I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no atmosphere.
You stand on the equator and hold your hands up to the air so that they are
a meter apart. [Relax, this is NOT a study in relative simultaneity like the
Barn/Pole thing.] As you stand there a huge spacecraft coasts by just
overhead, just beyond your reach. The ship seems motionless to you,
hovering, because it is going eastward at a speed to exactly match the
planet's tangential rotational speed. As you reach up, your outstretched
fingertips are just about touching the 842-meter mark and the 843-meter mark
on the rule graduated on the enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY assert that an
all-way light beacon pulse emitted midway between their ship's 842 &
843-meter marks will hit the two nearby meter marks simultaneously,
according to their native frame's clocks and such. Yet the guy on the planet
cannot make the same claim?? When does an arbitrary local span become
tantamount to an SR scenario. In spite of Sagnac, there must surely be some
carry-over; I mean you're just about TOUCHING that other frame, comoving.

-Ben

"Ben Bean" wrote in message
...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no
atmosphere.
You stand on the equator and hold your hands up to the air so that they
are
a meter apart. [Relax, this is NOT a study in relative simultaneity like
the
Barn/Pole thing.] As you stand there a huge spacecraft coasts by just
overhead, just beyond your reach. The ship seems motionless to you,
hovering, because it is going eastward at a speed to exactly match the
planet's tangential rotational speed. As you reach up, your outstretched
fingertips are just about touching the 842-meter mark and the 843-meter
mark
on the rule graduated on the enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY assert that
an
all-way light beacon pulse emitted midway between their ship's 842 &
843-meter marks will hit the two nearby meter marks simultaneously,
according to their native frame's clocks and such. Yet the guy on the
planet
cannot make the same claim?? When does an arbitrary local span become
tantamount to an SR scenario. In spite of Sagnac, there must surely be
some
carry-over; I mean you're just about TOUCHING that other frame, comoving.

-Ben



If you extrapolate that issue to encompass a span from New York to LA, and
if light were presumed to move relative to a cosmic aether, anchored at the
planet's center, then light's transit Eastbound would take about 50
nanoseconds longer than it would in the Westbound direction. [My
calculations are approximate but I think close.]

But light can *NOT* be presumed to be moving relative to any such aether
frame, so the 50 nanosecond differential is non-sequitor. Would there be a
differential at all? and if so, how much of one?

CERTAINLY, the minimal assertion is at least valid, that light is seen to
spread out evenly in both latitudinal directions from the perspective of an
observer sitting on the equator (or anywhere on the surface) of a rotating
planet... at least to some localized extent.

Let's not talk about gravity messing with this purist scenario: the planet
in question can be a reinforced hollow sphere of styrofoam, for that matter.

-BB

"Ben Bean" skrev i melding ...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no atmosphere.
You stand on the equator and hold your hands up to the air so that they are
a meter apart. [Relax, this is NOT a study in relative simultaneity like the
Barn/Pole thing.] As you stand there a huge spacecraft coasts by just
overhead, just beyond your reach. The ship seems motionless to you,
hovering, because it is going eastward at a speed to exactly match the
planet's tangential rotational speed. As you reach up, your outstretched
fingertips are just about touching the 842-meter mark and the 843-meter mark
on the rule graduated on the enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY assert that an
all-way light beacon pulse emitted midway between their ship's 842 &
843-meter marks will hit the two nearby meter marks simultaneously,
according to their native frame's clocks and such. Yet the guy on the planet
cannot make the same claim?? When does an arbitrary local span become
tantamount to an SR scenario. In spite of Sagnac, there must surely be some
carry-over; I mean you're just about TOUCHING that other frame, comoving.

-Ben

Of course the guy on the planet will agree that the light will hit the two metre
marks simultaneously. That is, if he had one clock at each side of himself,
and he E-synched those clocks, they would show the same when hit
by the light.
However, if the two clocks were showing UTC, they would NOT
show the same when hit by the light.
Clocks on the surface of the Earth showing UTC are NOT synchronous
in the Earth fixed frame. They are synchronous in the non rotating ECI-frame.

