# Why are massive particles clocks? Or are they not?

I recently came across a public lecture "Dark matter decay?" by Sir Roger Penrose. In his lecture he states that the two equations $$E=mc^2$$ and $$E=h\nu$$ can be combined to form a formula for the frequency $$\nu=mc^2/h$$ He also states that "massive particles are clocks". I didn't quite understand this statement. I understand the derivation but why does this equation show that "massive particles are clocks". What is the concept behind this statement?

• Possibly relevant. Seconding the request for a link to the lecture. – rob Jul 3 at 20:21
• – eeqesri Jul 3 at 20:26
• @user139383: When someone requests clarification or further information about a question, it's better to provide it by editing the question rather than in a comment. It saves readers the need to read the entire comment thread to find the relevant information. – Ben Crowell Jul 3 at 21:08