CHAPTER 1. SACRED GEOMETRY
1. There's a chance they may have also been totally wasted. S. M. Russell, “Some Astronomical Records from Ancient Chinese Books (Continued),” Observatory 18 (1985): 355.
2. A good starting point for reading summaries and translated texts from this era is Anniina Jokinen, “Medieval Cosmology,” Luminarium, January 31, 2012, http://www.luminarium.org/encyclopedia/medievalcosmology.htm.
3. For a fun recounting of the spread of Copernicus's viral idea, see Owen Gingerich, The Book Nobody Read: Chasing the Revolutions of Nicolaus Copernicus (New York: Walker, 2004).
4. I'm serious. Ann Blair, “Tycho Brahe's Critique of Copernicus and the Copernican System,” Journal of the History of Ideas 51, no. 3 (1990): 355.
5. Kitty Ferguson, Tycho and Kepler: The Unlikely Partnership That Forever Changed Our Understanding of the Heavens (London: Transworld Digital, 2013), Kindle.
6. Ibid.
7. Indeed, Kepler seems like an eager fanboy writing to a reluctant Galileo. Anton Postl, “Correspondence between Kepler and Galileo,” Vistas in Astronomy 21, no. 4 (1977): 325.
8. Of course I'm paraphrasing, because Kepler goes on and on about this stuff. For example, see a translation of a letter in Edwin Arthur Burtt, The Metaphysical Foundations of Modern Physical Science (Garden City, NY: Doubleday, 1954), p. 48.
9. Go ahead and give yourself a blast of a time by reading the whole hog: Johannes Kepler, Astronomia Nova, trans. William H. Donahue (Santa Fe, NM: Green Lion, 2015).
10. Gotta love the guy. Johannes Kepler, Harmonices Mundi, trans. Charles Glenn Wallis (Chicago: Encyclopædia Britannica, 1952).
11. These are available online today through the library of the University of Kiel in Germany: https://www.ub.uni-kiel.de/digiport/bis1800/Arch3_436.html.
12. A. Athreya and O. Gingerich, “An Analysis of Kepler's Rudolphine Tables and Implications for the Reception of His Physical Astronomy,” Bulletin of the American Astronomical Society 28 (1996): 1305.
13. Actually lots of books, and naturally, every author has his or her own agenda. For just an entry point into this saga, try Jerome Langford, Galileo, Science, and the Church (Ann Arbor: University of Michigan Press, 1992).
14. Galileo Galilei, Sidereus Nuncius, trans. Alvert Van Helden (Chicago: University of Chicago Press, 1989).
15. I absolutely need to mention that Brahe had a certain flair for his book titles: hammering the point home, he announced these particular findings in Concerning the Star, new and never before seen in the life or memory of anyone.
CHAPTER 2. A BROKEN UNIVERSE
1. Sadly, Maxwell, as much as I'm a fan of his, doesn't get to appear in our story. Sorry, buddy, you'll have to settle for a note: James Clerk Maxwell, “A Dynamical Theory of the Electromagnetic Field,” Philosophical Transactions of the Royal Society of London 155 (1865): 459.
2. Once again, I could list a few dozen books on the twisting and complicated paths to understanding the earliest moments of the universe. Many of them are, to put it as gently as possible, highly speculative and borderline philosophical. Not that there's anything wrong with philosophers, but physicists usually make for poor ones, and I urge you to keep a large bowl of salt handy when reading anything on this subject. That said, the study of the newborn universe is simultaneously an examination of fundamental physics, which I'm going to explain in a bit.
3. No matter how you pronounce his name, he's a pretty cool dude. Max Planck, “Über das Gesetz der Energieverteilung im Normalspectrum,” Annalen der Physik 309, no. 3 (1901): 553.
4. Told you so. For a good review of leading (not necessarily viable) solutions, check out Lee Smolin, Three Roads to Quantum Gravity (New York: Basic Books, 2017).
