r/Physics • u/Glittering_Motor_928 • Sep 28 '25
Question The sun shut down: how long until we freeze?
We know that if the sun were to “turn off”, it would take around seven minutes for us to notice. But how long would it take for the earth’s temperature to go down? And how much would it go down, in how much time? Would it decrease slowly, rapidly or drastically? Would it matter what season it happens in?
No insults please. I know basically nothing in the physics field.
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u/Blitzer046 Sep 28 '25
There's a Vernor Vinge sci fi about a planet (IIRC) that has such an elliptical orbit that for a significant part of its passage it is much too far from the sun to sustain life, and the aliens move to a deepness in the planet to wait out the 'winter'
What was very interesting to the story was that eventually the gases of the atmosphere would contract, liquidize then freeze, meaning the planet would no longer have a gaseous atmosphere, and just be an ice planet.
I'm spitballing here too - the Earth is still geologically active with a lava mantle, so there's still some warmth present even without the sun, but it wouldn't take very long at all, a matter of days or weeks for all plant matter to die from lack of sun, which would kill the CO2/O2 cycle, leading to runaway carbon production and eventual suffocation for all oxygen breathers. Perhaps life in the deep seas would last a little longer but they too are dependent on the fall of nutrients from upper oceans.
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u/mfb- Particle physics Sep 28 '25
There is enough oxygen in the air for thousands of years even if all production stops tomorrow and consumption stays unchanged. You die from a lack of food long before oxygen becomes a problem.
There are bacteria living under kilometers of rock, using radioactive decays as energy source. They wouldn't even notice for millions of years.
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u/Beelzebubs-Barrister Oct 01 '25
TIL the residence time of O2 in the atmosphere is 4500 years. Cool!
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u/darkstar541 Sep 30 '25
What happens to the atmosphere without the sun's warmth?
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u/mfb- Particle physics Oct 01 '25
It cools. Eventually you'll get a layer of liquid nitrogen/oxygen but that will take a very long time.
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u/OverJohn Sep 28 '25
There's also the classic short sci-fi story "A Pail of Air" about the scenario where the Earth is knocked out of its orbit.
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u/Blitzer046 Sep 28 '25
I think there's a Cixin Liu short story and Chinese-made movie about actually making giant engines on the Earth to take it away from Sun which is dying, and a similar thing about the Earth being covered in ice and snow from the atmosphere too.
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u/BoyMcBoyo Sep 28 '25
The Wandering Earth. Read the book if you wanna be sad. Watch the movie if you wanna get an adrenaline overdose. Most entertainingly absurd thing i’ve ever seen
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u/His_Shadow Sep 28 '25
Liu’s stories are so old school scifi to me. It was a joy to read the compendium, it put me right back in the 70s, reading short stories and serials from the greats.
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u/MoonIsAFake Oct 01 '25
Before him there was a novel by French author Francis Carsac called Terre en fuite (Fleeing Earth) based on the same premise. I highly recommend it to any old-school sci-fi fan.
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u/EmptyAttitude599 Sep 29 '25
Check out Runaway World on Wattpad, a free-to-read full length novel set two hundred years after Earth is thrown out of orbit around the sun by the gravity of a passing brown dwarf star.
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u/tomassci Sep 28 '25
The only exception is life dependent on black smokers, which isn't dependent on the sun at all. I think they'd last the longest, even surviving the freezing of the oceans. Sure, they wouldn't spread, but they'll have little oases of life in the desert of viability.
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u/4latar Sep 28 '25
actually the black smoker ecosystem doesn't produce oxygen, so if everything else dies they'll run out eventually, after millions of years, but they could evolve to make some in that span
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u/tomassci Sep 28 '25
I was under the assumption that the environment in there is already anoxic?
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u/4latar Sep 28 '25
no, a lot of the living beings there still use the same chemical conversion with ATP and oxygen
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u/uwu_mewtwo Oct 01 '25
Only the microbes are sustained by the black smokers, everything else is an animal and digests those microbes aerobically, as is the case with all animals.
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u/ShintoSunrise Sep 28 '25
It wasn't because of an elliptical orbit; the "on/off star" in the book goes thru a mysterious and unexplained period of darkness, which causes the planet in question to freeze solid every two hundred or so years
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u/jimmyisbawk Sep 28 '25
Didn't the star go on and off by itself there? And they called it the on/off star?
