Every human being is aware of the flow of time. This fact is embodied in the existence of such notions as the past and the future, the two domains being separated from each other by the single moment of the present. While the past is regarded as fixed and definite, the future is viewed as unknown, uncertain, and undetermined. The only perceivable moment is the present, the `now' - the ever-changing point moving from the past into the future. Physics tells us a different story: not only are the vast majority of physical laws time-reversible, but the concept of the `now' itself has no place at all in physics. In other words, the equations of physics do not distinguish between the past and the future and seem to be completely oblivious to the very idea of the present. This book discusses the biological and psychological aspects of perception of time, and the problems related to the determination of location arising from quantum physics, together with comments and opinions from philosophers and physicists.

Every human being is aware of the flow of time. This fact is embodied in the existence of such notions as the past and the future, the two domains being separated from each other by the single moment of the present. While the past is regarded as fixed and definite, the future is viewed as unknown, uncertain, and undetermined. The only perceivable moment is the present, the `now' - the ever-changing point moving from the past into the future. Physics tells us a different story: not only are the vast majority of physical laws time-reversible, but the concept of the `now' itself has no place at all in physics. In other words, the equations of physics do not distinguish between the past and the future and seem to be completely oblivious to the very idea of the present. This book discusses the biological and psychological aspects of perception of time, and the problems related to the determination of location arising from quantum physics, together with comments and opinions from philosophers and physicists.

In this book are reported the main results presented at the "Fourth International Workshop on Data Analysis in Astronomy," held at the Ettore Majorana Center for Scientific Culture, Erice, Sicily, Italy, on April 12-19, 1991. The Workshop was preceded by three workshops on the same subject held in Erice in 1984, 1986 and 1988. The frrst workshop (Erice 1984) was dominated by presentations of "Systems for Data Analysis"; the main systems proposed were MIDAS, AlPS, RIAIP, and SAIA. Methodologies and image analysis topics were also presented with the emphasis on cluster analysis, multivariate analysis, bootstrap methods, time analysis, periodicity, 2D photometry, spectrometry, and data compression. A general presentation on "Parallel Processing" was made which encompassed new architectures, data structures and languages. The second workshop (Erice 1986) reviewed the "Data Handling Systems" planned for large major satellites and ground experiments (VLA, HST, ROSAT, COMPASS-COMPTEL). Data analysis methods applied to physical interpretation were mainly considered (cluster photometry, astronomical optical data compression, cluster analysis for pulsar light curves, coded aperture imaging). New parallel and vectorial machines were presented (cellular machines, PAPIA-machine, MPP-machine, vector computers in astronomy). Contributions in the field of artificial intelligence and planned applications to astronomy were also considered (expert systems, artificial intelligence in computer vision).

In the book are reported the main results presented at the Third International Workshop on Data Analysis in Astronomy, held at the EUore Majorana Center for Scientific Culture, Erice, Sicily, Italy, on June 20-27,1988. The Workshop was the natural evolution of the two previous ones. The main goal of the first edition (Erice 1984) was to start a scientific interaction between Astronomers and Computer Scientists. Aim of the second (Erice 1986) was to look at the progress in data analysis methods and dedicated hardware technology. Data analysis problems become harder whenever the data are poor in statistics or the signal is weak and embedded in structured background. Experiments collecting data of such a nature require new and non-standard methodologies. Possibilistic approaches could be merged with the statistical ones, in order to formalize all the knowledge used by the scientists to reach conclusions. Moreover, the last decade has been characterized by very fast developments of Intelligent Systems for data analysis (knowledge based systems, ... ) that would be useful to support astronomers in complex decision making. For these reasons, the last edition of the workshop was intended to provide an overview on the state of the art in the data analysis methodologies and tools in the new frontieres of the astrophysics (y-astronomy, neutrino astronomy, gravitational waves, background radiation and extreme cosmic ray energy spectrum). The book is organized in two sections: - Data analysis methods and tools, - New frontieres in astronomy.

This book contains the invited and contributed lectures presented at a meeting organised in the context of the XVIII general assembly ofthe IAU, held in Patras, August 19, 1982. Roughly one hundred scientists attended this meeting, the discussions were livel- sometimes heated - and the original time span allocated to the meeting was as a result, comfortably exceeded by about 50 % . The aim of this meeting was to determine the role of galactic gamma-ray astronomy within the general concept of galactic astrophysics. The timing, at the end of the COS-B mission, was regarded as opportune, because it gives interested astrophysicists the possibility for interdisciplinary studies using the existing gamma-ray data base (e.g. comparison with infrared, radio, X-ray, etc. astronomies), as well as for theoretical studies. The next generation of gamma-ray detectors will probably not be in operation for another 5 to 10 years, and therefore it is hoped that the proceeding of this meeting can be used (in the intermediate time) as a basis for further studies, as a stimulation for more theoretical work and as an important contribution for defining the aims and operation of future gamma-ray missions. The interrelationship with other branches of astronomy, the astrophysical implications and the study of relevant physical processes using available measurements in the near-Earth environment were important results of the meeting. Many persons contributed to the success of the meeting, in particular all those who either presented a contribution and/or took part in the discussions.