We’ve heard the idea that our entire universe might just be an atom in some gigantic table leg or a spot on some celestial wall paper.

Apparently, according to recent physics, our entire universe could be the interior of a black hole existing in another universe. In a paper about the nature of space and the origin of time, Nikodem Poplawski, of Indiana University, suggests that a small change to the theory of gravity would imply that our universe inherited its arrow of time from the black hole in which it was born. Poplawski says that the idea that black holes are the cosmic mothers of new universes is a natural consequence of a simple new assumption about the nature of spacetime. He points out that the standard derivation of general relativity takes no account of the intrinsic momentum of spin half particles. However there is another version of the theory, called the Einstein-Cartan-Kibble-Sciama theory of gravity, which does. This theory predicts that particles with half integer spin should interact, generating a tiny repulsive force called torsion. In ordinary circumstances, torsion is too small to have any effect. But when densities become much higher than those in nuclear matter, it becomes significant. In particular, says Poplawski, torsion prevents the formation of singularities inside a black hole.

Now I’m not entirely sure what that means exactly, but I do understand that astrophysicists have long known that our universe is so big that it could not have reached its current size given the rate of expansion we see now. Instead, they believe it grew by many orders of magnitude in a fraction of a second after the Big Bang, the period known as known as inflation. Poplawski’s approach immediately solves the inflation problem, saying that torsion caused this rapid inflation, which means the universe as we see it today can be explained by a single theory of gravity without any additional assumptions about inflation.

A corollary of this is that it makes it possible for universes to be born inside the event horizons of certain kinds of black hole where torsion prevents the formation of a singularity but allows energy density to build up, with creation of particles on a massive scale via pair production followed by the expansion of a new universe. “Such an expansion is not visible for observers outside the black hole, for whom the horizon’s formation and all subsequent processes occur after infinite time,” says Poplawski. For this reason, he emphasizes, the new universe is a separate branch of space time and evolves accordingly. Poplawski’s theory also suggests an solution as to why time seems to flow in one direction but not in the other, even though the laws of physics are time symmetric.

Poplawski says the origin of the arrow of time comes from the asymmetry of the flow of matter into the black hole from the mother universe. “The arrow of cosmic time of a universe inside a black hole would then be fixed by the time-asymmetric collapse of matter through the event horizon,” he says.. Translated, this means that our universe inherited its arrow of time from its source. “Daughter universes,” he says, “may inherit other properties from their mothers,” implying that it may be possible to detect these properties, providing an experimentally falsifiable proof of his idea.

All of which seems to say, as far as my poor brain can fathom it, that we really don’t understand the universe very well at all.

Nikodem J. Poplawski (Department of Physics, Indiana University). Cosmology with torsion: an alternative to cosmic inflation (4 Jul 2010)

The Einstein-Cartan-Kibble-Sciama theory of gravity provides a simple scenario in early cosmology which is alternative to standard cosmic inflation and does not require scalar fields. The torsion of spacetime prevents the appearance of the cosmological singularity in the early Universe filled with Dirac particles averaged as a spin fluid. Instead, its expansion starts from a state at which the Universe has a minimum but finite radius. We show that the dynamics of the closed Universe immediately after this state naturally solves the flatness and horizon problems in cosmology because of an extremely small and negative torsion density parameter, Ω

_{S}≈ -10^{-69}. This scenario also suggests that the contraction of our Universe preceding the state of minimum radius could correspond to the dynamics of matter inside the event horizon of a newly formed black hole existing in another universe.

The universe as a black hole in isotropic coordinates (2 Jan 2009)

We show that the radial geodesic motion of a particle inside a black hole in isotropic coordinates (the Einstein-Rosen bridge) is physically different from the radial motion inside a Schwarzschild black hole. A particle enters the interior region of an Einstein-Rosen black hole which is regular and physically equivalent to the asymptotically flat exterior of a white hole, and the particle’s proper time extends to infinity. Because the motion across the Einstein-Rosen bridge is unidirectional, and the surface of a black hole is the event horizon for distant observers, an Einstein-Rosen black hole is indistinguishable from a Schwarzschild black hole for such observers. Observers inside an Einstein-Rosen black hole perceive its interior as a closed universe that began when the black hole formed, with an initial radius equal to the Schwarzschild radius of the black hole

r, and with an initial accelerated expansion. Therefore the model of a universe as a black hole in isotropic coordinates explains the origin of cosmic inflation. We show that this kind of inflation corresponds to the effective cosmological constant Λ = 3/_{g}r_{g}^{2}, which, for the smallest astrophysical black holes, is ∼ 10^{-8}m^{-2}. If we assume that our Universe is the interior of an Einstein-Rosen black hole, astronomical observations give the time of inflation ∼ 10^{-3}s and the size of the Universe at the end of the inflationary epoch ∼ 10^{32}m.