Paul

On Wed, 20 Oct 2004 21:06:20 +0200, Paul B. Andersen wrote:


"Ben Bean" skrev i melding
...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no
atmosphere. You stand on the equator and hold your hands up to the air
so that they are a meter apart. [Relax, this is NOT a study in relative
simultaneity like the Barn/Pole thing.] As you stand there a huge
spacecraft coasts by just overhead, just beyond your reach. The ship
seems motionless to you, hovering, because it is going eastward at a
speed to exactly match the planet's tangential rotational speed. As you
reach up, your outstretched fingertips are just about touching the
842-meter mark and the 843-meter mark on the rule graduated on the
enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY assert
that an all-way light beacon pulse emitted midway between their ship's
842 & 843-meter marks will hit the two nearby meter marks
simultaneously, according to their native frame's clocks and such. Yet
the guy on the planet cannot make the same claim?? When does an
arbitrary local span become tantamount to an SR scenario. In spite of
Sagnac, there must surely be some carry-over; I mean you're just about
TOUCHING that other frame, comoving.

-Ben

Of course the guy on the planet will agree that the light will hit the two
metre marks simultaneously. That is, if he had one clock at each side of
himself, and he E-synched those clocks, they would show the same when hit
by the light.
However, if the two clocks were showing UTC, they would NOT show the same
when hit by the light.
Clocks on the surface of the Earth showing UTC are NOT synchronous in the
Earth fixed frame. They are synchronous in the non rotating ECI-frame.

Paul, what do you mean by "Earth fixed frame"? Do you mean the
inertial frame which is momentarily comoving with the surface at one
particular point?


--
I can be contacted through http://www.physicsinsights.org

"sal" skrev i melding news
On Wed, 20 Oct 2004 21:06:20 +0200, Paul B. Andersen wrote:


"Ben Bean" skrev i melding
...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no
atmosphere. You stand on the equator and hold your hands up to the air
so that they are a meter apart. [Relax, this is NOT a study in relative
simultaneity like the Barn/Pole thing.] As you stand there a huge
spacecraft coasts by just overhead, just beyond your reach. The ship
seems motionless to you, hovering, because it is going eastward at a
speed to exactly match the planet's tangential rotational speed. As you
reach up, your outstretched fingertips are just about touching the
842-meter mark and the 843-meter mark on the rule graduated on the
enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY assert
that an all-way light beacon pulse emitted midway between their ship's
842 & 843-meter marks will hit the two nearby meter marks
simultaneously, according to their native frame's clocks and such. Yet
the guy on the planet cannot make the same claim?? When does an
arbitrary local span become tantamount to an SR scenario. In spite of
Sagnac, there must surely be some carry-over; I mean you're just about
TOUCHING that other frame, comoving.

-Ben

Of course the guy on the planet will agree that the light will hit the two
metre marks simultaneously. That is, if he had one clock at each side of
himself, and he E-synched those clocks, they would show the same when hit
by the light.
However, if the two clocks were showing UTC, they would NOT show the same
when hit by the light.
Clocks on the surface of the Earth showing UTC are NOT synchronous in the
Earth fixed frame. They are synchronous in the non rotating ECI-frame.

Paul, what do you mean by "Earth fixed frame"? Do you mean the
inertial frame which is momentarily comoving with the surface at one
particular point?

No, I mean the rotating frame fixed to the Earth and rotating along
with the Earth. A clock on the ground will be stationary in this frame.

What I meant to say above is that clocks on the Earth showing UTC
simultaneously (according to Einstein's definition) show the same in
the non rotating frame where the centre of the Earth is stationary
(the ECI-frame).
One way of saying this is that if you could imagine a flash of
light emitted from the centre of the (transparent) Earth, all the clocks
should show the same when hit by the light front.

If you imagine two such clock on the equator, say 1km from each
other, they will NOT simultaneously show the same in a local
inertial frame momentarily comoving with the surface.
If you measure the speed of light with those two clocks,
you will measure c+/-v (sign depending on the direction of the light),
where v is the peripheral velocity of the Earth in the ECI-frame.
This is usually called the "Sagnac effect".

The reason why UTC clocks are synched like this, is that it
is impossible to globally E-sync clocks to each other in
a rotating frame. If you could imagine a chain of clocks around
the equator, and tried to E-synch them one by one to the previous
clock all around the Earth, you would find that the last clock would
not be E-synched to the first.

Paul

"Paul B. Andersen" wrote in message
...

