Xevet

The Tachyon Alignment buff allows that player to deploy a Vex force field, identical to what Atheon - “Time's Conflux” - used to detain Guardians and remove them from the timeline in the Vault of Glass raid. Tachyons within Destiny 2’s fictional setting may play a role in cutting an observer off from their physical reality, bringing them into the pre-wavefunction-collapse state that manifests the Vex network, where the set of sensory information that a human being experiences as “reality” has not yet been defined. 

Traveling the Vex information network means metaphor superimposed on the flat planes of reality. Techno-biological synesthesia. Merkwelt, wirkwelt, umwelt. I step through a portal held open by the calculations of a Gate Lord, feel it in its true form as my Vex do, even as the Human part of me grasps for interpretation: Fourier transforming down the crest of a wave, knowing the water is angry below. █ Source: III. Down? 

The Agraios encounter shows us all three iterations of the Temporality status effect simultaneously: Absolute Temporality, Constant Temporality, and Cyclical Temporality. These refer to versions of the time parameter associated with branches of physics other than relativity. 

Absolute Temporality - or absolute time - provided the theoretical foundation for Newtonian (classical) mechanics. Newton believed that time existed independent of the perspective of any observer, and flowed at a consistent rate throughout the universe. This was written into his original five laws: the three Laws of Motion that we still use to this day, absolute time, and absolute space.  Newton's 4th Law (the postulate of absolute time):  Absolute, true, and mathematical time, of itself, and from its own nature, flows equally without relation to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year. Excerpt from Elements of Newtonian Mechanics. 

Constant Temporality is similar. In quantum mechanics, time is described as a constant background parameter. At the most fundamental levels, time may not exist at all. 

Consider: what do we - humans - experience as time? The answer is change– the rising and setting of the sun, the growling of our bellies when it has been a while since our last meal, the cooling of a hot beverage. Take away watches, numbers, and the demand to attend appointments, and we would still experience those changes. Therefore it seems intuitive to say, “Of course time exists!” …doesn’t it? 

At the scale of elementary particles, this change manifests as the transfer of quantum entanglement. As entangled particles interact with outside systems, entanglement is transferred, and information associated with the original collection of particles is lost– like a single drop of red dye dispersing in the blue ocean. 

Below that scale - the scale of entangled systems - nothing changes, as far as we know, and so time ceases to exist. This is the postulate of physicists Don Page and William Wootters, which was demonstrated experimentally by a team of researchers at the Istituto Nazionale di Ricerca Metrologica (National Institute of Meteorological Research) in Italy: we experience the passing of time because we are part of the universe’s systems of entangled particles, but an observer outside our system of entanglement would perceive a static universe. 

In the Vault time frays and a needle moves through it. The needle is the will of Atheon. I do not know the name of the shape that comes after the needle. █ Source: Vault of Glass

Cyclical Temporality refers to the fact that almost all of our best known and understood laws of physics obey time-reversal symmetry, or T-symmetry. Forces, inertia, collisions, gravity, electromagnetism, and the strong nuclear force (which holds protons and neutrons together to form the nuclei of atoms) would all function exactly the same whether we were moving forward or backward in time. 

For example, consider H₂O molecules. They form solid ice, liquid water, or gaseous steam as the temperature surrounding them changes. Water can be cooled to form ice, and ice can be heated to form water, repeatedly. 

The process of water molecules changing their configuration, therefore, obeys T-symmetry. It remains the same, regardless of the hypothetical direction in which time is flowing. 

From the names of these status effects, the Vex appear not to have a concept of relative temporality. This seems to be the advantage that the Nine hold over them: the Vex are masters of quantum effects, and can move information across timelines, while the Nine have some degree of control over incompatible, relativistic effects: interacting with gravity, affecting spacetime within the fictional universe’s discrete timeline. 

Dialogue from the Edge of Fate campaign: “The Nine exist outside of time. When one intervenes in our dimension, it causes tears in spacetime– pulls things through.”  Note: “Dimension” in this context is being used to mean “timeline.”

Dialogue from the Edge of Fate campaign: “Orin… Can the Nine only pull objects forward in time?”

Dialogue from the Edge of Fate campaign: “Only forward, never backward. When I was Emissary, I knew this truth as I knew my own pulse. The rule of chronal flow is the Nine’s oldest, and their cruelest.”

The Vex’s experiments with the dark matter accumulated from III’s corpse, then, are likely intended to acquire the same mastery over relativistic phenomena that they have over quanta. 

If physics is a set of rules that the cosmos uses to calculate itself, perhaps the Vex seek to worm their way into these calculations: to become a law of reality, inseparable from existence. A virus in the system. Perhaps Atheon was the centerpiece of this project, a command nexus that unified efforts across time. █ Source: Atheon, Time’s Conflux

Koregos

The final boss we face is Koregos, the Worldline: a “worldline” being the path that a given object, such as a particle or observer, traces through spacetime. A worldline is the sequence of events by which the entity has interacted with spacetime; its causality, each effect brought about by each cause as a result of that entity’s existence in the universe. 

