Half-life: On The Limited Lifespan Of Everything

The half-life in physics is the time required for one-half of an atomic nuclei to decay by virtue of radioactivity. We can apply half-life broadly as the time taken for something to halve its quantity. Unstable atomic particles have a half-life. But so does information, memories, knowledge, drugs, marketing campaigns, food, and all sorts of other things. The concept is present in every area where the quantity or strength of something decreases over time.

Half-lives are based in probabilistic thinking. If the half-life of something is ten days, it is most probable that half of the atoms—or the thing we are concerned with—will have decayed in that time frame. In biology, this is the half-life taken for a substance to lose half its effects. Take, for instance, caffeine. The half-life of caffeine—or for half of the substance to have left the body—is roughly six hours. Since this is a biological marker, it must be taken with a grain of salt. A dysfunctional liver or specific genes can make the metabolism of caffeine longer. Even how much we eat prior and whether or not that meal contained grapefruit juice can greatly influence the half-life of the substance. And this, of course, applies not only to our beloved bean juice.

The half-life of drugs vary from seconds to weeks. Biological half-lives are further complicated by the fact that they can be different in different areas of the body. Lead lingers for a month in the blood. But it lives rent-free for a decade in bone. Plutonium survives half a century in bone, but less than half of that in the liver. Marketing campaigns also have complicated half-lives: the time taken to receive half of the total responses. A tweet can have a half-life of minutes, whilst a brochure could survive weeks. Calculating this is how advertisers decide whether to push forth another message.

Even facts themselves have a half-life. That is, facts decay over time until they are no longer factual or complete. The time taken to replace or disprove facts is their half-life. Over time, one set of facts replaces the other. As our tools and knowledge get more advanced, we discover more, and sometimes our findings contradict what we “know” to be “true”. Thus we update our data based on the available research. Human intelligence happens this way. It is why most published scientific articles are false. By definition, most of them have long been rendered obsolete, and only the recent findings can be, as we say it, “science-based”.

Facts change incessantly. A glance at an old newspaper will tell you everything you need to know. Coke—the drink—was once thought of and marketed as a panacea, a miracle drug that could cure many diseases, and 7-Up was originally an antidepressant. The people of the past were not any stupider or smarter than we are. They just believed facts that have since decayed. The world is changing, and they simply had no basis to know what we now know. Since knowledge decays, this means we have to constantly update our knowledge to stay on top of the game.

Real life implications of half-lives:

• Physics: Uranium-238 has a half-life of about 4.5 billion years, critical for dating how old the Earth is, and understanding radioactive half-life helps scientists safely manage nuclear materials and assess environmental risks;

• Pharmacology: medications and drugs like paracetamol have a half-life, determining dosing schedules; this is how doctors calculate dosing intervals to ensure therapeutic drug levels are always present in your system;

• Business: product obsolescence typically follows a half-life pattern, where market relevance decays over time, and companies can analyze half-life to anticipate when they need to innovate or push upgrades; an instance is smartphones, which typically have a “market relevance half-life”, forcing companies to shift rapidly;

• Learning: the “forgetting curve” in education is a perfect illustration of the half-life of knowledge in our brains, and this is why we use spaced repetition to refresh our knowledge at intervals that match it’s retention half-life;

• Social trends: memes and trends have a cultural half-life, where their popularity declines exponentially after reaching its peak, and marketers use this information to anticipate when they should follow-up their campaigns effectively;

• Investments: the value of assets like vehicles declines over time in a half-life-like pattern, and you can employ the lens to see when an asset should be replaced or sold before it loses too much value;

• Habit: good habits often fade, where the intensity and/or frequency diminishes over time; bad habits do as well, as we put forth the effort and commit to small, sustained actions to weaken negative habits and replace them with positive ones.

How you might use half-life as a mental model: (1) track decay over time, applying it to predict how long a process, substance, or habit will take to diminish by a significant amount; (2) set realistic expectations, recognizing that substantial changes typically occur gradually, following a half-life pattern; (3) optimize your interventions, identifying key points in the half-life of something to act, like scheduling product updates or advertising boosts in intervals when attention starts to wane; (4) balance patience and persistence, using the model to remain patient during long-form processes; (5) strategically time your actions by leveraging the half-life of trends.

Thought-provoking insights. “Time erodes all things, but it does so predictably.” screams the half-life model’s thesis of how decay occurs systematically and can be hinged against. “We don’t just forget; we forget at a measurable rate.” reflects the half-life of knowledge and the need for deliberate reinforcement. “Nothing truly disappears; it only diminishes.” even after multiple half-lives, remnants of the original persist. Half-lives are a structured model for understanding decline and decay. Apply them where you want to allocate your resources most efficiently.