**The basic ideas of TGD relevant for blackhole concept**

My own basic strategy is to not assume anything not necessitated by experiment or not implied by general theoretical assumptions - these of course represent the subjective element. The basic assumptions/predictions of TGD relevant for the recent discussion are following.

- Space-times are 4-surfaces in H=M
^{4}× CP_{2}and ordinary space-time is replaced with many-sheeted space-time. This solves what I call energy problem of GRT by lifting gravitationally broken Poincare invariance to an exact symmetry at the level of imbedding space H.

GRT type description is an approximation obtained by lumping together the space-time sheets to single region of M

^{4}, with various fields as sums of induced fields at space-time surface geometrized in terms of geometry of H.

Space-time surface has both Minkowskian and Euclidian regions. Euclidian regions are identified in terms of what I call generalized Feynman/twistor diagrams. The 3-D boundaries between Euclidian and Minkowskina regions have degenerate induced 4-metric and I call them light-like orbits of partonic 2-surfaces or light-like wormhole throats analogous to blackhole horizons and actually replacing them. The interiors of blackholes are replaced with the Euclidian regions and every physical system is characterized by this kind of region.

Euclidian regions are identified as slightly deformed pieces of CP

_{2}connecting two Minkowskian space-time regions. Partonic 2-surfaces defining their boundaries are connected to each other by magnetic flux tubes carrying monopole flux.

Wormhole contacts connect two Minkowskian space-time sheets already at elementary particle level, and appear in pairs by the conservation of the monopole flux. Flux tube can be visualized as a highly flattened square traversing along and between the space-time sheets involved. Flux tubes are accompanied by fermionic strings carrying fermion number. Fermionic strings give rise to string world sheets carrying vanishing induced em charged weak fields (otherwise em charge would not be well-defined for spinor modes). String theory in space-time surface becomes part of TGD. Fermions at the ends of strings can get entangled and entanglement can carry information.

- Strong form of General Coordinate Invariance (GCI) states that light-like orbits of partonic 2-surfaces on one hand and space-like 3-surfaces at the ends of causal diamonds on the other hand provide equivalent descriptions of physics. The outcome is that partonic 2-surfaces and string world sheets at the ends of CD can be regarded as basic dynamical objects.

Strong form of holography states the correspondence between quantum description based on these 2-surfaces and 4-D classical space-time description, and generalizes AdS/CFT correspondence. Conformal invariance is extended to the huge super-symplectic symmetry algebra acting as isometries of WCW and having conformal structure. This explains why 10-D space-time can be replaced with ordinary space-time and 4-D Minkowski space can be replaced with partonic 2-surfaces and string world sheets. This holography looks very much like the one we are accustomed with!

- Quantum criticality of TGD Universe fixing the value(s) of the only coupling strength of TGD (Kähler coupling strength) as analog of critical temperature. Quantum criticality is realized in terms of infinite hierarchy of sub-algebras of super-symplectic algebra actings as isometries of WCW, the "world of classical worlds" consisting of 3-surfaces or by holography preferred extremals associated with them.

Given sub-algebra is isomorphic to the entire algebra and its conformal weights are n≥ 1-multiples of those for the entire algebra. This algebra acts as conformal gauge transformations whereas the generators with conformal weights m<n act as dynamical symmetries defining an infinite hierarchy of simply laced Lie groups with rank n-1 acting as dynamical symmetry groups defined by Mac-Kay correspondence so that the number of degrees of freedom becomes finite. This relates very closely to the inclusions of hyper-finite factors - WCW spinors provide a canonical representation for them.

This hierarchy corresponds to a hierarchy of effective Planck constants h

_{eff}=n× h defining an infinite number of phases identified as dark matter. For these phases Compton length and time are scale up by n so that they give rise to macroscopic quantum phases. Super-conductivity is one example of this kind of phase - charge carriers could be dark variants of ordinary electrons. Dark matter appears at quantum criticality and this serves as an experimental manner to produce dark matter. In living matter dark matter identified in this manner would play a central role. Magnetic bodies carrying dark matter at their flux tubes would control ordinary matter and carry information.

