Why Language Models Hallucinate

Series
School of Mathematics Colloquium
Time
Thursday, October 2, 2025 - 11:00am for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Santosh Vempala – Georgia Tech – vempala@cc.gatech.eduhttps://faculty.cc.gatech.edu/~vempala/
Organizer
Harold Blum, Xiaoyu He, Julia Lindberg, Rose McCarty, John McCuan, Dmitrii Ostrovskii, and Wei Zhu

Large language models often guess when uncertain, producing plausible yet incorrect statements instead of admitting uncertainty. Such "hallucinations" persist even in state-of-the-art systems. We analyze this phenomenon from a mathematical perspective and find that the statistical pressures of current training pipelines induce hallucinations; moreover, current evaluation procedures reward guessing over acknowledging uncertainty. The talk will be fact-based, and the speaker will readily admit ignorance. 

 
This is joint work with (and mostly by) Adam Kalai.