PROLOGUE
One day about seventy-five thousand years ago: A. R. Templeton, “Genetics and Recent Human Evolution,” International Journal of Organic Evolution 61, no. 7 (2007): 1507–19. See also Supervolcano: The Catastrophic Event That Changed the Course of Human History; Could Yellowstone Be Next? (New York: MacMillan, 2015).
Stark evidence of this cataclysm: Although there is universal agreement that the eruption of the supervolcano at Toba was a truly catastrophic event, it should be pointed out that not all scientists believe it altered the direction of human evolution. One group, from Oxford University, analyzed sediments in Lake Malawi in Africa going back tens of thousands of years into the past. By drilling into the lake bottom, one can retrieve sediments that were deposited in the ancient past and hence re-create ancient weather conditions. Analysis of this data from the time of the Toba volcano showed no significant sign of permanent climate change, which casts doubt on the theory. However, it remains to be seen if this result can be generalized to other areas besides Lake Malawi. Another theory is that the bottleneck in human evolution about seventy-five thousand years ago was caused by slow environmental effects rather than a sudden collapse of the environment. Further research is required to definitively settle the question.
CHAPTER 1: PREPARING FOR LIFTOFF
As a youth, he spent most of his time: Newton’s three laws of motion are:
· An object in motion stays in motion, unless acted on by an outside force. (This means that our space probes can reach the distant planets with minimal fuel once they are in space, because they basically coast their way to the planets, since there is no friction in space.)
· Force equals mass times acceleration. This is the fundamental law behind Newtonian mechanics, which makes possible the building of skyscrapers, bridges, and factories. At any university, a first-year course in physics is basically solving this equation for different mechanical systems.
· For every action, there is an equal and opposite reaction. This is the reason why rockets can move in outer space.
These laws work perfectly well when shooting space probes throughout the solar system. However, they inevitably break down in several important domains: (a) extremely fast velocities approaching the speed of light, (b) extremely intense gravitational fields, such as near a black hole, and (c) extremely small distances found inside the atom. To explain these phenomena, we need Einstein’s theory of relativity and also the quantum theory.
“To place one’s feet on the soil of asteroids”: Chris Impey, Beyond (New York: W.W. Norton, 2015).
“That Professor Goddard”: Impey, Beyond, p. 30.
Wernher von Braun would take the sketches, dreams, and models: Historians still debate precisely how much cross-fertilization there was between pioneers like Tsiolkovsky, Goddard, and von Braun. Some claim that each worked in near total isolation and independently rediscovered one another’s work. Others claim that there was considerable interaction between them, especially because much of their work was published. But it is known that the Nazis made inquiries to Goddard, asking for his advice. So it is safe to say that von Braun, because he had access to the German government, was fully aware of the developments of his predecessors.
“I plan on traveling to the Moon”: Hans Fricke, Der Fisch, der aus der Urzweit kam (Munich: Deutscher Taschenbuch-Verlag, 2010), pp. 23–24.
“I reach for the stars, but sometimes I hit London”: See Lance Morrow, “The Moon and the Clones,” Time, August 3, 1998. For more on the political legacy of von Braun, see M. J. Neufeld, Wernher von Braun: Dreamer of Space, Engineer of War (New York: Vintage, 2008). Also, parts of this discussion were based on a radio interview I conducted with Mr. Neufeld in September 2007. Many have written about this great scientist, who opened up the space age but did it using financial backing from the Nazis, and have come to differing conclusions.
While the U.S. rocketry program proceeded by fits and starts: See R. Hal and D. J. Sayler, The Rocket Men: Vostok and Voskhod, the First Soviet Manned Spaceflights (New York: Springer Verlag, 2001).
“Congress came to see NASA primarily as a jobs program”: See Gregory Benford and James Benford, Starship Century (New York: Lucky Bat Books, 2014), p. 3.
CHAPTER 2: NEW GOLDEN AGE OF SPACE TRAVEL
“The whole idea is to preserve the Earth”: Peter Whoriskey, “For Jeff Bezos, The Post Represents a New Frontier,” Washington Post, August 12, 2013.
In the 1990s, an unexpected discovery caught scientists by surprise: See R. A. Kerr, “How Wet the Moon? Just Damp Enough to Be Interesting,” Science Magazine 330 (2010): 434.
