[Harri (OP)]

I have a basic understanding of both the large world of relativity and the small quantum world, again 'basic'. If I understand correctly, there are efforts being made to unify the 2 worlds to provide us with a unified theory of the 'whole' universe?

Why does there have to be unification? Why can't they exist independent of each other?

[evan_au]

Why can't they exist independent of each other?

They can, in a "weak gravitational field" environment, such as our Solar System and on Earth.
- So for our practical purposes, there is no conflict
- For interactions of things on the size of a human, a planet or a star, gravity dominates, and quantum effects are too small to matter
- For interactions of things on the size of a photon, proton or even small molecules, quantum effects dominate, and gravitational effects are too small to matter

However, physicists want a theory that works everywhere, including very near the event horizon of a black hole.
- Relativity says nothing can get out of the event horizon
- Quantum theory says that things can tunnel out of places that (classically) they should not
- There is a conflict here
- All quantum gravity theories so far have produced infinities in this extreme environment
- And a mathematical trick called "renormalisation" which has successfully bypassed infinities in previous theories does not work with quantum gravity.

See: https://en.wikipedia.org/wiki/Renormalization

[Kryptid]

- Relativity says nothing can get out of the event horizon
- Quantum theory says that things can tunnel out of places that (classically) they should not
- There is a conflict here

From what I understand, tunneling can only happen if the particle moves to an energy level equal to or lower than the one it started with. Tunneling into a higher energy level (such as against a gravitational potential) would seem forbidden by the first law of thermodynamics. Am I mistaken?

[evan_au]

Tunneling into a higher energy level (such as against a gravitational potential) would seem forbidden by the first law of thermodynamics.

Hawking Radiation can be considered as a pair of virtual particles, one of which escapes from the black hole, and the other is swallowed by the black hole. In this case, I guess the one which is swallowed balances the one which escapes?

But a mathematical treatment of quantum gravity in the strong-field regime remains an unsolved problem.

See: https://en.wikipedia.org/wiki/Hawking_radiation

[Harri (OP)]

If relativity holds true, and quantum mechanics hold true, and they only break down when you try to unify them in a so called 'black hole', then maybe what we think we know about black holes does not hold true?

[evan_au]

quantum gravity in the strong-field regime remains an unsolved problem

maybe what we think we know about black holes does not hold true?

What part of "unsolved problem" is the part that "we think we know"?

In reality, the recent gravitational wave observations of black-hole mergers has proven (once again) that General Relativity has been a spectacularly successful theory for just over a century. This measured the properties of black holes down to a scale of less than 20km, and it agreed with General Relativity.

However, the quantum scale is often measured in distances of less than a nanometer, and gravitational wave detection in the 50Hz-1kHz spectrum will not give us that spatial resolution.

Nor will the ongoing "Event Horizon telescope" project that has completed its first data collection phase, and is now (presumably) confirming calculations and (possibly) submitting papers for review.

So I'm afraid that resolution of general relativity and quantum theory must wait for some mathematical breakthroughs, or else require a microscopic examination of a black hole (an expedition that will require technologies that we don't currently possess).

See: https://en.wikipedia.org/wiki/List_of_gravitational_wave_observations
https://en.wikipedia.org/wiki/Event_Horizon_Telescope

[jeffreyH]

During the initial phases of the big bang it is thought that only one force dominated. This was a combination of the strong, weak, electromagnetic and gravitational forces. As the big bang evolved the forces started separating, with gravity being the first to become distinct. This is where a unified theory would help.

[Bill S]

Hawking Radiation can be considered as a pair of virtual particles, one of which escapes from the black hole, and the other is swallowed by the black hole.

Isn’t this misleading? My understanding is that the “escaping” particle never crosses the EH in the inward direction.  It evades capture, rather than escaping after being captured.  (?)

[yor_on]

hey Evan, take this with a pinch of salt as I'm both inebriated., and on drugs due to circumstances :)
I do agree though.

[guest47899]

What causes a photon to deaccelerate from c?  What causes a photon particle to seperate from the light wave? 

