The End Is Nigh.
—Walter Kovacs, aka Rorschach, from Alan Moore's Watchmen (1986)
This isn't the happiest of chapters. Fittingly placed at the end of this book, the chapter is all about endings. As long as time has a direction, then atoms, humans, the earth, the sun, the Milky Way, and the universe will all at some point…just end. Everything has an expiration date. This final chapter explains the how and why of some of the grand finales.
SPEAKING OF ENDINGS (AN AUTHOR'S CONFESSION)
I remember one time when I was standing by the side of the road holding up a sign that read, The end is near! Turn around and save yourself! This rude driver shot me the finger as he passed, yelling that I was an apocalyptic a-hole.
To be honest, it sort of hurt my feelings. Anyway, next I heard tires screeching and a loud splash. Then it hit me. My sign should probably have said, Bridge out. Oh well, live and learn, or die.
Okay, back to the science.
THE END OF THE INDIVIDUAL
All life, all the way down to cells, has a metabolism, and all metabolisms wear down. Chapter 9 covered fraying telomeres and the Hayflick limit along with other aging indicators. So, evidence of you getting older does exist. For some people, looking into a mirror just isn't enough. Chapter 9 also gave some scientific hope for biological immortality, and then chapter 10 hinted at downloading your mind into a computer.
It isn't just us carbon-based organics who wear out. Whether they are our friends or overlords, machines need to be considered in this ending game. If it has moveable parts, it ages over time and ages more quickly with use (wear and tear).
If you think we can all go on forever as posthumans who share our virtual living space with AIs, then you need to know one key fact: the party could go on for quite a while, just not forever. Thanks a lot, entropy! I will tell you all about the “e” word soon. For now, just know that both metabolic and mechanical systems need fuel. Someday the universe will be unable to provide it.
As you continue along the path of this chapter, you will discover that all the trails toward immortality fade away. The word immortality should include “really, really long but temporary” in its definition.
THE END OF THE HUMAN SPECIES
Something to ponder: our species might be the first to notice an upcoming extinction event ahead of time.
Unlike the end of an individual, the end of humanity is very speculative. Many different statistical models predict the number of years we might have left. Some include extinction-level events like asteroid strikes, a nuclear war, and overpopulation, all of which chum up the science fiction waters.
Others are based on the average number of years a hominid species has survived in the past. In a speech given at Oxford University's debating society, Stephen Hawking stated his belief that, unless we get off the earth, our species has about one thousand years before extinction.1
This is more optimistic than the fifty-fifty chance of surviving until the end of this century astronomer Martin Rees proposed in his gloomy book Our Final Hour: A Scientist's Warning—How Terror, Error, and Environmental Disaster Threaten Humankind's Future in This Century—On Earth and Beyond.2 His probability calculation is based on the danger of us not truly understanding how destructive our technology really is. I wonder if he reads a lot of science fiction.
I'm not going to give you any odds based on my beliefs. Instead I'll present some facts and you can draw your own conclusions. Let's begin with a few of the local endings from our past. Today it is estimated that 99.9 percent of all species that have ever existed are gone.3 The culprits behind the extinctions are volcanic eruptions, asteroid impacts, and temperature change. These are natural causes. The human-made ones were discussed in chapter 11.
The greatest “hits” of Earth extinctions:
Ordovician-Silurian 440 million years ago (MYA), 60 percent to 70 percent of all species went extinct. The probable cause was a combination of falling sea levels and glaciation.4
Late Devonian 360 MYA, 70 percent of all species went extinct. The probable cause was global cooling and depleted oxygen in the oceans.
Permian-Triassic (also known as the Great Dying) 250 MYA, 96 percent of all marine species and 70 percent of land species were extinct. The cause might have been the acidification of oceans from dissolved carbon dioxide thanks to volcanic eruptions. So much for the bulk of the species coming out during the Cambrian explosion. (See chapter 8 for what exploded.)
Triassic-Jurassic 200 MYA, 70 percent to 75 percent of all species became extinct. The probable cause was the sudden release of carbon dioxide from volcanic activity.
Cretaceous-Paleogene (also known as the K-T extinction) 65 MYA, 75 percent of all species became extinct. Bye-bye, dinosaurs. The possible cause could have been an asteroid impact, or volcanism, or a combination of the two.