The Chinese have announced that they will put their astronauts on the moon: See B. Harvey, China’s Space Program: From Conception to Manned Spaceflight (Dordrecht: Springer-Verlag, 2004).
One factor that limits how long our astronauts can stay on the moon: See J. Weppler, V. Sabathier, and A. Bander, “Costs of an International Lunar Base” (Washington, D.C.: Center for Strategic and International Studies, 2009); https://csis.org/publication/costs-international-lunar-base.
CHAPTER 3: MINING THE HEAVENS
Planetary Resources estimates that the platinum: See www.planetaryresources.com.
CHAPTER 4: MARS OR BUST
“Failure is an option here [at SpaceX]”: For more quotes from Elon Musk, see www.investopedia.com/university/elon-musk-biography/elon-musk-most-influential-quotes.asp.
“They say Mars is the new black”: See https://manofmetropolis.com/nick-graham-fall-2017-review.
“I really don’t have any other motivation”: The Guardian, September 2016; www.theguardian.com/technology/2016/sep/27/elon-musk-spacex-mars-exploration-space-science.
“I’m convinced”: The Verge, October 5, 2016; www.theverge.com/2016/10/5/13178056/boeing-ceo-mars-colony-rocket-space-elon-musk.
“I think it’s good for there to be multiple paths to Mars”: Business Insider, October 6, 2016; www.businessinsider.com/boeing-spacex-mars-elon-musk-2016-10.
“NASA applauds all those”: Ibid.
Bill Gerstenmaier, of NASA’s Human Exploration and Operations Directorate: See www.nasa.gov/feature/deep-space-gateway-to-open-opportunities-for-distant-destinations.
CHAPTER 5: MARS: THE GARDEN PLANET
“Actually, it was Sputnik”: Interview on Science Fantastic radio, June 2017.
Another outlandish attempt to form an isolated colony: See R. Reider, Dreaming the Biosphere (Albuquerque: University of New Mexico Press, 2010).
CHAPTER 6: GAS GIANTS, COMETS, AND BEYOND
Using Newton’s laws, astronomers can calculate: The calculation of the Roche limit and tidal forces requires only an elementary application of Newton’s law of gravity. Because a moon is a spherical object and not a point particle, the force of attraction from a gas giant like Jupiter is larger on the side facing Jupiter than the gravity on the far side. This causes the moon to bulge a bit. But one can also calculate the force of gravity, which holds the moon together via its own gravitational pull. If the moon gets close enough, the force of gravity that is pulling the moon apart balances the force of gravity that holds the moon together. At that point, the moon begins to disintegrate. This gives us the Roche limit. All the rings of the gas giants that have been documented lie within the Roche limit. This indicates, but does not prove, that the rings of the gas giants were caused by tidal forces.
Beyond the gas giants, at the outer reaches of our solar system: Comets from the Kuiper Belt and Oort Cloud probably have different origins. Originally, the sun was a gigantic ball of hydrogen gas and dust, perhaps a few light-years across. As the gas began to collapse because of gravity, it began to spin faster. At that point, some of the gas collapsed into a spinning disk, which eventually condensed into the solar system. Since this spinning disk contained water, this created a ring of comets in the outer reaches of the solar system. This became the Kuiper Belt. However, some of the gas and dust did not condense into this spinning disk. Some of it condensed into chunks of stationary ice, roughly tracing out the original outlines of the original protostar. This became the Oort Cloud.
CHAPTER 7: ROBOTS IN SPACE
“AlphaGo can’t even play chess”: Discover Magazine, April 2017; discovermagazine.com/2017/april-2017/cultivating-common-sense.
In 2017, a controversy arose between two billionaires: Many fear that AI could revolutionize the job market, putting millions of people out of work. This may very well happen, but there are other trends that might reverse this effect. New jobs will open up—in designing, repairing, maintaining, and servicing robots—as the industry explodes in size, perhaps rivaling the automobile industry. Furthermore, there are many classes of jobs that cannot be replaced by robots for decades to come. For example, semiskilled, nonrepetitive workers—such as janitors, police, construction workers, plumbers, gardeners, contractors, et cetera—cannot be replaced by robots. Robots, for example, are too primitive to pick up garbage. In general, jobs that will be difficult to automate with robots include jobs involving (a) common sense, (b) pattern recognition, and (c) human interactions. For example, in a law firm, the paralegal might be replaced, but lawyers are still needed to argue cases before a live jury or judge. Middlemen, especially, may find themselves out of work, so they will have to add value to their services (i.e., intellectual capital). This means adding analysis, experience, intuition, and innovation, which robots are deficient in.
