i read an article in howstuffworks.com a while ago about the speed of light and how light always moves at the speed of light from all frames of reference, and the author used an example where a parked car turns on its lights and the light hits a person standing down the street at the speed of light, and then a car driving at 50 mph turns on its lights and the light still hits the person at the speed of light, instead of the speed of light + 50 mph(small difference, i know). then there were other examples, and it started to confuse me... i'll have to find the article again and paste a link to it... anyway, me and a friend were talking about light recently and i'm still having a hard time grasping the whole concept, so if anyone could answer a few questions for me, i'd appreciate it 1. my first question is about the concepts of "frame of reference" and speed, i just want to make sure i have the basics down: i'd be correct in saying speed is always relative, right? like if i was running on the ground at ten miles an hour and threw a ball in front of me at 20 miles an hour, from the earths frame of reference the ball is moving at 30 mph, from my frame of reference the ball is moving 20 mph and the earth is moving at 10 mph, and from the balls frame of reference i'm moving at 20 mph and the earth is moving at 30 mph. is everything i said correct, am i using the term "frame of reference" properly? 2. if everything i said is true, then what causes time to slow down/speed up depending on an objects speed? since from an objects own frame of reference it's constantly still and speed can only be measured from other frames of reference (the surface of the earth, the sun, etc), what is it that determines for whom time will "slow down"? i'm assuming it has something to do with the shift in momentum, whichever object accelerates/decelerates, is that it? 3. gonna make an ascii drawing: ........................---O-------------->.................................. .........................ball B............x...............................|>= flashlight ....................................ball A O..................................... lets say you have a flashlight, and a ball(ball A) that isnt moving (from the flashlight's frame of reference), and another ball is flying towards the flashlight at 100 mph (ball B), and when ball B passes ball A at point X, the flashlight turns on... both balls are an equal distance from the light when it turns on and light always moves at the speed of light from all frames of reference, including ball A and ball B, so (this is where i get completely lost) the light hits both balls at the same time? i've asked a few people about this, and they answered "yes, because time slows down for ball B, so even though ball B will hit the light first, if you had a clock on both ball A and ball B both clocks would read that the light hit at the same time", but what if ball B were going in the other direction at the same speed? time would be still be slowed down except now the distance between the light and the ball have increased instead of decreased, so wouldnt it be hit much later then ball A in that case? 4. if a spaceship were flying away from the sun at half the speed of light then turned left 45 degrees, would it catch more sunlight if it wasnt moving but still facing away from the sun at the same angle? how would the sun apear to the people inside the ship, would it look like an oval? so far i'm still having a tough time grasping this whole thing. these are the explanations i've come up with to explain it so far: A. the way i see of "frames of reference" and relativity is wrong, and speed is a constant compared to some point in the universe, and that light always moves at the speed of light no matter what speed the source is traveling at. though this wouldn't really explain some of the examples i've seen... B. the way objects stretch/shrink when passing other objects is relative to the speed the object is coming toward or moving away from the other objects frame of reference(the speed at which the distance is being closed between the two objects), rather then just its relative speed. like if a man was standing 100 feet from a highway and a car was driving down at 50 mph, the speed at which the car is closing the gap between itself and the man would kind of resemble the way y=x^3 looks on a graph, and it's from this shrinking/stretching that distance is calculated when dealing with objects that are moving. this would explain why the light would hit both objects at the same time in the example with the balls i gave above: the distance is relative to each frame of reference, though this explanation contradicts with some things i've read so i don't think this is it either... C. when light comes out from a source(a star for example), it doesnt come out in a sphere but rather in a weird amobea-like shape, stretching in areas to hit moving objects, so that it hits all objects that were equidistant from the lights source at the same time. it's completely ridiculous and i don't believe it, but it's the only explanation that works with most of the examples i've seen so far :P if anyone could shed any light on this (no pun intended) that'd be great, TIA!