Here are some characteristic vignettes of modern life.

First, a man sitting on a train in the first-class compartment. The train is not full; it is, for once, a calm, pleasant environment. He has earphones on, attached to an MP3 player. In front of him, his laptop is open at some spreadsheet. Next to him, his mobile phone is lying face up, and from time to time his attention moves from the laptop to the mobile, to answer some text or speak into it. A woman gets on, and asks if the seat opposite is occupied. He does not look up; he just gestures at the empty seat.

Second, a girl walking down the road. In her hands is a small object: a BlackBerry, or similar device. Her head is down over it. Both her thumbs are working furiously. It is a beautiful day. She glances up briefly and, still texting, steps out into the road. A cyclist swerves round her, swearing like crazy. She looks up again, steps back, goes on texting.

Third, the window of a branch of a coffee shop. It is late morning. At the front, overlooking the street, four people on stools next to each other. The four of them each have a laptop open. On investigation, three are writing emails or looking at websites; the fourth has earphones in and is watching a film, which you recognise over his shoulder as Inception. Apart from the two coffee workers asking customers what they would like, the café is as silent as the grave.

Opportunities for absorption in the public sphere have expanded in recent times to cover, potentially, almost all of waking life. Small electronic devices have been invented, and have been marketed, to allow us to conduct any number of private, absorbing tasks in the street, in shared spaces, while transporting ourselves from one place to another.

Within living memory, these were some of the activities which required someone to visit a special place and a devoted setting. To carry out a phone conversation with someone, you needed to be by your (non-moving) phone, or in a phone box. To watch a film, you needed to be in a cinema; to listen to music, to be by a radio or record player; to write a letter or to type something, you would usually be at a desk for the purpose.

Portable devices have done away with all that; the laptop, the MP3 player, the mobile phone with its apps and SMS, the iPad, and so on. We carry everything with us like refugees. And the result is not just an increase in convenience, an ability to carry out the tasks we would be carrying out anyway, but a huge shift in our awareness of ourselves.

Since 2007, a New York state senator has been trying to have a law passed which would ban the use of electronic devices while crossing streets in large cities. Carl Kruger, a senator from Brooklyn, believes that a number of accidents in New York in recent years are simply down to the absorption induced in pedestrians by mobile phonesand other devices.

The passing of laws hardly seems the right, or a sufficient way to curb the huge shift in public behaviour. Anyone stupid enough to be checking their emails on a mobile device while crossing a busy New York street will probably be taught a lesson fairly quickly, whether a law is in place or not.

The curious thing is that these devices, which isolate users so effectively from the world around them, are often propagated as means of social connection. Of course that is partly true. I value and enjoy my friendships on Facebook as much as anyone. But there is no doubt that those connections are supplementary to real-life friendships, or preparatory to them, and not the genuine article. The illusion of connectivity, through social networks, texting and emailing, is not the opposite to the prophylactic absorption of watching a film on the go, or sticking earphones firmly in your ears when you leave the house. It is, basically, much the same thing.

The case of Simone Back and her 1,082 "friends" is quickly becoming as significant as that of Kitty Genovese. In 1964, 38 separate people watched Kitty Genovese being raped and murdered from their apartment windows in New York, and did nothing. At Christmas 2010, Simone Back announced on Facebook that she was desperate, and about to commit suicide. Her 1,082 friends discussed it; ridiculed her; did nothing. Simone went ahead and killed herself. In both cases, the social bonds had been weakened to the point of non-existence. Only in the 2010 case were the bystanders described as "friends", however.

A couple of weeks ago, I was in the Vauxhall Tavern. It's the oldest gay bar in London, probably. Gay men have been meeting each other there since the Second World War, and maybe before that. As a community, we are early adopters of technology, and it doesn't surprise you to see people showing each other their new phone app, or whatever. What did surprise me the other day was glancing over someone's shoulder, and seeing, on a crowded Sunday afternoon, that he was consulting the iPhone app Grindr.

For innocent readers, I should explain that Grindr is an application which allows gay men to identify their geographical location; it will, in turn, show you the geographical location of your nearest Grindr subscriber. I can see it would be highly useful to your gay Welsh sheep farmer, who could discover that the nearest gay man was a postman called Gwilym, six kilometres away. But there must have been 300 gay men inside the Vauxhall Tavern. If you wanted to meet one, you just needed to turn to the left and say "Hello", without the aid of satellites and expensive location technology. At this point, you have to wonder whether absorption has become, not a means to a meeting, but an end in itself.

Fifty years ago, the sight of London commuters raising their newspapers against each other on the train to work was a standard of comedy. Now, we all live our lives in this defensive way, with our batteries and our ever more portable bubbles. Would we not be better setting them down, and turning to each other? Well, probably, but I don't think it is going to happen.