Time Travel IRL!
Time Travel
Imagine stepping into a machine, an elaborate chamber of brass, gears, and humming coils. You sit down, pull a lever, and suddenly the world outside your window blurs. The clock on the wall no longer ticks in neat, familiar seconds. Instead, time itself bends and stretches like taffy. Days whirl past in moments, centuries collapse into a single breath, and before you can even blink, you’re no longer where or when you started.
This vision has haunted and thrilled humanity for centuries. Time travel is more than a trope in science fiction. It is a longing, a human ache to rewrite tragedy, to see our ancestors, or to leap forward and glimpse what awaits us. From myths of enchanted slumber to modern physics equations scribbled on chalkboards, the dream has never left us.
The truth is that both myth and science point us toward fascinating answers. Ancient storytellers gave us tales of travelers who stepped outside of time and returned to find their worlds forever changed. Later, writers like H.G. Wells transformed those dreams into concrete visions of machines that could conquer the clock. And finally, physicists like Albert Einstein shook the scientific world with equations showing that time is not absolute; it bends, stretches, and, under the right conditions, might even loop back on itself.
So today, we’re going to take a journey of our own. We’ll explore the myths and the literature that gave birth to the idea of time travel. We’ll examine the real-life scientists and dreamers who tried to build machines to make it happen. And we’ll look at the profound theories, from Einstein’s relativity to modern wormhole physics, that suggest time travel isn’t just possible in fiction, but within the very laws of our universe.
Origins of Time Travel Imagination
Long before laboratories, equations, and particle colliders, humanity imagined stepping outside of time. Ancient myths across cultures tell stories that, in hindsight, feel like prototypes for modern science fiction.
In Hindu mythology, the Mahabharata tells of King Kakudmi, who traveled to the realm of the creator god Brahma with his daughter, Revati, to find her a suitable husband. There, he and Revati waited while listening to a musical performance. When they approached Brahma, Brahma burst into laughter. He told the king that while he and Revati were waiting, thousands of years had gone by. All the potential husbands on Kakudmi’s list were long dead.
In Japan, the tale of Urashima Tarō describes a fisherman who rescues a turtle and is rewarded with a journey under the sea. He stays only what feels like a few days, but when he comes home, centuries have slipped by, and his entire life is unrecognizable. These stories capture the essence of what physicists would one day call time dilation, where time does not pass equally for everyone.
By the 18th and 19th centuries, Western literature had begun to formalize the theme. Washington Irving’s Rip Van Winkle (1819) gave American audiences a man who fell asleep in the Catskill Mountains and awoke twenty years later, bewildered by the revolutionized world around him. Charles Dickens, too, in A Christmas Carol (1843), used the device of spectral journeys through past, present, and future to force Ebenezer Scrooge into redemption. These tales were not scientific, but they captured something profound: time could be manipulated. It could be jumped across, even if only in imagination.
But the actual turning point came in 1895, when H.G. Wells published The Time Machine. Wells didn’t just tell a story; he invented the language we still use today. He coined the very phrase “time machine,” and more importantly, he treated time as a dimension, just like height, width, and depth. His Time Traveler doesn’t rely on magic or divine intervention. Instead, he uses a machine built with logic and engineering to travel through centuries. Wells turned time travel from a dream into a concept that could be visualized, debated, and, perhaps someday, tested.
Only a decade later, in 1905, Albert Einstein published his theory of Special Relativity. In it, time was no longer absolute. It was elastic, depending on how fast you moved. The faster you travel, the slower time passes for you relative to others. Suddenly, science was speaking the same language as Wells had imagined. Einstein’s later work on General Relativity in 1915 showed that gravity itself could bend time, opening the door to the possibility of closed time loops and wormholes.
The leap from Wells’ fictional Time Traveler to Einstein’s mathematical spacetime was monumental. One showed us the dream in narrative form; the other gave us equations proving that the dream might, under certain conditions, be reality. Fiction and physics were no longer separate worlds; they were now part of the same conversation.
This is where our story pivots. From here on, time travel would not only belong to storytellers but also to scientists who wondered: if time is malleable, then how far could we push it? Could a Wells’ machine ever be more than a metaphor?
