Black holes: Not endings, but beginnings? Theoretical study delves into 'white holes'

Our understanding of black holes, time and the mysterious dark energy that dominates the universe could be revolutionized, as new University of Sheffield research helps unravel the mysteries of the cosmos.

Black holes—areas of space where gravity is so strong that not even light can escape—have long been objects of fascination, with astrophysicists, theoretical physicists and others dedicating their lives to revealing their secrets. This fascination with the unknown has inspired numerous writers and filmmakers, with novels and films such as "Interstellar" exploring these enigmatic objects' hold on our collective imagination.

According to Einstein's theory of general relativity, anyone trapped inside a black hole would fall toward its center and be destroyed by immense gravitational forces. This center, known as a singularity, is the point where the matter of a giant star, which is believed to have collapsed to form the black hole, is crushed down into an infinitesimally tiny point. At this singularity, our understanding of physics and time breaks down.

Using the laws of quantum mechanics, a fundamental theory describing the nature of the universe at the level of atoms and even smaller particles, the new study proposes a radically different theoretical standpoint where, rather than a singularity signifying the end, it could represent a new beginning.

The new paper, titled "Black Hole Singularity Resolution in Unimodular Gravity from Unitarity," published today in Physical Review Letters, aims to illustrate the point where our current grasp of physics and time falters.

While black holes are often described as sucking everything, including time, into a point of nothingness, in the paper, white holes are theorized to act in reverse, ejecting matter, energy and time back into the universe.

The study uses a simplified, theoretical model of a black hole, known as a planar black hole. Unlike typical black holes, which have a spherical shape, a planar black hole's boundary is a flat, two-dimensional surface. The researchers' ongoing work suggests that the same mechanism could also apply to a typical black hole.

"It has long been a question as to whether quantum mechanics can change our understanding of black holes and give us insights into their true nature," said Dr. Steffen Gielen, from the University of Sheffield's School of Mathematical and Physical Sciences, who co-wrote the paper with Lucía Menéndez-Pidal from Complutense University of Madrid.

"In quantum mechanics, time as we understand it cannot end as systems perpetually change and evolve."

The scientists' findings demonstrate how, using the laws of quantum mechanics, the black hole singularity is replaced by a region of large quantum fluctuations—tiny, temporary changes in the energy of space—where space and time do not end. Instead, space and time transition into a new phase called a white hole—a theoretical region of space thought to function in the opposite way to a black hole. As such, a white hole could be where time begins.

"While time is, in general, thought to be relative to the observer, in our research time is derived from the mysterious dark energy which permeates the entire universe," Dr. Gielen continued.

"We propose that time is measured by the dark energy that is everywhere in the universe, and responsible for its current expansion. This is the pivotal new idea that allows us to grasp the phenomena occurring within a black hole."

Dark energy is a mysterious, theoretical force that scientists believe drives the accelerating expansion of the universe. The new study uses dark energy almost as a point of reference, with energy and time as complementary ideas that can be measured against one another.

Tantalizingly, the theory that what we perceive as a singularity is actually a beginning suggests the existence of something even more enigmatic on the other side of a white hole.

"Hypothetically you could have an observer—a hypothetical entity—go through the black hole, through what we think of as a singularity and emerge on the other side of the white hole. It's a highly abstract notion of an observer but it could happen, in theory," Dr. Gielen added.

Beyond such theoretical musings, the suggestion of a profound connection between the nature of time at the most fundamental level and the mysterious dark energy that governs the cosmos will be explored further in the months and years ahead.

The new research also suggests novel approaches to reconciling gravity and quantum mechanics, potentially paving the way for new fundamental theories and breakthroughs in our understanding of the universe.