In the slit experiment the wave is seperated from the particle. the wave upon entering into the split diffracts into a diffused wave pattern. the subsequent light into the split proceeds as particles. The process repeats. Defracted diffused waves, followed by particle light. Once a defracted wave becomes a slower diffused wave, a light wave becomes visble in a band pattern. This band pattern represents a bending deacceleration of light. These bands are representaive of a disruption of the invisible light wave into an on - off band pulse. These on - off pulses represent a slowly of c. Once the on - off band pulses are present, particle light becomes evident as dots on the screen. The majority of particle light falls on the on portion of the deaccelerated band pattern.

When a light particle separates from the light wave it must do so following a repeatable mathematical function, as demonstrated by the reproducible double slit experiment. This mathematical function will unify quantum and GR. The function however is not a left to right mathematical function, where the equation produces the result. It is a right to left mathematical function where the answer/result produces the equation.

The unifying of quantum with GR in a mathematical equation must resolve quantum to GR not GR to quantum.

[guest47899]

addendum, 

Once the constant of the Speed of Light has been deaccelerated, Light particles become evident.

[evan_au]

My understanding is that the “escaping” particle never crosses the EH in the inward direction.  It evades capture, rather than escaping after being captured.  (?)

I'm afraid that I can't follow the maths of Hawking radiation, so I must rely on simplistic analogies.

However, my primitive understanding of Hawking radiation is that the mass/energy that is lost via Hawking radiation is energy that previously added to the mass of the black hole. So the Hawking radiation leads to eventual "evaporation" of the black hole, provided the effective temperature of the black hole is higher than the effective temperature of the CMBR - and no further matter falls into the black hole.

Hawking identified a quantum loophole that might allow mass/energy to escape from a black hole without physically crossing the relativistic event horizon in the outward direction.

[Bill S]

The best "hitch-hiker" level explanation of Hawking radiation I have found was by Soul Surfer, here:

https://www.thenakedscientists.com/forum/index.php?topic=34454.0

Somewhere, I have an explanation by Chris Baird which also helped me greatly.  I'll post it when I trace it, but who wants to be hunting for that sort of thing on Christmas Day?

Have a great Christmas, folks.

[Bill S]

Found the comments by Chris Baird.  This was in response to a question as to whether or not it would make any difference which off a particle/antiparticle pair fell into a BH.

"It is not the capture of an antiparticle that reduces the black hole's mass. Antiparticles have regular positive mass. So when an antiparticle falls into a black hole, it increases the mass of the black hole. Rather, the mass is lost from the black hole the moment the particle/antiparticle pair is created. When a particle/antiparticle pair is created, because they both have regular positive mass, the energy to create them must come from somewhere. Because of quantum uncertainty, the pair can pop into existence without any energy input as long as they pop back out of existence in a very short amount of time, so that over long time scales, there is no net gain or loss of energy out of nowhere. In order to stick around (i.e. turn from virtual to real particles), they have to get the energy that was needed to create their mass from somewhere. In this case, it is from the black hole itself. The black hole loses mass as the pair is created, then one particle falls into the black hole and returns half of this mass back, while the other particle zips off, permanently carrying mass away from the black hole." 

[Janus]

If relativity holds true, and quantum mechanics hold true, and they only break down when you try to unify them in a so called 'black hole', then maybe what we think we know about black holes does not hold true?

