If all humans died, when would the last light go out?
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- เผยแพร่เมื่อ 7 ก.พ. 2025
- Get a copy of What If? 2 and Randall’s other books at: xkcd.com/books
More serious answers to absurd questions at: what-if.xkcd.com/
If every human somehow simply disappeared from the face of the earth, how long would it be before the last artificial light source would go out?
Randall Munroe is the author of the New York Times bestsellers What If? 2, How To, What If?, and Thing Explainer; the science question-and-answer blog What If?; and the popular web comic xkcd (xkcd.com). A former NASA roboticist, he left the agency in 2006 to draw comics on the internet full time.
Henry Reich is the creator of MinutePhysics and executive producer of MinuteEarth and MinuteFood and founder of Neptune Studios (the parent company for all three youtube channels).
Credits
Narrated by and based on "What If?" by Randall Munroe
Written & Directed by Henry Reich
Illustration and Video Editing by Lizah van der Aart
Illustration and Animation by Ever Salazar
Music & Sound Effects by Know Art Studios
What If? The Video Series is the official adaptation of the What If? books by Randall Munroe and is produced by Neptune Studios LLC.
©2024 xkcd, inc.
I need a version of this video where he says "If every human somehow simply disappeared from the face of the earth" and then just 5 minutes of silence after the stick figure gets vaporized
and the "disappeared" word fades with an echo
All the slides continue as normal, but nothing is being said
I give it a week at most and _someone_ will post a link below me 😂
Edit: It took _significantly_ less time than a week.
@@Jarvalicious th-cam.com/video/zywVTreggrk/w-d-xo.html
@@Jarvalicious i cant post links but put this at the end of the youtube url: watch?v=zywVTreggrk
There is something immensely sad about the thought of an emergency phone in a remote location still being functional even though the world is now void of human life. So if you were the last human, and you found it, you could make a call, but nobody would be there to answer.
And the last human voice you ever hear is a recording going "The number you are trying to reach has been disconnected."
Well, aren't you fun at parties? (Sorry, couldn't resist.)
That was my immediate thought. Very sad.
@@GeoEstes As long as nobody starts discussing apocalyptical hypotheticals, I'm fine. :p
And somehow, inexplicably, machines still call that last phone line to explain that a car warranty is about to expire.
Honestly that would make such a great set piece for some apocolyptic art piece. It really is a haunting thought
The check engine light in my car will always be shining
I'm calling the cops on you for the attempted murder you just committed where I nearly choked to death. Man you gotta put a warning on a joke that good, homie.
This is why God created electrical tape.
@@AnonymousTH-camr69 engineers
Merc, BMW or audi I guess. The typical German horse shit.
I do not have a car, someone explain 😭
Have you guys ever watched something brand new and it immediately feels old-timey? I cannot explain it but it feels like this is something I would've watched 10 years ago. Very comforting to know people are still making content like this. Shorter videos, straight to the point, informative and NO SPONSORS.
I literally just made a comment on another video of theirs about this. Its so refreshing that it brought drunk me to tears
That's probably because it kinda is "old-timey"- these videos are all from his blog and web comics from many years ago
@@meirr.4840Also this question is basically an old episode of Life After People (I think there it was the last human voice?)
@@pokemonprimed nah, he made this long before that, he's just uploading to yt now
10 years is old-timey lol
If a fire set by mankind counts as an "artificial light source", the Centralia PA mine fire could continue burning for 250+ years by some estimates.
Or the Darvaza gas crater fire, which has been burning since the 80s......just no idea when its going to go out.
Centralia was ignited relatively recently (1962). The New Straitsville mine has been burning since 1884, and some believe it could keep burning for thousands of years.
The fucking what
@@Henry-I-H-N-I Please Dont Say Bad Words On This Site 💀💀💀
@@Henry-I-H-N-I I suggest you throw "Centralia" into the youtube search bar and enjoy yourself
The scarier part isn't that the sign at 3:00 was changed from Everyone to 0, but the question who change it?
The man himself who caused everyone to dissappear
Codsworth
Cats. Cats with thumbs.
A particularly clever monkey?
Rogue AI?
"Check out this glowing blue stick I found in that hole past all the spikes!"
"Huh. Must be a place of honour. Highly esteemed deeds must be commemorated there. Stuff that's valued must be there. I bet what is there is cool and awesome to us."
I know all the humans are gone. These are bird people or something idk
And then they discover what radiation is again and realize they have messed up.
There was actually a commission formed to try and come up with a warning sign for radioactive waste that would still be understandable as a warning in ten thousand years, long after every presently known language and iconography was no longer in use. I can't tell you what they came up with, though.
@@Mereologistthey failed
@@Mereologist Yes, that commission (or a similar endeavour) was who created or commissioned the creation of the quote that the OP was riffing off of in their comment.
The immortal hamster powering the White House:
what is this referring to?
@@francoiturriaga4655 an immortal hamster powering the white house
@@lucaspro7117 how could i've been so blind
@@francoiturriaga4655some simply are not ready for this knowledge
it's powering Biden's brain... barely
Imagine you are somehow a survivor and make it through another 50 years or so and somewhere in a remote location you see a light powered by a solar panel... Would be an emotional moment
Not sure the batteries would last 50 years.
@@paulsengupta971 In some setups, the lights can run directly from the solar panels after the battery is long gone, or there could be a tiny little LED that shines whenever the panel is getting power.
@@ChristmasEve777 An LED being on when the thing is charging would be an idea, but they're normally set up so the light comes on when the sun stops shining!
i'd probably be using generators for all 50 years. I'm not sure how much I'd travel, but I'd have electric lights.
