As a Christian scientist, Dr. Bohlin is open to examining the theories of both young-earth and old-earth scientists to explain what we can observe today. The Grand Canyon provides an excellent venue to consider the theories of both groups on how the geological layers were formed and when this occured.
If the door is already attached, swing it open and closed to see how much inertia it has. An average hollow-core door usually weighs around 25 to 30 pounds, so if you can lift or swing the door with minimal effort, it is probably hollow-core. Solid-core doors are usually 25 to 30 pounds heavier than their hollow counterparts, so if the door has some heft to it, it's probably solid-core.
For that application, a 'solid' core door is as strong as your hinges. However, the door skins (1/8) on a 'hollow' core door won't hold a screw for anything heavier then an 8x10 picture... It would work on a hollow core door if you used a 1x2 across the top of the door and screwed each end into the 'solid' side stiles (there is a 1 1/2 solid wood frame around the edges of a 'hollow' core door), then screwed the CD racks to the 1x2's...