Grandfather paradox “solved” by a simulation

grandfather paradoxPhysicists have “solved” the grandfather paradox in a new simulation by using quantum physics.

In the world of physics time travel is possible in theory. Although notables like Stephen Hawking thinks the idea is laughable nothing in modern physics prohibits it. In popular Hollywood movies no plot device causes as many plot holes and enraged internet forum users than time travel. This is often due to time travel causing tons of paradoxes.

The Grandfather Paradox

The grandfather paradox is the question of what will happen if you travel back in time and kill your grandfather. Since your grandfather is dead, you will never be born to travel back in time. Since you were never born to travel back in time you couldn’t have killed your grandfather, trippy shit, i know.

Now recently scientist “solved” this paradox by experimentally simulating a system similar to time travel, and it has all been done using a quantum system. Quantum physics isn’t exactly “known” for it’s ability to solve things. In the study the scientists perform an experiment using photons set up in a novel way.

Instead of a time traveling human the scientists uses a particle generating machine. In the machine the particle generated flips a switch on the machine generating the particle itself. This is meant to simulate the grandfather paradox in particles instead of in humans. If the particle activates the switch, it generates the same particle that goes back in time to switch on the machine once again. If the particle don’t activate the machine then no particle is emitted, which stops the loop.

In this setup there is no predetermined series of events, just a probability of switching on the particle machine to create the particle. This probability is what enables the scientists to “solve” the grandfather paradox.

The system originally devised by physicist David Deutsch, now tested by Tim Ralph and colleagues has the insights to count on self consistency. This means that any particle that enter the “time loop” must have the same properties as the particle activating the switch. In probabilities it means that a particle that enters the loop with a 50% probability of activating the switch will leave the loop with the same probability. In the human variant of the paradox this would mean born with a 50% chance of killing their grandfather. This also means that the grandfather have a 50% chance of avoiding death which is good enough odds to close out the time loop and avoid the the grandfather paradox altogether.

In the experiment Ralph and his colleagues studied this approach by using pairs of polarized photons within a quantum system. Instead of using time travel, since that is fairly difficult presently, they observed the interaction between photon pairs. They designed the system so that the 2nd photon acted as a “past” variant of the first photon. However hard this is to grasp, when the scientists ran the simulation the self consistency seemed to work. The photon that came out of the simulation had the same polarization as the photon that went into the simulation to begin it, even though they were separate particles. They had cloned a quantum state.

If this model of the time loops is correct, it means that you can clone quantum states. This would have huge implication in quantum cryptography since you would be able to violate the Heisenberg uncertainty principle. There is however competing models that also have had some successful evidence from experimentation. Which one is correct and if the grandfather paradox can be resolved is still up in the air.

Sourced in part from an article in scientificamerican.com

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