A New Star Phase
Quantum gravity is an interesting topic that aims to understand gravity with the concepts put forth by quantum mechanics. It becomes difficult to measure quantum gravitational effects due to its small scale of visibility, the Planck scale. Here, the authors suggest that quantum gravity could be used as a solution to the information paradox. They propose that there is a new phase in a star’s life, which they call a Planck star.
A Planck star forms when the energy of a collapsing star condenses into a highly compressed core. This core has a density on the order of the Planck density (1096).
What is really interesting is the lifetime of a Planck star. When viewed from a large distance, the lifetime of the star is also very long. But when on the star itself, the lifetime is very short, about the time it would take for light to travel a distance of the star’s radius. This would be an example of gravitational time dilation: time slows down the closer an observer is to the massive Planck star. As a result, an explorer who came from far away would find himself in the future upon landing on the star.
Because of the large lifetime when observed from a far distance, the Planck star still behaves like a conventional black hole. But due to the short lifetime when viewed from the Planck star itself, the star appears to collapse and then bounce back. To those far away, this bounce happens in slow motion, which is why the star still appears as a black hole.
During this phase, the outer horizon shrinks and meets the growing internal horizon. At this point, a horizon no longer exists and any information trapped can now escape, thus solving the paradox.
Image: A sequence of light cones for a non-evaporating Planck star.