Time, a brief history

Brokenpride With what do you measure space Brokenpride? With what do you measure time?In measuring space we can only do so by reference to a fixed location.
In measuring time we can only do so by reference to a fixed location as well.We measure time by the movement through space of a device designed to maintain a regular sequence to which we can refer and thus assign a meaning to the passage of events.
Eliminate time and what physical meaning can you give to the measure of space? Eliminate space and what physical meaning can you give to time? They are joined at the hip in the deepest meaning of the phrase.As a check up on your understanding of measurement let us conduct a thought experiment that Albert Einstein used to forge his arguements.Imagine yourself on a train moving at a constant velocity past a railway crossing. You open a window and take rock and drop it from the train. Now, ignoring air resistance, on the train you observe the rock to follow a straight line path to the ground.
On the ground outside the train a person watches you perform this misdeed and observes the rock to follow a curved path {Parabola} to the same point on the ground.The question to ponder is this. Which path is the correct one? A straight line or a curved one? Since both are observed to have occured how can we reconcile the fact that a curved path is a greater length that a straight line path if both paths began at the same location and ended an a different location but the same point on the ground in both cases?
Get back to me when you think you have it figured out.This message has been edited by sidelined, Fri, 2006-03-24 12:24 AM

Brokenpride Why do you say that? Please explain what prevents him from seing motion in any dimension. If the rock were to move forward or backward or in towards the interior of the car he is quite capable of observing this.
The path taken is a straight line relative to the train. When something drops gravity accelerates it downward. The constant motion of the train relative to the ground is what imparts an acceleration forward. However neither of these arguements answers the central question of which path is "real". Since the starting points and end points are the same for both paths how can the path be different lengths {a curve between 2 points requires a greater length than a straight line} ?Now to make the situation even more baffling if we reverse the situation and have the man on the ground drop the rock while the man on the train goes by the man on the ground watches it travel a straight line while the man on the train sees it follow a curved path.

Posit The example I used is an accurate {though paraphrased } desription of one found in the book RELATIVITY {The Special and General Theory} published by Thre River Press New YorkHe was making the case that " there is no such thing as an independently existing trajectory but only a trajectory relative to a particular body of reference". He was dealing with classical mechanics as pertains to space and time and was laying the groundwork for showing the steps by which he would argue his position for the validity of special relativity.

Brokenpride Of course it would. This is because they now both have the same reference frame.{the ground} However, we are trying to find out why there should be a different path for the same starting and ending points between the train moving at a constant velocity and a person on the ground. Of course they would because they now share an equivalent frame of reference.They would also make the observation that neither train is movingrelative to the other.Therefore it is logically consistent that the paths they would observe for the rocks would be the same. Actualy you mean say measure the velocity {since velocity change over a range of time reveals its acceleration.}Regardless, you now see by this statement of yours the inseperabilty of spacetime in describing an event.This is direct contradiction of your earlier statement{Post # 23} that space and time are different.

Brokenpride Really? Try to make a measurement in the absence of a time component. How would this be accomplished since without time an action of measurement cannot take place. Velocity is defined as a displacement in space over a set time period {meters per second, miles per hours}.
To make it actually correct we must also include a direction in dealing with velocity.

Son Goku If light from another galaxy does not experience time does the information it carries also not experience time?