Re: A friendly request to Ken Seto from Uncle Ben

On Nov 26, 10:49 am, Uncle Ben <b...@greenba.com> wrote:

Wrong again: points in space-time are indicated by (x, t) and (x', t').
Thus the t' are NOT "transit times from locations" (= time intervals) but
moments in time (in this case: the point in time of each strike).

Success!
Harald

I thought t'1 and t'2 were the transit times from +x and -x locations.
I didn't know that they represent the transit times from the locations
of the ends of the train after the lightning happened simultaneously.
Your problem is that you can't comprehend that the locations of the
ends of the train got nothing to do with how light propagates from the
points of strikes at +x and -x locations.

Ken Seto

I thought you had already shown the equations for t'1 and t'2 and had
shown that they differed in proportion to (x2-x1).  Now that you know
that x1 and x2 are different, that shows that the starting times of
the light flashes from the back and from the front are now not
simulotaneous.

You proved it yourself!

Uncle Ben

There is no t'1 and t'2. There is t'. Why? Because once the flashes
happened at the ends of the train the location of the ends become
irrelevant. The only important thing is the transit time of the light
fronts from the original points of the flashes (+x and -x) to arrive
at M'.

Ken Seto

And with regard to the times, if t'1 >0 and t'2 <0, it means that t'2
occurred before t'=0 and t'1 occurred after t'=0.  These are
coordinates, not transit times.

Uncle Ben

                                 M
<- -x    -------x1----------------0++++++++++++++++x2+++++++++    +x -

                                 M'
               tttttttttttttttttttttttttttttttttttt
                          (train)

Can you see that x1 = -x2?

Uncle Ben

On Nov 25, 5:15 pm, "Dirk Van de moortel"
<dirkvandemoor...@nospAm.hotmail.com> wrote:

Yes I did forgot the gamma factor.

Right....This means that the transit time for the arrival of the light
fronts from the strikes is the same in both the -x direction and the
+x direction and thus the light fronts arrival at M' simultaneously.

Why? The same transit time for both directions.

This is a bogus assumption....x1 always equal to x2 (because the speed
of light is isotropic). Once the flashes occurred simultaneously the
motion of the ends of the train has no effect on how the light fronts
will propagate in the M and M' frames. BTW that's why the speed of
light is isotropic and independent of the motion of the source.

Ken Seto

kenseto <kenseto@erinet.com> wrote in message
 b2924e9e-19bb-4351-a1a3-fa21040a2283@k8g2000yqn.googlegroups.com

You forgot the gamma factors. Make that
       t'1 = - gamma v x1 / c^2
       t'2 = - gamma v x2 / c^2

Remember that x1 and x2 and coordinates, not distances.
So make that
       x1 = -x2
and you get
       t'1 = - gamma v x1 / c^2
       t'2 = - gamma v x2 / c^2
and thus
       t'1 = - gamma v x1 / c^2
       t'2 = + gamma v x1 / c^2
meaning that
       t'1 = - t'2
meaning that 1 and 2 will *not* arrive at M simultaneously, but,
assuming that x1 > 0 (on the right, so to speak) and thus x2 < 0
(on the left), then 1 arrives first (before t' = 0), and 2 arrives later
(after t' = 0).

A transformation transforms coordinates. Not distances.

Dirk Vdm

Event 1  t'1 = gamma(t1 - vx1/c*c)    Lorentz Transformation, track ->
train
Event 2  t'2 = gamma(t2 - vx2/c*c)    Lorentz Transformation, track -

When M and M' coincide with each other t1 = t2 =0
Therefore:
Event 1 arrive at M':
t'1 = -vx1/c^2
Event 2 arrive at M':
t'2 = -vx2/c^2

Since x1 = x2  therefore the light fronts from events 1 and 2 will
arrive at M simultaneously.

Ken Seto

- Hide quoted text -

What you say may or may not be true, but I don't see any Lorentz
Transformation yet.  What is the Lorentz Transformation?

When M and M' are coincide with each other:
The transit time for the light fronts from +x and -x arrive at M
simultaneously is L/c from both directions.
The light path length for the light fronts from +x and -x to arrive at
M' is gamma*L
Therefore the transit time for the light fronts from +x and -x to
arrive at M' simultaneously is gamma*L/c.

Ken Seto

Dear Ken,

For weeks now you have been telling me, as we discuss elementary
problems in Specialk Relativiy, that I have been executing the Lorentz
Transformation incorrectly.

Maybe you are right, Ken.  Educate me a little.  Tell me, what is the
Lorentz Transformation?  In particular,

1. What is it for?  It is a tool, I know, but what is it used for?

2. Show me a very simple example of how it is used for any problem you
like.

If it turns out that I have bveen misusing the Lorentz Transformation
for all the years I have taught relativity, I will be very forever
grateful to you for correcting me.

Uncle Ben