It’s my 25th year visiting Lacock Abbey in Wiltshire, England, arriving early as usual. As I sit in the hire car, I replay in my mind the day I realized how I might manipulate time. Ever since my doctorate in astrophysics, I’d been researching the equations of general relativity, focusing on the crossover between relativity and the quantum world. But my true interest was “closed timelike loops”—what some might call a time machine.
It was here, 25 years prior, I had worked out how a quantum computer could use a loophole in Einstein’s gravitational field equations to make time travel possible. I was in England for a conference on quantum gravity and took the opportunity to visit the home of a personal hero, 19th-century photography pioneer William Henry Fox Talbot. Every moment remains etched in my memory and I have tried to repeat them each year since.
The first anniversary I brought a sheaf of printer output from Monte Carlo simulations run on a Thinking Machines CM-5 in Cambridge, permutating the variables I could alter. A step here, a pause there, attempting to recreate what happened that day. Each year since I have tried as many walkthrough variants as I could. And each year I have failed. I need to use the rest of my time keeping my career alive, so I limit myself to the anniversary. Now I’ve written a smartphone app to guide me, but the approach is the same, with each detail recreated as best I can. But this year has to be different.
Figure. Oriel window in Lacock Abbey photographed by William Fox Talbot in 1835.
I began that first visit at the Fox Talbot museum near the abbey. The exhibits led up to the moment on Lake Como in 1834 when Fox Talbot had his inspiration. He enjoyed clever toys, trendy optical devices like the camera lucida for projecting an image onto sketching paper to guide an artist. I’d like to say, cue the light bulb over Fox Talbot’s head, except electric light hadn’t been invented yet. Fox Talbot was studiously tracing an image. Yet he knew that compounds of silver darkened when exposed to light. So why not soak the paper in silver salts and let the drawing produce itself?
In August 1835, Fox Talbot set up a camera obscura, projecting an image of a window in the South Gallery of Lacock Abbey onto treated paper. The result (or at least a copy) is on the wall beside the window where the picture was taken. It’s tiny—only 1.2 inches by one inch—the world’s first photographic negative. Other early processes produced one-off images, but Fox Talbot’s negatives provided unlimited prints. Forget the idea that the Victorian information age started with Charles Babbage’s mechanical computers. What Fox Talbot invented was visual information processing, but his bits were silver crystals, in a mechanism that became the mainstay of photography for over a century and a half.
Special relativity tells us all we need to do is move… and the faster we go, the quicker we get to the future.
A display of photographs from Fox Talbot’s time stood near the exit. That was where my time journey began. One showed a group outside a country cottage. Mostwere stiffly Victorian, but one, a young woman, smiled engagingly at the camera. And next to her … I squinted to see better … hand on her waist, was me. I gasped. Was this proof that in the future I would build a machine to travel back in time? How else could I appear in an image produced in the 19th century?
Moments later I was backpedaling. Plenty of Englishmen had beards at the time. It could be a passing resemblance. But genuine or not, the photograph inspired me to recall the field equations of the general theory. Going forward in time is easy; we do it every moment of every day. Special relativity tells us all we need to do is move … and the faster we go, the quicker we get to the future. But traveling back is far more complicated—even theoretically. Ideas for backward time travel usually involve an effect called “frame dragging,” whereby rotating masses like black holes twist the fabric of space-time as if they were spoons in honey until time loops back on itself.
I realized that to make backward time travel practical I might try another oddity of relativity, that energy, like mass, produces gravity. If I could pick up on the quantum fluctuations of energy in empty space I could set up a feedback loop whereby the energy produced gravity, feeding back to produce yet more energy … warping space-time sufficiently to make the journey without a black hole. But there was a problem. As the great physicist Richard Feynman pointed out in 1982, you can only fully simulate quantum systems with a quantum computer. Without quantum computing, the process would be impossible to control—and at the time of my first visit, quantum computing was little more than a theoretical concept.
Still, that old photograph gave me hope that in the future I might yet use such a computer to travel into the past. To test my hypothesis, I needed a prediction I could check. I’d explored the history and science of Fox Talbot’s earliest negative many times. It featured no human figures, but I knew exactly where and when it was taken. So, if I could build a time machine, I’d make sure I was outside the window at precisely the moment Fox Talbot exposed his chemically sensitive paper. If I now looked at the negative and I was in it, holding some clearly identifiable object, say, star-shaped—the first shape that occurred to me—I would know the mechanism worked.
If I fail, I’ll simply cease to exist.
I had to see the image again, recalling it was in Fox Talbot’s house, by the window where it had been taken. As I hurried from the museum onto the curving driveway, I caught a glimpse of that jewel of a building—Lacock Abbey—glowing in the sunlight. I went round the corner, momentarily losing it in a clump of trees, passing a small, surprisingly lifelike statue of an Egyptian sphinx. Round another corner and up a shallow flight of steps leading into a vaulted hall. I couldn’t allow myself to pause to enjoy a notice saying NO PHOTOGRAPHY, here of all places, continuing through the dining room into the abbey’s South Gallery.
It was the smallest center oriel window that provided Fox Talbot’s subject. When I arrived, a lively discussion was under way between the room’s guide and a lone visitor, with the guide pointing out that the gallery was narrow, making it difficult for Fox Talbot to project an image. But the visitor paid little attention, peering instead through the window, taking in the same view as in the photograph, now nearly 200 years on.
“Were those trees there when Fox Talbot took the picture?” he asked the guide. The windowpane had the faded translucency of age, making it difficult to see out. “You see,” he said, “it’s this blob.” We stepped up to the enlarged version of the Fox Talbot negative framed on the gallery wall. Sure enough, I could make out a shape on its right-hand side. My heart leaped. “I’ve always wondered what the blob on the right is,” said the visitor.
I knew there had never been a blob in the photograph. Until now…
“Someone could have chopped down a tree,” said the guide helpfully.
I approached the negative, restraining myself from touching it and leaving a mark. “Is it a person?” I said. “Could the blob be a person?” As I looked more closely, I could make out some detail. It was surely a bearded man. And in his right hand he was holding (my stomach clenched) a star.
It was going to happen. Here was the evidence I could build my machine to harness the feedback loop and travel back. Desperate to channel my thoughts, I hurried back to the hire car where I’d left my notebook. The exit route took me though a dark part of the old abbey, a dismal, dusty place with empty stone coffins lined up on the floor as if waiting for their future occupants. It was here I began to ask myself whether quantum computers would ever be capable of such sophistication in my lifetime. Had I imagined everything? Instead of heading for the car, I hurried back to the museum … to see again the first photograph in which I’d appeared.
There they stood, as they always had, the group in front of the house. I recognized the woman’s impish smile. But the man next to her, hand on her waist, was nothing like me, but shorter, rounder, clean-shaven.
So each year I return, hoping the latest developments in quantum computing are about to make my kind of time travel possible. I run my simulations and, prompted by my app, time myself and count my steps, walk different routes, pause different lengths of time at each exhibit, yet fail to appear in the images.
But now I’ve found records of an ancestor of mine who lived near Lacock in Fox Talbot’s time, sharing my name and birthday. If I’m in that photograph again, with my hand on the woman’s waist—I’ll have travelled back to become my own great, great, great grandfather. If I fail, I’ll simply cease to exist. I’ll keep uncertainty from my mind and fix the reality of the future and the past, like Fox Talbot developing a photographic print. I’m sure I can do it. It’s only a matter of time.
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