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，也是现代物理学的中心。爱因斯坦的相对论关注的是时间的性质，因为它影响着恒星和行星，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行为的强烈影响。然而，这些理论似乎往往与人类最令人震惊的时间体验无关：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功，而在没有这种功的情况下，无序的增加是不可阻挡的。在20世纪，人们建立了深刻而优雅的理论，来量化熵，并理解为什么我们观察到从过去到未来的时间箭头。然而，许多重要的问题仍然没有得到回答。特别是，理论预测系统中将发生哪些过程，但它们不能预测它们发生的速度，也不能预测自然过程可能如何被人类或机器抵制。我的研究关注的是这些问题，但大多数科学家都认为，我们还远远没有找到这些问题的全部答案。出于这个原因，我考虑了与这些问题相关的具体制度。然后我的目标是将不同系统的结果结合在一起，以得出一般原则。举一个具体的例子，玻璃是一种几个世纪以来一直吸引着建筑师、设计师和艺术家的材料。加热时，它会变软，可以像液体一样流动；如果然后快速冷却，它就会变硬，变成固体玻璃，保留液体的透明度，以及花瓶和装饰品熟悉的流动形状。从这个意义上说，玻璃处于液体和固体之间。对我的研究来说，关键是液体顺着时间之箭往下流，但固体有固定的形状，不流动。如果玻璃真的是液体，它是如何抵抗流动的呢？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的科学辩论的核心。特别是，目前还不知道是否存在一种理想的玻璃：一种通过无限缓慢流动来抵抗时间的液体。如果自发性流动确实可能完全停止，这将对时间之箭理论产生根本影响。第二个例子，考虑当病毒在种群中传播时会发生什么。在受感染有机体的细胞内，分子自发组装成不到千分之一毫米大小的有序结构。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，时间至关重要：如果病毒发展得足够快，它就可以杀死细胞，而如果病毒发展得太慢，细胞就可以检测并摧毁病毒。这些问题听起来可能本质上是生物学的，但物理学在这方面有很大贡献。我的研究调查了有序结构的组装速度，以及它们可能如何加速或减速。物理定律似乎对组装设定了速度限制，我的目标是利用和控制这一点。最后，我还考虑了如何将来自生物组装过程的洞察力应用于人造结构，这些人造结构像生物病毒一样微小，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基础，这些机器可能会被用来对抗癌症等疾病。通过致力于建立一种组装和控制这种结构的理论，我的研究旨在发展物理学的基本理论，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.