A small change to the theory of gravity implies that our universe inherited its arrow of time from the black hole in which it was born.
"Accordingly, our own Universe may be the interior of a black hole existing in another universe." So concludes Nikodem Poplawski at Indiana University in a remarkable paper about the nature of space and the origin of time.
The idea that new universes can be created inside black holes and that our own may have originated in this way has been the raw fodder of science fiction for many years. But a proper scientific derivation of the notion has never emerged.
Today Poplawski provides such a derivation. He says 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.
Poplawski 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 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.
That's interesting for a number of reasons. First, it has important implications for the way the Universe must have grown when it was close to its minimum size.
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, a process known as inflation.
The problem with inflation is that it needs an additional theory to explain why it occurs and that's ugly. Poplawski's approach immediately solves this problem. He says that torsion caused this rapid inflation.
That means the universe as we see it today can be explained by a single theory of gravity without any additional assumptions about inflation.
Another important by-product of Poplawski's approach is that it makes it possible for universes to be born inside the event horizons of certain kinds of black hole. Here, torsion prevents the formation of a singularity but allows a HUGE energy density to build up, which leads to the creation of particles on a massive scale via pair production followed by the expansion of the new universe.
This is a Big Bang type event. "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, the new universe is a separate branch of space time and evolves accordingly.
Incidentally, this approach also suggests a solution to another of the great problems of cosmology: 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.
In other words, our universe inherited its arrow of time from its mother.
He says that daughter universes may inherit other properties from their mothers, implying that it may be possible to detect these properties, providing an experimental proof of his idea.
Theories of everything don't get much more ambitious than this. Entertaining stuff!
In this philosophical paper, we explore computational and biological analogies to address the fine-tuning problem in cosmology. We first clarify what it means for physical constants or initial conditions to be fine-tuned. We review important distinctions such as the dimensionless and dimensional physical constants, and the classification of constants proposed by Levy-Leblond. Then we explore how two great analogies, computational and biological, can give new insights into our problem. This paper includes a preliminary study to examine the two analogies. Importantly, analogies are both useful and fundamental cognitive tools, but can also be misused or misinterpreted. The idea that our universe might be modelled as a computational entity is analysed, and we discuss the distinction between physical laws and initial conditions using algorithmic information theory. Smolin introduced the theory of "Cosmological Natural Selection" with a biological analogy in mind. We examine an extension of this analogy involving intelligent life. We discuss if and how this extension could be legitimated. Keywords: origin of the universe, fine-tuning, physical constants, initial conditions, computational universe, biological universe, role of intelligent life, cosmological natural selection, cosmological artificial selection, artificial cosmogenesis.