10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 is a very large number. An observation from the Obvious Things Are Obvious Department, but it's an interesting one to think about, if you're the sort of person who finds massively incomprehensible things interesting to think about. (You should be.) That's 10^100, a 1 followed by 100 zeros, a number so many times bigger than our usual yardsticks for very large numbers that we have a hard time conceptualizing how big it is:
For example, the number of grains of sand on all the beaches in the world is often trotted out as an example of an incomprehensibly large number. However, a rough estimate shows that the total number of sand grains is about 10^23, a 1 followed by 23 zeros, a big number but still hopelessly inadequate to the task. How about the number of stars in the sky? The number of stars in our galaxy is close to one hundred billion, again a relatively small number. The number of stars in all the galaxies in our observable universe is about 10^22, still far too small. In fact, in the entire visible universe, the total number of protons, the fundamental building blocks of ordinary matter, is only 10^78, still a factor of ten billion trillion times too small!
From the introduction to The Five Ages of the Universe by Fred Adams and Greg Laughlin (Touchstone, 1999). It is the authors' first attempt at explaining the scale of their chosen topic: the past, present, and future evolution of our universe, all the way from its beginning 14 billion years ago to a distant era 10^100 years in the future, the point at which, while the universe may still exist, "interesting" things will stop happening. In that context, as big and weird as it is to us now, the universe is still in its infancy. It has a long way to go.
Adams and Laughlin break up the lifespan of the universe into five stages:
1) The Primordial Era, encompassing the first 10,000 years of the universe's life, from Big Bang through the subsequent period of inflation to the first formation of hydrogen atoms;
2) The Stelliferous Era, where we are now, in which the universe is dominated at every level by the life and death of stars;
3) The Degenerate Era, which would be an awesome band name, and also represents the stage after nuclear fusion has ceased in the very last ordinary star and the universe is dominated by stellar weirdos in the form of brown dwarfs, white dwarfs, neutron stars, and black holes;
4) The Black Hole Era, an even better band name if your band favors a science fictional aesthetic, during which even the last white dwarfs have died and all that's left everywhere in the universe, anywhere in the universe, are black holes;
And finally 5) the Dark Era, which is a little too on the nose to be a decent band name, representing the whole incomprehensible length of time after the last black hole has evaporated and the only matter that remains are enormous exotic self-annihilating atoms consisting of a single positron and a single electron with a radius many times larger than the size of the current (expanding) known universe.
In the scenario presented by Adams and Laughlin, by the time the calendar counts its way up to 10^100 years in the future, there haven't been stars or planets for trillions and trillions of years. There aren't black holes anymore. There isn't even ordinary matter anymore. But the universe still exists, in a way. Never has the proverb "this too shall pass" been more ominous or more final.
After a certain point the story Adams and Laughlin are telling is as much speculation as scientific extrapolation, which they happily admit. But it's worth speculating about as a way to test the limits of how far our current understanding of the universe can take us, both backward to the beginning and forward to a distant and unknown end. The physics can be a bit dense in places, but it's never wholly impenetrable, although I wouldn't like to be presented with a pop quiz requiring me to explain degeneracy pressure. (A quantum mechanical process that occurs in very dense gases; another great band name.). The long-term evolution and eventual fate of the universe is framed as a battle between gravity and entropy, which I appreciated, because gravity is my favorite fundamental force, and because the authors are continually framing the ever-changing details of the narrative in terms of that single endless interplay.
I also enjoyed the discussions of how complexity arises and collapses in each cosmological era. We live in a very complex universe right now, with our exploding stars and swirly galaxies and crunchy planets, but it won't always be that way. White dwarfs are simpler than ordinary stars, and black holes are simpler still, but that doesn't mean the eras dominated by those stellar forms aren't capable of their own types of complexity. All that's required for complex systems to arise, really, is energy and time, two things the universe has in abundance.
The book was published in 1999 and it could definitely use an update (their current age of the universe is too low, for example), but even if the specifics change, the array of potential futures is a fascinating one.
Equally interesting to me, as a person for whom reading about science is roughly 60% learning about the universe, 30% trawling for story ideas, and 10% anxiety management (I find reading about physics very soothing), there are two particular aspects of this book that I keep thinking about, even though I finished a couple of weeks ago.
The first is about the eventual fate of life in our universe. The authors recognize that their readers are selfish squishy living things and want to know if life can survive beyond our comfy spot in the early days of the Stelliferous Era. They don't address this question using biology or chemistry—not their areas of expertise—but instead considering a far more abstract view of life, and suggesting only what theoretical structures might be considered alive in, for example, a universe defined by extremely low mass density, extremely low wavelength radiation, and time scales so great we have to order extra zeros to represent them. It's a lot of wild speculation, a lot of hand-wavey theorizing, but it's fun to decouple the question of alien life from known biochemistry and see what happens when all you have to work with are a few scarce white dwarfs and the energy they produce.
I'm particularly fond of the possibility that even after our star-dominated era is over, rare and isolated events might produce lingering main sequence stars just like our beloved Sun, and those stars might have planets, and those planets might exist long enough for complex life to evolve—but it will happen in a dark universe, a one in which there are no stars in the night sky. Should intelligent life evolve on such a world, what would they think about their universe? Equally fun to contemplate is the potential for an engineered cascading phase change via quantum tunneling overtaking the entire universe and reinventing it with different physical laws. Don't worry about how plausible it is; just think about who could do such a thing, and why, and what must happen to get an individual or a society to the point.
Which brings me to the second topic, and that's how the story presented in this book has completely exploded my idea of what constitutes far future. I tend to get my ideas about possible distant futures from fiction rather than cosmology; fiction has spaceships and my heart is forever weeping because I can't be an interstellar spaceship captain when I grow up. But most science fiction doesn't tread very far into the future at all. Even the most far-flung space opera futures take place, oh, about next Thursday in the lifespan of the universe. You barely even need to borrow any extra zeros to get there. There are still planets. There are still stars. There are still galaxies. The large-scale structure of the universe has not changed. That's tomorrow.
I'm sure there must be examples out there, but I've never read a science fiction story that takes place after the nuclear fusion of conventional stars has died out but acknowledges a long future ahead, and none that take place after ordinary matter has begun to degrade and the structure of the universe is dominated by black holes. It would be interesting to see more of that, those possible concepts of a far future that stretches far beyond embellishments on our current universe and into a setting in which you can't even count on stars to be around for comfort. The science is weird and highly uncertain, yes, but it's even weirder to imagine what the universe looks like from the point of view of an intelligent life form living in one of those future eras.
In conclusion: The Five Ages of the Universe is an enjoyable popular science book that will make you look forward to the inevitable whimpering disintegration of everything that has ever existed and ever will exist with barely contained nihilistic glee, and Cosmological Heat Death is yet another a great band name, but I'm reserving that one for myself, just as soon as I get together the other three members of my theremin quartet.