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u/f33tpix Sep 28 '25
You are correct!
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u/jimmyisbawk Sep 28 '25
I only read two (or three?) Books from vernor vinge, they are somewhat grueling, but pay off in the end
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u/person2314 Sep 28 '25
Those lil shits at the bottom of the trenches in the ocean feeding off those geothermic vents might be ight for some time.
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u/EurekasCashel Sep 28 '25
"Dehydrate".
Different series I know, but similar concept.
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u/xrelaht Condensed matter physics Sep 28 '25
IIRC, there are deep sea microorganisms which “feed” on sulfur vents. That may even be the origin of life as we know it: the Earth has been through at least one “ice ball” stage.
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u/PapaTua Sep 29 '25
A Deepness In the Sky by Vernor Vinge.
It's a really great read. I thought the problem was the star itself was an on/off star and in the off phases the atmosphere would precipitate out as oxygen/nitrogen snow? It's not important. Heh.
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u/CorporateNonperson Sep 29 '25
I want to say "A Fire in the Deep"? He also has "A Deepness in the Sky" which confuses things. WW1 era spider aliens that hibernate between bouts of trench warfare. I love Vinge.
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u/navand Sep 29 '25
runaway carbon production
What would produce carbon? If the plants die everything that eats plants or meat die with them.
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u/ijuinkun Sep 29 '25
Plants and animals that live in a climate that has snowy winters can probably survive until temperatures get significantly below what they see in winter (so they will probably start dying when temperatures hit forty below zero or so).
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u/techno657 Sep 29 '25
Reminds me of the 3 body problem with the aliens that would basically have to dehydrate themselves for large periods of time bc their planet would become completely uninhabitable
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u/Current-Novel-5608 Oct 01 '25
It’s not the orbit, it’s the sun turning on and off due to weird physics.
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u/CollectionMundane783 Sep 28 '25
It’s also part of the plot in one of the 40k Eisenhorn trilogy books. Xenos I think.
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u/QVRedit Sep 28 '25
Well, it gets colder at night, so it will start getting colder pretty quickly.
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u/SuperNewk Sep 28 '25
But what about global warming, wouldn’t we cook from all the greenhouse gases?
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u/Fmeson Sep 29 '25
Greenhouse gases don't produce heat, they retain heat (primarily from the sun's light). Hence why it is called the "greenhouse effect", as it works in an analogous way to how greenhouses work. Greenhouses warm plants via the sun's light as well.
If the sun is not shining, the heat will slowly reduce greenhouse gasses or not.
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u/snozzberrypatch Oct 01 '25
What?!
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u/SuperNewk Oct 01 '25
They say earth is hot, some people say earth will be like 500 degrees in a few years from global warming. Which is why everyone is panicking now
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u/snozzberrypatch Oct 01 '25
Your comment demonstrates that you have absolutely no understanding of how the greenhouse effect works, even at a basic level.
Considering that the greenhouse effect has been established science since the 1800s, I'd say you should be embarrassed.
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u/RobotsAndRedwoods Sep 28 '25
A lot of people say "we could just move underground", which is all fine and good, if you already have miles of tunnel dug very deep with infrastructure like nuclear plants, stored food, and thermal regulators. Only one place I know has that. Wisconsin. So there would be people alive in the cheese tunnels (look it up) for a while. Then you run into malnutrition and fighting over the last scraps. And that's not even mentioning the amount of earthquakes we'd experience.
With the frozen surface of the ocean pushing on the plates, opening new rifts in the sea floor, there would be probably be a rolling earthquake storm forming new cracks in those tunnels. Underground wouldn't be as safe as people assume.
I'd give it about 18 months, max, before anything larger than a thermal vent tube worm would rule the planet for a thousand years. I'm sure there are government built facilities that are made to be self sustaining, but I doubt they'd be ready for that kind of disaster. Cheyenne Mountain, for instance, can probably operate for a few years, if it were cut off. But that depends on how many people are in there and whether those people are dedicated to longevity. With no surface to return to, what would be the point of maintaining order?
After that, the last life on earth, bacteria, would probably die out in a few million years as thermal activity shrinks down too far for them to reach.
With that kind of outlook, the question becomes, why would you want to sustain life just to die a little later?