One of the first mechanics that a person may notice in this encounter is the blue beam that this gigantic Harpy fires at the players. Upon dying to this beam, the text in the upper-right corner, describing what killed the player, reads “Time’s Arrow.”

A prompt seen after dying to Koregos’s laser: “Time’s Arrow.”

This references the Arrow of Time paradox, or Loschmidt’s Paradox. In both quantum and relativistic physics, most or all physical processes obey T-symmetry: they would be exactly the same if, hypothetically, they occurred with the direction of time reversed. On the scale in which we live our day-to-day lives, however, we only experience time flowing in a single direction, like an arrow released from a bowstring– from past to future. How can a foundation of processes which obey time-reversal symmetry result in a macroscopic universe that does not? 

Earlier, H₂O molecules were used as an example: water can be cooled to form ice, and ice can be heated to form water, repeatedly. The process of water molecules changing their configuration obeys T-symmetry. 

Yet if a human being were to watch a video of ice melting into a puddle of water, and then the same video played in reverse, it would be immediately obvious which video was which. In our day-to-day lives, puddles of water do not spontaneously rearrange themselves back into the form of ice cubes. 

Why the discrepancy? 

What we experience as the Arrow of Time lies in the Second Law of Thermodynamics: the entropy in a closed system, such as a universe, can never be decreased. It can only remain the same, or increase. 

Entropy is a measure of the tendency of thermal energy to equalize. Imagine a cup of coffee sitting on a desk in a room. The room is heated to a comfortable temperature of 68° F (20° C). The coffee, just before being placed in the room, was heated to a temperature of 140° F (60° C) for drinking. 

The difference between the temperature of the room, and the temperature of the cup of coffee, will equalize. The ambient temperature of the room will rise by an imperceptible fraction of a degree, and the coffee will cool to room temperature. When whoever forgot the cup of coffee on their desk retrieves it, they will likely take a sip and think, “Ugh, this tastes like feet!” 

What happened? Entropy increased. 

That increase in entropy is what we perceive as the Arrow of Time: a physical reason why room-temperature coffee never spontaneously heats itself, eggs never spontaneously unscramble and return to their unbroken shells, and we only experience time flowing from past to future, never reversed.  

Entropy is often described as synonymous with chaos and disorder. We humans tend not to like many of the ways in which we notice the increase of entropy. We don’t want tepid coffee. We don’t want the parts in our electronics and appliances to overheat as kinetic and electrical energy is transferred. Though we won’t be around to experience it, we don’t like the idea that all of the energy (except that inherent to mass) throughout the universe will eventually equalize, and it will be impossible to transfer energy in order for things to happen. 

Another way to describe entropy is in terms of how easily the state of a system can be disturbed. Low-entropy states tend to be fragile, and easily pushed into becoming higher-entropy states. Meanwhile, higher-entropy states are more stable and more difficult to change. An egg is more easily dropped and broken than it is scooped back up from the floor into its broken shell, and the shell taped or glued back together. A bowl of scrambled eggs cannot be separated back into its constituent raw eggs, because on the scale of atoms and molecules, the scrambled state of the egg is more probable and more difficult to disturb than its earlier, uncooked and unbroken state. 

Researcher Ludwig Boltzmann approached entropy from this perspective, and developed an equation that correlates the number of possible configurations of a microscopic system with the entropy-based changes that we observe on a macroscopic level. For any given system, there are many more possible higher-entropy states than lower-entropy states that the system could progress to; therefore, a greater probability of progressing into a higher-entropy state than a lower-entropy state. This effect compounds as the complexity of the system increases: from atoms to molecules to chemical compounds to cells to multicellular organisms… Once we reach the scale on which humans experience our day-to-day lives, the probability of encountering a random fluctuation from a higher-entropy state to a lower-entropy state is so low that it is effectively indistinguishable from zero, leading to what we experience as the Arrow of Time. 

The Big Bang theory arises from the Second Law of Thermodynamics: the universe began in a low-entropy state, and since the Big Bang, entropy has been increasing. From that point in spacetime, in which the universe existed as a single infinitely hot and dense point, it has been moving in a single direction: expanding. 

But could the expansion of the universe obey T-symmetry? What if it goes through cycles of expansion and contraction, like a heartbeat? This is the subject of the Big Bounce theory: the universe may be expanding until the force that drives its expansion can no longer overcome gravity, at which point it begins to collapse back into the condensed state from which the Big Bang originated. 

