Many people think the fourth dimension is simply time, and for some astronomical equations, it is.
Einstein used time as a fourth dimension to describe a coordinate system called space-time. In Einstein's Theories of Relativity, time helps us understand the three-dimensional experience of gravity. But time is not a true spatial dimension like the three we're familiar with. In this way, time merely serves as a yardstick for our personal experiences and our laws of physics. To assist you in imagining space curved in four dimensions, pay a visit to Flatland, a two-dimensional world full of square, triangular, and circular beings.