The materials approach to quantum spacetime

引力的作用是众所周知的：它既造成了苹果的坠落，也造成了行星的轨道运行，但它仍然是自然界中最不为人所知的力。在我们对引力的概念化过程中，一个悬而未决的问题是信息是否会在引力过程中被破坏。黑洞是恒星坍缩形成的，是这些想法的一个美丽的试验场。考虑一本日记，其中包含了必须不惜一切代价不让公众看到的个人秘密。有没有可能通过将日记扔进黑洞来破坏其中包含的信息？虽然这在实践中似乎很有用，但对基础物理学的影响将是灾难性的。一个自洽的物理理论不应该允许信息破坏，因为这意味着基本上无法预测实验的结果;否定整个科学方法的范式和假设检验的有效性。霍金的信息悖论明确表明，在爱因斯坦的广义相对论框架内，黑洞确实会破坏信息。这意味着我们必须寻找一种理论来取代爱因斯坦的广义相对论，同时又能在天文学和宇宙学领域再现它所有成功的预言。这是一项艰巨但必要的任务。黑洞并不是爱因斯坦方程显示不一致的唯一领域：天文观测表明我们的宇宙正在膨胀，与黑洞类似，膨胀的宇宙可能会破坏日记中的信息，如果让它独自呆着。如果我们要理解膨胀宇宙的起源，我们就必须建立理论模型，准确地描述膨胀空间，而不会造成信息丢失的问题。为了找到信息悖论的症结，我正在研究最终可能取代广义相对论的框架。我的方法是把空间的结构当作一种“材料”来进行实验。当然，作为一个理论物理学家意味着我的实验将是“思想"或”思考“实验，但尽管如此，爱因斯坦的方程揭示了在某些条件下，或者在存在某些类型的物质的情况下，时空会发生相变，就像温度和压力超过特定值时水变成气体一样。我的目标是用这样的思想实验来指导对新的微观理论的探索，这些理论将提供对宇宙结构及其宇宙起源的更好理解。这些新的理论仍将描述引力的已知特征，但没有问题的信息丢失，同时有可能揭示时空和我们宇宙的新的未发现的性质。

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.