Thought experiment 2 describes what you see when a train moves not around in a circle but follows a race track.
Thought experiment 2 identical as thought experiment 1. The main difference is that the track is not any more a circle but has the shape of a race track. The circle was split into two halves. One half was moved to the right and the two halves were connected by straight segments. The observer is at the centre of the left half circle.
Before continuing first try the test now and then continue reading. A test means increase the speed and see what happens with the length of the train when the speed is constant.
Now perform the program: THOUGHT2.EXE
From the Test Selection Display:
Compared to the first thought experiment there are three main differences what the observer sees:
First when the train moves away from the observer (i.e. moves to the right) the length of the train, as observed, becomes smaller. The opposite is also true: when the train approaches the observed then the length of the train, as observed, becomes larger. This is independent of the speed of the train and is also the case when the train stops. This is in agreement with normal day experience that how further away something is, the smaller you see it.
Second there is a difference in the length of the train because the angle of the direction in which the train moves is different. When the train moves in a circle this angle is 90 degrees. The length of the train (observed) is than at its maximum. When the train moves straight away from the observer (or towards the observer) this angle is 0 and the length of the train (observed) becomes zero. This effect is also independent of the speed of the train.
Third there is an additional difference in the length of train when a train moves away from the observer or towards the observer at a certain distance. When the train moves away the length of the train is seen smaller as strictly based on its distance. When the train moves towards the train is seen larger as strictly based on its distance. This effect is dependent about the speed of the train.
To explain the third when the train moves away: Consider we are now at a moment t0 and the train is at a certain distance d0 moving away from the observer. Light from the back will take a time t1 to reach the observer and light from the front will take a time t2 to reach the observer. t2 is greater then t1 because light from the front has to follow a longer path (because the front of the train is further away) in order to reach the observer.
Consider we are now a moment t1 later what will we see. First the real train is not any more at distance d0 but further away. The observer sees the back of the train where the train was at moment t0 but not the front of the train where the train was at moment t0. Light from the front of the train at t0 will reach the observer a time t2-t1 later. The observer will see at the moment t1 the front of the train at a position where the train was a time approximate t2-t1 earlier i.e. closer to the observer. That means the train seems to be shorter.
To explain the third when the train moves towards you: Consider we are now at a moment t0 and the train is at a certain distance d0 moving towards the observer. (That means on the opposite side of the track, compared with above) Light from the front will take a time t1 to reach the observer and light from the back will take a time t2 to reach the observer. t1 is smaller then t2 because light from the front has to follow a shorter path (because the front of the train is closer) to reach the observer.
Consider we are now a moment t1 later what will we see. First the real train is not any more at distance d0 but closer. The observer sees the front of the train where the train was at moment t0 but not the back of the train where the train was at moment t0. Light from the back of the train at t0 will reach the observer a time t2-t1 later. The observer will see at moment t1 the back of the train at a position where the train was a time approximate t2-t1 earlier i.e. further away from the observer. That means the train seems to be longer.
Now repeat the experiment
Now perform the program: THOUGHT2.EXE
From the Test Selection Display:
The same question applies as thought experiment 1:
The simulation only consists of one test: test 1
Test 1 shows 2 partly circles: one white one and one yellow one
On the train are two red circles. One at the beginning of the train and one at the end of the train. They represent the virtual position.
In order to move the train use the UP and DOWN arrows. The UP arrow is used to increase the speed of the train. The DOWN arrow is used to decrease the speed of the train.
The length of the train is shown in the middle.
The speed of light is shown in the top right corner.
The speed of the train is shown in the top left corner.
It is possible to freeze the picture: Select F (and F again to continue)
Return back to CHAPTER3.TXT
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 light. Standard value = 30
5 = Delta time in seconds between each calculation cycle.
Standard value is 0.1