New Proof Settles Decades-Old Bet About Connected Networks
According to mathematical legend, Peter Sarnak and Noga Alon made a bet about optimal graphs in the late 1980s. They’ve now both been proved wrong. The post New Proof Settles Decades-Old Bet About Connected Networks first appeared on Quanta Magazine

In the late 1980s, at a conference in Lausanne, two mathematicians named Noga Alon and Peter Sarnak found themselves locked in a friendly debate. Both were deeply engaged in the study of graphs, the mathematical structures that represent networks of nodes and edges. Their particular focus was on a peculiar type of graph known as an expander. Expanders are graphs that, despite having a relatively small number of edges, exhibit exceptional connectivity. This paradoxical property makes them invaluable in various applications, from computer networking to cryptography.
The debate between Alon and Sarnak centered on the question of what makes an expander graph optimal. They were trying to determine the conditions under which a graph would be the most efficient at balancing its size and connectivity. It was during this discussion that they made a bet, a wager that would end up being a significant part of mathematical folklore.
Over the decades that followed, the bet between Alon and Sarnak became a topic of conversation among mathematicians. It was a testament to the complexity of the problem and the passion of the two scientists involved. The bet was not just about the outcome; it was also about the journey of discovery that would unfold as mathematicians delved deeper into the intricacies of expander graphs.
Now, nearly four decades later, a new proof has emerged that settles the decades-old bet. This development has been met with excitement and curiosity within the mathematical community. The proof not only resolves the question that Alon and Sarnak posed but also sheds new light on the properties of expander graphs.
The breakthrough came from a team of mathematicians who approached the problem with a fresh perspective. By leveraging advanced techniques and building on previous research, they were able to provide a definitive answer to the question that had puzzled experts for so long. The proof has been meticulously reviewed by the mathematical community, and its validity has been widely accepted.
The implications of this new proof are far-reaching. Expander graphs have numerous applications in computer science and engineering, particularly in the design of efficient networks and algorithms. Understanding the optimal structure of these graphs is crucial for advancing these fields. The resolution of the Alon-Sarnak bet not only confirms the correctness of certain theoretical predictions but also opens up new avenues for research and innovation.
The story of the Alon-Sarnak bet is a testament to the power of curiosity and the relentless pursuit of knowledge in mathematics. It highlights the importance of interdisciplinary collaboration and the potential for breakthroughs to emerge from seemingly obscure questions. As the mathematical community continues to explore the intricacies of expander graphs, the legacy of this bet serves as a reminder of the enduring impact of intellectual challenges and the joy of discovering the unknown.
In the end, the bet between Alon and Sarnak was not just about the outcome; it was about the spirit of inquiry and the shared passion for understanding the complexities of connected networks. The new proof that has settled the bet is a celebration of this spirit and a testament to the enduring quest for knowledge in the world of mathematics.










