I'm not sure where to put this question, but relativity sounds about right. Suppose all human race were blind and had no idea that em radiation even exists; suppose we "saw" with echolocation. How does this now effect relativity? Simultaneity is now heavily skewed because now the speed that information comes to us is very much smaller. Does the maximum speed, c, change? obviously not, but I don't know enough about relativity to prove why.