"Ben Bean" skrev i melding
...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no
atmosphere.
You stand on the equator and hold your hands up to the air so that they
are
a meter apart. [Relax, this is NOT a study in relative simultaneity like
the
Barn/Pole thing.] As you stand there a huge spacecraft coasts by just
overhead, just beyond your reach. The ship seems motionless to you,
hovering, because it is going eastward at a speed to exactly match the
planet's tangential rotational speed. As you reach up, your outstretched
fingertips are just about touching the 842-meter mark and the 843-meter
mark
on the rule graduated on the enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY assert
that an
all-way light beacon pulse emitted midway between their ship's 842 &
843-meter marks will hit the two nearby meter marks simultaneously,
according to their native frame's clocks and such. Yet the guy on the
planet
cannot make the same claim?? When does an arbitrary local span become
tantamount to an SR scenario. In spite of Sagnac, there must surely be
some
carry-over; I mean you're just about TOUCHING that other frame,
comoving.

-Ben

Of course the guy on the planet will agree that the light will hit the two
metre
marks simultaneously. That is, if he had one clock at each side of
himself,
and he E-synched those clocks, they would show the same when hit
by the light.
However, if the two clocks were showing UTC, they would NOT
show the same when hit by the light.
Clocks on the surface of the Earth showing UTC are NOT synchronous
in the Earth fixed frame. They are synchronous in the non rotating
ECI-frame.

Paul


Great answer! Uh, but, whereas I know what ECI stands for, I am at a loss as
to what UTC stands for. But I think it matters not. You say that Earth's
surface clocks can all be synched to the non-rotating ECI, which suffices. I
don't necessarily buy your dismissal of Sagnac (of course I am
misinterpreting perhaps), but your answer suggests that a light signal takes
the same time to go from NY to LA as the reverse, as long as you use the
non-rotating ECI clocks as your basis. I guess that makes sense alright, but
it's insufficient. The guy reaching up and touching the inertially moving
space ship -- he has a wrist watch on each arm and he claims they are
synchronized. His clocks belong to a frame that IS rotating. I'm just not
sure. Again, what is UTC, Universal Time something?

The central question is, "How does light behave in the frame of the man
standing with his arms outstretched (over his head), and ONLY according to
that man's native clocks & measures"? Can the man say that a light signal
emitted midway between his hands arrives at each hand at precisely the same
time? Probably not. But light would clearly not move relative to a
theoretical aether fixed at the planet's center either. So there must be
some give. Light must take less time to go westward than eastward (on the
spinning planet), which would be in line with the Sagnac findings, but not
so much less time as would be predicted by imagining the light travelling
through some fixed aether frame anchored at the planet's center.

It's confusing alright.

"Ben Bean" skrev i melding ...

"Paul B. Andersen" wrote in message
...

"Ben Bean" skrev i melding
...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no
atmosphere.
You stand on the equator and hold your hands up to the air so that they
are
a meter apart. [Relax, this is NOT a study in relative simultaneity like
the
Barn/Pole thing.] As you stand there a huge spacecraft coasts by just
overhead, just beyond your reach. The ship seems motionless to you,
hovering, because it is going eastward at a speed to exactly match the
planet's tangential rotational speed. As you reach up, your outstretched
fingertips are just about touching the 842-meter mark and the 843-meter
mark
on the rule graduated on the enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY assert
that an
all-way light beacon pulse emitted midway between their ship's 842 &
843-meter marks will hit the two nearby meter marks simultaneously,
according to their native frame's clocks and such. Yet the guy on the
planet
cannot make the same claim?? When does an arbitrary local span become
tantamount to an SR scenario. In spite of Sagnac, there must surely be
some
carry-over; I mean you're just about TOUCHING that other frame,
comoving.

-Ben

Of course the guy on the planet will agree that the light will hit the two
metre
marks simultaneously. That is, if he had one clock at each side of
himself,
and he E-synched those clocks, they would show the same when hit
by the light.
However, if the two clocks were showing UTC, they would NOT
show the same when hit by the light.
Clocks on the surface of the Earth showing UTC are NOT synchronous
in the Earth fixed frame. They are synchronous in the non rotating
ECI-frame.

Paul


Great answer! Uh, but, whereas I know what ECI stands for, I am at a loss as
to what UTC stands for.

