In a universe full of bizarre objects, recent research suggests that hypothetical phenomena known as kugelblitze — black holes made from light — simply cannot exist.
If you have never heard of kugelblitze — directly translated as “ball lightning” — don't feel bad. According to new research, they don't exist — and can't exist (though they might have once existed a very long time ago).
Defined as black holes made of light, they present an oxymoronic concept. Traditionally, a black hole is black because light itself cannot escape its gravitational abyss. So a black hole created out of light — a kugelblitz (singular) — is a counterintuitive idea, but lots of counterintuitive things happen in our quantum universe.
Hypothetically, this version of a black hole is formed from “humongous amounts of electromagnetic radiation,” according to theoretical physicist Eduardo Martin-Martinez, who recently helped “settle the debate” over whether such a thing is actually possible. The title of their recent paper is unusually brief and to-the-point: “No black holes from light.”
“While it would be scientifically wonderful if we could create microscopic black holes using very intense lasers,” Martin-Martinez explained in an interview with FirstPrinciples, “our research shows that this is not possible.”
The kugelblitze conquerors
Martin-Martinez along with his collaborators — José Polo-Gómez, Luis J. Garay and Álvaro Álvarez-Domínguez — have harboured doubts about this phenomenon for years, but their skepticism was “not widely shared” in the astrophysics community, he says.
“I first thought of investigating the idea when about 10 years ago I was present in some discussions about far future experiments involving optics and lasers,” recalls Martin-Martinez, a professor of mathematical physics at the University of Waterloo and associate faculty member at Perimeter Institute and the Institute for Quantum Computing. (Read our Q&A with Martin-Martinez.)
“The possibility of creating kugelblitze was mentioned, and I raised some reservations that quantum effects may actually make it impossible to concentrate enough light. I was particularly concerned about the phenomena of vacuum polarization and the Schwinger effect, which involve the creation of electron-positron pairs in the presence of very strong electromagnetic fields and that very likely would dissipate the energy concentrated in the form of light.”
Their initial skepticism turned out to be well founded. The team scrutinized the concept through a framework that combines quantum field theory with general relativity. Between blackboard sessions and long video calls, the team worked out analytical solutions for all the differential equations modelling the energy dissipation due to Schwinger effect in areas of “humongous amounts of electromagnetic radiation.”
While they were not particularly surprised to rule out kugelblitze, they were quite surprised by the strength and implications of their findings.
“Our results show even stronger restrictions than we originally thought of,” says Martin-Martinez.
”This work not only settles the debate about whether it is possible to create strong gravitational phenomena with electromagnetic fields generated by technological means, but also that no astrophysical phenomenon that we can conceive in our current universe would be able to get even close to the regimes where these theoretical black holes can be formed.”
In other words, kugelblitze don’t exist because they can’t, and the math says so. However, that doesn’t necessarily mean they have not existed in the distant past. It’s conceivable, the team concedes in the paper, that the extreme conditions of the very, very early universe (the cosmic soup that simmered shortly after the big bang) could potentially have been hospitable to these elusive spheres of energy.
The post-kugelblitze universe
The realization that kugelblitze do not and cannot exist in the contemporary universe is a bittersweet discovery. If black holes made of light were out there in the universe, astronomers would have new exotic objects to hunt in space.
Martin-Martinez says we shouldn’t mourn them, as they may have never existed in the first place, but we should instead apply similar analytical scrutiny to other unsolved puzzles. The team is now keen to explore the consequences of quantum effects for strong gravity phenomena, and how Schwinger-like effects may hinder the formation of other astrophysical objects.
"As we mention in the article, it may be interesting to look at the prospect of these kugelblitze as potential dark matter components and the possibility that they form in the primordial stages of the universe.”
The researcher team is particularly interested in the gravitational properties of quantum matter, especially where it violates traditional energy conditions. What that means, says Martin-Martinez, is that quantum matter could give rise to "exotic spacetimes” with strange phenomena like repulsive gravity, the Alcubierre warp drive, or even traversable wormholes.
Concepts like warp drives and wormholes may seem even stranger than the kugelblitze, yet their potential existence remains open to scientific inquiry.
