Star Points for January, 2000; by Curtis Roelle The End of the Universe As We Know It. Last month we discussed the future evolution and eventual death of our sun according to the current theory. If humanity expects to survive it will jettison our current solar system no later than several billion years from now and find another. What will the future hold after that? What changes will occur over time in the universe of our descendants? To understand the future we first visit the past. The current prevailing creation theory is known as the "big bang." An observation supporting this theory is that galaxies appear to be receding from each other like shrapnel hurled from a primeval explosion. If we assume that this interpretation is correct then the next question is, will the expansion continue forever or will the combined pull of gravity from all other galaxies eventually end the expansion and perhaps cause the universe to contract in a "big crunch?" A "closed" universe is one in which ceasing expansion leads to contraction. The notion of a contracting universe has led some to consider the concept of time reversal in which clocks will begin running backward! This conjecture leads to absurd conclusions such as brown leaves leaping onto trees and then turning into buds. The trees themselves shrink into acorns which that fly up to connect themselves onto tree branches. Can photons of light spray from our eyes and be absorbed by the stars? Ideas such as these are illogical in a universe where time is observed to move only in the forward direction. Recent estimates of how much mass exists in the visible universe indicates that there is far less than what is needed to halt the expansion. Astronomers conclude that the universe may instead be "open" and will continue expanding forever. If this is so then how will the universe change over the course of eons? London mathematician Jamal Islam discusses the future in his book, "The Ultimate Fate of the Universe." In the future the expansion of the universe will cause galaxies we see today to appear smaller and fainter as they drift away. At the same time the stars in our own galaxy will stay nearby and remain visible. In order to survive in the future the human race would need to migrate from star to star every several billion years as each host sun ages and dies. Through parallel migrations over time countless solar systems may eventually be colonized throughout the Milky Way. During such a migration a segment of civilization might pack up its things and shuttle off for a journey lasting generations. Having arrived at their new destination the narrative of their collective adventure would form a slice of the cultural heritage passed down through succeeding generations, perhaps not unlike the story of Noah's ark. Stars are formed out of gas and dust. Over the course of a star's life and eventual death material gets ejected that eventually gets recycled in new stars. However, any matter that has been converted into metals such as iron is no longer suitable for making young stars. The available supply of raw star materials will be used up and in perhaps as little as 100 billion years the final generation of stars will have burned themselves out. All galaxies, including our own, will eventually darken as their stars cease to shine. The light emitted from every star that ever lived will have been radiated into space at the speed of light. Massive stars will have long since collapsed into black holes. Black holes are theorized to be produced when extraordinarily massive stars explode as a supernova. Great quantities of energy, much of it in the form of X-rays, gets emitted as material spirals into a black hole, heating up before disappearing. If a civilization could find a black hole to live near it may be possible to generate energy by discarding trash into the black hole and collecting the energy released. Unfortunately the supply of trash is a finite non-renewable resource. You end up with a limited energy supply and a fatter black hole. Wouldn't it be nice if you could "withdraw" energy from a black hole? Fortunately, Roger Penrose and Stephen Hawking discovered a method for doing so. The conventional wisdom is that nothing, including light, may ever leave a black hole once it has gone in. Using mathematics Hawking demonstrated that black holes can indeed lose mass and energy through an "evaporation" process. Penrose has described a process where the decay of radioactive particles in the vicinity of a rotating black hole can "steal" energy away from it. The black hole feels the effect as a reduction in its spin rate. How long could a civilization survive around a stellar mass black hole? Over time gravitational encounters between three or more black holes will cause 99% of them to be ejected from the galaxy. Those that remain will collect near the center of galaxy where they will coalesce into a single galactic black hole with a radius of half the distance from the sun to the planet Pluto. The clusters of galaxies we see today will be clusters of galactic black holes when the universe reaches the age of one billion billion (ten to the 18th power) years. Gravitational interactions will cause 99% of the galactic black holes to be ejected from the system. When the universe is one billion billion billion (ten to the 27th power) years the remaining galactic black holes will have formed a supergalactic black hole with a mass of perhaps one hundred billion suns. A civilization that has learned the techniques of "farming" energy from rotating black holes could exist as long as they have access to them. However, all black holes regardless of mass are expected to have evaporated by the time the universe is 10 billion billion billion billion billion billion billion billion billion billion (ten to the 100th power) years old. The trick will be avoiding the 99.99% of black holes that get ejected into an isolated existence in deep space. Instead, pick one that remains near the center of the galaxy where it may coalesce with other black holes and grow. The bigger the black hole, the longer it will last. Once the black holes are gone the universe continues grows ever colder. Astronomers currently estimate the age of the universe to be between 10 and 15 billion years. Stars will shine for the first 100 billion years and then the universe turns forever dark as the black holes slowly evaporate over the countless eons. One blink of an eye during the epoch of light is, by comparison, many times longer than the epoch of light is to the future age of darkness ruled by black holes. In an open universe a finite amount of available energy must last for all eternity. After that life will be forced to cease its dependence on the physical universe in ways we may only speculate about. Will life eventually evolve into a form of consciousness without need of water, flesh, blood, or even bodies? The answers to these questions are far beyond the scope of the Sunday morning hobby page. May these questions serve as food for your Sunday afternoon thought and meditation.