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The maximally extended Schwarzschild solution (Kruskal diagram) envisages a white hole, which is the time-reverse of a black hole, i.e. a part of spacetime from which things can escape to us, while we can never get there. It is a singularity in the past, out of which the universe appears to spring.

My questions are:

  1. Are you aware of any theory or author which/who uses the white hole model to explain the birth of the universe?

  2. If Yes, which features in the white hole scheme are confirmed by the current cosmological observations?

  3. If Not, which features in the white hole scheme are contradicted by the current cosmological observations?

  4. Possible links?

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  • $\begingroup$ IINM, there are time-like geodesics in this geometry that do not 'come out of' the white hole region. Assuming that is correct, in what sense would the universe appear to spring from the singularity in the past? $\endgroup$ – Alfred Centauri Aug 19 at 17:41
  • $\begingroup$ The universe cannot be specifically a Schwarzschild white hole, as the question suggests, because the spatial geometry inside the horizon is a 3-cylinder expanding in only 2 out of 3 dimensions. This is inconsistent with the observed uninform expansion of the universe in all 3 dimensions. If the universe is a white hole, then it is not of the Schwarzschild type (or Kerr or any other vacuum solunion). $\endgroup$ – safesphere Aug 20 at 7:19
  • $\begingroup$ @Alfred Centauri. "The universe appears to spring" simply means that any massive object or light ray occurring in the white hole region escapes to the Schwarzschild universe (or to the parallel universe) in the Kruskal diagram. $\endgroup$ – Michele Grosso Aug 20 at 16:59
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A quick googling produced this: “Out of the White Hole: A Holographic Origin for the Big BangarXiv:1309.1487 which interprets cosmological singularity of braneworld scenario as occurring inside the white hole horizon.

From the abstract:

While most of the singularities of General Relativity are expected to be safely hidden behind event horizons by the cosmic censorship conjecture, we happen to live in the causal future of the classical big bang singularity, whose resolution constitutes the active field of early universe cosmology. Could the big bang be also hidden behind a causal horizon, making us immune to the decadent impacts of a naked singularity? We describe a braneworld description of cosmology with both 4d induced and 5d bulk gravity (otherwise known as Dvali-Gabadadze-Porati, or DGP model), which exhibits this feature: The universe emerges as a spherical 3-brane out of the formation of a 5d Schwarzschild black hole. In particular, we show that a pressure singularity of the holographic fluid, discovered earlier, happens inside the white hole horizon, and thus need not be real or imply any pathology. Furthermore, we outline a novel mechanism through which any thermal atmosphere for the brane, with comoving temperature of 20% of the 5D Planck mass can induce scale-invariant primordial curvature perturbations on the brane, circumventing the need for a separate process (such as cosmic inflation) to explain current cosmological observations. Finally, we note that 5D space-time is asymptotically flat, and thus potentially allows an S-matrix or (after minor modifications) AdS/CFT description of the cosmological big bang.

Current cosmological observations do not rule out Dvali–Gabadadze–Porrati model on which this interpretation is premised.

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  • $\begingroup$ Can't the universe simply be an Oppenheimer-Snyder white hole? $\endgroup$ – safesphere Aug 20 at 7:09
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The best known among BH to WH bouncing cosmologies may be Nikodem J. Poplawski's "cosmology with torsion" (described at https://arxiv.org/abs/1007.0587 and https://arxiv.org/abs/0902.1994), which is based on the ECSK (Einstein-Cartan-Sciama-Kibble) theory of gravity. ECSK originated through discussions between Einstein and the mathematician Elie Cartan in the late 1920's, and was modified much more recently by Sciama and Kibble. Poplawski and others consider it to be a version of GR, although it differs from simpler and more widely-used versions by requiring that fermions should have a (tiny) spatial extent. It's reportedly more complex (mathematically) than the standard version of GR, and equally adequate for confirmation of GR's observational proofs.

