0 Members and 1 Guest are viewing this topic.

The geometry of the universe means that moving objects have certain allowed trajectories and that the overall space-time has a certain geometry.

Geezer, I think just because the x,y,z,t axes are not orthogonal (as in Euclidean space) doesn't mean that there are not 4 dimensions. It is considered that there are (at least, in fact). The surface of a sphere can be considered as 2 dimensional even though these dimensions are not orthogonal (longitude and latitude). As you say, it depends on the underlying geometry.

However, I think you're wrong that time isn't a dimension. It surely is to any given observer. Just as any observer sees three space dimensions, no matter how much you rotate them, they still see one time dimension no matter how much you speed them up. Not all observers agree on the definition of this time dimension, but each still has a single (1D) time dimension.

Quote from: JP on 22/02/2011 05:06:25However, I think you're wrong that time isn't a dimension. It surely is to any given observer. Just as any observer sees three space dimensions, no matter how much you rotate them, they still see one time dimension no matter how much you speed them up. Not all observers agree on the definition of this time dimension, but each still has a single (1D) time dimension. Yes, but [], wouldn't the purpose of assigning spacetime four dimensions be to permit an unambiguous definition for a location in spacetime that all observers can agree on? It seems that won't work unless we add more information.Maybe we need to add another dimension to fix it []