‘Stunningly beautiful and amazingly simple’ — Albert Einstein to Ludwig Hopf on developing his theory of general relativity

In February 1912, Albert Einstein was a month shy of his 33rd birthday. He’d been a professor of theoretical physics at Prague’s Charles University for less than a year, but was held in high esteem by his peers because of the four papers he had published in 1905, while working for the Swiss Federal Patent Office. Produced in the year that came to be known as Einstein’s annus mirabilis, they fundamentally revolutionised how space, time, mass and energy were understood. The third in the sequence established that the speed of light is constant for all observers, a theory called ‘special relativity’. The fourth extended this idea to state that mass and energy are interchangeable, introducing the world’s most famous equation: E = mc².

Ever since then, in the back of his mind, Einstein had been ruminating on the possibility that special relativity could be developed into something much bigger — a theory that incorporated gravity. In February 1912, he had his eureka moment. Einstein quickly fired off a letter to his former assistant, Ludwig Hopf. In rows of neat cursive script, he describes his ‘stunningly beautiful and amazingly simple’ discovery — the earliest surviving evidence for his formulation of the theory of general relativity.

Five weeks later, Einstein wrote another letter, this time to his close friend and scientific sounding board Michele Besso. Over seven pages, he guides Besso through his new concept in great detail. Einstein’s excitement is palpable: ‘I was working in a frenzy,’ he says, adding that while ‘each step is devilishly difficult’, the results are ‘staggering’.

Throughout his career, Einstein would remain notoriously tight-lipped about the specifics of where his ideas came from, and correspondence outlining his development of relativity is incredibly rare. Together, these letters paint a sublime picture of the 20th century’s most important scientist at the precise moment of a critical breakthrough.

In June 1913, Einstein and the Swiss mathematician Marcel Grossmann co-published a paper that comprehensively outlined general relativity for the first time.

That same month, Michele Besso came to stay with Einstein in Zurich. The pair sat together day after day and tested Einstein’s theory to the limits, producing more than 50 pages of dense calculations. In particular, they wanted to establish if it could account for the known flaw in Newtonian physics, which didn’t accurately predict the movement of the planet Mercury. Their results were inconclusive — the theory wasn’t yet complete.

The following year, Einstein moved to Germany to take up prestigious academic positions at the Friedrich Wilhelm University of Berlin, the Prussian Academy of Sciences and the planned Kaiser Wilhelm Institute for Physics. These new roles meant that he was supported by a salary but not burdened with lecturing, so he was free to double down on his efforts to fix his theory.

In November 1915, the answer came to him in a flash. Over four papers published in as many weeks, he outlined updated equations for the theory of general relativity, using his former calculations established with Besso to predict Mercury’s orbit correctly.

The Einstein-Besso Manuscript sold at Christie’s in Paris in 2021, fetching more than €11.6 million. The 16 pages of notes offered as Lot 55 on 8 July — some hastily recorded on graph paper, reused envelopes and old letters — are the drafts of Besso’s contribution to a document that led to one of the most fundamental breakthroughs in modern physics.

In 1918, the German theoretical physicist Max Planck was awarded the Nobel Prize in Physics for his discovery that energy travels in packets, rather than a smooth, continuous wave. Planck’s transformational finding earned him the epithet ‘the founding father of quantum theory’.

In October the following year, Planck penned a letter to Ludwik Silberstein, an American-Polish physicist who had published his own theory of relativity five years earlier. In the letter, Planck responds to Silberstein’s account of a meeting of the British Association for the Advancement of Science, where Arthur Eddington, a professor at Cambridge, had championed Einstein’s theory of general relativity.

In order to test Einstein’s idea that gravity would bend light when it passed by a massive body, Eddington had travelled to the island of Príncipe, off the west coast of Africa, to observe a rare solar eclipse. His observations, he revealed, proved Einstein right.

‘What do I think of Einstein’s theory of gravity?’ Planck wrote to Silberstein. ‘Unfortunately, I cannot say in a single word. Initially, I found this theory very unappealing, especially because of the limiting conditions at infinity, even though I found no logical contradiction in it.

