Human knowledge is based on memory. But does the digital age force us to remember too much? Viktor Mayer-Schönberger argues that we must delete and let go

When Viktor Mayer-Schönberger's stepfather died, he left a collection of 16,000 heavy glass photographic slides, his visual record of decades travelling the world. His stepson had to decide what to do with them. "I had two rules in working out whether to keep a slide. One, if there was anybody in it I knew or might know. Two, if it was beautiful. Know how many I kept? 53."

His stepfather also kept a diary of his travels. Mayer-Schönberger doesn't expect to publish it any time soon. "The entries were so dull! What was the temperature, if the butter was good."

But maybe there was a point in his stepdad recording butter quality at some otherwise forgotten breakfast. In his book Delete: The Virtue of Forgetting in the Digital Age, Mayer-Schönberger, professor of internet governance and regulation at the University of Oxford's Internet Institute, writes: "Time is quite simply a very difficult dimension of human memory for humans to master."

Mayer-Schönberger says: "My stepfather's diary was probably incredibly meaningful for him because when he read some banal detail about butter, maybe that triggered the memory of the place for him. He externalised what was important for him, so he would have the cues he needed to remember something later."

In Delete, Mayer-Schönberger traces the history of such external memories – cave paintings, scrolls, photographic slides, diaries – and their importance to the flourishing of human knowledge. "Since the early days of humankind," he writes, "we have tried to remember, to preserve our knowledge, to hold on to our memories and we have devised numerous devices and mechanisms to aid us. Yet through millennia, forgetting has remained just a bit easier and cheaper than remembering."

No longer. Because of the digital revolution, he argues, it is easier to keep everything – the drunken email you sent your boss, the photo you put on Facebook in which you're doing something non-CV-enhancing to an inflatable cow – rather than go through the palaver of deciding what to consign to oblivion.

That's because so many of our external memories – digital pictures, emails – are now hardly as heavy as Mayer-Schönberger's stepfather's glass slides, but lighter than bees' wings. The overabundance of cheap storage on hard disks means that it is no longer economical to even decide whether to remember or forget. "Forgetting – the three seconds it takes to choose – has become too expensive for people to use," he writes. If Mayer-Schönberger's stepdad had taken digital photographs, his stepson wouldn't have had to bother thinking about which to delete.

But isn't it great that digital memories correct fallible human ones? "Many of my critics say that forgetting is a weakness of the human mind that we should be happy to get rid of. I agree we benefit from digital memories, but not if that means we lose the capacity to forget because that capacity is valuable."

The dream of overcoming human memory's fallibility was expressed by HG Wells when, in the 1930s, he wrote of a "world brain" through which "the whole human memory can be . . . made accessible to every individual". Today, perhaps we have that world brain, and it is called Google. Mayer-Schönberger sounds an Orwellian note about this: "Quite literally, Google knows more about us than we can remember ourselves."

His point is that a comprehensive memory is as much a curse as a boon. He cites the case of a 41-year-old Californian woman called AJ who, since she was 11, has remembered the events of her every day in agonising detail – what she had for breakfast three decades ago, what happened in each episode of every TV show she watched. That inability to forget, Mayer-Schönberger argues, limits one's decision-making ability and ability to form close links with people who remember less. "The effect may be stronger when caused by more comprehensive and easily accessible external digital memory. Too perfect a recall, even when it is benignly intended to aid our decision-making, may prompt us to become caught up in our memories, unable to leave our past behind."

And not being able to leave our past behind makes humans, he argues, more unforgiving in the digital age than ever before. In 2006, Vancouver-based psychotherapist Andrew Feldmar was crossing the Canada-US border to pick up a friend from Seattle airport – something he'd done many times before. This time, though, the border guard searched online and found that in 2001 Feldmar had written in an academic journal that he had taken LSD in the 1960s. As a result, Feldmar was barred entry to the US. "This case shows that because of digital technology, society's ability to forget has become suspended, replaced by perfect memory."

In the 19th century, Jeremy Bentham envisaged a prison called a panopticon in which guards could watch prisoners without them knowing whether they were being watched. In the 20th century, Michel Foucault argued that the model of the panopticon was used more abstractly to exercise control over society. In the 21st century, Mayer-Schönberger argues that the panopticon now extends across time and cyberspace, making us act as if we are watched even if we are not. He worries that this "perfect memory" will make us self-censor. "That's becoming standard. In the US most colleges have a mandatory class on how to clean up your Facebook account."

But isn't it good that digital technology encourages us to modify our behaviour? "Not necessarily. If you increase utility of storage, you risk collateral damage. In my home country of Austria, the DNA database keeps samples of everybody who left traces at a crime scene. It even means there are two classes of people – suspects and non-suspects and the class of suspects includes those who have been mugged or raped who have their DNA samples on the database."

Mayer-Schönberger took part in a radio phone-in recently. One caller related how her children's classmates found her image on a website publishing mugshots of convicts. "In the US, there are companies who buy up mugshots of prisoners and put them online – unless you pay $500 to take them down." Surely that's inimical to the spirit of the law whereby convictions become spent and offenders are rehabilitated? "It is inimical, but that's not a question that troubles their business model."

Suddenly this woman was punished again for an offence she had committed more than a decade ago and for which she had spent time in prison. Friends and neighbours treated her as a criminal, even though a day before they had entrusted their children to her care. Mayer-Schönberger writes in the new edition of Delete: "Digital memory, in reminding us of who she was more than 10 years ago, denied her the chance to evolve and change." This story, he argues, typifies how digital memory denies us the capacity to forgive.

