Naked Truth Investing: Is now a good time to invest?

This is part of a new series of columns called "The Naked Truth," by retirement expert Dan Solin. Please bring him your questions, in the comments box, and he will answer as many as he can.

This is a very common question: How do you know when to invest? Have the markets bottomed out? Or are we in for a precipitous decline?

Here is the answer: No one knows.

Here is what we do know: