Well, there' s a number of ways to think about what dimensions are. I hope we all know where three dimensions are, which you can say are left, right: forward, backward; up, down. And if you think about it, three, we say there are three dimensions of space. And sometimes we need three coordinates to locate some objects in space. So, you can say longitude, latitude and altitude. So if there were more dimensions, you would need more coordinates. Now of course for whatever reason we are not physiologically designed to observe those dimensions, but that doesn't mean they don't exist. One way of thinking about it is, Maybe the best way of thinking about it is the way that someone named Edwin Abbott did it in the late 19th century in a book called flatland. And he said suppose there were wo dimensional creatures living in a two dimensional universe. They would have the same trouble conceptualizing three dimensions that we have when we try to conceptualize more than three, such as four. And so, he asked questions like, "What would observers in this two dimensional universe see, say if a three dimensional object like a sphere passed through the universe?" And what this flatland universe would see would be a series of disks that grow in size and then decreased in size. In the same way that we can certainly think about a two dimensional world inside a three dimensional world, it could be that we observe three dimensions but really there are more. And if a hyper sphere say a four dimensional sphere passed through our universe.