Recently I gave an interview to local media where I explained some basic open problems in billiard dynamics.


After a 45 min interview the reported asked me what "real life" problems can be solved using billiards...and I gave a really vague answer.


I'm looking for a precise example of a "real life" problem (besides the billiard game of course) that can be modeled using billiard dynamics.


"real life" = applied (I'm not english native speaker)



What "real life" problems can be solved using billiards?

> 
> [The
>  billiard-ball computer](https://en.wikipedia.org/wiki/Billiard-ball_computer), also known as a conservative logic
>  circuit, is an idealized model of a reversible mechanical computer
>  based on Newtonian dynamics, proposed in 1982 by Edward Fredkin and
>  Tommaso Toffoli. Instead of using electronic signals like a
>  conventional computer, it relies on the motion of spherical billiard
>  balls in a friction-free environment made of buffers against which the
>  balls bounce perfectly. It was devised to investigate the relation
>  between computation and reversible processes in physics.
> 
> 
> 


The billiard-ball computer was never realized in this form, but it played a significant role in the development of the quantum computer. Since the unitary evolution of quantum mechanics is reversible, it cannot employ the irreversible logical operations of a conventional computer. (This story is told [here](https://web.archive.org/web/20160308084641/https://www.bcs.org/upload/pdf/gsharman-141113.pdf).)




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For an altogether different application of billiard ball dynamics, to semiconductor device physics, see [Billiard model of a ballistic multiprobe conductor](https://openaccess.leidenuniv.nl/bitstream/handle/1887/3338/172_042.pdf) (1989).


