We still have to see the promise of Blockchain, but companies and scientists are already close to launching a technology that could theoretically break it: quantum computers.
Such machines can calculate data exponentially faster than traditional computers. At the start of this year, Google began testing Bristlecone, a quantum chip that its creators think will soon reach "quantum supremacy", the moment it can outperform the world's fastest supercomputers.
This technology undermines the fundamental characteristic of Blockchain: security. Quantum computers could be so powerful that hackers can use them to crack the cryptographic codes used to protect Blockchain data.
"Looking at the future Blockchain, one can imagine a quantum arms race between exotic forms of cryptography and quantum algorithms to break them," according to an article published by New York University and researchers in China and Japan.
The solution, therefore, seems obvious enough: to fight fire with fire. Build a quantum blockchain.
The quantum blockchain and Einstein
First, let's discuss what exactly a quantum computer is and why technology is much more powerful than normal computers. To do this, we must understand a little bit of physics.
Albert Einstein's theory of general relativity established rules on how the universe operates on a large scale: thinking about black holes, the Big Bang, gravitational waves, the curvature of space-time.
Quantum mechanics applies to things that are very small, smaller than even atoms. In this strange world, Einstein's rules come out of the window. The particles appear spontaneously and then disappear. A particle located on one side of the world can influence a particle thousands of kilometers away, a phenomenon that Einstein called "distant spectral action" and to which we call "entanglement". (Scientists still have to understand why).  Processing in the normal world involves encoding data on "bits", represented by one or zero. In the "spectral" quantum world, data can exist as one and one at the same time. As a result, quantum computers can do many different calculations at the same time, making them much faster than normal computers.
To defend themselves from hackers armed with quantum computers, researchers from the University of Wellington in New Zealand propose to build a quantum Blockchain. And it's quite funny.
Recalls the "spectral action", in which particles can be entangled even if they are miles away. According to quantum mechanics, even the particles that exist at different points in time can be connected. In other words, a particle of 2018 can influence a particle in 3018. So the entanglement applies to both time and space.
The researchers propose the construction of a Blockchain that exploits this curious phenomenon. Specifically, they would code the Blockchain in a way that links the current records in a record block that exist only in the past.
This technique, the researchers say, would provide better security for the Blockchain. With a normal Blockchain, the system will detect an attempt to alter a block and prevent any further blocking on the chain.
With a quantum Blockchain, they exist simultaneously and passed. Messing with the photons present in the current block will automatically alter the photons encoded in the previous blocks, thus invalidating the entire chain. This is because, in the quantum world, the photons of the present and the photons of the past are somehow intertwined even if the latter no longer exist in the present time. And unless they can travel back in time, hackers obviously can not target photons that exist only in the past.
"The (quantum Blockchain) adds a much greater advantage as the attacker can not even attempt to access the previous photons since they no longer exist," says the researchers report. "They can at most try to tamper with the last remaining photon, which would invalidate the complete state, so in this application of quantum information, we see that entanglement over time provides a much greater security advantage than an entanglement. in space. "
The biggest takeaway is that we are on the cusp of creating and using technology that can influence time itself. We can do things in the present that alter the past. In other words, a quantum Blockchain could be the first example of a real-time machine.
Eat your heart to Doc Brown.
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