I’m expecting neo to return to the source any day now.
By “how the world ends,” do you mean “extinction of human life on Earth,” or do you mean “Earth ceases to exist in any recognizable form?”
I’ll give my odds on the former:
K-T Extinction (human) via comet/asteroid: 90%
Deadly pathogen (virus, bacterium, prion) evolves naturally and wipes out human population: 8%
Dealy pathogen (virus, bacterium, prion) is created in a laboratory and accidentally or intentionally released on human population: 1%
Rogue black hole (or similar astronomical event): .25%
Starvation due to inability to cultivate food as a result of climate change: .25%
Thermonuclean annihilation: .25%
Wrath of a vengeful diety: .25%
I’d put my money on deadly pathogen. Once we reach critical mass of overpopulation, starvation, and no fresh water, that’s a pathogen’s playground.
I strongly doubt that a comet or asteroid on the scale of the one that caused extinction events in the past would actually end humanity. It could easily end civilization as we know it, but we’re an incredibly scrappy species. A big-enough comet or asteroid could do so.
My money is on being outcompeted by our own creation. Either AI that decides it wants us gone, or a mistake in some bio or nanotech lab sometime in the future.
I think a full-scale nuclear attack could do it, depending on how dirty and widespread the fallout from it is.
Natural pathogens tend to be self-limiting for the same reason that predator populations don’t grow exponentially; because growth is limited by the topology of vector (or predatory) manifolds; in other words, when enough people start dying (or prey populations reduce) the ability of a pathogen (or predator) to expand is highly restricted. Obviously engineered or enhanced pathogens that are dispersed by artificial vectors can exceed the constraints on natural vectors, but the reality is that it is very difficult to effectively weaponize pathogens. Pathogens need us to survive, and the more virulent pathogens just don’t survive long enough to spread widely (e.g. the hemorrhagic fevers).
Stranger
Biological warfare. Some terrorist outfit is going to come up with The Satan Bugor its equivalent and turn it loose.
illudium Q-36 explosive space modulator - even money.
The odds of a coming Zombie Apocalypse are rapidly approaching 1.
What you need is a highly contagious, highly infectious pathogen that allows infected people to travel around for a couple of days before putting them down with the actual illness.