When we measure the speed of light, it's always in two directions. Measuring it in one direction may be impossible.

Your experience of time is relative because it depends on motion – more specifically, your speed and acceleration.

If you were traveling in a rocket moving at 75% of the speed of light and your friend throws the ball at the same speed, you would not see the ball moving toward you at 150% of the speed of light.

Why does time change when traveling close to the speed of light? – Timothy, age 11, Shoreview, Minnesota Imagine you’re in a car driving across the country watching the landscape.