How the aging put stress on the economy

There are short falls in social security? Say it ain't so!

The idea of something like social security is a great one, but it must not become a burden on the work force. If the government could in some way just invest the money that is paid in by each individual so that it can earn interest the system could work more effectively.

My father is about to retire and he told me that when he does the return on his "inestment" in social security would be roughly 5%. While this is a higher intrest than most banks will pay for a savings account, if the money was put into a mutual fund that only earns average returns it would be more along the lines of 10% intrest.

So why is it that the government can't manage the same return on the money?