The other tiny hope for natural wormholes is the big bang creation of the universe. It is conceivable, but very unlikely, that traversable wormholes could have formed in the big bang itself. Conceivable for the simple reason that we don’t understand the big bang well at all. Unlikely because nothing we do know about the big bang gives any hint that traversable wormholes might form there.
Can Wormholes Be Created by an Ultra-Advanced Civilization?
An ultra-advanced civilization is my only serious hope for making traversable wormholes. But it would face huge obstacles, so I’m pessimistic.
One way to make a wormhole, where previously there were none, is to extract it from the quantum foam (if the foam exists), enlarge it to human size or larger, and thread it with exotic matter to hold it open. This seems like a pretty tall order, even for an ultra-advanced civilization, but perhaps only because we don’t understand the quantum gravity laws that control the foam, the extraction, and the earliest stages of enlargement (Chapter 26). Of course, we don’t understand exotic matter very well either.
At first sight, making a wormhole seems easy (Figure 14.8). Just push a piece of our brane (our universe) downward in the bulk to create a thimble, fold our brane around in the bulk, tear a hole in our brane just below the thimble, tear a hole in the thimble itself, and sew the tears together. Just!
In Interstellar, Romilly demonstrates the same thing with a sheet of paper and a pencil (Figure 14.9). As easy as this may look from the outside, playing with pencils and paper, it is horrendously daunting when the sheet is our brane and these manipulations must be carried out from within the brane, by a civilization that lives in our brane. In fact, I have no idea how to execute any of these maneuvers from inside our brane except the first, creating a thimble in our brane (which requires only a very dense mass, such as a neutron star). Moreover, if it is possible at all to tear holes in our brane, it can only be done with the help of the laws of quantum gravity. Einstein’s relativistic laws forbid tearing our brane, so the only hope is to make the tear where his laws fail, in a realm of quantum gravity. We then are back to the domain of terra almost incognita (Figure 3.2).
The Bottom Line
I doubt the laws of physics permit traversable wormholes, but this may be pure prejudice. I could be wrong. If they can exist, I doubt very much that they can form naturally in the astrophysical universe. My only real hope for forming them is artificially, in the hands of an ultra-advanced civilization. But we are extremely ignorant of how such a civilization could do it. And it appears more than daunting, at least from inside our brane (our universe), even for the most advanced of civilizations.
In Interstellar, however, the wormhole is thought to have been made, held open, and placed near Saturn by a civilization that lives in the bulk, a civilization whose beings have four space dimensions, like the bulk.
This is terra extremely incognita. Nevertheless, I discuss bulk beings in Chapter 22. In the meantime let’s talk about the wormhole in Interstellar.
15
Visualizing Interstellar’s Wormhole
The wormhole in Interstellar is thought to have been constructed by an ultra-advanced civilization, most likely one that lives in the bulk. In this spirit, when laying foundations for visualizing Interstellar’s wormhole, Oliver James[28] and I pretended we were ultra-advanced engineers. We assumed that wormholes are allowed by the laws of physics. We assumed the wormhole’s builders had all the exotic matter they needed to hold the wormhole open. We assumed the builders could warp space and time in whatever way we wished them to, inside and around the wormhole. These are pretty extreme assumptions, so I labeled this chapter for speculation.
The Wormhole’s Gravity and Time Warping
Christopher Nolan wanted the wormhole to have a mild gravitational pull. Strong enough to hold the Endurance in orbit around itself, but weak enough that a modest rocket blast would slow the Endurance, letting it drop gently into the wormhole. This meant a gravitational pull much less than the Earth’s.
Einstein’s law of time warps tells us that the slowing of time inside the wormhole is proportional to the strength of the wormhole’s gravitational pull. With that pull weaker than the Earth’s pull, the slowing of time must be smaller than on Earth, which is only a part in a billion (that is, one second of slowing during a billion seconds of time, thirty years). Such slowing is so tiny that Oliver and I paid no attention to it at all when designing the wormhole.
“Handles” for Adjusting the Wormhole’s Shape
The ultimate decision about the wormhole’s shape was in the hands of Christopher Nolan (the director) and Paul Franklin (the visual-effects supervisor). My task was to give Oliver and his colleagues at Double Negative “handles” (or in technical language, “parameters”) that they could use to adjust the shape. They then simulated the wormhole’s appearance for various adjustments of the handles and showed the simulations to Chris and Paul, who chose the one that was most compelling.
I gave the wormhole’s shape three handles—three ways to adjust the shape (Figure 15.1).
The first handle is the wormhole’s radius as measured by an ultra-advanced engineer looking in from the bulk (analog of Gargantua’s radius). If we multiply that radius by 2π = 6.28318…, we get the wormhole’s circumference as measured by Cooper when he pilots the Endurance around or through it. Chris chose the radius before I began to work. He wanted the wormhole’s gravitational lensing of stars to be barely visible from Earth with the best large-telescope technology then available to NASA. That fixed the radius at about a kilometer.
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Recall that Oliver James, chief scientist at Double Negative, wrote the computer code that underlies