...the big issue, which appears to be at least in part that the question is how "much" of a deviation occurs.
Is this really a big issue?
I would agree that these are inside baseball discussions. Fun, but we're definitely in the weeds on this thread. 
Is this really a big issue?
Yeah I am still channeling the AA Long article and the Sedley article on the swerve deriving from free will rather than physics.
1. Anything more than the slightest deviation would play into the hands of those saying that an unstable universe needs a superintending God, and
2. Is anything more than the swerve of a single atom at a single moment in time necessary to start the chain of collisions needed to bring everything into existence?
Quote from DonAnd my take is that this was the primordial situation with all atoms falling in parallel "straight down." However, once a couple collisions happened, the order was interrupted by collisions and conglomerations in parts of the cosmos. In other parts, the parallel falling continued. And so on.
I've never been able to reconcile a 'primordial' downward movement with the concurrent claim that there was no beginning.
I have been considering this point as well.
Epicurus' third elementary principle proposes that "the universe is as it always was and always will be". If the distribution of matter in the universe has always been the same, it seems to follow that there would not have been a period where most particles were moving in a consistent, parallel stream in the same, perfectly "downward" movement. At all points in time, there was never an absolute "up" and "down", and at all points time, particles were falling against each other, so a deviation from perfectly straight paths would not be necessary, because linear motion can describe this.
Perhaps primordial is not so much a time, as it is a state or condition. An uncoupled atom, a "first beginning" or "seed of things" in Lucretian terms, is the atom in its primordial state. It 'falls' along an inertial path in whatever direction, swerves unpredictably, 'falls' again, couples with another atom, joins other couplings to form a body, dissolves, and falls away in an endless cycle of accretion and dissolution.
I think primordial is the wrong word. (I'm now waiting for Don or Nate to go find where Epicurus used exactly that word
I think the image of atoms falling in parallel was an imaginary construction Epicurus used as evidence that there must be a swerve. I don't think it was intended to describe an actually existing state of the universe.
If there were no swerve, there would never be anything other than isolated atoms falling in parallel. Nothing more complex than individual atoms would ever come into existence. But other things do exist. Therefore...
It's time:
1. That a "Swerve" Is Necessary For Nature To Create:
…corpora cum deorsum rectum per inane feruntur
ponderibus propriis, incerto tempore ferme
incertisque locis spatio depellere paulum,
tantum quod momen mutatum dicere possis.
quod nisi declinare solerent, omnia deorsum
imbris uti guttae caderent per inane profundum
nec foret offensus natus nec plaga creata
principiis; ita nihil umquam natura creasset. (DRN II 217-225)
“…when first-bodies are being carried downwards straight through the void by their own weight, at times quite undetermined and at undetermined spots they push a little from their path: yet only just so much as you could call a change of trend. But if they were not used to swerve, all things would fall downwards through the deep void like drops of rain, nor could collision come to be, nor a blow brought to pass for the first-beginnings: nature would never have brought aught to being.” (DRN II 217-225; trans. Bailey)
“…when the atoms are being drawn downward through the void by their property of weight, at absolutely unpredictable times and places they deflect slightly from their straight course, to a degree that could be described as no more than a shift of movement. If they were not apt to swerve, all would fall downward through the unfathomable void like drops of rain; no collisions between primary elements would occur, and no blows would be effected, with the result that nature would never have created anything. (DRN II 217-225; trans. Smith)
“Though atoms fall straight downward through the void | by their own weight, yet at uncertain times | and at uncertain points, they swerve a bit— | enough that one may say they changed direction. | And if they did not swerve, they all would fall | downward like raindrops through the boundless void; | no clashes would occur, no blows befall | the atoms; nature would never have made a thing.” (DRN II 217-225; trans. Copley)
2. That a "Swerve" Is Required To Refute a Deterministic Universe:
quare etiam atque etiam paulum inclinare necessest
corpora; nec plus quam minumum, ne fingere motus
nec plus quam minimum, ne fingere motus
obliquos videamur et id res vera refutet.
namque hoc in promptu manifestumque esse videmus,
pondera, quantum in <se> est, non posse obliqua meare,
ex supero cum praecipitant, quod cernere possis;
sed nihil omnino <recta> regione viai
declinare quis est qui possit cernere sese?
