Copyright � 2026 by Shane
Tourtellotte
Wormholes are close to a commonplace concept in modern physics, theorized and calculated almost as much as black holes even when proof of their existence was lacking. To pare it down ruthlessly, wormholes are tunnels between two points of the Universe, traversing a fourth-dimensional space outside the three-dimensional space we know. Not using our space means that the tunnel length can be far shorter than the standard distance between those points. The term “wormhole” was coined by physicist John Wheeler in the 1950s, in comparing the tunnel to one bored through an apple1.
This by itself doesn’t touch on time travel. What can be done with the openings of the wormholes does.
Take a wormhole with the mouths, A and B, right next to each other, just a few feet apart. Accelerate mouth B to relativistic speed, and send it speeding away in a loop about one light-minute long, while mouth A stays where it is. Mouth B comes back to its original spot about sixty-one seconds later -- by our clock. Due to relativistic time-dilation effects, however, it’s been a far shorter trip for mouth B. Where a clock just within mouth A may have advanced from 8:00:00 to 8:01:01, the clock within mouth B has gone from 8:00:00 to 8:00:01, one minute behind the stationary mouth.
One second later, you send a particle into mouth B. The length of the wormhole itself, mouth to mouth, is arbitrarily small (no matter how distant the mouths are in our universe), so transit time is effectively instantaneous. By the clock just within mouth B, the particle enters at 8:00:02. By the clock inside mouth A, and by your own clock, it exits at 8:01:02, having traveled forward in time one minute.
One second after this, you perform the reverse operation. You shoot a particle into mouth A of the wormhole at 8:01:03. After its arbitrarily short transit through the wormhole, it exits at 8:00:03, having traveled one minute backward in time.
The one practical hitch with this is that the particle emerged from the wormhole rather a large distance from you. It was running its relativistic lap, remember?
Take a two-minute break, and try it again. The particle enters mouth A at 8:03:03. It emerged from mouth B promptly at 8:02:03, again one minute in the past. You missed it, because you forgot to be looking at the other end of the wormhole one minute before you were scheduled to shoot in that next particle.
Don’t sweat it. Time travel is not particularly intuitive. You’ll need a little experience to catch up with having effects precede causes. It also lets us defer the question of a possible paradox: to wit, what would have happened if you had seen the particle emerge from B, but then didn’t shoot it into A? I will get deep into the paradoxes later, with examples a bit more practical than these silly anonymous particles.
You may have noticed one similarity that the wormhole time machine currently shares with other ones I discussed last chapter. The act of moving one orifice of the wormhole at relativistic speeds makes the wormhole a time machine, but as with cosmic strings and Tipler cylinders, you can only travel backward to the point at which the time machine was created, not before.
This is a big problem, an apparent show-stopper for your hopes of seeing the battle of Agincourt or the Hanging Gardens of Babylon. Keep it in the back of your mind, because I still have to discuss the other ways in which a wormhole time machine appeared to be impossible.
We’re not able to create wormholes, and the scientific knowledge necessary to do so remains far beyond us. Luckily, wormholes are all around us, all the time. They’re just invisible and barely last any time at all.
The uncertainty principle is a cornerstone of modern quantum mechanics. Boiled down, it says you cannot know everything about something you observe, because observing it alters what you’ve observed. Certain pairs of variables simply cannot be measured exactly. Position and momentum are one well-known example; another is time and energy.
One effect of this is that, on a sub-microscopic level utterly beneath our notice, something termed a quantum foam is fizzing with activity. Particles are always popping into existence, and then popping back out, on remarkably short timescales. The usual example is matter-antimatter pairs, but the principle extends as far as wormholes being created and almost instantaneously vanishing back into the nothingness from which they emerged.
Here is your source for wormholes, as many as you could want. All you need to do is capture one in the micro-instant before it disappears and hold it in existence. Simple, right?
The next step reaches a new order of impossibility. The wormhole is extremely small, meaning you’re not going to fit through it. You need a way to expand the mouths of the wormhole from Planck scale2 to classical scale, meaning a size at which the physics familiar to us, rather than quantum physics, dominates3. The scientists who first postulated taming a wormhole had no idea how to accomplish this, which was all right, because they didn’t know how to make it stick, either.
A wormhole of classical size would need to be stabilized, to prevent it collapsing on itself. The tension at the aperture of a wormhole would be akin to the pressure at the center of a neutron star, a massive one as neutron stars go. (Much more massive, and it would be a black hole.) We have no materials that could remotely bear such pressure, so we would need an energy field of enough strength to balance that tension. If you think running your air conditioner during a Houston summer is energy intensive, have I got news for you.