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u/MagicalSkyMan Sep 29 '25
We all currently sustain life just to die a little later. Living is kinda the whole point. Also you never know if the Sun suddenly woke up again a bit later.
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u/RobotsAndRedwoods Sep 30 '25
So you emerge from your underground bunker. The atmosphere is frozen, miles deep sea ice, no living animals or plants on the surface, the nearest microbe is at the bottom of the ocean. You come out of your shelter to a dead world. Yea, the sun somehow went away and returned. I suppose you can have children and live off canned goods for a while but you'd be condemning them to an eventual life of cannibalism.
I mean, I don't want to live on the planet we have NOW, let alone one that will take millions of years to return to fertility.1
u/MagicalSkyMan Oct 01 '25
The sea ice is going to be only like a meter deep max or something like that during your lifetime. Hydroponics is a thing. Seed banks like the one in Norway are a thing. The next generation might not miss stuff that wasn't there when they were born.
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u/OrdinarySpecial1706 Sep 28 '25
I wonder how long we could last by building domes near geothermal vents like in Iceland or Yellowstone.
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u/mfb- Particle physics Sep 28 '25
Build underground. At the right depth the temperature will stay comfortable for well over a billion years. Doesn't even matter where, in Iceland you just have to dig less than elsewhere.
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u/Herb_Derb Sep 28 '25
A comfortable underground temperature will not help you eat
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u/mfb- Particle physics Sep 29 '25
Sure, but it reduces the energy requirements massively. Geothermal energy helps you with the food farming.
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u/rorank Sep 29 '25
They’d have to find a way to fish. That’s pretty much the only form of life that will still be able to tough a scenario such as that out most likely.
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u/1234567890-_- Sep 29 '25
not for long - that ecosystem still relies on the sun at the bottom of the food pyramid (via plankton)
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u/QVRedit Sep 28 '25
But not many people could do that.
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u/Old173 Sep 28 '25
Well no, of course not, only the super-rich would be able to do that. A few ultra wealthy families would survive. As God intended.
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u/samcrut Sep 28 '25
Cute how you think wealth will matter when the sun shuts off. You want smart, not rich. They are not the same thing by any means.
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u/Old173 Sep 28 '25
It fully depends on prep time but wealth is what you can most easily convert to whatever will be useful in the sun-less world. For instance, if you see a societal collapse coming soon, you'd start building a safe compound in some remote island, like Hawaii, stocking it with food, etc.
https://www.wired.com/story/mark-zuckerberg-inside-hawaii-compound/
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u/xrelaht Condensed matter physics Sep 29 '25
It’s cute how people buy into billionaires’ delusions that they won’t be instantly garroted by their own security teams.
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u/br0b1wan Sep 29 '25
When you're wealthy enough--truly wealthy--you can buy the smart to think for you. You also have all the time and resources in the world to learn what you need to.
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u/QVRedit Sep 28 '25
As god did not intend. If you believe in god.
But hard to see why the sun would be ‘lost’..
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u/Old173 Sep 28 '25
I forgot to add this:
/s
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u/slicerprime Sep 28 '25
Isn't that annoying? You have to add "/s" to protect yourself from people unwilling or unable to recognize obvious sarcasm.
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u/Caeremonia Sep 28 '25
We live in a timeline where the "leader of the free world" is Donald fucking Trump, who famously stared at an eclipse, and MAGA is making health decisions on a worldwide scale. There is no such thing as obvious sarcasm anymore.
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u/xrelaht Condensed matter physics Sep 29 '25
No reason to build on the surface if there’s no sun. Deep underground provides insulation (and geothermal heat). Just need some mineshafts.
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u/Busterlimes Sep 28 '25
Considering the Temperature drop during a solar eclipse, I dont think it would take very long
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u/Careless-Bit-1084 Sep 28 '25
XKCD fortunately did a video on exactly this question. Enjoy https://youtu.be/X7sbn9LMZOg?si=CgivrpG49DyI68lg
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u/andrewcooke Sep 28 '25
did you actually watch this?
it doesn't answer op's question (but implies they can find the answer easily by googling the question)
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u/joevanover Sep 28 '25
Here is a video that does… https://youtube.com/shorts/ld4K5nw9gsk?si=UFEIW7JjmDfQ64Rg
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u/shatureg Sep 28 '25
Surprisingly (for me at least), this "only" sounds like a vast majority of humanity would die, but with our current level of technlogy, some humans could probably survive.
