The Half Life of Facts

“Everything that guy just said is bullshit. Thank you.”

- Vinny Gambini, My Cousin Vinny

Opening statement by defence counsel

Would it surprise you to know that most of what you learned at school will be proved eventually not to be true. I’m not talking maths, 2 plus 2 will always equal 4, but things such as physics, science, history, astronomy, sociology. . . 

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Some comments:

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Half-life is the term used to describe the amount of time required for a quantity to fall to half its value from a certain time. It is usually applied to describe something undergoing exponential decay and is constant over the lifetime of the decaying quantity, but does not need to apply only to something decaying exponentially. Hence radioactive decay is measured in half life amounts but is not always a constant half reduction. A more correct definition therefore would be "Half-life is the time required for exactly half of the entities to decay on average". 

Knowledge and facts have also been described as having half lives, but more of that later.

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The science of measuring and analysing science itself is known as scientometrics. One of its early exponents was mathematician Derek J. de Solla Price (1922-1983):

Based on a 13 year study, Price released his findings in 1960 that scientific knowledge had been growing steadily at a rate of 4.7 percent annually since the 17th century. According to Price, scientific data was doubling every 15 years and was expanding by a factor of 10 every 50 years.

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The consequence of knowledge expanding so dramatically is that some things that were believed to be true get shown to be incorrect as other facts and knowledge replace or expand the existing information.

At various times in the past it was believed, as fact, that:

• witches should be burned at the stake

• the Sun revolved around the earth

• Pluto was a planet

• evolution was heresy

• segregation was scientifically justified.

Those beliefs no longer hold true.

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If knowledge is expanding by factor of 10 every 50 years, at what rate do former facts disappear? 

Harvard mathematician Samuel Arbesman sought to answer this in his 2012 book “The Half-Life of Facts: Why Everything We Know Has an Expiration Date.” 

Samuel Arbesman

Some points made by Arbesman:

·Arbesman applied the concept of half-life of radioactive isotopes to facts and looked at how long it took for clinical knowledge about cirrhosis and hepatitis to decay. 

According to Arbesman, “the half-life of truth was 45 years.” In other words, half of what physicians thought they knew about liver diseases was wrong or obsolete 45 years later.

· Like radioactive decay, we cannot predict which individual facts are going to be proved false, but we can know how long it takes for half the facts in a discipline to become obsolete.

· Facts and knowledge break down at different rates. 

Arbesman: 

“Medicine still has a very short half-life; in fact it is one of the areas where knowledge changes the fastest. One of the slowest is mathematics, because when you prove something in mathematics it is pretty much a settled matter unless someone finds an error in one of your proofs.”

· When we integrate new facts or changed facts into our minds and psyches, we do so as part of the store of facts we already have. 

Arbesman: 

“We persist in only adding facts to our personal store of knowledge that jibe with what we already know, rather than assimilate new facts irrespective of how they fit into our worldview.” 

· Arbesman: 

“Exponential knowledge growth cannot continue forever. Knowledge growth is slowing compared to major leaps in the past, all the low-hanging fruits having been taken. 

In some fields science is getting harder, but I would not say that science as a whole is becoming more difficult. We are still adding new scientists every year, but the rate of growth has slowed and science is increasingly being done by large teams. But there are many areas where we thought there is nothing left to explore, only for someone to come along and say that there is something there, after all. 

In mathematics there was an extreme case of this in the 1990s, when two high-school students figured out a new way to prove one of Euclid's theorems, something that had not been done in a thousand years. So even though basic geometric proofs are not the frontier of mathematics, there are still things you can do. And even where things slow down in science, often that slowing forces scientists to be cleverer, both in finding ways to create new knowledge but also in finding new ways to combine disciplines. Plus nowadays new technology is a real driving force; the new computational tools have created the potential for a scientific revolution."

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Some criticisms of Arbesman’s half-life of facts concept:

· Facts and knowledge do not break down exponentially.

· It is unclear that there is any way to establish what constitutes "knowledge" in a particular area, as opposed to mere opinion or theory.

· Knowledge cannot be quantified.

· Falsification of a doctrine is not comparable to the exponential decay process that atomic nuclei go through.

· The whole concept is imprecise and varies from discipline to discipline.

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What’s useful about the concept?

· It highlights that a lot of what we know and believe will be unreliable next generation.

· Arbesman: “Stop memorizing things and just give up. Our individual memories can be outsourced to the cloud.”

In other words, simply google it when you need to know.

· Arbesman:

“I want to show people how knowledge changes. But at the same time I want to say, now that you know how knowledge changes, you have to be on guard, so you are not shocked when your children coming home tell you that dinosaurs have feathers. You have to look things up more often and recognise that most of the stuff you learned when you were younger is not at the cutting edge. We are coming a lot closer to a true understanding of the world; we know a lot more about the universe than we did even just a few decades ago. It is not the case that just because knowledge is constantly being overturned we do not know anything. But too often, we fail to acknowledge change.”

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“The only thing that is constant is change -”

-Heraclitus

534-574 BC