That's kind of the whole point.  "What" exactly is it that we think we know about black holes doesn't hold true?  GR makes really good predictions when applied on large scales, but predicts the oddity of a singularity at the center of a black hole.  Quantum mechanics works really well at small scales but so far doesn't seem to be compatible with the GR model of gravity.
The predicted singularity suggests that somewhere before it is reached, The GR model fails to make accurate predictions.  The best explanation for this is that QM effects come into play which prevent the singularity.  However, As I pointed out earlier, no one has been, as of yet, been able to develop a definitive  "quantum gravity" theory; a theory that explains how gravity behaves at the quantum level which still makes the same predictions at grand scales (at least to accuracy of present measurement) as GR.   It's not enough to say "From here to here, QM rules, but from that point on GR takes over". 
At what point?.  Why that point and not some other? What causes the switch over from one set of rules to another?  Why should gravity be any different than everything else?  (We have a quantum theory of electromagnetism that works smoothly from the sub-atomic to the macroscopic realms without any need to switch rules midstream)
These are the types of questions that drive science.  If you want to just throw up your hands and say we just have two separate theories and leave it at that, there are a lot of points along the road of scientific discovery where we could have done that.   We  once had separate models for magnetism and electric charge, until Maxwell combined them, and in doing so, predicted the existence of electromagnetic waves, which in turn became the basis for a whole new branch of technology.

[evan_au]

It's not enough to say "From here to here, QM rules, but from that point on GR takes over". 
At what point?

For Christmas I received Martin Rees' classic book "Just Six Numbers" (1999) - almost finished it!

One of his numbers is N, which is the ratio of two forces between two protons: (Electrical Repulsion)/(Gravitational attraction). N has a value of around 10³⁶.

This crops up in many places in the book, from the large scale structure of stars and galaxies, down to the size of a micro black hole (which would need around N atoms to be crushed into the volume of 1 atom).

He quotes around the mass of Jupiter as the crossover point where gravity starts to overcome the forces that hold matter together. If an object gets much more massive than Jupiter,  you start to get deuterium fusion - a brown dwarf star.

On scales smaller than Jupiter, gravity is too weak to impact quantum effects significantly.

PS: The book is a bit old, but very readable, and still good for an introduction to cosmology.

PPS: Martin Rees is the UK Royal Astronomer; he commented that he is frequently asked if he casts the queen's horoscope.
- He replies that if the queen ever wanted a horoscope, he is sure she would ask him...
- You can hear a recent interview with him at https://after-on.com/episodes-31-60/037z

[yor_on]

The 'pair production' is thought to exist at the 'border' of a black hole, due to the energy existing there. One particle containing energy 'disappearing' out to the blue yonder, the other 'swallowed' by the black hole as far as I get it? So it 'steals' from the energy of a black hole, thereby diminishing its mass. I remember seeing other definitions in where the particle 'swallowed' was defined as being of a 'negative energy', but considering the definition in where 'gravity' is 'negative energy' that just made my head hurt.

[yor_on]

Actually, that explanation can't be the one Hawking thought up. First take a look here. http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/hawking.html

then here https://en.wikipedia.org/wiki/Hawking_radiation

" Hawking radiation is required by the Unruh effect and the equivalence principle applied to black hole horizons. Close to the event horizon of a black hole, a local observer must accelerate to keep from falling in. An accelerating observer sees a thermal bath of particles that pop out of the local acceleration horizon, turn around, and free-fall back in. The condition of local thermal equilibrium implies that the consistent extension of this local thermal bath has a finite temperature at infinity, which implies that some of these particles emitted by the horizon are not reabsorbed and become outgoing Hawking radiation. "

Or if we apply the idea of Earth accelerating at one gravity to that Black Hole. At the event Horizon the 'acceleration' must be close to infinity, and a rotating black hole should then add a angular momentum to it ( well, I think so anyway :) so the 'stationary observer' would then have to accelerate in a 'opposite direction' to this which then is assumed to force 'virtual particle pairs' into 'real particles', but only from the view of the accelerated frame (aka the 'stationary observer'), as far as I get it?

Not sure I'm getting any closer to this one. Especially as 'gravity' also can be seen as a 'negative energy'? We're not in that accelerating frame, so to accept that one we will have to imagine that all frames of reference must have a consequence even if we can't measure that Unruh effect seen by the accelerated frame. As far as I see.

Anyway, here's another mathematical proof stating that Black holes can't exist at all :)
https://arxiv.org/abs/1409.1837  " Back-reaction of the Hawking radiation flux on a gravitationally collapsing star II "