If someone stands up through the sunroof of a car travelling down the freeway at 60 mph and measures the speed of a beam of light they shine from a flashlight in the direction the car's going, they'll record it as c. This is intuitive (no need for relativity). Someone on the roadside, however, will also record it as c, since the speed of light is constant for all reference frames. Does this mean that the light actually slows down (with respect to the car) by 60 mph (this slowing down would not be detected by the person in the car since their ruler will shorten and clock will slow down)? If so, why? What causes the light to slow down? If not, what's going on? Thanks.