5. That's not much more informative, but GeV is a measure of energy: the amount required to accelerate one electron across a potential difference of one volt. In other words, how much you're going to sweat after making an electron do something it doesn't want to do. It seems arbitrary, but when your job is to make electrons do things they don't want to do—like slam together in a particle collider—it starts to make more sense. A weakly thrown baseball has a few trillion electron volts of energy due to its mass; a thin beam of charged subatomic particles with the same energy can and will punch a hole straight through you, so don't even think you can catch it. Trust me; they put up warning signs and everything.
6. Peter Higgs, “Broken Symmetries and the Masses of Gauge Bosons,” Physical Review Letters 13, no. 16 (1964): 508.
7. For an entertaining deep dive, it doesn't get much better than Richard P. Feynman, Robert B. Leighton, and Matthew Sands, The Feynman Lectures on Physics, vol. 2, The New Millennium Edition: Mainly Electromagnetism and Matter (New York: Basic Books, 2011), chap. 34.
8. Alan H. Guth, “Inflationary Universe: A Possible Solution to the Horizon and Flatness Problems,” Physical Review D 23, no. 2 (1981): 347.
CHAPTER 3. TALES FROM A BEWILDERING SKY
1. As recounted in Willian Stukeley, Memoirs of Sir Isaac Newton's Life, transcript, 1752, taken from University of Pennsylvania Online Books, http://onlinebooks.library.upenn.edu/webbin/book/lookupid?key=olbp49182 (accessed October 17, 2017).
2. You can get a copy of Newton's great Philosophiae Naturalis Principia Mathematica online, but if you want to hold some genius in your hands, then I suggest Isaac Newton, The Principia: Mathematical Principles of Natural Philosophy (Austin, TX: Snowball Publishing, 2010).
3. And you know you are. Edmund Halley, “Some Account of the Ancient State of the City of Palmyra, with Short Remarks upon the Inscriptions Found There,” Philosophical Transactions 19 (1695): 160.
4. And if you've ever seen a map of how an eclipse can be viewed, you can pretty much thank him. Jay M. Pasachoff, “Halley and His Maps of the Total Eclipses of 1715 and 1724,” Journal of Astronomical History and Heritage 2 (1999): 39.
5. Halley, “Some Account.”
6. Naturally it wasn't that simple—he initially thought it was a comet. William Herschel and Dr. Watson, “Account of a Comet, by Mr. Herschel, F. R. S.; Communicated by Dr. Watson, Jun. of Bath, F. R. S,” Philosophical Transactions of the Royal Society of London, 71 (1781): 492.
7. For a history of its publication and additions, as well as links to some pretty pictures, visit: “Charles Messier's Catalog of Nebulae and Star Clusters,” Messier Catalog, last modified August 12, 2011, http://www.messier.seds.org/xtra/history/m-cat.html (accessed November 15, 2017).
8. This tale and more about Galileo's perplexity are recounted in David Whitehouse, Renaissance Genius: Galileo Galilei and His Legacy to Modern Science (New York: Sterling, 2009), p. 100.
9. Also of note is that this book contains one of the most powerful explanations for why we do science, in this case applied to the problem of Saturn's rings: “When we have actually seen that great arch swung over the equator of the planet without any visible connection, we cannot bring our minds to rest.” James Clerk Maxwell, On the Stability of the Motion of Saturn's Rings (Cambridge: Macmillan, 1859), p. 1.
10. I mean, come on, dude, really? Auguste Comte, The Positive Philosophy of Auguste Comte: Freely Translated and Condensed by Harriet Martineau, book 2, Astronomy, C. I: General View (Cornell, NY: Cornell University Library, 1896).
11. Edward Harrison, Darkness at Night: A Riddle of the Universe (Cambridge, MA: Harvard University Press, 1989).
12. Ann Blair, “Tycho Brahe's Critique of Copernicus and the Copernican System,” Journal of the History of Ideas 51, no. 3 (1990): 355.
CHAPTER 4. THE DEATH OF ANTIMATTER
1. P. A. M. Dirac, “The Quantum Theory of the Electron,” Proceedings of the Royal Society A 117, no. 778 (1928): 610.
2. Go ahead, take a crack at it. I'll wait. Erwin Schrödinger, “An Undulatory Theory of the Mechanics of Atoms and Molecules,” Physical Review 28, no 6 (1926): 1049.
