Why do gravitons travel slightly slower than photons (99%) and why do neutrinos travel slightly faster than photons (101%)? What is an intuitive interpretation of why a joule is a gram multiplied by the speed of light squared? For a layman like me, this seems very unintuitive - first of all what role the speed of light plays in this relationship and why it's squared (m^2/s^2). I also see the speed of light to some power N>2 in other physics formulas. How can I intuitively interpret this speed of light to some power?