regular-article-logo Tuesday, 30 May 2023

The End

It is coming, in maybe 100 billion years. Is it too soon to start freaking out?

Dennis Overbye Published 22.05.23, 04:16 AM
A massive star that exploded about 340 years ago

A massive star that exploded about 340 years ago

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 aprofound pearl of wisdom? Anexpletive?

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 rejectedas 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.

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, US, 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 awaythe oceans. A few billion years later the sun itself will die, burningEarth and anything that remains of us to a crisp.

There is no escaping to space. The galaxies themselves willcollapse 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 willbe a last creature to die, a last thought. A last sentient being, as 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 curseor be grateful. Part of the pain isthat 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.

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, US, 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.

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.


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