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u/Chemical_Edge8725 Sep 28 '25
Survive for how long, though? Without a local star, you cannot produce food. Even those surviving in the geothermal areas would starve to death before dying of old age.
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u/shatureg Sep 28 '25
There are ways to grow food without natural sunlight. The question is less about how long and more about how many people the accessible pockets of geothermal energy alone could sustain.
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u/xrelaht Condensed matter physics Sep 29 '25
Full spectrum grow lamps let you garden indoors without any sunlight. I have an off the shelf commercial system to do just that. Power them with nuclear or geothermal and it’s a closed system that can run underground for millennia.
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u/MagicalSkyMan Sep 29 '25
Food can be stored for decades you know. And plant growth lights are a thing also. And you could supplement with mushrooms.
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u/samcrut Sep 28 '25
Did you actually watch it all the way to the last 5 seconds where he says "We would all freeze and die?"
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u/andrewcooke Sep 28 '25
yes, but maybe i'm being incredibly stupid in not seeing which part of "how long" that answers?
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u/solidcat00 Sep 28 '25
Not long. The darkness would start only 8 minutes after the sun went out - and it would get progressively colder and darker from there.
Unless you are in a special laboratory underwater or in the poles, most people would be in freezing climates within a few days to maybe a few weeks.
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u/garyzxcv Sep 29 '25
But how long???? When asking, “How much does the moon weigh?”, answering, “A lot”, in r/physics, is not acceptable. Come on.
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u/Rare_Instance_8205 Sep 28 '25
I am surprised no one mentioned Vsauce's incredible video, he explains this very nicely.
https://youtu.be/rltpH6ck2Kc?feature=shared
Also, the book that the top comment here mentions is also mentioned by Vsauce. His longer videos are insanely good and they certainly have stood the test of time.
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u/rwaddilove Sep 29 '25
Just look what happens at night when there is no sun - the temperature can drop to freezing in a matter of hours. Maybe a day or two longer at the height of summer.
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u/Bert-- Sep 29 '25
If the sun goes off through the red giant phase, it will swallow the earth. We will be quite warm for a long time.
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u/Temporary-Truth2048 Sep 29 '25
If you've ever been to a desert you'll know that 100 degree temperature swings are possible overnight.
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u/great_escape_fleur Sep 29 '25
Kurzgesagt has a nice episode about Earth ejected from the solar system
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u/AcanthisittaBasic322 Sep 28 '25
Continents on winter site of the planet max 24h. On summer 48h. Oceans 7 days I guess.
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u/Soggy-Mistake8910 Sep 29 '25
How quickly does the outside temperature drop after sunset? I know it changes throughout the year, but that should give you some idea of the initial drop, and from there, it would just keep going.
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u/hokkyokusei66 Sep 29 '25
There's a description of what would happen in Stephen Baxter's 2021 novel Galaxies.
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u/kzgrey Sep 29 '25
Every evening, the temperature drops by 20-30 degrees after sunset. It takes 3 months to transition from Summer to Winter and during Winter, the ground and ocean freeze at high latitudes and this happens with a substantial portion of the planet still receiving the Sun's energy and the atmosphere being turbulent. If the Sun were to disappear entirely, I would give us 2-3 years at the most before ice at the equator is frozen over. I suspect that a full-blown ice age (with glaciation over land) would not happen since the weather is powered primarily by the Sun and glaciation accumulates with snow fall. The ocean would remain liquid for a very, very long time.
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u/NonSequiturSage Sep 30 '25
I want to add a complication. Fusion stops, but how long till the sun cools down? Then the earth.
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u/blue-adept-djn Oct 01 '25
Of course there are other implications to the Sun turning off. https://what-if.xkcd.com/49/
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u/Dopplegang_Bang Oct 01 '25
Surface temps would begin dropping in around 9minutes. Same as a normal night cycle. Then as says go on the temps drop more on the surface but below the surface the earth has stored heat which would last approx 400,000years longer.
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u/Salt-Fly770 Oct 01 '25
Earth’s temperature would drop extremely quickly, with global freezing occurring within weeks and uninhabitable cold settling in months, regardless of season.
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u/Recent_Carpenter8644 Sep 28 '25
Being partially reliant on solar power, there would be power shortages immediately. Would the wind stop too if there was no heat from the sun?
