"Mitchell Jones" <mjones@21cenlogic.com> wrote in message
news:mjones-391371.06495101012007@news.thundernews.com...

In article <AeydnWrVFLJmdAXYnZ2dnUVZ8qijnZ2d@bt.com>,
"Martin Hogbin" <goatREMOVETHIS123@hogbin.org> wrote:

"Mitchell Jones" <mjones@21cenlogic.com> wrote in message
news:mjones-88E441.03262501012007@news.thundernews.com...

Consider an example of a sort oft repeated by relativists,

Who or what are 'relativists'?

***{Proponents of Einstein's "theory of relativity," of course. --MJ}***

These are called physicists.

Einstein's relativity is the only theory
of space and time used and taught the world over.

wherein a
train is moving along an embankment. An observer is standing on the
train, moving past a second observer standing on the ground, and two
events occur. Each event acts as a source of constant-velocity...

What do mean by 'constant-velocity' here?

***{I'm setting up an example, for purposes of discussion. Relativists
talk about these sorts of examples all the time, using various emissions
(light, sound, etc.) that are presumed to be constant velocity within
the context of the discussion. I simply chose to state that explicitly,
rather that count on it being assumed. --MJ}***

I asked what you meant, not why you said it. What exactly do
you mean by 'constant-velocity' here?

...wavelike
emanations (light, sound, seismic waves, or whatever)

Do you consider all of these to be 'constant-velocity'?

***{They can be. All I'm trying to do is limit my example to situations
in which they are, for the sake of simplicity. --MJ}***

Until you make clear what you mean by 'constant velocity' I
cannot comment.

that pass through space

Seismic waves pass through space?

***{Space is the expanse in which all entities are located. Seismic
waves pass through solid bodies such as the Earth, which are located in
space. Hence the seismic waves pass through space. All motion is motion
through space, in the sense in which I am using the term. Moreover, it
is not an uncommon usage: people speak of the "space" in their
refrigerators, for example, even though their refrigerators contain air.
In such cases, the air is viewed as filling the space, which in turn is
viewed as an expanse in which entities, such as air molecules, are
located. Space doesn't have to be empty, to be space. Hence "vacuum" and
"space" are not equivalent terms, though some usages equate them.
--MJ}***

Seismic waves have a medium, the earth, light does not,
it travels through space.

from their sources to each of the two observers. One event, call
it A, is directly behind the train, and the other, call it B, is
directly ahead. The question asked by relativists is whether it is
possible to objectively determine if A and B are simultaneous. That is,
is there a method for determining simultaneity which ensures that all
observers who reason correctly will come to the same conclusion?

That is not the question asked by physicists.

***{There are hundreds if not thousands of examples proving your
assertion to be false. In particular, it is the question asked by
physicists who comprehend what must be demonstrated, in order to
establish the relativism of simultaneity. For if an objective method for
determining simultaneity exists, then it makes no sense to claim, as
relativists do, that the answer depends on the frame of reference one
chooses.

'Objective measurement of simultaneity' does not really have any
meaning in this context. What do you mean by 'objective'?

Here is a quote from a fairly typical statement of this issue:

"Supposing that as a result of ingenious considerations an able
meteorologist were to discover that the lightning must always strike the
places A and B simultaneously, then we should be faced with the task of
testing whether or not this theoretical result is in accordance with the
reality. We encounter the same difficulty with all physical statements
in which the conception ³simultaneous² plays a part. The concept does
not exist for the physicist until he has the possibility of discovering
whether or not it is fulfilled in an actual case. We thus require a
definition of simultaneity such that this definition supplies us with
the method by means of which, in the present case, he can decide by
experiment whether or not both the lightning strokes occurred
simultaneously. As long as this requirement is not satisfied, I allow
myself to be deceived as a physicist (and of course the same applies if
I am not a physicist), when I imagine that I am able to attach a meaning
to the statement of simultaneity." [Source:
http://www.bartleby.com/173/8.html]

Subsequent to the above paragraph, the author argues that there is no
method by means of which it can be decided by experiment whether two
events occurred simultaneously, and so he concludes that:

"Events which are simultaneous with reference to the embankment are not
simultaneous with respect to the train, and vice versa (relativity of
simultaneity). Every reference-body (co-ordinate system) has its own
particular time; unless we are told the reference-body to which the
statement of time refers, there is no meaning in a statement of the time
of an event."

"Now before the advent of the theory of relativity it had always tacitly
been assumed in physics that the statement of time had an absolute
significance, i.e. that it is independent of the state of motion of the
body of reference. But we have just seen that this assumption is
incompatible with the most natural definition of simultaneity..." And on
and on he goes.