“We are ourselves creating our own successors”: Samuel Butler, Darwin Among the Machines; www.historyofinformation.com/expanded.php?id=3849.
“I visualize a time when we will be to robots what dogs are to humans”: For more quotes from Claude Shannon, see www.quotes-inspirational.com/quote/visualize-time-robots-dogs-humans-121.
“It is ridiculous to talk about such things so early”: Raffi Khatchadourian, “The Doomsday Invention,” New Yorker, November 23, 2015; www.newyorker.com/magazine/2015/11/23/doomsday-invention-artificial-intelligence-nick-bostrom.
When addressing the Zuckerberg/Musk controversy: The debate about the dangers and benefits of AI has to be put into perspective. Every discovery can be used for good or evil. When the bow and arrow was first invented, it was mainly used to hunt small game, like squirrels and rabbits. But eventually, it evolved into a formidable weapon that could be used to hunt other humans. Similarly, when the first airplanes were invented, they were used for recreation and delivering the mail. But eventually, they evolved into weapons that can deliver bombs. Similarly, AI for many decades to come will be a useful invention that can generate jobs, new industries, and prosperity. But eventually, these machines can pose an existential risk if they become too intelligent. At what point will they become dangerous? I personally believe that tipping point will occur when they become self-aware. Currently, robots do not know they are robots, but that could change radically in the future. However, this tipping, in my opinion, probably won’t be reached until near the end of this century, giving us time to prepare.
He believes that by 2045, we will reach the “singularity”: One should be careful when analyzing one aspect of the singularity: that future generations of robots can be smarter than the previous generation so that one can rapidly create superintelligent robots. One can, of course, create computers that have increasingly large amounts of memory, but does this mean that they are “smarter”? In fact, no one has been able to demonstrate even a single computer that can create a second-generation computer that is more intelligent. There is, in fact, no rigorous definition of the word smart. This does not mean that it is impossible for this to happen, it only means that the process is ill defined. In fact, it is not clear how this will be accomplished.
In order to create self-aware machines: The key to human intelligence, in my opinion, is our ability to simulate the future. Humans constantly plan, scheme, daydream, ponder, and muse about the future. We can’t help it. We are prediction machines. But one of the keys to simulating the future is understanding the laws of common sense, of which there are billions. These laws, in turn, depend on understanding the basic biology, chemistry, and physics of the world around us. The more accurate our understanding of these laws, the more accurate our simulation of the future will be. At present, the common sense problem is one of the major hurdles in AI. Massive attempts to codify all the laws of common sense have all failed. Even a child has more common sense than our most advanced computer. So in other words, a robot that tries to take over the world from humans will fail miserably because it doesn’t understand the simplest things about our world. It is not enough for a robot to try to dominate humans; one has to master the simplest laws of common sense in order to carry out a plan. For example, giving a robot the simple goal of robbing a bank will ultimately result in failure because the robot cannot realistically map out all possible future scenarios.
CHAPTER 8: BUILDING A STARSHIP
In a subsequent phase of the project: R. L. Forward, “Roundtrip Interstellar Travel Using Laser-Pushed Lightsails,” Journal of Spacecraft 21, no. 2 (1984): 187–95.
Laser-propelled nanoships: See G. Vulpetti, L. Johnson, and L. Matloff, Solar Sails: A Novel Approach to Interplanetary Flight (New York: Springer, 2008).
“There will some day appear velocities far greater than these”: Jules Verne, From the Earth to the Moon. Quoted at www.space.com/5581-nasa-deploy-solar-sail-summer.html.
The idea was developed by nuclear physicist Ted Taylor: G. Dyson, Project Orion: The True Story of the Atomic Spaceship (New York: Henry Holt, 2002).
There are several ways in which to release the power of fusion peacefully: S. Lee and S. H. Saw, “Nuclear Fusion Energy—Mankind’s Giant Step Forward,” Journal of Fusion Energy 29, 2, 2010.