3. We get this constraint from detailed observations of the cosmic microwave background, which I haven't introduced yet, but feel free to get the scoop now. Planck Collaboration, “Planck 2015 Results. XIII. Cosmological Parameters,” Astronomy & Astrophysics 594 (2016): id.A13.
4. Michael S. Turner and David N. Schramm, “The Origin of Baryons in the Universe,” Nature 279 (1979): 303.
5. Don't say I didn't warn you. A. Karel Velan, “Quantum Chromodynamics, the Strong Nuclear Force” in The Multi-Universe Cosmos (Boston: Springer, 1992).
6. I'll leave that to David Griffiths, Introduction to Elementary Particles (New York: Wiley, 2008).
7. Edward Kolb and Stephen Wolfram, “Baryon Number Generation in the Early Universe,” Nuclear Physics B 172 (1980): 224.
8. Which is a shame, because neutrinos don't get a lot of airtime. Try this out if you do want to follow that lead: Ray Jayawardhana, Neutrino Hunters: The Thrilling Chase for a Ghostly Particle to Unlock the Secrets of the Universe (New York: Scientific American, 2013).
9. Speaking of random papers, here's the one that really kicked this idea off: Ralph Alpher, Hans Bethe, and George Gamow, “The Origin of Chemical Elements,” Physical Review 73 (1948): 803.
CHAPTER 5. BEYOND THE HORIZON
1. The light-year is used as a way to easily communicate to the public the large distances to the star he had just confidently measured. Thanks, dude! Fredrich Bessel, “On the Parallax of the Star 61 Cygni,” London and Edinburgh Philosophical Magazine and Journal of Science 16 (1839): 68.
2. Henrietta S. Leavitt and Edward C. Pickering, “Periods of 25 Variable Stars in the Small Magellanic Cloud,” Harvard College Observatory Circular 173 (1912): 1.
3. A great resource for the origins of the debate, papers published summarizing the debate itself, and—the juicy bits—reactions by the attendees is “The Shapley—Curtis Debate in 1920,” NASA Astronomy Picture of the Day, https://apod.nasa.gov/diamond_jubilee/debate_1920.html (accessed December 2, 2017).
4. Edwin Hubble, “Cepheids in Spiral Nebulae,” Publications of the American Astronomical Society 5 (1925): 261.
5. Seriously, the dude was a pretty snappy writer. Edwin Hubble, “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae,” Proceedings of the National Academy of Science 15, no. 3 (1925): 16.
6. Fritz Zwicky, “On the Red Shift of Spectral Lines through Interstellar Space,” Proceedings of the National Academy of Sciences 15, no. 10 (1929): 773.
7. If you want to see how long someone can make it, I invite you to read Charles Misner, Kip Thorne, and John Archibald Wheeler, Gravitation (New York: W. H. Freeman, 1973), a.k.a. “The Grad Student's Bane.”
8. From the man himself: “Space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.” Hermann Minkowski, “Space and Time,” in Hendrik A. Lorentz, Albert Einstein, Hermann Minkowski, and Hermann Weyl, The Principle of Relativity: A Collection of Original Memoirs on the Special and General Theory of Relativity (New York: Dover, 1952), pp. 75–91.
9. Albert Einstein, “Kosmologische Betrachtungen zur allgemeinen Relativitatstheorie,” Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften Berlin (1917): 1: 142.
10. Ibid.
CHAPTER 6. BATHED IN RADIANCE
1. Simon Mitton, Fred Hoyle: A Life in Science (Cambridge: Cambridge University Press, 2011), p. 129.
2. For an accessible summary of the problems with tired light, plus links to the research papers, check out Edward L. Wright, “Errors in Tired Light Cosmology,” UCLA Division of Astronomy and Astrophysics, April 24, 2008, http://www.astro.ucla.edu/~wright/tiredlit.htm (accessed October 4, 2017).
