The BPU-6 Conference belongs to a series of triennial general physics conferences organized under the auspices of the Balkan Physical Union (BPU). The previous conferences were organized in Thessaloniki, Greece (1991), Izmir, Turkey (1994), Cluj-Napoca, Romania (1997), Veliko Trnovo, Bulgaria (2000), and Vrnjacka Banja, Serbia and Montenegro (2003). The BPU conferences are usually attended by about 80 scientists, educators and engineers involved in research, education and applications of physics. The Conference is open to all scientists from the Balkan countries working in physics and related areas. Participants from outside the Balkans are also welcome. Participation of young physicists and students is highly appreciated. The BPU-6 Conference covers the most important results and trends in the following fields of physics: Nuclear physics and nuclear energy; astronomy and astrophysics; gravitation and cosmology; atomic and molecular physics; high energy physics; condensed matter physics and statistical physics; optics and lasers; plasma and gas-discharge physics; theoretical and mathematical physics; computational physics; meteorology and geophysics; environmental physics; alternative sources of energy; econophysics; applied physics; biophysics and medical physics; physics education; history of philosophy of physics; meteorology and instrumentation.