The Belgian city where the Big Bang theory was born

In Leuven, a new festival celebrates the local priest who first proposed a revolutionary “day without yesterday.”

Published 23 Nov 2021, 12:13 GMT
Historic Leuven
The historic city of Leuven, Belgium, is a hub of scientific learning and home to the 15th-century university where the Big Bang theory was formulated in 1931.
Photograph by Scott Wilson, Alamy Stock Photo

Florence, London, and Prague—with their planetaria, astronomical clocks, and halls of learning—all attract travellers who like to geek out on astronomy and the origins of time.

But one such city brimming with scientific discovery and sparkling moments of thought remains neglected: Leuven, Belgium. This university town is where in 1931 Father Georges Lemaître, a little-known Belgian Catholic priest, produced his innovative hypothesis about the beginnings of the universe.

To put it another way, Leuven is where the Big Bang theory was first conceived. Or, as Lemaître called his concept at the time, “the day without yesterday.” Yet, the scientist’s influence as the “Father of the Big Bang” is only recently being widely celebrated.

Galvanising Leuven’s renewed interest in Lemaître today is this winter’s BANG! City Festival, running now through January 30, 2022. For the first time, the city is displaying rarely seen archival material from the scholar’s life, as well as staging exhibitions and events bridging the worlds of conceptual art and concrete science, at city venues such as the M Leuven museum.

Father of the Big Bang

Back in the 1930s, Lemaître’s theory was so wild and out-of-the-box that many of his contemporaries, including Albert Einstein, spurned his premise that the universe was expanding. At the time, the shock-haired theoretical physicist was said to have told him: “Your maths is correct, but your physics is abominable.”

Georges Lemaître (right) meets with Albert Einstein at Caltech in Pasadena, California, in 1933.
Photograph by of Archives of the Catholic University of Louvain, National Geographic

Born in 1894 in Charleroi, Belgium, Lemaître first trained as a civil engineer before pursuing mathematics at the Catholic University of Leuven (known today as KU Leuven), where he eventually became a professor. While identifying and refining a connection between Einstein’s theory of relativity and the universe’s embryonic expansion, the staunch Catholic also studied and prepared for the diocesan priesthood. Throughout his life, he explored the profound tensions at the intersection of science and spirituality.

His connection to the church became so important that Lemaître was chosen by Pope Pius XI to be a member of the Vatican City’s Pontifical Academy of Sciences, of which he later became president in 1960.

“Lemaître is one of the great forgotten men of science, both nationally and internationally,” says Thomas Hertog, a renowned Belgian cosmologist at KU Leuven, who worked on evolving the Big Bang theory with Stephen Hawking for 20 years.

Students study in the library at KU Leuven, one of the oldest universities in Europe, founded in 1425.
Photograph by Karl Bruninx

As Hertog explains, the priest’s story is one that was neglected because Lemaître was never interested in grandstanding or “building worlds around ideas.”

Indeed, Lemaître’s ground-breaking thesis, titled “The Beginning of the World from the Point of View of Quantum Theory,” ran a mere 457 words in its English version, and was published as a letter in the British weekly journal Nature. 

“It’s funny, really, because I didn’t hear a single thing about Lemaître when I was a student in Leuven in the 1990s. Not many people in Belgium did. Stephen [Hawking] didn’t know of him either, and it was only when I returned to Leuven as a professor that I discovered his story,” Hertog says.

Looking for Lemaître

Lemaître is such a low-key presence in the city that travellers need to know where to look. His sculpted bronze bust, with wiry spectacles and Roman collar, is now mounted on a plinth in the courtyard of the College van Premonstreit, which once housed the Physics Institute of the Catholic University of Leuven.

Within the confines of the 600-year-old KU Leuven, at the southern end of the old town, another highlight is Lemaître’s living and working quarters in Heilige-Geestcollege (Holy Ghost College). Here, in 1958, he proudly carried one of the first computers in Belgium into his attic to immerse himself in another new world—computational calculations.

Cafés, such as Oude Markt pictured here, dot Leuven’s historic city center.
Photograph by Sergi Reboredo, Alamy Stock Photo
Visitors explore an exhibit at KU Leuven’s library. The university is known for its focus on the sciences.
Photograph by Karl Bruninx
A visitor participates in one of many high-tech exhibits at Health House, in Leuven. A joint project by several local entities, including KU Leuven and the city of Leuven, Health House offers immersive exhibits that explore the future of healthcare.
Photograph by Roelof Pantjes, Health House

Religion remained a constant for Lemaître, and he served mass at St. Peter’s Church, which maintains its air of solemnity a world away from the nearby Oude Markt. This convivial hub, packed with 50-plus pubs today, serves straw-coloured Stella Artois pilsner, which was first brewed in the city in 1926.

Travellers can also find the scholar in neighbouring university town Louvain-la-Neuve. Here his statue poses at the Catholic University of Louvain’s Place des Sciences, with chalk in hand in front of a copper blackboard etched with a swoosh of atoms.

To travel between the two statues, the 21-mile-long Big Bang Route cycle path is marked by QR-coded signposts, revealing Lemaître’s story and creating a symbolic union between the two university towns where he lectured.

(Love science? Here are a few more mind-expanding destinations.)

Leuven’s legacy of innovation

It’s tempting, says Mohamed Ridouani, mayor of Leuven, to see this thread of technological curiosity and scientific brilliance running throughout the city, almost as lifeblood.

“The key word is innovation, and since the Middle Ages, Leuven has been a safe place for scientists to express their ideas freely,” Ridouani says. “There are 100,000 people living here, but more than 60,000 students. That’s a great framework in which to stimulate imagination.”

The city has long fostered boundary-pushing scientists. Among the erudite scholars are anatomist Andreas Vesalius, who produced the first complete account of the human body in the 16th century. Then there is cartographer Gerardus Mercator, whose work was influential in the development of GPS navigation, and Jean-Pierre Minckelers, who invented illuminating gas to light the world’s great cities for the first time.

The latest polymath, says Ridouani, is Professor Hertog himself, whose in-progress quantum theory builds on Lemaître’s 90-year-old breakthrough. The abstract—“to not hit the origins of time, but to lose the laws of physics itself,” says Hertog—is enough to short-circuit any traveler’s thoughts.

This, ultimately, is the brilliance of Leuven: It nurtures geniuses who go on to illuminate the universe.

Mike MacEacheran is an Edinburgh-based travel writer. Follow him on Twitter.

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