How Black Holes Nearly Ruined Time


Image: NAUTILUS
Quantum mechanics rescued our understanding of past and future from the black hole.

By Andrew Turner & Alex Tinguely |NAUTILUS

An Introduction to the Black Hole Institute

Fittingly, the Black Hole Initiative (BHI) was founded 100 years after Karl Schwarzschild solved Einstein’s equations for general relativity—a solution that described a black hole decades before the first astronomical evidence that they exist. As exotic structures of spacetime, black holes continue to fascinate astronomers, physicists, mathematicians, philosophers, and the general public, following on a century of research into their mysterious nature.

The mission of the BHI is interdisciplinary and, to that end, we sponsor many events that create the environment to support interaction between researchers of different disciplines. Philosophers speak with mathematicians, physicists, and astronomers, theorists speak with observers and a series of scheduled events create the venue for people to regularly come together.

As an example, for a problem we care about, consider the singularities at the centers of black holes, which mark the breakdown of Einstein’s theory of gravity. What would a singularity look like in the quantum mechanical context? Most likely, it would appear as an extreme concentration of a huge mass (more than a few solar masses for astrophysical black holes) within a tiny volume. The size of the reservoir that drains all matter that fell into an astrophysical black hole is unknown and constitutes one of the unsolved problems on which BHI scholars work.

We are delighted to present a collection of essays which were carefully selected by our senior faculty out of many applications to the first essay competition of the BHI. The winning essays will be published here on Nautilus over the next five weeks, beginning with the fifth-place finisher and working up to the first-place finisher. We hope that you will enjoy them as much as we did.

—Abraham (Avi) Loeb
Frank B. Baird, Jr. Professor of Science, Harvard University
Chair, Harvard Astronomy Department
Founding Director, Black Hole Initiative (BHI)


Black holes are mystifying objects that have captivated our imaginations since their existence was first proposed. The most striking feature of a black hole is its event horizon—a boundary from within that nothing can escape. Objects can cross the event horizon from outside to inside, but once they do, they can never cross back, nor can any information about them; anything that crosses the event horizon of a black hole is cut off entirely from the outside universe.

For many years, the existence of black holes seemed to threaten a fundamental tenet of modern physics called the second law of thermodynamics. This law helps us to distinguish the past from the future, thus defining an “arrow of time.” To understand why black holes posed this threat, we need to discuss time reversal and entropy.

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