Yes. They really do... They are observed in galactic centers.
I find people get most confused by the characterization of event horizons, as if the proverbial event horizon of a black hole is some unique new physical entity. We pass through event horizons constantly. space-like hyper-surface is an event horizon,
In my opinion, this sounds like some people beginning with Albert Einstein, just wanted to make things look complex, which can in no way be true. Real Nature and Universe are indeed complex, regarding their mathematical description. Of course Newton's theories were great achievements for their time, but it's like describing an object as you see its surface, having no idea what hides inside or where it comes from. Again, this in no way relegates the great work of Newton, who after all, had nothing more than a few of previous theories and very few observations - or what did that mean back then. But Einstein went a great way further with GR and finally found very innovative ways to express his ideas. I don't think that any mathematically rigorous prediction, can exist outside some rigorous treatment and I definitely agree that what we have so far in this regard, is GR. I think that black holes exist, but I also think that quantum world has a lot to reveal in the future.Do we need complex ideas like GR or curved space to predict black holes?
Of course Einstein didn't want to just make things look complex. In a Newtonian sense the acceleration of a small falling object shouldn't be affected even by a relativistic increase in its effective mass-energy. Absent other forces, can the impact velocity on any far object (even a neutron star) be given exactly by the formula v^2 = 2GM/r ?In my opinion, this sounds like some people beginning with Albert Einstein, just wanted to make things look complex, which can in no way be true.
My suspicion is that you are using a definition of "direct observation" here that it far more limited than you would use in other situations (just seeing with your eyes?). Because there are several direct observations of properties of black holes. Gravitational field strength is measured by timing orbits. Size is measured by observing radiation from infalling matter.I disagree. I am still unaware of any DIRECT OBSERVATION of Black Holes...
Light always travels in straight lines. In curved spacetime, this straight path is seen to be curved.Is the concept of curved space required to predict black holes?
Is the escape velocity from any large object (even a neutron star or black hole) described exactly by the formula v^2 = 2GM/r ? If the Schwarzschild radius (called SR) is defined as the radius where the escape velocity equals the speed of light, can we then simply say that SR = 2GM/(c^2)? The concept of an object with a mass/radius ratio large enough to contain light doesn't require curved space along with the concept of light always traveling in straight lines. Why can't we simply say that light bends around an object? If a neutral object from far away drops straight into a basic non-spinning and non-magnetic black hole, is its relative velocity c when it reaches the event horizon?Light always travels in straight lines....... in some ways, yes, curved space is necessarily part of the actual definition of what a Black Hole is ....
Because Light must travel in straight lines. If light was "bent" or curved, it would necessitate a change in velocity which necessarily entails a temporal metric which implies that light is not relativistic and violates both of Einstein's theories in one go.Why can't we simply say that light bends around an object??
Sure, a particle falling straight down towards a black hole will have Lorenz transformations, but do the Lorenz transformations at any point affect the velocity it will have?In your given equations, when dealing with relativistic speeds, one must factor in the Lorenz transformations, which you seem to be missing.
So do you accept that the gravitational field strength and size measurements are "direct" measurements? I can't tell from what you are saying. What is the difference between/definition of "direct/indirect" measurements"? Rather than direct/indirect measurements, you now seem to be talking about some sort of indirect properties, and I've never heard of such a thing either.No. By Direct Obsevration of a Black Hole, I mean, any measurement that detects the actual properties of a Black Hole directly, rather than an indirect inference from a measurement of some other property...
That's a different issue than whether the measurements are "direct". In science, theories predict properties and if properties are detected that match the theory and no other viable theories exist, then the theory is validated. Your line of logic sounds more like wishing another explanation will be found than accepting the scientific process that already found a viable explanation....which (ALTHOUGH HIGHLY UNLIKELY) may still be yet shown to be due to some other process.
Gravitational acceleration is caused by mass. Mass is a property of objects. So that's an observation of the property of mass of the object it is falling into.Infalling Matter tells us the gravitational power accelerating objects, there is no observation of to-what this matter is falling into.*
That's just the vanilla "you can't prove anything absolutely" fundamental reality of science. It's true of anything in science and nobody would ever claim black holes or anything else were 100% proven.I maintain that it's simply not enough to warrant any claim of confirming the definite, undeniable such a phenomena as a Black Hole.
Actually you may read more about BH Firewall Paradox.A black hole is a prediction of GR, but nobody has made any claims of knowing exactly what happens inside of the event horizon of a BH,
and obviously whatever does go on cannot be observed directly.
The fact that the simplest models end up with a mathematical singularity is a strong indication that some kind of presently unknown physics comes in to play.
However which ever way one chooses to interpret it, 'black hole candidates' do exist, and in particular the evidence for the SMBH in our galaxy's centre is overwhelming.
There are beyond any doubt star systems which are rapidly orbiting an extremely massive yet small invisible object.
Whatever object exists there it fulfils the GR description of a black hole, so until such time as there is contrary evidence we may as well call it a black hole.