I found a paper: 'A New Method of Finding the Distribution of Prime Number', saying

We stack discs and annuluses with certain rules then turn on the light to illuminate. The projection of annuluses corresponds prime number,and the projection of discs corresponds composite number.

See: http://en.cnki.com.cn/Article_en/CJFDTOTAL-HNKX201201010.htm

Are there other physics methods for number theory?

**Edit:** Answers and comments here and to the corresponding meta question have shown that the answer is yes, and much broader and more recent than the sieve of Eratosthenes. Also, a more informative link to the above paper is
http://wenku.baidu.com/view/1d602350be23482fb4da4cc6.html?re=view