This universe, or the next, could kill us at any moment.

While popular fiction is glutted with robot uprisings, zombie plagues, and apocalyptic warfare, none of our fictive inventions match fundamental physics for terrifying beauty and finality. To remedy any troublesome optimism or hope you may experience this fall, Engineer Jobs is pleased to present three cosmic disasters which could strike at any moment.

Gamma Ray Burst

Peeling back the layers of Earth’s history, we find five distinct biotic crises in her past. These mass extinction events signal massive disruptions in the biosphere, with catastrophic loss of life against a background of climatic upheaval.

While there are respectable arguments for the existence of more than five major biotic crises, the second most severe, according to the Raup-Sepkoski classification scheme, took place 440 million years ago, at the boundary of the Ordovician and Silurian periods. Over the course of 1 million years and two distinct spikes, somewhere around 70% of all species, 27% of families, and 57% of genera went extinct. (For comparison, the “background” extinction rate is two to five genera every million years or so.) Second only to the Permian-Triassic event (the “Great Dying”) in loss of life, the Ordovician-Silurian extinction event is one of the most terrifying and comparatively sudden waves of mass death in the history of Life itself.

The possible culprit? Ten seconds of intense gamma ray exposure.

How Gamma Ray Bursts Kill

When a sufficiently massive, rapidly rotating population III star collapses into a stellar black hole, a jet of high-energy particles and gamma rays is released along its axis. (There are other possible scenarios that yield comparable outputs, such as a collision of super-massive black holes, but the results are similar and the physics dense.) These gamma ray bursts are the most energetic events in the known universe, up to fifty times as energetic and twenty times as luminous as your typical, garden variety supernova. While they are narrowly targeted, in cosmological terms, anything in their direct path is in for the worst minute of its life.

In “Did a Gamma Ray Burst Initiate the Late Ordovician Mass Extinction?”(pdf), the authors use atmospheric modeling to demonstrate that a ten second gamma ray burst, originating 6,000 light years away, would create the conditions observed in the Ordovician-Silurian event.

The wave of energy strikes Earth’s atmosphere, breaking atmospheric nitrogen into free atoms. This starts a chain of global ozone destruction – N2 to N, which reacts with O2 to form NO, destroying ozone (O3) to form nitrogen dioxide, which interacts with molecular oxygen to form more ozone-depleting NO. Within weeks, according to atmospheric models, half of the ozone layer is destroyed and the planet covered in nitrogen smog. Recovery of the ozone layer takes upwards of five years, during which the surface is subject to massive amounts of UV radiation and an incredible, rapid, sharp drop in global temperatures. The resulting Ice Age plays havoc with sea levels (at the time, almost all life lived in the shallows), as entire oceans recede, return, and recede again until stability returns.

In short: everything but deep-ocean life freezes and fries, for years. Anything on land or in shallower waters starves, cooks, dries out, freezes, or simply dies of UV-radiation exposure.

A similar pulse today would leave us starving, cold, and riddled with cancer. Society would almost certainly collapse in an orgy of violent competition for food and resources; survivors of the resulting wars, deprivation, and cancer plagues, if not sterile, would spend generations burning the wreckage of human civilization for heat while praying dimly for another chance.

Opportunistic deep ocean life would thrive, radiating into new niches and possibly, eventually, returning to land revealed by retreating glaciers. You, I, and everything we were would be reduced to trace minerals and a curious layer of polymers in the geological record.

Compared to, say, heart attacks and asteroid strikes, the odds of a sufficiently powerful gamma ray burst striking the Earth are vanishingly small. It’s happened before, of course; the Ordovician-Silurian event remains hypothetical, but it’s not the only observed strike. A comparatively minor extinction event in the Pliocene can be traced to at least one supernova in the Scorpius-Centaurus OB association, and energy from GRB 090429B hit us more or less directly a few years back, though from too far away (13.14 billion light years) to cause noticeable damage. While gamma ray bursts occur every day, they are usually too distant to matter or are aimed elsewhere.

Rogue Black Holes

While the formation or merger of black holes could lead to show-stopping gamma ray bursts, another possible consequence of ancient mergers is the creation of intermediate-sized (1 to 100,000 Solar masses), wandering black holes. Should their trajectory intersect ours, the consequences would be inexorable, fatal, and spectacular.

In “Star Clusters Around Recoiled Black Holes in the Milky Way Halo”, O’Leary and Loeb demonstrate how relics of our galaxy’s formation could remain in its periphery, traveling with captive stellar clusters… or possibly alone and undetectable.

Before the formation of the Milky Way galaxy, stars were gathered in sparse, dwarf galaxies. The collision and accretion of these galaxies eventually created our current neighborhood, in a process broadly similar to the accretion of planetary bodies and moons. As these galaxies collided and coalesced, however, the gravitation wave emissions from interaction between their core black holes could have proved sufficient to accelerate one or both to the escape velocity of its original galaxy… but not the Milky Way itself.

