Avengers: Endgame — The Science of the Thanos Snap

Lon Harris
Movies Marvel
Movies Marvel MCU

Thanos: he’s a motivated, proactive alien go-getter with a lot of strong opinions about effectively running a universe. For all of his faults, it’s hard to argue that he’s not an outside-the-box thinker with a penchant for complex problem-solving.

So far, Marvel’s entire 20+ film ‘Infinity Saga‘ has revolved around the Mad Titan’s latest outlandish scheme: to “balance” the universe in perfect harmony by eliminating half of all living things in an instant.

Thanos presumes that doing so would eliminate modern-day concerns about limited natural resources and overpopulation. After all, with only 50% as many people, animals, plants, Kree, experimental raccoons, space pirates and humanoid Ducks to compete with, the survivors could permanently relax and take it easy, confident there will always be enough food to eat and frontier to explore. (Thanos boasts to his adopted daughter Gamora that her homeworld, Zen-Whoberi, is now a “paradise” after being Snapped.)

The Snap means substantially fewer of all species, including humanoid Ducks.

But what would ACTUALLY happen to a planet if you pulled a Thanos and eliminated half of all life forms with the snap of your oversized purple fingers? To find out, we spoke with research scientist Justin Christensen of the UCLA Physics Department, and got some input from Infinity War and Endgame writers Christopher Markus and Stephen McFeely into the bargain. For simplicity’s sake, we used Earth as our sample planet. You know, cause it’s the one where the Avengers live. Also we’re on it right now.

It turns out, Thanos’s heart was in the right place (if Titans actually have hearts), but he may have needed some help in the planning and execution stages. The post-Snap world sounds pretty grim… to the point that some Avenging may actually be in order.


OK, before we do any actual calculations, one huge question remains: does the Snap kill off 50% of ALL life or just SENTIENT life? All living things would include not just humans and animals, of course, but also plants and microscopic organisms. Everything from the massive redwood trees of Northern California down to the tiny bacteria living in your gut and helping you digest your popcorn would be at risk of Snappage.

It turns out, this remains a somewhat controversial decision on the internet in 2019. In a discussion with Fandom, Infinity War and Endgame writers Christopher Markus and Stephen McFeely said that the Snap only wipes out “sentient life” meaning humans, animals and aliens with consciousness and intelligence. Marvel Studios Chief Kevin Feige has largely agreed with this publicly, though a widely-shared discussion with Birth Movies Death following the release of Ant-Man and the Wasp muddied the waters a bit. Feige responded that the Snap wiped out “All life!” which was interpreted by some to also include plants and microbes. We know that Groot was wiped out, but whether or not he’s truly a plant or an alien with plant characteristics is a topic for another — probably fascinating — article.

Still, in the film itself, no distinction is drawn between ‘life’ and ‘sentient life’ and it’s entirely possible to imagine that Thanos — even accidentally — may have wiped out the plants and the bacteria and viruses along with the horses, dogs, and trees voiced by Vin Diesel. It’s a question that has certainly perplexed the Web since the film’s first release. For the purposes of this article, we’re going to consider both scenarios.

THE IMMEDIATE AFTERMATH: Chaos in the Air and on the Roads

Currently, the world population sits at around 7.6 billion people, which means the moment Thanos finished his Snap, 3.8 billion of them are just GONE. This may sound like a lot — and you’d probably be upset if you knew a bunch of them — but it’s worth noting that this only takes Earth’s population back to where it was in the year 1970. Exponential growth means that halving the population isn’t quite as effective as it sounds. If Thanos got his wish, and a utopia broke out following the Snap, we’d still be right back to 2019 population within another 50 years or so. Making that whole Infinity Gauntlet quest a lot of work for not much reward.

Speaking with Fandom about Infinity War, the film’s writers actually acknowledged the issue.

“Sadly if you cut the number of people on earth in half today, it only takes us back to 1970. We were very well populated at the time. It’s not like a devastated hellscape. It looks like ‘Mary Tyler Moore.’” Christopher Markus said.

Stephen McFeely added that the emotional reaction of everyone losing half of their friends, families and animal companions would turn it into a “hellscape” nonetheless.

But, of course, MANY more people would die following the Snap, not from the actual Thanos Effect, but as a consequence of so many humans disappearing. Christensen points out that, at most, there are as many as 20,000 airplanes in the sky, worldwide, at any time. If each plane has two pilots, approximately 25% of all planes flying at any given time would have both pilots disappear once Thanos snaps his fingers. If an average of 200 people were on board each flight, this would mean about 500,000 people would die in airplane crashes immediately following the Snap, as their plane was suddenly left without pilots.

But we’d also need to consider air traffic controllers! Currently, there are about 14,000 air traffic controllers working in the US, manning about 500 towers. If some towers lost all or most of their staff, they’d certainly have a hard time coordinating all of those active flights, leading to even more casualties. There are approximately 1 billion vehicles (cars, trucks, buses, etc.) in the world, and about 10% of them are in use at any given time. If you assume just 1% of the surviving drivers still on the road following the Snap are killed in crashes with suddenly driverless cars, that’s an additional half million fatalities.

