Consider reviewing in the mass-energy equivalence, always raises too many questions like, “Is the constant speed of light (photon energy), resulting from a natural accident?” or “what’s the difference between mass characteristics and energy features while the energy rate is fixed the speed of matter can be changed but it cannot reach the speed of light”. Meanwhile when the physical and chemical processes occur, some amount of matter is converted into energy; what happened during this process, that mass with non-constant speed is converted into energy with the constant speed? The main part of this Special Issue, according to the fundamental particle physics theories and energy issues in the production and decay of pairs of matter–antimatter are included in finding the common features between matter and energy. In this Special Issue , we try to propose a new light (as particle) theories which are substantiated by a number of theoretical and experimental results which better explain the nature and speed of light compared to the current "accepted" models.

This special issue is focusing on nuclear physics: theoretical and applied and its applications in various fields of research. We will focus on the latest research on particle and high energy physics and astrophysics, towards unification theory and discoveries of universe. We will focus also on present and new topics in dark energy and dark matter, also any new aspects of possible forms of life in the wide universe.

Applications of nuclear and radiation physics in various topics, especially of concern of health of human, environmental survey of natural and artificial radiation and doses arising from them, nuclear medicine, and other related topics . Various X-ray fluorescence techniques used in studying pollution of air and quantitative and qualitative analysis of various samples.

High pure gamma ray spectroscopy in studying samples for measurements in radioactivity and determination of equivalent doses arising from them is of our concern. Also radiation monitoring systems and the design and use of survey meters and personal dosimeters, will be considered. Protection from radioactivity and possible means to avoid nuclear reactors accidents can be discussed. Radiation safety and health physics is of our concern. Interaction of radiation with matter, Natural Radioactive Series and nuclear waste management are also, of concern.