Here’s a fun theoretical existential threat: false vacuum decay. If our universe is in a false vacuum state (maybe yes? maybe no? we don’t know!) and that vacuum someday suddenly shifts into a true vacuum state (decays), then worst case scenario this change propagates everywhere instantaneously and we experience “complete cessation of fundamental forces” including elementary particles and structures. Everything everywhere wiped out in a blink.
We can take some comfort in the fact that we’d never know it happened, and theorists have asserted that it’s highly unlikely a false vacuum of any size could exist for more than a moment in the presence of gravitational forces, plus physics within the bubble would be “super weird”, I think is the technical term.
Isn't "false vacuum state" equivalent to a non-zero vacuum energy ? Which we know is the case, because virtual particle pairs blinking into and out of existence ? Did I leave something important out ?
Supernova are powerful enough that even a star in a different solar system going nova can kill you, if it's a "nearby" system. But I believe there aren't any stars close enough that would go supernova any time soon.
A good premise for a sci-fi series: In the distant future, a large fleet of earth's best and brightest travels the stars while desperately trying to invent Earth's last ditch-effort to save its 12 billion inhabitants from a soon-to-be cataclysmic, near-earth supernovae: FTL travel. After decades of progress finally nears fruition, the fleet permanently loses contact with earth; humanity's home Solar System's remnants lost to the beautiful, nightmare... The fleet of 80,000 now works to save itself, the last of humanity.
Sounds like Battlestar Galactica without the Cylons.
Perhaps the story could have Cylons in it, but here they're allies with the humans, but after the supernova, some religious leader convinces most of them that their god wants them to destroy the humans.
Sounds like a cross over of The Age of Supernova and Tri-body Problem.
In the former Supernova radiation kills all people on earth except kids under 13.
Every star that is not our sun is in a different solar system.
Could you have meant to say a star in a different galaxy could toast us?
I think, ball park, a SN 500 light years out is considered safe e.g. Betelgeuse.
Our Milky Way galaxy is thought to be roughly 100,000 light years in diameter
so we should be safe from all but those within about a hundredth of the radius
of our galaxy from us.