The Holocene extinction (nicknamed the “sixth extinction” and also referred to as the Anthropocene extinction): this is happening now. Until the industrial revolution came along, two vertebrate species out of ten thousand went extinct every one hundred years. According to that number, nine species should have disappeared in the past century. Instead, 477 disappeared.5 If the increase in greenhouse gas continues at its current rate, one in six species will face extinction by 2099.
ROID RAGE (DESTRUCTION BY ASTEROID)
Fig. 21.1. Illustration of an asteroid hurtling toward Earth. (iStock Photo/RomoloTavani.)
Big rocky chunks are inconsiderate enough to crash down on Earth about every 500,000 years. This includes asteroids and their speedy comet cousins. The goodish news is that these rude drop-ins haven't all been extinction-level events. The badish news is that, according to the geological record, an asteroid extinction event has occurred every twenty-six million years.6
Scientists are seeking an explanation for this pattern. Here are some of their ideas for why the earth gets stoned, none of which are related to peer pressure. They are all speculative and extraterrestrial.
- Planet X
A Neptune-sized planet might be orbiting the sun every fifteen thousand years and periodically causing comet disturbances. Although not directly observed (if only it were that easy), its theorized existence is inferred from the gravitational tugs on stellar things we can see, most of which are things we don't want tugged. Hence our interest.
Astronomers estimate that Planet X has ten times the mass of the earth, so if we knew where to look, we'd probably be able to see it with a powerful telescope. For now, we can only theorize its orbit.7
- Companion star to the sun
A hypothetical star named Nemesis is postulated to be hanging out past the Oort cloud and circling our sun in a wide, elliptical orbit.8 With a name like Nemesis, how could it not be evil? As it periodically approaches, it disrupts billions of comets in the Oort cloud with its gravity and shooting them at the earth.
By the way, Nemesis's nickname is Death Star. The math for its orbit might work out, but there is no evidence for its existence. Remember, math can drive science, but it is not science itself.
If Nemesis does exist then it is probably a brown dwarf, a small star with insufficient mass to maintain the nuclear fusion of hydrogen. This means it will be small and dim and therefore hard to detect directly.
- Oscillations through the galactic plane
Instead of (or in addition to) another sun or planet perturbing the comets, it might be that our own sun's wavy journey through the Milky Way causes all or some of the problems. The sun moves up and down as it circles the center of the Milky Way. Its route is not much different than that of a wooden horse bopping up and down on a carousel.
This oscillation exposes our solar system to gravity differentials (changes in gravity) that affect material in the Oort cloud. The movement also changes how much cosmic radiation we are exposed to. For example, the sun passes through the north side (upper region) of the Milky Way about every sixty-two million years.9 Because it is exposed to an excess of cosmic rays during this time, our environment is impacted with weather changes.
For the record, there is no “up” or “north” in space.
Fig. 21.2. Illustration of the merry-go-round Milky Way.
- Dark matter
This is not about asteroids, but it does provide a possible explanation for the natural pattern of extinctions. As the sun bobs through the galaxy on its carousel, it might pass through clumps of dark matter, an acquaintance of yours from the third interlude. These particles will fly through the center of the earth and possibly affect the core's temperature. The results would be volcanic eruptions (hello, Krakatoa) and rising seas. This is the most speculative of the causes for mass extinction because, other than gravity, scientists aren't sure what dark matter interacts with.
IS ANYONE WATCHING OUT FOR THESE ROCKS AND ICE BALLS?
To detect these wandering asteroids and comets, astronomers rely on both ground-based and space-based telescopes. The Jet Propulsion Laboratory at the California Institute of Technology has recorded about fifteen thousand near-Earth objects (NEOs).10
Not all asteroids are created equal. The dinosaur killer of the Cretaceous-Paleogene extinction, which left its footprint in what is now modern-day Mexico, was about ten kilometers wide (6.2 miles).11 Ninety-five percent of asteroids this size or larger have been identified, and their orbits are tracked by NASA. Ninety percent of medium-sized asteroids, ranging from one to ten kilometers (0.62 to 6.2 miles) wide, are under similar surveillance.