@@noneuklid
No, fuel goes bad quickly. Your best bet for power is still solar panels. And for traveling electric cars. A well made EV could last decades, even the battery.
For years, scientists debated how to mark nuclear waste sites to protect our descendants.
Apparently recently they've decided the best approach is to just bury it deep enough in a secure enough place that any future civilization advanced enough to get at it will probably know what radiation is and be able to manage it.
A future civilisation. Mmmm.
Got to imagine future archaeologists going "yeah, they just put this to scare people away" and then when the people who visited the site start dying months later it's "the curse of blue glowing cave"
@@ZER0--Every civilization we know of has collapsed at some point, and there is no indication the current one is any different.
@@OrbObserver I think you're mistaking "country" for "civilization". Plenty of civilizations have lasted thousands of years even as their originating countries have fallen. Some have apparently even managed to pass down knowledge for over 10,000 years, orally, without writing (specifically Australian oral histories that date back before the end of the last ice age).
my favorite solution to this issue is the way the soviets did it, at some places they buried it and tried to build something that looks as instinctively terrifying as possible above. just random structures that gives you a really bad gut feeling.
I love the reference to your "What if everyone jumped at the same time?" Question where you teleported everyone to rhode island so the rhode island population everyone, was really funny.
Ah yes, that really funny time when the rhode island population everyone.
I had a stroke reading the second half
XKCDCU
Yes was really funny
and the same as the space submarine.
That solar panels segment seems missing one important note: although, the solar panel might produce electricity well past it's EOL which is about 25-30 years, it's the battery what will fail first after years of everyday charging cycles. Much much sooner than any solar panels lifespan. So after 20-25 years, the solar panel will be basically trying whole day to charge the dead battery, which means no more light during evening.
There's still some comfort in knowing that the solar panel is still working...
If you count radio waves as light, satellites could still be broadcasting.
One example of a satellite that's still operational after its batteries died, and later went from short to open, is AMSAT-OSCAR 7. Launched in the 1970s, and still working (though not well) today.
It actually depends on the type of battery. Some such as nickel-iron (Edison type) have such long lifespans that they can continue to operate for many decades of continuous use, and are used in some solar power systems. So long as the cell seals are good enough to prevent the electrolyte from drying out, one of those could potentially still be working after a full 100 years. Probably not at full capacity, but well enough for the light to come on at least briefly each night.
Nickel-hydrogen batteries likewise last an extremely long time, but you're unlikely to find those in terrestrial power systems due to prohibitively high cost. They're mostly used in spacecraft. But if a satellite with solar panels and Ni-H batteries also had a status LED...
@@matthewcox7985 they should have some kind of LEDs too, right?
@@matthewcox7985 Most would drift within a few decades. It would be miraculous to find one that's still in correct orbit AND operational at the same time.
I love the Tom Scott "cameo" at 1:56 !
"I'm here, in an XKCD video"
@@XIXXXVIVIII ...and I heard that in his voice!
Randall as a guest on Lateral when? :D
@@KernelLeak they seriosly need more guest variety tho.
@@jezusmylord How about Tom Scott, Tom Cardy, TomSka and Tom Lum for absolute tomfoolery?
This video is the type of thing that got me into TH-cam when it used to be a website
its still a website?
@@sheenakr7616No?
there are still plenty amount of good creators, u just messed up your algorithm
wdym "used to be a website"
@@gooddeath3816 exactly!
I found a digital clock in our attic that's been running for over 20yrs on AA batteries and it was only 5-6hrs off the actual time. Its still running without a battery change 6+months later I'll keep it around till it dies
It could have been several days inaccurate. Once it accumulates more than 12 hours of drift it starts trending back towards the actual time. Or: a clock can't be more than 12 hours wrong.
@@wowv The digital clock also displays the date, it was the correct day and month just 5-6hrs off
Some batteries won't leak. Especially helps to be drawing a very slow, constant amount of power from them.
It wouldn’t surprise us if there are Casio F91w watches still going after 20 years having only drifted a few minutes 😅
@@SproutyPottedPlant But if they are that good, the consumer will never have to buy a new one in time for the company to make more money... oh no!
someone in grade 7 asked this so we had an entire class with a documentary on earth after humans, it was really cool and she was my favourite teacher, love ya miss A
"Life After People" Its a series and its here on TH-cam. Still pretty good
Today I learned Tom Scott no longer makes TH-cam videos because he’s taken a job maintaining all wind turbines. Thank you for service, Tom Scott.
I do not believe that's true, not one bit
While doing a weekly podcast on the side. Infinite energy that guy. 😅
Where did he say this? Edit: womp womp turns out I’m stupid, didn’t see “all”
Man, some people wouldn't understand that this is a joke, even if you told them
@@felixw19some people are evidently unable to understand jokes without a /s at the end. I don't know how did they cope on the Internet until 2016 or so when the practice got widespread. I am pretty sure they are either robots or lizardpeople.
3:00 woah woah woah woah. So this hypothetical takes place in the same universe where everyone was teleported to rhode island and forced to jump? This opens up the theory of all videos takes place in the same universe, and in which case, the xkcd universe would be a terrible place to live
It's also the same universe where someone sent a sub to space, or at least did so in a movie.
I just wanna know who updated it to 0.
Magnitude 25 earthquake 😶
In this universe, some madlads are throwing baseballs at relativistic speeds and vaporizing entire cities. 💀
Let's not forget the hellscape that is the periodic table literally stacked upon one another...