- I started the work with the hierarchy of Planck constants from the proposal of Nottale stating that it makes sense to talk about gravitational Planck constant h
_{gr}=GMm/v_{0}, v_{0}/c≤ 1 (the interpretation of symbols should be obvious). Nottale found that the orbits of inner and outer planets could be modelled reasonably well by applying Bohr quantization to planetary orbits with tge value of velocity parameter differing by a factor 1/5. In TGD framework h_{gr}would be associated with magnetic flux tubes mediating gravitational interaction between Sun with mass M and planet or any object, say elementary particle, with mass m. The matter at the flux tubes would be dark as also gravitons involved. The Compton length of particle would be given by GM/v_{0}and would not depend on the mass of particle at all.

The identification h

_{gr}=h_{eff}is an additional hypothesis motivated by quantum biology, in particular the identification of biophotons as decay products of dark photons satisfying this condition. As a matter fact, one can talk also about h_{em}assignable to electromagnetic interactions: its values are much lower. The hypothesis is that when the perturbative expansion for two particle system does not converge anymore, a phase transition increasing the value of the Planck constant occurs and guarantees that coupling strength proportional to 1/h_{eff}increases. This is one possible interpretation for quantum criticality. TGD provides a detailed geometric interpretation for the space-time correlates of quantum criticality.

Macroscopic gravitational bound states not possible in TGD without the assumption that effective string tension associated with fermionic strings and dictated by strong form of holography is proportional to 1/h

_{eff}^{2}. The bound states would have size scale of order Planck length since for longer systems string energy would be huge. h_{eff}=h_{gr}makes astroscopic quantum coherence unavoidable. Ordinary matter is condensed around dark matter. The counterparts of black holes would be systems consisting of only dark matter.

- Zero energy ontology (ZEO) is central element of TGD. There are many motivations for it. For instance, Poincare invariance in standard sense cannot make sense since in standard cosmology energy is not conserved. The interpretation is that various conserved quantum numbers are length scale dependent notions.

Physical states are zero energy states with positive and negative energy parts assigned to ends of space-time surfaces at the light-like boundaries of causal diamonds (CDs). CD is defined as Cartesian products of CP

_{2}with the intersection of future and past directed lightcones of M^{4}. CDs form a fractal length scale hierarchy. CD defines the region about which single conscious entity can have conscious information, kind of 4-D perceptive field. There is a hierarchy of WCWs associated with CDs. Consciously experienced physics is always in the scale of given CD.

Zero energy states identified as formally purely classical WCW spinor fields replace positive energy states and are analogous to pairs of initial and final, states and the crossing symmetry of quantum field theories gives the mathematical motivation for their introduction.

- Quantum measurement theory can be seen as a theory of consciousness in ZEO. Conscious observer or self as a conscious entity becomes part of physics. ZEO gives up the assumption about unique universe of classical physics and restricts it to the perceptive field defined by CD.

In each quantum jump a re-creation of Universe occurs. Subjective experience time corresponds to state function reductions at fixed, passive bounary of CD leaving it invariant as well as state at it. The state at the opposite, active boundary changes and also its position changes so that CD increases state function by state function reduction doing nothing to the passive boundary. This gives rise to the experienced flow of geometric time since the distance between the tips of CD increases and the size of space-time surfaces in the quantum superposition increases. This sequence of state function reductions is counterpart for the unitary time evolution in ordinary quantum theory.

Self "dies" as the first state function reduction to the opposite boundary of CD meaning re-incarnation of self at it and a reversal of the arrow of geometric time occurs: CD size increases now in opposite time direction as the opposite boundary of CD recedes to the geometric past reduction by reduction.

Negentropy Maximization Principle (NMP) defines the variational principle of state function reduction. Density matrix of the subsystem is the universal observable and the state function reduction leads to its eigenspaces. Eigenspaces, not only eigenstates as usually.

