Science fiction fans love the possibility of other universes, even more so contemplating the possibility of being able to travel between them through exotic configurations of spacetime, notably wormholes, which are pretty much just black holes with an opening poking through the singularity.
Less well known is the equally exotic (and purely hypothetical) possibility of “white holes:” the opposite of black holes. Whereas matter and light can fall into a black hole and never escape, white holes would emit light and matter but wouldn’t take anything in, for example.
But while we see evidence for black holes in space, thus far there hasn’t been any observational evidence of white holes. Now a physicist at the University of Oregon in Eugene thinks he might be able to explain why.
Here’s the standard analogy for the formation of a wormhole: Picture a bed sheet stretched taut. Place a large bowling ball in the center of the sheet, and the sheet will bend inward in response, creating a gravitational pull.
Now imagine that the bowling ball is being squeezed, so that the same amount of mass must fit into a smaller and smaller space. The ball will become denser and denser as it becomes smaller and smaller. This causes the sheet to dip lower and lower, until finally the ball has been squeezed down to the size of a pinhead.
At that point, its density becomes so great and the gravitational force so strong that it pokes a small hole in the center of the sheet. That’s what would happen if a wormhole formed at the center of a black hole.
But what lies on the other side?
Always a stickler for symmetry in his equations, Einstein hypothesized that a “mirror universe” must exist on the other side: a “white hole.”