The 'Fermi Paradox' asks where all the aliens are. Surely, by now, our galaxy's earliest space-faring culture could have colonised every possible niche ? Faster or slower than light, there's been ample deep-time to do so at least thrice.

One long-standing suggestion was that planets were so few and far between, they could only be found and charted by visiting star-ships. Then 'Optical Doppler' found the first 'Hot Jupiters', and 'Transit' programs began racking hits. Within two decades, more than 5000 planets were spotted, often several to a star. And these were for just the fraction of stars with favourable alignment and/or placid solar activity, so there could be thrice as many unseen, perhaps more...

So, where are the aliens ?

UFOs ? Only 'Unidentified' if not 'Read In' to those [CLASSIFIED] projects and their oft-mischievous 'cover stories'. Mega-Mylar 'Weather Balloons' that secretly photographed wide swathes of USSR, sniffed fall-out from their nuclear tests ? Similar balloons lofting shaved mammals etc to the edge of space to study radiation and other hazards of space-flight ? Like 'Laika', some did not survive. 'Stealth' aircraft and [REDACTED] prototypes, some of which have subsequently 'broken cover' ?

Close Encounters ? Beyond the unpredictable effects of accidental ergotism, there's evidence geomagnetic storms, pulsed radar and such may induce 'fugue' states in the susceptible. Didn't that 'God Spot' Doc find tickling some folk's brains with 'Trans-cranial Magnetic Stimulation' triggered a profound 'Religious Experience' ?

So, where are the aliens ?

A plausible explanation for their absence was the 'Great Filter': Cultures wiped themselves out in wars before they could go inter-stellar, lacked the 'Outward Urge', or simply baulked at tackling the vast void, their projects 'Proxmired' by beset budget committees...

Here, Einstein had played with a notion called 'Teleparallel Gravity', but lacked the math to do it justice. A century later, it proved to have curious kinship with 'String Theory', culling most of that field's intractable, nigh-infinite zoo of variables. Then, young Patrick Smith, studying an obscure corner of high dimensions' geometry, serendipitously stumbled upon an arcane hack. His 'Smith Transform' broke the remaining log-jam, enabled a plausible version of 'String Theory', now with Gravity, too.

Electromagnetism took fifty years from Faraday's coils via Maxwell's equations to Hertz' tuned spark-gaps. 'String TG' needed but a decade before the famous paper by 'Wu, Li and Wen' described the first, clunky 'Field' hardware. It won them the Nobel Prize, but Ed 'Floater' Winters trumped those bespoke superconductors with Citizen Science 'Poles' you could build and run at home. Licensed them inexpensively, opened our Solar System. Then Pete Jones figured how to craft a 'Double Alcubierre Bubble', for FTL without nigh-infinite power or oodles of 'Unobtanium'...

'One Pole, null-g; Three thrust, five fly, Earth, Moon and Mars; Nine go to the stars !'

Research Ship 'Venture' did a 'Cook's Tour' of our outer solar system, planted a flag on Halley's Comet, fetched back Voyagers 1 & 2, which had finally run out of power. 'Venturer', whose name edged out 'Enterprise' and 'Endeavour', was much, much bigger, a true star-ship.

Optical Doppler predicted a 'terrestrial' planet in the Alpha Centauri / Proxima system. No-one expected to find a dead planet plus ample evidence of abandonment by a well-established, star-faring society. Wasn't obviously nuclear war, more like 'culture collapse': About five million years ago, the entire eco-system died, the atmosphere went anoxic.

Epsilon Indi ? A face-locked Mercury-analogue had been extensively mined, the 'Big Mars' was warm, wet, inhabited until five million years ago.

C'D-36 ? Extensive mining of asteroids and gas-giants' moons until, yes, five million years ago.

UV-Ceti ? Flare star, but its wide asteroid belt had been mined until...

Tau Ceti ? Eco-system, felinoid Sanku and mega-monotreme Saurs with a shared Iron Age culture, which had arisen in the five million years since...

Epsilon Eridani ? The system had been occupied, its now runaway-greenhouse 'terrestrial' planet habitable until, yes...

WTF ??

V's 'Second Mission', which surveyed the other side of our neighbourhood, found six more now-barren systems, all abandoned about five million years ago. Meanwhile, an urgent survey of Sol System found no evidence of 'Prior' use. None. Zilch. Nada. Nyet. Which raised more questions, mostly 'WTFFFF ???'

What happened about five million years ago ?? Well, the Earth looked much the same, albeit India and Australia were 250~~350 km to South, mere 'Tectonic Windage'. There were lots of mega-fauna, a zoo of hominoids and hominids. Had our space-faring neighbours left to give us freedom to develop ? There were indications those Sanku and Saurs evolved from feral pets...

Five million years...

Five million years...

Five million years ago, traces of supernova iron embedded in Antarctic ice.

Hmm. Wasn't that when Sol-system entered the 'Local Bubble' ? A near-cavity in our arm of Milky Way galaxy, its 500 light-year 'thinning' blown clear by a succession of supernovas, a bunch of big, new stars that had lived fast, died young ? Very fast, very young, some a mere million years from first light to mega-bang...

And, five million years ago, give or take, the slow galactic orbits of Sol, tau Ceti and many of our neighbours had crossed into that expanding zone. Given its storm-front was violent enough to spawn new star formation across a wide arc of sky, what would it do to high tech ?

Though not as 'hot' as a full-on 'Gamma Ray Burst', those have but a short duration. No, this would likely resemble Earth's 'Carrington Event' or the 'Quebec Storm', scaled to mega-tsunami. It would pulse lethally for decades, possibly millennia. No star-ship could endure such disturbed space. Those Priors would have seen the vast storm approaching, have ample time to shrug, pack their bags, leave, and keep going ahead of its inexorable spread...

So now we know: No Prior ETs, they've fled. Any neighbours have arisen since. In a couple of million years, Sol-system's orbit will overtake the storm-front, out-bound. Either we migrate back along the orbit, or figure how to cross the Great Firewall...

   Thank you kindly Nik! Nice one !

Stars, that lived fast & died young, ... sounds almost like James Dean, or almost like Paul Walker?

If aliens supposedly invented microwave ovens technology,   I wonder when we might get replicator technology, like in Star Trek, ... instant 3D printed bowl, with instant 3D-printed chopsticks, in 3D printed 2-second noodles. Truly fast food .

From what I last heard, there are some '3D printed' foods. Like, you just fill it with liquid ingredients (as if it were ink), & it 'bakes' the food for you.

Too many artificial stuff, if you ask me, ... we need less preservatives, & more naturally grown fruit & veg.

Which leads me to my next thought. In most sci-fi stories, you never see or hear about how aliens eat. If they don't use their mouths for communication, then what do they use them for?

What if the alien races, dies out from starvation? If they mined out the planets, causing erosion, leading to dust storms, infertile ground contaminated with toxic solutions used to purify the minerals.

Or a swarm of alien locusts, which migrate from planet to planet, plagued them & ate all the plantlife?