if a black-hole exists in a galaxy then why does the galaxy still emit light ?
black-holes are nothing more than a mathematical extension of Einstein equations which have no basis in reality
I’m certain proximity plays a role.
Would help if you knew a few simple facts about black holes before you make comments such as this. You clearly don’t understand what one is. The radius of the black hole thought to be at the centre of the galaxy is much smaller than the radius of the galaxy. Hence light escapes without a problem.
The Einstein equations agree with reality on all scales tested.
Have you another theory of gravity that doesn’t predict black holes but does predict all experimentally tested results???
Just to add to the above: read up on “event horizons”.
I honestly thought this thread would touch on something a lot more fascinating about the arguable existence of black holes. It so happens that the deeper one is within a gravitational field, the more time dilates towards the ‘slower’ end relative to someone closer to the outskirts of the field. It is said that the event horizon marks the limit of such time dilation, in which case time “stops” there. So does a black hole get the chance to “form”? Will it ever form? From the perspective of anyone outside the EH, the BH doesn’t yet exist - it never will.
I think that’s an interesting one to ponder.
gib,
I agree. According to Hawking’s original theory, anything that falls past the EH is lost. But according to Susskind and the black hole complementarity, the information is scrambled, but not lost. I think Hawking has since come to agree with Susskind’s position. The ramifications are staggering – a person pulled into a black hole through the EH is both ripped apart (quantum mechanics) and floats past it (general relativity). Both killed and not killed. Wild.
I don’t understand how the holographic principle follows from that though. Can anyone can explain that [size=85](in a “Physics for Dummies” style)[/size]?
Obviously, you’ve gone beyond me in your understanding of this. I’ve never heard of Susskind and his scrambling theory - can you enlighten me?
Leonard Susskind and Hawking had a long-running disagreement about Hawking’s description of how black holes behave. When Hawking discovered that black holes evaporate, he concluded that the information (matter/energy) that had been sucked in was simply gone. Very problematic, but Hawking stuck to his guns for many years.
Susskind eventually theorized that the information is not, in fact, lost; rather it was scrambled, or spread out among the event horizon – so from the outside, the information would seem to disappear into the black hole, but in actuality, it was still very much present and could, in theory, be reconstituted to its original form (the Black Hole Complementarity).
And from that came the holographic principle, which asserts that the EH is like a hologram, a 2-dimensional sheet that conveys 3D information. And in that sense, the universe is like a hologram. That’s where he loses me.
That is a very non-scientific explanation, so any physicists out there feel free to correct or add to the above.
You lost me at “event horizon.” 
Wow! That sounds fascinating. Do you understand what he means by “reconstituted”? I would think that any attempt to recapture the information at the EH would result in you yourself (or whatever probe you sent it to re-acquire it) would get trapped and scrambled itself.
Now here’s a thought for Fin666 (since he seems like the resident physics expert here):
This just ocurred to me: just as time “stops” at the EH, does length contract to the point of extinction? I mean, does any distance regardless of the length collapse to a singularity? If that’s the case, then the EH doesn’t only represent the point of no return, but the end of the universe as well. What’s inside the BH? Nothing! - not even space! In fact, if length is maximally contracted at the EH, then the entire BH is one huge blown-up geometric point - a collossal singularity. That really puts a nasty twist on any classical conception of geometric “points”, doesn’t it?
I think the key phrase there is “in theory.” In other words, all of the pieces are there, so theoretically you could reconstruct the original “information” because nothing was lost. Whether or not you actually had the means to recreate the original is not addressed.
At least, that’s my interpretation, which could be totally off. 
The philosophical question here is: Did north say that just to see the reactions or is this post a completely random quantum fluctuation of cyberspace? 
There is no proof a a black hole, they are merely mathematical contrivances to counterpoint Universal Expansion. The fact that LIGO cannot find gravitational waves proves there are no black holes and that gravity is ill-defined, by pomo physicists.
