The materials approach to quantum spacetime

点击翻译按钮获取中文摘要

The effects of gravity are known to all of us: responsible both for falling apples and planetary orbits, but it remains the least well-understood force in nature. An open question in our conceptualization of gravity regards whether information is destroyed in gravitational processes.Black holes, formed from the collapse of stars, are a beautiful testing ground for these ideas. Consider a diary, containing deeply personal secrets that must be kept from public view at all costs. Is it possible to destroy the information contained within by throwing the diary into a black hole? While this might seem useful in practice, the implications for fundamental physics would be disastrous. A self-consistent physical theory should not allow for information destruction, as this would imply a basic inability to predict the outcomes of experiments; negating the entire paradigm of the scientific method and the validity of hypothesis testing. Cue Hawking's information paradox, which definitively shows that, within the framework of Einstein's general relativity, black holes do indeed destroy information. This suggests that we must search for a theory that can replace Einstein's general relativity, while nevertheless reproducing all of its successful predictions in the realm of astronomy and cosmology. This is a daunting but necessary task.Black holes are not the only realm where Einstein's equations reveal inconsistencies: astronomical surveys suggest that our universe is expanding, and similarly to black holes, an expanding universe potentially destroys the information in the diary, if left alone for eons. If we are to understand the origins of our expanding universe, it is imperative that we build theoretical models that accurately describe expanding space without the problematic information loss.To get at the crux of the information paradox, I am looking at frameworks that could eventually replace general relativity. My approach is to treat the fabric of space as a `material' to be experimented on. Of course, being a theoretical physicist means that my experiments will be `thought-' or `gedanken-' experiments, but nonetheless Einstein's equations reveal that under certain conditions, or in the presence of certain types of matter, spacetime exhibits phase transitions, much like how water turns to gas if the temperature and pressure are tuned beyond specific values. My goal is to use such thought experiments to guide a search for new microscopic theories that will provide a better understanding of the fabric of the universe and its cosmic origins. These new theories will still describe the known features of gravity, but without the problematic information loss, and simultaneously have the potential to reveal new undiscovered properties of spacetime and our universe.