Is there any experimental or observational evidence that conclusively shows gravitational forces acting on mass that is less than the Planck mass? thx
No need to make it smaller. The Planck mass is 22 micrograms, so such a grain of sand would be about a tenth of a millimeter across, easily visible to the naked eye.As I said, less than the Planck mass. Let's keep dividing that grain of sand by 2.