Previous Year Question

Statement 1 is correct. “Microwaves in space” here refers to the cosmic microwave background radiation. It is the faint remnant radiation from the early hot and dense universe. As the universe expanded, the wavelength of this radiation stretched and its temperature decreased. It is now observed across the sky as microwave radiation with a temperature of approximately 2.7 kelvin. Its existence is important evidence of a hot early universe followed by cosmic expansion.

Statement 2 is correct. Spectral lines in light received from distant galaxies are observed to be shifted towards longer, redder wavelengths. This is called cosmological redshift. As space expands, distances between galaxies increase and the wavelengths of the light travelling through that space are stretched. In general, the farther a galaxy is, the greater its observed redshift. This relationship provides direct observational evidence for the expansion of the universe.

Statement 3 is incorrect. The movement of asteroids is governed mainly by the gravity of the Sun and other astronomical bodies and by their orbital motion. It is not evidence of the overall expansion of the universe. Locally gravitationally bound systems, such as the solar system, do not expand along with the universe in this manner.

Statement 4 is incorrect. The mere occurrence of supernova explosions is not evidence of cosmic expansion; it is a phenomenon of stellar evolution. However, measurements of the distances and redshifts of particular Type Ia supernovae are used to study the expansion rate and the accelerating expansion of the universe. The statement mentions only the occurrence of explosions and is therefore not correct.