Compared to What? - Part III
Desynchronized Motion

"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science. He to whom this emotion is a stranger, who can no longer pause to wonder and stand rapt in awe, is as good as dead: his eyes are closed."
-- Albert Einstein --

The Universe is strange indeed, and full of mystery. At least mysterious when you look beyond your normal reality of events occurring with familiar speeds, sizes, distances, etc. We grow so accustomed to viewing events from our local frame of reference that we sincerely believe that this is the way the whole universe behaves. But nothing could be farther from the truth. Turns out there are no absolutes. How we see things is only our local reality and others may see the same events differently with each one have a totally real and valid and different viewpoint. You may want to review topics such as 'frames of reference' in Compared to What? and perhaps the last piece Compared to What? - Part II before looking at Desynchronized Motion.

Let's go back to our small fleet of space ships all in a row in the middle of space somewhere. These ships are all traveling through space at a constant velocity relative to your frame of reference. You see them moving along all at the same speed with a constant equal distance between them. In their frame of reference there is also no movement between them and they remain at a fixed distance to each other. But note there are two frames of reference. You the oberver from a distance, and the guys in the ship who see no motion among themselves.

Now let's suppose the captain, in the middle ship, gives the order for the fleet to accelerate. From your viewpoint, the rear ship will receive the order first.



The filmstrip above illustrates the point starting with frame 1 on the bottom. The signal to accelerate is represented by the expanding circle. Now, since the rear ship receives the signal first, he starts to accelerate first, and actually starts closing the gap between ships. The lead ship hasn't received a signal yet so is still going at the same original speed. So the overall effect is that from our viewpoint, in our frame of reference, the ships seem to bunch up (look close at the spaces between the ships in the film strip). Yet from the frame of reference of the fleet, since the speed of light is the same when they are traveling a constant velocity, whether going forward or backward, they see the all the ships accelerating at the same time, and don't see them as bunching up. Thus the desynchronization of the two observers motion.



If an order was given deaccelerate then the reverse would happen. From our viewpoint the ships would seem to spread apart, whereas the fleet would see no such motion. This bunching together and and spreading apart (see Figure 3-6) is a phenomenon of special relativity and a part of our world.

As a matter of fact, when you have one frame of reference in motion, at a constant velocity, in relation to another virtually nothing is measured the same. Lengths are different, masses are different, time is different, yet, all viewpoints are correct. There are no absolute correct answers. Not intuitive at all, is it. Oh well, its all relative.

Note: The illustrations above come from the book Relativity Visualized by Lewis Carroll Epstein. This is a marvelous book which is full of diagrams and illustrations to present the data in its most intuitive form, as much as is possible with a rather non-intuitive topic. Epstein has a total grasp of the subject and leads one on a journey through all the nooks and crannies of Relativity in a visual, non-mathematical way.