Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

What is the “point” (purpose) of the S&P 500?
I hate to point to Wikipedia as an answer, but it does describe exactly what you are looking for... The S&P 500 is a free-float   capitalization-weighted index   published since 1957 of the prices of   500 large-cap common stocks actively   traded in the United States. The   stocks included in the S&P 500 are   those of large publicly held companies   that trade on either of the two   largest American stock market   exchanges; the New York Stock Exchange   and the NASDAQ. The components of the S&P 500 are   selected by committee... The committee   selects the companies in the S&P 500   so they are representative of the   industries in the United States   economy. In addition, companies that   do not trade publicly (such as those   that are privately or mutually held)   and stocks that do not have sufficient   liquidity are not in the index. The S&P is a capitalization weighted index.  If a stock price goes up, then it comprises more of the total index.  If a stock goes down, it comprises less, and if it goes down too much, the committee will likely replace it. So to answer your question, if one stock were to suddenly skyrocket, nothing would happen beyond the fact that the index was now worth more and that particular stock would now make up a larger percentage of the S&P 500 index.