Baku, June 27, AZERTAC

Albert Einstein’s theory of relativity may be too complicated for some to understand. But the expected price of a letter the scientist wrote makes a great deal of sense.

A missive that Einstein sent to President Franklin D. Roosevelt in 1939 will hit Christie’s auction block in September, where it’s expected to hammer down for up to $6 million, according to Yahoo. In the letter, the scientist warns Roosevelt about the possibility of Germany creating an atomic bomb. In response, the president formed a committee that would become the precursor to the Manhattan Project, The Wall Street Journal noted.

“Roosevelt wouldn’t have understood the science right away, but he would’ve trusted the sender,” William Harris, the director of the Franklin D. Roosevelt Presidential Library and Museum, told the WSJ.

Harris’s institution actually has the original letter than Einstein sent to Roosevelt. The one coming up for sale at Christie’s is a second, shorter missive that Einstein’s friend and fellow scientist Leo Szilard kept in his possession until he died. Szilard had helped Einstein write the letter to FDR while the two were at a cabin on Long Island’s North Shore, The Wall Street Journal wrote.

After Szilard died in 1964, his heirs sold the letter, and it eventually ended up in the hands of Malcolm S. Forbes. The publisher and collector then auctioned off the letter in 2002, when it was snatched up by the Microsoft cofounder Paul Allen for $2.1 million.

“He undoubtedly knew it was one of the most important documents in the history of the 20th century, and that’s not the kind of thing you just hang in your office,” Marc Porter, the chairman of Christie’s Americas, told the WSJ. Rather, Porter believes that Allen kept the letter safe, somewhere where it wouldn’t be affected by sunlight.

Christie’s is bringing the Einstein letter to auction as part of a larger sale of Allen’s belongings, which is being split among three separate auctions. Other notable pieces include a computer from 1971 ($30,000 to $50,000) and a Gemini spacesuit that belonged to the astronaut Ed White ($80,000 to $120,000). And while the Einstein missive may break the record for a letter written by the scientist—which was set in 2018, when one of his notes sold for $2.8 million—it’s unlikely to achieve the $13 million that a theory-of-relativity record hammered down for in 2021.

Even still, very few people can say that they have such an important piece of scientific history.