Quantum Gravity Could Reverse Cause and Effect

Image: Timothy Yeo/Centre for Quantum Technologies/National University of Singapore

Any theory of quantum gravity is going to have to grapple with some weird time stuff.

Stephanie Pappas | SPACE.com

You’ve probably heard of Schrödinger’s cat, the unfortunate feline in a box that is simultaneously alive and dead until the box is opened to reveal its actual state. Well, now wrap your mind around Schrödinger’s time, a situation in which one event can simultaneously be the cause and effect of another event. 

Such a scenario may be inevitable in any theory of quantum gravity, a still-murky area of physics that seeks to combine Albert Einstein’s theory of general relativity with the workings of quantum mechanics. In a new paper, scientists create a mashup of the two by imagining starships near an enormous planet whose mass slows time. They conclude that the starships could find themselves in a state where causation is reversed: One event could end up causing another event that happened before it. 

„One can devise this kind of scenario where temporal order or cause and effect are in superposition of being reversed or not reversed,“ said study co-author Igor Pikovski, a physicist at the Center for Quantum Science and Engineering at Stevens Institute of Technology in New Jersey. „This is something we expect should take place once we have a full theory of quantum gravity.“

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