The materials approach to quantum spacetime

万有引力的影响是众所周知的：对落下的苹果和行星轨道都负有责任，但它仍然是自然界中最不为人所知的力量。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。恒星坍塌形成的黑洞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深度个人秘密。把日记扔进黑洞，有没有可能破坏其中包含的信息？尽管这似乎在实践中有用，但对基础物理学的影响将是灾难性的。自洽的物理理论不应该允许信息破坏，因为这将意味着根本无法预测实验的结果；否定科学方法的整个范式和假设检验的有效性。霍金的信息悖论，它明确地表明，在爱因斯坦广义相对论的框架内，黑洞确实摧毁了信息。这表明，我们必须寻找一种理论来取代爱因斯坦的广义相对论，同时复制爱因斯坦在天文学和宇宙学领域的所有成功预测。这是一项艰巨但必要的任务。黑洞并不是爱因斯坦方程式揭示矛盾的唯一领域：天文调查表明，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，如果亿万年不加理会的话。如果我们要了解我们不断膨胀的宇宙的起源，我们必须建立理论模型，准确地描述膨胀的空间，而不会造成有问题的信息损失。为了找到信息悖论的症结所在，我正在寻找最终可能取代广义相对论的框架。我的方法是把太空的结构当作一种“材料”来进行实验。当然，作为一名理论物理学家意味着我的实验将是“思想的”或“格丹肯的”实验，但尽管如此，爱因斯坦的方程式表明，在某些条件下，或者在某些类型的物质存在的情况下，时空表现出相变，就像如果温度和压力被调节到超过特定值时，水如何变成气体一样。我的目标是利用这种思维实验来指导寻找新的微观理论，这些理论将提供对宇宙结构及其宇宙起源的更好理解。这些新理论将仍然描述引力的已知特征，但不会丢失有问题的信息，同时有可能揭示时空和我们的宇宙新的未被发现的属性。

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.