The end is coming in maybe 100 billion years

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 collapse, 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, trillions 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, signifying nothing. What do we do with a universe like this?