The S&P 500 index hit 5,000 for the first time ever, propelled by Wall Street's optimism the Federal Reserve is going to cut interest rates.

The index surged over 1% to hit a record high, surpassing the previous peak hit around two years ago, driven by big gains in large tech companies and by hopes about the economy.

The S&P 500 has surged this year, but most of those gains are thanks to a handful companies nicknamed "The Magnificent Seven." And that's worrying Wall Street.