Time Travel And Particle Cloning Throw Theoretical Wrench In Quantum Encryption

By Ben Wolford on December 10, 2013 8:39 AM EST

Time Travel
New secret-coding capabilities could be hampered by new time-traveling possibilities. (Photo: Shutterstock)

Online passwords for banking or social media sites are encrypted in a way that's difficult to hack into, but not impossible. The codes are based on difficult mathematics, and it's possible for somebody with smart enough software to crack them. But emerging advances in quantum mechanics (using the same basics as the quantum computing) are creating new opportunities for bulletproof encryption.

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These new encryption techniques are said to be unbreakable because they rely on hard-and-fast physical properties rather than on mathematical equations. Tiny particles, such as electrons or photons (particles of light), have different states that can be interpreted — for example, their polarity, momentum, or position. But the more accurately one of those binary quantum bits of information (or qubits) is measured, the less accurately the others can be measured. Physicists call that the uncertainty principle, and it means that no quantum data can be copied. Already quantum cyrptography is being developed in which "quantum keys" are needed to access the data. The wrong key spoils the qubits and exposes the fraud.

But new research offers one theoretical weak spot: time travel. According to physicist Mark Wilde, of Louisiana State University, if the quantum data showed up at different points in time, it would enable them to be copied. Yes, he's serious. His paper, co-written by colleagues at the University of Southern California and the Autonomous University of Barcelona, was published last month in Physical Review Letters.

Basically their position states that one could, in fact, copy quantum data if one were to jettison it through a spiraling wormhole into the past. It would reappear at intervals during previous times, allowing its information to be "cloned." This, Wilde says in an LSU press release, "allows for copying of the particle's data at many different points in space because you are sending the particle back many times. It's like you have multiple versions of the particle available at the same time." He goes on to add that "if an adversary, if a malicious person, were to have access to these time loops, then they could break the security of quantum key distribution."

So there it is. Just get yourself a time loop. Easy as that sounds, there still may be complications. Anybody who's ever thought long enough about time travel knows this: When you change the past, it messes with the present. Ask Marty McFly. But actually, that's a real thing that physicists ponder, and it has a name. It's called the Grandfather Paradox, which refers to the quandry, "If I go back in time and kill my grandfather, could I really have existed to go back in time in the first place?" Wilde and the team drew upon one solution to that problem (there are several) from a contemporary Oxford University physicist who said you can change the past as long as you do it in a "self-consistent manner."

That's the problem. If somebody looking at a quantum particle as it reappears back in time understands it and effectively makes copies of it, well, that person has changed the past. So Wilde had to come up with a starting point that wouldn't threaten its own existence in the past. "That," he says, "was the major breakthrough. ... It just worked." So, good luck with that, quantum hackers.

Above photo courtesy of Shutterstock

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