Planck force is the derived unit of force resulting from the definition of the base Planck units for time, length, and mass. It is equal to the natural unit of momentum divided by the natural unit of time.
The Planck force is also associated with the equivalence of gravitational potential energy and electromagnetic energy and in this context it can be understood as the force that confines a self-gravitating mass to half its Schwarzschild radius:
where G is the gravitational constant, c is the speed of light, m is any mass and rG is half the Schwarzschild radius, rs, of the given mass. Since the dimension of force is also a ratio of energy per length, the Planck force can be calculated as energy divided by half the Schwarzschild radius:
As mentioned above, Planck force has a unique association with the Planck mass. The gravitational attractive force of two bodies of 1 Planck mass each, set apart by 1 Planck length is 1 Planck force. This unique association also manifests itself when force is calculated as any energy divided by the reduced Compton wavelength (reduced by 2π) of that same energy:
Here the force is different for every mass (for the electron, for example, the force is responsible for the Schwinger effect; see page 3 here ). It is Planck force only for the Planck mass (approximately 2.18 × 10−8 kg). This follows from the fact that the Planck length is a reduced Compton wavelength equal to half the Schwarzschild radius of the Planck mass:
which in turn follows from another relation of fundamental significance:
The Planck force appears in the Einstein field equations, describing the properties of a gravitational field surrounding any given mass:
Since 1993, various authors (De Sabbata & Sivaram, Massa, Kostro & Lange, Gibbons, Schiller) have argued that the Planck force is the maximum force value that can be observed in nature. This limit property is valid both for gravitational force and for any other type of force.
Planck force as a tension constant of the space time fabric
According to new research  Planck force might be a tension constant of the space time fabric:
where is the Estakhr tensor which is inverse of Einstein tensor. so then in a different representation of Einstein field equations : Planck force turn out to be actually "a tension constant of the space time fabric" constant.
Notes and references
- "Gravity and the Photon". HyperPhysics. Georgia State University. Retrieved 2012-09-12.
- "Planck Force is Tension of Spacetime (General Relativity & Estakhr's expression of Einstein Field Equation)". APS. American Physical Society. Retrieved 2016-10-28.