3. The steady party got started with Hermann Bondi and Thomas Gold, “The Steady-State Theory of the Expanding Universe,” Monthly Notices of the Royal Astronomical Society 108 (1948): 252.
4. Robert Dicke et al., “Cosmic Black-Body Radiation,” Astrophysical Journal 142 (1965): 414.
5. Arno Penzias and Robert Wilson, “A Measurement of Excess Antenna Temperature at 4080 Mc/s,” Astrophysical Journal 142 (1965): 419.
CHAPTER 7. REAPING THE QUANTUM WHIRLWIND
1. Told you we would come back to him. Max Planck, “Über das Gesetz der Energieverteilung im Normalspectrum,” Annalen der Physik 309 (1901): 553.
2. Albert Einstein, “Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt,” Annalen der Physik 17, no. 6 (1905): 132.
3. Like his (in)famous delta function, as introduced in Paul Dirac, The Principles of Quantum Mechanics, 4th ed. (Oxford: Clarendon, 1958).
4. The term “quark” itself came from Murray Gell-Mann basically looking around for a weird and cool name for his recently unearthed theoretical construct. The individual monikers came later as physicists just made up stuff from the top of their heads. Murray Gell-Mann, The Quark and the Jaguar: Adventures in the Simple and the Complex (New York: Henry Holt, 1995), p. 180.
INTERLUDE: A GUIDE TO LIVING IN AN EXPANDING UNIVERSE
1. It only took the heroic efforts of hundreds of scientists and engineers, a lot of money, fancy satellite missions, and independent measurements. You know, science stuff. Planck Collaboration, “Planck 2015 Results. XIII. Cosmological Parameters,” Astronomy & Astrophysics 594 (2016): id.A13.
CHAPTER 8. BEHOLD THE COSMIC DAWN
1. Starting with Tom Kibble, “Topology of Cosmic Domains and Strings,” Journal of Physics A: Mathematical and General 9, no. 8 (1976): 1387.
2. So many constraints, so little time. Thanks to Planck Collaboration, “Planck 2013 Results. XXV. Searches for Cosmic Strings and Other Topological Defects,” Astronomy & Astrophysics 571 (2014): id.A25.
3. Seriously, this is one of the weirdest and most fascinating manifestations of quantum theory: the empty vacuum of space itself influencing motion. Hendrik Casimir, “On the Attraction between Two Perfectly Conducting Plates,” Proceedings of the Royal Netherlands Academy of Arts and Sciences 51 (1948): 793.
4. Most notably with the COBE (Cosmic Background Explorer) mission. One of its leaders, George Smoot, went on to win a Nobel for his efforts and wrote a nice book recounting the adventures. George Smoot and Keay Davidson, Wrinkles in Time (New York: W. Morrow, 1993).
5. Listen, I'm not just plugging the Planck mission because I played a minor role in the data analysis efforts. It seriously is perhaps the most detailed and exacting astronomical measurement ever taken.
6. To get your feet wet, try Brian O'Shea et al., “First Stars III Conference Summary” (Santa Fe, NM: Proceedings of First Stars III, July 2007).
7. It depends on how much you trust your simulation (the answer is almost always “about as much as I can simulate throwing it”) and how much we understand the physics of this era. At the “small” end, we expect masses forty times that of the sun. So still pretty big, but, you know, not as big. Hosokawa Takashi et al., “Protostellar Feedback Halts the Growth of the First Stars in the Universe,” Science 334 (2011): 1250.
8. Wellllll, maybe. But close enough for our purposes. Abraham Loeb and Steven Furlanetto, The First Galaxies in the Universe (Princeton, NJ: Princeton University Press 2013), p. 213.
9. There are even curious relationships between black hole mass and properties of their host galaxies, implying symbiotic coevolution. Kayhan Gultenkin et al., “The M-σ and M-L Relations in Galactic Bulges, and Determinations of Their Intrinsic Scatter,” Astrophysical Journal 698 (2009): 198.