Another contender are gas lamps, ammonia-cycle fridges, and appliance pilot lights hooked up to private wells, those will keep on burning until the pipes feeding them are too rusted to carry more gas. A private gas well out in the countryside isn't particularly rare, and with only the load of a few pilot lights, an absorption fridge, and a porch/yard light on them, that well can keep em burning for decades or centuries. I've got relatives in West Virginia who still live on the family farmstead from the 1800s and their fridge hasn't been turned off in about 120 years, there's no moving parts in it except ammonia and water.
That comes down to whether we include things that generate light incidentally to their intended purpose versus actual proper lights. I think the proper answer is probably a solar powered light. The others should probably be a separate category for when the last manmade light emitting item goes dark.
@@SmallSpoonBrigadeby that logic though, the video's conclusionary light from radioactive waste would be excluded though.
@@mnxs yes, they said solar powered light would be the proper answer.
@@mnxs This would include light emitting watch faces winch emit light for a while after exposure to natural or bright light and will continue to do so indefinably until the watch face is buried or obscured from the sun when left exposed. While only producing light enough to read the face by for a a couple dozen minutes at most a night, these watch faces would be producing light for centuries at worst.
If you have a watch with such dials, holding the backlight on for a a moment will leave the hands and numbers glowing for a short moment as they fade, natural light leaves them more 'charged' and they can glow in the dark for a few minutes if you step into an unlit room from outside. These are still a manmade light as under bright conditions they do emit enough light to read by in the short time they are that bright.
Huh... private gas wells... never heard of that. heard of water wells contaminated with gas, but I suppose it makes sense. cool. All it would take is for a them to leave the porch light on during the great evaporation, and that makes it count as an artificial light source. I would also imagine there would be industrial users of the same reservoir, without powerplants and factories using it, thats a loooong time. you get my vote, sir.
I love how its a silly, whimsical, light-hearted question, but the ending is so dark.
4:46 That last line is somehow simultaneously concerning and comforting.
Worst consolation prize ever, am I right?
Yeah, oddly enough it did feel comforting.
in true XKCD fashion
Highly disturbing
It's a bit sad. The longest lasting survivor of humanity is our trash.
The last thing remaining of human light technology being garbage is philosophical as fuck
Archaeology is 90% digging through Human garbage dumps.
when we are gone, the last thing left will be the mess we created. Dam
Holy shit it is actually you? I watchrd so many of your lyrics vids. Amazing! Than you for your great work!
_The last thing remaining of human light technology being garbage is philosophical as..._
...and there comes the word that will probably be the final one of all to be spoken. ;)
@@FennecFoxFluff You can see it in a positive way - even in the worst toxic wastes we've created, some beauty will still exist,
I love the references to the previous episode.
The sign of Rhode Island showing the change of population from "everyone" to 0 and the sign in the desert showing an advertisment for a submarine in space :D
E
Who changed the sign to 0 though
@@huskykid0295idk
I guess the lesson we can get from this is that no matter how much you lock away or drown it, the worst things youve done will still glow brightly
What If was one of my favorite books as a child, seeing it be brought to life on TH-cam made my day. I’ve been a fan for over a decade, thank you Randall!
Well that's made me feel old
@@kouriiI'm old enough to remember when some tech savvy people knew what "shibboleet" means.
Zombie movies usually ignore the fact that you need people to maintain power stations.
They ignore all the facts to entertain us with brain dead trama.
is there one that doesnt?
And sometimes people who watch these movies, forget that zombies propably wont start suddenly spawning from everywhere in the world, they propably are spreading, so you have time to pass the knowlodge for the next person to keep power going on, and prepare to block zombies outside
A zombie outbreak doesnt have to be worldwide and if theres a safe country it could still provide electricity to other places. So hmm
Give one example
"Sweetie, you don't need to be afraid of the dark. This blue night light has been in our family for hundreds of years..."
You just need to be afraid of the light.
I'm your only friend
I'm not your only friend
But I'm a little glowing friend
But really I'm not actually your friend
But I am
pretty sure if the blue light is there the family line wont last hundreds of years
@@zeff241 By the two century mark, the radiation levels will have dropped pretty far. It's a question of whether the radiation before that will have been enough to render the line sterile prior to reproduction.
Aw, come on, surely _somebody_ else knows the words?? 😜
binge watching all of these, thank you
I work at a hydroelectric generating station. For us, it's a clogged cooling water strainer that would stop our generator long before the trash rack at the intake would clog. Then the generator would trip because of low cooling water flow or high bearing temp. It would be especially quick during the spring runoff when the water is full of silt. This would vary greatly from plant to plant. Maybe Hoover Dam doesn’t have much of a silt problem. I’ve also seen cooling water strainers that flush themselves automatically.
My understanding is Hoover dam is infected by an invasive mussel they have to clear out of their intake pipes every few months or it completely blocks water flow.
NCR engineers managed to get the dam running again
My plant has systems to auto backwash some strainers, but like anything in systems close to the ocean, the salt water/moist air causes corrosion that needs work every so often, but a brand new system could work for a few years without maintenance.
Small correction: wind turbines are not allowed to operate when the grid is down. So when the grid dies, wind turbines will automatically shut down and stop producing until the grid comes back. The backup power or batteries in the wind farm will last for a few days, maybe weeks.
Private wind turbines are a thing. No they aren't as massive but if you aren't worried about connecting to a load balancing grid and only need to power one or two buildings on a farm or research station or something that isn't an issue.
