Even now, six years after its debut, some people are uncertain about bitcoin. Many consumers still seem to prefer paying for things with old-fashioned cash and credit, while investors remain divided on whether the computer-based crypto-currency is a financial revolution or just an elaborate, money-burning fad.

Fool's gold? Possibly. But some experts say there's a nugget or two of the real thing in the technology that makes bitcoin work.

The blockchain, according to its proponents, is an effectively unhackable system that could introduce trust and transparency to any online transaction.

It's a "key technological innovation," according to The Bank of England, and the focus of a joint effort revealed this week by nine of the world's biggest financial institutions.

Goldman Sachs, Barclays, UBS and others said Tuesday they have linked with New York-based financial tech firm R3 to develop a way to use blockchain technology in the markets.

But its most enthusiastic proponents say blockchain technology has even greater potential.

What is blockchain?

The blockchain is the system that keeps track of bitcoin transactions. Think of it as a giant, decentralized ledger that's shared and maintained by many different computers in bitcoin's online community.

Every bitcoin transaction that has ever taken place is noted in the ledger and can never be erased. It is constantly growing as more transactions are added in chronological order.

How does it work?

When a bitcoin transaction is made, the details are encoded and transmitted across the currency's online community. Other computers then try to decode the message. As soon as one succeeds it shows its work to the others, which double check.

The transaction is approved and the computer that cracked the message is rewarded with some bitcoins as payment for its efforts.

Once a transaction is approved it's recorded in the blockchain, copies of which are maintained separately by computers across the community.

The computers continually compare their copies of the blockchain, checking for discrepancies.

The system is considered tamper-proof because any attempt to make a false transaction — say, by spending the same bitcoin twice — would not match the records held, in consensus, by the community. That transaction would be rejected.

What's the big deal?

Proponents say blockchain technology brings "trust to the trustless world" of online transactions. Because every part of the system is continually checking the work of the others, the system is thought to be unhackable.

Or at least, insanely difficult to hack.

Imagine 100 people witness a car crash. Getting a fake transaction into the blockchain would be like getting a majority of those eyewitnesses to tell identical false accounts of that crash — simultaneously, with no prompting or warning.

The records are public?

Yes, but privacy is maintained. Transactions are noted in full, but bitcoiners use pseudonyms.

How else can it be applied?

In any online transaction that requires trust — which is an awful lot of them, when you think about it — we trust that our bank has not been hacked and is showing our actual bank balance. We trust that our anti-virus software is doing its job and all those emails are actually being delivered. That trust is placed in particular, centralized third parties such as RBC, Avast and Gmail.

Because blockchain technology appears to remove the need for the middlemen of finance — banks, governments, notaries and even paper currency — it's thought that its system of decentralized consensus could be applied elsewhere.

"Think about digital signatures, digital contracts, digital keys [to physical locks, or to online lockers], digital ownership of physical assets such as cars and houses, digital stocks and bonds and digital money," noted venture capitalist and bitcoin booster Marc Andreessen wrote in a 2014 op-ed for The New York Times.

"All these are exchanged through a distributed network of trust that does not require or rely upon a central intermediary like a bank or broker."

What's the catch?

A few things: Critics have already noted that all the electricity sucked up by high-powered bitcoin computers is less than ideal for the environment. (The virtual currency represents a "real-world environmental disaster," according to one Bloomberg op-ed.)

Some also wonder whether a blockchain that never stops growing is sustainable for even the most powerful computers.

And then there's the matter of why those computers do the work decoding all those transactions. They do it so their owners can earn bitcoins — a currency that, at times, has seemed about as stable as the Somali shilling.

If bitcoins lose value and those computers can't turn a profit for their owners, how long can they be expected to stay with the blockchain gang?