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Name: Flavian
Status: student
Grade: 9-12
Country: Romania
Date: Spring 2012

My question is about the LHC and any other particle accelerator, if the 2 matter beams travel at about 99% of the velocity of light relative to the ground in opposite directions don't they travel at 2x that relative to each other? What is actually going on?

Flavian, How fast an object moves depends on the observer. When approaching the speed of light, the only reliable reference is you. Such velocities do not add like day-to-day velocities. Both distance and time measurements are different for those in different reference frames. The second matter beam might travel at a greater distance as seen by a particle in the first beam, but the time it takes to do it, as measured by the first beam, will also be greater. The distance divided by the time (i.e. speed) will be greater than 99% of light speed but less than 100%.

Dr. Ken Mellendorf Physics Instructor Illinois Central College

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