Half-Life of Knowledge: Everything you Know Has an Expiration Date
Medium | 20.12.2025 20:03
Half-Life of Knowledge: Everything you Know Has an Expiration Date
Learning how to learn is 21st century superpower
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Think about this: how much of what you learned in school is still true today?
If you’re honest with yourself, the answer might be: less than you think.
In this fast-paced era, information ages faster than ever. What was an unquestionable fact yesterday could be an obsolete myth tomorrow. And if you’re someone who wants to learn, grow professionally, or simply understand the world, this detail changes everything.
Today I want to talk to you about a fascinating concept: the half-life of knowledge.
I’m going to explain what it means, why it affects everything you learn, and — most importantly — how you can adapt so you don’t fall behind in a world that’s moving faster and faster.
In this era, the ability to learn is becoming a superpower…
1. What is half-life?
Half-life is the time it takes for half of something to disappear.
Yes, I know it sounds a bit abstract. Let me explain: the term comes from nuclear physics. Ernest Rutherford observed that some chemical elements lost unstable atomic particles at a rate that could be calculated. That characteristic time — when half of the element disappears — is called its half-life.
And although it may sound strange, the concept applies to many things.
From how long it takes your body to eliminate caffeine, to the lifespan of a marketing campaign. Even, as we’ll see, to knowledge.
2. Half-life in marketing and social media
Advertisers talk about the half-life of a campaign to refer to the time it takes to receive half of the responses they expect. To give you an idea…
- A LinkedIn post has a half-life of 24 hours.
- A tweet, just minutes.
In fact, I wrote some time ago about the half-life of online content, and why choosing Substack over Twitter or Instagram isn’t a matter of taste — it’s a strategy. Some platforms give your ideas time to breathe; others kill them before they can grow. If you understand half-life, you’ll know when and where to invest your efforts.
Take a look if you want to know which platforms are optimal for your project.
3. The half-life of knowledge
Sociologist Samuel Arbesman explains it in his book The Half-Life of Facts.
Knowledge has an expiration date.
What we believe to be true today will, over time, be corrected, refined, or refuted. This is what he calls the half-life of knowledge. The famous example is that of human chromosomes. Until 1965, it was taught that humans had 48 chromosomes, even though in 1956 two researchers had shown that the number was 46. For years, many scientists who found 46 assumed they were wrong (Arbesman, 2013).
Think about it: how much knowledge we accept today will be obsolete tomorrow?
It happens in nutrition, medicine, technology, psychology… and in thousands of other fields. Much research is never replicated, yet we continue to accept it as true. Asimov summed it up well: people aren’t stupid — they simply believe based on the facts they know.
Think of a Sumerian from thousands of years ago.
With the knowledge he had, concluding that the Earth was flat was logical. He wasn’t ignorant; he was working with the tools available. In a thousand years, someone will look back at us and think the same about many of the things we defend as true today.
Almost everything we rely on is being built on the fly.
4. The half-life of careers
A century ago, the half-life of an engineering degree was 35 years (Jones, 1966).
In the 1960s, it dropped to just 10 years before 50% of the knowledge became obsolete — but that was in the 60s. Imagine today… 5 years? Everything is advancing extremely fast. How much time would you need to spend each week just to stay up to date?
It’s like running on a treadmill that never stops accelerating.
You have to run faster and faster just to stay in the same place.
That’s why we increasingly hyper-specialize. We become experts in tiny slices of human knowledge. The advantage is that you can truly master an area. The disadvantage is that your worldview narrows, and interdisciplinary collaboration becomes indispensable for almost anything.
It’s the inevitable consequence of the growth of human knowledge.
5. What to do now
Knowing that knowledge expires isn’t enough.
If you try to absorb everything, you’ll end up exhausted — and you still won’t succeed. The key is to accept that learning isn’t something you do once; it’s a continuous process. It doesn’t end when you get your degree or formal training.
That means three things:
- Invest time in learning every week, even if it’s just a little.
- Prioritize fundamental principles over less solid data.
- Accept that unlearning and relearning are an inevitable part of the game.
The faster the world changes, the more valuable the ability to update yourself becomes. The half-life of knowledge reminds us that education isn’t a place you arrive at. It’s a path that never ends. And that, perhaps, is the best news of all.
If you want to go deeper into this, I’ve written several articles on how to master the art of intentional learning. Here’s a selection of the best ones:
- Feynman Technique: How to master the learning process
- Double-loop learning: How to get out of autopilot and really learn
- Root Method: From Passive Reading to Active Learning
✍️ Your turn: Have you personally experienced the “half-life of knowledge” in your field of study or work, and how have you adapted to it?
💭 Quote of the day: “The skill I was learning was the most crucial one of all: patience — to read things I could not yet understand.” — Tara Westover, Educated: A Memoir.
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References 📚
- Arbesman, S. (2013). The Half-Life of Facts: Why Everything We Know Has an Expiration Date.
- Jones, T. F. (1966). The Dollars and Sense of Continuing Education. IEEE Transactions On Aerospace And Electronic Systems, AES-2(2), 140–142. URL
