Videos

Hot Topics: Interactions between Harmonic Analysis, Homogeneous Dynamics, and Number Theory: A Journey Through Normality

Presenter
March 7, 2025
Keywords:
  • Projection theorems
  • Unipotent flows
  • Effective equidistribution
  • Diophantine approximation
  • decoupling theory
MSC:
  • 11F66 - Langlands $L$L-functions one variable Dirichlet series and functional equations
  • 11J83 - Metric theory
  • 22E30 - Analysis on real and complex Lie groups [See also 33C80 43-XX]
  • 28A80 - Fractals [See also 37Fxx]
  • 37A17 - Homogeneous flows [See also 22Fxx]
  • 37C85 - Dynamics induced by group actions other than $\mathbb{Z}$\mathbb{Z} and $\mathbb{R}$\mathbb{R} and $\mathbb{C}$\mathbb{C} [See mainly 22Fxx and also 32M25 57R30 57Sxx]
  • 42B15 - Multipliers for harmonic analysis in several variables
  • 42B20 - Singular and oscillatory integrals (Calderón-Zygmund
  • etc.)
Abstract
They say the only normal people are the ones you don't know very well. But what about numbers? Which ones are normal, and how well do we really know them? A real number x is normal in base b if every block of digits of the same length appears in the b-adic digit expansion of x with equal limiting frequency. While the concept is easy to define, proving that specific numbers are normal often requires deep and intricate methods. The study of normal numbers connects diverse areas of mathematics, including harmonic analysis, ergodic theory, Diophantine approximation, and fractal geometry. In this talk, I will survey key results and techniques in the study of normal numbers, explore the challenges posed by long-standing open problems, and present the recent resolution of a conjecture by Kahane and Salem regarding the properties of partially normal numbers. This work draws on methods from Fourier analysis, geometric measure theory, and probabilistic number theory. Joint work with Junqiang Zhang.