ﻻ يوجد ملخص باللغة العربية
It is shown that, contrary to an existing claim, the near equality between the lifetime of the sun and the timescale of biological evolution on earth does not necessarily imply that extraterrestrial civilizations are exceedingly rare. Furthermore, on the basis of simple assumptions it is demonstrated that a near equality between these two timescales may be the most probable relation. A calculation of the cosmic history of carbon production which is based on the recently determined history of the star formation rate suggests that the most likely time for intelligent civilizations to emerge in the universe, was when the universe was already older then about 10 billion years (for an assumed current age of about 13 billion years).
Abridged: The interest towards searches for extraterrestrial civilizations (ETCs) was boosted by the discovery of thousands of exoplanets. We turn to the classification of ETCs for new considerations that may help to design better strategies for ETCs
The search for extraterrestrial intelligence (SETI) is a scientific endeavor which struggles with unique issues -- a strong indeterminacy in what data to look for and when to do so. This has led to attempts at finding both fundamental limits of the c
Bars have a complex three-dimensional shape. In particular their inner part is vertically much thicker than the parts further out. Viewed edge-on, the thick part of the bar is what is commonly known as a boxy-, peanut- or X- bulge and viewed face-on
We study the time until first occurrence, the first-passage time, of rare density fluctuations in diffusive systems. We approach the problem using a model consisting of many independent random walkers on a lattice. The existence of spatial correlatio
For centuries extremely-long grazing fireball displays have fascinated observers and inspired people to ponder about their origins. The Desert Fireball Network (DFN) is the largest single fireball network in the world, covering about one third of Aus