Time Travel in Physics
If H.G. Wells gave us the dream of a time machine, Albert Einstein gave us the blueprint, or at least the equations that hinted at one. Einstein’s work at the beginning of the twentieth century changed everything about how scientists thought of time. Up to that point, time was treated as a constant, ticking along in the same rhythm for everyone, everywhere. But Einstein showed us that time doesn’t march; it stretches, bends, and even loops under the right circumstances.
Special Relativity: Time Dilation and the Twin Paradox
In 1905, Einstein introduced his theory of Special Relativity. Its key idea was revolutionary: the faster you move, the slower time passes for you compared to someone standing still. This isn’t science fiction; it’s been measured.
To make sense of this, physicists often describe the Twin Paradox. Imagine two twins. One stays on Earth. The other boards a spaceship traveling close to the speed of light. To the spacefaring twin, the journey might feel like a few years. But when they return home, they’ll find their sibling has aged decades more. In other words, traveling near the speed of light lets you move into the future faster than those who stay behind.
That’s time travel, at least one-way. You can leap forward in time simply by moving very, very fast. The catch? Achieving those speeds takes astronomical amounts of energy. But the principle is sound.
General Relativity: Curved Spacetime and Closed Timelike Curves
Ten years later, Einstein expanded his ideas with the theory of General Relativity. This theory didn’t just describe how objects move; it redefined gravity itself. Instead of an invisible force pulling objects together, gravity became the curvature of spacetime. Imagine spacetime as a stretched rubber sheet. A bowling ball placed on the sheet sinks into it, bending the surface. Smaller marbles roll toward the ball not because the ball is pulling them, but because the sheet is curved.
Now, replace the sheet with spacetime and the bowling ball with a planet or star. Spacetime curves around mass, and objects, including light and time itself, must follow those curves. That’s why light bends near stars and why time slows down near strong gravitational fields.
General Relativity also introduced a wild possibility: closed timelike curves. These are paths through spacetime that loop back on themselves. If you follow one, you could, in theory, return to your own past. In everyday life, we walk forward in space but never circle back to where we started in time. Closed timelike curves would change that, offering a kind of built-in cosmic time machine.
Physicists like Kurt Gödel and Frank Tipler explored such solutions mathematically. Gödel, for example, proposed a model of the universe that rotated, creating a structure where time could loop back endlessly. It was strange, impractical, and probably not our universe, but it showed that General Relativity did not forbid time travel.
Experimental Proof: The Hafele–Keating Experiment
The first tangible test of Einstein’s ideas about time came in 1971 with the Hafele–Keating experiment. Two physicists, Joseph Hafele and Richard Keating, carried four cesium-beam atomic clocks. They flew eastward around the Earth, then westward, and compared the airborne clocks with identical ground-based clocks at the United States Naval Observatory.
The results? The airborne clocks showed measurable differences in elapsed time compared to those on Earth. Flying eastward, with the planet’s rotation, the clocks lost time. Flying westward, against rotation, they gained time. The differences were tiny, mere billionths of a second, but exactly what Einstein’s theories predicted.
Was this the first true experiment in time travel? In a sense, yes. The airplanes didn’t vanish into the past or visit the year 3000. Still, they demonstrated that time moves differently depending on speed and gravity. Time travel, even if only in fractions of a second, had been observed and measured.
Cosmic Possibilities: Black Holes and Gravitational Time Dilation
If airplanes can shift clocks by fractions of a second, imagine what massive cosmic objects can do. Near a black hole, where gravity is intense, time slows dramatically compared to regions farther away.
Physicists call this gravitational time dilation. If you orbited safely near the edge of a black hole, hours for you might equal years for someone far away. In fact, the movie Interstellar drew directly from real physics when it showed astronauts experiencing a few hours near a black hole, only to return to find that decades had passed for their colleagues. The science behind that scene was advised by Kip Thorne, one of the foremost physicists of our time.
This effect is one-way, toward the future. You could never use a black hole to go back and stop yourself from falling in. But you could, in theory, use gravity to leap ahead into the future far faster than those who remain behind.
