At some point, there will be more dead Facebook users than living ones – and for those left behind, it is transforming how we experience the death of those around us.

The day after my Aunt’s passing, I discovered she’d written me a lovely note on the front page of the Shakespeare collection she’d given me. “I know how important the written word is to you,” it read, “this then is my gift to you.”

With all of my love, as always,

Aunt Jackie

Deeply moved, I opened my laptop and found my way over to her Facebook page. I thought it would be comforting to see pictures of her, and to read some of her witty posts, and to imagine her speaking them in her brassy, brazen, Baltimore screech. At the top of her Facebook feed was a video posted by my cousin showing two elephants playing in water. (My aunt loved elephants. She had thousands of pieces of elephant kitsch all over her house.) Below that were some tributes from former students, as well as the obituary posted by her sister-in-law.

I scrolled back up. According to Facebook, Aunt Jackie studied English Education at Frostburg State University, was a former English Department Head for Baltimore City schools, and lives in Baltimore, Maryland.

Lives? I thought.

She doesn’t live anywhere. She’s gone.

But if you happened to come across her profile on Facebook and didn’t scroll down to the obituary, then you wouldn’t know that.

She would still be, in some sense, alive. She would be … here. On Facebook.

I thought back to the night my family and I stood around Aunt Jackie, hooked to wires and machines, and watched her pass.  

How is our continuing presence in digital space changing the way we die?

Observing that phenomenon is a strange thing. There she is, the person you love – you’re talking to her, squeezing her hand, thanking her for being there for you, watching the green zigzag move slower and slower – and then she’s not there anymore.

Another machine, meanwhile, was keeping her alive: some distant computer server that holds her thoughts, memories and relationships.

While it’s obvious that people don’t outlive their bodies on digital technology, they do endure in one sense. People’s experience of you as a seemingly living person can and does continue online.

How is our continuing presence in digital space changing the way we die? And what does it mean for those who would mourn us after we are gone?

The numbers of the dead on Facebook are growing fast. By 2012, just eight years after the platform was launched, 30 million users with Facebook accounts had died. That number has only gone up since. Some estimates claim more than 8,000 users die each day.

At some point in time, there will be more dead Facebook users than living ones. Facebook is a growing and unstoppable digital graveyard.

Some estimates claim more than 8,000 Facebook users die each day  

Many Facebook profiles announce their owners have passed; they are “memorialised”. The profile is emblazoned with the word “remembering”, and they stop appearing in public spaces, like People You May Know or birthday reminders.

But not all Facebook users who have passed away are memorialised.

Kerry, one of my college dorm mates, killed himself a few years ago, and his wife and family and friends regularly post updates on his page, and when they do, Kerry’s profile populates in my Facebook feed.

Neither Kerry nor my Aunt Jackie are memorialised, which means, for all intents and purposes, their deaths haven’t been recognised by Facebook, or by the unwitting users who chance upon them. Their digital identities continue to exist.

Social media has taught us about the power of the moment – connecting right now with people around the globe over awards show, television programmes, football games, social justice issues, and whatnot. But now it may be time to consider what comes after all that: our legacy.

It used to be that only certain prominent people were granted legacies, either because they left written records for their forebears, or because later inquisitive minds undertook that task. But digital technology changes that. Now, each of us spends hours each week – more than 12, according to a recent survey – writing our autobiographies.

We might think of our public social media record as some type of digital soul

As I’ve told my mother, my grandchildren may be able to learn about her by studying her Facebook profile. Assuming the social network doesn’t fold, they won’t just learn about the kinds of major life events that would make it into my mom’s authorised biography. They’ll learn, rather, the tiny, insignificant details of her day to day life: memes that made her laugh, viral photos she shared, which restaurants she and my father liked to eat at, the lame church jokes she was too fond of. And of course, they’ll have plenty of pictures to go with it. By studying this information, my grandchildren will come to know about their great grandmother.

We might think of our public social media record as some type of digital soul: those perusing my Facebook know my religious beliefs, my political reservations, my love for my partner, my literary tastes. Were I to die tomorrow, my digital soul would continue to exist.

What if you could live forever as a digital avatar?

In the past few years, several tech companies have extended the idea of a digital soul. Eterni.me, launched in 2014, promises to create a digital version of “you” that will live on after your death. Death is certain, admits the website — but what if you could live forever as a digital avatar, “and people in the future could actually interact with your memories, stories and ideas, almost as if they were talking to you?”

If programs like Eterni.me succeed, not only will my grandchildren be able to study my mother’s life, if they want they’ll be able to ask her avatar – their intelligent, digital “great grandmother” – questions and receive answers that my mother, before she passed away, would have probably given them.