Denique si semper motu conectitur omnis
et vetere exoritur <motus> novus ordine certo
nec declinando faciunt primordia motus
principium quoddam, quod fati foedera rumpat,
ex infinito ne causam causa sequatur,
libera per terras unde haec animantibus exstat… (DRN II 244-256)
“Wherefore, again and again, it must needs be that the first-bodies swerve a little; yet not more than the very least, lest we seem to be imagining a sideways movement, and the truth refute it. For this we see plain and evident, that bodies, as far as in them lies, cannot travel sideways, since they fall headlong from above, as far as you can descry. But that nothing at all swerves from the straight direction of its path, what sense is there which can descry? Once again, if every motion is always linked on, and the new always arises from the old in order determined, nor by swerving do the first-beginnings make a certain start of movement to break through the decrees of fate, so that cause may not follow cause from infinite time; whence comes this free will for living things all over the earth…” (DRN II 245-257; trans. Bailey)
“So I insist that the atoms must swerve slightly, but only to an infinitesimal degree, or we shall give the impression that we are imagining oblique movements—a hypothesis that would be contradicted by the facts. For it is a plain and manifest matter of observation that objects with weight, lell to themselves, cannot travel an oblique course when they plunge from above—at least not perceptibly; but who could possibly perceive that they do not swerve at all from their vertical path? Moreover, if all movements are invariably interlinked, if new movement arises from the old in unalterable succession, if there is no atomic swerve to initiate movement that can annul the decrees of destiny and prevent the existence of an endless chain ofcausation, what is the source of this free will possessed by living creatures all over the earth?” (DRN II 245-257; trans. Smith)
“And so again and again atoms must swerve | a little—the tiniest bit: we must not picture | crosswise movement, for facts would prove us wrong. | For this, we see, is obvious and clear: weight of itself can never move transversely; | it drops from above straight down, as we observe. | But that no atom ever swerves at all | from the perpendicular, who could sense and see? | To continue: if all movement is connected, | (new movement coming from old in strict descent) | and atoms never, by swerving, make a start on movement that would break the bonds of fate | and the endless chain of cause succeeding cause, | whence comes the freedom for us who live on earth?” (DRN II 245-257; trans. Copley)
3. That Freedom of Mind Is Facilitated By "the Tiny Swerve":
…sed ne res ipsa necesssum
intestinum habeat cunctis in rebus agendis
et devicta quasi cogatur ferre patique,
id facit exiguum clinamen principiorum
nec regione loci certa nec tempore certo. (DRN II 289–293)
“But that the very mind feels not some necessity within in doing all things, and is not constrained like a conquered thing to bear and suffer, this is brought about by the tiny swerve of the first-beginnings in no determined direction of place and at no determined time.” (DRN II 289–293; trans. Bailey)
“But the factor that saves the mind itself from being governed in all its actions by an internal necessity, and from being constrained to submit passively to its domination, is the minute swerve of the atoms at unpredictable places and times.” (DRN II 289–293; trans. Smith)
“…all things are not caused by blows—external force; no internal power | controls the mind in every move it makes, | a helpless captive bound by what must be: | this comes from the tiny swerving of the atoms | at no fixed place and no fixed point in time.” (DRN II 289–293; trans. Copley)
I am not sure that Lucretius' propositions (1.) and (3.) are supported by Epicurus' writing. (1.) His first point seems to imply that there was a previous time when all particles had the same orientation (the same "down"), prior to those particles becoming entangled to generate compound things. This seems to contradict the propositions of the temporal consistency of the universe (EH 39.2-6, 44.6-7) and the relativity of individual particles' orientations (EH 60.1-12).
(3.) Epicurus' existing writing are filled with discussions about choice, comparison, and contemplation, but they do not seem to require the ΠAPEΓKΛIΣIΣ to explain. In the same way that sentience is proposed to originate from complex arrangements of insentient matter, it would be consistent to suppose that the capacity to make decisions originates from complex arrangements of choiceless matter. Given doubts on (1.), I am more prone to doubt (3.).
