimus Iunius Iuvenalis
(aka Juvenal) in Book III of his Satires had written Rarus enim ferme sensus
communis – Common sense is generally rare.” Much later, Mark Twain and
Will Rogers added their own contributions: I’ve found that common sense ain’t
so common. In any case, common sense, based as it is on our past experiences
in a macroscopic world, turns out to be a poor guide in QM.
A.5.2 Black Body Radiation
A black body, when cold, is a perfect absorber of radiation, i.e. all radiation
that falls on it is absorbed; none is reflected or re-emitted. When heated, a
black body is the most efficient emitter of radiation allowed by the laws of
physics. Normal objects, such as iron bars or lamp filaments, are less efficient
radiators than black bodies.
A black body can be approximated in the laboratory by hollowing out a
cavity in a metal ingot. Light falling into the cavity is repeatedly reflected
around inside it before being finally absorbed. (A similar effect happens with
narrow-necked bottles that are used in summer to trap flying insects.) As none
of the light that enters escapes, the cavity appears black. However, if the ingot
is heated, the cavity appears to be brighter than the metal around it, because
the cavity is a better emitter than the surrounding metal.
A.5.3 Nature Does not Make Jumps
Natura not facit saltus or Nature does not make jumps was a truism of classical
science, attributed by some to Gottfried Leibniz, co-founder of the calculus.
It is the belief that nature does not allow sudden changes. In biology, it was
used by Charles Darwin to support his theory of the evolution of species
through small gradual changes, rather than through the sudden appearance
of new species. In physics, Quantum Mechanics, with its sudden transitions
between states, violates this principle. Also in biology, the discovery of the
roles of DNA and mutations in genetics shows that sudden changes, even if
small, are indeed possible.