If that were to happen, the assumption is that entropy would continue to increase, even in a cycle of contraction, preserving the Arrow of Time– because we currently have no physical evidence to suggest that entropy ever decreases. Science does not encompass that which we cannot observe; this domain is left to philosophy. 

Time is, ultimately, a mystery that science has yet to fully understand. We have yet to ask the right questions, formulate the right hypotheses, and develop the tools to run the right experiments, to fully explain time as a physical parameter, and how our own human experience of time relates to it. 

We may never be able to solve this mystery simply because the human species will not exist long enough to make all of the required observations about the physical universe. We can never have a full picture of the entirety of time. 

In the Destiny 2 universe, paracausality is defined by a decrease in entropy– however, it never violates the perceptual Arrow of Time. Guardians spontaneously generate energy and matter (the Hunter’s Arc Staff, for example, seems to be a combination of both), but they do not remember the future or influence the past. This is explained in the Clovis Bray logbook: Clarity (Clovis’s name for the Darkness) violates T-symmetry. Therefore a human observer would never have a perception of time flowing in the opposite direction; the original process is never time-reversed. 

It is worth noting that this is empirical evidence that Guardians are, indeed, not the same people who died in their former, mortal lives. The mortal death is not time-reversed; instead, something new emerges when the entropy is lowered.

Clarity violates established symmetries and conservation laws. In doing so it defies Noether's theorem, the most fundamental and beautiful cornerstone of physics.

Symmetry and conservation are two sides of the same coin. "All things are transformations of one thing, without gain or loss," as my childhood tutor put it. "If A can become B, then B can become A. We say that state B (say, a mixed drink) comes after state A (say, sugar and water) only because there are more probable pathways from A to B. Wait long enough—longer than the universe—and your drink really can return to state A, spontaneously unmixing itself."

But Clarity is NOT always symmetrical. For example, it violates time reversibility. Consider the simple equation:

Clarity(A) -> B.

This is the application of Clarity to state A to produce a lower-entropy state B. (Clarity is fond of removing portions of a state configuration, harrowing the phase space down to only its most robust inhabitants.)

Time symmetry suggests that we should be able to run this process in reverse and retrieve the original:

reverseClarity(B) -> A.

But in fact, we obtain:

reverseClarity(B) -> C,

where C is the same as in

Clarity(B) -> C.

Clarity's effects cannot be used to return a transformed state to its original state. Instead, we obtain a second transformed state, further yet from the original configuration. █

Source: Clovis Bray’s Logbook

Upon clearing Koregos’s final stand, we see the prompt, “Decoherence imminent!” before the boss falls from the sky: 

A prompt seen at the end of the Koregos encounter: “Decoherence imminent!”

Quantum decoherence is the loss of information associated with entangled quantum states. 

Imagine that you have a piece of paper with information written on it. You tear the paper in half. It's easy to put the two halves together and obtain the information written on the paper. 

You tear it into quarters, then eighths, then sixteenths. It's harder to put the torn paper back together now. You tear it into one-centimeter squares. Reassembling the information has become an inordinately time-consuming puzzle, but maybe, if one were extremely determined and had no greater priorities, it would be possible. 

And then, in this hypothetical scenario, you tear it so small that it has been separated into its individual molecules of wood pulp and ink. Whatever information was on that sheet of paper can no longer be recovered. 

Something conceptually similar happens to entangled elementary particles as they interact with systems outside of their own entanglement. Wavefunctions mix, and entanglement is transferred. The system of entanglement becomes so complex that information associated with the original entangled states can no longer be discerned. 

The information has been lost to quantum decoherence. 

The Vex use the transfer of entanglement to take over and convert entities; the quanta making up the non-Vex entity become assimilated into the Vex’s system of entangled quanta. 

“Basically, the Vex use cascading quantum entanglement, but…” █ Source: Thrilladrome Lost Sector

This was the fate that befell Asher Mir: his consciousness - the information that defined him - was lost to decoherence in the Vex network. 

The whorls of writhing data did not abate. They surged in endlessly, straining the signal's parameters, eroding, overwriting. There was no time to adapt. A picosecond later and there was nothing left of the signal but a dim ripple of spite.

—and all the stories have the same ending, shouted in a single voice, the toll of the bell that heralds the end of time—

It is as I said all along, the signal thought bitterly as it unspooled into the datastream. █ Source: Scribetrace Shell

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This document was written by @Chaostructure-Crafts. (And a “helpful” kitty!)

I love the way that the Destiny universe integrated their fictional concepts with real-world physics. It makes their world feel so very detailed and immersive to me. I understand, however, that to a person without a background in physics or engineering, it might be intimidating, frustrating, or pointless to engage with. I put this document together hoping I can break down some of those complicated physics concepts into terms that a wider audience can process more easily, so that others can enjoy the deep, detailed connection to this universe as I do.