The nuclear fusion rocket is conceptually sound: The fundamental reason why magnetic fusion has not yet been attained on the Earth is because of the stability problem. In nature, giant balls of gas can be compressed so that the star ignites, because gravity compresses the gas uniformly. However, magnetism involves two poles, north and south. Therefore, it is impossible to compress gas uniformly using magnetism. When you squeeze gas magnetically in one area, it bulges out the other end. (Think of trying to squeeze a balloon. If you pinch the balloon in one place, it expands in another.) One idea is to create a doughnut-shaped magnetic field and have the gas compressed on the inside of the doughnut. But physicists have failed to compress hot gas for more than a tenth of a second, which is too brief to create a self-sustaining fusion reaction.
They would utilize the greatest energy source in the universe: Although antimatter rockets convert matter into energy with 100 percent efficiency, there are also some hidden losses. For example, some of the energy of a matter/antimatter collision is in the form of neutrinos, which cannot be harvested to create usable energy. Our bodies are continually radiated by neutrinos from the sun, yet we feel nothing. Even when the sun sets, our bodies are irradiated by neutrinos that have gone right through the planet Earth. In fact, if you could somehow shine a beam of neutrinos through solid lead, it might penetrate a light-year of lead before it is finally stopped. So the neutrino energy created by matter/antimatter collisions is lost and cannot be used to generate power.
The ramjet fusion rocket is another enticing concept: R. W. Bussard, “Galactic Matter and Interstellar Flight,” Astronautics Acta 6 (1960): 179–94.
Space elevators would be a game-changing application: D. B. Smitherman Jr., “Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium,” NASA pub. CP 2000-210429.
“Probably about fifty years after everyone stops laughing”: NASA Science, “Audacious and Outrageous: Space Elevators”; https://science.nasa.gov/science-news/science-at-nasa/2000/ast07sep_1.
One day, a boy read a children’s book and changed world history: Einstein’s theory of special relativity is based on the simple sentence: “The speed of light is constant in any inertial frame [i.e. in any uniformly moving frame].” This violates Newton’s laws, which say nothing about the speed of light. In order for this law to be satisfied, there have to be vast changes in our understanding of the laws of motion. From that one statement, one can show that:
· The faster you move in a rocket ship, the slower time beats inside that rocket.
· Space is compressed within that rocket the faster you move.
· You get heavier the faster you move.
As a result, this means that at the speed of light, time would stop and you would become infinitely flat and infinitely heavy, which is impossible. Hence, you cannot break the light barrier. (In the Big Bang, however, the universe expanded so rapidly that the expansion exceeded the speed of light. This is not a problem, because it’s empty space that is stretching faster than light. Material objects, however, are forbidden to go faster than light.)
The only way known to go faster than light is to invoke Einstein’s general theory of relativity, where space-time becomes a fabric that can stretch, bend, and even tear. The first way is via “multiply connected spaces” (wormholes), in which two universes are joined together like Siamese twins. If we take two parallel sheets of paper and then punch a hole that connects them, then this gives us a wormhole. Or, you could somehow compress space in front of you, so that you can hop over the compressed space and travel faster than light.
Although physicists have seen no evidence of negative matter: Stephen Hawking proved a powerful theorem, which states that negative energy is essential to any solution of Einstein’s equations that allows for time travel or wormhole starships.
Negative energy is not allowed under ordinary Newtonian mechanics. However, negative energy is allowed by the quantum theory via the Casimir effect. It has been measured in the laboratory and found to be extremely tiny. If we have two large parallel metal plates, then the Casimir energy is proportional to the inverse distance of separation of the plates raised to the third power. In other words, negative energy rapidly increases in energy as the two plates are brought together.
The problem is that these plates have to be brought together to within subatomic distances, which is not possible with today’s technology. We have to assume that a very advanced civilization has somehow mastered the ability to harness vast amounts of negative energy to make time machines and wormhole spaceships possible.
I once interviewed the Mexican theoretical physicist Miguel Alcubierre: See M. Alcubierre, “The Warp Drive: Hyperfast Travel Within General Relativity,” Classical and Quantum Gravity 11, no. 5 (1994): L73–L77. When I interviewed Alcubierre for the Discovery Channel, he was confident that his solution of Einstein’s equations was a significant contribution, but he was wary of the difficulties it faced if one actually tried to build a warp drive engine. First, the space-time inside the warp bubble was causally separate from the outside world. This meant that it was impossible to steer the starship or direct it from the outside. Second, and most important, it required vast amounts of negative matter (which has never been found) and negative energy (which only exists in minute quantities). So, he concluded, major hurdles have to be solved before a workable warp engine can be built.