Some of the larger wind farms may keep generating, depending on their design. Here in Australia some of our large solar farms are also grid-forming, and designed to continue to output power in the case of a grid failure, to assist with black starting large coal power stations. Of course this won't help ordinary people as the retail loads will all trip, to ensure as much power as possible is available to get the large generators back online as quickly as possible.
The solar lights on my patio will run for a long time but the wind turbines I work on likely won’t. And even if they did operate in “self-sustain mode” as they do when there’s a grid outage they probably won’t be supplying power to anything because the substation will have tripped when the grid went crazy. In a closed-loop system a turbine or solar panel could power lights until a mechanical failure occurs, but because most generation stations are part of a larger grid, I doubt they’d power very many lights once the coal and nuclear plants trip. But it’s interesting to think about.
@@hackerx7329 There are 3 MW private turbines close to where I live. I know of two, as I worked on those projects.
Not sure if it matters to your point but his point about the wind turbines is that they have a status LED on them somewhere. Even if they ‘shut down’ does that mean they stop spinning? Even if they weren’t supplying the grid but showed a red LED then that’s still a light.
This channel is perfect at answering questions I didn’t know I had
E
Check out the books these videos are based on if you want. Some of the questions are probably not going to make it into a video, so you get even more out of it.
How many years could you go back in time and still have breathable air?
Probably some time around the middle of the precambrian era
But im not a scientist so dont trust my word for it xd
How many years into the future, for that matter?
@@chriskaprys 10 years into future
3:56 thanks for the little nod towards the radium girls
Yeah that was a real 💀 of a detail to see.
I would have drawn her licking the paint brush to get a fine tip 😞
E
,
huh?
You’ve been traveling by foot on one of the old roads for several days. The sun is setting and it’s almost time to make camp. You’ve almost run out of lamp oil. Some distance down the road, a light on a pole flicks on so suddenly that you flinch. It’s a flickering, strange light, the likes of which you’ve never seen before. It feels like seeing a ghost.
In Yokohama Kaidashi Kikou (A Yokohama Shopping Trip) there is a scene where at night all the old street lights and traffic lights come to life even though the city had been submerged under the ocean for generations.
No explanation for where the electricity is coming from. But it looks beautiful. Magical.
Wow, this thread is amazing. So much writing flair.
@@davidwuhrer6704 Also, trees start to glow. Not human made - or are they? YKK is an enigmatic masterpiece.
and then you get closer and the light gets bigger and you realize
it's your mom
@@NewWesternFront LOL WHAT
My parents used to live in Cyprus. They had a civil war there and some people were forced to leave their homes in a hurry - someone left their light on and their house was in a no-go zone.
That was 1974.
25 years later the light was still on. A normal incandescent bulb.
Obviously it had the advantage of a continuous power source but it does hint at what a post apocalyptic world might be like.
I always wondered who paid the bill.
Iirc, incandescent bulbs mainly deteriorate by being turned off and on, the heating/cooling makes the filament brittle. So yeah, if it went on and stayed on constantly without being touched, I can see it lasting a real long time.
@@Yesnaught IIRC, the record for lifespan of an incandescent light bulb is something like a century. And, it's because it's a light bulb that never gets turned on or off apart from when there's a power outage.
The two main things that cause light bulbs to fail are that heating/cool cycle as well as the seal maintaining the vacuum failing.
I assume that whether the bill kept being paid is irrelevant- older types of meters cannot be checked or shut off remotely, and if the homeowner can't return the meter-reader sure as hell isn't gonna go out there
I feel like the power company wouldn't expect you to pay the bill after 25 years either, most would probably give you a forgiveness on your debt or whatever
What's stranger is that the power grid to the area wasn't cut off sometime within the first few years of a semi-solid border forming. Of course, there's a war going on, but cyprus has a small power grid. I would expect next time they service a power line going into the area, they sever it just before the current border
Then again, a shocking number of abandoned buildings still have power on, all around the world, even when the power company or the property owner could shut off the power- maybe I'm being overly mindful of every last watt when most would give up
Another thing which affects the life-span of an incandescent bulb (besides being turned off and on) is its wattage, which is pretty much synonymous with the temperature at which the filament operates. The lower the temperature at which the filament operates, the longer the filament will last. That's why the famous "fire-house light" has kept on burning almost continuously (barring power outages) for many decades. It has a 240V globe plugged into a 120V light outlet, so it operates at a far lower temperature than it's designed for. It's horribly inefficient of course, but it will probably last for decades longer because the filament isn't boiling its surface away as happens with globes which operate close to their rated voltage. (The boiled-off tungsten is attracted back to the filament and re-fuses with it until a spot wears thin enough for the inrush current to burn through the metal)
@@briannem.6787 ive been told a lot of abandoned buildings that are taken up by things like the bank still keep their power simply due to the fact that not heating the building in the winter at least a little bit can cause the building to quickly fall into disrepair. i could be wrong though so take it with a grain of salt.
the vocal sound effects are icing on the cake of these videos
Love that Rhode Island callback 😂
I was looking for a comment mentioning it!
Yes. But the mystery is, who corrected the sign to 0?
@@FuelDropforthewin The few people at the edge of that event who escaped. Before they rebuilt society with warnings to never go to Rhode Island, and then were disappeared for this event.
And the space submarine callback
Fr
I absolutely *LOVE* the callback to the jumping video. Seriously, all these videos are top notch. My only complaint is that I came across your channel on your second video, instead of finding it after you'd been releasing them for a decade so I could binge watch your content for hours.
Please remember to turn off the light
I have trouble turning off my Cesium-137 source.