Wormholes: Bridges Through Spacetime
Black holes may slow time, but wormholes, also called Einstein–Rosen bridges, promise shortcuts. Imagine spacetime not as a flat sheet but as a folded piece of paper. If you draw two dots on opposite ends of the paper, the shortest path is a straight line. But fold the paper so the dots touch, and suddenly they’re connected by a single point. That’s the idea of a wormhole: a tunnel connecting two regions of spacetime.
Kip Thorne and his colleagues explored whether wormholes could, in theory, allow not just travel between distant parts of space, but also different points in time. The mathematics suggest that if one mouth of a wormhole experiences time differently from the other, say, by placing it near a black hole, then stepping through could deliver you into the past relative to where you started.
The obstacles? Immense. Wormholes may collapse instantly without exotic matter to hold them open. Exotic matter is hypothetical material with negative energy density, something we have no evidence for. Still, wormholes remain one of the most popular theoretical blueprints for time travel, because the equations allow them.
Transition: From Theory to Attempts
What Einstein revealed, and what experiments and cosmic objects continue to suggest, is that time is not fixed. It is flexible, relative, and deeply tied to the fabric of the universe. Time travel to the future has already been proven in airplanes, satellites, and near massive objects. The harder challenge, the holy grail, is traveling to the past.
And that challenge was irresistible. It wasn’t enough for scientists to sketch wormholes on chalkboards or for theorists to imagine closed timelike curves. Some inventors, physicists, and even dreamers outside the mainstream began asking: Can we build a machine to make it happen?
Serious Scientific Proposals and Paradoxes
So far, we’ve seen how relativity bends time, how black holes slow it down, and how wormholes might connect one moment to another. But the deeper that physicists push into the math, the stranger the possibilities become. Some proposals offer real, if wildly impractical, ways of bending time into loops. Others run headfirst into paradoxes, those logical dead ends that make your brain itch.
Gödel’s Rotating Universe
In 1949, the mathematician Kurt Gödel, famous for his incompleteness theorems, applied his genius to Einstein’s equations. He discovered a solution describing a universe that rotated on a cosmic scale. In this spinning cosmos, time itself would curve into closed loops, meaning you could, in theory, circle back to your own past.
Sounds amazing, right? The catch: Gödel’s universe didn’t match reality. Our universe isn’t rotating that way. Still, Gödel proved that Einstein’s equations don’t forbid time loops. Gödel’s physics pointed out that maybe the universe doesn’t mind a little backward stroll.
Einstein admired Gödel’s brilliance but found the idea disturbing, believing that backward time travel should be impossible even though he had no formal proof. He could dismiss Gödel’s model on the grounds that our universe clearly wasn’t rotating that way. Still, his discomfort ran deeper: philosophically, he valued causality, the simple idea that causes precede effects, and practically, he likely suspected that additional, still-unknown laws, perhaps from quantum physics, would close off Gödel’s time loops. For these reasons, Einstein never validated Gödel’s theory; he respected the mathematics but treated it as a curiosity rather than a description of reality. Privately, though, he seemed troubled that his own equations permitted something he found absurd, a tension that later inspired Stephen Hawking to suggest his “Chronology Protection Conjecture” as a way to close the very loopholes Gödel had exposed. Before I get to Hawking, Speaking of chronology, let me tell you first about physicist Frank Tipler.
Tipler Cylinders: Cosmic Tunnels of Time
The Tipler Cylinder (≈400 words)
Frank J. Tipler (b. 1947) is an American mathematical physicist who studied under John Wheeler (the same Wheeler who coined the term “black hole”). In the 1970s, Tipler was working on solutions to Einstein’s General Relativity equations, asking what kinds of spacetime geometries might allow for unusual effects, including time travel.
Decades after Kurt Gödel spun up his rotating universe, another physicist decided to test the limits of Einstein’s equations. In 1974, American physicist Frank Tipler proposed what became known as the Tipler cylinder, a kind of blueprint for a relativistic time machine.