I admit to having on occasion approached the question of providence with kid gloves in the past, chiefly because many of the people I care about accept providence. Hell, they even accept petitionary prayer. But the denial of providence and the Epicurean approach to suffering is perhaps the thing that *most* draws me to Epicureanism and the thing I think the Modern Stoics are most disingenuous about (the second being 'preferred indifferents'). So while I applaud the authors who try to address the providential elephant in the room, my experience is that they: 1) lapse into Epicureanism without knowing it (see, for example, the Irvine passage attached, which is pretty much textbook Epicureanism); 2) say something like 'let's agree to disagree (see Pigliucci); or 3) just redefine providence to mean something it's not (like accepting that the past is fixed).
On the other point: I suppose the thing that intrigues me about the '[insert agreed upon swerv-ish term here]' is that these are, in my admittedly limited understanding, two places where stochastic processes are most commonly invoked at high levels of science--in particle physics and in the shocking amount of spontaneous activity happening in the brain.
I admit to having on occasion approached the question of providence with kid gloves in the past, chiefly because many of the people I care about accept providence. Hell, they even accept petitionary prayer.
I hear you. I would never (probably) share these sentiments with certain family members, but it does feel pleasurable to me to vent them here 
1) lapse into Epicureanism without knowing it (see, for example, the Irvine passage attached, which is pretty much textbook Epicureanism)
I certainly see where you're going with that. Some modern Stoics I've read sound very Epicurean in their attempt to contort "their" philosophy into something palatable.
Then again, with respect to (1.), Epicurus does discuss the creation of worlds (EH 45.5), so perhaps Lucretius is merely referring to the creation of a world-system, and not the universe as a whole. (I am imagining – as a reasonable, modern analog – a contracting, pre-solar nebula that flattens into a protoplanetary disc that then rotates around a hot protostar until the rotating matter accretes into planetesimals that eventually develop into different worlds.) I might have been getting stuck on the idea that "nature creating" refers to a universal beginning rather than a local beginning.
"...such a world may come into being both inside another world and in an interworld, by which we mean a space between worlds; it will be in a place with much void [...] this occurs when seeds of the right kind have rushed in [...] little by little they make junctions and articulations, and cause changes of position to another place [...] and produce irrigations of the appropriate matter until the period of completion and stability, which lasts as long as the underlying foundations are capable of receiving additions." (EP 89.2-90.1). So Epicurus does identify a preceding stage of instability, per kosmos.
Therein, particles moved from a stage of "falling raindrops" (DRN II 223) "first", "and gradually grew in size by the aggregations and whirlings of bodies of minute parts" (EP 90.8-91.1). At some point "stability" is reached. I am comfortable with "creation" when taken as the development of a system of celestial bodies ... however, I still don't see the need for the "swerve" to create this arrangement. Perhaps one particle re-bounded from an "interworld" and started a cascade amid the cloud of "falling raindrops" (rather than one drop in the cloud "swerving" into another).
Overall, I question whether or not the "swerve" served any other function for Epicurus besides providing a rational counter-point to Democritus' determinism. Epicurus explained how world-systems develop to Herodotus and Pythokles without discussing the "swerve", and he explained choice and contemplation to Menoikeus without referring to an atomic "swerve". I am speculating that the declinando or clinamen in De Rerum Natura – described as a world-building and thought-forming agent – was more of a poetic embellishment by Lucretius than a reflection of Epicurus.
Sedley, in Lucretius and the Transformation of Greek Wisdom, posits that the swerve doesn't show up in the letter to Herodotus because the letter only covers On Nature books 1-10. He further conjectures that the swerve showed up in book 25 or books in that area, but there's no surviving fragments of book 25 that contain mention of it.
I doubt Lucretius would have included the swerve without justification from a source text. That said, it certainly doesn't seem pivotal or foundation to Epicurus's philosophy. It could be part of a specific argument against Democritus and his physical determinism but may have become overblown with later commentators and critics.
what do you make of Erik Anderson's translation of U56 that renders ΣTOIXEIΩΣEIΣ ΔΩΔEKA as "Doctrine of the Elements (12 Books)"?
Thank you for asking this question!
Yeah, I'm not seeing this as "12 volumes" but rather as a summary of something with 12 items.
I agree. Thank you for your comments here Don. my guess is one book about 12 principles, but I have no further evidence beyond what you have already provided.
There's no way to tell what those 12 basics were (other than the 1, 2, or 3 stated there
Sad but true. Still, I cannot help but appreciate the efforts of those who try to make a list (because I am not so bold).
