Question 36

One of the most significant pillars of modern cosmology is the existence of the Cosmic Microwave Background, or CMB. Interestingly, its discovery in the 1960s was entirely accidental. Two radio astronomers, Arno Penzias and Robert Wilson, were experimenting with a sensitive antenna when they encountered a persistent background noise that they could not eliminate, regardless of where they pointed the device. They initially suspected everything from urban interference to pigeon droppings on the antenna, but eventually realized they were detecting a faint signal coming uniformly from every direction in the sky. This signal turned out to be the thermal radiation left over from the time of recombination in Big Bang cosmology. Essentially, it is the cooled remnant of the first light that could travel freely through the universe. The discovery of the CMB was crucial because it provided the strongest evidence yet against the rival Steady State theory, confirming that the universe indeed had a hot, dense beginning. While the radiation appears almost uniform, tiny fluctuations in its temperature map the seeds of all future structures, explaining how galaxies eventually formed.