86 HEURISTIC
VIEW OF
LIGHT
Doc. 14
ON
A
HEURISTIC POINT
OF
VIEW
CONCERNING
THE PRODUCTION
AND
TRANSFORMATION OF
LIGHT
by
A.
Einstein
[Annalen
der
Physik
17
(1905):
132-148]
[1]
There
exists
a
profound
formal difference
between
the
theoretical
conceptions physicists have formed about
gases
and
other
ponderable
bodies,
and
Maxwell's
theory
of
electromagnetic processes
in so-called
empty
space.
While
we
conceive
of
the
state of
a body as
being completely
determined
by
the
positions and
velocities
of
a
very
large
but nevertheless finite
number
of
atoms and electrons,
we use
continuous spatial functions
to
determine the
electromagnetic state
of
a
space,
so
that
a
finite
number
of
quantities
cannot
be
considered
as
sufficient for the
complete
description of
the
electromagnetic
state of
a
space. According
to
Maxwell's theory,
energy
is
to
be
considered
as a
continuous spatial function for
all
purely electromagnetic
phenomena,
hence
also for light, while
according to
the
current
conceptions of
physicists
the
energy
of
a
ponderable
body
is
to
be described
as a sum
[2]
extending
over
the
atoms and
electrons.
The energy
of
a
ponderable
body
cannot
be broken
up
into arbitrarily
many,
arbitrarily
small
parts,
while
according to
Maxwell's
theory
(or,
more
generally,
according
to
any
wave
theory)
the
energy
of
a
light
ray
emitted
from
a
point
source
of light spreads
continuously
over
a
steadily increasing volume.
[3]
The
wave
theory
of
light,
which
operates
with continuous spatial func-
tions,
has
proved
itself
splendidly
in
describing
purely
optical
phenomena
and
will
probably
never
be
replaced
by
another
theory.
One
should
keep
in
mind,
however,
that
optical
observations
apply
to time
averages
and not to
momentary
values,
and
it
is conceivable that despite the
complete
confirmation
of
the
theories
of
diffraction,
reflection,
refraction,
dispersion, etc.,
by
exper-
iment, the
theory
of
light,
which
operates
with
continuous spatial functions,
may
lead
to
contradictions with
experience when
it is
applied
to
the
phenomena
of
production and
transformation
of
light.
Indeed,
it
seems
to
me
that the observations
regarding "black-body
[4]
radiation,"
photoluminescence, production
of cathode
rays
by
ultraviolet
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