UTC means "Coordinated Universal Time", and to say it simple,
it is the same as local mean time.
See also my response to "sal".

But I think it matters not. You say that Earth's
surface clocks can all be synched to the non-rotating ECI, which suffices.

Yes, and I say that this IS how we synchronize clocks on the Earth.

I
don't necessarily buy your dismissal of Sagnac (of course I am
misinterpreting perhaps), but your answer suggests that a light signal takes
the same time to go from NY to LA as the reverse, as long as you use the
non-rotating ECI clocks as your basis.

UTC clocks on the Earth ARE "rotating" along with the Earth.
I said they are synchronised (simultaneously showing the same)
in the ECI-frame, NOT that they are stationary in the ECI-frame.
And if you measure the time light takes to go from NY to LA with
these UTC clocks, you will find that it is different from the time
it takes to go in the reverse direction.
This IS the "Sagnac effect".

I guess that makes sense alright, but
it's insufficient. The guy reaching up and touching the inertially moving
space ship -- he has a wrist watch on each arm and he claims they are
synchronized. His clocks belong to a frame that IS rotating. I'm just not
sure. Again, what is UTC, Universal Time something?

If this guy claims his writs watches to be synchronized, he will
probably mean that they simultaneously show the same in
his instantly inertial rest frame. (The inertial frame in which he
instantly is at rest.)
And his clocks will stay in synch.
If he measure the speed of light with these clocks, he will find
that it will use the same time in both directions.

But if he compare them to two adjacent UTC clocks, he will
see that they are different, because his watches are NOT
synchronous in the ECI-frame.

The central question is, "How does light behave in the frame of the man
standing with his arms outstretched (over his head), and ONLY according to
that man's native clocks & measures"? Can the man say that a light signal
emitted midway between his hands arrives at each hand at precisely the same
time? Probably not.

Yes, he can.
He will use his local frame.

But light would clearly not move relative to a
theoretical aether fixed at the planet's center either. So there must be
some give. Light must take less time to go westward than eastward (on the
spinning planet), which would be in line with the Sagnac findings, but not
so much less time as would be predicted by imagining the light travelling
through some fixed aether frame anchored at the planet's center.

It's confusing alright.

Yes, it IS confusing. :-)
But remember this:
According to SR, the speed of light is c _in an inertial frame_.
As long as you remember this, it is quite obvious that if you
emit light in both directions from some point on the equator,
and guide the light (mirrors) around the Earth, the two light beams
will meat each other at the same point _in the ECI frame_
as they were emitted from. But then the point on the Earth
has moved, so one of the light beams has already passed
this point, while the other one has not yet reached it.
So _because_ the speed of light is c in the ECI-frame,
the two beams will NOT simultaneously reach the point
on the Earth from where they were emitted.
A clock at that point will thus measure the light to use
different times around the Earth in opposite directions.

Paul

"Paul B. Andersen" wrote in message
...

"Ben Bean" skrev i melding
...

"Paul B. Andersen" wrote in message
...

"Ben Bean" skrev i melding
...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no
atmosphere.
You stand on the equator and hold your hands up to the air so that
they
are
a meter apart. [Relax, this is NOT a study in relative simultaneity
like
the
Barn/Pole thing.] As you stand there a huge spacecraft coasts by
just
overhead, just beyond your reach. The ship seems motionless to you,
hovering, because it is going eastward at a speed to exactly match
the
planet's tangential rotational speed. As you reach up, your
outstretched
fingertips are just about touching the 842-meter mark and the
843-meter
mark
on the rule graduated on the enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY assert
that an
all-way light beacon pulse emitted midway between their ship's 842 &
843-meter marks will hit the two nearby meter marks simultaneously,
according to their native frame's clocks and such. Yet the guy on
the
planet
cannot make the same claim?? When does an arbitrary local span
become
tantamount to an SR scenario. In spite of Sagnac, there must surely
be
some
carry-over; I mean you're just about TOUCHING that other frame,
comoving.

-Ben

Of course the guy on the planet will agree that the light will hit the
two
metre
marks simultaneously. That is, if he had one clock at each side of
himself,
and he E-synched those clocks, they would show the same when hit
by the light.
However, if the two clocks were showing UTC, they would NOT
show the same when hit by the light.
Clocks on the surface of the Earth showing UTC are NOT synchronous
in the Earth fixed frame. They are synchronous in the non rotating
ECI-frame.

