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February 6, 2023

Building a Better Black Hole
How little black holes could power starships in the future—and could have fine-tuned the laws of physics in our past.
by Scott Dodd
FQXi Awardees: Louis Crane
January 29, 2010
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Louis Crane
It’s not easy to follow a conversation about theoretical physics with Louis Crane—and he knows it. He talks of building artificial black holes to power starships and how intelligent space-faring beings from another universe could have fine-tuned the laws of our own. Oh, and he has also co-developed a theory of quantum gravity. "I really have gotten to a place where I’m out there by myself," Crane says. "It’s sort of like crossing Alaska by dogsled. The view is wonderful, but there really aren’t that many people to share it with."

Not that he doesn’t try. I recently spent a long evening on the phone with Crane, an FQXi Awardee and professor of mathematics at Kansas State University in Manhattan, Kansas. Crane was trying to elaborate on the implications of the Barrett-Crane Model of loop quantum gravity, developed with fellow physicist John Barrett. To do that, he had to explain some innovative ways of doing math that I had barely even heard of. "I wish you could see my hands," Crane told me at one point. "I think you could understand it better if you could see my hands."

I doubt it, especially after receiving an e-mail from one of Crane’s early collaborators, Lee Smolin of the Perimeter Institute for Theoretical Physics. I had asked Smolin for his impressions of Crane’s recent work. Smolin replied that he had found "lots in (Crane’s) last few papers that I don’t understand technically."

So at least I’m in good company.

Defying Categorification

"Louis Crane is a mathematician by training and he tends to think and present his ideas in a very mathematical way," says physicist Christopher Isham, whose work overlaps with Crane’s, "Only a tiny fraction of theoretical physicists are familiar at all with the branches of mathematics that he uses."

It’s been that way for Crane all of his life. A mathematical prodigy who took graduate-level courses at age 14, Crane studied at the University of Chicago under Saunders Mac Lane, one of the most influential American mathematicians of the 20th century. Mac Lane cofounded of a branch of math called "category theory."

It’s sort of like crossing
Alaska by dogsled. The
view is wonderful, but
there really aren’t that
many people to share
it with.
- Louis Crane
Crane would later add his own term to the mathematical lexicon, "categorification." Like Mac Lane, Crane incorporates advanced mathematical models known as sheaves and topos theory into his calculations.

Learning category theory from one of its originators sent the young Crane off on some very unusual directions. While in high school, he set out to reconcile Mac Lane’s new mathematical concepts with theoretical physics. "I decided that I wanted to stop thinking about spacetime as a continuum," he says, then adds—and I can’t quite tell if he’s joking—"Everyone just assumed I’d get over it."

Crane was determined, though, to bridge the gap that he perceived between math and physics, so he has taken courses in both throughout his career. "Right now, I’m spending half of my time reading astrophysics and the other half thinking about category theory," he says. "Some people think I’m crazy."

A Desire for Collabor-ification

Crane’s need to find people that he can share his ideas with is one of the reasons that he applied for a grant from The Foundational Questions Institute. The $135,247 award that he has received will help him travel and collaborate in person with other physicists—something that Crane thinks is vital to his work. When he and Barrett were working on their quantum gravity model, for instance, they sent each other frustrating e-mail after e-mail. But when they got in a room together for five minutes, they figured it out quickly, Crane says. "I went to England this summer because there were two people I thought I could explain this to," he says, talking about his latest work. One was Barrett, and the other is Isham, with whom he also collaborates.

Isham acknowledges that it’s hard to judge the long-term significance of the work that he and Crane do. "If successful, (we) would have a major impact on the progression of quantum gravity studies," Isham says. "But to be honest, (we) are very much shooting in the dark. It is high-risk research!"

Despite that, Crane says he keeps pursuing his work because "it’s beautiful, and most other things are ugly." Besides, he adds, "We’re going to have to know the quantum theory of gravity if we’re ever going to build little black holes."

Sure, but, wait a minute. What was that?

Black Hole-ification

Of course, Crane continues, to do so, we’ll need armies of self-replicating space robots and focusing lasers the size of an asteroid. "I haven’t spent a lot of time on the engineering," Crane concedes. "It would be very tricky."

Just as a spectrum of colors is produced by sunlight streaming through
a prism, this image from the Chandra X-Ray Observatory shows
the spectrum of a black hole.

Credit: NASA/CfA/J.McClintock & M.Garcia
This time, his line of thinking actually isn’t so hard to follow. If we can fully understand—and ultimately control—gravity, then building tiny black holes to power starships could make sense. They would generate enormous amounts of power. "I think it’s the only thing imaginable that would actually get us to the stars," Crane says. "It’s extremely difficult to make, but I don’t think it’s impossible."

And if it is possible, then a custom-built black hole might have already been created somewhere in the past—giving rise to our own cosmos, says Crane. He cites a theory by Smolin, which suggests that our universe is only one of many, and that new universes arise within black holes. Crane reasons that long ago, intelligent beings with the ability to make artificial black holes for spaceships might have littered their universe with them. A lot of black holes could mean a lot of daughter universes—possibly including our own.

I think it’s the only
thing imaginable that
would actually get us
to the stars.
- Louis Crane on artificial black holes
As long as they were making black holes, those previous space-farers would probably have tailored them so that any daughter universe born from them would have the right kind of physics to support life as they knew it. The model may thus explain why our universe seems so peculiarly well suited for life to exist.

If all of this is true—and we’re piling up a lot of "ifs" here— then maybe, Crane says, he’s a link in the long chain that moves humanity toward fulfilling our purpose of creating more universes.

"Maybe that’s why I do it," he says. "Maybe that’s why I don’t quit."

Now that’s a concept that I have no problem understanding.

Read Louis Crane’s essay, “Stardrives and Spinoza” (pdf), which won first prize in FQXi’s essay contest 2009.

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Recent Comments

Dears Jody and Jason,

you can find the paper here:



Dear Scott, dears all,

you could be interested that, together with my colleague Herman Mosquera Cuesta, I recently found an exact solution to Einstein field equation which remove black holes singularity at the classical level, i.e. WITHOUT quantum argumentations. In our work, we have also given a new integration of the famous Oppenheimer-Volkoff Equation for the gravitational collapse.

The paper has been accepted for publication in Mod. Phys. Lett.A.

You can find the...

I would be interested as I have ideas along those lines as well. Tell me a little about it

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