@@oysteinalsaker you can check out any time you like, but you can never leave... the light off
hey, who turned out the lights?
@@renakunisaki Hotel Cherenkov
Last one to leave, please turn out the lights
4:12 fun fact: legendary Godzilla’s atomic breath and blue glow are actually Cherenkov Radiation
Fun fact: it’s actually VFX
@@yosoyflakoo9285😐
If infrared lamps count, would an RTG from Voyager 1 or New Horizons count as a lamp?
That was my first thought as well. Do any more modern RTG powered probes have an LED on them somewhere (even if just for testing while on the ground)? And do they keep working ever dimmer with decreasing power, or is there a cut off where below a certain voltage they simply switch off?
I think that "light" implies visible light, i.e. between ca 400 and 700 nm.
@@QuantumHistorian LEDs have a forward voltage (a few volts usually, depends on the model/colour though) that must be reached for them to glow, so they will get a bit dimmer, then turn off.
In the first _What if?_ book, Randall answers this question in more detail. He actually does consider rovers, satellites, and space probes, but rules them out. The Curiosity rover has an RTG and lights, but the lights wouldn’t be on unless a human told them to turn on. Some satellites have LEDs, but they would most likely be taken out by space debris, or their orbits would decay.
i'd be surprised if there was no rtg on a test stand somewhere hooked up to a bread board with an led on it
1:36 As an icelander I have to make a correction here. Not with your facts, but the name.
And not the way you might expect, you pronounced Svartsengi basically perfectly.
But Svartsengi isn't an island. Like, at all.
The only way I can imagine this mistake having made it into the script is that you found a source with the name as "Svartsengi, Ísland" somewhere out there.
But the important part here is that "Ísland" (the s IS pronounced) isn't the icelandic word for "island"... it is the icelandic word for ICELAND, the name of the COUNTRY
but yeah. Sorry for the nitpick, it just hit me by surprise (especially since you said the name correctly! just added an erroneous "island" that didn't belong)
Great video though!!! Loved it
Thank you, that's actually a useful and informative correction. It's such a novelty.
I just visited Iceland last week! Amazing place, and yeah the Svartsengi plant definitely isnt an island lol, I visited the blue lagoon which is fed by it. Very cool place, although I just barely missed yesterday's eruption! Just left a few days before it happened.
He is technically correct :). Iceland is an island. So Svartsengi island is Iceland.
Besides that, the power plant does not seem to be a good example of maintenance-free...
Technically it may run quite long without maintenance, but it requires permanent defense against lava streams running towards it.
@@Rob2 Not sure if this was a joke or not, but gonna answer it as if were completely serious
You are of course referring to the current eruption, but if we were counting natural disasters then that would also be accounted for every other power plant. A lot of countries experiences far more natural disasters than Iceland does volcanos, and even with the volcanos they are basically almost never so close that they threaten a powerplant.
It is terrible bad luck rn, but it is not something you'd assume is common when calculating for this, especially when we assume the power plant would already stop working in just around three year timeframe (volcanos are frequent here, but frequent in geological scales still mean there might be decades or even centuries between eruptions in certain volcanic systems, impossible to really predict)
And again, we are talking about how long it would last without maintenance, not how long it would last without humans stepping in during a natural disaster. It had after all run without worrying about lava streams for around 48 years already
This is assuming this mass human disappearance wouldn't happen exactly today, but even if it did, it is still up in the air whether the lava will flow to it and breach the barriers or not. If we all disappeared it could still end up ok and working until important parts rust away
3:00 I love the callback to the 'jump' episodes
E
@@EEEEEEEEE
"When the last light goes out" is a hell of a title for a post apocalyptic movie/book
Yeah, or just "Last Light".
@@chriskaprys Nah the first one feels more ominous
On the other hand, "There is a light that never goes out" is a hell of a title for a post punk song.
@@chriskaprys That's what I thought. "Last Light" Is much better. "When the last light goes out" Is a mouthful and feels chaotic.
@@aldeayeah The Smiths beat you to it
I don't know who was involved and what needed to happen for official "xkcd what if? Videos" to be a thing, but it's easily my favourite thing that happened in 2024.
don't forget about RTG powersources in remote locations, those can run for hundreds of years without supervision which is why they are used.
yeah, the USSR was obsessed with them and there are still "lost" ones dotting the area of the former soviet union
This is the answer
@@iplaygames8090 I see you have also watched those vids about the busted open RTGs
RTG?
@@colatf2 Radioisotoope Thermoelectric Generator
I found old batteries to play with my game boy when I was a kid, I was sad because I didn't have any battery left and wanted to play more, but after searching for a while in my mother's stuff, I found an old package of batteries, but I didn't recognize the usual brand I used, my mom told me there were pretty old but she never used them so it should be fine. I happily put them in my game boy, turned it up, saw the bright red light on the side, I was happy to play... Then the light quickly went weaker and weaker, and in ten seconds flat, the game boy went out of power again, I went from sadness, to happiness and sadness again very quickly. 😢
Those little solar powered lights on a stick that line people's walkways.
Around 1996 my parents got my brother and I electric toothbrushes with ni-cad batteries. I used it once, but didn't really know what I was doing, so shoved it in the cupboard and forgot about it. Around 2011 I found it when the bathroom was being renovated and pushed the button. It ran feebly for about 5 minutes!
HAHAHAHAHAHA
Oof
Now your mom will be sad at night...
the light she brings to my life could never be extinguished
4:18 Some years ago a nuclear disaster happened here at Brazil with Cesium 137, at Goiânia, Goiás, in September 13th, 1987. People started playing with it after it was discovered by some curious guys cuz it glowed blue, and it ended up a kid died from eating it, amongst other people. Sad, but true.
