The patient was elderly and lived alone. She was showing signs of depression, but it was clear that something more was amiss. She insisted she was trapped in the wrong timeline.

The ward to which she’d been committed was unstuck in time, she told her doctors. Outside, the future had already arrived, and it was not a good one. “She described then that the world outside the ward had been destroyed,” reported the doctors in Exeter, England, who wrote a report about the case in a 2019 issue of the journal Neurology and Neurosurgery.

The woman was diagnosed with a variation of Capgras syndrome. First defined a century ago, Capgras typically describes a person’s belief that someone close to him or her — a spouse or a child — has been replaced with a duplicate impostor. But in this case, the patient believed that the whole world — everything she could observe of it — was a duplicate, a fake.

I know a little bit how that feels.

So do you, probably.

It seems many of us have come to feel there are multiple realities and we’re stuck in the wrong one. For some, this sensation was occasioned by the outcome of the 2016 presidential election — as it was for Arthur Darvill, known for his role in the British television series “Doctor Who,” who tweeted on Nov. 9, 2016, “I think we landed in the wrong timeline.”

The Rev. Traci Blackmon, a Christian minister and civil rights activist who was active in protests at Ferguson, Mo., and counterprotests at Charlottesville, Va., tweeted about this feeling in 2018: “I believe I am trapped in an alternative universe.” At the time, I reached out to her to ask her about it. She explained that the racism she’d witnessed felt like a detour from the way she’d assumed history would unfold. “The gains we’d made in social equity and humanizing people — I thought these gains would result in a different world,” she said.

Now five years and one pandemic later, “Everything Everywhere All at Once,” a film about the idea that there are multiple universes, each containing a different version of you, swept the Oscars and struck a chord. Apparently many of us have this sense that, as Waymond Wang, played by Ke Huy Quan, says in the movie,“something is off.”

It’s easy to see the appeal of the multiverse, even as metaphor: the notion that we’re surrounded by a multitude of parallel selves, one of which might be living in a better timeline than the one we’re stuck in. It’s probably no coincidence that the idea has become so popular during an era of pandemic, climate change and political turmoil, when so many of us have felt helpless and trapped. Who doesn’t want to imagine a different world?

But it can also be a dangerous way of imagining the cosmos. Like the Capgras patient, we risk becoming detached from the world we can see and touch. Regardless of whether we can prove that the multiverse exists, the idea of it can distract us from doing the work we need to do to make this world better. This timeline is the only one we have access to, and it’s got to be enough.

As a species, we’ve long been haunted by spirit realms and ghostly domains. Plato conceived of an intangible world of forms realer than anything we can touch. Plutarch reported that Alexander wept when he heard the possibility of an infinite number of worlds, having not conquered all of this one.

C.S. Lewis was an early multiverse explorer with his Narnia books, in which siblings grow to adulthood as kings and queens on the other side of their magical wardrobe in a world that exists parallel to our own. He was also paying quite a bit of attention at the time to a new branch of science known as quantum physics. In 1957, a year after Lewis published his last Narnia book, a Princeton doctoral student, Hugh Everett III, published a dissertation bringing the ancient idea of the simultaneous existence of several worlds into the realm of modern science.

Mr. Everett was trying to solve a seeming paradox in quantum theory: Certain elementary particles (say, a photon) seemed to exist mathematically in many places at once but could be detected at only one location at a time.

Perhaps, Mr. Everett suggested, the act of detecting the particle splinters reality; perhaps the observer, and indeed the universe, splits into different possible timelines, one for each possible location of the particle. This would become known as the many-worlds interpretation. Physicists recoiled at the idea at the time.

It took a while for Mr. Everett’s idea to trickle into popular culture, but once it did, pulp fiction writers fell in love with it. In 1961, DC Comics published “Flash of Two Worlds!” in which the superfast hero vibrates his way into another universe to meet an alternate Flash. More recently, the multiverse has become the perfect framework for superhero-centric entertainment entities like Marvel Studios (and its licensees) to reiterate a seemingly endless series of franchise reboots. (A.O. Scott, writing in this newspaper, called this “a conceit that promises ingenuity and narrative abundance” but instead has delivered an “infinite recombination of cliché.” ) Thus, Spider-Man entered the Spider-Verse; Dr. Strange got lost in the Multiverse of Madness.

I first encountered the idea of a parallel world as a kid in the 1980s, watching the She-Ra cartoon movie. Princess Adora is separated at birth from her brother, Adam, and sent to grow up on the other side of a “tridimensional portal.”

I was an only child, and I was fascinated by the idea of some alternate plane where, like Prince Adam, I might discover a secret sibling, an end to loneliness.

When I was 12, my mother met a man, and suddenly the family I’d imagined for myself became real. I had an older brother who loved puns and an older sister who wrote poems.

But when I was 19, my stepfather died of melanoma; within a few years of recriminations and disputes, our blended family unblended itself.

I entered adulthood bereft and wrong-footed. I felt a horrible sense of vertigo as I watched the life I’d been expecting to live tilting away from me. In this new timeline, my stepsiblings were no longer my siblings; they would become, instead, just people I knew for a while in high school.

All this because a photon of sunlight had collided with a segment of my stepfather’s DNA. A quantum event — a whole universe of grief unfurled from a minuscule catastrophe that could just as easily not have happened.

For years, I couldn’t stop thinking about other, better timelines where it didn’t happen, where my stepfather was still alive and my family intact. It helped me understand what was missing, but it did not allow me to mourn what I’d lost.

And that’s the peril of the multiverse; I was becoming unreal to myself, nostalgic not for a time before the death happened but for a timeline in which it never happened at all. At the climax of the Narnia series, Lewis renounces his beloved fantasy land as a “shadow of a copy” of a newer, realer Narnia. “The new one was a deeper country,” he writes. “Every rock and flower and blade of grass looked as if it meant more.” A shadow of a copy — that’s how I felt.

In “Everything Everywhere,” Joy, the character played by Stephanie Hsu, has become aware of every possible timeline. She succumbs to nihilistic despair. If everything is happening, then nothing can matter. It’s hard not to recall the real-life fate of Mr. Everett’s daughter, Elizabeth, who ended her life in 1996, saying in her farewell note that she hoped she would go on to a “correct parallel universe” where both she and her father were still alive.

I reached out recently to Ms. Blackmon, the activist who tweeted about an alternate universe, to see how she’s feeling about the timeline in 2023. Because she “is still trapped here, she has no updates,” a representative wrote back.

But it’s telling that Ms. Blackmon never stopped fighting for what she believes in, striving to improve this world, serving the United Church of Christ and, most recently, leading a group of religious leaders in an effort to block Missouri’s abortion ban. We can joke or wonder whether we’re in the wrong timeline. But we can’t lose sight of the fact that this timeline is the only one we’ve got.

In my 30s, I knew I had to save myself from the enticements of alternate realities. So I envisioned a new cosmology of time. Instead of a linear, branching timeline with multiple, parallel possibilities — so much more vivid than my real life — I tried to imagine time as a sphere always expanding away from me in every direction, like the light leaving a star.

In this model of time, instead of the past receding behind me, it expands outward to surround me, always there and always present. The future is at the very center of the sphere, curled up infinitely small inside of me, waiting to be realized. That way, I can believe that there is nothing to come that I do not already contain.

As a cosmology, it’s no more tangible than the multiverse. But if we have to believe in something invisible, let me believe in a version of the universe that keeps my focus where it belongs: on the things I can touch and change.