Thought experiment 3 explains the concepts virtual reality and virtual position of an object or event. Those concepts are compared with the real reality and the real position of an object or event.
Thought experiment 3 consists of three tests:
One of our senses is hearing. We hear when someone speaks. When the person who speaks or the cause of the sound is close we hear immediate. When the cause is far away, there is a time delay (dt) between what caused the sound and when you become aware of the sound.
In general, when you become aware of an event, you become aware of something that happened some time dt ago. dt depends about the distance between what caused this event to happen and the speed with which the effects propagate.
For sound dt is equal is to the distance between the observer O and the cause of the sound divided by the speed with which sound propagates. For example: when the distance of the event is 900 meter and the speed of sound is 300 meters per second, then you observe the sound with a 3 seconds time delay.
During this time dt the source can have moved. The virtual position is the position where the cause (an object) was some time dt ago.
In general to calculate the virtual position is rather difficult because it depends about the path that the object or event followed.
When an object moves away from the observer the virtual position is closer to the observer because that was the position where the object was earlier. When an object moves towards the observer this is the opposite.
A simple case is when object moves in a straight line away from the observer.
For example: in the above case when the event moves with a speed of 10 meters/sec away from the observer then the virtual position is 900 - 10*3 = 870 meters (i.e. closer).
For our eyes and what we see the same concepts apply. There is however a major difference between what we hear and what we see: at close distances we see what happens immediate. The reason is because the speed of light is much greater then the speed of sound.
As a consequence is the virtual position for light much closer to the real position.
In the next paragraph a more accurate description of the virtual point calculation is supplied. This paragraph can be skipped.
In the simulation the virtual position and dt are calculated in the following way:
From those positions you can calculate the distance d
The initial value of dt is equal to:
With that value you can calculate the position of the object dt ago.
This past position is called the virtual position.
Repeat the steps 2,3 and 4 until x1p and y1p do not change any more.
This is what is called the slow method.
The purpose of the slow method demonstration is the show the virtual position for sound propagation for different values of the direction and speed of the event that causes the sound.
The white dot is the final virtual position.
What the simulation shows is that when an object moves away from us, the virtual position approaches us and we observe it earlier. The simulation also shows the opposite, that when an object moves towards us, the virtual position moves away and we observe it later.
The fast method is almost identical as the slow method.
In the slow method the first value of the virtual position is the real position. In the fast method the first value of the virtual position is the final virtual position of the previous calculation.
In the above test what we hear and what we see are demonstrated.
The next question is what is the behaviour of gravity.
Return back to CHAPTER3.TXT
In order to start a simulation:
In order to stop a test
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 = 0.01 4 = Speed of sound. Standard value is 10
5 = Speed of light. Standard value is 1
6 = Delta time in seconds between each calculation cycle. Standard value is 1
7 = Delta angle. Standard value = 10