Paul


Great answer! Uh, but, whereas I know what ECI stands for, I am at a
loss as
to what UTC stands for.

UTC means "Coordinated Universal Time", and to say it simple,
it is the same as local mean time.
See also my response to "sal".

But I think it matters not. You say that Earth's
surface clocks can all be synched to the non-rotating ECI, which
suffices.

Yes, and I say that this IS how we synchronize clocks on the Earth.

I
don't necessarily buy your dismissal of Sagnac (of course I am
misinterpreting perhaps), but your answer suggests that a light signal
takes
the same time to go from NY to LA as the reverse, as long as you use the
non-rotating ECI clocks as your basis.

UTC clocks on the Earth ARE "rotating" along with the Earth.
I said they are synchronised (simultaneously showing the same)
in the ECI-frame, NOT that they are stationary in the ECI-frame.
And if you measure the time light takes to go from NY to LA with
these UTC clocks, you will find that it is different from the time
it takes to go in the reverse direction.
This IS the "Sagnac effect".

I guess that makes sense alright, but
it's insufficient. The guy reaching up and touching the inertially
moving
space ship -- he has a wrist watch on each arm and he claims they are
synchronized. His clocks belong to a frame that IS rotating. I'm just
not
sure. Again, what is UTC, Universal Time something?

If this guy claims his writs watches to be synchronized, he will
probably mean that they simultaneously show the same in
his instantly inertial rest frame. (The inertial frame in which he
instantly is at rest.)
And his clocks will stay in synch.
If he measure the speed of light with these clocks, he will find
that it will use the same time in both directions.

But if he compare them to two adjacent UTC clocks, he will
see that they are different, because his watches are NOT
synchronous in the ECI-frame.

The central question is, "How does light behave in the frame of the man
standing with his arms outstretched (over his head), and ONLY according
to
that man's native clocks & measures"? Can the man say that a light
signal
emitted midway between his hands arrives at each hand at precisely the
same
time? Probably not.

Yes, he can.
He will use his local frame.

But light would clearly not move relative to a
theoretical aether fixed at the planet's center either. So there must be
some give. Light must take less time to go westward than eastward (on
the
spinning planet), which would be in line with the Sagnac findings, but
not
so much less time as would be predicted by imagining the light
travelling
through some fixed aether frame anchored at the planet's center.

It's confusing alright.

Yes, it IS confusing. :-)
But remember this:
According to SR, the speed of light is c _in an inertial frame_.
As long as you remember this, it is quite obvious that if you
emit light in both directions from some point on the equator,
and guide the light (mirrors) around the Earth, the two light beams
will meat each other at the same point _in the ECI frame_
as they were emitted from. But then the point on the Earth
has moved, so one of the light beams has already passed
this point, while the other one has not yet reached it.
So _because_ the speed of light is c in the ECI-frame,
the two beams will NOT simultaneously reach the point
on the Earth from where they were emitted.
A clock at that point will thus measure the light to use
different times around the Earth in opposite directions.

Paul




**********************************
I REALLY REALLY GOT TO HAND IT TO YOU, PAUL B. ANDERSON...
That's some mighty fine STRAIGHT SHOOTING and you sure as dang heck got me
to understand PERFECTLY!

The guy can invent an inertial frame in which his two wris****ches are
synched (but NOT E-synched, which is WRT the non-rotating ECI frame), so
long as the times and distances are minute enough. I garner this from your

..Can the man say that a light signal emitted midway between
his hands arrives at each hand at precisely the same
time? Probably not.
Yes, he can.
He will use his local frame.


It must get messy if you try to concoct an inertial frame (too large) to
encompass eg. the span NY to LA for the duration it takes light to transit.

Yeah but nevermind -- I get it -- MANY MANY THANKS!

-BB

"Ben Bean" wrote in message
...

"Paul B. Andersen" wrote in message
...

"Ben Bean" skrev i melding
...

"Paul B. Andersen" wrote in message
...

