# We can't hear the shape of drum: revisited in 3D case

## TL;DR

This paper explores the construction of 3D isospectral models, extending the concept of iso-spectral domains from 2D to 3D, and verifies their spectral equivalence through numerical methods.

## Contribution

It introduces a novel method for constructing 3D isospectral models based on reflection rules and validates their spectral properties numerically.

## Key findings

- Successfully constructed 3D isospectral models
- Validated isospectrality through numerical verification
- Extended the reflection rule concept to 3D models

## Abstract

Can one hear the shape of a drum? was proposed by Kac in 1966. The simple answer is NO as shown through the construction of iso-spectral domains. There already exists 17 families of planar domains which are non-isometric but display the same spectra of frequencies. These frequencies, deduced from the eigenvalues of the Laplacian, are determined by solving the wave equation in a domain, which is subject to Dirichlet boundary conditions. This paper revisits the serials of reflection rule inherent in the 17 families of iso-spectral domains. In accordance with the reflection rule visualized by red-blue-black, we construct real 3D isospectral models successfully. What is more, accompanying with the proof of transplantation method, we also use the numerical method to verify the isospectrality of the 3D models.