Since the question specified that every human on earth was gone but not that the last light has to be on earth to be considered:
Some satellites like the Voyagers probes, that are very far from the sun and thus can't effectively gain energy from it, use radioisotope thermoelectric generators to generate electricity.
They basically use the heat of radioactive decay.
Now, I'm not sure whether any long-term space probes have any status LEDs (its not like someone is going to check them anytime soon) or how long exactly their RTGs would be strong enough to power them, but Wikipedia says that some variations may last up to 1000 years.
And even if these spacecraft don't have status LEDs... Spacecraft communicate via electromagnetic radiation. Light is electromagnetic radiation. So I think that should count.
So as long as a satellite still tries to transmit data or regain a connection to a ground station, there is still a human-made source of "light".
I like your argument about including non-visible electromagnetic waves. I think a geostationary satellite would probably beat a solar powered emergency light in the desert. The only thing I am still considering that might last longer is as sealed, air tight/water tight, nautical light. If there is one in a clear plastic box with all the electronics inside it, and it is air tight and even better if the atmosphere is replaced with an inert gas, could be the longest lasting. I think the limiting factor would be how long the clear box stays transparent. Also possible there is some osmosis and oxygen finds a way into the box.
In the book, Randall touched on the Mars Curiosity Rover, which has lamps meant for shining on rock samples. He said these lights, while they COULD last a long time, are only switched on when it needs to examine rock samples. With all the humans gone, there would be nothing to tell it to do that, and thus it would have no reason to switch on its lamps by itself.
If you're going with non-visible light the answer would be gamma rays from plutonium-244 which would last millions of years, or the fraction of tellurium-128 that is manmade with a half life trillions of times the age of the universe.
@@willythemailboy2 Are those isotopes man made or are they naturally occuring?
The Russians used RTGs to power lighthouses out in the middle of nowhere. Many of these RTGs are still there because it's too complicated and costly to retrieve them.
This video has strong "Life After People" vibes
I love that show!
I think a lot of younger people haven't seen it. They are now people in a life after Life After People.
Or the wonderful book it that show was based on "The World Without Us" really good read
Great show
Nice reference with the lady painting the clock hands with radium color....poor girls.
The fact that you did the d-d-d-dssssch soundeffect at 3:30 by yourself is an amazing detail ;)
he did all sound effects for the entire video.
Tritium vials would last for a long time as well. They are used as a replacement for Radium in modern watches,gun sights, and exit signs. The halflife is 12 years and most vials can go through 2 half lifes before they are considered too dim for casual use.
RTG's would trump that easy. Assuming there is some LED on the spacecraft
As a kid I connected a 90Volt battery to a tiny neon light. The light pulsed about once per second. Had it as a night light in my room, although it was just a reassuring little orange pip in the dark. It ran about 10 years!
your parents let their kid play with a 90 volt battery? yikes
@@jwnomad His last name is Addams...
@@jwnomad High volts, low amps
@@joedellinger9437 and no watts
assuming you meant 9 volt
It is kind of eerie to think that lone call boxes around the world would be the only source of light at night, years after the world goes dark.
Eerie for sure! The author did skipped they use batteries so maybe they would not last a century. It would be interesting to have solar powered lights during the day!
Some little solar powered string of party lights glimmering alone in an empty overgrown yard.
03:52 - Funny how the watch coated in radium is pretty old technology. But when the phosphorescent paint broke down, the dial was just black, and it looked like a smart watch when it's turned off :)
These were the not-very-smart watches. Could probably make a strong parallel with how both treated their workers, though.
@@Merennulli Yes, interesting point.
In Germany we sometimes have solar powered warning lights at highway building sites. I like the thought that even a century after human extinction, we will still be warning of where we used to build
As a German, I might add the sentence should be "as where we used to want to build". Seriously, whenever we're trying to build something in Germany it takes 5 years until the plans are done, another 5 years until the federal offices agree, another 5 years until the work actually begins and at least 10 more years for completion.
Germany hat a to wet enviroment. Plants will grow over highways and if no on cleans the solar panels dirt will accumulate. And then there is the problem with the batteries, they will fail after some years.
Germans: "It vill last for van souzands years."
History: "Best I can do is 10 years."
In the US currently, our highway roadworks are lit by 15-ft. high, diesel generator-powered lamps that are about as bright as the sun, and shine directly into motorists' eyes at night. So, unsurprisingly, we're working on the human extinction part of the equation.
I absolutely love the reference at 3:01 on the signboard 😂😂😂 iykyk
The callback to everyone on the planet suddenly being in Rhode Island made me chuckle, nice one
Hey Randall. I've been checking out your What If Physics website for years now and you always give such fun explanations for curious questions, some I didn't even know I wanted to know until I read it! Keep it up and these videos are good too!
I love that you answer a question progressively. If you didnt mean nuclear waste, the video ended satisfyingly with the solar panel light.
There are two answers depending upon whether you mean things that are deliberately being used for light sources and those that emit light incidentally as a result of human activity.
i like the solar panel ending better :(
With no observer everything is possible and nothing is possible - simultaneously.
With no human observer the possibilities,or lack of them,are without meaning - and with no observer,of any kind,..these very propositions never existed at all.
I had no idea you were on TH-cam. Instant sub.
These videos have been far better than I expected.
Thank you for the hilarious in-joke at 3:04! I really appreciated that! (And all your wonderful work!)
Reminds me of that show Life After People. Similar questions would be the last human speech, last structure, etc.
