The arXiv is the most popular preprint repository in the world. Since its inception in 1991, the arXiv has allowed researchers to freely share publication-ready articles prior to formal peer review. The growth and the popularity of the arXiv emerged as a result of  new technologies that made document creation and dissemination easy, and cultural practices where collaboration and data sharing were dominant. The arXiv represents a unique place in the history of research communication and the Web itself, however it has arguably changed very little since it's creation.  Here we look at the strengths and weaknesses of arXiv in an effort to identify what possible improvements can be made based on new technologies not previously available. Based on this, we argue that a modern arXiv might in fact not look at all like the arXiv of today.IntroductionThe arXiv, pronounced "archive", is the most popular preprint repository in the world.  Started in 1991 by physicist Paul Ginsparg, the arXiv allows researchers to freely share post publication-ready articles prior to formal peer review and publication. Today, the arXiv publishes over 10,000 articles each month from high-energy physics, computer science, quantitative biology, statistics, quantitative finance, and others (see Fig \ref{104668}). The early success of arXiv stems from the introduction of new technological advances paired to a well-developed culture of collaboration and sharing. Indeed, before the arXiv even existed, physicists were already physically sharing recently finished manuscripts via mail, first, and by email, later.  To understand the success of the arXiv it is important to understand the history of the arXiv. Below we highlight a brief history of technology, services, and cultural norms that predate the arXiv and were integral to its early and continued success.  The history of the arXivPrior to the arXiv, preprinting was performed by institutional repositories, such as the SPIRES-HEP database (Stanford Physics Information REtrieval System- High Energy Physics) at the Stanford Linear Accelerator Center (SLAC) and the Document Server at CERN. Developed in the early 70's, SPIRES created a bibliographic standard and centralized resource that allowed researchers across universities in high energy physics to email the database and request a list of preprints be sent to them.  Since papers themselves could not be emailed at the time, the system relied on traditional mail. This resource was immediately successful with requests numbering in the thousands within the first few years \cite{Elizalde_2017}.  While SPIRES greatly improved the flow of information, it still took weeks for articles (preprints) to be sent and received. A new typesetting system would soon emerge and change this.TeX, pronounced "tech", was developed by Donald Knuth in the late 70's as a way for researchers to write and typeset articles programmatically. Soon after the introduction of TeX, Leslie Lamport set a standard for TeX formatting, called LaTeX, which made it very easy for all researchers to professionally typeset their documents on their own.  This system made sharing papers easier and cheaper than ever before. Indeed, many, if not most, researchers at the time relied upon secretaries or typists to write their work, which then had to be photocopied in order to be sent via mail to a handful of other researchers. Tex allowed researchers to write their documents in a specified manner (binary) that could be emailed and then downloaded and compiled without the need for physical mail. Soon, physicists were emailing and downloading .tex files at great rates hastening the process of research communication like never before.Such a system immediately created a new problem for researchers: information overload. Researchers were exchanging emails containing preprints at great rates, and given the size of computer hard drives at the time, email servers were running out of space \cite{Ginsparg_2011}.  To address this problem, an automated email server, called arXiv, was set up in the early 90's. The arXiv would allow researchers to automatically request preprints via email as needed. It would soon become one of the world's first web servers and today still serves as one of the most open and efficient forms of research communication in the world.  The arXiv was a leader in introducing and utilizing new technology when it was launched, however it has arguably changed very little since its inception, despite a wealth of new technologies now available. Here we look at the strengths and weaknesses of the arXiv in an effort to identify what possible improvements can be made based on new technologies and tools and propose that a modern arXiv might in fact not look at all like the arXiv of today --- a development that will likely occur with or without arXiv.

MLT These notes are mostly inspired from reading Cox & Giuli (“Principles of stellar structure”); some insights are from A.Maeder (“Physics, formation and evolution of rotating stars”) and Kippenhahn & Weigert (“Stellar Structure and Evolution”) Pressure Scale Height In hydrostatic equilibrium we can define the total pressure scale height, $\hp$, as -{\D r} \equiv {\hp} = {\p} where $\p$ is the total pressure ($ + $). The pressure scale height is a measure of the distance over which the pressure changes by an appreciable fraction of itself.

