Lumpy ‘caterpillar wormholes’ may connect entangled black holes
Sometimes wormholes are lumpy
Shutterstock / Champhei
What happens when two black holes are connected by an inextricable quantum bond? Calculations suggest that this can give rise to an irregular space-time tunnel called an “Einstein-Rosen caterpillar”.
Albert Einstein’s name connects two very different physical oddities: the first is called the Einstein-Rosen bridge – a wormhole, or tunnel that connects distant points in space-time – and the second is known as the Einstein-Podolsky-Rosen pair, in which two particles are connected by an inseparable property called quantum entanglement. In 2013, physicists Juan Maldacena of Princeton University in New Jersey and Leonard Susskind of Stanford University in California suggested that when it comes to black holes, the two may be equivalent.
Brian Swingle of Brandeis University in Massachusetts and his colleagues found that this may only be true in some cases. They mathematically analyzed a set of entangled black holes and discovered that the situation is more complex – and more uneven – than previously appeared.
Swingle says that studying the wormholes that connect quantumly entangled black holes ultimately helps researchers better understand the interiors of black holes, which are poorly understood places full of mystery because of the remarkable force with which gravity acts there. Mathematical models show that the size of a black hole’s interior corresponds to its complexity – how complicated it is at the level of its quantum building blocks. The researchers wondered if there was a similar rule for wormholes connecting a pair of black holes.
This is a difficult task, because a complete understanding of black hole entanglement would require a complete theory of quantum gravity, which physicists have not yet formulated. Instead, the team used a model that connects quantum physics and gravity in an incomplete way, but which should resemble reality enough to offer valuable insights, Swingle says.
He and his colleagues discovered a mathematical correspondence between the amount of microscopic quantum randomness contained in a wormhole and its geometric length. Their calculations revealed that a typical wormhole is less likely to be smooth and more likely to contain bumps made of material, a characteristic that has earned it comparison to a caterpillar. Swingle says this differs from the 2013 result, which may apply to special, and therefore less common, cases where the entangled state of black holes led to a smooth wormhole in between.
Donald Marolf, of the University of California, Santa Barbara, says the new work adds information about entangled black holes, but still does not describe the most common case of such entanglement. He says that the collection of all theoretically possible states of black holes is rather large – larger than all the black holes that exist in our universe – and that it will take more theoretical research to say with certainty what type of connected state is most likely to be assumed by a pair of black holes.
Part of this future research could include using quantum computers as simulators of cosmic black holes and caterpillar wormholes, Swingle says. Because his team’s approach included connecting a simplified quantum theory and a theory of gravity, once quantum computers become more powerful and reliable, it might be possible to use them to learn more about quantum theory and new ideas about gravity, he says. The new calculation already uses some elements of quantum information theory. So there could be exciting developments in the other direction, where studying the mysteries of gravity would inspire new quantum computing algorithms, says Swingle.
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