On 20 July 1952, Albert Einstein wrote a letter to the director of the Büdingen Castle Museum (Hesse), about his second visit to the town in June 1952. The exact date of his visit was not known. A personal communication with Helmut Lang, a German living in Canada who claimed to be the grandson of Einstein's lost daughter, Marta Maric, suggests that the visit was not to the Büdingen Castle Museum but rather to search for Marta, Einstein's lost daughter from his first marriage. According to Helmut, around the same time as in Büdingen, two Americans were also encountered in the town of Bietingen, who wandered around the village for a few days looking for Einstein's missing daughter. Helmut lived with his grandmother in Bietingen from his birth in 1956 until 1974. He learned the reason for the strange visit and the true story of his grandmother's origin from her. This article explores why our interpretation of the past can sometimes revise history.

In May 1901, Einstein arranged a rendezvous with Mileva Maric at Lake Como in northern Italy, and together they travelled from there to Switzerland. Einstein's first child was conceived on this trip. Mileva wanted the baby to be a girl and proposed the name 'Lieserl', a diminutive form of Elizabeth. Einstein wanted a boy, so he proposed the name of the baby boy as 'Hanserl'. In his letters, he would talk of how, after the birth, he and Mileva could go back to being undisturbed by the world and continue her study. In July 1901, Mileva failed her examination for the second time. A few months later, she went to stay at a village close to Schaffhausen, Switzerland, where Einstein was working as a private tutor, but he seemed to visit her little and sometimes cancelled visits with the excuse that he didn't have enough money to make the journey.

Lieserl, a baby girl (later known as Marta Maric), was born in late January 1902, probably in or somewhere close to Mileva's hometown of Novi Sad (then in the kingdom of Hungary, today in Serbia). Einstein and Mileva were still an unmarried couple. Einstein wrote to Mileva 'It has really turned out to be a Lieserl, as you wished; is she healthy and does she cry properly? What kind of little eyes does she have? Which of us does she resemble more?... I love her so much and don't even know her yet. Even so, he didn't visit his newborn. In his letter, Einstein also talked about Mileva's study and how she went back to being undisturbed by the world and focused on her study.

In June 1902, Einstein was appointed as a Patent Office Clerk. But he was unlikely to survive the probationary period if he showed up with an illegitimate child. He, therefore, kept his daughter's news secret from all his friends. Mileva returned to Switzerland sometime in 1902 without the child. Shortly before Lieserl's first birthday, Mileva and Einstein were married on January 6, 1903, in Bern, after Einstein's father, Hermann Einstein, had given his consent on his deathbed - he died on October 10, 1902. In August 1903, Mileva returned to Novi Sad, where she reported that their daughter had survived an attack of scarlet fever. In response, Einstein asked how Lieserl was registered and urged Mileva to ensure that no difficulties would later befall the child. History suggests that no evidence of registration has been found. The letter of mid-September 1903, is the last known written communication about Lieserl by Mileva.

There have been numerous hypotheses about Lieserl's fate, and no recorded name or corroborating documentation of Lieserl's life has ever been found. One possibility is that the child was adopted by somebody else. One of the reasons for giving his daughter up for adoption emerges from a letter Einstein wrote 20 years later to his friend Paul Ehrenfest. Ehrenfest intended to place his son Vassily, who had Down syndrome, in a nursing home. Einstein encouraged him, saying: "Valuable people must not be sacrificed to hopeless causes" (Armin Hermann, "Einstein - A Biography," p. 120). The existence of the daughter only became public through the historian and the associate editor of the Collected Papers of Einstein, Robert Schulmann, who tracked down the letters of the young couple after Mileva's death. Marta was likely given away at the insistence of her father, Albert Einstein, but the documents of an adoption have not been found.

History suggests that Pauline Einstein, the mother of Albert Einstein, who found "this Miss Maric... utterly antipathy," did not want to abandon her granddaughter to her fate in Novi Sad, according to Helmut Lang. She sent a trusted person with a carriage to Novi Sad to bring Lieserl (known as the first daughter of Albert Einstein) back to Germany. According to Helmut, she was taken to Nordrach near Oberhamersbach in the Black Forest in December 1903. Due to the snow, she was not registered with the mayor until January 1904 in Staufen. Lieserl was taken in by the family of Michael Gießler (1864-1928) in Nordrach. Mr and Mrs Gießler then registered Marta in Staufen as their child, born on January 7, 1904. This is recorded in the Staufen city records.

Pauline Einstein moved from Milan to Hechingen in Württemberg after the death of her husband, Hermann, on October 10, 1902. She lived there with her sister, Fanny, and Fanny's husband, Rudolf Einstein, another member of the large Buchau family. Rudolf was a textile manufacturer in Hechingen, and Lieserl-Marta's chosen adoptive parents, the Gießlers, lived in Oberharmersbach in the Black Forest, not far from Hechingen.

