Two theoretical problem from the International Physics Olympiad (IPhO) are presented. First of them was assigned at the 42th IPhO in 2012 in Thailand. The motivation for the problem was to describe the motion of three satelites forming together the Laser Interferometry Space Antenna (LISA), the device designed to detect gravitational waves. The second presented problem (from 45th IPhO in 2014 in Kazakhstan) concerns the simplest models of gas discharges. and Jan Kříž, Filip Studnička, Ľubomír Konrád, Bohumil Vybíral.
Ve čtvrtek 11. února 2016 na tiskové konferenci ve Washingtonu oznámili vědci z Laser Interferometer Gravitational-wave Observatory (LIGO) [1], že na dvou detektorech nacházejících se na opačných koncích Spojených států se 14. září 2015 podařilo zaznamenat příchod gravitačních vln. Kromě důležitých astronomických dat toto pozorování představuje přímé potvrzení jedné z klíčových předpovědí Einsteinovy obecné teorie relativity (OTR) a přináší informace o událostech odehrávajících se za extrémních podmínek velmi silné gravitace, kdy se naplno projevuje nelinearita jako zásadní vlastnost této teorie., The existence of gravitational waves is a basic feature of general gravity but even Albert Einstein seriously doubted they actually exist. There is now indirect evidence that there are astrophysical sources, such as Binary pulsars, which generate gravitational waves, but their strength here on Earth was too small to be detected. However, after using advanced technologies to build large laser interferometric detectors (LIGO), detection sensitivity was significantly increased and, recently the profile of the first directly observed gravitational waves emitted by the inspiral and merger of two black holes was detected. It revealed surprisingly massive stellar black holes, which merged together a billion years ago., Tomáš Ledvinka, Jiří Bičák., and Obsahuje seznam literatury
Most of the work on exact models representing gravitational waves in general relativity has been concerned with spacetimes which are,at least in some directions, asymptotically flat. Here we treat gravitational waves in one of the simplest but everywhere curved cosmological model. We give the physical interpretation of exact "type - N solutions" of Einstein´s equations with cosmological constant presented recently by García Días and Plebanski. We show that some of these solutions may be interpreted as gravitational waves propagating in the de Sitter universe. (According to present consensus, this unvierse represents the inflationary stage of our Universe.) The analysis also reveals that tha solutions can serve as the illustration of the cosmological no-hair theorem: they approach the de Sitter space-time asymptotically in time.