PREVIOUS “A “MODERN SCIENTIST” MANIFESTO” In the 21st century science is growing more technical and complex, as we gaze further and further while standing on the shoulders of many generations of giants. The public has often a hard time understanding research and its relevance to society. One of the reasons for this is that scientists do not spend enough time communicating their findings outside their own scientific community. Obviously there are some exceptions, but THE RULE IS THAT SCIENTISTS WRITE CONTENT FOR SCIENTISTS. Academia is often perceived as an ivory tower, and when new findings are shared with the outside world, this is not done by scientists, but by the media or even the political class. The problem is that these external agents do not have the necessary background to digest and properly communicate this knowledge with the rest of society. They often misunderstand, over-hype and in some case even distort the results and views of the scientific community. IT’S IRONIC AND SOMEWHAT FRIGHTENING THAT THE DISCOVERIES AND RECOMMENDATIONS FOR WHICH SOCIETY INVESTS SUBSTANTIAL ECONOMIC AND HUMAN CAPITAL, ARE NOT DIRECTLY DISSEMINATED BY THE PEOPLE WHO REALLY UNDERSTAND THEM. At the same time transparency and reproducibility are at stake in the increasingly complex world of research, which is still using old-fashioned tools when packaging and sharing content. This is not only a big problem for research itself, but can give science a bad name in front of the public opinion, which increasingly does not understand and trust the work of scientists. To the average tax-payer science is often cryptic, with most recently published papers behind a pay-wall and the majority of research virtually inscrutable. In this scenario it is hard for the public to access and capture the relevance of scientists’ work. I strongly believe that a society that does not trust its scientists is set on a dangerous course. ACTION ITEMS. To improve the situation 21st century scientists need to: 1. Learn to efficiently share and communicate their research with the public at large. 2. Make their research more transparent and reproducible, so that it can be trusted and better understood by their peers and the public at large. 21st century scientists need to produce “PUBLIC-FRIENDLY OPEN SCIENCE” (PFOS).

"Like every great river and every great sea, the moon belongs to none and belongs to all. It still holds the key to madness, still controls the tides that lap on shores everywhere, still guards the lovers who kiss in every land under no banner but the sky". E.B. White The New Yorker, July 26, 1969Where does the Moon come from?Scientist believe that our Moon formed out of a ‘giant impact’ that occurred between a Mars-sized planet and the early Earth, some 4.5 billion years ago. The Moon was then formed from the coalescence of the orbiting debris scattered during the impact.Recent results seem to confirm this scenario

The power of the atomAt the beginning of the 20th century, major advancements in our understanding of fundamental physics led scientists to the discovery of nuclear energy. An unprecedented amount of power could in principle be released by combining (nuclear fusion) or breaking (nuclear fission) certain atomic species under special conditions. Nuclear fusion in particular was understood to be the process powering the immense luminosity of stars, including our Sun. Nuclear fusion is the energy source illuminating our Universe.Why so much energy?Burning fossil fuels releases chemical energy. This chemical energy is stored in the mild electromagnetic interactions between atoms in a compound. Nuclear energy, on the other hand, comes from the very central regions of the atom.  As the name suggests, it is stored in the nuclei, which are kept together by the strong force. The strong force is much stronger than all the other forces, including the electromagnetic one. As a result, nuclear fuel has an energy density about ten million times larger than chemical fuel. If your car was running on nuclear fuel, its gas mileage would be something like hundreds of millions of MPG. From light to darknessThe physics revolution that characterized the first three decades of the 20th century and led to the development of quantum mechanics and nuclear physics, was followed by the second World War. In 1942, the United States started a very ambitious project to build a nuclear weapon. The Manhattan Project, led by Robert Oppenheimer and gathering some of the best physicists on the planet, culminated with the successful Trinity experiment in 1945 (Fig.\ref{982837}). The first detonation of a nuclear weapon was the most shocking demonstration of the great power of science and the scientific method. Only less than a month later, two nuclear bombs were dropped over the Japanese cities of Hiroshima and Nagasaki, resulting in the end of WWII and the death of hundreds of thousands of people. The sheer destruction inflicted by the atomic bomb left an indelible mark on humankind's consciousness, formally starting a new era in the history of man. An era of greater responsibility. While no nuclear weapons have been purposely used in war ever since, more than 2000 nuclear tests have been performed after the Trinity, Hiroshima and Nagasaki explosions.