Even if we find enough energy for that, wormhole topology throws us a curve, literally. The aperture of a wormhole flares outward, which means the energy fields holding open the throats have to be stronger than the field keeping the connecting tube from collapsing. This means that, to some observers, the mass-energy density at the throat will be negative. Another way of interpreting this is to say that the aperture is being held open by a repulsive gravitational force.
This is a problem. Gravity is supposed to be always attractive, never repulsive, no matter what observer’s looking at it. That immense flux of energy holding the wormhole open is now violating physical principles, not just practical ones.
Even if all this is accomplished, we still have just a wormhole. Both openings are located in the same time. We need to do the relativist acceleration trick with one of the apertures to make the wormhole into a time machine. Accelerating things to, and decelerating them from, near light-speed is no trivial task, even if it’s uncomplicated compared to the other things we need to perform.
It’s enough to make you despair -- but you don’t need to. Exotic physics got us into this, and exotic physics gets us through.
Fine Tools For Fine Work
The two physicists who let us reach down to the quantum level may never have met in person -- or at least they’ve been cautious enough to leave that impression. The long-distance collaboration between Cornelis Bijlandt and Hanita Subramanya4 produced some elegant theories that, so far, have been borne out in practical testing.
Without the dozens of pages of equations in baffling notations, their conclusion was that focused emissions of the right wavelengths can “grasp” a Planck-scale wormhole at the instant it appears out of the quantum foam, and with quick work plus some luck stabilize it. The energy needed for the “grasping” fortunately doesn’t need to be much, due to the scale on which it’s working. The electronics needed for the operation must be very small: a supercollider can produce the energy, but wouldn’t get the effect. The tiny scale seems to bring it close enough to the quantum level to allow interactions not possible from larger equipment. It is effectively a bridge between classical scale and the Planck scale.
Getting the wormhole to stabilize is an apparent side-effect of the grasping process. The overall instability in the area of quantum foam remains the same, but it becomes distributed differently. Everything else gets a bit more unstable, while the grasped wormhole becomes much less so. With the right adjustments to the Bijlandt-Subramanya Field5, made automatically at speeds too unimaginably fast for humans to affect, the wormhole becomes meta-stable, no longer at risk of randomly popping back out of existence.
This is not a sure process. The chance to “grasp” a wormhole is rather low per attempt. The field-generating mechanism can make many attempts per second, so this tends to balance out. Still, you can get a run of poor luck that leaves your time machine sputtering like an old auto engine failing to turn over. This is highly inconvenient when you need to make a fast getaway, and is one good reason why you may wish to leave your wormhole in place while making your time visit.
The Bijlandt-Subramanya Field generator solves one problem, and points the way to solving several others. The quantum foam is not merely minuscule wormholes and particles. There is energy down at that level, virtual like the rest, but which you can make actual. The mechanism that can capture the wormhole likewise can, with different wavelengths and different resonances, tap into that energy.
This solves a multitude of problems, as with the proper adjustments the energy harnessed can perform numerous kinds of work. It can move a wormhole mouth with the relativistic speeds necessary to create the initial time difference between them6. It can expand the mouths to a size which will allow you to pass through. It will even reinforce them so they stay open when enlarged, though this requires a different kind of energy.
The quantum foam fizzes out pairs of particles and antiparticles, balanced yet opposite. Some of these will be particle pairs of positive and negative mass -- and negative mass produces a repulsive gravitational force. We don’t see objects of negative mass in ordinary life, but by now it’s clear the quantum level of existence is not what we would call ordinary.
That gravitational repulsion is what we need to hold the throats of the wormhole open. We cannot use the negative mass itself for various reasons, but we can use its equivalent in negative energy. Recall Einstein and that famous equation: mass and energy are different versions of the same thing. When positive energy comes effervescing out of the quantum foam, so does negative energy paired with it. We have differing but similarly vital uses for both.
Some readers have already come to a sharp halt, saying to yourselves “The heck7 with wormholes. Let’s talk about this unlimited free energy!” Sadly, the energy is neither.
There has been talk about harnessing the energy of the vacuum, sometimes called zero-point energy or ZPE, for decades. As usually propounded, it’s wishful thinking, getting the something of free energy from literally nothing, or as literally nothing as this universe has. If there is any solidity to the laws of thermodynamics, it is impossible.
Then how, you ask, is it providing all this energy to move, expand, and reinforce wormholes? The best theoretical answer we have is that, even when raised up to the classical scale, the wormhole and all of its attendant energies are still tied to the quantum realm. It is all borrowed, and eventually it must be repaid. From the foam it came, and to the foam it must return.
