Say Earth got flung out of orbit...

We'd need nuclear energy 'way beyond today's technology. Fusion at the very least.
All the energy we generate through nukes, hydro, fossil fuels, etc. is only a pittance of what falls on Earth everyday and it's THAT energy which keeps us warm, enables plants to grow, etc.

The heat flow from the interior of the planet is also just a fraction of what we get from the Sun.

In either case, I'm not asserting survival is impossible -- especially if we had years or decades to prepare -- but it would be a very stunted existence for just a fraction of the current population.

Exact scenario covered in "A Pail of Air" by Fritz Leiber.
gutenberg.org/ebooks/51461

No once we reach near Mar's orbit this planet enters an eternal ice age where the caps cover even the equator meaning we all die.

we ded unless someone rolls out their secret survival bunker with a fusion reactor and enough space to grow food

What's with all the fusion nonsense? Fission works just as well and is less likely to require super-high-tech replacement parts. Not to mention that it already exists and in great numbers. Although it will most likely fail after a while if world economy collapses, unless spare parts and uranium fuel is stored in huge amounts really fast by whatever government/entity still in control.

Also, there's no need to dig underground for warmth. Insulation is not scifi. Space stations, polar science stations and submarines work just fine in the cold.

Fusion because there's only so much uranium/thorium if you used it for EVERYTHING. Fission would do for awhile, but I'd work like hell on something better. Incidentally, you think fission plants are simple? I've worked in them. They're not.
Underground because dirt is cheap insulation Space stations lose heat slowly to vacuum, Antarctic bases have no soil to dig into, subs use waste heat from the power plant.

And if the ground is warmer than the air, might as well take advantage of it. Gonna be a loooooooong winter if we lost the Sun.

What do you mean?
Like orbit around the Sun?

youtu.be/JalSUkondr8

youtu.be/FXU1wYmSF6g

Is Vsauce a pseduinterdectual?

If you need a software engineer for the vidya, screen cap this. If i find your job advertisment i will send you a screencap

I won't be ready to do anything on that scale for years though, I just enjoy brainstorming ideas for stuff like this.
I had another idea for an RPG where the sun is about to die so humanity takes the bare minimum they need to survive and abandons the Earth.
It would either take place from the perspective of those on the ship or the ones left behind on Earth, or both if I feel ambitious enough.

There's plenty of uranium and thorium.

web.archive.org/web/20130114062518/http://sustainablenuclear.org/PADs/pad11983cohen.pdf

Quote: "We thus conclude that all the world’s energy requirements for the remaining 5×10^9 yr of existence of life on Earth could be provided by breeder reactors without the cost of electricity rising by as much as 1 % due to fuel costs."

Even non-breeder reactors would have plenty of uranium/thorium when you consider resources extractable at a higher price than today's value. Especially if you consider the scenario where the Earth has been flung out of its orbit in which case people would starve to death in the billions thus lowering energy requirements greatly. It's not like we could realistically keep farmland from not freezing over. We might be able to keep our current greenhouses warm and feed around 2 million people.

I do not think fission plants are "simple". But they are definitely more simple than most proposed fusion power plants. Some laser fusion thingie might be simpler but we can't really say because none are working.

Dirt is not cheap insulation. If it was, we would be building houses underground in cold climates. We are not. Moving dirt (digging and transportin it away) is very expensive compared to wool.

Why the hell does it still have mostly human forearms and calves? Those would objectively be the easiest and most useful parts to replace.

Sufficient for current purposes and even for a dozen times current purposes.
Insufficient to keep a sunless civilization warm and grow food unless, as you state, most of the world's population can be assumed to have died already.

I spent a few weeks in Canada once. Toronto, I think. There WAS an underground city. You never had to face winter.

I quite agree that current designs for fusion make it quite hard to imagine them developing into reliable power plants. I visited a tokamak once. Goldbergery that fired maybe one shot a week. But you have to start somewhere.

We have plenty of underground stuff here in Helsinki too. The main reason is that land prices are sky high in the city center. No one builds underground because they think ground is good insulation which it is not. Air is a better insulator than granite/dirt/whatever your basement is touching.

Google tells me that "underground temperature increases about 3 °C per 100 m depth".

The only reason why nuclear (fission breeder) power isn't enought to keep most peolpe alive during a no-sun-scenario is that it would cost way too much to insulate tens of millions of square km of farmland and build enough LEDs and also power them.

Most people would die, and a minority would survive. Conventional power plants would still work, and could heat buildings and provide light for greenhouses to produce food. If we had a few years warning ahead of earth leaving it’s orbit we could prepare for at least a few million people to survive, if it just suddenly happened much fewer people if any would survive

This leaves one major question: How do we get rid of the sun?

sell it to aliens