The concept that money literally has gravity of its own, and sucks other money toward it. This is backed up by the idea of loaning money at interest (also known as usury)- wealth begets more wealth. Thus, eventually all the money will collect in a few places. Signs of this happening in America are everywhere- large corporate mergers, the Bush tax proposal, the fact that the rich are getting richer, inflation, etc.

When the money collects in a small enough area, you create a financial black hole where the money leaves the economy, causing a depression. This theory explains why circulation of money is important. Of course, I suppose that under this model, communism would be heat death....

This concept partially invented by me, and partially stolen from David Gerrold.