In article ,
Mark McIntyre wrote:
[...]

Well, let's have one more try, this time with the spot-of-light
version. Consider a light source and a screen 2 light seconds away (a
bit further than the distance from the earth to the moon), the screen
being 2 light seconds wide. The screen is curved so all points on it
ar two light seconds away. The source and screen are at rest relative
to each other and all measurements are performed in that frame. Where
does the following sequence go wrong? You may not have time to teach
me relativity, but you can surely tell me which is the first false or
impossible statement:

Experiment 1:

1 I turn on the light pointing at one end of the screen at time t=0.
At time t=2, the light reaches the screen.

2 At time t=4, I will see the reflected light illuminating a spot
at that end of the screen.

Experiment 2:

1 I turn on the light pointing at the other end of the screen at time t=0.
At time t=2, the light reaches that end of the screen.

2 At time t=4, I will see the reflected light illuminating a spot
at that end of the screen.

Experiment 3:

1 I point the light at one end, and turn it on at time t=0.
At time t=2, the light reaches that end of the screen.

2 At time t=0 I start turning the light to point at the
other end, finishing the turn at t=1. This is just a small
movement of my light source at low speed.
Light starts travelling to the far end at time t=1.

3 At time t=3, the light transmitted at t=1 reaches the other
end of the screen (the speed of light is not affected by
the motion of the source).

4 At times between t=2 and t=3, the light will have arrived at
intermediate positions on the screen.

5 The illuminated spot on the screen will have moved 2 light seconds
in one second.

6 At time t=4 I will see the illuminated spot at the first end.

7 At time t=5 I will see the illuminated spot at the other end.

8 Between times t=4 and t=5 I will see the spot moving across a
screen 2 light seconds wide in 1 second.

-- Richard