[EvaH (OP)]

Dean asks:

How long could humanity survive if the sun went out?

What do you think?

[Bored chemist]

I'm guessing, about as long as the nuclear submarines can stay underwater.

[CliffordK]

All heat wouldn't disappear overnight, but within a few days the Earth would be plunged into sub-zero temperatures.  And, within a month, perhaps down to a few degrees Kelvin. 

Geothermal energy would last for quite some time.  So deep mines and caves would offer substantial protection potentially for years. 

Growing new food would become a major problem, but say there were a few thousand survivors, they might be able to scavenge food for decades.  Likewise, the oxygen/CO2 cycle would be problematic, but our existing atmosphere could support a small group of survivors for a very long time.

Planning would be key, so if given years or decades warning, people could dig underground, store supplies, build robots,etc.  Ensure longterm nuclear power.  Of course, it would be better for longevity of the planet if the survivor numbers were kept low.

[alancalverd]

I'd vote for the nuclear subs. Everyone else will start killing one another within a few weeks.

[Petrochemicals]

Theres humanity and the greater human populace, nuclear reactors in the sahara should sustain us inevitably.

[Kryptid]

Theres humanity and the greater human populace, nuclear reactors in the sahara should sustain us inevitably.

I'm not entirely sure what you mean by this. Did you mean "indefinitely" instead of "inevitably"? I suppose, in principle, nuclear reactors could supply the energy needed to give light and warmth to greenhouses in order to grow crops (because all plants outside would die pretty quickly). However, what kind of head start would you need in order to pull that off effectively? If sunlight stopped in an instant, you'd be pretty hard-pressed to build a nuclear-powered greenhouse in time to supply a self-sustaining population of humanity. The vast majority of people would die pretty quickly due to some combination of starvation and freezing. Eventually, even the atmosphere itself would become cold enough to condense. Our prospects would be pretty poor.

[evan_au]

if the sun went out?

Are you implying that it goes out with a bang or a whimper?

If it went out with a bang (supernova), even a nuclear submarine would not protect you - the oceans would boil (and the prompt neutrinos would get you too).
- Fortunately, with what we know, the Sun will not go out with a bang

If the Sun  goes out with a whimper (eg red giant, then white dwarf), we will have plenty of warning to go elsewhere before the oceans boil dry (billions of years - assuming we last the next 1,000 years!).

If the Sun gets snatched away from us (eg nearby passage of a stellar-mass black hole flinging us out of the Solar System), the earthquakes would destroy most things on land, but the nuclear submarine option might keep you going for a few months...

This is the way the world ends
This is the way the world ends
This is the way the world ends
Not with a bang but a whimper.

[ProfNewton22]

Hey there,
if I had to say a definite number I'd say at the latest after a couple of years. The first problem would be that the temperatures would drop to a critical degree, where it's hard for humans to survive. Photosynthesis would stop, since there's no more light that the plants could use. This would cause death for many plants, who provide us with oxygen. Further the oceans would freeze due to the cold temperatures. That would ruin a lot of ecosystems... All in all we'd be dead for sure 
But luckily there's no sign of the sun disappearing anytime soon.
Greetings!

[gem]

Hi all
Humanity wouldn’t last one night !

[evan_au]

Humanity wouldn’t last one night !

I don't know about where you live, but around here, the Sun goes out every night.
- And nearly all of us are still here the next morning!

Of course, if the evening news reported that the Sun had gone out just after dusk, that might set off a bit of a panic!

[gem]

Good day sport. Evan _au

I believe whichever way you look at it my post is correct,
I will leave you, to go figure. 🙃

[TommyJ]

The heat humans could keep, using energy of the Earth itself (e.g. power supplied chambers).
But not only temperature will go down. The atmosphere will change, the orbit will change. If at that time no technology comes that can keep a human thousands of years alive, humanity will instantly disappear.

[Eternal Student]

Hi.

the orbit will change.

   We may need some discussion on that.  The sun went out, it wasn't stated that it lost mass.

The rest of it could be a little more cheerful but ... C'est la vie.

Best Wishes and stay well.

[TommyJ]

We may need some discussion on that.  The sun went out, it wasn't stated that it lost mass.

The rest of it could be a little more cheerful but ... C'est la vie.

I like to dig for more optimistic evidences

The discovered exoplanets have brought data that by calculations and simulations made surprisingly show that in rare cases survivor planets may remain bound to the supernova remnants, finding new orbits around the neutron stars or black holes left behind by the explosions.
There are studies showing that climate, geodynamical, and biogeochemical processes might be able to keep life, having oceans with thermal vents, where energy flow may still be enough.
Based on physics, calculations and simulations show that even a small planet would not be destroyed mechanically. Also a planet won’t be bounced from  it’s orbit due to the momentum of an exploding star. If a star loses too much mass, a planet would leave. Also, if a star's collapse is asymmetric then the star itself can leave the planetary system.

According to the model, when stars at least 7 to 10 times the mass of our sun go supernova, the blast swallows any inner planets, those orbiting out to several times the distance between Earth and the sun.

The Earth might remain habitable in certain conditions, e.g. the Moon survives as well and provides tidal heating.
Other suggestions, as already mentioned in this discussion, are that the Earth will get frozen through several weeks. Not humans, but microorganisms might survive millions of years.

Another glimpse to survival is that another solar planet or moon may become habitable for humans.

[yor_on]

I would say that the submarine would stay there, in a very uncomfortable state, for a very long time.
 It gets quite cold after a while :)

[Bored chemist]

I would say that the submarine would stay there, in a very uncomfortable state, for a very long time.
 It gets quite cold after a while

They might be OK if they can find some thermal vents to keep them warm.
But I think that wouldn't last forever.
It would probably outlast the crew.

If half the crew killed the other half then the stores would last (slightly more than) twice as long.
Calling that "humanity" would be debatable, but the only people left alive to debate it...

[yor_on]

I think you're on to something there BC.

:)

[Origin]

I'd vote for the nuclear subs. Everyone else will start killing one another within a few weeks.

Once the oceans freeze, which won't take too long, a sub is not going help.  When the atmosphere freezes that is going to ruin everybody's afternoon.

[Bored chemist]

Once the oceans freeze, which won't take too long,

Bits of the oceans are "boiling" hot- over 100 C* heated by geothermal energy which isn't going to run out quickly.

* (They don't actually boil because the pressure is so high)

[Zer0]

Hello Dean.

From a Very different perspective...

Humanity might cease quickly, but Life hmm might go on.

PS - So wat if d Garden getz bulldozed...Seeds are meant to be buried.
👍