In two years' time, we'll all have smooth, full-motion video delivered on demand to mobile phones, desktop computers, notebooks and PDAs. We'll be able to video-conference with friends and colleagues in perfect, 25-frames-per-minute glory. And cats will learn to fly.

Before anything like this could happen (apart from the cats), something exotic would have to change in the fundamental structure of the Web. Consider the facts. Over 30 million Internet domain names have been registered so far. Even if only half of those are currently pointing to a Web site, that's 15 million potential sources of information.

How many people have access to the Web world-wide? Not as many as you'd guess from the hype, and some countries censor the sites to which their citizens have access. Even so, probably 10 percent of the world's population has some form of Web access, whether at work, at home, or at a library or other community centre. Call it 600 million people - 20 for each registered domain name - and growing fast. All wanting text, graphics, video, sound and other files. And wanting them more often, as access charges drop. There just isn't enough bandwidth available for them all.

Bandwidth reality is everywhere. The next generation of mobile phones, after the disappointment that is/was WAP, will have limited bandwidth; there just aren't enough frequencies available. And that's leaving aside the bandwidth limitation imposed on health grounds - after all, holding a powerful microwave transmitter next to your head isn't widely regarded as a good idea. So forget the idea of full-motion video on your mobile phone. A couple of frames per second is all you'll get, probably in monochrome.

It doesn't matter whether you have V.90, ISDN, satellite or ADSL connections. There's always a bottleneck somewhere to slow down your access (in our case, it takes time to scan various Web sites for specific IT news). Service providers know it too. BT has recently announced trials of a type of autonomous network connection, where small nodes work out the best way to handle their particular traffic, rather than a single piece of software controlling the whole network. There's now just too much traffic for an 'overseeing' program to cope, and this piecemeal approach should be more adaptive and efficient.

But just like the British road system, in the long term that won't help. The amount of traffic rises to fill the available capacity. Many ISPs restrict Web site traffic to a monthly 2GB limit, with penalties for those who exceed this. There may even come a time when governments have to intervene in a similar way, to prevent bandwidth hogging or theft of public data links. We might even have to return to pure text, like Teletext in the UK and Minitel in France.

Petrol was the key to infrastructure in the 20th century. Bandwidth will be the key in the 21st. Shortages of the latter are likely to be just as damaging to the 'new' economies as shortages of the former are to the 'old' economies.