Correction: Nothing in our observations suggest the existance of singularities. Our observations do suggest black holes, and the simplest models of black holes all contain singularities. It is possible or even likely that quantum gravitational effects might prevent a singularity from forming, in which case the center of a black hole would be a very small region of insanely high but finite density, instead of a zero-size, infinite density singularity. In either event, however, the central core of a black hole is well inside the event horizon (at least for any black hole of astrophysical origin, which are the only ones we have any evidence for), so it doesn’t much matter whether it’s a singularity or not.
And there are some serious scientists, working in the field of relativity, who legitimately doubt the existance of black holes. These scientists put forth vague quantum gravitational conjectures containing almost-black hole objects such as the so-called “gravatars” or “dark energy stars”. Such black hole skeptics are rare, and I and most other relativists think they’re wrong, but they are genuine scientists working in good faith. Then again, I doubt that there’s any scientific theory which commands truly unanimous acceptance by all scientists in that field, so I don’t think it’s too relevant to note the doubters.
I think it might be explained by the fact that masses do weird things in the quantum world. For instance, the mass of a nucleon is very different from the sum of the masses of its three constituent quarks, the rest being made up of binding energies.
Also, remember that mass-energies, strictly speaking, aren’t real numbers but elements of an R-torsor – you can take their difference but you can’t really add them.
Heck, I suppose that renormalizing away a Planck mass is no worse, really, than the more usual trick of renormalizing away an infinite mass. But you’re right to call such claims speculative: So far, none of them have advanced beyond the status of a toy model. That is to say, such microscopic black holes would have some of the properties of subatomic particles, and it can be instructive to study such similarities, but nobody has yet figured out a way to make them have all of the right properties.
May I add, Mathochist, that your last line there completely lost me.
It rather throws most people at first, but really makes a lot more sense once you grok G-torsors. Essentially, given a group G a G-torsor is a G-space which is isomorphic to G with the standard right action. An affine space is a V-torsor for the vector space with which it’s usually confounded. I don’t want to go way too far afield from the OP here, but you can search on Baez’ This Week’s Finds archive or start a new thread for discussing torsors in general.
I stand corrected of equating “black hole” with “singularity”. Any sufficiently (relatively) compact, highly massive object could have an event horizon. At any rate, the theory (that electrons could be micro black holes) is entirely speculative, a plaything of string theorists and other bleeding edge cosmologists. It also bears noting that such a tiny black hole should be unstable and evaporate into Hawking radiation in short order (like, fractions of picoseconds or faster) and therefore proponents have to come up with some unknown mechanism which retards evaporation.
Although there may be scientists who would argue that these things are something other than what we consider black holes.
You wouldn’t know it with a large enough black hole though. With a supermassive black hole, the change in tidal forces is small enough that you would have no idea that you crossed the event horizon.
You couldn’t hover there, if that’s what you’re thinking. You’d be falling through the event horizon at nearly the speed of light. If a zombie bit your toe, by the time your head realized it, your head would be inside the event horizon as well.
There was a recent article in Scientific American positing that instead of black holes there are actually black stars. From a distance they look the same, but up close there is no event horizon and no singularity of infinite density. There are a few hypotheses describing the exact mechanism of black stars, but they are all merely extremely dense rather than infinitely so, and light can escape them. This would account for observations of Hawking radiation from suspected black holes. These various hypotheses are an attempt to reconcile relativity and quantum theory, and also resolves the problem with regular black hole theory that allows information to be destroyed at the event horizon.
From the point of view of someone just inside that radius, then, what would it look like? I imagine it would appear as though the universe outside the radius begins to accelerate away from me at a rate that makes it impossible for me to catch up?
There has been no Hawking radiation observed from black holes, as for any stellar-mass black hole the Hawking radiation would be insignificant compared to other effects.