On the other hand, Population II and III stars, the ancient supermassive stars who fused the metals that enabled the birth of Population I stars and the formation of planets, are all extinct now. Only the light of distant specimens, which has traveled for more than half of the univere's existence, still bears witness to their reign.
But at one point, we will enter a Third Age. Light from distant galaxies will dim. Light from the earliest moments in history will grow too far to reach us as the universe unceasingly expands faster and faster. Still, our own little corner of space is still alive, stars still emerge. But they are dim and weak compared to the stars of old. When they die, they bloat and fizzle out. The last supernova in the galaxy was billions of years ago. It will remain like this for a long time.
And then we enter a Fourth Age. The universe is dying. Fuel has ran out for new star formation. Even on the best nights, the majority of the night sky is pitch black. Black holes outnumber everything else. Except for a few galaxies, the rest of the universe is out of reach. The expansion has reached such a velocity that even travelling at the speed of light you will never reach another region of the universe ever again. Every day, another light goes out in the night sky, never to be replaced. This process is slow. The universe's death is immensely slow and dragged out. But it's not inhospitable to life. The vast majority of stars in this age are small, but exceptionally long-lived. They can support planets, and all the elements necessary for life. Seeing as life will eventually arise if the environment supports it, the universe will be booming with it. The overwhelming majority of all that will ever live will live in this Fourth Age. Cosmologists call it the Degenerate Era. To the species living in this age and their civilisations, the mysteries of the universe will forever be inaccessible. They can only observe the diminutive, extinguishing fragment of the universe, now spread out across distances many orders bigger than they are today. It will be a very populated, yet lonely universe.
Eventually, the universe will die. Stars will flame out one after another. Planets will freeze. This phase dwarfs even the Fourth Age. It lasts seemingly forever. Slowly, the atoms in all that exists decompose as even their age starts to show. The universe itself becomes fundamentally incompatible with life. Only black holes seem unaffected.
But even they are slowly dying. Ever so slowly. Not that it matters. Once time itself has lost all meaning, they start to slowly evaporate, until the universe is just a dead sea of energy, with naught but tiny ripples born from quantum randomness.
After that, it will take an infinity of time for anything to happen. But anything can happen, and maybe, eventually, by pure quantum randomness, all the energy in the universe may coalesce into one point, and it can all start over again.