4:48 did anyone elses youtube borders around the video turn red before the video did? Im on dark mode, felt like I was tripping out
Yeahh
It’s a feature
There are a bunch space probes powered by radioisotope thermoelectric generators, which is essentially a nuclear battery that's designed to power the craft for decades, but will produce some (ever decreasing) power for centuries. Surely one of them has an LED on it somewhere that will keep running on even milliwatts of power for a *very* long time.
That was my first thought as well, but I wonder about the assumption that there is an LED. The power consumption is so carefully assigned on a craft like that, there might not be any room to have something that draws energy without providing any function.
True in a sense. Transmissions are radio, which is on the em spectrum. Not visible light, but hey, why stick to visible? All the humans are gone.
@@irjake It could provide a function if the light also produced heat to help warm the guts of it.
There are/where a number of Russian lighthouses in the Arctic that used the same technology. If there is a prototype in a more friendly environment, that could possibly also last a very long time
@@michaelrudolph7003 Couldn't you just use the heat from the RTG for that?
Anyone see the show "Life After People?" It was a cool History Channel show that talked about stuff like this. Things like kudzo taking over Atlanta, buildings decaying and using real life examples of abandoned places.
(I developed a head!canon for the show since they never go into where all the humans dissappeared to. It was something rapture-like but they apparently had enough warning at least to stop their cars and, in many cases, leave doors open so pets could get out.)
wait i think i used to watch that
About hydro power, not all hydro plants are connected to a grid. Some are local only to a single building and are also built strong without a high load, meaning they can keep spinning for much longer than the gearboxes in wind mills and big dams.
I’ve been reading these sense I was a kid I’m so glad you put them into a video format
Man did Rhode Island dirty 💀 3:01
pretty sure its a reference to the last video about putting everybody in a singular place (rhode island) and having them all jump at the same time
@@spectre818 ya
@ThatOneGuy5540 so how exactly did he: "[do] Rhode Island dirty"?
@@Ten_Thousand_Locusts By sending the entire world's population there and rendering it a "graveyard of billions," I guess?
1:56 I love that randall also is a Tom Scott fan.
What interesting thought: what if the entire atmosphere was oxygen?
All I’ve thought of so far is the obvious ‘you can hold your breath for much longer,’ as well as the fact fires would be much stronger. Could be fun to look into that in more depth.
wouldn't there be a global explosion as soon as there was any kind of spark?
@@benselander1482 No. There would be no fire apart from volcanic activity, because absolutely everything that could be oxidized or burnt - would already be.
@@PatrickKQ4HBD the hypothetical wasn’t totally specific, but I assumed it was the atmosphere suddenly changing to all oxygen. Since the example given involves someone (presumably a non-incinerated person) holding their breath for longer.
But I like your approach of: under what conditions could this atmosphere exist?
Last time there was a large abundance of O2 we had giant bugs and things..
That would be a cool concept! However pure oxygen can be harmful to humans, and at normal pressure can give us oxygen poisoning! Maybe we would be able to breathe longer, but it probably wouldn't be pleasant. Fires would definitly become much more intense/ignite into an explosion!
That's so cool that he is animated these now!! Childhood memories reading these
3:27 i would like to see at least the first movie in that series, it seems fun
2:20 nah I think the ncr will step in
I thought no one would comment something like this, new vegas truly is a game
Ah a man of culture I see
Very awesome concept and video! I just subscribed. Keep up the great work!
I've read all your books and they're all so interesting and when i found out you were making videos too i was extremely exited!!! I love your books and content!
I love the reference to the video where we put everyone in Rhode Island (3:00)
There's gotta be a satellite with an LED whose electronics and solar panels won't corrode due to being in space that could outlast the Cesium right?
Wouldn't their orbit decay eventually?
@@robertlewis6915 For near-Earth satellites, I could see that being an issue, but for ones that are further out, I'm not so sure it couldn't rival the Cesium amount of time.
No. Due to the nature of radioactive decay, so long as there is one glass-sealed atom of Cesium somewhere, the last photon of light has not been emmited yet.
Let's say there is 5 000 kg of Cesium. It will take 368.63 years to reduce it to 1 kg. But that is 7.3 moles, or 4.40E24 atoms. To reduce that to 1 atom, you would need additional 2 455.90 years, after which you can expect the last atom to pop in the next 60 years.
So in total, it would take around 2884 years to reduce 5 tonnes of Cesium to nothing, with every doubling of mass adding another 30 years.
I don't think any of the probes can expect to remain functional for 3000 years or so.
the issue isn’t decay it’s all those micro collisions
@@frantisekvrana3902 It's kind of cheap saying that a single photon emitted by a radioisotope created by humans thousands of years ago counts as an artificial light source, since you can't see it.
I still think an LED on a solar-powered deep space satellite would be the longest lasting light source.
Excuse me, but Morrissey assured me there was a light that NEVER goes out.
Ever see 'Life After People'? Loved that show and just found it on Amazon Prime Video. The 'end of days' type of videos and docs are fascinating, so glad I found this channel. Oh another thing, A book "Solar Flare" is a fictional book about the entire energy system shut down and how people lived through it.
I remember reading a thing ages ago about an underground fire (a coal seam, I think?) which was started by a fire at a mine, burns slowly due to the low amounts of oxygen it can draw in, and is expected to burn for a hundred years until it consumes the entire seam.
No idea how accurate or exaggerated the story was; but if there's a glow from that fire illuminating some inaccessible cave, would it count as an artificial light source?