Picture it: an unimaginably massive cylinder, infinitely long, spinning at nearly the speed of light. The faster it spins, the more it drags spacetime around with it, a phenomenon we call frame dragging, which satellites have actually observed around Earth. Now crank that effect up on a cosmic scale. Near Tipler’s cylinder, spacetime itself would twist so severely that time would bend into loops called closed timelike curves. Fly a spaceship close enough, Tipler argued, and you could trace a path through spacetime that carried you into your own past.
It’s elegant on paper, but there’s a catch, or several. First, Tipler’s solution requires the cylinder to be infinite in length. Not very practical. Finite versions have been studied, but the math shows that once you cut the cylinder down to size, the time loops disappear. Second, the amount of mass required is absurd, comparable to compressing an entire star into a structure that spins at nearly light speed. And finally, later physicists, including Stephen Hawking, argued that even if you could build such a device, quantum effects would likely make it collapse before any time traveler could take a ride.
So does Tipler’s idea hold validity? Mathematically, yes, it’s a rigorous solution to Einstein’s field equations. Physically, no, at least not in any way we could hope to engineer. Most scientists view it as a thought experiment, a way to test the outer boundaries of relativity rather than a literal blueprint. Still, Tipler’s cylinder remains important. Like Gödel’s rotating universe, it demonstrated that Einstein’s equations don’t forbid time travel outright. They leave the door cracked open, if only by a sliver.
Tipler himself later ventured into controversial territory, blending cosmology with theology in his “Omega Point” theory. But his cylinder endures as a reminder that sometimes, even impossible machines matter. They push the conversation forward, daring us to imagine what relativity really allows. As with so many attempts at time travel, the Tipler cylinder wasn’t a failure; it was a proof of possibility, written in equations.
Hawking’s Chronology Protection Conjecture
By the late twentieth century, physicists had already produced a series of strange solutions to Einstein’s equations, Gödel’s rotating universe, Tipler’s infinite cylinder, and theoretical wormholes, which all suggested time loops might be possible. The math was there, and it was unsettling. Suppose relativity allowed these so-called closed timelike curves. What was to stop someone from jumping into the past and undoing history?
Stephen Hawking decided to confront that question directly. In 1991, he introduced what he called the Chronology Protection Conjecture. His idea was straightforward but profound: while the equations of relativity might allow time travel in principle, the laws of physics as a whole conspire to prevent it in practice. The very act of trying to create a time machine, he argued, would cause the time machine to destroy itself to prevent any events from happening that would alter history.
The Grandfather Paradox is one of the most famous logical problems in time travel theory. It questions the consistency of traveling to the past and altering events that would prevent the traveler’s own existence. The paradox goes as follows: if a person were to travel back in time and kill their grandfather before he had children, then the time traveler would never have been born, and therefore could not have traveled back to commit the act in the first place. This creates a causal contradiction, because an event (the time traveler’s existence) both occurs and does not occur. Physicists and philosophers use the paradox to illustrate the potential incompatibility between classical causality and hypothetical backward time travel.
In theoretical physics, solutions to the paradox include the Novikov self-consistency principle, which asserts that the laws of physics prevent paradoxical events from happening (Novikov, 1983), and the many-worlds interpretation of quantum mechanics, which suggests that traveling to the past creates a new branching timeline, leaving the original history intact (Deutsch, 1991). The Grandfather Paradox remains a cornerstone in debates about whether time travel to the past can be logically or physically possible within the framework of relativity and quantum theory.
Then there is the Bootstrap Paradox, also called the causal loop. Imagine you go back in time and hand Shakespeare a copy of Hamlet. He publishes it under his own name. Centuries later, you study Hamlet in school, then bring that same copy back to Shakespeare. Here’s the question: Who actually wrote Hamlet? The play exists, but it has no origin. It’s a Möbius strip of causation.
These paradoxes can sound like riddles or jokes, but they pose serious challenges to physics. If time travel to the past were possible, would logic itself break?
Another escape hatch is the multiverse idea. According to this view, traveling back in time creates a branch in the timeline. Instead of erasing your own existence, you spin off an alternate universe where events play out differently. You’d still exist in your original timeline, but the new one would continue without you. Science fiction fans will recognize this from countless movies where characters hop between branching realities.