The small ones, less than one kilometer wide, are largely unknown. They can drop down faster than a bullet. Most of them will explode in orbit due to the kinetic energy involved with hitting the atmosphere. Those that survive are most likely to land in oceans. If they were to hit land, cities could be damaged, but they do not pose extinction-level threats.
A twenty-meter meteor, labeled 2012 DA14, exploded twelve miles above Chelyabinsk Oblast in Russia in 2013.12 The explosion was about thirty times greater than the atomic bomb dropped on Hiroshima. The shock wave spread out and damaged thousands of buildings, but fortunately no deaths were reported.
IF THE BIGGER NEOS TARGET EARTH, CAN THEY BE STOPPED?
Detection is only half of our defense system. The other is deflection. To stop an asteroid, you need to nudge it a bit and alter its path. Early detection is therefore crucial. The farther away the uninvited guest is, the less of a nudge is necessary to change its trajectory. If it is far enough out from Earth, our space engineers might only need to change its velocity by a couple of millimeters per second.
How could they do it? The boring answer is that they hit it with a projectile. A more elegant solution is to use a gravity tractor. This is when you send an object (artificial or otherwise) to a position near the asteroid and allow the nearly infinitesimal gravitational attraction between them to nudge the asteroid slightly.
An offending comet might be treated a little differently, and in a way that is a little showier: launch a rocket and detonate a nuclear bomb close to the ice ball. If the math is calculated correctly, enough of the surface will boil away to change the comet's trajectory so that it bypasses Earth. If this happened in science fiction, the engineer would be sweating out the complicated calculations. Keep in mind that comets travel twice as fast as asteroids, and your team has only one rocket.
No matter your choice of deflection, it will clearly have more chance of being effective than the non-science method used for the 1998 film Armageddon. That idea was so zany it isn't worth addressing in a book interested in science. I will, however, comment on the crazy way the heroes get to the asteroid, which involves a slingshot maneuver of a 1990s’ NASA space shuttle around the moon and then landing it on the offending rock.
I'm not certain how they failed to notice an asteroid the size of Texas until it was only eighteen days away.
As fate (coincidence, or possibly film studio competition) would have it, the movie Deep Impact came out the same year. This one is about a comet hurtling toward Earth, and the plot attempted to include actual science. And it didn't do a bad job. Not perfect, but not bad. Keep in mind that an Orion-class ship is a nuclear rocket (see chapter 17 for details), not one that uses a chemical engine as is mentioned in the movie.
Some social circles (they call themselves Whovians) claim that the asteroid that killed off the dinosaurs was sent by the transhuman Cybermen in an effort to destroy Earth. Doctor Who companion Adric tragically sacrifices himself in the attempt to save our planet. It didn't work for the dinos, but it worked out okay for mammals. For Adric haters, it was a complete success. I can nitpick this episode until tomorrow's breakfast, but the science of this Doctor Who episode makes more sense than that of Armageddon.
THE SUN AND EARTH: A RELATIONSHIP THAT ENDS WHEN THE LIGHTS GO OUT
Our sun is 4.5 billion years old. It is nearing the halfway point of its yellow phase where its energy predominately comes from fusing hydrogen into helium. We like this phase. It has been good for life on Earth. However, you should know one important thing. Although our sun appears yellow through our atmosphere (don't look at it unfiltered!), it is really white. The yellow wavelength travels all the way through the atmosphere while the blue wavelength is scattered (blue skies smilin’ at me, and all that). I'll call it a yellow star to avoid confusion.
Now, don't get too comfortable thinking that human civilization has at least another 5.5 billion years before we must exit this planet as the sun goes into its red phase. Over the next two billion years, the sun will expand and grow hotter as it begins to run out of hydrogen to burn. Helium will look tastier and tastier as an energy choice.
The increase in heat that will result will change Earth's carbon cycle. This will lead to more water vapor in the air and runaway greenhouse effects. We will be the new Venus on the block. If humans are still on the planet during this two-billion-year transition, they will hopefully have moved toward the poles or underground. At the very least, we would need to set up the solar shields described in chapter 11 to block out the rays.
In about 5.5 billion years, as the ratio of helium to hydrogen fusion increases (ending its yellow phase), the sun will become red and bloat outward. The Goldilocks habitable zone will be pushed farther and farther outward. The sun will also become lighter. The drop in gravity will cause all the planetary orbits to widen. This is where the physics get really tricky, and by tricky I mean there is no consensus on the amount of mass that will be lost or the degree of orbital changes. Will our red giant sun expand far enough to engulf Earth, or will Earth's expanding orbit save it?
