what happens when share prices keep going up?

Sometimes when a stock gets pretty high and volume slows down the company will split the stock. In a 2 for 1 split each shareholder has twice the number of shares at half the price. So, its a zero sum gain. Thats a forward split. Sometimes companies with low priced stock may do a reverse split. Which is the exact opposite. They have half the shares, or whatever the split ratio is, at twice the price. This is usually done to maintain listing on an exchange and make the stock more attractive to institutional investors like mutual funds.