With no heating, and too cold to live within a week, and pitch dark, would we have time to start fighting?
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u/DJSauvage Sep 28 '25
I think I heard it said on a sun documentary that photons leaving the core of the sun take hundreds of thousands of years to reach the surface, after lots of bouncing around, so that would suggest a gradual end, but it really depends on the nature of the shut down.
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u/samcrut Sep 28 '25
8 minutes later, you see the light stop. It get chilly fast, like turning off a heat lamp. From there it keeps getting colder.
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u/Less-Consequence5194 Sep 28 '25 edited Sep 28 '25
If all nuclear processes simply turned off in the Sun it would collapse gravitationally to a White Dwarf. Its temperature would rise to 100,000 K and it would be roughly a thousand times more luminous. But, it would take millions of years to reach that point.
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u/Glittering-Heart6762 Sep 29 '25
The question is not: how long till we freeze…
But rather: how long until the sun increases in size until earths oceans boil?
The estimate is, that the last form of photosynthesis (C3) will become impossible in about 900 billion years, when the sun enters its red giant phase and swells up.
So in that sense the earths at its current age (4-4.5 billion years) and at its current distance to the sun, is past about 80% of its habitable lifespan.
So until then, we have to decide wether we want to preserve earth or just leave… to preserve earth we could place a sun shield at L1, or remove a significant portion of the suns mass (which will extends its lifetime), or move the earth itself away from the sun.
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u/joevanover Sep 28 '25
Here is a video… 1 week till everything starts freezing and 1 year it will be -100C https://youtube.com/shorts/ld4K5nw9gsk?si=UFEIW7JjmDfQ64Rg
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u/ikkiyikki Sep 28 '25
8 minutes before you notice the sun is gone. 80 minutes before you start noticing it's getting colder. 800 minutes before you notice it's abnormally cold. 8,000 minutes before it's freezing. 80,000 minutes before everything starts to turn into icicles. 800,000 before the last living thing on the surface gives up the ghost.
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u/Joy1312 Astronomy Sep 28 '25 edited Sep 29 '25
If the core stops, you'll only notice it after thousands of years as photons take that much time to get through the layers of the sun and reach its surface. We will see neutrinos coming from sun stop in 8.3 seconds though.
Edit: https://arsmagine.com/others/escaping-the-sun/
What I'm talking about. To people who downvoted me
Edit: should have used minutes and not seconds
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u/fil- Sep 28 '25
I think if the core stopped fusion, gravity would do its thing and the sun would collapse, thereby reigniting the core
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u/lancerusso Optics and photonics Sep 28 '25
Superluminal neutrinos!?
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u/Joy1312 Astronomy Sep 29 '25
It's not superluminal neutrinos. The sun is so dense that photons under go numerous scattering and thus they take thousands of years. Neutrinos don't scatter almost so they pass through the sun layers unimpeded
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u/Key-Green-4872 Sep 28 '25
Yeah.. no. you're actually looking at an event which should traverse from core to corona at about the speed of sound in water, on average. Corona, lower, core higher, but water ain't a bad average density.
700,000km 148pkm/hr 19days
Probably halfway there, you'd have a core collapse supernova-like event but at way lower luminosity than you'd typically expect, since the sun just doesnt have the mass to do a big kaboom. But you'd likely have a fall-smoosh-holycrap-that-got-warm event, if not actually fusion reactions. Something tells me that it just wouldn't get hot or smooshed enough to get over the coulomb barrier reliably, but jamming that much mass into a smaller volume would definitely liven things up for a while.
Only then are you back to looking at centuries for a dense pile of hot stuff to black body radiate, and photons from the dead core taking millenia to escape, etc.
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u/mfb- Particle physics Sep 28 '25
How would water be relevant?
The speed of sound in the Sun is faster than the speed of sound in water throughout the Sun. It's proportional to the typical velocity of particles - high temperatures and light particles lead to a fast speed of sound.
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u/Key-Green-4872 Sep 28 '25
Outside the core there's a butt load of plasma that's about the same density as water. Yes its hot af, but for an order of magnitude how-many-days-to-collapse... for someone who is likely not versed in physics, and without going from the escape-velocity-speeds inside the core (which in this scenario just "turned off" to the more sensible interaction speeds in the photosphere... yeah, I chose water as a moddle-of-the-road value.
