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
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,
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.
Brian Clegg ( www.brianclegg.net) is a science writer
based in the U.K. His most recent books are Are Numbers
Real?, an exploration of the relationship between math
and reality, and The Reality Frame, an exploration of
relativity and frames of reference.
© 2018 ACM 0001-0782/18/11 $15.00
ject, say, star-shaped—the first shape
that occurred to me—I would know the
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.
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
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
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 ob-
[CONTINUED FROM P. 176]
If I fail,
cease to exist.