Black holes may transition into white holes, ejecting matter and even time back into the Universe, according to a new study by physicists from the University of Sheffield and the Universidad Complutense de Madrid.
Steffen Gielen & Lucía Menéndez-Pidal study the quantum dynamics of a planar black hole, requiring unitarity in the natural time coordinate conjugate to the cosmological constant of motion appearing in unimodular gravity. Image credit: Sci.News.
According to Einstein’s theory of general relativity, anyone trapped inside a black hole would fall towards 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.
“While black holes are often described as sucking everything, including time, into a point of nothingness, in the new paper, white holes are theorized to act in reverse, ejecting matter, energy and time back into the Universe,” said University of Sheffield’s Dr. Steffen Gielen and Dr. Lucía Menéndez-Pidal from the Complutense University of Madrid.
In their study, the authors use 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’ 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,” Dr. Gielen said.
“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. 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 said.
“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.”
In the study, the physicists use 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 said.
The team’s paper was published this week in the journal Physical Review Letters.
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Steffen Gielen & Lucía Menéndez-Pidal. 2025. Black Hole Singularity Resolution in Unimodular Gravity from Unitarity. Phys. Rev. Lett 134, 101501; doi: 10.1103/PhysRevLett.134.101501
