Imagine you go shopping and checkout, but your card doesn't work. It turns out that your bank has experienced a computer breakdown and none of its customers, including you, can pay for anything.
But what if the cash register had access to a record or ledger of your credit and debit card balance that was updated every time you bought something?
Even if the bank's systems fail, your card will work in the supermarket, since the cash register itself knows your account balance.
This is just one way that a distributed ledger, also known as a blockchain, offers. The technology has been around for over a decade and has been heavily hyped.
It sounds pretty practical, but is rarely used in practice. So what happened?
Blockchain struggles to find a purpose that goes beyond powering cryptocurrencies like Bitcoin.
In this scenario, the blockchain acts as a universal record of every Bitcoin transaction ever made. The blockchain is a ledger or log of these transactions, and users on the network work together to review new transactions as they occur. You will be financially rewarded for this effort – a company known as "bitcoin mining".
The basic idea of not storing information centrally but distributing it to many different users met with great interest.
Proponents have long argued that it could be a better alternative to traditional databases.
But how transformative would blockchain-style alternatives really be? Dave Birch, an author and advisor for digital financial services, has suggested the example of checkout and has criticized some proposed blockchain concepts in the past.
"I'm ready to buy that," he says. "I think it has some value."
There are other ideas. Prof. Gilbert Fridgen, a financial services expert at the University of Luxembourg, proposes a distributed book system that tracks the certificates and degrees issued by universities.
No organization would be responsible for it. Rather, copies of the ledger would be kept by multiple parties and individuals could check that the records of their own qualifications were correct.
It would certainly be useful. In 2018, a BBC survey found that thousands of fake degrees were in circulation, so a decentralized skills tracking system could be attractive to employers.
However, Prof. Fridgen notes that nothing about a blockchain can prevent even some corrupt people from adding fraudulent information. Additional tests are required.
If these trust problems can be solved, blockchains could have real advantages.
News emerged from recently Members of the Windrush generation the Commonwealth migrants, whose legal status has been questioned because records of their residence permit not being kept were not kept. In the future, such mistakes could be avoided by keeping information like this in a distributed ledger instead of relying on the government to look after it.
Some large companies have integrated the technology into their operations.
Take the shipping giant Maersk. It uses blockchain technology in TradeLens, a new system for tracking customs documentation for goods that are shipped internationally. The idea is that everyone involved in the process, from the port to the customs authorities, can quickly look up details about a shipment.
According to Maersk, 10 million shipping events are now registered in the system every week.
Unlike Bitcoin, TradeLens uses an approved blockchain. This is a non-public ledger to which access is controlled.
However, a similar system could also be achieved with other technologies, such as cloud-based general ledger databases, which encrypt data and control who can access which information.
Another interesting project is the real estate system tested by the Swedish land registry Lantmäteriet. A blockchain was developed to track documents while selling a property. The buyers and sellers, brokers and banks involved were all able to participate in the sale and track it digitally.
Although the trial has shown that such a system is possible, legislation would need to be changed before the system could be expanded in the future, explains Mats Snäll, Chief Innovation Officer at the Swedish Land Registry.
"It was never integrated into the land registry's production system," he told the BBC.
In Thailand, cryptocurrency company Zcoin developed a blockchain-based system so that members of the Thai Democratic Party could cast digital votes for their new leader in late 2018. Instead of having to trust a central authority for counting votes, they were instead collected the Zcoin blockchain.
Voting took place in polling stations or via a mobile app in which voters had to submit a photo of themselves when voting.
These digital voices were also checked by the election commission, a spokesman for Zcoin told the BBC. According to Zcoin, there are plans to launch a larger program with “millions” of voters in the near future.
These are activities that make you think. However, there remains a debate over whether a blockchain is essential for one of them.
Some say blockchain-style systems may turn out to be the most efficient option for organizing data on a large scale. The entrepreneur Helen Disney is one of them.
"In many cases, costs have to be saved once the initial hurdle has been overcome. Of course, it is expensive to introduce a new system," she says.
While blockchain bluster will certainly continue, even skeptics like Mr. Birch believe that there are some focused applications that may prove worthwhile. So far, blockchain may not have changed the world – but many people have thought about it.