The ancients believed that the universe was immortal, and it is easy to understand why. Crops wither and grow, the moon waxes and wanes and the stars circle round and round. Yet contemporary cosmology suggests that the universe will end. The only variables are how and when.
Approximately 13.7 billion years ago the universe exploded into existence in a heated event known as the big bang. A question mark hangs over what lit the blue torch. The physicist Stephen Hawking notes that asking what happened before the big bang is like asking what is north of the North Pole. Time began with the big bang and will end once the dust settles.
Scientists believed for years that the universe would end in a big crunch. Time and space are expanding. Astronomers thought gravity would overcome cosmic expansion and cause the universe to collapse. Astronomers were therefore shocked to discover in 1998 that the expansion of the universe is speeding up rather than slowing down.
Cosmologists attribute the expansion of the universe to dark energy, which is a mysterious repulsive force that increases with distance. Dark energy is a placeholder. Cosmologists are in the dark about the nature of dark energy. What cosmologists do know is that the fate of the universe rests in the hands of dark energy.
According to the big crunch theory, dark energy weakens over time and sways negative. Positive dark energy is a repulsive force, whereas negative dark energy is an attractive force like gravity. The expansion of the universe slows down, hits the brakes and sky rockets backwards. Galaxies would spiral into a point of infinite inferno as small as the period at the end of this sentence.
Physicists have a difficult time understanding time under these conditions. Some physicists speculate that the big crunch creates another big bang. The universe oscillates between big bang and big crunch from time without end. History really does repeat itself.
Or so it seems. There are multiple problems with the cyclical model of the universe. First, if the universe is infinitely old, then the universe should be at a maximum state of entropy, which is a fancy way of saying absolute disorder. The universe is not at a maximum state of disorder; therefore, the universe is not infinitely old. Second, black holes germinate with each cycle of time, growing so large that they consume the entire universe. Far from bouncing back, the universe is swallowed whole.
According to an alternative theory known as the big rip, the universe lives hard and dies young. Dark energy increases with time, overcomes gravity and causes the universe to expand indefinitely. The rate of expansion eventually exceeds the speed of light. Dark energy fueled at these speeds is known as phantom energy. One would think this violates some sort of Einsteinian law that states nothing can travel quicker than light. Yet Einstein’s law only applies to objects within the vacuum. The vacuum can do whatever it wants.
Phantom energy would consume the universe from the outside-in. Galaxies would be stripped of their stars, planets would be plucked away from their fiery caretaker and indivisible atoms would be cut into pieces. The universe would be a dilute sea of radiation. Existence would barely be heard humming on the cosmic hard drive. Far from ending in music, the universe ends in silence.
A wormhole could save the universe from a big rip but not a big gulp. Wormholes are hypothetical tunnels that connect separate regions of spacetime and feed on phantom energy. A wormhole with a heavy appetite could grow so large that it consumes the entire universe. The belly of the wormhole is a mystery. No one really knows where the universe would go if it were gobbled up by a wormhole for lunch.
The effects of dark energy seem to have two extreme consequences; a big crunch or a big gulp. A middle ground between the two possibilities is that dark energy is a constant that is evenly spread throughout space. The vacuum energy has a value close to zero. The amount of energy stored in a volume the size of the Earth, for example, is comparable to the amount of energy stored in a few hundred barrels of petroleum, which isn’t much considering the Earth’s size. Physicists suspect that vacuum energy is driving the expansion of the universe.
The problem is physicists do not understand why dark energy has the value that it does. Physicists understand how dark energy could add up to zero but not next to zero. Some physicists speculate that the universe is evolving toward a state where the vacuum energy is zero; others suggest that the value is happenchance and varies from big bang to big bang. Whatever the case may be, dark energy is the most perplexing phenomena facing contemporary physics.
Dark energy may not have monopoly on how the universe will end. It is possible that the universe could quantum tunnel into a different state. The constants of physics would shift across the universe, giving rise to a new heaven and a new earth. The probability that these constants would fall within the life permitting range is low. Given an infinite amount of time however, the laws of physics are bound to shuffle a deck of cards suitable for life. To paraphrase the infamous Walter White, from growth and decay springs transformation!
People have been obsessed with the end since the beginning. Yet why should we care about how the universe will end? If the universe does not care about us why should we care about the universe? In one way the end of the universe is significant to human life. Life is valuable not only because it is finite but because we live in a time when the universe is capable of sustaining life. Whether it is by a big crunch, a big rip or quantum tunneling, the fate of the universe affects not just how we view the future but how we view the now.
By Nathan Cranford