So recently there's been this whole big fuss over Stephen Hawking claimed there are no black holes with event horizons and people are saying "There are no black holes!" and other people are saying "What are you talking about he just said there are no event horizons" and well a hell of a lot of silly things are being said when, as I understand it, nothing complicated is going on, just a bunch of sloppiness with language. As far as I can tell, this is all just a question of what we mean by the phrase "black hole". (Maybe. See bottom.)
Originally, "black hole" meant a body so massive even light could not escape from it, regardless of direction of travel. That is to say, having an event horizon was a defining characteristic of a black hole. These were hypothetical objects and none were known.
Then, candidates for black holes were found, and more evidence confirmed it, and astronomers were like "Yay, we've found black holes!" Of course, such objects weren't necessarily black holes as such; just something close to it. Still, one way or another, these objects have become referred to as black holes.
Now Stephen Hawking is saying there are no event horizons. This does mean there are no black holes in the original sense. It does not mean the various objects that have been called "black holes" do not exist, just that they are not quite black holes in the original sense.
Now here's what's bugging me here -- what in space is new about any of this?
Some time ago I asked relativist Sarah Kavassalis on Formspring (now lost to the internet) just how sure we are that black holes can actually form in finite time. I don't have her exact answer to hand, obviously, but essentially it was: Black holes cannot form in finite time in general relativity. What astronomers call black holes, and what relativists call black holes, are not really the same thing, and one day she should really get around to writing something about this. (Apologies to Dr. Kavassalis if I'm misremembering.)
So if that's really true... what's the big deal? Didn't we already know this? (Of course, if that's really true... why does it seem nobody really talked about this before now?)
Anyway, it seems to me there's really not much going on here, it's just a language issue. I am worried though that I might be missing here. If that's the case, can anyone clarify?
-Harry
Originally, "black hole" meant a body so massive even light could not escape from it, regardless of direction of travel. That is to say, having an event horizon was a defining characteristic of a black hole. These were hypothetical objects and none were known.
Then, candidates for black holes were found, and more evidence confirmed it, and astronomers were like "Yay, we've found black holes!" Of course, such objects weren't necessarily black holes as such; just something close to it. Still, one way or another, these objects have become referred to as black holes.
Now Stephen Hawking is saying there are no event horizons. This does mean there are no black holes in the original sense. It does not mean the various objects that have been called "black holes" do not exist, just that they are not quite black holes in the original sense.
Now here's what's bugging me here -- what in space is new about any of this?
Some time ago I asked relativist Sarah Kavassalis on Formspring (now lost to the internet) just how sure we are that black holes can actually form in finite time. I don't have her exact answer to hand, obviously, but essentially it was: Black holes cannot form in finite time in general relativity. What astronomers call black holes, and what relativists call black holes, are not really the same thing, and one day she should really get around to writing something about this. (Apologies to Dr. Kavassalis if I'm misremembering.)
So if that's really true... what's the big deal? Didn't we already know this? (Of course, if that's really true... why does it seem nobody really talked about this before now?)
Anyway, it seems to me there's really not much going on here, it's just a language issue. I am worried though that I might be missing here. If that's the case, can anyone clarify?
-Harry