"Ben Bean" skrev i melding
...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no
atmosphere.
You stand on the equator and hold your hands up to the air so that
they
are
a meter apart. [Relax, this is NOT a study in relative
simultaneity
like
the
Barn/Pole thing.] As you stand there a huge spacecraft coasts by
just
overhead, just beyond your reach. The ship seems motionless to
you,
hovering, because it is going eastward at a speed to exactly match
the
planet's tangential rotational speed. As you reach up, your
outstretched
fingertips are just about touching the 842-meter mark and the
843-meter
mark
on the rule graduated on the enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY
assert
that an
all-way light beacon pulse emitted midway between their ship's 842
&
843-meter marks will hit the two nearby meter marks
simultaneously,
according to their native frame's clocks and such. Yet the guy on
the
planet
cannot make the same claim?? When does an arbitrary local span
become
tantamount to an SR scenario. In spite of Sagnac, there must
surely
be
some
carry-over; I mean you're just about TOUCHING that other frame,
comoving.

-Ben

Of course the guy on the planet will agree that the light will hit
the
two
metre
marks simultaneously. That is, if he had one clock at each side of
himself,
and he E-synched those clocks, they would show the same when hit
by the light.
However, if the two clocks were showing UTC, they would NOT
show the same when hit by the light.
Clocks on the surface of the Earth showing UTC are NOT synchronous
in the Earth fixed frame. They are synchronous in the non rotating
ECI-frame.

Paul


Great answer! Uh, but, whereas I know what ECI stands for, I am at a
loss as
to what UTC stands for.

UTC means "Coordinated Universal Time", and to say it simple,
it is the same as local mean time.
See also my response to "sal".

But I think it matters not. You say that Earth's
surface clocks can all be synched to the non-rotating ECI, which
suffices.

Yes, and I say that this IS how we synchronize clocks on the Earth.

I
don't necessarily buy your dismissal of Sagnac (of course I am
misinterpreting perhaps), but your answer suggests that a light signal
takes
the same time to go from NY to LA as the reverse, as long as you use
the
non-rotating ECI clocks as your basis.

UTC clocks on the Earth ARE "rotating" along with the Earth.
I said they are synchronised (simultaneously showing the same)
in the ECI-frame, NOT that they are stationary in the ECI-frame.
And if you measure the time light takes to go from NY to LA with
these UTC clocks, you will find that it is different from the time
it takes to go in the reverse direction.
This IS the "Sagnac effect".

I guess that makes sense alright, but
it's insufficient. The guy reaching up and touching the inertially
moving
space ship -- he has a wrist watch on each arm and he claims they are
synchronized. His clocks belong to a frame that IS rotating. I'm just
not
sure. Again, what is UTC, Universal Time something?

If this guy claims his writs watches to be synchronized, he will
probably mean that they simultaneously show the same in
his instantly inertial rest frame. (The inertial frame in which he
instantly is at rest.)
And his clocks will stay in synch.
If he measure the speed of light with these clocks, he will find
that it will use the same time in both directions.

But if he compare them to two adjacent UTC clocks, he will
see that they are different, because his watches are NOT
synchronous in the ECI-frame.

The central question is, "How does light behave in the frame of the
man
standing with his arms outstretched (over his head), and ONLY
according
to
that man's native clocks & measures"? Can the man say that a light
signal
emitted midway between his hands arrives at each hand at precisely the
same
time? Probably not.

Yes, he can.
He will use his local frame.

But light would clearly not move relative to a
theoretical aether fixed at the planet's center either. So there must
be
some give. Light must take less time to go westward than eastward (on
the
spinning planet), which would be in line with the Sagnac findings, but
not
so much less time as would be predicted by imagining the light
travelling
through some fixed aether frame anchored at the planet's center.

It's confusing alright.

Yes, it IS confusing. :-)
But remember this:
According to SR, the speed of light is c _in an inertial frame_.
As long as you remember this, it is quite obvious that if you
emit light in both directions from some point on the equator,
and guide the light (mirrors) around the Earth, the two light beams
will meat each other at the same point _in the ECI frame_
as they were emitted from. But then the point on the Earth
has moved, so one of the light beams has already passed
this point, while the other one has not yet reached it.
So _because_ the speed of light is c in the ECI-frame,
the two beams will NOT simultaneously reach the point
on the Earth from where they were emitted.
A clock at that point will thus measure the light to use
different times around the Earth in opposite directions.

