Inertia has never been understood, it has just been assumed that “Things keep going in a straight line, unless you push on them”, but why? Quantised inertia (QI) explains why.

This diagram shows an object (the black circle) accelerating to the left. Quantum mechanics states that all accelerated objects see a warm bath of thermal (random) radiation called Unruh radiation (orange) that has now been observed at CERN (Lynch et al., 2021). Relativity states that information from the far right will never catch up to the object since it is limited to the speed of light (c) (the black area to the right). The new assumption of quantised inertia (QI) is that the object & horizon (edge of the black) damp the Unruh radiation between them, as in the Casimir effect (the blue area) so more radiation pushes the object from the left than the right – this model predicts inertia (McCulloch, 2013).

This is how QI gets rid of the need for the gravitational constant G. The lower the acceleration, the longer the Unruh waves. Physics must act to make sure that the length of the Unruh waves is less than the cosmic diameter, so in any volume there must be at least enough gravity to keep the acceleration above the minimum acceleration, so

GM/r^2 >(2c^2)/Θ

Since Θ=2r and we’ll assume it is on the threshold, then

G=(c^2 Θ)/2M

This relation has long been known to work (try putting numbers in). Now quantised inertia explains it. Since we know the speed of light, c, the cosmic size Θ (to 10%) and the cosmic mass, to within a factor of 10, from counting galaxies, we can calculate G and replace G in all the equations with the right hand side above. This new physics also predicts that G varies in time, as Θ increases. So, next time someone mentions the gravitational constant, tell them it isn't, and furthermore that it is not needed at all!

**References**

McCulloch, M.E., 2013. Inertia from an asymmetric Casimir effect. EPL, 101, 59001. Link

McCulloch, M.E., 2017. Galaxy rotations from quantised inertia and visible matter only. Astro. Sp. Sci., 362,149. Link

Lynch, M.H., et al, 2021. Experimental observations of acceleration-induced thermality. Phys. Rev. D., 104, 025015. Link