I guess the question is, is there enough wealth in the world to buy all the wealth in the world? I think the answer is no. As soon as people try to move too much of their imaginary wealth the value of that wealth would wither away.
There is not enough cash to cover all the cash people have access to.
But it's odd. Obviously I get a paycheck and I can turn that into cash. Most people are like me in that way. But most wealth is not paid via a paycheck. But a company has to have actual cash on their books to pay their employees, to pay their electric bill, to pay their suppliers, to purchase real property, to acquire other companies. All that takes cash on the books or a bank that will pay cash and give the company credit. But these banks can't just offer loans on money they don't have. They have to have access to that cash in one form or another. So, I'm just wondering, does the fed have a way to meet the demand for liquid assets as it grows?
And if anyone else wants to take a crack at the hypothetic (hint, this is not a realistic scenario and has nothing to do with a billionaire paying a million dollars for a gallon of milk), if all the billionaires in the world wanted to pile their cash in their front room so they could look at it for a day, all on the same day, before putting it all back in the bank, would there be enough cash in the world to cover it?