Luckily the borrowing and the timeframe of repayment are not on the quantum scale, but they aren’t infinite either. The longer a wormhole exists, the greater the accumulation of energies, positive and negative, are bound up with it, and the closer it is to a destabilization that sends it plunging back into the quantum realm, to vanish as it was meant to8.
This threshold of tolerance hasn’t been nailed down yet, but it is high, otherwise a lot fewer time-travelers would be returning from their trips. The larger a wormhole, and the greater the length of time it traverses, the higher the energy accumulation needing to be paid back there will be. This, among more mundane matters of detection, is why you want to shrink the wormhole back into or near the quantum scale, if you’re keeping it open while visiting your destination era. Doing this minimizes the energy accumulation, delaying its destabilization.
Adding to the positive energy employed from your machine’s own stores helps in deferring destabilization. Operation of the machine requires some energy input not provided by the quantum foam anyway, but this adds to the potential drain. As I’ll outline in an upcoming chapter, this will be a bigger problem with some time machines than others.
The Recursive Reel
Capturing and manipulating a wormhole this way is an immense technological achievement, a grand-scale triumph on the smallest of scales, but an apparently insurmountable obstacle remains. That wormhole, like the time machines involving Tipler cylinders and cosmic strings, can only take you back in time as far as the creation of the machine.
That’s how it works for classical matter, such as yourself. It works a different way for entities summoned out of the quantum foam. That includes the wormhole itself.
The scientist in question, whom I shall leave nameless, was a rich combination of supremely insightful, supremely deluded, and supremely reckless. He9 formed his theory, took the risk of running an experiment based on it, and found the answer to freeing time travel from the chains of causality. He took a captured wormhole, ran one mouth through a dilation loop, then enlarged the mouth that had stayed stationary and passed the time-dilated end through that mouth. And repeated the action. And kept repeating it10.
It was the Ouroboros, the snake swallowing itself from the tail up, over and over. But a snake is classical matter; a wormhole obeys different rules. The smaller, time-dilated mouth emerged from the first pass having gone back in time by the increment of its dilation. It repeated this on each of its pre-programmed passages through the larger mouth, until it was 1.86471 hours in the past11, long before the wormhole had come into existence.
It is here that one might solemnly proclaim that time had been mastered -- if it had been. His theory of time travel has since been tested by others, and found in several particulars to be false. He was wrong on most of his work, interesting or even comprehensible mostly to other theoretical physicists alone. He was right on one point, the one that gave us time travel.
Why he was right, that a wormhole could do this anatomically impossible thing to itself, nobody has yet explained. How could one mouth of a wormhole pass through its own other opening at a time when it should not exist? His original theory, now exploded, was itself vague on the matter.
Some leading surmises say the attempt to pass through itself seems to present a choice of impossibilities. Either it can pass through, in defiance of common sense about time, or it cannot pass through, meaning one end of the wormhole exists but the other does not, which also defies common sense. The universe seems to choose the time impossibility as less offensive, or perhaps as less impossible. The larger mouth is somehow present both in your present and in the past, or future, toward which the smaller mouth is propelling itself. There is much both about time and quantum mechanics that runs counter to common sense, so this may add up on a level we haven’t yet grasped theoretically.
In effect, objects on Planck scale can somehow sidestep the restrictions on Tipler cylinders and the like, and this persists even when a foam-born wormhole is expanded onto the classical scale. To get witty about it, you can take the wormhole out of the quantum realm, but you can’t take the quantum realm out of the wormhole.
Unexplained explanations aside, the mechanism for time travel had been discovered. You can command one end of a wormhole to pass through its other end multiple times, and move it backward or forward in time12. The passages are pre-programmed and thus pre-counted, so you can take the number of loops, multiply it by the amount of time dilation you created between the wormhole mouths, and come up with the amount of time displacement, forward or backward.
The time needed to produce the desired displacement depends both on the length of the initial time-dilation loop one end of the wormhole takes and the rate at which you can cycle one mouth through the other. The latter is very high, as the mouth is traversing distances in shouting range of Planck length at speeds in shouting range of light-speed. Even when the diameter of the needle-threading circuit it’s running is much wider than the eye of the proverbial needle itself, this is extremely quick13. The “warm-up” of a long initial circuit is a plus if you know in advance what time you’re visiting, but given a reasonably capable Bijlandt-Subramanya generator, the Ouroboros loops can be run fast enough to make them the greater determining factor in overall preparation time.