10. Jonathan Gardner et al., “The James Webb Space Telescope,” Space Science Review 123 (2006): 485.
11. An example of just one such mission is David DeBoer, “Hydrogen Epoch of Reionization Array (HERA),” Publications of the Astronomical Society of the Pacific 129, no. 974 (2017): 045001.
CHAPTER 9. OF MATTERS DARK AND COLD
1. Fritz Zwicky, “On the Masses of Nebulae and of Clusters of Nebulae,” Astrophysical Journal 86 (1937): 217.
2. Vera Rubin and Kent Ford Jr., “Rotation of the Andromeda Nebula from a Spectroscopic Survey of Emission Regions,” Astrophysical Journal 159 (1970): 379.
3. Albert Einstein, “Erklärung der Perihelbewegung des Merkur aus der allgemeinen Relativitätstheorie,” Königlich Preussische Akademie der Wissenschaften (1915): 831.
4. The full story is recounted in Tom Standage, The Neptune File: A Story of Astronomical Rivalry and the Pioneers of Planet Hunting (London: Walker, 2000).
5. With gedankenexperiment (“thought experiment”) the obvious rival.
6. Mordehai Milgrom, “MOND Theory,” Canadian Journal of Physics 92 (2015): 107.
7. Constantinos Skordis, “Topical Review: The Tensor-Vector-Scalar Theory and Its Cosmology,” Classical and Quantum Gravity 26 (2009): 143001.
8. Douglas Clowe et al., “A Direct Empirical Proof of the Existence of Dark Matter,” Astrophysical Journal 648 (2006): L109.
9. It's that good old-fashioned big bang nucleosynthesis: Ralph Alpher, Hans Bethe, and George Gamow, “The Origin of Chemical Elements,” Physical Review 73 (1948): 803.
10. George Blumenthal et al., “Formation of Galaxies and Large-Scale Structure with Cold Dark Matter,” Nature 311 (1984): 517.
11. Gerard Jungman et al., “Supersymmetric Dark Matter,” Physics Reports 267 (1996): 195.
12. David Weinberg et al., “Cold Dark Matter: Controversies on Small Scales,” Proceedings of the National Academy of Sciences 112 (2015): 12249.
CHAPTER 10. THE COSMIC WEB
1. For a while, astronomers thought that clusters were the biggest thing and were more or less scattered around the universe randomly, much as we used to think stars filled the universe. But deeper surveys revealed the beginnings of what we now call superclusters, and what really kicked things off was the discovery of the great voids—vast regions of no clusters at all. It was that discovery that led astronomers to think that something big was afoot. Stephen Gregory and Laird Thompson, “The Coma/A1367 Supercluster and Its Environs,” Astrophysical Journal (1978): 784.
2. Margaret Geller and John Huchra, “Mapping the Universe,” Science 246 (1989): 897.
3. It's easiest to see this in simulations, where we can probe finer structures without having to deal with temperamental telescopes, as in Miguel Aragon-Calvo and Alexander Szalay, “The Hierarchical Structure and Dynamics of Voids,” Monthly Notices of the Royal Astronomical Society 428 (2013): 3409.
4. And it still continues to be tested today. Here's a random paper on the subject, pulled out of a hat: Rodrigo de Sousa Goncalves et al., “Cosmic Homogeneity: A Spectroscopic and Model-Independent Measurement,” Monthly Notices of the Royal Astronomical Society 475 (2018). Available online at https://arxiv.org/abs/1710.02496 (accessed July 13, 2018).
5. There is even an entire galaxy survey devoted to measuring this: “BOSS: Dark Energy and the Geometry of Space,” SDSS III, 2013, http://www.sdss3.org/surveys/boss.php (accessed December 12, 2017).
6. This “bottom-up” way of building the universe is in contrast to a “top-down” style, where giant blobs of gas fragment into ever-smaller lumps that we end up calling galaxies.
7. Brent Tully et al., “The Laniakea Supercluster of Galaxies,” Nature 513 (2014): 71.
CHAPTER 11. THE RISE OF DARK ENERGY
1. The machinery you need to use a particular set of solutions to general relativity first derived from the mustachioed Alexander Friedmann, “Über die Krümmung des Raumes,” Zeitschrift für Physik 10 (1922): 377.
