all our judgments in which time plays a part shall always be judgments of
simultaneous events.

if at the point x of space there is a clock, an observer at x shall be able
to determine the time values of events in the immediate proximity of x by
finding the positions of the hands which are simultaneous with these events.

if there is at the point y of space another clock in all respects resembling
the one at x, it shall be possible for an observer at y to determine the
time values of events in the immediate neighborhood of y.

it shall not be possible, however, to compare, in respect of time, an event
at x with an event at y.

if the "time", however, required by light to travel from x to y equals the
"time" it requires to travel from y to x, a common "time" for x and y shall
have been established, and the two clocks synchronize. let a ray of light
depart from x at the time tx, and be reflected at y at the time ty, and
reach x again at the time t'x. if ty - tx = t'x - ty, then the clock at y
shall synchronize with the clock at x.

2xy / (t'x - tx) = c

(1) the principle of relativity:

the laws by which the states of physical systems undergo change shall not be
affected, whether these changes of state be referred to the platform or the
carriage in uniform translatory motion.

(2) the principle of the constancy of the velocity of light:

any ray of light shall move in the platform with the determined velocity c,
whether the ray be emitted by a stationary or by a moving carriage.

let the carriage be stationary relative to the platform; and let its length
be l as measured by a measuring-rod which is also stationary. we now imagine
the axis of the carriage lying along the axis of x of the platform, and that
a uniform motion of parallel translation with velocity v along the axis of x
in the direction of increasing x is then imparted to the carriage. we now
inquire as to the length of the moving carriage, and imagine its length to
be ascertained by the following two operations:

(a) an observer moves together with the given measuring-rod and the carriage
to be measured, and measures the length of the carriage directly by
superposing the measuring-rod, in just the same way as if all three were at
rest.

(b) by means of stationary clocks set up in the platform and synchronizing,
the observer ascertains at what points of the platform the two ends of the
carriage to be measured are located at a definite time. The distance between
these two points, measured by the measuring-rod already employed, which in
this case is at rest, is also a length which may be designated "the length
of the carriage."

the length to be discovered by operation (a) we shall call "the length of
the carriage in the moving system", and shall be equal to the length l of
the stationary carriage.

the length to be discovered by operation (b) we shall call "the length of
the moving carriage in the platform". this length shall be determined on the
basis of the principle of relativity and the principle of the constancy of
the velocity of light, and it shall differ from l.

a moving carriage at the epoch t shall not in geometrical respects be
perfectly represented by the same carriage at rest in a definite position.

imagine that at the two ends x and y of the carriage, clocks are placed
which synchronize with clocks on the platform, that is to say that their
indications correspond at any instant to the "time of the platform" at the
places where they happen to be. These clocks are therefore "synchronous in
the platform."

imagine further that with each clock there is a moving observer, and that
these observers apply to both clocks the criterion established for the
synchronization of two clocks. Let a ray of light depart from x at the time
tx, let it be reflected at y at the time ty, and reach x again at the time t'x.

Taking into consideration the principle of the constancy of the velocity of
light we find that

ty - tx = rxy/(c - v) and t'x - ty = rxy/(c + v)

where rxy denotes the length of the moving carriage--measured in the
platform.

why is it that ty - tx = rxy/(c - v) and t'x - ty = rxy/(c + v)?

Observers moving with the moving carriage would thus find that the two
clocks were not synchronous, while observers in the platform would declare
the clocks to be synchronous. why?

we shall not be able to attach any absolute signification to the concept of
simultaneity.

two events which (viewed from the platform) are simultaneous, shall no
longer be looked upon as simultaneous events when envisaged from the
carriage which is in motion relatively to the platform

"francisco" wrote in message
. ..
all our judgments in which time plays a part shall always be judgments of
simultaneous events.

if at the point x of space there is a clock, an observer at x shall be
able
to determine the time values of events in the immediate proximity of x by
finding the positions of the hands which are simultaneous with these
events.

if there is at the point y of space another clock in all respects
resembling
the one at x, it shall be possible for an observer at y to determine the
time values of events in the immediate neighborhood of y.

it shall not be possible, however, to compare, in respect of time, an
event
at x with an event at y.

If the clock at x records an event and the clock at y records an event then
if they are synced we can compare times. It is this requirement for syncing
that is at the bottom of a lot issues in relativity. One assumption of an
inertial frame is the clocks have been synced in some reasonable way - it
may be by light beams or firing bullets from a gun or slow clock transport
or other methods I am sure you can think of - they simply have to be
reasonable.


if the "time", however, required by light to travel from x to y equals the
"time" it requires to travel from y to x, a common "time" for x and y
shall
have been established, and the two clocks synchronize. let a ray of light
depart from x at the time tx, and be reflected at y at the time ty, and
reach x again at the time t'x. if ty - tx = t'x - ty, then the clock at y
shall synchronize with the clock at x.

2xy / (t'x - tx) = c

(1) the principle of relativity:

the laws by which the states of physical systems undergo change shall not
be
affected, whether these changes of state be referred to the platform or
the
carriage in uniform translatory motion.

