This is a sum­ma­ry ver­sion. The full (long) ver­sion is here: Case II First Contact

What Case II is

The five cas­es, from a 2023 tax­on­o­my, are mutu­al­ly exclu­sive at the moment of con­firmed con­tact, though a sto­ry can lat­er migrate from one case to another:

1. Human­i­ty detects alien trans­mis­sions or artifacts.
2. Aliens detect human­i­ty and reply with transmissions.
3. Aliens detect human­i­ty and visit.
4. Human­i­ty detects aliens and then vis­its them.
5. Nei­ther side knows the oth­er exists until they meet in deep space or on a neu­tral world.

Case II is pho­tons, not ships: they pick up our leak­age, a METI bea­con (Areci­bo 1974, Luyten’s Star 2017), a space­craft, or some oth­er arti­fact, and they design a reply to be noticed. No probe or crew has arrived. Arecibo’s tar­get is so dis­tant a reply is unlike­ly; a reply from Luyten’s Star could not arrive before 2041.

Sagan’s Con­tact shows the migra­tion: it starts as Case I (we hear them) and becomes Case II once it is clear they heard us and addressed us. The sci­en­tif­ic premise is geo­met­ric: a radio sphere expands at light speed, so who­ev­er detects the oth­er first holds the initiative—silence, reply, vis­it, or terms of the encounter.

What they would actually hear

Earth’s space-escap­ing radio sig­na­ture effec­tive­ly begins in the mid-1930s (1936 Berlin Olympic TV around 40 MHz, then high-pow­er radar). By the mid-2020s that bub­ble is about 90 light-years across (~10,000 stars, a few hun­dred Sun-like). A cen­tu­ry from now ~190 ly; a mil­len­ni­um ~1,090 ly.

The bub­ble is not uni­form. Mid-20th-cen­tu­ry ana­log TV car­ri­ers and military/planetary radars were bright and nar­row-band. Lat­er dig­i­tal, cel­lu­lar, Wi-Fi, and fiber-era traf­fic pro­duces weak­er and more noise-like sig­nals. So a dis­tant lis­ten­er may see a bright his­tor­i­cal shell—a finite mid-cen­tu­ry pulse—then a fainter inte­ri­or, not a per­ma­nent lighthouse.

An Areci­bo-class (or SKA-class) tele­scope could, in prin­ci­ple, pull ana­log car­ri­ers out of the noise at tens of light-years with long inte­gra­tions; the strongest radars far­ther still if the observ­er is in the beam. Present-day dig­i­tal mur­mur needs a much larg­er aper­ture, a clos­er van­tage, or pri­or knowl­edge of when and where to look. Any­one already inside that ~90 ly sphere with radio astron­o­my at least as good as ours has had decades in which our analog/radar fin­ger­print was above the detec­tion floor. Beyond that sphere, they have not had time to see us yet.

Why a reply is hard

• Light-time is geom­e­try, not engi­neer­ing. Round-trip delay is 2D years. Vega (~26 ly), as in Con­tact, means a ~52-year wait from detec­tion. Hun­dreds of light-years means cen­turies. Insti­tu­tions must out­last sci­en­tists; real-time dia­logue is unre­al­is­tic; one-way mono­logues (bea­cons, archives, primers) fit bet­ter than conversation.
• Pow­er and point­ing. Detectabil­i­ty is flux at Earth. Inverse-square falloff makes a reply as faint as our leak­age use­less unless it is much more pow­er­ful or tight­ly beamed. A Kar­da­shev Type I civ­i­liza­tion with a large aper­ture and a nar­row-band beam could be vis­i­ble at inter­stel­lar range; Type II (stel­lar-scale ener­gy) could do it triv­ial­ly. An Areci­bo/­FAST-class trans­mit­ter aimed at Earth might work at tens of light-years; the same pow­er, isotrop­ic, would not. The beam must lead Earth’s future posi­tion. A beam nar­row­er than the point­ing error miss­es us; a wider beam costs flux. By the time they reply, Earth may already be radio-qui­eter than the mid-cen­tu­ry wave­front they locked onto.
• Con­tent must look arti­fi­cial. Echoes of our own sig­nal, primes, phys­i­cal con­stants, and hydro­gen-line / “water hole” car­ri­ers help. Lay­ered design: a robust atten­tion bea­con, then a primer, then images or sci­ence data with redundancy—not com­pres­sion or encryp­tion. The receiver’s band­width and whether they are even look­ing SETI-style is unknown.
• Silence is data, not proof that we are alone. No reply with­in our radio sphere bounds the prod­uct of den­si­ty × life­time × com­mu­nica­tive frac­tion (rar­i­ty, short-lived radio cul­tures, non-radio chan­nels, zoo/quarantine silence, or our own incom­plete search­es). It does not pick which fac­tor is small.

