For now, these ideas are barely more than scribbles on the back of an envelope, and critics have myriad complaints about their plausibility. For example, how exactly would matter or spacetime change state during the collapse of a star? Physicist Scott A. Hughes of the Massachusetts Institute of Technology says, "I don't see how something like a massive star--an object made out of normal fluid, with fairly simple density and pressure relations--can make a transition into something with as bizarre a structure as a gravastar." Mainstream theories of quantum gravity are far better developed. String theory, for one, appears to explain away the paradoxes of black holes without abandoning either event horizons or relativity.
Observationally, the new conceptions of black holes could be hard to distinguish from the classical picture--but not impossible. Gravitational waves should reveal the shape of spacetime around putative black holes. A classical hole, being a simple object without a true surface, has only a couple of possible shapes. If one of the gravitational-wave observatories now going into operation finds a different shape, then the current theories of physics would be yet another thing in the universe to get torn to shreds by a black hole.?