“While a human may survive 80 years, these stones will last much longer, for thousands of years. And the solar system will last billions of years. Everything has a length in time as well as space. Traveling in time means traveling though this fourth dimension. To see what that means let’s do a bit of normal everyday traveling to get a feel for it…

Drive in a straight line and you’re traveling in one dimension. Turn right or left and you add the second dimension. Drive up or down a twisty mountain road and that adds height. So, that’s traveling in all three dimensions. But how in earth do we travel in time? How do we find a path through the fourth dimension?” – Into The Universe With Stephen Hawking

This video belongs to Discovery Communications and is being used for educational purposes only.