Dear Colleagues,

Undoubtedly, the first detection of gravitational waves on 14 September 2015 was a momentous achievement in science. It is rare that a theoretical prediction takes more than a century to be rejected or confirmed. In the case of gravitational waves, this shows not only the power of the theory but also the tremendous advances in technology that had to occur to make this happen. Since the first event was detected, the fields of gravitational physics, astronomy, and astrophysics have gained considerable momentum, not least due to the new window that has opened up to explore the universe in hitherto unknown ways.

The phenomenon of gravitational waves has always been a driving force in the efforts to explore and understand the theoretical and mathematical foundations of Einstein's theory of gravitation and in the development of new experimental techniques. They have also been a strong motivation for the creation of modern computational methods for solving Einstein's equations. Yet, we are still left with questions: how do we describe gravitational waves and the energy-momentum they carry in cosmological space-times? What is their role in the very early universe? How do we model concrete sources for them? How do we compute their emission from sources? How do we accurately numerically model the asymptotic region where they manifest themselves? Do we need to improve or redesign our detectors?

Thus, gravitational waves are central to current developments in gravitational physics. The attempt to understand them draws from many different sources, ranging from purely mathematical works to computational simulations to experiments and observations. Therefore, it is very timely to devote a Special Issue of Universe to the topic of gravitational waves.

We invite colleagues to submit papers on the following topics:

• Mathematical issues of gravitational waves
• Asymptotic structure of space-time
• Gravitational waves in cosmological space-times
• Gravitational waves in the early universe
• Sources for gravitational waves
• Computational and approximation methods in gravitational wave physics
• New developments in gravitational wave detection

Prof. Dr. Jörg Frauendiener
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• Gravitational waves in cosmology
• Gravitational wave background
• Gravitational wave sources
• Compact binaries
• Gravitational wave propagation
• Gravitational wave detection
• Approximation methods
• Numerical methods for Einstein's equations
• Asymptotic properties of space-times