Course 3 on Lorentz-Four-Contractions, Session 8, Part 1

So, the relative time and length of any material object when it is moving as a unit varies as the object travels at different speeds. The changes in relative time and length, however, are not significant unless the given object goes either from a "common" speed to near light speed, or from near light speed to a common speed. If an individual in a spaceship was traveling near light speed, and another person was somehow able to measure its length as it went by, the person measuring the length of the ship would measure the ship to have a relatively short length, while the individual who was in the ship would ascertain the length of the ship to be at the same length that it had before it took off. So, the length that is measured by a person who is not moving very fast of something that is moving near light speed is shorter than what is observed by the one moving very fast, and the time that one notices in the fast moving object is smaller than the time observed by the one not moving very fast, according to the equation given last week. Yet, this is as measured by one who is stationary. Yet, the time and length of an object that is going near light speed still seems normal to the person who is traveling in that object, as long as that person is not theoretically moving at light speed. At light speed, one would not notice time passing. So, what the actual time elapsed is for an object as well as what its actual length is is not concrete! What something's length and time are is an actual entity, yet the amplitude of these parameters not only is dependent upon the existence and shape and form of the object, yet also upon how fast that object is moving in a given direction. Why direction too? This is because detection requires the existence of light, and if an object is traveling in different directions, then the object is also altering its way of being detected.