Posts Tagged ‘ stars ’

Why Our Universe Must Have Been Born Inside a Black Hole

From Technology Review:

“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.

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Revised theory of gravity doesn’t predict a Big Bang

Lisa Zyga in PHYSORG:

The Big Bang theory has formed the basis of our understanding of the universe’s origins since it was first proposed in 1927 by Georges Lemaitre. And for good reason: the theory is supported by scientists’ latest observations and experiments, and is based on Einstein’s widely accepted theory of general relativity. But scientists are always on the lookout for any evidence that might suggest an alternative to the Big Bang. The latest in this area of research comes from astrophysicists Maximo Banados and Pedro Ferreira, who have resurrected a theory of gravity from the early 20th century and discovered that a modified version of the theory may hold some surprises.

In a recent study published in , Banados and Ferreira have reconsidered the theory of gravity proposed by Arthur Eddington, a contemporary of Einstein. Eddington is perhaps best known for his trip to the Island of Principe on the west coast of Africa in 1919, where during a solar eclipse he observed that the Sun’s gravity does indeed bend starlight, providing one of the earliest confirmations of general relativity.

Although Eddington played a significant role in developing general relativity, during the following decades he became more interested in finding a theory to unify gravity and  – a task that is still being studied today. In 1924, Eddington proposed a new “gravitational action” as an alternative to the Einstein-Hilbert action, which could serve as an alternative starting point to general relativity. In astrophysics, a gravitational action is the mechanism that describes how gravity can emerge from space-time being curved by matter and energy. However, Eddington’s theory of gravity only worked for empty space and didn’t include any source of energy such as matter, making it an incomplete theory.

Since Eddington’s proposal, scientists have attempted various ways of including matter into the theory, although they have run into problems. In this study, Banados and Ferreira have tried a new way to extend the theory to include matter by using a gravitational action called the Born-Infeld action.

In their analysis, the scientists found that a key characteristic of Eddington’s revised  is that it reproduces Einstein gravity precisely in the vacuum conditions (with no matter), but it produces new effects when matter is added. Due to this characteristic, the revised theory has implications especially for high-density regions, such as in the very early Universe or within a black hole. For instance, the theory predicts a maximum density of homogeneous and isotropic space-time, which could have implications for black hole formation.

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