In a universe with the same physical laws, but which is mostly water with little bubbles in it, do the...

physics/bubbles Added material

Problem

In a universe with the same physical laws, but which is mostly water
with little bubbles in it, do the bubbles attract, repel, or what?

Show solution

A bubble should produce a gravitational field that is the negative of
that produced by an equal volume of water in an empty universe.  This is
because a point in space would be affected only by the water in the
symmetric image of the bubble with respect to that point.  The effect
on another bubble in that field would be to attract that bubble since
it would be pushing the water around it away.  Therefore, the bubbles
should attract.

Additional material

[ Editor: A correction to the archive solution, posted as "Physics
Archive Error: bubble": ]

The first part of the answer is correct: an empty bubble in a universe
that's mostly matter will act as if it were a negative-matter bubble
in a universe that's mostly empty.  But the effect on this bubble will
be that it will expand, since it will push the water around it away.
When there are two bubbles, they will both expand AND BOTH MOVE AWAY
FROM EACH OTHER.  However, the bubbles expand faster than they move
away from each other, so eventually the edges of the two bubbles will
meet to form a bigger bubble.

-- Lord Clump <lordclump@aol.com>