You might be thinking of the Centralia Mine Fire: en.wikipedia.org/wiki/Centralia_mine_fire
yep, that's just north of here in Centralia, PA.
Halda Ema, is an artificial hill in Ostrava, made of gangue from local mines.
It is technically on fire, and has been from it's founding in 1920. But the surface is cool enough, only the inside is hot.
It does mean that the vegetation there is like from south Europe, rather than central Europe.
I remembered hearing about there being one in the Middle East, so I started googling other eternal fires. There's several! (Tho the one I was thinking of [Darvaza, Turkmenistan) was put out in 2022.
There's Burning Mountain in Australia they think has been burning for 6,000 years. (Not human caused [probably] but points to how long these might last! )
@@CelestialAnamoly There's also the naturally occurring 'nuclear reactor' in the Oklo uranium deposits in West Africa
edit: Ah my bad it was already long 'extinct' when it was discovered in the '72. Well, still awesome!
Imagine aliens find Earth, humans long gone, just a bunch of solar powered LED street lights. Imagine the aliens trying to figure that out.
recently saw someone pull a musical birthday card out of a box from the 70s and it still worked when opened?
So quick interjection, Geothermal power plants and grid scale wing would shut down quickly for the exact same reasons nuclear would.
Generators are designed to run at normal grid frequency. A large drop would be cause for the breaker to open automatically.
In most, if not all, geo plants, they would be at full load when this happens (cause base load generators) and would quickly overspeed before the governor could respond. This would cause the governor and stop valves to slam shut to prevent the turbine undergoing rapid unplanned disassembly.
Wind turbines would behave similarly because their governors simply dont have the response time to prevent an overspeed from disconnect under any load, let alone full. Their brakes basically immediately kick in if its not a normal shut down.
The way he casually says he talked to a nuclear reactor operator like it’s nothing😂 0:42
Well, you can find nuclear power stations in the phone book.
Phone book. It's a thing we... oh, never mind.
@@RichWoods23 internet also works, old man
2:38 Battery lights would all be off within a few dozen years . . . where can I get some of these super batteries?
You missed the most important of all: Children's star havens, which recharge every day by the sun and glow for half an hour. There are bunkers in Germany build by the Nazis with florescent paint, which works perfectly today, still. So the paint has no issue surviving 85 years or so :)
One bedroom in my house has a glow in the dark star sticker on the trim around the closet door. As near as I can tell, the last time an owner of the house had children here was in the late 1950s, and it still glows.
@@moconnell663yeah but it doesn’t emit light by itself since it depends on another light source directly shining on the material. I forgot the why tho,
@@JunkerFunker3Like every other ones
Saw this out of nowhere, glad that xkcd is doing videos as well now! I might be late to the party lol
0:50 ahaha using one of your comics about log scales. I love it
3:07 nice reference to previous video!
okay, first I thought "when he will bring up ISS", with the idea that there's solar panels on the station, so limiting factor will be slowing down from Earth atmosphere, but on second thought... what about satellites in general? since question doesn't specify "artificial light source on Earth", and solar powered satellites almost definitely have some sort of light source on them...
the thing is, all those satalites and the ISS are in slowly decaying orbits so without any orbital corrections getting sent they would all burn up in less than 10-15 years.
@@deathfuzz well, not quite all of them; low Earth orbit satellites (like the ISS, and thousands more), sure. But geostationary, for example... would be fine for a lot longer! The only question is whether they do, indeed, have any light sources. And the other point of note was "if every human disappeared off the face of the Earth, implying they might not care about space! In fact, the astronauts on the ISS wouldn't vanish, under the initial premise)
Pretty much every low and medium altitude satellite's orbit would decay and cause it to burn up long before all the streetlight solar panels failed, and the ones that are far enough out to be less affected by atmospheric drag are more affected by solar radiation etc. Best bet for electricity in non-earthbound objects is deep space probes running on RTGs, but TBH I doubt that high orbit satellites and probes actually have the light sources y'all are referencing...
@@EcceJack The ISS is still in Earth's thermosphere.
Very few satellites have an expected lifespan of greater than 50 years. Yes, they aren't going to oxidize where there's no oxygen, but they can still be taken out by solar flares and impacts with stray objects. Keep in mind, too, that the whole problem with chlorofluorocarbons in the ozone layer was that cosmic rays caused chemical changes that were all but impossible in normal terrestrial conditions.
Emergency call boxes being one of the last lights to go out in case of "rapid earth dehumanisation" is kind poetic.
Good one! But I think they use batteries, that was not mentioned (The solar and the light don't work at the same time.)
damn it this is such an underrated channel bruh. love your video
3:06 RHODE ISLAND MENTIONED ‼️‼️‼️
Yeah woooo!!
There are diesel generator setups that charge batteries in the case of a power outage. Assuming there's such a setup that has only a single small LED as its load, the generator will only start when the battery is getting low. Yes, the battery will degrade with time, but such a setup could technically last a few decades as the generator only starts once every few years as battery discharges slowly.
But diesel generators themselves need regular maintenance - the starter battery would probably die first with nothing to charge it, if it is in a cold location it needs a block heater to get started, and over time the diesel fuel gets contaminated with moisture.
@@lego-redhat The generator runs off the battery it charges.
IF it's cold, then there's a generator somewhere that is still a good temperature for generators and batteries. So that keeps running fine.
And that place is also dry as a bone, no real moisture to speak of.
Did anyone else notice the Rhode Island sign at 3:05 referencing one of their previous videos (the "what if everyone on earth jumped at once" video)?? It's such a fun little callback lol I love it