In its halo, the authors describe a Milky Way surrounded by ancient rogues, some trailing a tight stellar cluster (<1 pc) pulled into its wake as it escaped its home galaxy. These clusters – which O’Leary describes as “lighthouses” – would be difficult to distinguish from single stars without spectral analysis or extensive observation (as their speed and trajectory would reveal the additional unseen mass of the rogue black hole).

As black holes are invisible without active accretion – unless “feeding”, to wax poetic – we must trust the author’s math that such ancient rogues aren’t found anywhere near the Earth, even in cosmological terms. What would the end look like, though, should a rogue head our way? Without its lighthouse cluster, would we notice its approach in time to fire off a memorial probe at our nearest neighbors?

How Rogue Black Holes Kill

The approach of a rogue black hole would be marked by the X-ray bursts of accretion events, as it trapped and devoured smaller masses on its way to end life on Earth. High-energy observatories would capture these energies, no doubt putting the pieces together in time to create global panic.

(Imagine, if you will, the trail of X-ray sources leading inexorably towards us, from the edge of intergalactic space. Certainly, we would observe and understand such a phenomena in time to do… something?)

Once the rogue reached the Oort cloud – roughly 5.91 billion km away – we would have a little less than eighteen days (422 hours) to appreciate our coming deconstruction. As it tore apart the gas giants, their gaseous atmosphere would glow with friction, accompanying the invisible X-ray bursts of mass being pulled into the singularity. A blurry new star would be visible on clear nights, growing brighter and closer as the days passed. Then, it would be our turn.

A black hole devouring a star is a sight best appreciated from another star system. Tidal forces tear the star apart, surrounding the black hole with a nimbus of super-heated hydrogen (friction, again) as it consumed the outer layers. Distant observers could track our sun’s demise through spectral analysis: first the hydrogen, then helium, then… perhaps a final flare of X-rays. The debris of our solar system would trail the rogue through interstellar space, a cold and dark analogue to O’Leary’s lighthouse clusters.

Someone or something, in a star system far away, would write a paper on how lucky they were to observe the process.

Image Credit: Adam Evans

Vacuum Decay

Our universe depends on certain constants in its underlying quantum structure, which give rise to physics, chemistry, and every aspect of the reality on which we depend. But what if we exist in a transitory, high-energy state? Collapse into a more stable, low-energy vacuum entails a complete, instantaneous rewriting of our universe’s physical constants; in essence, reality would be wiped and re-emerge as a consequence of an entirely new physics.

Whether or not we exist in a stable vacuum state – i.e., atop a more or less permanent basic reality – remains to be determined. Calculating from the masses of the Higgs and top quark, it should be possible to determine whether our universe runs on top of a false vacuum (a transient, high-energy state, doomed to inevitable decay), a metastable vacuum (enduring within a range of conditions, but subject to possible disruption), or a true one (a stable set of constants emerging from an indefinitely sustainable background energy level). More precise measurements of top quark mass will settle the matter, but it appears likely our universe is the result of constants emerging from a metastable vacuum; reassuringly solid, unless poked just… so.

Should we exist in either a false or metastable vacuum, the end of Universe 1.0 is mathematically assured. Either through random perturbations in vacuum, or the encouragement of tunnelling effects through a concentrated, high-energy event, a bubble of Universe 2.0, running atop a true vacuum, will eventually nucleate and spread.

For all we know, it’s happened already.

How Vacuum Decay Kills

Once Universe 2.0 comes into existence, the energy imbalance between its vacuum and ours will feed its expansion at nearly the speed of light. Given the rate of expansion, distances involved, and our inability to observe the bubble’s propagation, it is entirely possible that Universe 2.0 is already on its way. As nucleation through tunnelling effects is necessarily random, 2.0’s origin point could be anywhere in the space currently occupied by 1.0. The odds, therefore, are well against local instantiation; an oncoming bubble of vacuum decay will more likely take billions of years to swallow us.

As the wall of the bubble advanced through our solar system, however, it could prove impossible to observe its approach. The expansion of its borders at light speed would necessarily involve immense kinetic energies and gravitational effects, but whether or not observable effects could propagate to us through Universe 1.0 in time to be noticed is another matter. “Observable effects” seems a dry way to address the spread of stress fractures through a dying reality, but the process is so far outside of human experience, so terminally without context, that description may prove impossible.

We will never see the border itself, nor across it into the new reality. From one instant to the next, the very physics on which we depend will cease.

And that will be that.

Share your favorite esoteric worst-case scenario in the comments, or tweet @EngineerJobs.