CHAPTER 9: KEPLER AND A UNIVERSE OF PLANETS
Bruno, Galileo’s predecessor: William Boulting, Giordano Bruno: His Life, Thought, and Martyrdom (Victoria, Australia: Leopold Classic Library, 2014).
“This space we declare to be infinite”: Ibid.
A big breakthrough came with the 2009 launch of the Kepler spacecraft: For more on the Kepler spacecraft, see the NASA website: http://www.kepler.arc.nasa.gov.
The Kepler spacecraft focused on one tiny spot in the Milky Way galaxy. Even then, it has found evidence of four thousand or so planets orbiting other stars. But from that tiny spot, we can extrapolate to the entire galaxy and hence get a rough analysis of the planets in the Milky Way. Succeeding missions after the Kepler will focus on different regions of the Milky Way galaxy, hoping to find different types of extrasolar planets, and more Earth-like ones.
“There are planets out there that have no counterpart in our solar system”: Interview with Professor Sara Seager, Science Fantastic radio, June 2017.
“This is a game changer in exoplanetary science”: Christopher Crockett, “Year In Review: A Planet Lurks Around the Star Next Door,” Science News, December 14, 2016.
“It’s absolutely phenomenal”: Interview with Professor Sara Seager, Science Fantastic radio, June 2017.
“This is an amazing planetary system”: See www.pressreader.com/uk/the-herald/20170223/281556585596579.
CHAPTER 10: IMMORTALITY
Yet another proposal to colonize the galaxy is to send embryos: A. Crow, J. Hunt, and A. Hein, “Embryo Space Colonization to Overcome the Interstellar Time Distance Bottleneck,” Journal of the British Interplanetary Society 65 (2012): 283–85.
“Every sign, including genetics, says there’s some causality”: Linda Marsa, “What It Takes to Reach 100,” Discover Magazine, October 2016.
The mechanism of aging is slowly being revealed: It is sometimes said that immortality violates the second law of thermodynamics, which indicates that everything, including living organisms, will eventually decay, rot, and die. However, there is a loophole in the second law, which states that (in a closed system) entropy (disorder) will inevitably increase. The key word is closed. If you have an open system (where energy can be added from the outside), then entropy can be reversed. This is how a refrigerator works. The motor at the bottom of the refrigerator pushes gas through a pipe, which causes the gas to expand, causing the refrigerator to cool down. When applied to living things, it means that entropy can be reversed as long as energy is added from the outside (which is sunlight).
So our very existence is possible because sunlight can energize plants, and we can consume these plants and use this energy to repair the damage caused by entropy. Hence, we can reverse entropy locally. When discussing human immortality, one can therefore evade the second law by adding new energy locally from the outside (such as in the form of changes in diet, exercise, gene therapy, absorbing new types of enzymes, et cetera).
“I don’t think the time is quite right, but it’s close”: Quoted in Michio Kaku, The Physics of the Future (New York: Anchor Books, 2012), p. 118.
What happens if we solve the problem of aging?: The point here is that, in the main, all the pessimistic predictions of population collapse made back in the 1960s failed to materialize. In fact, the rate of expansion of the world population is actually slowing down. But the point is that the absolute population of the world is still increasing, especially in sub-Saharan Africa, so it is difficult to actually estimate the world population in 2050 and 2100. Some demographers, however, have claimed that, if trends continue, ultimately the world population could flatten out and become stable. If so, then the world population could reach a plateau of some sort and hence avoid a population catastrophe. But this is still conjectural.
“I’m as fond of my body as anyone”: See https://quotefancy.com/quote/1583084/Danny-Hillis-I-m-as-fond-of-my-body-as-anyone-but-if-I-can-be-200-with-a-body-of-silicon.
CHAPTER 11: TRANSHUMANISM AND TECHNOLOGY
“It just completely changes the landscape”: Andrew Pollack, “A Powerful New Way to Edit DNA,” New York Times, March 3, 2014; www.nytimes.com/2014/03/04/health/a-powerful-new-way-to-edit-dna.html.
