Me and my friends were having a discussion today on what actually is the 4th dimension. Many said that it's "time". But I don't think so. Though I don't have an answer to what is actually the 4th dimension is but 'time' is definitely not the answer. Reason 1:- We cannot measure a two dimensional quantity of a one dimensional object. e.g.:- we can't measure the breadth of a line segment also we can't measure the height of a square. But we can measure the time taken by a particle moving rectilinearly to cover a certain distance. (we are measuring a 4th dimension quantity in a one dimensional motion. This doesn't seem well!). Hence "time" is definitely not the fourth dimension. Reason 2:- Time is a relative concept. But things like length used to define dimensions are well defined. What are your view's? Please reply if you have some different view's.