(click image to see entire strip)
Having just purchased the handsomely-discounted complete three-volume set of Calvin and Hobbes (on Amazon.com for $67!), I've been setting aside some time every day to read a couple of pages. At the rate I'm going I suppose I'll be finished some time next year. (BTW, you can view the entire collection here in chronological order.)
The cartoon above was part of the few I skimmed this morning a short while after having breakfast. The cartoon was still on the mind later in the day when I came to a shocking realization that gravity, the force that keeps us mere mortals firmly planted on terra firma is also responsible for that Calvin losing his balloon, for that blimp soaring overhead, and keeping watergoing vessels afloat. Gravity is not arbitrary in that sense that it only applies to certain bodies, but not all.
The revelation of course is intuitive-- the relative density of interacting bodies is the key to deciding via gravitational force which objects will force their way towards other bodies of mass, upsetting and forcing aside less dense materials in the process.
The balloon thus floats away from Calvin because denser molecules of air are pushing to occupy the space that less dense gases dare occupy hidden within their rubber spheroids.
The next step from there is quite unclear to me; yet if you have a rigid, yet lightweight balloon 'filled' with vacuum, I'm supposing that it will float away from earth so long that the density of the air that displaces the entire volume of the balloon exceeds the density of the material comprising the skin of the balloon.
Better yet, if we fill that balloon with anti-matter, or 'negmatter' as Robert L. Forward calls it, we should have ourselves a true anti-gravity device, not one that simply takes advantage of relative density in a gravitational field.