In Poplawski's cosmology, the trajectories of newly-materialized fermions (separated by tidal effects, on opposite sides of the outward-propagating event horizon of a rotating star undergoing gravitational collapse, from their former partners in virtual particle-antiparticle pairs, during that horizon's outward propagation) are accelerated and reversed during contact with much larger stellar fermions. (I should point out that all or most stars, as well as the black holes into which the larger ones eventually collapse gravitationally, have at least a faint residual rotation; also, all fermions--even the "point-like" ones of standard GR--spin.)

Poplawski's views are consistent with the conventional view of time's "arrow" (the subjectively-experienced direction of time's "passage") as being thermodynamic in nature, and see that direction as initially determined by the spatial direction of material falling toward the center of the collapsing star. (His views are also consistent with the "block universe" or "eternalist" view of physical time, in which every duration contains every briefer duration: This view is often considered to be implied by the paradoxes of Special Relativity, and appears consistent with the observational proofs of GR.)

In his cosmology, each new local universe (or temporal iteration) is formed when the accelerated particles reach a zone, still within the collapsing star's original volume, that he analogizes to a 3-dimensional version of the surface of a sphere (i.e., like "the skin of a basketball"): Beyond that region of spacetime, their trajectories are extended more-or-less inertially, but, since the region beyond might lie mainly or entirely within the vast zone within which all subatomic particles (possibly excepting the proton) decay, it would contain few or no live observers.

Poplawski's 2015 collaboration with Desai, "Non-parametric reconstruction of an inflaton potential" at https://arxiv.org/abs/1510.08834 , clearly reveals it (through CMB data obtained via the Planck satellite) to be a version of cosmic inflation, albeit without the subatomic "inflaton" particles which (in spite of their resemblance to the Higgs particle already observed) have not yet been found at the masses appropriate for asymptotically-exponential spatial expansion, in attempts to confirm the possibility of whatever cosmic inflation may be caused by scalar fields. (The gravitational collapse of many large stars, on the other hand, has been apparent for decades, primarily thru the elliptical or nearly-circular orbits of their former partners in binary pairs.) The inflationary spatial expansion hypothesized by Poplawski can be seen as as an application of Maupertuis' "Principle of Least Action", described at https://en.wikipedia.org/wiki/Principle_of_least_action. In the work with Desai, he posits a sequential version of that expansion, which might perhaps explain the acceleration of inflation that was revealed by the supernova 1A observations of 1998 and 1999.

The difference in scale between each "parenting" LU & its "baby" is huge (by a factor of 10^32), but, because the "Cartan radius" of the fermion nevertheless remains much greater than the Planck length, it's not as great as that difference between particles and black holes that's discussed by Susskind in his 2014 "ER=EPR" lecture, available free on YouTube.

Although standard GR may be scale-invariant only thru application of the Weyl Curvature Hypothesis that's been much-discussed since the 1970's, I frankly have to suspect that huge variations in spacetime scale remain "suspect" in physics only due to the strange combination of a conception of ourselves as grandiose with a patronizing attitude toward children's use of toys.

In conjunction with the notion that each local universe in Poplawski's cosmos might contain black holes of its own on sequentially smaller scales, I believe that, in combination with the motions and rotation rates of most of them in relation to the others, his cosmology might have unusually strong potential for explaining the huge discrepancy between the theoretical vacuum energy and the observed one. Its potential for bypassing the cosmological singularity has already been widely noted.

The aspect of all this about which I'm most hopeful of receiving comments is the possibility that the evaporated local universes of one iteration might comprise either the virtual particles (or fields) of another OR its black holes, perhaps in relation to Feynman and Wheeler's notion of particles as antiparticles travelling "backwards in time", and vice-versa: It's because of those possibilities that I've included a reference to Susskind's 2014 "ER=EPR" lecture at https://www.youtube.com/watch?v=OBPpRqxY8Uw , the best I've ever seen. (Before seeing it, I'd thought that the causal separations associated with event horizons were more-or-less a temporal thing: It hadn't occurred to me that the scales of material in the separated regions might differ enough to prevent their interactions, or, at least, to greatly rarefy them.)

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