Vanishing act: the Italian physicist Ettore Majorana, who disappeared in 1938. Photo: Kanijoman/Flickr
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The vanishing particle physicist and the puzzle he left behind

Ettore Majorana was an Italian physicist, the best of his generation, who disappeared in mysterious circumstances in 1938.

You probably haven’t heard of Majorana fermions. You probably haven’t heard of fermions, for that matter – nor of Ettore Majorana. Prepare yourself: it’s a story of mystery and frustration.

Let’s deal with the man first. Majorana was an Italian physicist, the best of his generation, who disappeared in mysterious circumstances in 1938. He emptied his bank account, bought a ticket for a boat ride from Palermo to Naples and left a note for his colleagues apologising for the inconvenience he was about to cause. He may have committed suicide but his body was never found. There are rumours of subsequent sightings in Buenos Aires. Some think that he abandoned physics and disappeared to live out his days in a secluded monastery.

Majorana’s specialism was quantum theory and it is tempting to think that he engineered his disappearance to reflect the subject’s strange ambiguities. A quantum particle such as an electron can be in two places at once, or simultaneously moving in two different directions; Majorana seemed to want his friends to wonder whether he could, too.

And so to his fermions. Just before his vanishing trick, Majorana predicted the existence of a particle with highly unusual properties. Although we have never seen one directly, there is every reason to think that it does exist and scientists on the 77-year-long hunt are tantalisingly close to pinning it down. This month, a group of Princeton University researchers added to the accumulating pile of evidence that the Majorana fermion is a real and fundamental building block of nature.

A fermion is one of the two types of particle that make up all matter. You have probably heard of the other one, the boson, because of all the Higgs fuss. Fermions are just as interesting. The building blocks of the atom – protons, neutrons and electrons – are all fermions. Majorana fermions have an added twist. Unlike protons, neutrons and electrons, they are their own antiparticle.

That is very odd. Matter and antimatter annihilate each other when they come into contact. Bang an electron and its antiparticle, the positron, together and they will disappear in a flash of energy. So how can a Majorana fermion be its own antiparticle?

To find out, we have to get one we can observe, hence the hunt. And in a peculiar case of life (or death) imitating art (or science), Majorana fermions are offering glimpses of their properties in materials crammed with ghostly particles that don’t actually exist.

When a solid conducts electricity, it does so because it contains negatively charged electrons that can move through the material. As they leave their usual position, the electrons leave behind a network of “holes”. Viewed from one perspective, these behave like real particles that have a charge opposite to the electron. The details get complicated but, in some materials, this can create a situation in which the moving charges and holes amount to something that behaves exactly like a Majorana fermion. That’s what the Princeton researchers have seen.

It has been very difficult to get this far. The material containing the Majorana fermion was just one atom wide and three atoms thick and had to be cooled to -272°C, one degree above the coldest temperature allowed by the laws of physics. The fermion was so small that it required a scanning-tunnelling microscope two storeys high to see it.

That said, although the observed particle is a good facsimile, it is frustratingly still more like a Majorana fermion’s shadow puppet than the real thing. Majorana’s legacy still eludes us. That note was not apologetic enough. 

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

This article first appeared in the 22 October 2014 issue of the New Statesman, Why Britain and Germany aren't natural enemies

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“A cursed project”: a short history of the Facebook “like” button

Mark Zuckerberg didn't like it, it used to be called the “awesome button”, and FriendFeed got there first. 

The "like" button is perhaps the simplest of the website's features, but it's also come to define it. Companies vie for your thumbs up. Articles online contain little blue portals which send your likes back to Facebook. The action of "liking" something is seen to have such power that in 2010, a class action lawsuit was filed against Facebook claiming teenagers should not be able to "like" ads without parental consent. 

And today, Facebook begins trials of six new emoji reaction buttons which join the like button at the bottom of posts, multiplying its potential meanings by seven: 

All this makes it a little surprising that Facebook CEO Mark Zuckerberg spent a good portion of the noughties giving the like button a thumbs down. According to Andrew Bosworth, Vice President of Advertising and Pages at Facebook (and known simply as "Boz") it took nearly two years to get the concept of an approval button for posts off the ground.

In a fascinating Quora thread, Boz explains that the idea of a star, plus sign or thumbs up for posts first came up in July 2007, three years after "TheFacebook" launched in 2004. Throughout these initial discussions, the proposed bursts of positivity was referred to as an "awesome button". A few months later someone floated the word "like" as a replacement, but, according to Boz, it received a "lukewarm" reception. 

The team who ran the site's News Feed feature were keen, as it would help rank posts based on popularity. The ad team, meanwhile, thought "likes" could improve clickthrough rates on advertisements. But in November 2007, the engineering team presented the new feature to Mark Zuckerberg, and, according to Boz, the final review "[didn't] go well". The CEO was concerned about overshadowing the Facebook "share" and comment features - perhaps people would just "awesome" something, rather than re-posting the content or writing a message. He also wanted more clarification on whether others would see your feedback or not. After this meeting, Boz writes, "Feature development as originally envisioned basically stops". 

The teams who wanted the button forged ahead with slightly different features. If you were an early user, you might remember that News Feed items and ads collected positive or negative feedback from you, but this wasn't then displayed to other users. This feature was "ineffective", Boz writes, and was eventually shut down. 

So when Jonathan Piles, Jaren Morgenstern and designer Soleio took on the like button again in December 2008, many were skeptical: this was a "cursed project", and would never make it past a sceptical Zuckerberg. Their secret weapon, however was data scientist Itamar Rosenn, who provided data to show that a like button wouldn't reduce the number of comments on a post. - that, in fact, it increased the number of comments, as likes would boost a popular post up through the News Feed. Zuckerberg's fears that a lower-impact feedback style would discourage higher value interactions like reposting or commenting were shown to be unfounded. 

A bigger problem was that FriendFeed, a social aggregator site which shut down in April 2015, launched a "like" feature in October 2007, a fact which yielded some uncomfortable media coverage when Facebook's "like" finally launched. Yet Boz claims that no one at Facebook clocked onto FriendFeed's new feature: "As far as I can tell from my email archives, nobody at FB noticed. =/". 

Finally, on 9 February 2009, "like" launched with a blogpost, "I like this", from project manager Leah Pearlman who was there for the first "awesome button" discussions back in 2007. Her description of the button's purpose is a little curious, because it frames the feature as a kind of review: 

This is similar to how you might rate a restaurant on a reviews site. If you go to the restaurant and have a great time, you may want to rate it 5 stars. But if you had a particularly delicious dish there and want to rave about it, you can write a review detailing what you liked about the restaurant. We think of the new "Like" feature to be the stars, and the comments to be the review.

Yet as we all know, there's no room for negative reviews on Facebook - there is no dislike button, and there likely never will be. Even in the preliminary announcements about the new emoji reactions feature, Zuckerberg has repeatedly made clear that "dislike" is not a Facebook-worthy emotion: "We didn’t want to just build a Dislike button because we don’t want to turn Facebook into a forum where people are voting up or down on people’s posts. That doesn’t seem like the kind of community we want to create."

Thanks to the new buttons, you can be angry, excited, or in love with other people's content, but the one thing you can't do is disapprove of its existence. Championing positivity is all well and good, but Zuckerberg's love of the "like" has more to do with his users' psychology than it does a desire to make the world a happier place. Negative feedback drives users away, and thumbs-down discourages posting. A "dislike" button could slow the never-ending stream of News Feed content down to a trickle - and that, after all, is Facebook's worst nightmare. 

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.