“No one really has the guts to say it”: See Michio Kaku, Visions (New York: Anchor Books, 1998), p. 220 and Michio Kaku, The Physics of the Future, p. 118.
“My prediction is that by the year 2100”: Kaku, The Physics of the Future, p. 118.
Francis Fukuyama of Stanford has warned: F. Fukuyama, “The World’s Most Dangerous Ideas: Transhumanism,” Foreign Policy 144 (2004): 42–43.
CHAPTER 12: SEARCH FOR EXTRATERRESTRIAL LIFE
“We only have to look at ourselves”: Arthur C. Clarke once said, “Either there is intelligent life in the universe, or there is not. Either thought is frightening.”
“If you live in a jungle”: Rebecca Boyle, “Why These Scientists Fear Contact with Space Aliens,” NBC News, February 8, 2017; www.nbcnews.com/storyline/the-big-questions/why-these-scientists-fear-contact-space-aliens-n717271.
This is called SETI: At present, there is no universally accepted consensus concerning the SETI Project. Some believe that the galaxy may be teeming with intelligent life. Others believe that perhaps we are alone in the universe. With only one data point to analyze (our planet), there are very few rigorous guidelines to direct our analysis, other than the Drake equation.
For another opinion, see N. Bostrom, “Where Are They: Why I Hope the Search for Extraterrestrial Intelligence Finds Nothing,” MIT Technology Review Magazine, May/June 1998, 72–77.
But all this still leaves one persistent, nagging question: E. Jones, “Where Is Everybody? An Account of Fermi’s Question,” Los Alamos Technical Report LA 10311-MS, 1985. See also S. Webb, If the Universe Is Teeming with Aliens…Where Is Everybody? (New York: Copernicus Books, 2002).
“Some of these pre-utopian worlds”: Stapledon, Star Maker (New York: Dover, 2008), p. 118.
Another possibility is that they want to steal the heat: There are many other possibilities that cannot be easily dismissed. One is that perhaps we are alone in the universe. The argument here is that we are finding more and more Goldilocks zones, meaning that it becomes increasingly difficult to find planets that can fit within all these new Goldilocks zones. For example, there is a Goldilocks zone for the Milky Way galaxy. If a planet is too close to the center of the galaxy, there is too much radiation for life to exist. If it is too far from the center, then there are not enough heavy elements to create the molecules of life. The argument is that there might be so many Goldilocks zones, many of them not even discovered yet, that there might be only one planet in the universe with intelligent life. Each time there is another Goldilocks zone, it vastly decreases the probability of life. With so many of these zones, the collective probability of intelligent life is nearly zero.
Also, it is sometimes said that extraterrestrial life may be based on entirely new laws of chemistry and physics that are far beyond anything we can create in the laboratory. Hence, our understanding of nature is simply too narrow and simplistic to explain life in outer space. This may be true. And it is certainly true that entirely new surprises will be found once we explore the universe. However, it does not further the debate to simply state that alien chemistry and physics might exist. Science is based on theories that are testable, reproducible, and falsifiable, so simply postulating the existence of unknown laws of chemistry and physics does not help.
CHAPTER 13: ADVANCED CIVILIZATIONS
The tabloid headlines blared: See David Freeman, “Are Space Aliens Behind the ‘Most Mysterious Star in the Universe’?” Huffington Post, August 25, 2016; www.huffingtonpost.com/entry/are-space-aliens-behind-the-most-mysterious-star-in-the-universe_us_57bb5537e4b00d9c3a1942f1. See also Sarah Kaplan, “The Weirdest Star in the Sky Is Acting Up Again,” Washington Post, May 24, 2017; www.washingtonpost.com/news/speaking-of-science/wp/2017/05/24/the-weirdest-star-in-the-sky-is-acting-up-again/?utm_term=.5301cac2152a.
“We’d never seen anything like this star”: Ross Anderson, “The Most Mysterious Star in Our Galaxy,” The Atlantic, October 13, 2015; www.theatlantic.com/science/archive/2015/10/the-most-interesting-star-in-our-galaxy/41023.
This classification of advanced civilizations was first proposed: N. Kardashev, “Transmission of Information by Extraterrestrial Civilizations,” Soviet Astronomy 8, 1964: 217.
