(NOTE) THIS POST WAS ORIGINALLY BY 
What is Blockchain?
Blockchain has been talked about in many contexts and has been looked at through many angles. It is revolutionizing the financial industry.
It has two main problems: Immutable writing and high energy consumption.
We hear 'Can we afford to employ it with ever-growing greed for energy?'
TO understand that, we need to know exactly what we are talking about when we say 'blockchain'.
Architecture
The photo above, taken at a recent conference in Lille (France) entitled "Blockchain, Open Education and Digital Citizenship" underlines this: the keyword when analyzing a new technology is "architecture" - software architecture. The idea of this particular slide presented by Alex Grech is from an article in the New York Times in January 2018:
"If there's one thing we've learned from the recent Internet story, it's that seemingly esoteric software architecture decisions can set in motion global forces as soon as the technology is adopted on a large scale. "
Blockchains, not blockchain
I was a little surprised to have to explain and clarify at a conference dedicated to blockchain technology in 2019 the role played by the consumption of large amounts of energy in the operation of this technology.
My explanation was made to emphasize a series of essential points:
By saying "blockchain" we are talking about software that behaves as their architects wanted it. If Bitcoin and other software inspired by it, like Ethereum, consume a lot of energy, it is because their creators programmed them like that.
Resistance to censorship. The legitimate question that follows automatically is, of course: "Why?"
The answer takes much longer to formulate and understand, but if we had to summarize it, it would boil down to "resistance to censorship".
Bitcoin and the blockchains that subsequently emulated it was designed by people revolted by the abuses and excesses of the globalized financial system, people often harboring "anarcho-capitalist" sympathies. By studying the recent history of attempts to create an "alternative financial system" they concluded that "the system" would not let anyone freely develop a competing currency, and that they would try to destroy it, to censor it.
From then on, the only way to make money was to like this and make it "censorship-resistant".
Among the measures taken in this direction, the anonymity of Satoshi Nakamoto but also, and above all, the opportunity offered to everyone to start a "node" bitcoin and to join the network, without having to ask permission from anyone, without having to be self-congratulatory.
The Sybil attack
This ability to join the network without asking permission and while remaining anonymous does not come without serious weaknesses, the most critical being called in jargon "Sybil attack" - the possibility that a malicious actor instantiate a large number of "nodes" in order to gain the majority and potentially submitting or gaining control of the network.
Thus the energy consumption arises from a software architecture decision to ask each node not to "prove its identity" or "honest intentions" but to demonstrate that it "works for the network" ("proof of work ").
A small summary in English on the slide below:
Conclusion
"Blockchain" is not synonymous with "high energy consumption". The high energy consumption is a consequence of bias of the creator of bitcoin and other blockchains inspired by it: the idea that, to resist any attempt by a government to ban it, a node of the network Bitcoin must be able to be instantiated by anyone, without the need for permission.
It follows that a blockchain architecture that requires any actor wishing to operate a network node to identify itself and obtain permission before being able to join the network can do without "proof of work" and high consumption of data. associated energy.
We have recently demonstrated this in practice in the framework of the EFTG project, with a blockchain derived from steem and which consumes only 2W inactivity.
