 Finally, there is considerable disagreement over the significance of singularities. Many eminent physicists believe that general relativity's prediction of singular structure signals a serious deficiency in the theory: singularities are an indication that the description offered by general relativity is breaking down. Others believe that singularities represent an exciting new possibility for physicists to explore in astrophysics and cosmology, holding out the promise of physical phenomena differing so radically from any that we have yet experienced as to signal, in our attempt to observe, quantify and understand them, a profound advance in our comprehension of the physical world. 