Astronomy Study Guide

The Big Bang theory describes the universe's origin, proposing that it began from an extremely hot, dense point and has been expanding and cooling ever since. Key evidence supporting this theory includes red-shift and cosmic microwave background (CMB) radiation. Red-shift is the observed phenomenon where light from distant galaxies appears shifted towards the red end of the electromagnetic spectrum. This occurs because the galaxies are moving away from us, stretching the wavelengths of the light they emit. The greater the red-shift, the faster the galaxy is receding, which is consistent with an expanding universe. The detection of CMB radiation provides further strong support. This faint, uniform electromagnetic radiation fills all of space and is believed to be the cooled-down remnant energy from the Big Bang itself, dating back to when the universe was about 380,000 years old and sufficiently cool for atoms to form, allowing light to travel freely.

The discovery of Cosmic Microwave Background (CMB) radiation provided crucial evidence that solidified the Big Bang theory as the most widely accepted model for the Universe's origin. Before its detection, the Big Bang theory predicted that the early Universe was extremely hot and dense, and as it expanded, it would cool down. This cooling process would leave behind a faint glow of electromagnetic radiation, stretched to microwave wavelengths due to the Universe's continued expansion. In 1964, Arno Penzias and Robert Wilson, while working with a new antenna, detected a persistent background noise that they could not eliminate. This noise was isotropic, meaning it came from all directions, and had a temperature of about 2.7 Kelvin, corresponding to microwave radiation. This accidental discovery perfectly matched the predicted properties of the leftover radiation from the Big Bang. The existence of CMB radiation, acting as a 'fossil' of the early Universe, strongly supported the idea of an initial hot, dense state, offering compelling observational proof that the Universe indeed originated from a singular, extremely hot event and has been expanding and cooling ever since. This discovery provided a more robust explanation for observations like redshift and the abundance of light elements, integrating them into a cohesive cosmological model.