Hoyle and his colleagues cooked up a version of eternity, the Steady State universe, in which matter was created in the voids left as the galaxies sped away from one another, so over all the cosmos remained the same. The Steady State idea died in the 1960s and the Big Bang won.

Now a new version of the Big Bang, known as eternal inflation, is ascendant, in which there seem to be an endless number of universes bubbling violently forth from a background of primordial energy — “false vacuum,” in the jargon.

And so it goes, restless change manifested as immortality. Which part of the picture you think is most meaningful might depend on who you think you are — a citizen of this planet and universe, or a creature of the endless possibilities of existence somewhere, at some time. Is there solace to be found in the vision of places and people we can never know or reach?

For we need solace. The latest cosmological wrinkle is dark energy, which is speeding up the flight of galaxies from one another. And the great question is whether this dark energy is going to suck the light and energy out of the universe so completely that some day billions of years from now nothing is left: no memory even of Homer, Jesus, Mozart, Elvis or Nelson Mandela, not to mention the rest of us.

Is this, then, the end of time, at least in our lonely corner of the multiverse, as it is known?

In the four-dimensional reality of Einstein’s relativity, other times — from the Big Bang to the Big Freeze — are as real as other places. Nothing changes; we’re just passing through. As Einstein once wrote, “People like us, who believe in physics, know the distinction between the past, present and future is only a stubbornly persistent illusion.”

Dr. Smolin, like many philosophers, complains that this coldblooded mathematical formulation doesn’t do justice to the experience we all have of being in time. Moreover, the only way to understand why the laws of physics are as they are, he says, is to imagine them changing — like the Darwinian evolution of species — in cosmic time. Real time. But neither he nor anyone else can say how it would work.

The party line among many theoretical physicists recently is that time (and space) are “approximations” that emerge out of a more primal entity, maybe information in some quantum process. You may wonder who cares what time is and whether it is worth your tax dollars. It’s not a question that moves the markets, but as Bohr understood, it moves our hearts.