“The premise is that any highly advanced civilization”: Chris Impey, Beyond: Our Future in Space (New York: W. W. Norton, 2016), pp. 255–56.
“Logic tells me that it is reasonable to look for godlike signs”: David Grinspoon, Lonely Planets (New York: HarperCollins, 2003), p. 333.
The LHC has made many headlines: It is sometimes said that creating giant accelerators, like the LHC and beyond, will create a black hole that might destroy the entire planet. This is impossible for several reasons:
First, the LHC cannot create enough energy to create a black hole, which requires energies comparable to those of a giant star. The energy of the LHC is that of subatomic particles, much too small to open a hole in space-time. Second, Mother Nature bombards the Earth with subatomic particles more powerful than those created by the LHC, and the Earth is still here. So subatomic particles with energies greater than the LHC are harmless. And lastly, string theory predicts that there might be mini black holes that one day might be found with our accelerators, but these mini black holes are subatomic particles, not stars, and hence pose no danger at all.
Currently the only one capable of doing this: If we naïvely try to join the quantum theory with general relativity, we find mathematical inconsistencies that have stumped physicists for almost a century. For example, if we calculate the scattering of two gravitons (particles of gravity), we find that the resulting answer is infinite, which is meaningless. Hence, the fundamental problem facing theoretical physics is to unify gravity with the quantum theory in a way that gives finite answers.
At present, the only way known to eliminate these troublesome infinities is to use superstring theory. This theory has a powerful set of symmetries in which the infinities cancel each other out. This is because in string theory every particle has a partner, called a “sparticle.” The infinities coming from ordinary particles cancel precisely against the infinities coming from the sparticles, and hence the entire theory is finite. String theory is the only theory in physics that selects out its own dimensionality. This is because the theory is symmetric under supersymmetry. In general, all particles of the universe come in two types, bosons (which have integer spins) and fermions (which have half-integer spins). As the number of dimensions of space-time increases, the number of these fermions and bosons also increases. In general, the number of fermions rises much faster than the number of bosons. The two curves cross, however, at ten dimensions (for strings) and eleven dimensions (for membranes, like spheres and bubbles). Hence the only consistent supersymmetric theory is found in ten and eleven dimensions.
If we set the dimension of space-time at ten, then we have a consistent theory of strings. However, there are five different types of string theories in ten dimensions. For a physicist, searching for the ultimate theory of space and time, it is hard to believe that there should be five different self-consistent string theories. Ultimately, we want just one. (One of the guiding questions asked by Einstein was, Did God have a choice in making the universe? That is, Is the universe unique?)
Later, it was shown by Edward Witten that these five string theories can be unified into a single, unique theory if we add one more dimension, making it eleven-dimensional. This theory was called M-theory, and it contains membranes as well as strings. If we start with a membrane in eleven dimensions, and then we reduce one of these eleven dimensions (by flattening it, or slicing it), then we find that there are five ways in which a membrane can be reduced to a string, giving us the five known string theories. (For example, if we flatten a beach ball, leaving only the equator, then we have reduced an eleven-dimensional membrane down to a ten-dimensional string.) Unfortunately, the fundamental theory behind M-theory is totally unknown, even today. All we know is that M-theory reduces down to each of the five different string theories if we reduce eleven dimensions down to ten, and that, in the low-energy limit, M-theory reduces down to eleven-dimensional supergravity theory.
If you then kill your grandfather before you are born: Time travel poses yet another theoretical problem. If a photon, a particle of light, enters the wormhole and goes back in time a few years, then years later it can reach the present and reenter the wormhole once again. In fact it can reenter the wormhole an infinite number of times, and hence the time machine will explode. This is one of Stephen Hawking’s objections to time machines. However, there is a way to escape this problem. In the many-worlds theory of quantum mechanics, the universe constantly splits in half into parallel universes. Therefore, if time is constantly splitting, it means that the photon only goes back in time once. If it reenters the wormhole, it is simply entering a different parallel universe, and hence it only makes a single pass through the wormhole. In this way, the problem with infinities is solved. In fact, if we adopt the idea that the universe is constantly splitting into parallel realities, then all the paradoxes of time travel are solved. If you kill your grandfather before you are born, you have simply killed a grandfather in a parallel universe who resembles your grandfather. Your own grandfather in your universe was not killed at all.