His conclusion: the notion that simultaneity is independent of the state
of motion of the body of reference must be discarded. Simultaneity, in
his view, is relative to the state of motion of the reference body,
hence his use of the term "the relativity of simultaneity."

My view, on the other hand, is that what he calls "the most natural
definition of simultaneity" is, in fact, a straw man set up for the
explicit purpose of knocking it down. In fact, the method I described is
the most natural method, and, contrary to the assertions of relativists,
that method leads to the same answer, irrespective of the frame of
reference of the person applying it.

Einstein makes clear that his views on simultaneity are based
on his two, well-knwn, postulates.

You can propose yout own postulates but you must make
clear what they are.

The
relativists say the answer is no, that simultaneity is relative; and I
say the answer is yes, when the determination is made using the method
explained below.

Let the speed of travel of the emissions by which events A and B are
detected be represented by V. Let the distances from the locations of
the events to an observer's location(s) at the times of detection be
represented by Da and Db, respectively, and let the times of occurrence
be represented by Ta and Tb, respectively. Result: if an observer
detects an emanation from A at a time T1, he knows that A occurred at
Ta
= T1 - Da/V, and if he detects an emanation from B at a time T2, he
knows that B occurred at Tb = T2 - Db/V. Hence the events are
simultaneous if Ta = Tb, and otherwise they are not simultaneous.

None of the above makes any sense until you explain what you
mean by 'constant-velocity wavelike emanations'.

***{As noted above, the statement was made merely to simplify the
example. If variable velocity particulate emanations (e.g., bullets) had
been included, I would have had to refer to average velocities, and,
since the average velocities of bullets that travel greater distances
are less, other things equal, than those of bullets that travel lesser
distances, I would have had to reference two values for V, e.g., V1 and
V2. But that would have been pointless. The goal of the example was to
elucidate the principle I had in mind--to wit: that when one focuses on
the distances between the points of emission and reception of the
emanations, rather than on the states of motion of the observers, all
the difficulties in measuring simultaneity simply disappear. Thus I
opted for the simplest presentation that would convey the principle.
That's all there is to it. --MJ}***

The method of determination of simultaneity, then, is as follows:

(1) Each observer jots down the times T1 and T2 when he receives the
emanations.

(2) Each observer determines the speed, V, of the emanations, by
consulting the appropriate reference materials, doing any needed
calculations, etc.

On what basis does the observer do 'calculations etc.' ?

***{If, for example, the emanations are sound waves, then since the
speed of sound depends on the absolute temperature, one would have to do
a calculation to determine it. --MJ}***

You really need to try to understand whart relativity is all about
before you try to criticise it.

***{And you really need to learn the difference between substantive
argument, empty assertion, and ad hominem statements, if you intend to
participate in reasoned discussions. --MJ}***

I am waiting for some substantive argument from you.

(3) Each observer measures the distances, Da and Db, between the
emissions locations and the reception locations. In the case of the
observer standing on the ground, there will be only one reception
location, whereas the moving observer on the train will be at one
location when he receives the emanations from A, and at another when he
receives the those from B. (Note: The moving observer could just as
well
be two fixed observers, one observing A from location L1, the other
observing B from location L2, and, later, getting together to compare
notes. The two cases are equivalent because it is not the observer's
state of motion, but his location when he makes the observations, that
is of importance.)

(4) Each observer calculates the values of Ta = T1 - Da/V and Tb = T2 -
Db/V, and sees if they are the same. If they are the same for one
observer, they will be the same for all observers.

The key point here is that the measurement of simultaneity requires
that
the observer determine not merely the time at which each emanation is
received, but also the distance between the location of the source when
the emissions were sent out, and his own location at the time when the
emissions were received. If that is done, simple mathematics will
suffice to decide whether the two events are simultaneous or not, and,
most importantly, such decisions about simultaneity will be the same
for
all observers.

It is simple pick an arbtrary basis for simultaneity that all observers
could agree on, but what does this achieve?

***{It's not an arbitrary basis. To say that two events are simultaneous
is to say that they occurred at the same time. Unfortunately, our
knowledge that events occurred comes to us via signals that propagate
through space at finite velocities. Result: we must determine the
velocities of the signals, the distances across which they propagated,
and their times of arrival, and use that information to calculate when
the events occurred.

Agreed, but we must also decide on what speed our siganls
propagate at in all frames. Einstein makes this clear, you do not.

If the calculated times of the events are equal,
then the events were simultaneous; if not, not. There isn't anything
arbitrary about such a procedure.

That is correct, once you have come to some agreement on the
way signals propagate. You have not made that clear you use a
completely undefined term 'constant-velocity wavelike emanations'.

Martin Hogbin