If all humans died, when would the last light go out?

this question comes from Allan who asks 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 we'll start with the obvious most lights wouldn't last long because the major power grids would go down relatively quickly without people there would be less demand for power but our fridges and air conditioners and lava lamps would still be running fossil fuel plants which Supply the vast majority of the world's electricity require a steady supply of fuel and their supply chains do involve people doing things as colon oil plant started shutting down in the first few hours other power sources would get hit with that extra load this kind of situation is difficult to handle even with human guidance and the result would be a rapid series of cascading failures leading to a blackout of all the major power grids nuclear reactors of course don't require a steady supply of fuel one reactor operator I talked to said that if their core settled into low power mode it could continue running almost indefinitely a cube of uranium contains about 6 million times as much stored energy as a similar sized cube of coal unfortunately although there's enough fuel most nuclear reactors wouldn't keep running for long as soon as something went wrong the core would go into automatic shutdown every part of a reactor control system is designed so that a failure causes it to rapidly shut down this would happen quickly many things can trigger a shutdown but the most likely culprit would be the failure of the power grid however plenty of light comes from sources not tied to the major power grids let's take a look at a few of those and when each one might turn off many remote communities like those on farflung Islands get their power from diesel generators these can run until their tanks run out of fuel which in most cases could be anywhere from days to months off-grid generating stations that don't need a human provided fuel supply would be in better shape geothermal plants can run for a fair bit of time without human intervention according to the maintenance schedule for the fangi island geothermal Planet Iceland every 6 months The Operators must change the gearbox oil and regrease all electric motors and couplings without humans to perform these sorts of Maintenance procedures some clamps might run for a few years but they'd all succumb to corrosion eventually lights relying on wind power would last a bit longer wind turbines are designed so that they don't need constant maintenance for the simple reason that there are a lot of them and they're a pain to climb the gser wind turbine in Denmark was installed in the late 1950s and it generated power for 11 years without maintenance modern turbines are typically rated to run for 3 years without servicing and there are no doubt some which would run for decades and one of them would probably have at least a status LED in it somewhere eventually most of the wind turbines would be stopped by the same thing that would destroy the geothermal plants their gear boxes would seize up generators that convert falling water into electricity will also keep working an operator at the Hoover Dam once said that if everyone walked out the facility would continue to run on autopilot for several years though if the power grid is down all that electricity would have nowhere to go in the end the dam would probably succumb to clogged intakes or the same kind of mechanical failure that hit the wind turbines and geothermal plants battery powered lights wouldn't Faire much better and would all be off within a few Dozen Years even without anything using their power batteries eventually self- discharge some types last longer than others but even batteries advertisers having long shelf lives typically only hold their charge for a decade or two solar power is probably the most promising candidate there are many off-grid solar powered buildings weather stations and other remote infrastructure around the world emergency call boxes often found along the side of the road in remote locations are frequently solar powered they usually have lights on them which provide illumination every night like wind turbines they're hard to surfice and so they're built to last for a long time solar panels will generally last as long as the electronics connected to them and as long as the panels are kept free of dust and debris the wires and circuits will eventually succumb to corrosion but solar panels in a dry place with well-built electronics could easily continue providing power for a century if they're kept free of dust by occasional breezes or rain on the exposed panels if we follow a strict definition of lighting solar powered lights in remote locations could conceivably be the last surviving human light source but there's another Contender and it's a weird one spent nuclear fuel contrary to popular portrayals radioactivity isn't usually visible which is part of why we need warning signs around areas with radioactive materials or waste sure watch tiles used to be coated in small amounts of radium to help them glow in the dark but the glow didn't come from the radioactivity itself it came from the phosphorescent paint on top of the radium which glows when it's irradiated once the phosphorescent paint breaks down the watch tiles are still radioactive but no longer glow watch tiles however are not our only radioactive light source when radioactive particles travel through materials like water or glass they emit light through a sort of optical Sonic Boom this light is called sharing COV radiation and it's seen in the distinctive blue glow of nuclear reactor cores some of our radioactive waste products such as CM 137 are melted and mixed with glass which cools into a solid block before being wrapped in more shielding for transport and storage and in the dark these glass blocks glow blue ccm1 37 has a half life of 30 years which means that 2 centuries later the blocks will still be glowing with 1% of their original radioactivity since the color of the light depends only on the particle Decay energy and not the amount of radiation it will fade in brightness over time but keep that same blue color and thus we arrive at our answer centuries from now deep in concrete vaults the light from our most toxic waste will still be shining

Channel: xkcd's What If?

Views: 2,751,991

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Id: 8fADp43wJwU

Length: 5min 4sec (304 seconds)

Published: Tue May 28 2024