: how do you know that there are black holes if you haven't already seen them? How can you know that there is singularity within them if you can't go in and you've never actually seen one?

Kim, there is a lot of evidence that strongly points to the existence of a black hole. A major reason is that astronomers have noticed that they get REALLY strong readings of high energy and fast-moving objects and stars at the center of our galaxy. (Actually, recently astronomers have posited that perhaps EVERY galaxy is powered by a black hole at its center.) And if I am not mistaken, a few years ago a picture of a black hole was released in a newspaper article. The picture strongly advocated its existence since the region around the black hole had these "waves" (suggesting that the light did indeed reach us) while the center of the object was pitch black (inferring that the light did not escape). A great bestselling book to read on this topic is "Black Holes and Time Warps" by Kip S. Thorne. Please read it if you can.