 If time is a flowing river we must think of events taking time to float down this stream, and if we say ‘time has flowed faster today than yesterday’ we are saying that the stream flowed a greater distance today than it did in the same time yesterday. That is, we are postulating a second timescale with respect to which the flow of events along the first time dimension is measured … Furthermore, just as we thought of the first time dimension as a stream, so will we want to think of the second time dimension as a stream also; now the speed of flow of the second stream is a rate of change with respect to a third time dimension, and so we can go on indefinitely postulating fresh streams without being any better satisfied.