I accidentally posted this under another forum user's topic, sorry about that My question was regarding matter gaining mass when it is accelerated. My question originated from an explanation of the large hadron collider; the explaination stated that when the protons in the LHC are sped up to 99.9% the speed of light, instead of gaining more speed, they get heavier. Someone posted that everything gains mass when it is accelerated, but there is no significant change until near light speed. How does this added energy translate into weight? The particles themselves are only individual protons, how does one proton gain weight, and where does that weight come from? I'm completely in the dark about this, so if my question doesn't make sense, please set me straight, thank you.