This simulation aims at showing in a straightforward way what the Einstein's Theory of Relativity is all about. To begin with, the physicist declared that fundamental postulate:
“The laws of physics are the same in every inertial frame of reference, regardless of position or velocity”
This is further explained with another postulate that says that light always moves through empty space with the same constant speed. If source of light is already moving at great speed, particles of light that emanate from it will still move at the speed of light.
More precisely, particles of light or photons move at the immutable speed of 299 792 458 meters per second ( 1 ). That translates to the equivalent speed of 1 079 252 849 kilometers per hour, as shown in the following illustration:
Photons that come from the car's headlights are moving to the right at the unchanging speed of 1 079 252 849 km/hr and not at the cumulative speed of the car and of the photons.
On the basis of this information, the simulation undertaken on the underlying page attempts to demonstrate that a clock moving at a significant fraction of light speed will see its time slowed, i.e. the tick-tock of this special clock will occur less frequently as the speed of clock and the one of light are closer.
As illustrated on the primary web page, such clock is made of two mirrors facing each other. You provide the distance between the mirrors or you select one of the proposed lengths in a drop-down list. Bouncing back and forth between them is a small photon that, intrinsically, travels at light speed.
As light speed is extraordinary high and that real distance on the screen between the mirrors is just a little more than a couple of centimeters, we could not see the photon moving. Since this simulation is based on real physics, it's necessary to inject really great distances to appreciate any effect, such as millions of meters.
If the speed assigned to a photonic clock (horizontal speed) is really near the speed of light, we will see the photon so busy following the clock device that it won't have “much time” reaching the upper mirror; hence its apparent vertical stillness. Here, we have to remember that a photon travelling horizontally at a pace approaching light speed, could not simultaneously reach -at light speed- the upper mirror. Otherwise, vector sum of both speeds would exceed the immutable light speed as well as physics laws!
If a wrist watch is attached to a photonic clock moving a little below light speed, the watch's hands are indeed slowed. And if such clock moves exactly at light speed, then the watch would be simply stopped. It goes the same for photons which have not aged one second since the big bang, some 14 billion years earlier!
Unfortunately not. If you live 100 years in a sedentary fashion or at near light speed, you will subjectively feel like living the same 100 years. In the latter case, metabolic functions are just slowed, exactly like the hands of the watch. But your life experience as well as its length, subjectively, remain the same. Sorry!
We wish to thank Brian Greene who so admirably explained the basics of relativity in his bestseller The Elegant Universe where string theory is the main topic.
( 1 ) This assumes that the experience is made in absolute vacuum where light speed is indeed of 299,792,458 m/s. In water, it would be of 225,563,000 m/s, and in glass, 200,000,000 m/s...