(2) the principle of the constancy of the velocity of light:

any ray of light shall move in the platform with the determined velocity
c,
whether the ray be emitted by a stationary or by a moving carriage.

let the carriage be stationary relative to the platform; and let its
length
be l as measured by a measuring-rod which is also stationary. we now
imagine
the axis of the carriage lying along the axis of x of the platform, and
that
a uniform motion of parallel translation with velocity v along the axis of
x
in the direction of increasing x is then imparted to the carriage. we now
inquire as to the length of the moving carriage, and imagine its length to
be ascertained by the following two operations:

(a) an observer moves together with the given measuring-rod and the
carriage
to be measured, and measures the length of the carriage directly by
superposing the measuring-rod, in just the same way as if all three were
at
rest.

(b) by means of stationary clocks set up in the platform and
synchronizing,
the observer ascertains at what points of the platform the two ends of the
carriage to be measured are located at a definite time. The distance
between
these two points, measured by the measuring-rod already employed, which in
this case is at rest, is also a length which may be designated "the length
of the carriage."

the length to be discovered by operation (a) we shall call "the length of
the carriage in the moving system", and shall be equal to the length l of
the stationary carriage.

the length to be discovered by operation (b) we shall call "the length of
the moving carriage in the platform". this length shall be determined on
the
basis of the principle of relativity and the principle of the constancy of
the velocity of light, and it shall differ from l.

a moving carriage at the epoch t shall not in geometrical respects be
perfectly represented by the same carriage at rest in a definite position.

imagine that at the two ends x and y of the carriage, clocks are placed
which synchronize with clocks on the platform, that is to say that their
indications correspond at any instant to the "time of the platform" at the
places where they happen to be. These clocks are therefore "synchronous in
the platform."

imagine further that with each clock there is a moving observer, and that
these observers apply to both clocks the criterion established for the
synchronization of two clocks. Let a ray of light depart from x at the
time
tx, let it be reflected at y at the time ty, and reach x again at the time
t'x.

Taking into consideration the principle of the constancy of the velocity
of
light we find that

ty - tx = rxy/(c - v) and t'x - ty = rxy/(c + v)

where rxy denotes the length of the moving carriage--measured in the
platform.

why is it that ty - tx = rxy/(c - v) and t'x - ty = rxy/(c + v)?

Observers moving with the moving carriage would thus find that the two
clocks were not synchronous, while observers in the platform would declare
the clocks to be synchronous. why?

we shall not be able to attach any absolute signification to the concept
of
simultaneity.

two events which (viewed from the platform) are simultaneous, shall no
longer be looked upon as simultaneous events when envisaged from the
carriage which is in motion relatively to the platform

The above, with its reference to moving carriages looks suspiciously like a
quote form a book - specifically the popular book Einstein wrote on
relativity you sometimes see confusion about on this forum. I wonder what
the purpose of such is? And it is not good form to give quotes without
proper attribution - in fact it is illegal.

Bill

Bill Hobba wrote:
"francisco" wrote in message
. ..
all our judgments in which time plays a part shall always be judgments of
simultaneous events.

if at the point x of space there is a clock, an observer at x shall be
able
to determine the time values of events in the immediate proximity of x by
finding the positions of the hands which are simultaneous with these
events.

if there is at the point y of space another clock in all respects
resembling
the one at x, it shall be possible for an observer at y to determine the
time values of events in the immediate neighborhood of y.

it shall not be possible, however, to compare, in respect of time, an
event
at x with an event at y.

If the clock at x records an event and the clock at y records an event then

wrong, clock never record

if they are synced we can compare times. It is this requirement for syncing

i told you, _we_ "can compare times", not the clocks

that is at the bottom of a lot issues in relativity. One assumption of an
inertial frame is the clocks have been synced in some reasonable way - it
may be by light beams or firing bullets from a gun or slow clock transport
or other methods I am sure you can think of - they simply have to be
reasonable.


if the "time", however, required by light to travel from x to y equals the
"time" it requires to travel from y to x, a common "time" for x and y
shall
have been established, and the two clocks synchronize. let a ray of light
depart from x at the time tx, and be reflected at y at the time ty, and
reach x again at the time t'x. if ty - tx = t'x - ty, then the clock at y
shall synchronize with the clock at x.

2xy / (t'x - tx) = c

(1) the principle of relativity:

the laws by which the states of physical systems undergo change shall not
be
affected, whether these changes of state be referred to the platform or
the
carriage in uniform translatory motion.

(2) the principle of the constancy of the velocity of light:

any ray of light shall move in the platform with the determined velocity
c,
whether the ray be emitted by a stationary or by a moving carriage.

let the carriage be stationary relative to the platform; and let its
length
be l as measured by a measuring-rod which is also stationary. we now
imagine
the axis of the carriage lying along the axis of x of the platform, and
that
a uniform motion of parallel translation with velocity v along the axis of
x
in the direction of increasing x is then imparted to the carriage. we now
inquire as to the length of the moving carriage, and imagine its length to
be ascertained by the following two operations:

(a) an observer moves together with the given measuring-rod and the
carriage
to be measured, and measures the length of the carriage directly by
superposing the measuring-rod, in just the same way as if all three were
at
rest.

