The one-way speed of light and the Milne universe

In Einstein’s special theory of relativity, all observers measure the speed of light, c, to be the same. However, this refers to the round-trip speed, where a clock at the origin times the outward and return trip of light reflecting off a distant mirror. Measuring the one-way speed of light is fraught with issues of clock synchronisation, and, as long as the average speed of light remains c, the speeds on the outward and return legs could be different. One objection to this anisotropic speed of light is that views of the distant universe would be different in different directions, especially with regard to the ages of observed objects and the smoothness of the Cosmic Microwave Background. In this paper, we explore this in the Milne universe, the limiting case of a Friedmann–Robertson–Walker universe containing no matter, radiation, or dark energy. Given that this universe is empty, it can be mapped onto flat Minkowski space-time and so can be explored in terms of the one-way speed of light. The conclusion is that the presence of an anisotropic speed of light leads to anisotropic time dilation effects, and hence observers in the Milne universe would be presented with an isotropic view of the distant cosmos.

Regulations and Technology Behind HFT Latency, Batch Auctions and Payments for Order Flow in the US and EU

Since the appearance of high-frequency trading in the 1990s, speed has become one of the key issues in trading and with it, the controversy around High-Frequency Trading. In recent years, there have been many discussions and analyses of how high-frequency trading may affect the financial market – but still without any clear conclusions. Leaving these opinions behind, many adjustments have already been made in the US and Europe - both to regulations and market rules, impacting not only High-Frequency Trading but general electronic trading as well. These rules and regulations are the result of technological developments in electronic trading and more specifically, High-Frequency Trading and the practice of Payments for Order Flow. The question remains as to how deep regulations should go, especially in the case of HFT which can be severely affected by harsh regulatory requirements or procedures. Because two of the most important issues in HFT are time and information, some of the rules and regulations affect aspects such as not only what type of information and how it should be gathered, but also clock synchronisation and time-stamp granularity. Another issue that may be considered controversial in the field of HFT (although it is not a practice limited to HFT) is Payment For Order Flows. Under this mechanism, wholesale market makers pay brokers for their client’s order flow – a practice that performed in great amounts and at high speeds may give a considerable level of “inside” information. Regulations, especially from ESMA (MiFID II). try in great part to thus mitigate the practice of Payments For Order Flows.The aim of this paper is to present technological advancements in the field of trading communications used, not only by HFT firms, but also by exchanges. Additionally, the objective is to underline some challenges regarding regulatory changes that try to adapt to the current level of technology – for example, those related to clock synchronisation and data processing. One last issue brought forward is the possibility of converting markets from continuous-time auctions to discrete-time auctions - a concept that is aimed at liquidating the speed advantage and competition only to price level and hence, eliminating HFT advantages.