2. And for the three-peat, Planck Collaboration, “Planck 2015 Results. XIII. Cosmological Parameters,” Astronomy & Astrophysics 594 (2016): id.A13.
3. And that number hasn't budged much in the decades we've been measuring it. For example, here's another random paper measuring it: Rachel Mandelbaum et al., “Cosmological Parameter Constraints from Galaxy-Galaxy Lensing and Galaxy Clustering with the SDSS DR7,” Monthly Notices of the Royal Astronomical Society 432 (2013): 1544.
4. Walter Baade and Fritz Zwicky, “On Super-Novae,” Proceedings of the National Academy of Sciences 20 (1934): 254.
5. OK, maybe a lot of finagling. The methods are far from perfect and introduce their own source of uncertainty, as evidenced when, for example, it was applied to a mere seven supernova and produced a very inaccurate result. Saul Perlmutter et al., “Measurements of the Cosmological Parameters Ω and Λ from the First Seven Supernovae at z > = 0.35,” Astrophysical Journal 483 (1997): 565.
6. I present you the two towers of dark energy: Adam Riess et al., “Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant,” Astrophysical Journal 116 (1998): 1009; Saul Perlmutter et al., “Measurements of Ω and Λ from 42 High-Redshift Supernovae,” Astrophysical Journal 517 (1999): 565.
7. Dragan Huterer and Daniel Shafer, “Dark Energy Two Decades After: Observables, Probes, Consistency Tests,” Reports on Progress in Physics 81 (2018): 016901.
8. David Weinberg et al., “Observational Probes of Cosmic Acceleration,” Physics Reports 530 (2013): 87.
CHAPTER 12. THE STELLIFEROUS ERA
1. David Devorkin, “The Origins of the Hertzsprung-Russell Diagram,” Proceedings of the International Astronomical Union, no. 80 (1977): 61.
2. Joe D. Burchfield, Lord Kelvin and the Age of the Earth (Chicago: University of Chicago Press, 1990), pp. 57–80.
3. Frank Dyson, A. S. Eddington, and C. R. Davidson, “A Determination of the Deflection of Light by the Sun's Gravitational Field, from Observations Made at the Solar Eclipse of May 29, 1919,” Philosophical Transactions of the Royal Society A220 (1920): 571.
4. Jeanne R. Wilson, “An Experimental Review of Solar Neutrinos,” Prospects in Neutrino Physics Conference Proceedings (April 16, 2015).
5. Edwin Hubble, “Extra-Galactic Nebulae,” Astrophysical Journal 64 (1936): 321.
6. We'll leave that for scientists like these folks: Mark Vogelsberger et al., “Properties of Galaxies Reproduced by a Hydrodynamic Simulation,” Nature 509 (2014): 177.
CHAPTER 13. THE FALL OF LIGHT
1. Piero Madau and Mark Dickinson, “Cosmic Star-Formation History,” Annual Review of Astronomy and Astrophysics 52 (2014): 415.
2. Jacques Laskar, “Large-Scale Chaos in the Solar System,” Astronomy & Astrophysics 287 (1994): L9.
3. As you might imagine, there isn't exactly a lot of research on the long-term fate of stars and galaxies, if for no other reason than the simple fact that there aren't going to be any observations—at least for a while—to test any hypotheses. Thus the following reference is the go-to standard for most of this story, and in the decades since its publication, there haven't been any major complaints or corrections, except that the authors didn't know that we live in a universe full of dark energy, which does modify the story. Fred Adams and Gregory Laughlin, “A Dying Universe: The Long-Term Fate and Evolution of Astrophysical Objects,” Reviews of Modern Physics 69 (1997): 337.
4. This phenomenon was first figured out by the supremely talented Subramanian Chandrasekhar, “The Maximum Mass of Ideal White Dwarfs,” Astrophysical Journal 75 (1931): 81.
