EINSTEIN
ON THE THEORY OF RELATIVITY
I
Einstein
was
the first
physicist
to formulate
clearly
the
new
kinematical
foundation
for
all
of
physics
inherent in
Lorentz's
electron
theory.
This kinematics
emerged
in 1905 from
his critical examination
of
the
physical significance
of
the
concepts
of
spatial
and
temporal
intervals. The examination, based
on a
careful definition
of
the
simultaneity
of
distant
events,
showed that the
concept
of
a
universal
or
absolute time,
on
which
Newtonian
kinematics
is based,
has to be
abandoned;
and that the Galilean
transformations between
the coordinates
of
two inertial frames
of
reference has to be
replaced by a
set
of
spatial
and
temporal
transformations that
agree formally
with
a
set that Lorentz had
introduced
earlier,
with
a
quite
different
interpretation. Through
its
interpretation
of
these transfor-
mations
as
elements
of
a space-time symmetry
group
corresponding
to the
new
kinematics,
the
special theory
of
relativity,
as
it later
came
to be called,
provided physicists
with
a
powerful guide
in the search for
new dynamical
theories
of
fields and
particles,
and
grad-
ually
led to
a deeper appreciation
of
the role
of
symmetry
criteria in
physics.
The
special
theory
of
relativity
also
provided philosophers
with abundant material for reflection
on
the
new
views
of
space
and time. The
special theory,
like Newtonian
mechanics,
still
assigns
a privileged
status
to the class
of
inertial frames
of
reference. The
attempt
to generalize
the
theory
to include
gravitation
led Einstein to formulate the
equivalence
principle
in
1907. This
was
the
first
step
in his search for
a new theory
of
gravitation
denying a privi-
leged
role to inertial
frames, a theory
that
is
now
known
as
the
general
theory
of
relativity.
Einstein
presented
the
special theory
in
Einstein
1905r
(Doc.
23),
a paper
which
is
a
landmark
in
the
development
of
modern
physics.
In the first
part
of
this
paper
Einstein
presented
the
new
kinematics,
basing
it
on
two
postulates,
the
relativity
principle
and the
principle
of
the
constancy
of
the
velocity
of
light.
In the second
part,
he
applied
his kine-
matical results to the
solution
of
a
number
of
problems
in the
optics
and
electrodynamics
of
moving
bodies. This volume includes
a
number
of
other
papers on
relativity.
Three
of
these,
Einstein 1905s
(Doc. 24),
1906e
(Doc. 35),
and 1907h
(Doc.
45),
present
argu-
ments
for
one
of
the
most
important consequences
of
the
theory,
the
equivalence
of
mass
and
energy.
Two
papers,
Einstein
1906g
(Doc. 36)
and 1907e
(Doc.
41),
suggest new
experimental
tests
of
the
theory.
In his
reply
to
a
paper
by
Ehrenfest,
Einstein
1907g
(Doc.
44), Einstein clarified the kinematical nature
of
the
special theory.
Einstein
1907j (Doc.
47) is
the first
major
review
of
the foundations
of
the
theory, as
well
as
of
its
applications
to date
(corrections
appeared
in Einstein 1908b
[Doc. 49]).
The review also
contains
dis-
cussions
of
several
topics
Einstein had not
previously
treated.
Particularly
notable
are
Einstein's
comments
on
the
equivalence
principle
and its
relationship
to the
problem
of
gravitation.
A
brief
discussion
comment,
Einstein
et
al.
1909b
(Doc. 59),
concerns an
objection
to the
theory.
Two
papers on
the relativistic
electrodynamics
of
moving
media
were
written in collaboration with Jakob
Laub,
Einstein
and
Laub 1908a
(Doc.
51),
1908b
(Doc. 52).
These
papers
and corrections
in
Einstein
and
Laub
1908c,
1909
(Docs.
53 and