Everyone from JP Morgan Chase CEO Jamie Dimon to billionaire investor Carl Icahn has predicted a recession so far this year.

The U.S. is already in a recession according to some experts.

Musk said in May that the U.S. was likely in a recession that could last up to 18 months. The CEO of the world's richest man agrees with the idea of rising inventories at retailers as a sign of weakness in the economy.

The technical definition of a recession is a period of two consecutive quarters ofGDP contraction.

They received some evidence from one of America's central banks. It's at its website.

According to the Federal Reserve Bank of Atlanta, second-quarter GDP will decline by 1%. The tracker had predicted an increase of 1.3% in the second quarter, but that has been revised down.

If the Atlanta Fed is correct, the GDP decline in the first quarter will lead to a recession.

What determines a recession is not the same as what determines a down quarter. A recession is defined by the National Bureau of Economic Research as a decline in economic activity that lasts more than a few months.

Since World War II, every recession has included a two-quarter decline in GDP.

Multiple GDP trackers have moved into negative territory for the second quarter according to a research note written by George Saravelos. The U.S. economy may already be in a technical recession.

Saravelos argued that, for the stock market, weaker economic growth and recession fears are now the main market drivers, taking the place of inflation, which hit a four-decade high in May.

On the same day, another analyst, Guggenheim's Matt Bush, also wrote a note saying the slowing economy likely signaled the start of a recession.

The newest GDP tracker data doesn't mean that we've hit a real recession.

It is increasingly likely that the U.S. economy will contract in the first half of the century. Bill Adams, chief economist for Comerica Bank, told Fortune on Friday that unless the US starts to see job losses, this period looks more like a slump than a recession.