Going Down a Size
Once you have the far end of the wormhole at the desired time14, there’s nothing left but to go through the wormhole and travel through time. This is not without its complications, but after what we’ve just gone through, they are refreshingly slight.
The natural shape of a wormhole mouth is spherical, and simply opening one of these up at the macroscopic scale for your passage is certainly possible, but there are drawbacks. First, any portal large enough to pass yourself and your time machine will be quite conspicuous. While this needn’t be a problem at the present end, it does make it much likelier to draw attention to you at your destination time. Some risk of notice is irreducible, unless you’re going somewhere and somewhen without people, but this raises the risk.
Another problem is inevitable with certain kinds of time machines, and possible with others15. If a fixed-size wormhole mouth moves around your machine to carry it and you to its destination time, it will not take just you and the machine. The air it scoops up won’t be a serious problem, but the piece of the ground or floor beneath you will be more of one. Hopefully the scoop won’t be so clumsily excessive as to take a piece of a nearby wall as well.
This is why you prefer to put in the added technical work to make the wormhole mouth size and shape conformable to the objects passing through it. With the proper fine-tuning of the negative energy holding the mouth open, it will take the time machine and you, and nothing else. The phenomenon is relatable to surface tension, where on a small enough scale water can hold itself in certain shapes and prevent things passing through it, such as insects skittering across the surface of a calm pond.
Finding the right balance is important. If the boundary tension of the wormhole mouth is too loose, it will still scoop along air, ground, flooring materials, roadway, etc. If the tension is too tight, your machine might leave behind a few peripheral things you thought were firmly attached to it. If you’re using a human-portable time machine, overly tight tension could cause you to leave behind some equipment or baggage you’re carrying. If it’s bad enough, it could strip away your clothes. Don’t wear anything too loose.
There are other technical matters awaiting you at the far end of the wormhole, the biggest of which is making sure you end up, not only when you’re going, but where you’re going. The next chapter moves on from the technological miracle of wormholes to the other great scientific breakthrough that makes the time machine not only possible but practical.
Footnotes:
Around the same time, he was involved in formulating a famous interpretation of quantum mechanics known as the Many-Worlds Hypothesis, which I’ll talk about in another chapter. Some years later, in 1967, he would coin the term “black hole.” Some years earlier, in the 1940s, he and his graduate student, future Nobel Prize winner Richard Feynman, developed theories about radio waves that could travel back in time, and about antimatter itself being matter moving backward in time. John Wheeler ought to be far better known than he is.
The scale at which it can spontaneously pop into existence.
“Classical scale” does not mean large enough to fit a classical orchestra, playing Beethoven’s Fifth Symphony for example. If you get a wormhole mouth this big, though, it should serve your purposes admirably.
Both names are almost certainly pseudonyms. You won’t find papers under their names in scientific journals, and if they had tried to publish their joint work in the standard places, they would have been professionally ruined at best. It’s all right: they found enough of an audience.
The best argument that the two scientists aren’t using pseudonyms is that they would have chosen names that didn’t produce such an unfortunate abbreviation. The best argument that Cornelis Bijlandt is a credit hog is that he didn’t put Subramanya’s name first to avoid the unfortunate abbreviation.
A wormhole mouth at Planck scale is so close to being massless that it takes little energy to produce this acceleration.
Almost certainly not the word you used, but I’m sticking with it.
It was originally supposed that equal amounts of positive and negative energy would cancel each other out for purposes of stabilization, but experiments have shown this isn’t true. It would have made time-travel wormholes effectively fully stable, given judicious use of the balancing energies, so this is an inconvenience for time-travelers. It’s less of an inconvenience than time travel being impossible would have been.
That the scientist in question was male is the only hint you’re getting out of me. That, and he wasn’t born on a Leap Day.
Whether the little mouth is emerging from the mouth that it was putatively entering, or from the other end of the wormhole, which is to say itself, is not clear. The underlying theory gave an answer, but that doesn’t help us, as you will see.
The scientist’s notes were clear on this point, and later reproductions of his experiment have shown the measurement to be exact down to those five decimal places. He may have been crazy, but he was thorough.
For travel to the future, one reverses the operation: the stationary wormhole is passed through the time-dilated one.
This, along with energy concerns and other factors, is why you keep the wormhole mouths near quantum-scale small during this stage. But not too near, or that pesky uncertainty principle will make it too likely that your wormhole mouth will miss its target.
And place, but we will examine the challenges that raises in the next chapter.
A later chapter will run through the several models of time machine, covering more of their strengths and flaws.
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