SpaceX in your index fund, explained

AUUUUUGH | Image: Cath Virginia / The Verge, Getty Images Index funds are touted as one of the safest ways to invest. Rather than picking and choosing individual stocks, index funds let you bet on the market as a whole. So what happens when a company like SpaceX - a giant gamble , and, in my opinion, terribly overpriced - is fast-tracked into the Nasdaq-100?