Number theoretic entropy makes sense for the algebraic extensions of rationals and can be negative unlike ordinary entanglement entropy. NMP can therefore lead to a generation of NE if the entanglement correspond to a unitary entanglement matrix so that the density matrix of the final state is higher-D unit matrix. Another possibility is that entanglement matrix is algebraic but that its diagonalization in the algebraic extension of rationals used is not possible. This is expected to reduce the rate for the reduction since a phase transition increasing the size of extension is needed.

The weak form of NMP does not demand that the negentropy gain is maximum: this allow the conscious entity responsible for reduction to decide whether to increase maximally NE resources of the Universe or not. It can also allow larger NE increase than otherwise. This freedom brings the quantum correlates of ethics, moral, and good and evil. p-Adic length scale hypothesis and the existence of preferred p-adic primes follow from weak form of NMP and one ends up naturally to adelic physics.

**The analogs of blackholes in TGD**

Could blackholes have any analog in TGD? What about Hawking radiation? The following speculations are inspired by the above general vision.

- Ordinary blackhole solutions are not appropriate in TGD. Interior space-time sheet of
*any*physical object is replaced with an Euclidian space-time region. Also that of blackhole by perturbation argument based on the observation that if one requires that the radial component of blackhole metric is finite, the horizon becomes light-like 3-surface analogous to the light-like orbit of partonic 2-surface and the metric in the interior becomes Euclidian.

- The analog of blackhole can be seen as a limiting case for ordinary astrophysical object, which already has blackhole like properties due to the presence of h
_{eff}=n× h dark matter particles, which cannot appear in the same vertices with visible manner. Ideal analog of blackhole consist of dark matter only, and is assumed to satisfy the h_{gr}=h_{eff}already discussed. It corresponds to region with a radius equal to Compton length for arbitrary particle R=GM/v_{0}=r_{S}/2v_{0}, where r_{S}is Schwartschild radius. Macroscopic quantum phase is in question since the Compton radius of particle does not depend on its mass. Blackhole limit would correspond to v_{0}/c→ 1 and dark matter dominance. This would give R=r_{S}/2. Naive expectation would be R=r_{S}(maybe factor of two is missing somewhere: blame me!).

- NMP implies that information cannot be lost in the formation of blackhole like state but tends to increase. Matter becomes totally dark and the NE with the partonic surfaces of external world is preserved or increases. The ingoing matter does not fall to a mass point but resides at the partonic 2-surface which can have arbitrarily large surface. It can have also wormholes connecting different regions of a spherical surface and in this manner increase its genus. NMP, negentropy , negentropic entanglement between h
_{eff}=n× h dark matter systems would become the basic notions instead of second law and entropy.

- There is now a popular article explaining the intuitive picture behind Hawking's proposal. The blackhole horizon would involve tangential flow of light and particles of the infalling matter would induce supertranslations on the pattern of this light thus coding information about their properties to this light. After that this light would be radiated away as analog of Hawking radiation and carry out this information.

The objection would be that in GRT horizon is no way special - it is just a coordinate singularity. Curvature tensor

does not diverge either and Einstein tensor and Ricci scalar vanish. This argument has been used in the firewall debates to claim that nothing special should occur as horizon is traversed. So: why light would rotate around it? No reason for this! The answer in TGD would be obvious: horizon is replaced for TGD analog of blackhole with a light-like 3-surface at which the induced metric becomes Euclidian. Horizon becomes analogous to light front carrying not only photons but all kinds of elementary particles. Particles do not fall inside this surface but remain at it!

- The replacement of second law with NMP leads to ask whether a generalization of blackhole thermodynamics does make sense in TGD Universe. Since blackhole thermodynamics characterizes Hawking radiation, the generalization could make sense at least if there exist analog for the Hawking radiation. Note that also geometric variant of second law makes sense.

