Physics

A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because the matter has been squeezed into a tiny space. This can happen when a star is dying. Because no light can get out, people can't see black holes.

A hologram is a physical structure that uses light diffraction to make an image, the image can appear to be three dimensional. Holography is the science and practice of making holograms. Typically, a hologram is a photographic recording of a light field, rather than an image formed by a lens.