2. (a) Describe the Doppler effect in the de-Sitter universe ds2 = (1-) dt -(1-) dr- (b) 3 r(de + sin 0 do) where R = +8 OR Obtain the red-shift for the non-static form of de-Sitter universe ds2 = dt2-e2kt [dr + r(de + sin 0 do)] Where K is a constant. 3. (a) Write notes on Hubble's law. (b) 4. (a) (b) Write notes on the Weyl postulate for non- static universe. Discuss the age of universe for the matter- dominated eracosmological model. OR Write notes on Black-hole. Also explain why black-holes are black?