Well, if the particle is moving in the extra dimensions, it means it has momentum in these other dimensions, which means it has extra energy. But since the particle is not moving in our dimensions, we would experience that extra energy as extra mass (remember that mass and energy are the same according to Einstein). In other words, you would notice if a particle was moving in extra dimensions because it would be heavier than a particle that wasn’t. This is how we can use particle colliders to detect extra dimensions. If we smash particles together, and one day we see a particle that looks, for
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