It was an accidental hoax. A screenshot from Back to the Future got passed around this summer, showing that June 27, 2012 was the date when the DeLorean hurtled forward in time. After a certain period of excitement, posts, and retweets, people soon realized that the image had been modified: the "actual" date wasn’t for three more years. Turns out this wasn’t even the first time this had happened. A similarly fudged screenshot of the DeLorean’s time counters spread across the internet just two years before (though that was an intentional hoax).

Not only were people spreading incorrect information, but the collective internet consciousness didn’t even recognize the return of the same error. And even when we do recognize such errors, we can’t fix them as easily as we might like. Just ask Philip Roth about how difficult it was to correct an entry on his own Wikipedia page – he had to publish an open letter in the New Yorker to satisfy the requirement for a more reputable secondary source.

[#contributor: /contributors/59322ee5edfced5820d0ed2b]|||Samuel Arbesman is an applied mathematician and network scientist. He is currently a senior scholar at the Ewing Marion Kauffman Foundation and a fellow at the Institute for Quantitative Social Science at Harvard University. He blogs for Wired on [Social Dimension](https://www.wired.com/wiredscience/socialdimension). Arbesman’s book [The Half-Life of Facts](http://halflifeoffacts.com/) is released today.|||

Knowledge changes around us all the time. Yet we don’t always have the most up-to-date facts. This is true, I’d argue, even in an age of instant and massive information. Despite our unprecedented ability to rapidly learn new things and crowdfix mistakes, Knowledge and its sinister twin Error continue to propagate in complex and intriguing ways. Errors persist among us for far longer than they should and even when there is more accurate knowledge elsewhere. Newer knowledge does not spread as fast as it should and weaves its way unevenly throughout society.

The problem isn’t just epistemological – it can have serious consequences. Doctors might not realize there is a newer and better treatment. Teachers might not have the most current materials. Parents might not have the latest child-rearing techniques. Entire fields of science invest time, money, and other resources recapitulating the findings of others due to their ignorance of other fields’ advances.

While ongoing scientific inquiry is one solution to improving knowledge and rooting out error, the diffusion of accurate facts is far from instant or guaranteed. For example, many retracted scientific papers still get cited years after they have been retracted. The number of citations may drop quite rapidly once a finding is retracted (due to error, fraud, or other reason), but it can still be cited long after the study has been discredited or otherwise rendered obsolete. Some of this spread comes down to the complicated structure of social networks, as well as cognitive quirks that make each of us predisposed to either accept new information or ignore it entirely. There is a burgeoning field of network science devoted to studying and addressing how the structure and other properties of our interactions can affect the spread of information and misinformation. But what we know about this is far from complete.

Here’s a seemingly innocuous example having to do with the health benefits of spinach. The iron content of spinach was measured back in the 19th century, but due to the transposition of a decimal point, for decades it was thought that spinach had 10 times more iron than it actually did. In the early 1980s, an eminent physician published a paper – aptly and tersely titled "Fake!" – in a medical journal to root out such errors:

In the year that Popeye became once again a major movie star it is salutary to recall that his claims for spinach are spurious. Popeye’s superhuman strength for deeds of derring-do comes from consuming a can of the stuff. The discovery that spinach was as valuable a source of iron ... was fraudulent; German chemists reinvestigating the iron content of spinach had shown in the 1930s that the original workers had put the decimal point in the wrong place and made a tenfold overestimate of its value. Spinach is no better for you than cabbage, Brussels sprouts, or broccoli. For a source of iron Popeye would have been better off chewing the cans.

After carefully tracking down this paper, I shared this story in my forthcoming book The Half-Life of Facts as one of many examples about how knowledge grows and changes.

Well, funny thing. This story about correcting a scientific error itself seems to be erroneous.

According to a professor at Nottingham Trent University, a sloppy measurement – rather than a typographical mistake – caused the error about the high iron content of spinach. And like the DeLorean hoax of this summer and a couple of years ago, the error had already been corrected by the early 20th century. But just as the original sloppy measurements still got cited decades later (so some of the claims about the error’s persistence seem to be true – the story is wonderfully complicated), the erroneous myth-busting in the medical journal has also been cited for decades. All of this was debunked in 2010 – 29 years later! – by Nottingham’s Mike Sutton (and even acknowledged by the original journal author). But news of it did not arrive to me until after my book had already gone to press.

Far from being disconcerting, however, this is exciting.

It would be so convenient and predictable if all knowledge stood the test of time. But if that were the measure of being a scientist, then no one would be a scientist. No one would explore or write or even be willing to read about our latest (even if recapitulated or inaccurate) findings. Of course, we still have to be scrupulous; but the good news is that while knowledge is fickle and changing, the way it changes does obey some rules and regularities. There is a method to the madness.

So we should all keep in mind what a former professor of mine said after lecturing his classes on a certain scientific topic on a Tuesday. On Wednesday, he read a paper that was published and that invalidated the lecture. On Thursday, he went into class and told his students, "Remember what I told you on Tuesday? It’s wrong. And if that worries you, you need to get out of science."

UPDATE: The plot thickens. With the spinach error, there seems to have been confusion about iron oxide and iron as well, but the story is still in progress... See Mike Sutton's comment below.

Editor: Sonal Chokshi @smc90