Everything you learned in school is slowly rotting. Not because your teachers lied to you, but because knowledge itself has an expiration date.
It's a weird thought. We treat facts like solid rocks—unchanging, sturdy, dependable. But in reality, facts are more like radioactive isotopes. They decay. This concept, known as the half life of facts, suggests that over a predictable period, half of the information in a specific field will be proven wrong or superseded by something more accurate.
If you're still relying on a medical textbook from 1970, or even a tech manual from 2018, you're walking around with a head full of "knowledge" that isn't actually true anymore.
The Man Who Measured the Decay of Truth
Samuel Arbesman is the guy who really put this on the map. He's a complexity scientist, and in his book The Half-Life of Facts, he looks at how knowledge doesn't just change randomly. It happens in patterns.
Arbesman wasn't just guessing. He looked at the hard data. He examined how long it takes for a discovery in fields like mammalogy or hepatitis research to be overturned. The results are kinda terrifying if you value being "right." He found that in certain areas of medicine, the half-life of a fact is about 45 years. That sounds like a long time, right? It isn't. It means if you're a doctor who graduated in the late 70s and didn't keep up with the journals, roughly half of what you "know" to be true about the human body is now officially nonsense.
Why facts actually "die"
Knowledge doesn't just vanish. It gets refined. We used to think the Earth was the center of the universe. Then we realized the Sun was. Then we realized the Sun is just a tiny speck in a massive arm of a galaxy that is itself one of billions. The old "fact" wasn't a total lie—it was the best approximation available with the tools of the time.
But today, our tools are getting better. Fast.
When we look at the half life of facts through the lens of modern technology, the decay is accelerating. In the 1920s, if you learned how to fix a steam engine, that knowledge stayed useful for your entire career. Today, if you learn a specific coding framework, it might be legacy code within thirty-six months. Information is being generated at such a massive scale that the sheer volume of new data forces the old data out of the door.
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Looking at the Data: Medicine vs. Physics
Not all facts are created equal. Some things stick around. Gravity isn't going anywhere (well, our understanding of it might shift at the quantum level, but you’ll still hit the floor if you trip).
Medicine is the most famous example of rapid decay. A study published in the Journal of the American Medical Association (JAMA) once tracked the validity of clinical conclusions over time. The researchers found that after about 10 to 15 years, nearly half of the "gold standard" findings were either contradicted or significantly weakened by newer, better-designed studies.
- In the 1940s, we thought lobotomies were a breakthrough. They won a Nobel Prize.
- In the 1990s, the "food pyramid" told us to eat massive amounts of bread and pasta while fearing all fats. We know better now. Sorta.
- Even the number of chromosomes in humans was "wrong" for thirty years. Scientists thought we had 48. Everyone taught 48. It was in all the textbooks. It turns out, we have 46. We just couldn't count them right until 1955.
Physics, on the other hand, moves a bit slower. The "facts" of physics are often mathematical certainties within specific frameworks. But even there, the half life of facts shows its teeth. When we discovered dark matter, it didn't just add a new page to the book; it rewrote the whole chapter on how the universe holds together.
The Social Half-Life: Why We Cling to Dead Facts
Why is it so hard to update our internal databases?
Honestly, it's a mix of ego and biology. Once you’ve invested time into learning something, your brain treats that information like an asset. Letting go of it feels like losing money. This is what psychologists call "belief perseverance." Even when people are presented with new evidence that contradicts what they know, they tend to double down on the old, decayed fact.
There's also the "social" half-life. We live in bubbles. If your entire social circle believes a specific diet is the "truth," you aren't going to look at the new data suggesting it’s actually damaging your kidneys. You’d rather be wrong and have friends than be right and be lonely.
This creates a lag. There is a gap between when a fact is "disproven" by experts and when the general public actually stops believing it.
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The Google Problem
Search engines should help, right? In theory, yes. In practice, they sometimes keep dead facts on life support.
When you search for a health tip, Google’s algorithm looks for "authority." Often, authority is measured by how many people have linked to a page over time. If a blog post from 2012 about the benefits of a specific supplement has 10,000 links, it might still outrank a 2024 study that says that supplement is useless.
The internet has a long memory. It’s hard to delete the past. This means the half life of facts is actually being artificially extended by the way we organize information online. We are surrounded by "zombie facts"—information that is dead but still walking around, influencing our decisions.
How to Survive the Decay of Knowledge
You can't stop facts from changing. It’s the nature of progress. If facts didn't have a half-life, it would mean we’d stopped learning. That would be worse.
So, how do you manage your own mental library?
You have to adopt a "Beta" mindset. Think of your knowledge as software. It needs patches. It needs updates. It’s never "finished." If you graduated university ten years ago and haven't radically changed your mind about anything in your field since then, you are probably operating on outdated data.
Specific Tactics for a High-Decay World
First, check the "born-on" date. Whenever you consume information, look at when it was produced. In tech or medicine, anything older than five years should be treated with extreme skepticism. In social sciences, maybe ten years.
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Second, seek out the "Update." Don't just search for a topic; search for "[Topic] + recent developments" or "[Topic] + controversy." You want to see where the cracks are forming in the current consensus. That’s where the facts are starting to decay.
Third, embrace "intellectual humility." It sounds like a buzzword, but it’s basically just the realization that you might be wrong about everything. It’s the willingness to say, "Based on the data I had in 2020, I believed X. But the 2026 data says Y, so I’m moving to Y."
The ROI of Knowing Less
There is actually a massive advantage to understanding the half life of facts. It allows you to focus on "Lindy" knowledge.
The Lindy Effect is a concept that says the future life expectancy of some non-perishable things—like an idea or a book—is proportional to their current age. If a book has been in print for 50 years, it’s likely to be in print for another 50. If a "fact" has survived for 2,000 years (like the principles of Euclidean geometry), it probably has a much longer half-life than a "fact" about the best way to optimize an Instagram ad.
If you want to build a foundation of knowledge that doesn't rot, spend more time on the fundamentals. Physics, logic, basic psychology, and classic literature have very long half-lives. The "tactics" of the week have the half-life of a fruit fly.
Actionable Steps to Audit Your Knowledge
Stop trusting your memory. Your brain is a warehouse of old, dusty boxes.
- Audit your professional credentials. If you hold a certification or degree, look up the current curriculum for that same program today. What are they teaching now that wasn't even a concept when you were a student? Those are your blind spots.
- Follow the "Citing Articles" trail. If you rely on a specific study or book, use Google Scholar to see who has cited it recently. Are they citing it to support it, or are they citing it as an example of an old theory that has been debunked?
- Diversify your information sources. If you only read one type of journal or follow one group of experts, you’ll be the last to know when their "facts" start to decay.
- Practice "Productive Forgetting." Consciously decide to let go of old ways of doing things. Delete the old templates. Trash the old notes. If the half-life of your industry is short, your ability to unlearn is actually more valuable than your ability to learn.
The world isn't getting simpler. Information is moving faster, which means the half life of facts is getting shorter. Staying relevant in 2026 and beyond isn't about knowing the most; it's about being the fastest to realize when what you know is no longer true. Stop clinging to the "truth" of yesterday. It’s already decaying.