A 1916 letter from Albert Einstein to his closest friend, Michele Besso, made £293,000 ($376,866) in a sale of books and manuscripts at Christie’s today.

That’s more than three times its £90,000 ($115,803) estimate, demonstrating the continued demand for quality Einstein documents.

Einstein and Besso became friends as students in Zurich 

It’s a detailed explanation of one of Einstein’s biggest mistakes, the so-called cosmological constant.

Up until 1929, when Edwin Hubble discovered the universe was expanding, stars were believed to remain static.

For his general theory of relativity to hold together, Einstein had to explain why they wouldn’t be attracted and destroyed by the gravitational pull of other stars.

The cosmological constant was what he called the repulsive force that had to exist as a result.

Years later he would describe this as his “biggest blunder”.

His calculations gave evidence for universal expansion, but he had missed it.

At the end of the letter Einstein returns “back to earth, which is only so ugly because we see and experience it too closely”.

The letter is written from Berlin, where Einstein had moved to further his career.

He asks after Besso and his family in Zurich and looks forward to visiting them soon.

Another letter from Einstein to Besso on the subject of “Time’s Arrow” sold for £100,000 ($128,670).

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