Illusion or Reality?

You probably have the following experiences:
1. You were flying on a plane from one destination to another (say Sydney to Hong Kong). The plane was so smooth and quiet that you could hardly feel any movement. You remained seated without moving around in the plane. So you thought you were not in motion. You threw a ball straight up in the air, and the ball fell straight down back into your hand, indicating that you were not in motion at all. But on a second thought, you knew the plane was moving at a ground speed of 500 km/hr away from Sydney. You also knew you yourself were moving (together with the plane) similarly at a very fast ground speed of 500 km/hr away from Sydney.
2. You were traveling on a train from one city to another. You felt tired and fell into a nap. The train was so smooth and quiet that, when you woke up, you didn't know whether the train was moving or not. You thought the train was stationary at a train station. You looked through the window on the left side of your train. You saw another train overtaking yours slowly carriage by carriage from your back to the front at a speed of about 10 km/hr. You then turned your head and looked through the window on the right side of your train. From the views outside, you then realized that your train was in fact moving forward at a very fast speed of 100 km/hr passing non-stop over the station. You then also realized that the other train on your left was in fact moving forward at a even faster speed of 110 km/hr passing non-stop over the station.
3. On another similar occasion, you woke up from your nap on a long train journey. You thought the train was stationary at a train station. You looked through the window on your left side. You saw another train passing by yours, carriage by carriage from your front to the back. When all the carriages had passed over, you could see other views outside the window. You then realized that the other train was in fact stationary at the train station, and your train was in fact moving forward passing non-stop over the station at a speed of 100 km/hr.

Your experiences above indicate that:
1. Your position at any time is determined by some point of reference. After an hour, you were still in the middle of the PLANE, but you were 500 km away from SYDNEY.
2. If your position (to some point of reference) doesn't change over time, you are stationary and not in motion (to the same point of reference). During the entire hour, you remained seated in the PLANE, you were stationary and not in motion (with reference to the PLANE).
3. If your position (to some point of reference) changes over time, you are in motion (to the same point of reference). During the same hour, you were further and further away from SYDNEY. So you were in motion (with reference to SYDNEY). Hence, motion is the change of position (to some point of reference) over time.
4. As motion is the change of position over time and position is determined by some point of reference, so motion is also determined by some point of reference. While you were on the train, your train was moving at 100 km/hr (passing over the STATION), but the other train on your left side was moving at 10 km/hr (passing over YOUR TRAIN).
5. Likewise, non-motion (being stationary and not in motion) is also determined by some point of reference. You were not in motion (in the PLANE) although both YOU and the PLANE were moving at a very fast speed (away from SYDNEY).
6. If you are moving (with reference to some point of reference) and the point of reference is also moving (with reference to some other point of reference), then you are also moving (with reference to that common point of reference). The train on your left side was (overtaking YOUR TRAIN) at 10 km/hr, and your train was moving forward at 100 km/hr (passing non-stop over the STATION), then the train on your left side was also moving at 110km/r (passing non-stop over the STATION).
7. When there is no common point of reference, motion can only be relative. As in your experience 3 above, without any common point of reference (the STATION), it can be regarded that either YOUR TRAIN was in motion and the OTHER TRAIN was stationary, or YOUR TRAIN was stationary and the OTHER TRAIN was in motion. Hence, without any common point of reference, it can only be regarded that YOUR TRAIN and the OTHER TRAIN were moving towards each other at a speed of 100 km/hr.

As motion is the change of position over time, apart from being determined by some point of reference, it is also determined by TIME. We shall leave the discussion of TIME in some later blogs as TIME permits.