The Joy of the Brain-Bender
Here’s the fun part: paradoxes are less about breaking physics and more about stretching our minds. They’re cosmic riddles, forcing us to ask what “cause and effect” really mean. And paradoxes do something else: they remind us that time travel isn’t just about building machines. It’s about philosophy, logic, and the limits of what we can even imagine.
Real-world research and development
Ronald Mallett’s Laser Loop
But some people weren’t satisfied with theory or imagination; they wanted to build a time machine. Doctor Ronald Mallett, a theoretical physicist at the University of Connecticut, was inspired by personal tragedy: his father died when he was ten years old. That tragic event inspired him to pursue a career in physics at the University of Connecticut, where he became known for his research on Einstein’s theories of relativity and black holes, and for his pioneering work toward building a theoretical time machine.
Doctor Mallett is a professor emeritus in the University of Connecticut’s Physics Department. His work is notable and he has received several awards for his theories and work including the Ford foundation senior postdoctoral fellowship in 1982, an honorable mention for the gravity Research Foundation essay award in 2001, an honorary member of the Connecticut Academy of Arts and Sciences in 2005 an outstanding alum award from the Pennsylvania State University at Altoona in 2006 and an alumni fellow award from Pennsylvania State University.
Mallett’s tangible design is based on Albert Einstein’s gravitational field equations. He describes this in his book Time Traveler, where he shows that by applying the standard approximation for a weak gravitational field to Einstein’s equations, he was able to reduce the number of terms in the equations. He then calculated the gravitational field of the ring laser that he was working with in this design. After weeks of intensive work, he found that his ring laser had actually produced a gravitational field similar to a vortex. This vortex could produce minute effects of frame dragging. This evidence of frame dragging suggests the existence of closed timelike loops. These closed timelike loops? This is time travel. If you want to read more about this, he describes it in his memoir, Time Traveler: A Scientist’s Personal Mission to Make Time Travel a Reality (2006).
And, I have exciting news! If you are interested in hearing more about Doctor Mallet’s discovery, Tune in next Tuesday at Math Science History to hear my interview with Doctor Mallett and his theory and how he obtained tangible evidence of time travel.
Where We Stand Now
So, where does all this leave us? Are we any closer to traveling through time than when H.G. Wells first put pen to paper?
The answer is: closer, but not quite there.
Failures as Successes
Science thrives on iteration. Each failed attempt, whether it’s a myth like the Philadelphia Experiment or a real design like Ronald Mallett’s laser loop, isn’t wasted effort. Instead, these efforts act like stepping stones. They narrow the possibilities, clarify what won’t work, and sometimes open unexpected new doors.
Mallett’s critics argue his design won’t produce usable time travel, but his work highlights a crucial truth: attempts at time travel are experiments that work in another direction. They show us where physics bends, and where human imagination presses hardest against the unknown.
What Physics Tells Us Today
We now know that time travel into the future is not only possible but already demonstrated, through relativity, atomic clocks, and GPS satellites that must correct for time dilation every day. Travel to the past remains the thorny problem, tangled in paradoxes and practical barriers. Wormholes remain mathematically possible but unproven. Exotic matter, needed to stabilize them, hasn’t been found.
Still, Einstein’s equations haven’t closed the door. They leave cracks, little mathematical whispers, that hint at the possibility. As Stephen Hawking put it, “the best evidence we have that time travel is not possible… is that we have not been invaded by hordes of tourists from the future.” But that doesn’t mean the book is closed.
Looking Ahead
What matters isn’t whether a machine has been built yet. What matters is the persistence, the willingness to try, fail, and try again. Every “failure” sharpens our theories and teaches us more about the universe. And in that sense, the search for time travel is already a success. It inspires new generations of scientists to push limits, not only in physics but in human imagination.
If time travel is ever achieved, it will be because people like Ronald Mallett refused to give up despite the challenges and critics. In science, as in life, failure isn’t the end. It’s the path.
So, with that said, please tune in next week for this special interview with Dr. Mallett! Thank you for listening to Math Science History. And until next time, carpe diem.
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