Not sure if this is a scientefic question but i am sure there must be a formula of some sort.Who is buying all the shares when the stock market crashes?

So there are 100 shares in total (the whole stock exchange) and they are worth $10 each, sudenly some sells there 50% steak at $9 the market panics and the value drops to $6 then someone sells there 30% and the price drops to $2 and the last 20% is sold for $1 and the market collapses.........who buys all these shares?