Paul




**********************************
I REALLY REALLY GOT TO HAND IT TO YOU, PAUL B. ANDERSON...
That's some mighty fine STRAIGHT SHOOTING and you sure as dang heck got me
to understand PERFECTLY!

The guy can invent an inertial frame in which his two wris****ches are
synched (but NOT E-synched, which is WRT the non-rotating ECI frame), so
long as the times and distances are minute enough. I garner this from your

..Can the man say that a light signal emitted midway between
his hands arrives at each hand at precisely the same
time? Probably not.
Yes, he can.
He will use his local frame.


It must get messy if you try to concoct an inertial frame (too large) to
encompass eg. the span NY to LA for the duration it takes light to
transit.

Yeah but nevermind -- I get it -- MANY MANY THANKS!

-BB



PBA:
I'm here to fix an apparent misunderstanding I had of your terminology. What
E-synched (capital E) implies I'm not 100% certain, but it is NOT
specifically associated with UTC. The standing man can synchronize the
watches on his left and right hands WRT a concocted inertial frame that
closely approximates the actual arc he is moving on, and thus conclude that
any light/radio pulse emitted halfway between his hands arrives at those
hands simultaneously. This works for the suitably small scale, but not the
large?? ie. NY to LA.

HONEST! I understood every word of your explanation (Many thanks) about how
Sagnac truth messes up any hope of surface-resident synchronized clocks,
except by resorting to UTC (which is ECI-based); but under that UTC scheme
you cannot make the claim which the standing man so yearns to make, ie. that
light will expand outward uniformly east/west from a source point, per his
vantage.

Further jabber would be welcome, too; if the above isn't right on.

-Ben

"Ben Bean" skrev i melding ...

"Ben Bean" wrote in message
...

"Paul B. Andersen" wrote in message
...

"Ben Bean" skrev i melding
...

"Paul B. Andersen" wrote in message
...

"Ben Bean" skrev i melding
...
I am eager to hear wisdoms in answer to the quandary below stated.

SCENARIO: You stand on a planet just like Earth, but there's no
atmosphere.
You stand on the equator and hold your hands up to the air so that
they
are
a meter apart. [Relax, this is NOT a study in relative
simultaneity
like
the
Barn/Pole thing.] As you stand there a huge spacecraft coasts by
just
overhead, just beyond your reach. The ship seems motionless to
you,
hovering, because it is going eastward at a speed to exactly match
the
planet's tangential rotational speed. As you reach up, your
outstretched
fingertips are just about touching the 842-meter mark and the
843-meter
mark
on the rule graduated on the enormous ship's straight exterior.

Here's the quandary: the spaceship occupants can EMPHATICALLY
assert
that an
all-way light beacon pulse emitted midway between their ship's 842
&
843-meter marks will hit the two nearby meter marks
simultaneously,
according to their native frame's clocks and such. Yet the guy on
the
planet
cannot make the same claim?? When does an arbitrary local span
become
tantamount to an SR scenario. In spite of Sagnac, there must
surely
be
some
carry-over; I mean you're just about TOUCHING that other frame,
comoving.

-Ben

Of course the guy on the planet will agree that the light will hit
the
two
metre
marks simultaneously. That is, if he had one clock at each side of
himself,
and he E-synched those clocks, they would show the same when hit
by the light.
However, if the two clocks were showing UTC, they would NOT
show the same when hit by the light.
Clocks on the surface of the Earth showing UTC are NOT synchronous
in the Earth fixed frame. They are synchronous in the non rotating
ECI-frame.

Paul


Great answer! Uh, but, whereas I know what ECI stands for, I am at a
loss as
to what UTC stands for.

UTC means "Coordinated Universal Time", and to say it simple,
it is the same as local mean time.
See also my response to "sal".

But I think it matters not. You say that Earth's
surface clocks can all be synched to the non-rotating ECI, which
suffices.

Yes, and I say that this IS how we synchronize clocks on the Earth.

I
don't necessarily buy your dismissal of Sagnac (of course I am
misinterpreting perhaps), but your answer suggests that a light signal
takes
the same time to go from NY to LA as the reverse, as long as you use
the
non-rotating ECI clocks as your basis.

