Thought experiment 5 shows how waves propagate.


Consider a bathtub filled with water.
Pore some red paint slowly in the bath on the left side. The water on the left side will become red but not on the right side.
Now put your left hand on the left end and your right hand on the right side just above the water. Both your hands are dry.
Now move your left hand slowly in the water and put it back out. Your left hand will become wet and red.
Repeat that for a couple of times for example 10 times.
When you do that you will see waves moving from left to right. Every time when the wave reaches your right hand, your right hand will become wet. Will your right hand become red? Most probably not.
That means that there is no relation between waves and the actual (horizontal) transport of the water. Water propagates waves, waves don't (necessary) propagate water.


In the middle of a lake is a boat, moving up and down, there by producing waves. Consider your self floating above this boat. What will you see. What you see are concentric circles. The center of those circles are the boat. The circles become larger the further away you come from the boat i.e. they move away from the boat.

What is happening? What is not happening that the water moves over the same distance as the circle moves. The circle is like a shape. What moves is this shape. A shape in the water. A shape of water particles. The water particles that "build" this wave also move but not more then the boat. When the boat moves down the water particles around the boat move away and when the boat moves up the water particles around the boat move back. The water particles that move away to the right, press the water particles on their right side to the right (with a small delay) etc. The same water particles that moved away to the right a little later will move back and the same with their water particles to the right.

On the average the water particles don't move.

This picture changes when the lake is emptied through a hole. In that case there is an average forward movement of water particles towards the hole.

This picture also changes when the boat moves. The center of the circles moves. In the direction in which the boat moves the waves are more closely together. In the opposite direction the waves are more further apart.

This picture also changes when you move. When you move in "space" you will not see concentric circles but the some thing slightly different. When you move just above the water (in an hover craft) you will feel the same as if the boat moved (in opposite direction). On the other hand and that is the most important the shape of each wave (i.e. the reality) stays the same i.e. is independent of your movement.


What is the difference between water waves and the movement of sound. Is there a difference.

In the case of sound it is the air that moves (slightly) compared to the water particles. On the average the air does not move assuming there is no wind.

Again if you move there is no change in the movement pattern of the sound. What you see (indirectly) and hear is different.


As we have seen above there is no basic difference between the movement of water waves (water particles) and sound (air) except speed.

Does light also behaves the same ?

The bearers of light are photons (equivalent like water particles) The question is do they move with the source that generated those photons (like the boat in the lake) or are they in rest.

To decide this is the objective of this thought experiment.

In the simulation there are 4 players. One player is the master or source. The three other players are slaves. What the master does he or she sends out a signal. What the slaves do, immediate when they receive a signal they send a signal back. So finally the master will receive three signals back. The question is when.

Two types of movement are considered:
  1. The four players can move. When they move all players will move in the same direction with the same speed.
  2. The medium of the signal can move. This is called wind.

The test is done under 4 different conditions.

  1. In the first test there is no movement. The players are in rest and there is no wind.
  2. In the second test the players are in rest and there is wind.
  3. In the third test the players move and there is no wind.
  4. In the fourth test both the players move and there is wind.

The speed of the signal is twice the speed of the players and/or the wind

Now perform the program: THOUGHT5.EXE
From the Test Selection Display:
Select test 1

Now perform the program: THOUGHT5.EXE
From the Test Selection Display:
Select test 4

The outcome of both the tests is the same: the observer O will the signal receive the signals back from each of the 3 players A, B and C at the same moment i.e. there is no preference.

Now perform the program: THOUGHT5.EXE
From the Test Selection Display:
Select test 2

Now perform the program: THOUGHT5.EXE
From the Test Selection Display:
Select test 3

The outcome of both tests is the same i.e. it is not possible to decide if the medium moves and the players are in rest or the players move and there is no wind.
On the other hand there is one major difference. The Observer will receive the signals from A and B back at the same time and not from C. The Observer will always receive the signals back at the same time from two players which are opposite from each other. This is the same situation as in thought experiment 3: "A Duel in the Mist"

Return to CHAPTER3.TXT


In order to simulate the different conditions the parameter selection display is used


From the Parameter Selection Display the following parameters can be changed:

        0 = Select test display

1 = Set standard parameters.

2 = Screen mode. Valid values are 7,8,9 and 12. Standard value = 9 3 = Wait time in second. Physical wait time between each simulation cycle. Standard value = 0.1 4 = Speed of Sound. Standard value = 4

5 = Delta time in seconds between each calculation cycle. Standard value = 0.2

6 = Alpha in degrees. Standard value = 0

7 = Basic Speed. Standard value = 2