It won't matter. At that point, it won't be habitable for human life. Earth is done with us. The atmosphere and oceans will have evaporated from the increased heat. But we already left, right? I bet that Saturn's moon Enceladus is looking pretty good right now. The temperature on Mars might not be too bad. I hope that before this era arrives, our geoengineers have read chapter 12 and worked on terraforming other locales in the solar system.
The sun has one more set of fireworks to ignite. After about 150 million years performing as “Big Red,” it will run out of helium to burn. This will signal its final curtain call. It will shrink until helium from its outer regions pushes down on the core, ignites the outer layer, and blows it into space in clouds of gas and dust. The process will repeat until only the core remains.
The core will continue to collapse for another 500,000 years. Eventually the sun enters its elderly phase and will be known as a white dwarf. No more fusion occurs, but it is still hot. Whatever is left of humanity can steer their asteroid colonies or self-contained VR servers close enough to stay warm and absorb energy to fuel their uploaded minds. This will work until the white dwarf fades to black over another (speculated) trillion years. After that? We had better have moved to other stars.
WHY WILL ONLY SUPERSIZED GALAXIES EXIST IN THE FUTURE?
The Milky Way galaxy is part of a gang made up of fifty-four galaxies. Astronomers came up with the intimidating name Local Group for these thugs. Most of the gang members are small, but the Milky Way is a big player along with the Andromeda and Triangulum galaxies.
The Local Group is gravitationally bound, meaning that the gravity holding the members together is stronger than the universe's expansion. This will be true for a long time but not forever. Gravity will lose in the long run to the stretching (dark energy) of the expansion. As nonmember galaxies move away from Earth, the stars of the Local Group are actually getting closer.
A rumor claims that the gang members don't always get along well. The word on the street is that in about four billion years, the Andromeda and Milky Way galaxies are going to clash.13 Yes, a collision is imminent. They will first pass through each other (our fading sun will be safe because stars aren't all that close to each other). Then, thanks to gravity, they will snap back toward each other.
This will happen over and over until they combine into a single galaxy. And if the super massive black holes at the core of these galaxies collide as predicted, a lot of energy will be released as gravitational waves. Eventually, this galactic martini shaker will apply mixology between all fifty-four gang members until only a single super-galaxy that I shall now name DAVID is left. This naming is unofficial. I'm not authorized to name this new hybrid galaxy in the science world. But in the universe of this book, I am almighty.
This process will happen to all local groups across the entire universe. All that will be left are super-galaxies separated due to expansion.
WE CAME ALONG AT A GOOD TIME (TO PREDICT THE END OF THE UNIVERSE)
We have evolved in the universe at a very fortunate time. It hasn't grown so big that we can't come up with really cool cosmological models that describe its origin and its future. Future civilizations might not be so lucky.
If an intelligent race of beings evolved in one of the super-galaxies, what could they learn about the universe? More importantly, what could they learn of the DAVID system? Nothing, actually. They will not be able to see any other galaxies once the other super-galaxies have faded over the horizon faster than the speed of light. They won't know about DAVID.
Their observational science will determine that theirs is the only galaxy in the universe. No evidence for an expanding universe or a big bang will exist. A large portion of our universal history is written in the cosmic background radiation (even more chapter 4 goodness), which at some point will have been stretched so thin it will become undetectable. This civilization will conclude that the universe is eternal and unchanging and that they are the only galaxy in it.
THERMODYNAMICS WILL BE THE END OF US, BUT FIRST LEARN ITS LAWS
As the prefix thermos- suggests, thermodynamics is the study of heat, and three laws govern this area. A zeroth law about temperature change kicks it off. Below is a description of the laws followed by an easy summary sentence to help you remember and understand the meaning of each.14
0.If the temperature is higher in a system that comes into contact with another system, its temperature will fall while the temperature in the other system will rise until both temperatures are the same.
Easy way to remember: there is a game and you must play.
1.Energy and matter cannot be created or destroyed within a closed system. This law is called the law of conservation of energy.
Easy way to remember: you can't win; you can only break even.
