Archive of Our Own

2) "The sun stood still in the sky at Joshua's command"

• Joshua was a leader of the ancient Israelites. When the Israelites were at war with the Amorites, Joshua commanded the sun and moon to stay in place, in order to give the Israelites more time to win a decisive battle.

3) "Elijah flew across the sky"

• Elijah was a major Old Testament prophet, and one of the few biblical figures who never died. Rather, Elijah was (without any warning) taken to heaven by a chariot pulled by horses made of fire (for good measure, the chariot itself was also made of fire).

4) "The characters in the painting are two-dimensional beings"

• Dustin’s explanation is a loose paraphrase of a thought experiment that first appeared in Flatland, an 1884 novel by Edwin Abbott Abbott.

5) "The LORD brought us out of Egypt"

• This is from a Deuteronomy, which describes the ancient Israelites’ escape from Egypt. This event - better known as the Exodus - was accompanied by a string of miracles, including God cursing the Egyptians with a series of plagues and (later on) the parting of the Red Sea by Moses

Chapter 2 - All That Is Solid

6) "It's called emergentism"

• The branch of philosophy concerned with the nature of the human mind is called philosophy of mind, and the branch concerned with the nature of human agency is sometimes called philosophy of action. That’s what Will studies.
• One of the major questions in this area of philosophy is whether the existence of free will is compatible with determinism. Determinism is the idea that the universe is composed solely of physical matter, and that everything is caused by matter interacting with matter in a (more or less) predictable way.
• If you believe that free will exists and determinism is true, you’re a compatibilist.
• If you believe that free will exists and determinism is false, you’re a libertarian (which doesn’t have anything to do with political libertarianism).
• If you believe that free will doesn’t exist and determinism is true, you’re a determinist.
• If you believe that free will doesn’t exist and determinism is false, you’re an indeterminist.
• Libertarians usually end up arguing that there’s a non-material substance called “mind”, which functions sort of like a soul. This position is typically called substance dualism (because there are two fundamental “substances”, matter and mind). It’s possible to be a dualist without being religious or believing in an eternal soul.
• Emergentism is an alternative libertarian argument. It’s the idea that the human mind emerges from matter, but isn’t thereafter determined by material processes (including those happening in the brain). More generally, an “emergent property” is a property of a complex system that none of the system’s component parts possess
• What Will is saying is that he’s a libertarian who leans towards dualism, but is exploring emergentism because it sounds less “magical.”

7) "All that is solid melts into air"

• This is from The Communist Manifesto, by Karl Marx and Friedrich Engels. The full quote is: “All that is solid melts into air, all that is holy is profaned, and man is at last compelled to face with sober senses his real conditions of life, and his relations with his kind.” As Will acknowledges, the actual meaning of the quote isn’t relevant in the context of the story, but it’s supposed to express the idea that economic conditions are all that matter, and everything else is a distraction.

8) "Will is the Pale Rider"

• The Pale Rider is Death, one of the Four Horsemen of the Apocalypse. Will and Mike have a whole conversation about the Four Horsemen in Chapter 7. Somewhat confusingly, “pale” refers to the colour of the horse, not the colour of the rider.

9) "He is Joshua at the Walls of Jericho" 

• The Israelite leader Joshua (the same one who ordered the sun to stop moving) was trying to conquer the walled city of Jericho. He marched around it once a day for six days, and then seven times on the seventh day. Then, he blew a horn, and the city’s legendary walls collapsed all at once.

Chapter 3 - Apokatastasis

10) Title

• In Christianity, “apokatastasis” is a Greek term for universal salvation (the idea that everyone and everything will eventually be restored to God and go to heaven). The idea is controversial, but it’s been around since the early days of Christianity, and many influential Christian thinkers have endorsed either it or something like it.

11) "God literally turned himself into a human" 

• You’re seeing Christianity through the eyes of someone who’s not that familiar with it, and Will’s descriptions of Christian beliefs tend to gloss over some of the nuances. What he says here is accurate enough.

12) "Let himself get tortured to death" 

• All Christians believe that Jesus’ death and resurrection were necessary to make salvation possible, although there’s never been any consensus as to why. There are three or four well established theories.

13) "Just so everyone would have a chance to get to heaven" 

• This is something on which Catholics and Protestants have historically disagreed. Protestants have traditionally believed that God alone decides who gets saved and who doesn’t. This is called predestination, and Catholics reject it.