Once lost, it's difficult to reconstruct. Germany's lawmakers tried prohibiting HR departments from Googling job applicants – thereby compelling institutional forgetting. "It was impossible to operationalise. They couldn't stop HR department workers Googling at home, for instance."

Mayer-Schönberger believes his book struck a chord. "Nine out of 10 Americans want the right to force websites and advertising companies to delete all stored information about them. And for US digital natives [those born after the introduction of digital technology] the figure is 84%."

Why is there such a concern? "People feel vulnerable online and don't trust organisations to protect their personal information. Google was clumsy in dealing with complaints about StreetView. Think of Facebook: it's in their DNA to keep information because they can monetise it."

He's intrigued by what Facebook does to human identity. "In the analogue era, it was relatively simple to keep your lives separate. If my main leisure pursuits were being in the golf club and in an S&M circle, it was essential that no one at the former knew about the latter. Facebook, by not allowing you to have two accounts, problematises that separation. The response is that individuals employ strategies to hack the system – almost all my colleagues have two Facebook accounts, to keep different parts of their lives boxed in."

What can be done to reverse the demise of forgetting? "I suggest we reset the balance and make forgetting just a tiny bit easier than remembering – just enough to flip the default back to where it has been for millennia, from remembering for ever to forgetting over time." He argues that digital storage devices (cameras, mobiles, computers) should automatically delete information that has reached its expiration date.

How? He suggests that users, when saving a document they have created, would have to select an expiration date in addition to the document's name and location on their hard disk. "Expiration dates are about asking humans to reflect – if only for a few moments – about how long the information they want to store may remain valuable."

This chimes with Harvard cyberlaw expert Jonathan Zittrain's idea that we should have a right to declare reputation bankruptcy – ie to have certain aspects of one's digital past erased from the digital memory. Such a right might have helped the woman caller to Mayer-Schönberger's phone-in.

Mayer-Schönberger envisages that each digital camera could have a built-in process to select expiration dates for a photo. Before taking a picture the camera would send out "picture requests" to what he calls "permission devices" (about the size of a key fob that, perhaps, might dangle from our necks) that respond to the request with the owner's preferred expiration date. That date could range from zero to three years to 100 years from now (an option reserved for really memorable pictures).

He concedes expiration dates are no overall solution to the problem, but what he likes about them is that they make us think about the value of forgetting and, also, that they involve negotiation rather than simply imposing a technical solution to a technical problem. There are alternatives, such as turning your back on the digital age. "I don't like digital abstinence. I want us to embrace participation in digital culture and global networks. Just not at any cost."

He argues that digital memory intrudes into our most intimate relationships. "Think of my old love letters. I hope they were destroyed or they're rotting in some attic. There's an implicit ethical agreement that they won't be used against me or published." In the digital age, such implicit ethical agreements are rendered obsolete. So much of our past is so readily retrievable in the digital age that we can't help but stumble across things we'd do better to forget. In Delete, he imagines a sad little story of two friends meeting after not seeing each other for years. John and Jane arrange to go for coffee at an old haunt to reminisce. But Jane can't quite remember the name of the cafe. So she has a brainwave – she'll check through her old emails to John. As she looks for the cafe address, she stumbles across an exchange with him that poisons her attitude to him. Instead of forgiving and forgetting, she is overwhelmed with old resentment and, quite possibly, won't turn up for that coffee.

Our digital footprints, that's to say, can trip us up later on – unless we self-censor assiduously. Given that, what information is Viktor Mayer-Schönberger prepared to disclose to me about himself – given it will be Googlable for the forseeable? He tells me he was born in a small Austrian alpine resort called Zell am See 45 years ago. Little Viktor started computer programming when he was 12, invented a new computer language aged 14, and before he was out of his teens had won awards at the International Physics Olympics and the Austrian Young Programmers Contest. Aged 18 he started a data security company called Ikarus Software.

He sold Ikarus at 26, amassed degrees from Salzburg, Cambridge, Harvard and the LSE. He worked for his father's tax law practice, then spent 10 years on the faculty of Harvard's John F Kennedy school of government. Last October, he took up his Oxford appointment. He has John Lennon glasses, and sounds – thanks to all those Stateside years – like Steve Buscemi. He has a wife and one child and hopes that this information will never be used against him. But, given how little we know about the future, who knows if that will happen?

When we finish this interview the professor did not activate a permission device to change preset expiration dates for the online version of this article, which was kind of him. In future, journalism may well not be like that.

"One thing that's pleased me since I've been working in this area is some online services have implemented expiration dates for information." Among them was drop.io, which offered private file sharing with expiration dates – and was bought up by Facebook last year. Google also now has a facility to set dates after which a web page will no longer be included in its search results displayed to users. He is heartened too by the tendency to encourage digital users to set privacy settings. "When Apple launched iCloud , it allowed you to sync privacy setting across devices – that's incredibly nifty."

Mayer-Schönberger is now researching what he calls "institutions of remembering". "We set up institutions of memory to help us remember important things – such as the Holocaust, for example. But with Google and Flickr and other sites offering seemingly comprehensive memory, we might be prompted to devalue these established institutions of memory. They risk being drowned out by stuff online. My fear is that the digital age, while benefiting us enormously, impoverishes us too."

Delete: The Virtue of Forgetting in the Digital Age is published in paperback on 25 July by Princeton University Press, £12.50.