I received an interesting link from Ulla about blackholes. The claim of physics professor Laura Mersini-Houghton is that black holes cannot be created in star collapse. The collapse of star would involve at endphases a "swelling" which evaporates the blackhole candidate as Hawking radiation so that no blackhole would be formed!
One positive consequence would be that this would put an end to the endless prattling about blackhole entropy, firewalls, etc.. which to my opinion are just gnawing of an old bone. Even better: no-one would waste time to a desperate attempt to reduce QCD, nuclear physics, or condensed matter physics to the physics of blackholes in 10 dimensions!
Personally I take blackholes only as a singularity of GRT. For some reason colleagues seem to be unable to admit that GRT space-time is not enough. String theories do not bring anything new since strings as such have too low dimension to tell anything about space-time physics and their long length scale limit is (or is hand-waved to be) just Einstein-YM type theory. In the theory next to GRT blackholes must be replaced with something more well-defined.
This sounds extremely blasphemous, but after 37 years or hard work I can safely state that TGD is one of the very few real candidates for the theory next to GRT.
- In TGD framework one can imbed Schwarschild solution down to some critical radius. Something happens at the horizon of blackhole. Scwartchild-Nordström solution suggests what. By an arbitrary small deformation of the radial component grr=1/(1-2GM/r) so that it becomes finite at horizon r=rS=2GM the determinant of 4-metric becomes vanishing. CP2 is one of the extremals of Einstein-Maxwell action with cosmological constant.
This observation suggests that horizon in improved theory is the 3-surface at which the signature of the metric transforms from Minkowskian to Euclidian. Euclidian space-times are used in the quantization of GRT as a mathematical trick in an attempt to make some sense about path integral by transforming it to functional integral but are not taken seriously physically.
- In TGD space-time surfaces indeed consist of both Minkowskian and Euclidian regions and Euclidian regions correspond to the 4-D lines of generalized Feynman diagrams. A good model is as deformations of CP2 type vacuum extremal which are locally just CP2 but whose imbedding to M4× CP2 is non-standard having light-like random curve as M4 projection giving rise to conformal invariance and Virasoro conditions. Blackhole would be replaced with particle like object identifiable as line of generalized Feynman diagram. All material objects would have space-time sheet which has Euclidian signature of induced metric and represents the object as particle like object.
- Einstein-Yang-Mills space-time is obtained from the many-sheeted space-time of TGD by lumping together the sheets and describing it as a region of Minkowski space endowed with an effective metric which is sum of flat Minkowski metric and deviations of the metrics of sheets from Minkowski metric. Same procedure is applied to gauge potentials to get standard model.
- The motivation is that test particle topologically condenses at all space-time sheets present in given region of M4 and and the effects of the classical fields at these sheets superpose. Thus superposition of fields is replaced with superposition of their effects and linear superposition with set theoretic union of space-time sheets. TGD inspired cosmology assumes that the effective metric obtained in this manner allows imbedding as vacuum extremal of Kähler action. The justification of this assumption is that it solves several key problems of GRT based cosmology. One can also represent a subset of solutions of Einstein's equations as vacuum extremals but in the generic case the many-sheeted space-time cannot be approximated by single space-time sheet.
- The number of field patterns in TGD Universe is extremely small - given by preferred extremals - and the relationship of TGD to GRT and YM theories is like that of atomic physics to condensed matter physics. In the transition to GRT-Yang-Mills picture one gets rid of enormous topological complexity but the extreme simplicity at the level of fields is lost. Only four CP2 coordinates appear in the role of fields in TGD framework and at GRT Yang-Mills limit they are replaced with a large number of classical fields.
- We indeed see everywhere outer boundaries: they could be identifiable as effective or genuine boundaries of space-time sheets in TGD framework: this depends on whether one adds to Kähler action a boundary term allowing the presence of boundaries or not. If not, the space-time sheets are pairs of sheets glued together along would-be boundaries. Seeing is however not believing. We must somehow measure the presence of space-time sheets before we can take them seriously!
- In many-sheeted space-time signal from say supernova can arrive along several space-time sheets simultaneously and the arrival time depends on the sheet. In case of SN1987A this effect was observed for neutrinos and photons as one can learn from Wikipedia article).
- The "dropping" of particles from smaller to larger space-time sheet at the boundary of smaller one provides a possible mechanism of metabolism since the zero point kinetic energy decreases.
Addition: Lubos has been highly emotional about Laura Mersini's paper. It is a pity that Lubos experiences all questioning of cherished assumptions as an organized attempt to destroy quantum mechanics, general relativity, or superstring theory and reacts accordingly. Also this posting is full of adjectives such as "nutty", "idiotic", "stupid", "silly","lunatic","crank","super-idiotic", to list few of the evergreens of Lubos. Everyone can decide whether to take seriously a person whose arguments are full of this kind of ad hominem attacks.
These bursts of anger do not change the fact that black hole represents a mathematical singularity of an otherwise highly successful theory. There is no doubt that GRT describes the physics outside the exterior of blackhole. The challenge is to find a theory which allows to understand what really happens in the interior. Essentially microscopic view about space-time replacing the GRT view, which is essentially "astroscopic" . Superstrings tried this but did not bring in nothing new since all predictions emerge from ad hoc hypothesis known as spontaneous compactification. Someone has correctly said that superstring theory predicts 10-dimensional Einsteinian gravity, the rest is an inflation of ad hoc hypothesis. Also Big bang cosmology is very successful but "What is the real physics behind and before what we identify as inflation?" is the question which we should approach with an open mind.