14) "In the Bible or anything" 

• If you read the note at the end of the epilogue, you know what “apocryphal” means. Here, Will is describing a story from the Book of Bartholomew, an apocryphal text. The part about Jesus descending into hell in between his death and resurrection isn’t apocryphal; that’s core Christian belief (it’s called the Harrowing of Hell). The part that’s apocryphal is the part about Jesus saving all but three people. Will mentions two of the three: Cain (from the Cain and Abel story) and Herod the Great (Will doesn’t mention him by name, but he gets the story right). The third was Judas Iscariot, who betrayed Jesus to the Roman authorities.

15) "The vagueness people can defend themselves" 

• This is an actual area of study in contemporary philosophy, and Mike’s example illustrates the basic problem (or part of it, anyway) reasonably well. There’s a point at which someone isn’t bald, and then a point at which they are, but there’s no obvious, specific point at which someone becomes bald. You can do this with other things, too. How tall does someone have to be before they’re “tall”? Is someone who’s in the process of using a revolving door inside the building, or outside of it? And so on.

Chapter 4 - Depressed German Philosophers

16) "Devouring the DSM-IV" 

• The DSM is the Diagnostic and Statistical Manual of Mental Disorders, which is published by the American Psychiatric Association and seeks to formally define (and identify the criteria for diagnosing) mental illnesses. The DSM-IV is the fourth edition, which was published in 1994. The fifth and current edition (the DSM-5) was published in 2013. The DSM has always been controversial (it listed homosexuality as a mental illness until 1973) and isn’t universally accepted, but it carries significant weight.

17) "And behold a great red dragon" 

• This is from the Book of Revelation, and the dragon in question is generally identified with Lucifer. This verse appears shortly before the description of the “war in heaven”, which comes up later on.
• There are many English translations of the Bible. For most quotations, I used the New Revised Standard Version, which is the translation that Will would be familiar with (because it’s used by the Catholic Church). This quotation, however, is from the King James Version, which is the oldest and most culturally significant English translation. The language is older (it’s from 1611) and tends to be more dramatic, so I used it here. Artistic licence.

18) "Norton Shakespeare" 

• The Norton Shakespeare is one of the leading academic collections of Shakespeare's complete works. It’s also quite expensive.

19) "To count as evidence of free will" 

• Will is alluding to something called the hard problem of consciousness, which is basically: “Where does subjective experience come from?” If you’re a determinist, or if you believe that the universe is composed solely of physical matter, it can be quite hard to explain why we all have the experience of making choices, forming memories, and so on. Some determinists end up arguing that the whole experience of “selfhood” is just an illusion generated by the brain. That’s what Will is criticizing here.

20) "They're obsessed with how genitals work"

• The idea is that everything has a natural “purpose” or “function” that can be inferred from how it appears in nature. The basic ethical framework is called natural law, or sometimes teleological ethics. The argument here is that genitals and sex are intended for procreation, and it’s morally wrong to use them for any other purpose. That rules out gay sex, but it also rules any kind of sex - including the heterosexual kind - that isn’t at least theoretically open to procreation (so, no birth control either).
• Proponents of this position aren’t necessarily religious, although it is the official position of the Catholic Church (Protestants tend to have other reasons for disapproving of gay sex). In any case, it’s regarded as a serious philosophical argument, and Will would know that. He’s just being dismissive because he sees the whole thing as silly (as do I).

21) "Depressed German philosopher" 

• The quote is (allegedly) from Ludwig Wittgenstein, a twentieth-century philosopher. We’re not 100% certain the quote is authentic, and, in any event, it’s not related to his work in any significant way.

Chapter 5 - Blinding Lights; Bleeding Stars

22) "Mind-body problem"

• This is related to the hard problem of consciousness, although it’s a bit broader. Essentially, it asks: “What is the mind, what is the body, and how do they interact?” One answer is that the mind doesn’t really exist, and subjective experience is an illusion. Another is that “mind” is a distinct, non-material thing that directs the body through mysterious means.
• Will knows for a fact that the mind is in some way separable from the body, or at least not fully confined to the body. If it were fully confined, El’s powers wouldn’t be possible (among other things). That’s why he doesn’t think there’s a problem to be solved.

23) "Descartes' tortured soul" 

• René Descartes was a seventeenth-century philosopher who spent a lot of time thinking about what we could still know even if we couldn’t trust our senses. He ended up concluding that, because we have subjective experience (that is, because we think), we can be certain that we exist. You can’t be certain that anyone else exists, but the mere act of thinking is enough to establish that you yourself exist. That’s where the famous “I think, therefore I am” line comes from.
• Descartes was a dualist (he believed that the mind is distinct from the body in some fundamental way), and was genuinely bothered by his own inability to explain how mind and body interact.