Could the analog of Hawking radiation be generated in the first state function reduction to the opposite boundary, and be perhaps be assigned with the sudden increase of radius of the partonic 2-surface defining the horizon? Could this burst of energy release the energy compensating the generation of gravitational binding energy? This burst would however have totally different interpretation: even gamma ray bursts from quasars could be considered as candidates for it and temperature would be totally different from the extremely low general relativistic Hawking temperature of order

T

_{GR}=[hbar/8π GM ] ,

which corresponds to an energy assignable to wavelength equal to 4π times Schwartschild radius. For Sun with Schwartschild radius r

_{S}=2GM=3 km one has T_{GR}= 3.2× 10^{-11}eV.

_{gr}could make sense physically. Also the replacement r

_{S}→ R, where R is the real radius of the star will be made.

- Blackhole temperature can be formally identified as surface gravity

T=(h

_{gr}/hbar) × [GM/2π R^{2}] = [h_{gr}/h] × [r_{S}^{2}/R^{2}]× T_{GR}= 1/[4π v_{0}] [r_{S}^{2}/R^{2}] .

For Sun with radius R= 6.96× 10

^{5}km one has T/m= 3.2× 10^{-11}giving T= 3× 10^{-2}eV for proton. This is by 9 orders higher than ordinary Hawking temperature. Amazingly, this temperature equals to room temperature! Is this a mere accident? If one takes seriously TGD inspired quantum biology in which quantum gravity plays a key role (see this) this does not seem to be the case. Note that for electron the temperature would correspond to energy 3/2× 10^{-5}eV which corresponds to 4.5 GHz frequency for ordinary Planck constant.

It must be however made clear that the value of v

_{0}for dark matter could differ from that deduced assuming that entire gravitational mass is dark. For M→ M_{D}= kM and v_{0}→ k^{1/2}v_{0}the orbital radii remain unchanged but the velocity of dark matter object at the orbit scales to k^{1/2}v_{0}. This kind of scaling is suggested by the fact that the value of h_{gr}seems to be too large as compared by the identification of biophotons as decay results of dark photons with h_{eff}=h_{gr}(some arguments suggest the value k≈ 2× 10^{-4}).

Note that for the radius R=[r

_{S}/2v_{0}π] the thermal energy exceeds the rest mass of the particle. For neutron stars this limit might be achieved.

- Blackhole entropy

S

_{GR}= [A/4 hbar G]= 4π GM^{2}/hbar=4π [M^{2}/M_{Pl}^{2}]

would be replaced with the negentropy for dark matter making sense also for systems containing both dark and ordinary matter. The negentropy N(m) associated with a flux tube of given type would be a fraction h/h

_{gr}from the total area of the horizon using Planck area as a unit:

N(m)=[h/h

_{gr}] × [A/4hbar G]= [h/h_{gr}] × [R^{2}/r_{S}^{2}] ×S_{GR}= v_{0}×[M/m]× [R^{2}/r_{S}^{2}] .

The dependence on m makes sense since a given flux tube type characterized by mass m determining the corresponding value of h

_{gr}has its own negentropy and the total negentropy is the sum over the particle species. The negentropy of Sun is numerically much smaller that corresponding blackhole entropy.

- Horizon area is proportional to (GM/v
_{0})^{2}∝ h_{eff}^{2}and should increase in discrete jumps by scalings of integer and be proportional to n^{2}.

The reduction sequences consist of life cycles at fixed boundary and the size of blackhole like state as of any state is expected to increase in discrete steps if it participates to cosmic expansion in average sense. This requires that the mass of blackhole like object gradually increases. The interpretation is that ordinary matter gradually transforms to dark matter and increases dark mass M= R/G.

Cosmic expansion is not observed for the sizes of individual astrophysical objects, which only co-move. The solution of the paradox is that they suddenly increase their size in state function reductions. This hypothesis allows to realize Expanding Earth hypothesis in TGD framework (see this). Number theoretically preferred scalings of blackhole radius come as powers of 2 and this would be the scaling associated with Expanding Earth hypothesis.

See the chapter Criticality and dark matter" or the article TGD view about black holes and Hawking radiation.

For a summary of earlier postings see Links to the latest progress in TGD.

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