You could take this process even further, as several futurists predict. Consider a robot that was commissioned by the entrepreneur Martine Rothblatt, called Bina 48. The robot is almost identical in appearance to Rothblatt’s wife, and contains a database of her speech and memories.

Rothblatt, author of Virtually Human and the CEO of United Therapeutics, is a transhumanist whose motto is "death is optional". Rothblatt foresees a near-future world in which the dead can be reanimated thanks to mind clone software that can allow avatars to think and respond and be in an eerily similar way to those they’re cloning.

When asked about the concept of real, Rothblatt once said that these mind clones might end up being “truer” versions of ourselves than we are.

Read more: Back-up brains: The era of digital immortality

So, if the end-point is that a loved one carries on living, how does that change how we grieve?

That’s the catch of our brave new world: digital data does not allow us to forget

One of the seminal texts on grief is Elisabeth Kubler-Ross’s 1969 On Death and Dying, which outlines five steps of the grieving process: denial, anger, bargaining, depression, acceptance. Since its publication, modern experts have questioned and criticised its central claims, particularly the understanding that successful mourners let go of the departed and move on.

Today, many counsellors help mourners realise that their loved ones continue to be with them, in some sense, after they die. The relationship changes, but it is still there.

Still, part of the grieving process does necessitate moving on, and, well, forgetting in some sense. Not forgetting that our loved ones ever existed, but forgetting that they are in in this place with us.

That’s the catch of our brave new world: digital data does not allow us to forget.

In his 2009 book Delete: The Virtue of Forgetting in the Digital Age, Viktor Mayer-Schonberger argues compellingly that central to the human condition is the ability to forget, which allows us to "act in time, cognizant of, but not shackled by the past". Forgetting, he writes, lets us "live and act firmly in the present".

In The Memorius, a short story by Jorge Luis Borges, the central character has lost the ability to forget 

Mayer-Schonberger refers to Funes, The Memorius, a short story by Jorge Luis Borges whose central character has lost the ability to forget after a tragic riding accident. Funes is able to perfectly recall every book he has ever read, and can recount in vivid detail all the days he’s experienced.

But his talent is also a curse: his memory, he admits, "is like a garbage heap". His name, Funes, which translates as "ill-fated", is a clue that Borges pities his character, who, as Donna Miller Watts writes, is "an involuntary hoarder, a junkman of the mind". He ultimately becomes lost in the words in his mind, unable to generalise or to abstract, because "to think is to ignore (or forget) differences".

To Watts, Funes’ mental state recalls “the vast amounts of information” that have been “exposed to digital nets,” never to be forgotten. The lesson, writes Mayer-Schonberger, is, “Too perfect a recall … may prompt us to become caught up in our memories, unable to leave our past behind.”

Digital technology forces us to remember the dead. This is their vengeance, who, as the sociologist Jean Baudrillard warns, haunt us in their absence.

In Facebook, my Aunt Jackie exists in this medium just as I do. In a way, there is no moving on without her

In the past, remembering the dead had a physical element to it. You had to go somewhere to honour them: a graveyard, a church, a memorial. Or you had to take out a box of photographs or an album or an obituary clipping. You had to take some time from the present to think about your past, your history, your time with that person.

In Facebook, all places are present, all times are now. My Aunt Jackie exists in this medium just as I do. In a way, there is no moving on without her. There’s no moving on without any of the millions of dead Facebook users.

One of the eeriest stories I’ve ever heard was told to me by a circus clown named Dooby. Just before he went on stage for a performance, he listened to a voicemail from his dying grandfather telling him he loved him and that they’d talk later. The timing worked out such that by the time Dooby heard the voicemail, his grandfather was already dead.

A clown listening to a dead man’s voice – that’s perhaps the only way I know how to describe the feeling of coming across my Aunt Jackie’s Facebook profile. She’s in this space just as I am, but I know that she’s also dead.

There’s a word we have for feeling as if something bad is going to happen: premonition, from a word that means “warning.” Stumbling across a dead Facebook user is not unlike that feeling, but with one important difference: we remember that something bad was at one time about to happen. We might call this re-monition, the reminder that we’ve already been warned.

As of yet, there’s no good solution to the problem of dead data, of digital ghosts. The only hope is that the internet’s memory will at some point begin to fade.

"The truth," writes Borges, "is that we all live by leaving behind."

Join 500,000+ Future fans by liking us on Facebook, or follow us on Twitter, Google+, LinkedIn and Instagram

If you liked this story, sign up for the weekly bbc.com features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.