5. Naturally, black holes have a long and storied history worth retelling in another book. Their origins, however, are quite mundane: they appear in one of the simplest solutions of general relativity: Karl Schwarzschild, “Über das Gravitationsfeld eines Massenpunktes nach der Einsteinschen Theorie,” Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften 7 (1916): 189.
CHAPTER 14. THE LONG WINTER
1. There's continuing and ever-evolving research on this topic, but a solid review can be found in Antonio Riotto, “Theories of Baryogenesis,” (lecture; Summer School in High Energy Physics and Cosmology, Trieste, Italy, June 29–July 17, 1998 [1999]).
2. Sigh, here we go. The usual story is that a particle-antiparticle pair appears in the vacuum of space near an event horizon, with one on the wrong side of the line. It's consumed by the black hole while its partner runs off scot free. This is a “bonus” particle given to the universe, so the energy has to come from somewhere—hence, the black hole loses mass. While this isn't a technically wrong story, I don't think it really represents the underlying mathematics, which is more about the relationship between quantum fields (remember those?) and the sapping of energy from a forming black hole, which leads to its eventual dissolution down the road. But whatever, don't take my word for it. Just read Hawking's original paper on it: Stephen Hawking, “Black Hole Explosions?,” Nature 248 (1974): 30.
3. And the award for most clever article title in these notes goes to Don Page and M. Randall McKee, “Eternity Matters,” Nature 291 (1980): 44.
4. Wendy Freedman, “Correction: Cosmology at a Crossroads,” Nature Astronomy 1 (2017): id. 0169.
5. Alexander Bednyakov et al., “Stability of the Electroweak Vacuum: Gauge Independence and Advanced Precision,” Physics Review Letters 115 (2015): 201802.
6. If you want to go down this particular rabbit hole, you're going to have to follow Max Tegmark, “The Multiverse Hierarchy,” in Universe or Multiverse?, ed. B. Carr (Cambridge: Cambridge University Press, 2007).
EPILOGUE: A GAME OF CHANCE
1. It's the Karman Line, a nice round number close enough to the height where the atmosphere is so thin that normal airplane physics doesn't work so well anymore. Dennis Jenkins, “Schneider Walks the Walk; Extra Feature: A Word about the Definition of Space,” NASA, October 21, 2005, https://www.nasa.gov/centers/dryden/news/X-Press/stories/2005/102105_Schneider.html.
2. You know, plus or minus a few hundred billion. Takahiro Sumi et al., “Upper Bound of Distant Planetary Mass Population Detected by Gravitational Microlensing,” Nature 473 (2011): 349.
3. Rachel Brazi, “Hydrothermal Vents and the Origins of Life,” Chemistry World, April 16, 2017, https://www.chemistryworld.com/feature/hydrothermal-vents-and-the-origins-of-life/3007088.article.
4. Dimitra Atri and Adrian Melott, “Cosmic Rays and Terrestrial Life: A Brief Review,” Astroparticle Physics 53 (2014): 186.
5. Seth Shostak, “Fermi Paradox,” SETI Institute, April 19, 2018, https://www.seti.org/seti-institute/project/fermi-paradox (accessed December 8, 2017).
6. Before you jump on me, I should say that of course interstellar travel is possible. Objects travel from system to system in our galaxy all the time, and we humans have even hurled a few chunks of metal out into the interstellar wastelands. But what we usually mean by “travel”—the same way we might travel by train or plane to another city—is so far beyond the energy generation capabilities of our civilization, and projections of said capabilities into the far, far, far future, that we might as well discount it as a feasible process for all intents and purposes. And it may never be feasible, even if we could harness unimaginable amounts of energy. In short: you're not going to another star, and neither are your kids’ kids’ kids’ kids’ kids’ kids. You can probably safely add a few more generations onto that last sentence. Space is big; don't mess with it.
7. Emily Petroff, “Identifying the Source of Perytons at the Parkes Radio Telescope,” Monthly Notices of the Royal Astronomical Society 451 (2015): 3933.
8. “The Drake Equation Revisited,” Astrobiology Magazine, September 29, 2003, https://www.astrobio.net/alien-life/the-drake-equation-revisited-part-i/.