You are right in that there is no incontrovertible proof of black holes, but a great deal of supporting empirical data points to that conclusion, and Einstein’s General Theory of Relativity predicts the existence of black holes. Because Einstein’s theory has been validated in many other ways, it doesn’t seem inappropriate to have a certain amount of confidence in its predictions.
LIGO is still analyzing and collecting data, and most likely will be for many years.
I’m not familiar with other theories explaining the tremendous amount of matter – equal to some 2.6 million suns – at the center of the Milky Way, or explaining the star that orbits that center moving at 11 million mph. Are there other more promising theories that you’re aware of and that you support?
It’s math supporting math, that’s all. There are flaws with GR in every aspect. LIGO is a failure, Hubble’s Law has been shown to be wrong. On and on…it’s sad that the science community has chased the wild goose for so long. Thankfully some of us stayed on task.
OMG
People from the twin cities are scary smart.
I don’t have any thing useful to contribute.
Except maybe that a black hole, as a simple contrivance, appears to have failed, because physicists now have to add dark matter to keep the whole thing going.
Hey, I’m from the Twin Cities…
I agree, however. Not that modern physics hasn’t done fantastic things, but it chased the wild goose and forgot where it once was. Thankfully some of us took the other path…
Uh - embarrassingly, some of us from the Twin Cities are not scary smart. Muscular, can you expand a little on what you mean by staying “on task”? Are you working on alternate theories to refute General Relativity? If so, can you explain them at the “enthusiast” level rather than the expert level?
[size=90][I have enthusiasm to spare when it comes to this stuff, but not a particle of expertise.][/size]
GR is over-extended. That’s the best way I can put it. It may be easier if you ask a specific question, because I may ‘start’ at the incorrect point. Or PM me if you like.
the imbalance of gravity is the core theory of black-holes
so that matter in a sense implodes on its self
but in most galatic cores there is no evidence that this is actually happening
there is NO evidence that there is a matter flow directed towards the center core of the galaxy
I think people here are confusing mathematical terms with physical ones…
Now i can’t talk about what hawkins says or what anyone else says… but I am familiar with general relativity and quantum mechanics… The concept of a singularity is basically a nullification of activity… “information” is a term refering to physical states in a system. As you reduce the possible states in a system the “information” contained is lost.
A “bit” of information is basically one state… which in classical physics is either true or false “on” or “off”… a “bit” of information in quantum mechanics is a dimensional vector. “Losing” information in a black hole is basically saying that this state is no longer an option… or this vector is no longer possible…
reducing the number of states in a system “speeds” it up but also means it dosn’t “change” very much at all. for example a system with only 2 states would be done one step after it began but it would be almost no different than when it began, and the only place to go from the second state would be back to the original state. There is very limited information there… there are only 2 “bits” of information.
A black hole or a singularity is a gravity well… where gravity by virtue of a uniform influence on each state gives us a unidirectional vector of all states reduce the number of possible states.
So if I have a system that goes from state 1 to 2 to 3 to 4 before going back to 1… If then i introduce gravity into this system such that it influences state 2 so as to lead back to state one… It would have reduced the “bits” of information. there would now only be 2 possible states.
A singularity is then when there is but one possible state… only one “bit” of information…
Now if the development of a system or operation of it were like in classical physics the system would be irreversably destroyed… There is no way to reach state number 3 from that 2 bit system…
But quantum mechanics operates on probabilities… each vector or “bit” of quantum information is operated, or shifted into the next state with a determined half-life… so the best you can ever achieve with a quantum state is to increase the half-life of state 1 to state 2… the information is still there… the shift is still possible… the half-life is merely extended to such a degree that the probability in each state is reduced to near infinite… but it will shift… so the information is maintained…
So one can sa things like “Chemistry is paused” in a singularity… but quantum states remain active…
If we were to imagine each “shift” of a quantum state as a precurser to another shift in the system, then a cascade effect is achieved… depending on its point of origin it might cascade past the gravitational influence thus “dispersing” the singularity… or fall back down into it.
It’s not something magical where “time stops”… whatever “time” is supposed to mean in that context…
But then… it’s been a long time since I read up on this stuff… I might be mixing it all together…