All put together, we’re talking an additional 0.3% of the world’s human population facing very real, violent, non-ash-related deaths immediately after the Snap from Snap-related vehicular accidents. But the deaths wouldn’t end there (hooray!). In the months after the Snap, our global infrastructure would likely start to crumble — you know, things like roads and bridges, and water filtration systems and power grids — without enough people around to maintain them. This is also going to have significant repercussions in terms of the remaining population.

Devastating Knock-On Effects: Access to Clean Water and Medicine Affected

If you’re thinking the world would go into nuclear meltdown with the sudden eradication of people manning nuclear power plants, or that explosions in factories across the world would wipe out further swathes of the remaining population, you’d probably be wrong. Failsafes are usually built into dangerous equipment so that if things become unstable, even if there’s nobody around, it will shut down. We wouldn’t see multiple scenes like the below, in other words. Indeed, if Ego had succeeded with his plan in Guardians of the Galaxy Vol. 2, it would have been way more destructive than Thanos’s attempts to restore balance to the universe.

Guardians of the Galaxy 2
Ego's Expansion in Guardians of the Galaxy Vol. 2 threatened to extinguish ALL life.

Indeed, perhaps most interestingly, and devastatingly — something that many of us won’t have thought of — is the effect the Snap would have on vital supply chains; the processes by which people all over the world gain access to things like food, clean water and medicine. With far fewer people around to drive the trucks, figure out the logistics, start the companies and provide the services means that many people will simply have to do without, causing additional fatalities.

“Without people to maintain and fix vital systems, things like electricity and clean water are likely to be lost to a large fraction of the remaining population. Many people will likely face food and medical supply shortages. How people react to these challenges, and how many people will die as a result is tough to say,” Christensen says, “but certainly more deaths will result.”

Ouch. Partly from deadly epidemics resulting from the drinking of dirty water and/or lack of vital medicines and vaccines and people to administer said antidotes, presumably.


Christensen says that specific predictions about how the “complex and fragile relationships between many different species” would be impacted by Thanos are difficult, but it’s clear that we would see “many ecosystems change completely, and there could be species that never recover.” For example, species that can reproduce quickly would likely be able to get back to their current population levels quickly, while more slowly reproducing species could take much longer to recover, or fail to recover entirely.

If we’re including the disappearance of half of the plants, this would dramatically alter the planet’s appearance and landscape, but when you consider that half of all humans are being wiped out at the same time, the transformation may not prove devastating to our way of life.

The Earth’s atmosphere contains a delicate balance of gases — about 78% nitrogen, 21% oxygen, 0.96% argon and 0.4% carbon dioxide — but there’s a surplus, so long as these proportions stay the same, we’d be alright. And because almost all production and consumption of these gases comes from life on earth, halving life on the planet is unlikely to significantly disturb the proportion of these gases in our air since production and consumption would remain constant, meaning we’d still be able to breathe normally. We certainly wouldn’t expect to see scenes like the below (we know this famous Total Recall moment takes place on Mars, but still):

And if somehow all photosynthesis stopped, it would take about 1,000 years before oxygen levels dipped to the point that humans were in danger of suffocation. There’s just that much oxygen stored already in our atmosphere.

Even the disappearance of microbes and bacteria may not lead to mass deaths —  though it could complicate things somewhat.

“Microbes affect every aspect of life on Earth,” Christensen explains, from decomposing physical waste in our environment and breaking down the food in our stomachs to providing plants with nitrogen they need to survive. (Did you know there are 10 times as many bacterial cells in the human body than there are human cells? IT’S TRUE!)

Because the Snap would (theoretically) delete half of all microbial life, along with all other forms of life, it would greatly reduce competition for resources. Many microbial species would likely recover quite quickly, faster than the animals and plants that rely on them. A single E. coli cell can divide every 20 minutes, so even if Thanos left only 1 on Earth, within 20 minutes, we’d have 7 million of them.

Nonetheless, Christensen points out that “slowly reproducing microbes will take much longer to recover, and the disruption of any of life’s complex and fragile relationships with them can lead to large disruptions in our lives.” So we may not be ENTIRELY out of the woods, but it’s not as dire as you might initially assume.


Ultimately, the Snap would do very much what Thanos set out to do: kill half of all living creatures on Earth, thus leaving more resources for the survivors. Plus, it only sets the population back 50 years.

“Even if it took us double the time to recover, we still would quickly end up facing the same challenges of overpopulation, lack of resources, and destruction of our environment,” Christensen says.

So what would a UCLA physicist do with a fistful of Infinity Stones? “Stabilizing our population at a sustainable level is the only permanent solution to the inevitable problem humans face.”

OK, but can we add a few space battles?

But this isn’t exactly a pro-Thanos argument. Now, everyone on Earth has likely sunk into a deep malaise after losing their loved ones. As McFeely notes, “Reproduction [on Earth likely] slows way down, probably because of depression.”

So now we’re all bummed out and trapped in an emotional hellscape, and we’re STILL right back to where we started in just 50 years. Is there a “Maybe Do Some More Brainstorming On This One” Stone? Someone tell Thanos where to find that one.

Lon Harris
Lon writes for Screen Junkies and "Honest Trailers," Rotten Tomatoes, Inside Streaming and elsewhere. He still can't believe critics didn't like "Three Amigos" when it came out.