Fiction: Contact as the type specimen

The author treats Sagan’s Vega sequence as the clean­est Case II: an ampli­fied, Doppler-shift­ed replay of the 1936 Olympics (old enough to have reached Vega, cul­tur­al­ly damn­ing as humanity’s first call­ing card), then a ped­a­gog­i­cal primer from arith­metic and primes to a machine spec­i­fi­ca­tion. That turns an under-deter­mined SETI prob­lem into a con­struc­tion prob­lem. Strengths: The author address­es light-time direct­ly; the Olympic echo is a ver­i­fi­able “nonce” no nat­ur­al source or Earth hoax­er could fake; “they heard us first” is the psy­cho­log­i­cal payload.

The nov­el leaves open prob­lems: read­ers assert the ener­gy bud­get of such a direct­ed, infor­ma­tion-rich reply more than it proves it, and they under-deter­mine its motive (sig­na­ture, exis­tence test, moral mir­ror, bright­est file they had; machine as gift, invi­ta­tion, cohe­sion exper­i­ment, or filter).

Other variants

• Gunn’s The Lis­ten­ers: Capel­lan rebroad­cast of Earth’s leak­age; senders lat­er revealed extinct.
• Liu’s The Three-Body Prob­lem: “Do not answer”—a reply that acknowl­edges detec­tion and tries to enforce silence.
• Ear­ly pulp (Hamil­ton, Gallery): radio answer first, then the sto­ry slides toward visitation.
• Hypo­thet­i­cals: pure­ly math­e­mat­i­cal reply; warning/demand; auto­mat­ed bea­con of a dead civ­i­liza­tion; coor­di­nates or machine plans that open a path to Case III/IV; Clarke’s “The Sentinel”—an ancient arti­fact that, once trig­gered, trans­mits (bor­der of Case I and II, still pho­tons not ships).

Case II is a fam­i­ly of sce­nar­ios, not one plot: pri­or detec­tion of us, delib­er­ate EM reply, no phys­i­cal presence.

World-building takeaways

Delay is the engine: char­ac­ters must spend cap­i­tal while the sky stays emp­ty, and first con­tact becomes a con­ver­sa­tion with the past—who we (and they) will be when the pho­tons arrive. A ver­i­fied reply con­sti­tutes a civ­i­liza­tion­al event: gov­ern­ments, intel­li­gence ser­vices, reli­gions, and sci­ence all scram­ble over who may speak, whether to answer, and whether they should share or weaponize tech­ni­cal content.

Authors still have to choose: do they reveal a loca­tion? Invite dia­logue or send a one-way mon­u­ment? Does sig­nal pow­er imply a mod­est Type I shout or casu­al Type II infrastructure—and if the lat­ter, why isn’t the sky already full of arti­facts? The essay insists Case II stay inside the Fermi–Drake–Kardashev frame: one delayed mes­sage is a data point, not a reset that makes the qui­et sky irrelevant.

Close

Case II is the first moment the oth­er side demon­stra­bly knows we exist and says so. That is not friend­ship and not arrival; it is mutu­al aware­ness. Case III drops the dis­tance buffer: inter­pre­ta­tion becomes pres­ence, epis­temic risk becomes mate­r­i­al risk, and pow­er asym­me­try is hard to hide.

The five cas­es form a lad­der of increas­ing inti­ma­cy and decreas­ing con­trol. Macalester plans an orig­i­nal short sto­ry for each, using the case as pres­sure on char­ac­ter, pol­i­cy, and belief rather than as a label stuck on after the plot is done.

The full (long) ver­sion is here: Case II First Contact