Originally posted by @dj2becker
You do not have complete certainty that the moment you drop your pen it will fall to the ground?
There is a certain tiny probability all the air molecules in a room will congeal in one corner leaving vacuum everywhere else in the room. You never know.
There is the Casimir effect that states two flat plates, say a hunk of steel 10 mm thick and a meter on a side, two of those get pushed close together. Something strange happens.
The space between the plates shields the creation and annihilation of virtual particles, shielded by the plates themselves. This is a real effect.
The net result is because of the probabilistic nature of the creation and annihilation of these particles, there is a small force, not electric, not magnetic, not gravity, that pushes the plates together.
This was first proposed as a possibility by a scientist named Casimir in 1948 but was not actually measured till modern times.
https://aphyr.com/media/pwl-2014-casimir.pdf
This is an explanation of the effect. If you can follow it.
Just showing this effect to give you an idea of the statistical nature of matter, virtual particles come and go in an unpredictable but verified way and there is a real force pushing the plates together, tiny but measurable.