24) "Ryle's ghost in the machine" 

• “Ghost in the machine” is how Gilbert Ryle, a twentieth-century philosopher, described the dualist understanding of the mind. This was a criticism, and the implication was that there’s something “magical” about dualism (or belief in a free-floating “mind” more generally). The phrase “ghost in the machine” appears pretty frequently in popular culture (the Ghost in the Shell manga/anime franchise is one example).

25) "This is my body, given up for you" 

• This is a line from the Catholic mass. It’s what Jesus says at the Last Supper, before his execution (as described in the Gospels of Matthew, Mark, and Luke). He’s describing the sacrifice that he’s about to make for the good of all humanity. “This is my blood, poured out for you” follows shortly thereafter.

Chapter 6 - The Darién Gap

26) "Disturbed your circles" 

• According to legend, “Do not disturb my circles!” were the last words of the ancient Greek mathematician Archimedes, who was killed by Roman soldiers when they conquered the city of Syracuse. The soldiers found Archimedes drawing circles in the sand, trying to solve a geometry problem. He didn’t care about the battle; he was totally fixated on his geometry work.

27) "In Daniel, an angel grabs the prophet Habakkuk" 

• This is an odd story. It appears in a part of the Book of Daniel that’s regarded as apocryphal by Jews and Protestants, so you’ll only find it in Catholic and Eastern Orthodox versions of the Bible.
• Daniel was an ancient Israelite who experienced prophetic visions and dreams (the phrase “writing on the wall” is from one of his visions). He served a succession of Persian kings as a sort of court wizard, although his position at court wasn’t exactly secure. At one point, he was imprisoned and starving to death, so God had an angel tell the prophet Habakkuk - who lived six hundred miles away - to bring Daniel food. When Habakkuk said he’d never been to Babylon (the Persian capital) and had no idea how to get there, the angel picked Habakkuk up by the hair and flew him to Daniel.

28) "It's about whether you need agent-causation" 

• This is a real academic paper called “Why Agent Causation?” It’s by Timothy O’Connor (a professor at Indiana University), and was published in fall 1996. I just looked for a widely cited academic paper that a grad student like Will could theoretically have been reading in late 1997.
• Agent-causation and event-causation are different theories of how free will could work. Event-causation is the idea that actions can be caused by “events” and still be regarded as freely chosen; agent-causation is the idea that you really do need an “agent” (like a ghost in the machine) for free will to work.

Chapter 7 - Gorgon's Eyes

30) "The Ship of Theseus"

• This is a famous thought experiment that’s been around since the second century. Essentially, you have a ship, and, as pieces of the ship break down, you replace them. Eventually, none of the original pieces remain. Is it still the same ship? In the seventeenth century, the philosopher Thomas Hobbes asked what would happen if you added a second ship, made entirely of pieces removed from the first. Which of the two would be the original ship?
• The point is to shed light on the persistence of identity through time. You can do it for humans, too. Every cell in your body will eventually be replaced, but your “selfhood” persists regardless. How is that possible? How does your mind remember things that were experienced by a totally different assemblage of cells? What does that say about the nature of the mind?

31) "The Drake equation" 

• In 1961, the astrophysicist Frank Drake used known facts about the universe to estimate the number of advanced civilizations that might exist. He landed on anywhere between 100 and 100,000,000 in the Milky Way alone. There are many responses and criticisms, most of which I can’t pretend to understand. For example, it’s been suggested that, if you account for the age of the universe, it’s entirely possible that none of these advanced civilizations would exist at the same time.

32) "The Four Horsemen"

• There actually isn’t much else to say about this one. Some of what Will says is anchored in real analysis of the woodcut, but most of it is his own.

33) "Between phenomena and noumena" 

• This is a very complicated (and often confusing) area of philosophy that I’ve really only scratched the surface of, but metaphysical idealism is the theory that all of reality is fundamentally mental rather than physical. There are a number of different versions of idealism, and the phenomena vs noumena distinction is specific to the work of Immanuel Kant, an eighteenth-century philosopher. The basic idea is that we can never truly perceive things as they really are (the noumena); we can only perceive them as they’re constructed by our minds and senses (the phenomena). I should note that “constructed” may be a more or less literal account of what’s going on, depending on how you read what Kant is saying. Whether things have any kind of mind-independent existence at all is an open question.
• Idealism still has its defenders, but the twentieth century saw a major shift towards metaphysical realism, which is the theory that reality exists independently of the mind (which is how most people think about reality).
• If this all sounds very vague, it’s because idealism doesn’t really make sense unless you also understand a whole bunch of other things about how idealist philosophers saw the world, and I’m really not qualified to get into that level of detail.

