physicsElapsed : number
The physics update delta, in fractional seconds. This should be used as an applicable multiplier by all logic update steps (eg. preUpdate/postUpdate/update)to ensure consistent game timing. Game/logic timing can drift from real-world time if the systemis unable to consistently maintain the desired FPS. With fixed-step updates this is normally equivalent to 1.0 / desiredFps.
Source code: time/Time.js (Line 112)