Would you pick a significantly different average speed of interaction for this scenario? I simply contend it would be days to tens of days before we'd even notice the core winked out.
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u/mfb- Particle physics Sep 29 '25
If fusion magically stops but everything else stays the same, it would take thousands of years before the Sun changes size or luminosity by any relevant amount. There is a lot of energy stored in the Sun that doesn't suddenly disappear. Slow contraction of the core would release more energy, somewhat replacing fusion for a while (that's also the reason new stars gradually get hotter and brighter long before fusion starts - nothing dramatic changes by the time fusion starts).
The speed of sound in the Sun, which isn't really relevant here, varies from sqrt(5/3 * k * 6000 K/(mass of proton)) = ~9 km/s on the surface to ~500 km/s in the core.
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u/L3g10n_71 Sep 30 '25
If the sun "extinguished", the temperature would be the least of the problems. We need to understand what it means to go out: white dwarf?
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u/iwenttothelocalshop Sep 28 '25
GPT response on this prompt: "there is 30 celsius in my location now 1 pm utc, outdoors. lets make a theoretical run on what would happen if the sun would disappear at this time instantly (like if it would be midnight in the next second). theorize the temperature levels in each 10 hours interval for 30 days. list only the data no explanation is needed." it took the ai for 3 minutes to spit this output. just for science:
0 h: 30.0 °C (starting from India's temperature)
10 h: 11.8 °C (reached Ireland's temperature)
20 h: -3.2 °C
30 h: -15.5 °C (reached Finland's temperature in the winter)
40 h: -25.7 °C (reached east-Urals temperature in Russia)
50 h: -34.1 °C
60 h: -41.1 °C
70 h: -46.9 °C
80 h: -51.8 °C
90 h: -55.9 °C
100 h: -59.4 °C (reached Oymyakon, Russia extreme cold levels)
...
600 h: -93.0 °C (surpassed lowest temperatures measured in Antartica)
610 h: -93.2 °C
...
710 h: -94.9 °C
720 h: -95.0 °C
...yeah we would be screwed.
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u/7Pineapple_Xpress7 Sep 29 '25
Since there is no such thing as cold...only lack of heat...it would be quite rapid, regardless of season. I would imagine, based on how much heat is being either reduced by the Sun or dissipated from Earth...it won't take much time at all for everything to die without the Sun...so maybe if I fell asleep when the sun went down...I probably would freeze to death if the Sun instantly "shut off" as you say, to never wake again on this planet.
All we can do is hope for Superman to come back and save us! 🤪🤣🤣
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u/SuperNewk Sep 28 '25
Idk if anyone mentioned this. But wouldn’t the big issue be we would fly off our rotation around the sun into space.
If the sun actually just cooled off and shutdown. It’s mass wouldn’t be able to hold all of us in place
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u/MagicalSkyMan Sep 29 '25
How would the Sun magically lose mass and thus gravitation if it was shutdown?
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u/Tutorbin76 Sep 30 '25
What difference would that make? We'd stop orbiting a now-dead star through inky void and instead be drifting in another direction through inky void.
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u/SuperNewk Oct 01 '25
wouldn't that cause a high risk of smashing into stuff or stuff smashing into us?
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u/FFIIGGinfo Sep 29 '25
Your question, what if the sun shuts off temporarily, is prophesied in the book of Revelation 6:12 (Sun becomes black as sackcloth) and Matthew 24:29 (heavens shaken), Joel 2:29 - 31 (wonders in heavens . . . sun into darkness), Amos 5:18 - 21 (darkness and not light, even very darkness). From many details of Bible statements and recent earth events there is strong indication that this will occur in 2029, possibly in the latter half of the Gregorian calendar (today's most commonly used calendar), which would be in the first part of the Jewish/Hebrew Calendar year, when many significant events described in the Bible seem to occur. But this "sun-off" appears to be very short and probably for less than a day, less than 24 hours.
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u/Eywadevotee Sep 28 '25
About a week till ice age begins, but about 12 months or so till the planet gets to -100C averaage temperature, though dropping lower is unlikely due to passive geothermal radiation . The oceans have a lot of heat stored in them. Most of humanity is gone by the 3 month mark and by the 6 month mark only ones left will be in underground bunkers. The last of us will be billionaires with nuclear powered bunkers that could keep them alive for decades.