How fast does time flow? Dynamical behaviour in glasses, nano-science and self-assembly

时间的流动是人类经验的一个基本特征，也是现代物理学的核心。爱因斯坦的相对论关注的是时间的性质，因为它影响恒星和行星，而量子物理学解释说，系统中的时间流动可能会受到外部观察者的强烈影响。然而，这些理论往往似乎与最引人注目的人类时间经验无关：我们发现生物会变老和死亡，人造结构会随着时间的推移而崩溃。这些过程的物理基础在于无序或熵的增加：维持有序的结构需要外部的工作，如果没有这种工作，无序会无情地增加。在20世纪，建立了深刻而优雅的理论，以量化熵，并理解为什么我们观察到一个从过去指向未来的时间箭头。然而，许多重要问题仍然没有答案。特别是，理论预测系统中会发生哪些过程，但它们不能预测它们发生的速度，也不能预测人类或机器如何抵制自然过程。我的研究关注的是这些问题，但大多数科学家都认为，我们离找到这些问题的完整答案还很远。出于这个原因，我考虑与这些问题相关的具体系统。然后，我的目标是将不同系统的结果联合收割机结合起来，以得出一般性的原则。举一个具体的例子，玻璃是一种几个世纪以来令建筑师、设计师和艺术家着迷的材料。在加热时，它会软化，并可以作为液体流动;如果它然后迅速冷却，它会硬化成固体玻璃，保持液体的透明度，以及花瓶和装饰品所熟悉的流动形状。从这个意义上说，玻璃处于液体和固体之间的边界。对于我的研究，关键点是液体服从时间箭头向下流动，但固体有固定的形状，不流动。如果玻璃确实是液体，它是如何抵抗流动的？如果它是固体，为什么它与液体如此相似？这些听起来简单的问题实际上是长期科学争论的核心。特别是，我们不知道是否存在一种理想的玻璃：一种通过无限缓慢地流动来抵抗时间的液体。如果自发流动确实有可能完全停止，这将对时间之箭理论产生根本性的影响。第二个例子，考虑当病毒在人群中传播时会发生什么。在受感染生物体的细胞内，分子自发地组装成大小小于千分之一毫米的有序结构。反过来，这些有序的结构将发展成新的病毒，从而感染其他细胞或其他生物体。在这里，时间是至关重要的：如果病毒发展得足够快，那么它可以杀死细胞，而如果它发展得太慢，细胞可以检测并摧毁病毒。这些问题可能听起来本质上是生物学的，但物理学在这里有很大的贡献。我的研究调查了有序结构组装的速度，以及它们如何加速或减速。物理定律似乎为组装设定了速度限制，我的目标是利用和控制。最后，我还考虑了生物组装过程的见解如何应用于像生物病毒一样微小的人造结构，具有类似的复杂结构和功能。这种结构很难建造，但它们已经被提议用于下一代高效太阳能电池，甚至可以作为微型机器的构建模块，用于对抗癌症等疾病。通过努力建立这种结构的组装和控制理论，我的研究旨在发展物理学的基础理论，并在生物学和纳米技术方面提供实用的见解。

The flow of time is an essential feature of the human experience, and it also lies at the centre of modern physics. Einstein's relativity is concerned with the nature of time as it affects stars and planets, while quantum physics explains that the flow of time in a system may be strongly affected by the actions of an external observer. However, these theories often seem irrelevant for the most striking human experiences of time: we find that living creatures grow old and die, and man-made structures crumble over time. The physical basis of these processes lies in the increase of disorder, or entropy: maintaining ordered structures requires external work, and in the absence of such work, disorder increases inexorably.In the 20th century, deep and elegant theories were built, to quantify entropy, and to understand why we observe an arrow of time pointing from the past to future. However, many important questions remain unanswered. In particular, theories predict which processes will happen in a system, but they do not predict how fast they happen, nor how natural processes might be resisted by humans or machines. My research is concerned with such questions, but most scientists agree that we are still very far from finding full answers to them. For this reason, I consider specific systems in which such questions are relevant. I then aim to combine the results from different systems in order to arrive at general principles.To take one specific example, glass is a material that has fascinated architects, designers, and artists over centuries. On heating, it softens and can flow as a liquid; if it is then rapidly cooled, it hardens into solid glass, retaining the transparency of the liquid, and the flowing shapes that are familiar from vases and ornaments. In this sense, glass lives on the borderline between liquids and solids. For my research, the key point is that liquids obey the arrow of time by flowing downhill, but solids have a fixed shape, and do not flow. If the glass is indeed a liquid, how does it resist flow? If it is a solid, why does it resemble so closely the liquid? These simple-sounding questions are in fact at the core of long-running scientific debates. In particular, it is not known whether there can exist an ideal glass : a liquid that resists time by flowing only infinitely slowly. If it is indeed possible for spontaneous flow to stop completely, this would have fundamental consequences for theories of the arrow of time.For a second example, consider what happens when viruses spread through a population. Inside the cells of infected organisms, molecules assemble spontaneously into ordered structures that are less than a thousandth of a millimetre in size. In turn, these ordered structures will develop into new viruses, allowing infection of other cells or other organisms. Here, time is of the essence: if the virus develops quickly enough then it can kill the cell, while if it develops too slowly, the cell can detect and destroy the virus. These questions may sound essentially biological, but physics has much to contribute here. My research investigates how fast the ordered structures can assemble, and how they might be speeded up or slowed down. The laws of physics seem to set speed limits on assembly, which I aim to exploit and control. Finally, I also consider how insights from biological assembly processes might be applied in man-made structures that are as tiny as biological viruses, with similarly complex structure and functionality. Such structures are difficult to build, but they have been proposed for the next generation of efficient solar cells, or even as building blocks for tiny machines that might be used to fight diseases like cancer. By working towards a theory for the assembly and control of such structures, my research aims both to develop fundamental theories in physics, and to give practical insights in biology and nanotechnology.