(b) by means of stationary clocks set up in the platform and
synchronizing,
the observer ascertains at what points of the platform the two ends of the
carriage to be measured are located at a definite time. The distance
between
these two points, measured by the measuring-rod already employed, which in
this case is at rest, is also a length which may be designated "the length
of the carriage."

the length to be discovered by operation (a) we shall call "the length of
the carriage in the moving system", and shall be equal to the length l of
the stationary carriage.

the length to be discovered by operation (b) we shall call "the length of
the moving carriage in the platform". this length shall be determined on
the
basis of the principle of relativity and the principle of the constancy of
the velocity of light, and it shall differ from l.

a moving carriage at the epoch t shall not in geometrical respects be
perfectly represented by the same carriage at rest in a definite position.

imagine that at the two ends x and y of the carriage, clocks are placed
which synchronize with clocks on the platform, that is to say that their
indications correspond at any instant to the "time of the platform" at the
places where they happen to be. These clocks are therefore "synchronous in
the platform."

imagine further that with each clock there is a moving observer, and that
these observers apply to both clocks the criterion established for the
synchronization of two clocks. Let a ray of light depart from x at the
time
tx, let it be reflected at y at the time ty, and reach x again at the time
t'x.

Taking into consideration the principle of the constancy of the velocity
of
light we find that

ty - tx = rxy/(c - v) and t'x - ty = rxy/(c + v)

where rxy denotes the length of the moving carriage--measured in the
platform.

why is it that ty - tx = rxy/(c - v) and t'x - ty = rxy/(c + v)?

Observers moving with the moving carriage would thus find that the two
clocks were not synchronous, while observers in the platform would declare
the clocks to be synchronous. why?

we shall not be able to attach any absolute signification to the concept
of
simultaneity.

two events which (viewed from the platform) are simultaneous, shall no
longer be looked upon as simultaneous events when envisaged from the
carriage which is in motion relatively to the platform

The above, with its reference to moving carriages looks suspiciously like a
quote form a book - specifically the popular book Einstein wrote on
relativity you sometimes see confusion about on this forum. I wonder what
the purpose of such is? And it is not good form to give quotes without
proper attribution - in fact it is illegal.

what else is illegal?


Bill

"Bill Hobba" wrote in message
news
The above, with its reference to moving carriages looks suspiciously like
a
quote form a book - specifically the popular book Einstein wrote on
relativity you sometimes see confusion about on this forum. I wonder what
the purpose of such is? And it is not good form to give quotes without
proper attribution - in fact it is illegal.

Bill



"on the electrodynamics of moving bodies" by albert einstein. i gave proper
credit to a. einstein on his work on a previous message in this newsgroup.
see the message subject "on the definition of simultaneity and on the
relativity of lengths and times by a. einstein." my intention is (with a
friendly attitude) to reach a mutual understanding of the difficult subject
of relativity with the others in this newsgroup. i only want to focus on the
subject of relativity and related topics of physics. i do not want to do
anything else in this newsgroup.

francisco

"francisco" wrote in message
. ..

"Bill Hobba" wrote in message
news
The above, with its reference to moving carriages looks suspiciously
like
a
quote form a book - specifically the popular book Einstein wrote on
relativity you sometimes see confusion about on this forum. I wonder
what
the purpose of such is? And it is not good form to give quotes without
proper attribution - in fact it is illegal.

Bill



"on the electrodynamics of moving bodies" by albert einstein. i gave
proper
credit to a. einstein on his work on a previous message in this newsgroup.
see the message subject "on the definition of simultaneity and on the
relativity of lengths and times by a. einstein." my intention is (with a
friendly attitude) to reach a mutual understanding of the difficult
subject
of relativity with the others in this newsgroup. i only want to focus on
the
subject of relativity and related topics of physics. i do not want to do
anything else in this newsgroup.

Ok if that is what you want then please understand things have moved on
since that was published. More modern treatments that de-emphasize the role
of light can be found he
http://arxiv.org/abs/physics/0110076,
and ancient, but I still think excellent post by Tom Roberts
http://groups.google.com/groups?hl=e....ih.lucent.com
and chapter 10 of
http://www.courses.fas.harvard.edu/~phys16/Textbook/
under the heading of Relativity without c.

I would say they reflect current understanding better. The reason is than
it is now well recognized there is nothing in the laws of physics as they
are currently understood that rules out light having a very small but non
zero mass as described by say the Proca lagrangian (charge conservation
would only be approximately valid - but as long as it is below current
experimental accuracy no conflicts will arise). This means that light will
not strictly be the same in all inertial frames in violation of Einstein's
second postulate.

Bill


francisco