The magnitude of the four-acceleration is a , meaning it remains invariant across different inertial reference frames. Mathematical Formula :
Aμ=dUμdτcap A raised to the mu power equals the fraction with numerator d cap U raised to the mu power and denominator d tau end-fraction Uμcap U raised to the mu power is the four-velocity and 4 19 - Acceleration4
is the proper time. In standard inertial coordinates, proper acceleration is the rate of change of proper velocity with respect to coordinate time. The magnitude of the four-acceleration is a ,