fourth dimension is to move at c through the three spatial dimensions. Ergo the fourth dimension is moving at c relative to the three spatial dimensions. Georgina--you write: "If matter moved along the 4th dimension at c but light didn't then the light would not be visible. It must also be travelling along the 4th dimension at c to keep pace.In my opinion it is travelling afore-ward along the 4th dimension and across 3D space. (As these dimensions are perpendicular it can be thought of as two waves one the "magnetic" part travelling along 4th dimension the "electro" part travelling through 3D vector space.) " Yes--E/B duality stems from the fact that the B field is an E field in the fourth expanding dimension. Is it not curious that only *moving* charges ever feel a magenetic field? This is because *all* motion is accompanied by a rotation or boost into the fourth moving dimension, and thus the B field--which is invisible to the stationary particle, acts on the particle in motion. The "relative" interpretations of E fields and B fields depend entirely on one's relative motion; as the faster one travels the more a B field seems like an E field and vice versa. There is a great treatment of all this in Hidden Unity in Nature's Laws by John Clayton Taylor which I will be elaborating on in my own new forum: ttp://www.fqxi.org/community/forum/topi\\... Everything is moving at c through spacetime--every photon and every electron. There is but one velocity