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In the world around us, processes appear to follow a certain time-direction: Dandelions eventually turn into blowballs. However, the quantum realm does not play by the same rules. Physicists from the University of Vienna and IQOQI Vienna have now shown that for certain quantum systems, the time-direction of processes can be reversed. This demonstration of a so-called rewinding protocol has been published in Optica.

Everyday life is full of changes that are well understood, yet practically impossible to reverse; for example, the metamorphosis of a dandelion into a blowball. However, one could imagine undoing this transformation, step by step, if one knew precisely how each molecule in the plant moved in time. In the the problem gets even trickier: One of the core principles of quantum physics is that simply observing a system causes it to change.

This makes it impossible, even in principle, to track a system’s change in time and reverse the process. However, at the same time, the laws of quantum mechanics also open up new possibilities such as universal rewinding protocols. These allow for reversing changes in a quantum system without knowing what they were.

Injury to the spinal cord often leads life changing disability, with decreased or complete loss of sensation and movement below the site of injury. From drugs to transplantation, there are many scientific advances aiming to restore function following spinal cord injury.

One promising approach is the use of stem cell derived neurons to replace those damaged. New research from the Centre for Gene Therapy & Regenerative Medicine and Centre for Neurodevelopment at King’s College London hopes to improve on this approach by providing pure populations of neurons made from stem cells.

The spinal cord is a delicate structure, with neurons carry messages from your brain to the rest of your body to allow movement and sensation. Integral to this system are interneurons, or the cells that relay information between your brain and other neurons. Research has previously shown that transplanting a class of interneurons, ventral spinal interneurons, to treat spinal cord injury in animal models provides promising recovery of sensory and motor function.