Einstein's moving objects spaceships explains going symbol relative speed astronaut speed physics respect theory observations speed principles absolute between
Einstein
explained
that
when
two
objects
are
at
a
constant
as
the
motion
the
two
,
instead
of
appealing
to
the
ether
as
an
frame
of
reference
that
defined
what
was
on
.
If
you
and
some
,
Amber
,
are
moving
in
different
and
want
to
compare
your
,
all
that
matters
is
how
fast
you
and
Amber
are
moving
with
to
each
other
.
Special
relativity
includes
only
the
special
case
(
hence
the
name
)
where
the
motion
is
uniform
.
The
motion
it
is
only
if
you're
traveling
in
a
straight
line
at
a
constant
speed
.
As
soon
as
you
accelerate
or
curve
?
or
do
anything
that
changes
the
nature
of
the
motion
in
any
way
?
special
relativity
ceases
to
apply
.
That's
where
general
of
relativity
comes
in
,
because
it
can
explain
the
general
case
of
any
sort
of
motion
.
Einstein's
theory
was
based
on
two
key
:
The
principle
of
relativity
:
The
laws
of
don't
change
,
even
for
objects
moving
in
inertial
(
constant
)
frames
of
reference
.
The
principle
of
the
of
light
:
The
speed
of
light
is
the
same
for
all
observers
,
regardless
of
their
motion
relative
to
the
light
source
.
(
Physicists
write
this
speed
using
the
c
.
)