The S&P 500 is barreling toward record highs. The Fed will decide if it gets there.

• The S&P 500 has gained about 20% in 2023, and it's nearing all-time highs. 
• For stocks to keep momentum, experts say economic data needs to convince the Fed not to raise rates further. 
• "The way we see it, the Fed is the market and the market is the Fed," a source said. 

The S&P 500 has a new all-time high in sight, but for stocks to break any records anytime soon, it will largely come down to the Federal Reserve.

The benchmark index has gained about 20% in 2023, and on Tuesday it hovered near 4,575. That's within spitting distance of its record closing level of 4,796.56 reached in January 2022.