The End is coming, in maybe 100 billion years. Is it too soon to start freaking out? “There will be a last sentient being, there will be a last thought,” declared Janna Levin, a cosmologist at Barnard College, near the end of “A Trip to Infinity,” a new Netflix documentary directed by Jonathan Halperin and Drew Takahashi. When I heard that statement during a showing of the film recently, it broke my heart. It was the saddest, loneliest idea I had ever contemplated. I thought I was aware and knowledgeable about our shared cosmic predicament — namely, that if what we think we know about physics and cosmology is true, life and intelligence are doomed. I thought I had made some kind of intellectual peace with that. But this was an angle that I hadn’t thought of before. At some point in the future there will be somewhere in the universe where there will be a last sentient being. And a last thought. And that last word, no matter how profound or mundane , will vanish into silence along with the memory of Einstein and Elvis, Jesus, Buddha, Aretha and Eve, while the remaining bits of the physical universe go on sailing apart for billions upon billions upon billions of lonely, silent years. Will that last thought be a profound pearl of wisdom? An expletive? How did we humans get into this fix? The universe as we know it originated in a fiery burst 13.8 billion years ago and has been flying apart ever since. Astronomers argued for decades about whether it would go on expanding forever or someday collapse again into a “big crunch.” All that changed in 1998 when astronomers discovered that the cosmic expansion was speeding up, boosted by an anti-gravitational force that is part of the fabric of spacetime. The bigger the universe gets, the harder this “dark energy” pushes it apart. This new force bears a striking resemblance to the cosmological constant, a cosmic repulsion Einstein had proposed as a fudge factor in his equations as a way of explaining why the universe did not co lapse , but later rejected as a blunder. But the cosmological constant refused to die. And now it threatens to wreck physics and the universe. In the end, if this dark energy prevails, distant galaxies will eventually be speeding away so fast that we can’ t see them anymore. The more time goes on, the less we will know about the universe. The stars will die and not be reborn. It will be like living inside an inside-out black hole, sucking matter, energy and information over the horizon, never to return. Worse, because thinking takes energy, eventually there will not be enough energy in the universe to hold a thought. In the end there will only be subatomic particles dancing intergalactic distances away from each other in a dark silence, trill ions upon trillions of years after there was any light or life in the universe. And then, more uncountable trillions of eons to come, until there is finally no way to count the years, as Brian Greene, the popular Columbia University theorist and author, so Elegantly and devastatingly described it in his recent book, “Until the End of Time.” It’s hard not to want to scream at our own insignificance in all of this. If this is, in fact, what the universe will come to. The universe as we know it is now 14 billion years old, which seems like a long time but is only an infinitesimal sliver of the trillions and quadrillions of years of darkness to come. It will mean that everything interesting in our universe happened in a brief flash, at the very beginning. A promising start, and then an eternal abyss. The finality and futility of it all! In short, a tale full of sound and fury, signing nothing. What do we do with a universe like this? You may point out that it is way too soon to be prescribing a future for the universe. New discoveries in physics could provide an escape hatch. Maybe dark energy will not be constant; maybe it will turn around and recompress the universe. In an email, Michael Turner , the cosmologist emeritus formerly at the University of Chicago who coined the term dark energy, referring to the Greek letter symbolizing Einstein’s cosmological constant said, “Lambda would be the most uninteresting answer to the dark energy puzzle!” But for now, that is what we have to look forward to. Our goose will be cooked a billion or so years from now, when the Sun boils away the oceans. A few billion years later the Sun itself will die, burning Earth and anything that remains of us to a crisp .There is no escaping to space. The galaxies themselves will collapse into black holes in about 10^30 years.And black holes will finally release all that they have imprisoned as a thin spray of particles and radiation, to be scattered into the prevailing wind of dark energy whisking them apart. In some variations on the story, known as the Big Rip, dark energy could eventually grow strong enough to tear apart the tombstones that mark your grave. And so, just as there was a first living creature somewhere, sometime, to emerge from the splendid blaze of the Big Bang, there will be a last creature to die, a last thought. A last sentient being, as Dr. Levin pointed out. That idea is what stopped me short. It had never occurred to me that some individual being would have the last word on existence, the last chance to curse or be grateful. Part of the pain is that nobody will know who, or what, had the last word, or what was thought or said. Somehow that notion made cosmic extinction more personal, and I wondered what it would be like. Maybe as all the energy dwindles away over the horizon it will be like falling asleep. Or like Einstein mumbling his last words in German to a nurse who didn’t know the language. Or the computer at the end of time in Isaac Asimov’s classic story “The Last Question,” finally figuring out the secret of the universe and declaring, “Let there be light.” Might it be some blazing realization about the nature of string theory or the final secret about black holes? I hate to miss out on it. I’d like to think my last thought would be one of love or gratitude or awe or about the face of a loved one, but I worry about it would be an expletive. Wiser people than me ask, when I go on about this, why I don’t whine about the billions of years that passed before I was born? Perhaps it’s because I didn’t know what I was missing, whereas now I’ve had a lifetime to imagine what I’ll miss. If that worries you, here is an encouraging metaphor straight from Einstein’s equations: When you are inside a black hole, light pours in from the outside universe, which seems to speed up while you appear to be frozen. In principle, you could see the whole future history of the galaxy or even the whole universe speed past you as you fall toward the center, the singularity where space and time stop, and you die. Maybe death could be like that, a revelation of all of the past and future. In a sense, when we die the future dies too. Rather than whine about the end of time, most of the physicists and astronomers I talk to say the notion is a relief. The death of the future frees them to concentrate on the magic of the moment. The late, great astrophysicist, philosopher and black hole evangelist John Archibald Wheeler, of Princeton, used to say that the past and the future are fiction, that they only exist in the artifacts and the imaginations of the present. According to that point of view, the universe ends with me, and so in a sense I do have the final word. “Nothing lasts forever” is a maxim that applies to the stock market and the stars as well as to our lives and Buddhist sand paintings. A whiff of eternity can illuminate an entire lifetime, perhaps even mine. No matter what happens in the endless eons to come, at least we were here for the party, for the brief shining sliver of eternity when the universe teemed with life and light. We’ll always have the Milky Way.