‘Over time, however, I grew accustomed to the point of view of this theory and became increasingly receptive to the beauty of the roundedness it offers. Even my concerns about the limiting conditions at infinity faded when Einstein introduced the hypothesis that space is closed in itself, and therefore has no boundaries at all… and that is precisely why your report on the results of the review of the various measurements is so extraordinarily interesting to me.’

Planck goes on to commend Silberstein for working towards the resumption of international scientific exchange, which had been disrupted by the outbreak of the First World War, calling it ‘a truly noble aim’.

Louis Victor Pierre Raymond, 7th Duc de Broglie, was a French aristocrat and theoretical physicist. In 1929, he won the Nobel Prize in Physics for his contributions to quantum mechanics, building on Einstein’s and Planck’s work on light to suggest that all matter can move with wave-like properties.

De Broglie had published the idea as part of his PhD thesis in 1924. Three years later, he authored this manuscript, which proposes a five-dimensional model for reconciling his ideas about wave mechanics with Einstein’s theory of general relativity. His ultimate aim was to discover a new set of equations that could incorporate the missing element — electromagnetism — into Einstein’s theory of general relativity.

At the same time, Einstein, now established as the most famous scientist the world had ever known, began to ask the same question: could he make a new ‘theory of everything’? He called this mission ‘unified field theory’, and it became the holy grail he pursued for the rest of his life.

After a failed first attempt, his second was scuttled by the rise of the Third Reich, which forced him into exile in the United States. There, he imagined the universe in the five dimensions Brogile suggested in this paper, laying down new hypotheses that are still being explored today. Ultimately, however, Einstein’s quest for a theory of everything was unsuccessful, and it remains elusive.

The Austrian theoretical physicist Erwin Schrödinger won the 1933 Nobel Prize in Physics for ‘the discovery of new productive forms of atomic theory’. He was a great admirer of Einstein; the two men were colleagues at the Friedrich Wilhelm University of Berlin from 1927, and remained friends for many years. Their intense philosophical discussions famously inspired the 1935 thought experiment known as ‘Schrödinger’s Cat’, and Einstein once told him, ‘You are the only person with whom I am actually willing to come to terms.’

In 1943, Schrödinger began publishing papers on his own unified field theory. War-time blockades meant that Einstein was initially unaware of his work, but their renewed contact in 1946 led to a flurry of correspondence.

In January that year, Einstein sent Schrödinger two unpublished papers relating to his own unified field work. This manuscript, sent to Einstein in May 1946, formed part of Schrödinger’s response.

It comprises several sheets of highly technical mathematics, as well as an apology in advance for any errors in his calculations. By the last page, however, Schrödinger essentially admits defeat in his search for unification. ‘I have been trying for days,’ he writes. ‘Here I stand, I cannot do any better, God help me!’

Despite this, the pair’s bond was fractured the following year, when Schrödinger declared victory over Einstein in the race to discover a true and accurate unified theory of everything. Einstein pointed out several fatal flaws in his formula, but, undeterred, Schrödinger held a press conference to announce his breakthrough.

Publicly, Einstein offered a measured response, stating that Schrödinger’s theory offered ‘no special advantages over the theoretical possibilities known before’. In private, however, he didn’t take Schrödinger’s self-aggrandising well, and broke off their friendship. Schrödinger apologised to Einstein shortly afterwards, but they remained estranged. Not long after, Schrödinger gave up his work on unified field theory and reportedly never collaborated with another physicist again.

Today, Schrödinger’s papers are mostly housed in the Austrian Central Library for Physics at the University of Vienna, and the Research Institute Brenner-Archives in Innsbruck. His autograph letters remain rare in private hands, and this unpublished and formally unstudied manuscript appears to be the most significant ever offered for sale.

Valuable Books and Manuscripts including Cartography is on view until 7 July 2026 at Christie’s in London

Explore the London Classic Week sales

Related authors: Albert Einstein