The big one Could the internet collapse - and what on earth would we do if it did?

It is the morning after the internet went offline and, as much as you would like to think you would be delighted, you are likely to be wondering what to do.

- Aisha Down

You could buy groceries with a chequebook, if you have one. Call into work with the landline - if yours is still connected. After that, you could drive to the shop, as long as you still know how to navigate without 5G.

A glitch at a datacentre in the US state of Virginia last week reminded us that the unlikely is not impossible. The internet may have become an irreplaceable linchpin of modern life, but it is also a web of creaking legacy programs and physical infrastructure, leading some to wonder what it would take to bring it all down.

The answer could be as simple as some acute bad luck, a few targeted attacks, or both. Extreme weather takes out a few key datacentres. A line of AI-written code deep in a major provider - such as Amazon, Google or Microsoft - is triggered unexpectedly and causes a cascading software crash. An armed group or intelligence agency snips a couple of undersea cables.

These would be bad. But the real doomsday event, the kind that the world's few internet experts still worry about, is slightly different - a sudden, snowballing error in the creaky, decades-old protocols that underlie the whole internet. Think of the plumbing that directs the flow of connection, or the address books that allow one machine to locate another.

We'll call it "the big one". It could start when a summertime tornado cruises through the town of Council Bluffs, Iowa, laying waste to a low-slung cluster of datacentres that are an integral part of Google's offering.

This area, called us-central1, is critical to Google's cloud platform as well as YouTube and Gmail - a 2019 outage here downed these services across the US and Europe.

Dinners burn as YouTube cooking videos sputter to a halt. Workers across the world furiously refresh their suddenly inaccessible emails, then resign themselves to interacting in person. Senior US officials notice some government services have slowed.