The volume of Jupiter is mostly gas. If you increase the mass enough, at some point the higher gravity and thus higher pressure at the center causes a phase change of enough mass (from gas to liquid or liquid to solid) that the lost volume from the phase change exceeds the original volume of the added mass.
It’s like pushing a bunch of origami paper into a box until a bunch of them collapse and fall flat instead of filling the volume.
The volume of Jupiter is mostly gas. If you increase the mass enough, at some point the higher gravity and thus higher pressure at the center causes a phase change of enough mass (from gas to liquid or liquid to solid) that the lost volume from the phase change exceeds the original volume of the added mass.
It’s like pushing a bunch of origami paper into a box until a bunch of them collapse and fall flat instead of filling the volume.
My friend is silly - he was thinking of smaller as in by mass, not by volume. Thanks for explaining it to him.