CHAPTER 14: LEAVING THE UNIVERSE
In the fifth epoch, even black holes: Even black holes must eventually die. According to the uncertainty principle, everything is uncertain, even a black hole. A black hole is supposed to absorb 100 percent of all matter that falls into it, but this violates the uncertainty principle. Hence, there is actually a faint radiation that escapes from a black hole, called Hawking radiation. Hawking proved that it was actually a black body radiation (similar to the radiation emitted by a molten piece of metal) and therefore has a temperature associated with it. You can calculate that, over aeons, a black hole (which is actually gray) will emit enough radiation that it will no longer be stable. Then the black hole disappears in an explosion. So even black holes will eventually die.
If we assume that the Big Freeze takes place at some future time, we have to confront the fact that atomic matter as we know it might disintegrate trillions upon trillions of years from now. At present, the Standard Model of subatomic particles says that the proton should be stable. But if we generalize the model to try to unify the various atomic forces, we find that the proton may eventually decay into a positron and a neutrino. If this is true, then it means that matter (as we know it) is ultimately unstable and will decay into a mist of positrons, neutrinos, electrons, et cetera. Life probably cannot exist under these harsh conditions. According to the second law of thermodynamics, you can only extract usable work if there is difference in temperature. In the Big Freeze, however, temperatures drop to near absolute zero, so there is no more difference in temperature from which we can extract usable work. In other words, everything comes to a halt, even all possible life-forms.
What is causing this sudden change in our understanding: Dark energy is one of the greatest mysteries in all of physics. Einstein’s equations have two terms that are generally covariant. The first is the contracted curvature tensor, which measures the distortions in space-time caused by stars, dust, planets, et cetera. The second term is the volume of space-time. So even the vacuum has energy associated with it. The more the universe expands, the more vacuum there is and hence the more dark energy available to create even more expansion. In other words, the rate of expansion of the vacuum is proportional to the amount of vacuum there is. This, by definition, creates an exponential expansion of the universe, called de Sitter expansion (after the physicist who first identified it).
This de Sitter expansion may have given rise to the original inflation that initiated the Big Bang. But it is also causing the universe to expand exponentially once again. Unfortunately, physicists are at a loss to explain any of this from first principles. String theory comes closest to explaining dark energy, but the problem is that it cannot predict the precise amount of dark energy in the universe. String theory says that, depending on how you curl up ten-dimensional hyperspace, one can obtain different values for dark energy, but it does not predict precisely how much dark energy there is.
The final possibility is to create a wormhole: Assuming that wormholes are possible, there is still another hurdle to negotiate. One must be sure that matter is stable on the other side of the wormhole. For example, the reason why our universe is possible is because the proton is stable, or at least so stable that our universe has not collapsed down to a lower state in the 13.8 billion years of its existence. It is possible that the other universes in the multiverse may have a ground state in which, for example, the proton can decay to an even lower-mass particle, such as a positron. In this case, all the familiar chemical elements of the periodic table will decay, and this universe will consist of a mist of elections and neutrinos, unsuitable for stable atomic matter. So one must take care to enter a parallel universe in which matter is similar to ours and is stable.
All these speculations at first seem preposterous: A. Guth, “Eternal Inflation and Its Implications,” Journal of Physics A 40, no. 25 (2007): 6811.
Also, when we look in one direction: Inflationary theory answers several puzzling aspects of the Big Bang. First, our universe seems to be extremely flat, much flatter than usually proposed in the standard Big Bang theory. This can be explained by postulating that our universe had an expansion much faster than previously thought. A tiny portion of the original universe then inflated enormously and was flattened out in the process. Second, the theory explains why the universe is much more uniform than it should be. By looking in all directions in space, we see that the universe is quite uniform. But (because the speed of light is the ultimate velocity) there was not enough time for the original universe to mix thoroughly. This can be explained by assuming that a tiny piece of the original Big Bang was in fact uniform, but that uniform piece was inflated to give the uniform universe of today.
Beyond these two achievements, the inflationary universe theory so far agrees with all the data coming in from the cosmic microwave background. This does not mean that the theory is correct, only that it agrees with all the cosmological data so far. Time will tell if the theory is correct. One glaring problem with inflation is that no one knows what caused it. The theory works fine after the instant of inflation but says absolutely nothing about what caused the original universe to inflate.