Congratulations jobyts, you just discovered a problem in classical physics.jobyts said:If d is zero, won't the F be infinite?
Good question. In quantum mechanics, there is always uncertainty in position. With like-charged particles, the repulsive force will overwhelm all others, so the distance should never become zero. But with neutral or dissimilar charged particles, we have to consider further. When two dissimilar particles, (take proton and electron) are put together, you get an atom of hydrogen. The force of gravity cannot be infinite because the atom can be ionized (pulling the electron away). I would speculate that the uncertainty in position of the electron keeps the distance non-zero. I don't think two neutral particles (two neutrons) can occupy the same space because they are fermions, and thus obey the Pauli exclusion principle.jobyts said:is there a lower limit to d between two molecules/atoms
That's wouldn't be necessary, nor asuccessful endeavor, without a theory of quantum gravity. It would be sufficient, to eliminate infinites, that mass density be finite.Congratulations jobyts, you just discovered a problem in classical physics. When distances are very small (approaching zero in this case), you have to use quantum mechanics.
Good point, Phrak.Phrak said:It would be sufficient, to eliminate infinites, that mass density be finite.
The singularity in a black hole? :)Phrak said:I don't know of any infinitely dense masses.
I missed that one. (But is the map the territory?)Good point, Phrak.
Have the mass density of the fundamental particles been measured?
I have seen fundamental particles treated as point-like particles of infinite density.
I suspect this is not how they really are, and that they should have finite density.
Also, it would be interesting to find out wether the charge density looks like the mass density (for particles that have charge).
The singularity in a black hole? :)