Chapter 8 - Closer to Midnight

34) "Something to do with Russian politics"

• Winston Churchill once described observing Soviet politics as like watching “a bulldog fight under a rug.”

35) "Ligand-gated non-selective cation channels" 

• This is a real medical paper that was published in or around 1997. I have absolutely no idea what it’s about (other than what Lucas says). I just looked for a widely cited paper published around that time.

36) "Quantum indeterminacy"

• Some of the physical properties of subatomic particles seem not to be fixed. Physicists call this quantum indeterminacy. A famous example is Heisenberg’s uncertainty principle, which is the observation that you can’t know both where a particle is and how fast it’s moving. Importantly, the issue isn’t that we’re not technologically capable of measuring both at the same time; it’s that the properties themselves (location and speed) seem to be fundamentally undetermined in some way
• At the same time, this subatomic uncertainty doesn’t lead to uncertainty at the level of larger objects. That’s the point of the famous Schrödinger’s cat thought experiment, which comes up a lot in popular culture. The physical properties of larger objects (like cats) don’t seem to be undetermined at all, and we can know exactly what they are. Whether this (apparent) tension means anything for the existence of free will is a subject of debate (usually in philosophy, not physics).

37) "The love the dare not speak its name" 

• “The love that dare not speak its name” is a Victorian-era euphemism for gay love. It’s best known for being invoked by Oscar Wilde at his 1895 trial for gross indecency (gay sex, essentially), but it actually first appeared in a poem by Alfred Douglas (who was at one point Wilde’s partner)

38) "Measurement problem" 

• This is related to quantum indeterminacy. Some of the universe’s fundamental components, like light, seem to behave like particles when observed (or measured) and like waves when unobserved. In other words, the act of measurement seems to “do something” to the thing being observed, which is hard to explain.
• A number of different solutions have been proposed. One of them is that there really is a multiverse of some kind, and every possible universe really does exist. It’s not that that the observed thing’s fundamental properties are undetermined; it’s that every possible outcome occurs in a separate universe, and you (the observer) are just seeing the one that occurs in your universe. This is called the many-worlds interpretation. It’s also been proposed as a solution to the extreme improbability of the universe being able to support intelligent life.

39) "The Destroyer stays his blade" 

• The destroying angel is a recurring figure in the Old Testament. It appears at various points to visit judgment and destruction on enemies of God, the prophets, and the ancient Israelites. When there’s more than one of them, they’re referred to as “destroying angels,” “messengers of death” and a variety of other things. When there’s just one, the usual term is “Angel of the Lord.”
• Anything to do with angels is notoriously murky, and whether all these beings are intended to be the same being - or even the same type of being - is unclear. The figure of the Angel of Death is also in the mix. Interestingly, the name typically given to the Angel of Death - Azrael - actually originates in the Quran. That name appears nowhere in the biblical canon. It does appear in an apocryphal text called the Apocalypse of Peter, although the figure described there differs significantly from the more benevolent figure who appears in the Quran (and it’s the latter who seems to inform popular depictions of Azrael/the Angel of Death).

Chapter 9 - Habakkuk

40) "Quos Deus vult perdere, prius dementat"

• This version of the idiom uses the singular (and capitalized) “God” instead of the plural “gods,” but the idiom predates Christianity, and the “gods” version is more common in English.

41) "And war broke out in heaven"

• Revelation is primarily a vision of the future, but this passage is understood to be describing Lucifer’s rebellion against God, which is typically regarded as something that happened closer to the time of creation. 
• The reason for the rebellion is never explained in scripture. The apocryphal explanation is that Lucifer and some of the angels refused to bow to humans (when God told them to). Also, while the dragon is usually identified with Lucifer, the name “Lucifer” doesn’t appear in scripture. Rather, the Old Testament Book of Isaiah refers to a “morning star, son of the dawn” who had “fallen from heaven” and been “cast down to earth.” The Hebrew word for the morning star (now known to be Venus) was translated into Latin as “Lucifer”, which is simply the Latin name for the morning star.

42) "John of Patmos"

• Revelation is written in the first person, and the author identifies himself as John. On the island of Patmos, an “ascended” Jesus appears to him and gives him a vision of how the world ends. We know next to nothing about the author of Revelation; we only call him “John of Patmos” because he tells us that his name is John, and the vision occurs on Patmos.
• Revelation is a strange read. It’s visually rich and full of confusing, cryptic symbolism. It’s also (almost) universally understood to be not entirely literal. That is, very few Christians believe that every event described in Revelation will literally happen exactly as described. 

