The strange thing about astronomical time scales is that from the perspective of a human, a human time scale, they are all essentially the same. A human lives for how long? A century, a millennium? How long does a world exist for before a human exists on it? A million times that. How long does the universe exist before the human exists? Ten million times that. For how much of the world or the universe's existence does the human live? None.
How long does a red dwarf star live for? A trillion years? Longer than every single human lived, put together?
How much does a red dwarf star care?
To a first approximation, the significance of a single human life to any of this, is zero. And to a second and third approximation, it is zero too. And as you ascend the chain of cosmic events, into the deepest future, the time scales only become longer. The deep chasms of time, the black eventless vaults, become a kind of horror story. Eternity is frightening, in an abstract, impossible way. "Eternity", however, is a short, misleadingly comprehensible word. But a quadrillion years, every single one of those years, considered carefully and elapsing, second by second, between one event happening and the next, is an unnameable, concrete, mathematical nightmare.
This is not a story about humans but the beings it concerns are as near enough that it makes no difference.
When a future is so sparse, astonishing amounts of human existence can fill it and make no difference. Far out from here in time, a distance of time from here so immense that for a human to truly comprehend it would be fatal, pulverising their ego into oblivion, is a little galaxy of stars. It is still, earnestly, the beginning, the very earliest years of the universe, the opening eyeblink. But in this little galaxy are stars of a different capital-P Population, and ten billion years can pass in this little pocket, without it mattering too much. And orbiting one of the stars is a little world and on this little world a civilisation has shown up. And thousands of years of famine and war and suffering have passed, and then medicine, and then science, and slow, gradual enlightenment. And they have examined their ground and their sky, and they have reached valid, largely correct conclusions.
These people have realised that they live in the last meaningful aeons of a universe which is shutting down for a long darkness. There are billions of years of life left in their star, and in their galaxy. However, they have realised that they are absurd outliers. They know that there was a Big Bang, and they know that in prior ages of the universe's existence there were trillions of galaxies each with billions of stars. They know that their universe was once, relatively speaking, bright, and likely populous. And they have a decent estimate of how much time has passed since then, and they realise that statistics, and ultra-long-term gravitational dynamics, and normal stellar evolution, has caused those galaxies to flare up and disperse and die. And, through pure chance, a rough collaboration of matter has stayed together here, and they live in a galaxy which is one of what they hypothesise to be the second and final population of galaxies in their universe. There will not be more.
They cannot see other galaxies, but they guess others may exist, beyond their universe's observable limit.
And... because a person's existence is small, and a person's world is large relative to a person, it's difficult for most people to absorb this as a serious part of their context. Their civilisation is, broadly speaking, just getting started. They have what is, relatively speaking, a vast future ahead of them, an immensity of their own world and their solar system to explore, and, relatively speaking, indefinite time in which to explore it. There are a few, the astronomers and the cosmologists, who internalise what's happening, and truly get it. But only a few.
And those few live with a weird, dark cloud. The looming, gnawing gulf of nothing. We're all there is, they think to themselves. They have serious, accurate, reasonable guesses about what happens after this: more or less, nothing, for such a monumental period of time that to express it in seconds or millennia makes no difference. We're the last ones in the universe. No one's ever going to see this again. No part of this universe will understand what it is.
But that's billions of years in the future. Or hundreds of thousands. How long does a person live? A century? The Sun comes up again, every time. And it won't "ever" stop, and there is food and laughter and a fire and a manic dance. And so, who can reasonably care that, out of all the random sentients in all the galaxies in the universe, this might be the last one? There is a long future ahead, by a person's standards.
There is one other mystery.
There should not be a galaxy, still, here. A loose little agglomeration of a few hundred million stars? It should have become impossible, a quadrillion years ago, for so many stars to be in the vicinity of one another, long-term gravitational interactions and the expansion of the universe should have taken care of that. Pure dumb luck? There were trillions of galaxies, once. A one-in-a-trillion chance?
And there is, of course, the square star.
Nobody can make sense of the square star, but that's normal.
A representative is sent.
And then, some years after the representative has begin its shocking, drawn-out vivisection of the Sun, another representative, this one of the people, not of the square star, is sent to meet the first representative. The best ship that could be sent, using their meagre, millennia-young technology, a tiny capsule with barely the delta-vee to make it to the inner solar system, and one occupant, calm and well-trained.
The capsule passes the square star's representative several times, at five-day intervals, scanning it from behind a luminous reflective shade. As it orbits to a new closest approach, space folds around the capsule and it is swallowed up, and its occupant discovers herself landed in a facsimile of the grassy, pleasant, flower-sprinkled field behind her home town. Except that vertical, sheer grey walls are on three sides, and a grey wall overhead. And the last wall is missing, making for a long, extremely tall grey-walled tunnel. And at the far end, the echoing roar and blinding... what should be blinding... bright, but intensely heavily filtered light of the Sun.
The helionaut walks forward. She keeps the helmet on, drags her oxygen behind her. It's a long slog of a walk, more than a kilometre, to reach the far end of the corridor, and look down on her civilisation's Sun. To the left and right, the representative's magnetic fields are boiling away, leaching fusion energy.
The helionaut says, misting her helmet, "Would you stop this?"
A long silence ensues.
The helionaut says, "But what are the chances? Incalculably powerful aliens, we comprehend. We are far past belief in gods, but we can admit to your existence. The universe has existed for long enough. If anything is to survive, it would have to be something as monstrous, enduring and implacable as you. Something which leaches stars. Breeds and slaughters galaxies. There is little that we would not believe. You rely on solar fusion energy for... existence, or whatever grand tasks it is you carry out. You... squares.
"We have a theory, one of many, that this galaxy was assembled by you, as a last energy source. A closely guarded reserve. If finite. Six hundred million final stars. If you guard these long enough, some may continue to fuse for trillions more years. If you gather the dust together again, you may have another quadrillion.
"This computes, and it explains your square 'star'. But why now? What percentage of this system's existence is us? A millionth? This is no coincidence. What do you want with us? Why choose this moment of all to harvest our star? Just wait! Wait one million more years!"
The representative becomes a person and confronts the helionaut.
"We," she says to the helionaut, "were once... this." She gestures at the helionaut, who is almost shapeless in her immense, bulky pressure suit and with her oxygen and other equipment towed behind her. "Not with the same eyes or hands or locomotion as you, nothing like you in size or shape. But we were carbon-based tool users. I have never met you. I was curious how you would respond."
"That is all? Curiosity?"
"It has been a long time. It is... very difficult to meet new people, out here."
"Then we have met. What do you want? Anger? Tribute? Foul language? Will you uplift us? Just give us a million more years. This will be enough time for us to end our existence peacefully, but it is nothing to you."
"I... wanted to uplift you, yes."
"We have business of our own, square."
"No! I meant... you."
"Yes!" The representative appears confused.
The helionaut steps back a little. She earnestly considers this, frazzled. And finally, having considered all responses carefully, she opts for the instinctive one.
"I have business of my own, square!"
The capsule returns home.
The representative departs. And, as far as any person knows, and for as long as any person lives, it does not return.