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I'll take your comment in good faith, but there are very good reasons to believe black holes exist and that, for instance, the center of our galaxy contains a v
by podiki 9y ago
I'll take your comment in good faith, but there are very good reasons to believe black holes exist and that, for instance, the center of our galaxy contains a very massive black hole and not a neutron star. This is basic general relativity, which only has (physical and theoretical) evidence in support of it. While quantum gravity is still very much uncertain, that would (most likely) only have to do with understanding the possible singularity inside black hole. Otherwise, defining a black hole as "a thing with an event horizon" is purely a general relativity prediction, consistent with all of the other predictions and observations.
(Disclaimer: theoretical physicist)
- ars 9y agoYou skipped a step. Yes, the general relativity prediction of a black hole is solid once it exists. But you have to construct that black hole in the first place. And it's that part that's on shaky ground.
- dwaltrip 9y agoThis seem to be a contrarian view. Do you have any sources you can share with us?
- AnimalMuppet 9y agoYou seem to have missed the part where podiki offered the object at the center of the galaxy as evidence that a black hole currently exists. So you're arguing against the evidence when you say (over and over and over) that black holes can't form.
- podiki 9y agoThere are indeed people who closely study the process of forming a black hole from collapsing matter, hoping to understand things like the singularity and event horizon. I have not ever heard of any good results that show that a black hole for some reason cannot be formed, but I'm sure people are investigating. This would be very surprising if found, and there doesn't seem to be any evidence against black holes actually forming. So the mainstream, and as far as we can tell, correct, view is that black holes can, do, and have formed.
- wallace_f 9y agoOP's claim is that black holes infinite amount of time to form, because matter would take an infinite amount of time to fall into it. Personally, as a layman on the subject of black holes, what I understand is that mass does take infinite amount of time to fall into an event horizon. But I don't know about the formation process of how/when that event horizon is formed. Perhaps you can help me, and him, understand why his claim is false--that it would happen in finite time?
- JoeAltmaier 9y agoMaybe they never finish forming (keep collapsing forever). But once you have an event horizon, you have a black hole, right?
- Santosh83 9y agoSignals take an infinte amount of time to reach a distant observer from just outside the event horizon. Which means we cannot see the event horizon or what is beyond, and we cannot also 'see' the event horizon being formed, or any matter crossing the event horizon. When the star collapses, light takes progressively longer to reach an outside observer, and eventually becomes too dim to detect. The same thing happens with an object falling into a black hole. But since the gravitational effect can still be felt, we cannot also say that the black hole never formed. At all events, a region of spacetime that emits no discernable signals has formed. You can call it a black hole or speculate further about what it is, but the phenomenon is still right there.
- wallace_f 9y ago>we cannot also 'see' the event horizon being formed I think what you're saying here is the confusing part. If no observer in the universe can ever witness a black hole being formed, it stands to reason they cannot exist (within the reference frame of observers outside it). Now I'm not asserting this as true or not, because I wouldn't assert such contrarian conclusions on a subject I have not properly studied; rather I am just highlighting what appears to be the confusing bit here.
- 9y ago