Suppose some magical process causes our sun to stop producing new light photons.
I suspect humans wouldn’t even notice this immediately. Further, I think human society would chug along for at least a hundred years, but would be vastly reduced in number after 1000-10000 years, as plant life dies off (except the ones sustained by artificial lighting).
I think it would probably get kind of cold after a day or two. And by cold, I mean like negative temperatures.
It would start getting pretty chilly after about 8 minutes.
100 years? Not likely. Less than a year, I’d say. You’re talking about a permanent global night/winter that would be colder than the poles are now. That’s curtains for the human race - a few might hang on for a while, surviving on stored foodstuffs and fuel, but sustainably growing new food would be nearly impossible.
Wait a minute here. Wouldn’t it be, like, -200 degrees (pick your scale) in a matter of hours?
Out of curiosity, what is the thought process that leads you to this conclusion? I am honestly interested because it is beyond bizarre and it is one of the oddest things I have read in my entire life. 1000 years with no sun? The earth radiates heat all the time. Notice how it cools down at night and for a simplistic mental model, just follow the temperature plot down for a week or so. Besides that, plants will die quickly with no sun and plunging termperatures and livestock will die even if a few people managed to get themselves underground and use either geothermal heat or fossils fuels to keep them alive. Going deep underground is the only way that I can see people surving for more than a few days or weeks.
No, I don’t think so… certainly the folks on the night side of the planet do not experience -200 degree temps within a few hours.
Lordy, I’m no scientist, but our nice thick atmosphere likely contributes to keeping heat distributed over the planet to a considerable degree. (Pun not intended.) If there was no atmosphere, the difference between night-side and day-side is stark, as on the moon. But please, someone with actual science chops come in and confirm why the sun is essential for life, and dispel ignorance.
Edited to add that I concur with the “about 8.5 minutes” estimate…
It doesn’t at sundown.
I don’t think this happens, at least if you read the OP carefully. 
The conditions laid out in the OP do not remove the atmosphere.
Are you saying that you think it would take a long time for plant life to die off?
Yes! 
No, you aren’t understanding. I know the atmosphere isn’t being removed. I want to know your though process on how humans would chug along for 6 months let alone 1000 years without the sun.
Again, this is possibly the weirdest thing I have ever read on this board and I would like a forensic analysis on why you think this (seriously).
So you’re saying plants can just carry on living in the complete absence of light? What the hell are you smoking?
I should have clarified: I was thinking more along the lines of maybe 20 to 40 hours.
Hopefully someone with real scientific knowledge will come along soon, but as it stands I’m under the impression that, despite the fact that the planet radiates heat, the earth will be a block of frozen atmosphere and ocean, and rock, in no time flat. Just a guess. of course.
I think 8.5 minutes is a ludicrous idea as to how long it’d be before things were insanely cold. I have no idea but I bet it’d take at least a few days before all the stored heat was dissipated and a global winter happened.
Most humans would probably be dead within a month, we’d still have enough food stores and enough residual plant life that was still edible at that point, but not near enough shelter to keep people alive in temperatures as cold as Pluto; almost everyone would die from exposure.
I can imagine a few people escaping to deep underground where they could keep warm geothermally, and if they brought enough supplies they could eke out an existence for a few years.
If we were given say, 100 years notice that the Sun was going to go out suddenly on a date 100 years in the future I imagine a very small number of people could establish some sort of semi-sustainable existence deep under the earth, using geothermal energy and whatnot to generate electricity and distribute heat. Having no light from the sun would be very difficult to work around though, I think you could make hydroponic farms and keep small numbers of animals around in closely controlled environments. That might enable a small colony of humans to survive for a few hundred years, but even then they’d be dead eventually too I think, I think eventually that would just become an unsustainable lifestyle. And that is with a 100 year notice that the Sun is going to black out instantly, sans such a notice I don’t think there’s any way that you can avoid 90-99.5% of the population dying within the first month or two, then maybe a few very resourceful survivalists finally dying off and completing our extinction a few years later.
This completely ignores the issue of our planet’s motion through space, I have no idea what the Earth would start doing without the Sun’s gravity to dictate its path.
That’s because the planet is still being heated on the other side!
The OP states that if the Sun stops producing NEW photons. What about those pesky old photons bouncing around in the center of the Sun for a million years or so wanting to get out? I guess I’m saying that the Sun would take at least thousands of years to gradually cool off using the fuel it had before the big shutdown.
Oh, now that’s a possibility, but it’s a pretty underhand trick if that’s what the OP actually means.