2.The entropy of any closed system that is not in a thermal equilibrium will almost always increase. Thermal equilibrium means no temperature differences exist within the system. Entropy is the amount of a system's energy that is unavailable for work.
Easy way to remember: you can't break even.
3.Entropy in a closed system approaches a constant value as temperature approaches absolute zero. Absolute zero is the lowest temperature possible where movement of molecules has the least amount of kinetic energy (movement).
Easy way to remember: you can't quit.
Summary of thermodynamics: if you think things are a mess now, just wait.
HOW DOES ENTROPY EXPLAIN THE DIRECTION OF TIME?
From the second law of thermodynamics we derive entropy, the measure of disorder within an isolated system. Consider your bedroom. If you make no effort to clean it, it will gradually become messier. Perhaps quicker for some than others. The only way to prevent the messiness is to regularly clean the room.
In physics, the equivalent is to pump energy into a system. The addition of energy is the only way to slow down or reverse entropy. However, in an isolated system such as our universe, the first law of thermodynamics states that energy cannot be added, so entropy (disarray) will continue increasing. If no universal housekeeper pops in for a cleaning, everything everywhere will gradually fall into disarray.
The earth avoids complete disarray because our sun pumps some of its energy into our system and pushes back against entropy. Unfortunately, the sun will eventually run out of energy.
The general rise in entropy gives us a sequence of events physicists call the arrow of time. The arrow does not tell us that the past leads to the future. It only tells us that it goes from order to disorder. This is an important distinction. When entropy reaches its maximum value, the arrow of time will break.
HOW IT ALL ENDS
The first law sets us up for the fall. The law of conservation of energy ensures that the amount of mass and energy at the start of the universe remains constant throughout any point in its history or future. Thanks to the expansion, the universe is stretching out a fixed amount of matter. Eventually it will become so thin it will be as if it never existed. Thanks to dark energy, it will expand faster and faster. Matter and energy will thin out until at some point even individual atoms are pulled apart.
The third law of thermodynamics makes the dire prediction of the universe's ultimate fate. In the far distant future as the universe veers toward disorder, there will be no more thermodynamic energy (it will have been stretched too thin). This doesn't mean heat won't be present but that heat differentials will no longer exist. A single universal temperature will rule. This is called the heat death of the universe.
WHEN ALL THE SUNS TURN OUT THE LIGHTS
All the stars will eventually run out of fuel. The main sequence stars described in chapter 15 will become white dwarfs. After that, they cool down into black dwarfs that will feed the massive black holes left in the universe. In a nonillion years, all that will be left are black holes. That's pretty far in the future. A nonillion is described in chapter 4.
The black holes will try to feed on the tiniest bits of energy left, but the pickings will be slim, so they will begin to evaporate. Even the evaporated radiation isn't much to talk about. It will be stretched so thin that its energy (wavelength) will be negligible. The universe will get close to the absolute zero described by the third law of thermodynamics, the heat death with a broken arrow.
The universe will be an unchanging, cold place with no energy or mass. There can be no life, mechanical or organic, because that requires atoms and energy. There will not even be enough energy for thought.
LIFE AFTER THIS UNIVERSE
Perhaps before the heat death, if the universe stretched enough, spacetime itself might tear into another dimension into which posthuman life might escape.15 Or perhaps much earlier, posthumans of a type VI civilization (chapter 6) decided to tour the multiverse (although the multiverse technically isn't science). Now, a type VII civilization might try to pump in energy from the universes they have created outside the universe. This would drive back the entropy.
PARTING COMMENTS
I know. Not a happy chapter. You shouldn't feel too despondent because a bit of good news can be found. Science has not excluded the possibility that some life-forms (or artificial intelligences) might survive until the end of the universe…or possibly outlive it!
You might be the person to make it happen. I'm sure you could think up interesting and perhaps unexpected ways to combine the scientific ideas in this book. That's how much confidence I have in you. If you are not a scientist then perhaps you could use your ideas to create great science fiction or a cool video game.
This kind of speculation drives scientists and creators of science fiction into the realm of Arthur C. Clarke's second law of prediction: the only way of discovering the limits of the possible is to venture a little way past them to the impossible.16
Bye for now. There is a lot more science and science fiction to share in our universe.