We had the pleasure of hosting Professor Alexander Plakhov from the University of Aveiro (Portugal) for a fascinating lecture titled “Invisible Bodies with Specular Surface” today. The event was organized within the framework of the FeLow-D ERA-CHAIR project and drew a diverse audience.
In his engaging talk, Professor Plakhov introduced the audience to a remarkable intersection of mathematics and optics, exploring how mirror-like surfaces can be used to render physical bodies invisible from certain directions or points. Far from science fiction, the lecture was grounded in the principles of geometrical optics and presented through the lens of rigorous mathematical reasoning.
The core idea revolved around modeling the movement of light rays as billiard trajectories in the exterior of mirror-surfaced bodies. Professor Plakhov presented several examples of shapes that become invisible in one, two, or three specific directions, as well as from particular observation points. These intriguing constructions challenge our intuitive understanding of visibility and physical space.
Importantly, he also demonstrated that complete invisibility in all directions is mathematically impossible—an elegant result that sets clear boundaries on what can be achieved through purely specular reflection. Yet, the question of how many directions or points of invisibility are possible remains an open and stimulating problem for further research.
The lecture concluded with practical insights into the design of retroreflectors—devices that reverse the path of incoming light using reflective surfaces. These devices have significant real-world applications, from road safety to optical communication, and provided a compelling connection between theory and technology.
We are grateful to Professor Plakhov for sharing his expertise and for inspiring such thoughtful discussion. Today’s lecture was a testament to the power of mathematical inquiry and its ability to illuminate even the most elusive corners of physical reality.
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