UTC clocks on the Earth ARE "rotating" along with the Earth.
I said they are synchronised (simultaneously showing the same)
in the ECI-frame, NOT that they are stationary in the ECI-frame.
And if you measure the time light takes to go from NY to LA with
these UTC clocks, you will find that it is different from the time
it takes to go in the reverse direction.
This IS the "Sagnac effect".

I guess that makes sense alright, but
it's insufficient. The guy reaching up and touching the inertially
moving
space ship -- he has a wrist watch on each arm and he claims they are
synchronized. His clocks belong to a frame that IS rotating. I'm just
not
sure. Again, what is UTC, Universal Time something?

If this guy claims his writs watches to be synchronized, he will
probably mean that they simultaneously show the same in
his instantly inertial rest frame. (The inertial frame in which he
instantly is at rest.)
And his clocks will stay in synch.
If he measure the speed of light with these clocks, he will find
that it will use the same time in both directions.

But if he compare them to two adjacent UTC clocks, he will
see that they are different, because his watches are NOT
synchronous in the ECI-frame.

The central question is, "How does light behave in the frame of the
man
standing with his arms outstretched (over his head), and ONLY
according
to
that man's native clocks & measures"? Can the man say that a light
signal
emitted midway between his hands arrives at each hand at precisely the
same
time? Probably not.

Yes, he can.
He will use his local frame.

But light would clearly not move relative to a
theoretical aether fixed at the planet's center either. So there must
be
some give. Light must take less time to go westward than eastward (on
the
spinning planet), which would be in line with the Sagnac findings, but
not
so much less time as would be predicted by imagining the light
travelling
through some fixed aether frame anchored at the planet's center.

It's confusing alright.

Yes, it IS confusing. :-)
But remember this:
According to SR, the speed of light is c _in an inertial frame_.
As long as you remember this, it is quite obvious that if you
emit light in both directions from some point on the equator,
and guide the light (mirrors) around the Earth, the two light beams
will meat each other at the same point _in the ECI frame_
as they were emitted from. But then the point on the Earth
has moved, so one of the light beams has already passed
this point, while the other one has not yet reached it.
So _because_ the speed of light is c in the ECI-frame,
the two beams will NOT simultaneously reach the point
on the Earth from where they were emitted.
A clock at that point will thus measure the light to use
different times around the Earth in opposite directions.

Paul




**********************************
I REALLY REALLY GOT TO HAND IT TO YOU, PAUL B. ANDERSON...
That's some mighty fine STRAIGHT SHOOTING and you sure as dang heck got me
to understand PERFECTLY!

The guy can invent an inertial frame in which his two wris****ches are
synched (but NOT E-synched, which is WRT the non-rotating ECI frame), so
long as the times and distances are minute enough. I garner this from your

..Can the man say that a light signal emitted midway between
his hands arrives at each hand at precisely the same
time? Probably not.
Yes, he can.
He will use his local frame.


It must get messy if you try to concoct an inertial frame (too large) to
encompass eg. the span NY to LA for the duration it takes light to
transit.

Yeah but nevermind -- I get it -- MANY MANY THANKS!

-BB



PBA:
I'm here to fix an apparent misunderstanding I had of your terminology. What
E-synched (capital E) implies I'm not 100% certain, but it is NOT
specifically associated with UTC. The standing man can synchronize the
watches on his left and right hands WRT a concocted inertial frame that
closely approximates the actual arc he is moving on, and thus conclude that
any light/radio pulse emitted halfway between his hands arrives at those
hands simultaneously. This works for the suitably small scale, but not the
large?? ie. NY to LA.

More or less, yes.
Your shouting tells me that elaboration would be futile.

HONEST! I understood every word of your explanation (Many thanks) about how
Sagnac truth messes up any hope of surface-resident synchronized clocks,
except by resorting to UTC (which is ECI-based); but under that UTC scheme
you cannot make the claim which the standing man so yearns to make, ie. that
light will expand outward uniformly east/west from a source point, per his
vantage.

Let me say it like this:
I can claim that the light will expand uniformy from
the point it is emitted _in the inertial frame in which he
is instantly at rest when the light is emitted_.
He is not stationary in said frame, but during the 2 ns the light
takes to reach his hand, he will have moved 10^-33 meters
from the point of emission.
But 12 hours later, the light he emitted westwards will
be 12 light hours east of him.

Paul