Helmut Lang mentioned that 'In 1910, the Gießlers moved to the farm, which is now a restaurant called Schau ins Land or something similar, in the Black Forest... In 1913, the Gießlers bought farms in Brunnhausen near Pfullendorf. From there, she (Marta) came to Frankfurt... that was the shock of her life, when she was told who her real father was. It must have been around 1918; I suspect I'm the only person she (Marta) told this to; she never told her children. She was always transported like a cow, she said... from one day to the next, a carriage would arrive and load her up without much explanation. And she was taken to Frankfurt... There, she learned to cook (at the Hotel Prestige), etc., and was with the domestics... and they explained to her, under oath-she must never tell anyone-that Albert Einstein was her father and that her parents had taken her to adoption. According to Helmut, Einstein was aware of Lieserl's whereabouts. Helmut mentioned that, "He (Albert) knew through his friends in Tel Aviv, people quite high up in politics...and about the Prestige Hotel, where she (Marta) ended up at the end of the First World War."

In 1976, while working as a gardener in Pinneberg, Germany, Helmut visited Israel with a group of young gardeners as part of a German-Israeli youth exchange programme. During this trip, he was addressed as Jewish and asked about his grandmother by German-speaking Israelis. When he mentioned the place names Brunnhausen and Bietingen, the person asking was certain: "That's her," namely, Einstein's daughter. Helmut suspects that the descendants of the Frankfurt hotel owners brought the knowledge of Marta with them. In 1928, Marta Gießler-Maric returned to Brunnhausen near Pfullendorf, presumably because the hotel owners emigrated to Israel at that time. From Brunnhausen, Marta went to Bietingen, where she married the gardener Ernst Zolg. Pauline Einstein had died in Berlin in 1920; Albert Einstein was at the height of his fame. He likely heard that Marta had moved to Bietingen. The wedding announcement of Marta and Ernst Zolg was published in Bietingen Pentecost in 1928.

Bietingen is now a district of Gottmadingen near Konstanz. Marta and Ernst had three children: their first son, Karl (born 1930), died in October 2012; their younger son, Heinz (born 1932), died in 1981; and their daughter, Ilse (born 1934), married Karl Lang (born May 23, 1930). She is the mother of Helmut Lang and still lives in Bietingen.

It seems likely that Albert Einstein, if he knew anything at all, only had a vague idea of where to find his daughter. Helmut Lang suggests that Albert Einstein may have only known "Bietingen" by name, perhaps as "Büdingen." Bietingen and Büdingen sound very similar when pronounced in the Swabian dialect. Thus, Einstein's supposed visit to Büdingen in Hesse in June 1952 may have been a case of mistaken identity. Helmut suspects that Albert Einstein, at that time "a bit lost and disorganised," tried to see his daughter secretly. She was, after all, very disappointed. Marta had learned in Frankfurt, at the age of sixteen, "that the bigwig, as she called him, was her father." She simply couldn't comprehend why a married couple would give up their daughter.

Marta Gießler-Maric died in 1980 in Bietingen (Gottmadingen, Hegau) at the age of 78, or 76 if one goes by her birth registration in Laufen. Albert Einstein himself concealed the existence of a daughter until his death. It wasn't until around 1985 that Robert Schulmann found evidence of Lieserl's birth. Lang believes that those at Princeton and Tel Aviv University knew perfectly well that Albert's daughter lived in Germany. "But the agreement was gentlemen keep quiet..." until, during Helmut's visit to Israel in 1976, he finally received confirmation that his grandmother's origins were known there. Helmut recounts that his grandmother often had a picture of Einstein and Mileva on the table. But she never spoke about her ancestry with her children or with the villagers. "I myself had to promise to keep it a secret", as Helmut mentioned.

The question that historians need to explore is: How credible are Helmut Lang's statements? As a child, he lived with his grandmother until he was 18 and apparently had a close, trusting relationship with her, who told him all these things. After 1945, there was actually no longer any reason for Lieserl to keep her origins a secret. Other questions are unclear, such as why Albert Einstein sent the thank-you letter of July 20, 1952, to the museum director in Büdingen, Hesse, if he wanted to remain anonymous. Why is there no similar letter to the mayor of Bietingen? Did Albert Einstein or his representatives ever meet and speak with Marta in Bietingen?

Another story is running parallel to what was mentioned above. For example, American writer Michelle Zackheim, in her book 'Einstein's Daughter: The Search for Lieserl', mentioned that Lieserl died of scarlet fever in 1903. Chris Vuille, in his book 'Einstein's Daughter: The Story of Lieserl', imagined that Lieserl became a beautiful physicist who worked for the German atomic bomb project. She was not only jews but the illegitimate daughter of Einstein. First, the Gestapo throws her mother in a concentration camp, and then a Nazi admiral plots to acquire her as his mistress. This is also a plausible story, but whether real or fictional, is a question.

The paper trail to Lieserl had been blazed, but tracing the path of the real Lieserl has proved more daunting. Rumours about her abounded but yielded no documentary evidence, only some probable conjectures. Obviously, a DNA analysis could provide certainty as to whether Marta Gießler Maric was indeed the same Lieserl, and thus whether Helmut Lang is related to Albert Einstein. Helmut Lang, for his part, would be willing to undergo such a test.

Revisiting history is essential for modern progress. As new evidence, ideas and perspectives emerge, historians constantly re-evaluate the past. In that way one can contextualise present challenges and correct past historical evidence. Hope in this case, time will tell the truth.

Dr Konrad Kleinknecht, retired academic based in Munich, Germany and Dr Kanan Purkayastha, a retired academic, advisor and science writer based in the UK