There have been a lot of posts lately on relativity, with a lot of different theories. Now I'm going to try to give a crash course in the theory of relativity as I understood it from my physics teacher. What might help in understanding me is some knowledge in basic Newtonian physics and maybe some grade 11 math.

For additional information or just to clear up a few thing thrown around here, I refer you to a godsend for any high-school or university student, Sparknotes (http://www.sparknotes.com/) and, more specifically, Sparknotes' section on physics. (http://www.sparknotes.com/physics/)

There are two main precepts to relativity:

1. In a closed environment, you cannot ascertain your current velocity.

Without comparing your current velocity to the velocity of something around you, you can't determine your own velocity.
Example: What is your current velocity? You might be tempted to say 0 m/s because you’re immobile in front of your computer, but then the earth is going around the sun so you're not completely immobile, right? But how would you know that the earth is going around the sun? By looking at the sun and at the other planets, things that are outside of the "closed environment" that is earth.

2. The speed of light is always constant and nothing can go faster than the speed of light.

Whenever and wherever you are, the speed of light is always equal to c, or close to 3 * 10^8 m/s. Also, under any and all conditions, c serves as a speed LIMIT, as in nothing can go faster than c.

Okay, once you understand those two precepts, then you can really start discussing relativity.

Originally posted by Redrover
2. The speed of light is always constant and nothing can go faster than the speed of light.


Just a quibble, but this is a bit redundant. All you need is the first part of the sentence. The second part is a derived result of the two postulates, as Einstein pointed out on p.22 of this document:

http://www.fourmilab.ch/etexts/einstein/specrel/specrel.pdf

Yeah, but I want to keep it simple so I can refer to it easely later on in my explications.

Just a quibble, but this is a bit redundant. All you need is the first part of the sentence. The second part is a derived result of the two postulates, as Einstein pointed out on p.22 of this document

In which case, isn't anything said to describe special relativity, beyond the two postulates, redundant? After all, it's all derivable from those two postulates.

Originally posted by AD1
In which case, isn't anything said to describe special relativity, beyond the two postulates, redundant? After all, it's all derivable from those two postulates.

No, I meant that it is redundant as a "main precept" of SR because it is a derivable consequence of SR. But, Redrover is leaving the option open not to derive it in this thread, so he/she is presenting it at the outset.

Okay, I think I see what you mean now.