howabout1337 said:
OK, I think I am getting there.
Say two cars are traveling, one faster than the other.
Relative to some point on, say, the ground?
We'll call it car A and car B. Car A is faster than car B, not that much, but faster. When the person in car B looks at car A, he's going to say "Oh, he's traveling at his speed minus my speed".
Relative to car A, yes.
Me, the person who is "stationary", measures their speed to my speed, and say "hey they are traveling at their speed minus my speed".
Having said you were "stationary", what do you mean by "my speed"?
Obviously the person in car B looks at the person in car A's speed differently than I do. The person in car B calls me and say "hey that guy in car A is traveling at this speed", and I argue with him saying "he's not that speed, he's THIS speed". Obviously I didn't measure the speed between myself and the guy in car B.
I don't know what you mean by "this speed" or "that speed". Let's put specific numbers to this:
You, who are "stationary", standing on the side of the road have speed 0 relative to the road. Car B has speed 80 kph relative to the road and car A has speed 100 kph relative to the road.
Now:
Relative to you, you have speed 0, car A has speed 100 kph and car B has speed 80 kph.
(Exactly the same as "relative to the road", of course.)
Relative to the person in car A, you (and the road) have speed -100 kph, car A has speed 0, and car B has speed -20 kph.
Relative to the person in car B, you (and the road) have speed -80 kph, car A has speed 20 kph and car B has speed 0.
Now, someone behind me shines a laser pointer right in between all of us.
Now, the guy is car A cannot see the guy in car B, or me, or the guy behind me, and he performs experiment on speed of light from the laser pointer, and he's going to say "hey this is speed of light". The guy in car B is going to say, "look at that dumb guy in car A, he doesn't know he's moving, let me measure the REAL speed of light", and he measures the speed of light relative to himself, "he will say, look this is the REAL speed of light". On the other hand, I am thinking to myself, "both of these guys don't know what they are talking about, They both think they are stationary. The B guy think he's stationary and making fun of that guy in car A"
How do I know that the guy behind me is not saying "haha, so all of these guys don't know that they are on a moving train?"
I don't know why any of those guys would think anyone was dumb. They should understand that the speed of light would be measured to be the same at any speed.
Look at it this way: according to classical, Newtonian, Physics, we can add speeds: u+ v.
If I am standing at the side of the road, you approach me on the back of a truck going 60 kph (relative to me) and I throw a ball to you at 70 kph (relative to me) classical physics would say the ball will be going toward you at 60+ 70= 130 kpg relative to
you.
Similarly, if I shine a light at you with speed "c", relative to me, classical physics says you would see it coming toward you with speed 60+ c.
Now, relativity says you must use the formula (u+ v)(1+ uv/c^2).
In the first example, that would be (60+ 70)/(1+ (60)(70)/c^2)= 130/(1+ 4200/300000^2)= 129.999999 kph. The difference is, of course, so small it isn't noticed.
In the second example we would have (60+ c)/(1+ 60c/c^2)= (60+ c)/(1+ 60/c).
Multiplying both numerator and denonator by c we gave c(60+ c)/[c(1+ 60/c)]= c(60+ c)/(60+ c)= c. That is, the speed of light is the same relative to both of us.