43) "St. Michael the Archangel"

• Michael is one of seven named archangels, and is in some sense their leader. He’s usually depicted as a soldier and as commander of the armies of heaven. Revelation is probably his most significant appearance, but he appears in a number of other stories as well (sometimes by name; sometimes by implication).
• The Prayer to St Michael, part of which is quoted in Chapter 9, was composed in the late nineteenth century. The full text is:
• “Saint Michael the Archangel, defend us in battle; be our protection against the wickedness and snares of the devil. May God rebuke him, we humbly pray: and do thou, O Prince of the heavenly host, by the power of God, thrust into Hell Satan and all of the other evil spirits who prowl about the world seeking the ruin of souls. Amen”

Chapter 10 - Lower than the Angels

44) Title

• The title is taken from a phrase that appears for the first time in the Old Testament Book of Psalms and is then quoted in the New Testament Epistle to the Hebrews. The text as it appears in Hebrews is: “What are human beings that you are mindful of them, or mortals, that you care for them? You have made them for a little while lower than the angels; you have crowned them with glory and honour, subjecting all things under their feet.”
• Just to make this as confusing as possible, the text as it appears in contemporary English translations of Psalms reads: “You have them a little lower than God.” The reference to time (“for a little while”) is removed, and “the angels” is swapped out for “God.” The relevant Hebrew word is “Elohim”, which is translated as either “God” or “angels”, depending on the context. It’s also grammatically plural, which introduces further complexity.
• Anyway, the precise meaning of the phrase is the subject of debate. I say a little at the end of Chapter 10 about why I included it.

45) "All facts are brute facts"

• In contemporary philosophy, a brute fact is a fact that’s totally obvious, and can’t be explained with reference to other, more fundamental facts. The fact that the universe exists is an example (bearing in mind the distinction between explaining why the universe exists and explaining that it exists).

Chapter 11 - Celestial Navigation

46) "The past is a foreign country"

• This is the opening line of The Go-Between, a 1953 novel by LP Hartley.

47) "Everything is suddenly pink"

• On the third Sunday of Advent (Gaudete Sunday) and the fourth Sunday of Lent (Laetere Sunday), the main liturgical colour is pink. For the rest of Advent and Lent, it’s purple. This is specific to Catholicism; other denominations may use different colours (although some use the same ones).

48) "Station of the Cross"

• In many churches, you’ll see fourteen art pieces depicting different stages of Jesus being sentenced to death, crucified, and buried. These are known as the Stations of the Cross. They go in a specific order, and they’re normally positioned around the church in a way that creates a path to be followed.

49) "Way of Sorrows"

• This refers to two things. It can be another name for the Stations of the Cross (“Via Dolorosa” in Latin), or it can refer to the path in Jerusalem that Jesus walked on the way to the site of his crucifixion. The events depicted in the Stations of the Cross are generally things that happened while Jesus was being paraded along this path, although they include other things as well.

50) "Chain of contingency can't go on forever"

• This is a version of the cosmological argument, which is one of the traditional arguments for God’s existence found in Christian and Islamic philosophy. The idea is that the chain of causation can’t go on forever, and must at some point terminate in an “uncaused cause” or “unmoved mover.” The Big Bang can’t even have been random, because even random outcomes depend on some kind of input.

51) "Stabilize the Upside Down"

• This was obviously in the show, but the idea is a real one, and it works something like this: The ordinary operation of the laws of physics would cause a wormhole to collapse almost immediately (and become a black hole). In order to prevent that from happening, you’d need to “stabilize” the wormhole using something with negative energy density. My understanding is that negative energy is theoretically possible but has never been observed, and no one knows how to create it. Negative mass matter and tachyonic matter are types of exotic matter that would have negative energy (bearing in mind that all exotic matter is theoretical).

52) "Majestic 12"

• Majestic 12 is supposedly a secret government committee established in 1947 to investigate UFO crash sites (the first of which was the famous one in Roswell, New Mexico). It was “revealed” in 1987, when a British ufologist (someone who studies UFOs) claimed to be in possession of classified documents that proved the committee’s existence. The documents are now almost universally regarded as having been part of a hoax, but Majestic 12 still shows up in fiction and popular culture with some frequency.

Chapter 12 - Epilogue - The Oath

53) "Do you know Aslan?"

• What Mike says is true. Even if the books themselves weren’t clear on this point (and I think they probably are), CS Lewis confirmed in his private writings that Aslan is intended to literally be Jesus, not an allegory for him. Lewis was interested in this question: “What might Christ become like if there really were a world like Narnia and He chose to be incarnate and die and rise again in that world as He actually has done in ours?”