In the Large Hadron Collider, two streams of protons travel in opposite directions at near light-speed before they collide with each other. Does this mean that the two particle streams are moving at nearly twice the speed of light relative to each other?

This question gets to the heart of the special theory of relativity. Let’s take a simpler example to start with. Imagine someone standing on a moving railroad car and shining a flashlight. What is the velocity of that beam as seen by someone on the ground? According to the laws of physics instilled by Isaac Newton and Galileo Galilei, the person on the ground would just add the velocities of the car and the beam, and would see the beam moving faster than the speed of light.

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