kweagle said:
Thank you everyone for the replies, I really appreciate it. I have been scouring the web trying to learn more about time and what it really is, and I think I am starting to get some of the theories a bit more. I do have some follow-up comments/questions if you don't mind.
First let me explain what my personal concept of time has always been. To me, 'time' is a constant. It is linear, and it always passes at the same rate, no matter where you are, what you are doing, or what is around you, time never stops or slows down. What does change is what you are able to observe happening in time as a result of the time it takes for light to travel. Time keeping, however, is something developed by humans as a way to measure the passage of time. It has always been my thought that it was the measuring devices (the physical/quantum world) that is affected by speed/acceleration and gravity. I accept that this view is not correct, which is why I am here to try and understand it.
Relativity does make perfect sense to me, but it is the time dilation that does not. It seems to me that time dilation is simply a result of the time it takes light to travel based on relative speeds of two objects, therefore, I think a more accurate name would be 'light dilation'.
With that being said, here are my questions...
If the speed of light is considered to be a constant speed, no matter who is observing it, and no matter what velocity they are traveling or what gravitational forces they may be experiencing, would it be accurate to say that time as we know it in physics is derived directly from the speed of light, lightspeed being the base line for how time is measured, and this is why time changes with the speed of light?
I'm going to try and paint a picture of what is going on through an analogy.
Imagine two men( M1 and M2) walking side by side on a featureless plane. Without changing his pace, one of the men(M2) changes the direction in which he is walking. Each man judges forward progress as progress in the direction he is facing. So from each Man's perspective, the other man is now making less forward progress (even though by the other man's judgement nothing has changed and he is still walking at the same rate as before.), and falls further and further "behind".
Now M2 changes direction again, turning so that he is walking in the same direction as M1. What does he perceive? As he turns, the M1's apparent position with respect to the direction M2 is facing changes and goes from being "behind" M2 to Being "ahead" of M2, as judged by M2. ( as far as M1 is concerned, M2 remains behind him). Both men are now walking in the same direction, and their relative positions are constant and bot Men agree that M1 is ahead of M2.
If M2 continues his turn until his forward path intersects M1's path, As he turns, M1 will move a bit more ahead of him. After the turn, M1 will be ahead of him, but now not progressing "forward" as quickly. M2 will start to gain on him a bit. However, by the time he intersects M1's path, he will not have caught up to him. If he then turns to match M1's walking direction he will still find himself behind M1.
The above analogy is like the twin paradox, While moving at different speeds (walking in different directions), Time in the other frame runs slow ( the other man makes less forward progress). If a spaceship travels away from the Earth at some speed, turns around and comes back, (M2 changes direction so that he returns to the path of M1), It will find that it has aged less than the Earth has. (M2 finds himself behind M1)
In the analogy I gave, there is no universal fixed direction to which the concept of "forward progress" can be applied. each man has his own measurement of forward progress. In Relativity, there is no universal fixed "direction" to time measurement. Put another way, instead of a universe with 3 spatial dimensions and 1 time dimension which are fixed and separate from each other, we have a universe of 4 dimensional Space-time, where the "direction" for time depends on the relative motion's of the frame measuring it. Two observers with relative motion with respect to each other will judge the position of an event in time and space differently. Observer 1 could say that two events are separated by x meters and y sec, while Observer 2, with a relative motion with respect to Observer 1 would judge the same two events as being separated by w meters and z sec. Much as the way that two people facing in different directions would disagree as to how far to the right or left and how far to the front or back two objects are from each other.
The speed of light comes in in that it determines just how these differences perspective relate to each other. ( or conversely, the relationship between space and time determines what the speed of light is.)
If the speed of light is constant, why do we observe a redshift in stars that are moving away from us? Shouldn't they appear to look the same no matter how they are moving if light is always traveling at a constant speed?
I've heard this question a lot, and I've never quite understood the reasoning behind it. Doppler shift is not a result of how fast the light is traveling with respect to you, but how closely the Light waves are bunched together according to the observer.
Consider the following animation. In the first, the light source is stationary wit respect to the observers. The waves move out as circles, and hit both observers at the same frequency
In the second one, the source is moving towards the blue dot and away from the red.
The waves still move out as circles and at the same speed as they did before. ( the first wave even hits both observers at the same time, just as in the last animation.) However, as each successive wave is emitted, the source is closer to the blue dot than it is the red dot and the waves are more crowded together in this direction and more spread out in the other the other direction than they were in the first animation. The blue dot sees an Increase in frequency, and the red dot a decrease in frequency.
If two people left Earth traveling at near the speed of light, one going in a straight line and back, and the other simply orbiting the earth, both returning to the surface at the same moment, would time have passed the same amount for both of them when they got back? How much time would have passed for them and how much time would have passed on earth?
As long as we ignore gravitational effects and assume that the orbital speed and "straight line" speeds are the same, Then both people will have aged the same and less than someone on the Earth. The main difference is that the straight line traveler does all his acceleration turning the turn around while the "orbiting" traveler is under constant acceleration. (he wouldn't be in a true orbit as he would have to be constantly firing his engines inward towards the Earth in order to maintain a circular motion around it at such a high speed. )